- Vol. 21 (2)
- Vol. 21 (2)
- Vol. 21 (2)
- Vol. 22 (1)
- Vol. 22 (2)
- Vol. 23 (1)
- Vol. 23 (2)
- Vol. 24 (1)
- Vol. 24 (2)
- Vol. 25 (1)
- Vol. 25 (2)
Letters to Editor
Abstract
Various: Process of writing and revising structural standards in NZ; further recommendations for improvements in the Standards process; paper “Fire Performance of Hollow Core Floor Systems in NZ” using stiff end connections as the recommended end support conditions; Work carried out by Beca 36 years ago was referenced in Precast News 07; Semi Rigid Flange Bolted Joint at Auckland Airport
Technical Paper Economical Steel Bridge Solutions For New Zealand
Abstract
A common misconception is that short span steel bridges, with spans of between 10 and 30 metres, are more expensive than concrete bridges, particularly when precast concrete construction is employed. Moreover, another long held misconception is that concrete bridges are maintenance free and that, once construction is complete, the bridge will achieve a design life of 100 years with little or no maintenance. In reality, properly designed and maintained composite steel/concrete bridges provide a similar, or better, cost effective solution than their concrete counterparts.
This paper looks at the different costs associated with concrete and steel bridges, including a summary on selecting, specifying and determining the life cycle maintenance cost of a coating system. A cost effective superstructure configuration is determined and a concrete versus steel cost comparison is given in an example from two real bridge projects where steel was found to be more cost effective than concrete. Costs include the superstructure and substructure costs as well as the maintenance costs. A summary on the cost benefits of ladder deck and network arch bridge systems is also given.
Technical Paper Dependable Performance Of Steel Structures In Fire With Case Studies
Abstract
This paper describes the application of a structural fire model, known as the Slab Panel Method (SPM), developed by the New Zealand Heavy Engineering Research Association (HERA) in conjunction with the University of Canterbury. The SPM accounts for the inelastic reserve of strength available from composite Steel/concrete floor systems due to their two way deformation under fully developed fire conditions. The outcome of the performance based design process is a steel structure with fire proofing only to some of the Steel beams supporting the floor. Structural elements which are critical for stability are protected with fire proofing materials, while the floor beams for which fire proofing is not necessary for structural stability or Integrity are designed without this passive fire protection. This provides a structure which will remain stable for the expected temperatures and associated mechanical properties.
Recent project examples where the SPM has been successfully used in New Zealand are reviewed. These Include a 20 storey 350,000 sq ft. office building and a 12 storey 360,000 sq ft. mixed use office and apartment building, both under construction in New Zealand. Validation of one of the design solutions using finite element analysis to assess the actual performance for the range of structural fire severity expected is described. The paper concludes that design methods are maturing to a level where a dependable and robust performance can be predicted using the SPM, so that those parts of the structure which require fire proofing can be specified with enough protection to maintain structural stability, and those parts which do not need this passive fire protection can be safely constructed without fire protection. Opportunities for the application of SPM in the North American regulatory environment are discussed.
Technical Paper Boston Big Dig Tunnel Collapse – Lessons For Engineers
Abstract
During the 1990s an ambitious project was commenced to re-route the main east-west freeway at Boston (I-90) under the city centre. It was to become the largest transport infrastructure project in US history, worth an estimated US$14b. On 10 July 2006 a section of suspended concrete ceiling structure in one of the tunnels collapsed. A motorist was killed and expensive legal actions (criminal and civil) are unfolding. The National Transportation Safety Board (NTSB) has investigated and reported on the cause, with recommendations to many parties (private, public and industry) at local, state and national level. Unexpectedly, the stated fault was not a product failure (chemical anchors) but a failure of engineering processes controlled by many parties. This paper will review and explore the NTSB report, which includes detailed definition of the structures and issues involved, and what can be learned by all engineers in all fields as a result.
Technical Paper FRP Composites In Structural Engineering
Abstract
The authors have been part of a research team at Industrial Research Ltd. (a Crown Research Institution) investigating fibre reinforced polymers (FRP) materials for a variety of structural applications for about 15 years. IRL is currently pursuing the development of FRP structures for civil engineering applications within the framework of the FRST funded New Technology Rural Bridges programme. This programme was initially focused on vehicular bridges for rural roads but has now shifted towards load-bearing building structural elements, including floors, walls and roof panels.
Technical Paper Structural Failures – The Social Context
Abstract
1. Causes of Structural Failures
Some 80% of all structural failures appear to be due to some form of human error or error chain, “Structural failure” in this context, signifying that the structure (or part thereof) does not, or does no longer, fulfil the requirements of ultimate strength, serviceability and/or durability.
2. Human Error
The prevailing Management attitude towards human error in the workplace appears to be that of detection and rectification, with the accent on early detection in order to minimise the rectification cost, a reactive approach. The questions seldom asked are: “Why do people make errors in their work?” and subsequently: “What actions may be taken to improve quality performance by reducing the incidence of errors?” Seeking answers to these questions would constitute a proactive approach. Consideration of this problem clearly is in the realm of occupational psychology, a subject in the social sciences. The paper will deal in detail with the following emerging facets:
• The workplace “culture” prevailing in the construction industry,
• Tender evaluation practices,
• Leadership practices in the construction industry.
3. Remedial actions
The paper will recommend the following policy initiatives:
• Commencing a dialogue embracing the whole construction community with a view to replacing the prevailing adversarial culture by a co-operative one.
• Replacing tender evaluation practices based on minimum tender price by ones based on maximum project value.
• Replacing the present, mostly autocratic, cost-centred management style by a more democratic, value-centred one.
Technical Paper Maintaining Our Heritage
Abstract
When damaged or decaying timbers are found in a heritage building, the prospect of having to replace the historic beams can be devastating for the owners. The use of specially designed resins allows this to be achieved; not only can the repairs be carried out in an aesthetically pleasing manner, which in many cases are invisible to the untrained eye, but the structural capacity can also be maintained (and in the majority of cases significantly improved) whilst, of course, wastage of timber is kept to a minimum.
Article Composite Floor System Modelling Error
Abstract
This example relates to the modelling aspects and design process of a portion of composite floor. In this example the designer made adjustments to the load data to satisfy the requirements of the design program, yet without proper consideration of other aspects, resulting in unintended and un-conservative consequences.
Letters to Editor
Abstract
Various: Process of writing and revising structural standards in NZ; further recommendations for improvements in the Standards process; paper “Fire Performance of Hollow Core Floor Systems in NZ” using stiff end connections as the recommended end support conditions; Work carried out by Beca 36 years ago was referenced in Precast News 07; Semi Rigid Flange Bolted Joint at Auckland Airport
Technical Paper Boston Big Dig Tunnel Collapse – Lessons For Engineers
Abstract
During the 1990s an ambitious project was commenced to re-route the main east-west freeway at Boston (I-90) under the city centre. It was to become the largest transport infrastructure project in US history, worth an estimated US$14b. On 10 July 2006 a section of suspended concrete ceiling structure in one of the tunnels collapsed. A motorist was killed and expensive legal actions (criminal and civil) are unfolding. The National Transportation Safety Board (NTSB) has investigated and reported on the cause, with recommendations to many parties (private, public and industry) at local, state and national level. Unexpectedly, the stated fault was not a product failure (chemical anchors) but a failure of engineering processes controlled by many parties. This paper will review and explore the NTSB report, which includes detailed definition of the structures and issues involved, and what can be learned by all engineers in all fields as a result.
Technical Paper FRP Composites In Structural Engineering
Abstract
The authors have been part of a research team at Industrial Research Ltd. (a Crown Research Institution) investigating fibre reinforced polymers (FRP) materials for a variety of structural applications for about 15 years. IRL is currently pursuing the development of FRP structures for civil engineering applications within the framework of the FRST funded New Technology Rural Bridges programme. This programme was initially focused on vehicular bridges for rural roads but has now shifted towards load-bearing building structural elements, including floors, walls and roof panels.
Technical Paper Grade 500e Reinforcing Steel
Abstract
Tests on Micro-alloy and Quenched and Tempered samples available in New Zealand
Members’ Contributions
Abstract
This example relates to the modelling aspects and design process of a portion of composite floor. In this example the designer made adjustments to the load data to satisfy the requirements of the design program, yet without proper consideration of other aspects, resulting in unintended and un-conservative consequences.
Technical Paper Maintaining Our Heritage
Abstract
When damaged or decaying timbers are found in a heritage building, the prospect of having to replace the historic beams can be devastating for the owners. The use of specially designed resins allows this to be achieved; not only can the repairs be carried out in an aesthetically pleasing manner, which in many cases are invisible to the untrained eye, but the structural capacity can also be maintained (and in the majority of cases significantly improved) whilst, of course, wastage of timber is kept to a minimum.
Technical Paper Economical Steel Bridge Solutions For New Zealand
Abstract
A common misconception is that short span steel bridges, with spans of between 10 and 30 metres, are more expensive than concrete bridges, particularly when precast concrete construction is employed. Moreover, another long held misconception is that concrete bridges are maintenance free and that, once construction is complete, the bridge will achieve a design life of 100 years with little or no maintenance. In reality, properly designed and maintained composite steel/concrete bridges provide a similar, or better, cost effective solution than their concrete counterparts.
This paper looks at the different costs associated with concrete and steel bridges, including a summary on selecting, specifying and determining the life cycle maintenance cost of a coating system. A cost effective superstructure configuration is determined and a concrete versus steel cost comparison is given in an example from two real bridge projects where steel was found to be more cost effective than concrete. Costs include the superstructure and substructure costs as well as the maintenance costs. A summary on the cost benefits of ladder deck and network arch bridge systems is also given.
Technical Paper Dependable Performance Of Steel Structures In Fire With Case Studies
Abstract
This paper describes the application of a structural fire model, known as the Slab Panel Method (SPM), developed by the New Zealand Heavy Engineering Research Association (HERA) in conjunction with the University of Canterbury. The SPM accounts for the inelastic reserve of strength available from composite Steel/concrete floor systems due to their two way deformation under fully developed fire conditions. The outcome of the performance based design process is a steel structure with fire proofing only to some of the Steel beams supporting the floor. Structural elements which are critical for stability are protected with fire proofing materials, while the floor beams for which fire proofing is not necessary for structural stability or Integrity are designed without this passive fire protection. This provides a structure which will remain stable for the expected temperatures and associated mechanical properties.
Recent project examples where the SPM has been successfully used in New Zealand are reviewed. These Include a 20 storey 350,000 sq ft. office building and a 12 storey 360,000 sq ft. mixed use office and apartment building, both under construction in New Zealand. Validation of one of the design solutions using finite element analysis to assess the actual performance for the range of structural fire severity expected is described. The paper concludes that design methods are maturing to a level where a dependable and robust performance can be predicted using the SPM, so that those parts of the structure which require fire proofing can be specified with enough protection to maintain structural stability, and those parts which do not need this passive fire protection can be safely constructed without fire protection. Opportunities for the application of SPM in the North American regulatory environment are discussed.
Technical Paper Structural Failures – The Social Context
Abstract
1. Causes of Structural Failures
Some 80% of all structural failures appear to be due to some form of human error or error chain, “Structural failure” in this context, signifying that the structure (or part thereof) does not, or does no longer, fulfil the requirements of ultimate strength, serviceability and/or durability.
2. Human Error
The prevailing Management attitude towards human error in the workplace appears to be that of detection and rectification, with the accent on early detection in order to minimise the rectification cost, a reactive approach. The questions seldom asked are: “Why do people make errors in their work?” and subsequently: “What actions may be taken to improve quality performance by reducing the incidence of errors?” Seeking answers to these questions would constitute a proactive approach. Consideration of this problem clearly is in the realm of occupational psychology, a subject in the social sciences. The paper will deal in detail with the following emerging facets:
• The workplace “culture” prevailing in the construction industry,
• Tender evaluation practices,
• Leadership practices in the construction industry.
3. Remedial actions
The paper will recommend the following policy initiatives:
• Commencing a dialogue embracing the whole construction community with a view to replacing the prevailing adversarial culture by a co-operative one.
• Replacing tender evaluation practices based on minimum tender price by ones based on maximum project value.
• Replacing the present, mostly autocratic, cost-centred management style by a more democratic, value-centred one.
Technical Paper Grade 500e Reinforcing Steel
Abstract
Tests on Micro-alloy and Quenched and Tempered samples available in New Zealand
NZ Standards Update
Letter to Editor Re: B2 Durability – A Complex Mosaic of Liability and Risk
Abstract
Many Structural Engineers are being asked to sign or otherwise provide Design Producer’s Statements (PS1) forms which cite B2 Durability. Perhaps through a lack of knowledge, or through a simple desire to achieve a result for clients, there are a number of engineers who are complying with this council request. I have discussed this issue at some length with other engineers and can only conclude that this is not generally in the best interest of our Profession, nor of the public at large to whom we all owe our Duty of Care.
Letter to Editor Re An update to the ‘Seismic Retrofit Solutions’ project
Abstract
The project began in 2004 and has a dedicated web site at www.retrofitsolutions.org.nz, and readers are encouraged to visit the web site as it contains extra detail on project objectives and research personnel, plus an archive of published articles related to the project. The project is being overseen by an Industry Advisory Group whose membership was assembled by SESOC in collaboration with the New Zealand Society for Earthquake Engineering.
Introduction To Precast Double Tee Support Systems Study
Abstract
The draft Double Tee Support Systems paper was released in February. Following a period for comment, it has now been updated and follows this brief note.
Many readers may be aware that Precast New Zealand (PCNZ) has recently commissioned a further test. SESOC was not involved with the test, but has had the opportunity to review the report and has met with a PCNZ representative to discuss the outcome. The test was developed to investigate the performance of the loop bar detail or pigtail under seismic induced rotations and elongations.
Precast Double Tee Support Systems
Abstract
Precast Double Tee Support Systems have been reviewed in the context of concerns raised regarding the widespread use of details that may not have had sufficient design or testing verification for use under all load conditions that they may be subject to over their design life. Specific concern is addressed at the use of the loop bar or “pigtail” hanger.
This paper reviews current practice and outlines the performance parameters that must be considered in the
design and detailing of floor systems. It then goes on to review and discuss the perceived shortcomings in the
design and testing regime that has been in use to date, with recommendations as to the means to correct this
situation. Alternative practices are reviewed and recommended which may be verified by accepted design
practices using the existing New Zealand design standards.
The roles of the building designers and precasters are reviewed, with recommendations for the split of
responsibilities. This is intended to provide consistency of communication and coordination, the lack of which
appears to be a primary cause of difficulties observed to date. The need for an industry standard briefing
practice is highlighted, although not presented, as it will require further industry participation to complete.
Design Considerations For Green Roofs In New Zealand: A Case Study
Abstract
Green roofs are expected to become increasingly common in New Zealand as the demand for environmentally
sustainable building practices grows. A consequence of this is that Structural Engineers will more frequently
be required to consider green roofs when designing buildings. This paper provides a brief introduction into
green roofs, details some aspects that need to be considered by the Structural Engineer and outlines, as a case
study, the design of a green roof currently under construction in Aotea Square, Auckland, New Zealand. It can
be seen that research undertaken both internationally and within New Zealand is of sufficient quality and
quantity that green roofs can now be specified and designed with confidence by local building design professionals.
Sustainability Briefing – Green Roofs
Abstract
The term ‘green roof’ is a generic name for a roof of a structure that has some variety of plants installed on it. Traditionally grass has been installed on pitched roofs in agricultural environments, but more commonly for urban locations the ‘sedum’ species of plant or roof gardens are installed on flat roofs.
The primary reason for installing a green roof on a project is to increase bio-diversity for the site. This reduces the negative ecological impact of a project, and increases the points available on the BREEAM environmental scoring system. There are other benefits, which include good thermal performance, good sound insulation, air filtration, rain runoff reduction and attenuation.
Structural Implications Of Green Roofs, Terraces And Walls
Abstract
As green roofs, terraces, and walls are becoming more common, structural engineers appear to be unaware of the structural issues involved and how to address them. Green roofs, terraces, and walls are an architectural/
mechanical approach that tackles the sustainable design issues of storm water runoff, reduction of building
energy use, and an opportunity to provide usable space to building occupants. Structural engineers must understand the structural implications of such approaches with regards to static loads, dynamic loads, serviceability, durability, and anchorage. This document describes the structural implications of intensive green roofs/terraces, extensive green roofs, and green walls. An in depth discussion on assumed dead loads, live loads, seismic loads, wind effects, load combinations, serviceability concerns, and ASTM standards is provided. An analysis of tree loading, sloped roofs, seismic anchorage of green roofs, and recommended structural design specifications and strategies will also be presented. Lastly, strategies utilizing green roofs within the context of the sustainable metric systems such as USBGC’s LEED rating system will be addressed. This document will provide a resource for engineers looking to easily, safely, and effectively facilitate the integration of green roofs into their projects.
Development Of A Seismic Retrofit Model For The Ideers Competition
Abstract
A team of four postgraduate students represented the University of Auckland at the 2008 Asia-Pacific IDEERS
seismic design competition in Taiwan. The competition is an international seismic competition which aims to
promote the importance of earthquake engineering research. Hundreds of high school, undergraduate and
postgraduate students from around the world compete in this competition annually.
The competition involves the design and construction of a seismic retrofit scheme for a very weak, two storey
building model. The design must display base isolation and energy dissipation concepts and fail at a defined
performance level, when the peak ground acceleration (PGA) exceeds 1 g. The teams are judged on their ability to explain their retrofit ideas in a 15 minutes seminar, as well as the efficiency and the final performance of the model as tested on a biaxial shake table.
The final University of Auckland competition model utilised unorthodox materials to create a weak-beam strong column mechanism. This was coupled with a base isolation system to enhance its seismic resistance. The University of Auckland team finished second in the competition and was also awarded prizes for best structural and architectural design. This paper details the University of Auckland team’s design, the testing process prior to the competition and the team’s firsthand experience at the competition.
An Investigation Of Structural Engineer-Architect Collaboration
Abstract
The importance of collaboration between structural engineers and architects has long been recognized.
Collaboration leads to buildings possessing good seismic configuration and structure and architecture
being well-integrated. However, sometimes relationships between these two professional groups are strained.
Anecdotes of poor collaboration are recounted when individual architects and engineers are prompted.
A survey of practicing engineers and architects was undertaken in Wellington. Individual practitioners were
interviewed to explore the quality of their inter-disciplinary relationships and their perceptions of their
professional collaborators. Findings indicate that while there is little if any antagonism, and indeed an
overall culture of respect between professions, there is plenty of room for improving the quality of collaboration.
Structural engineers’ main concerns focus upon the following: architects’ lack of structural understanding;
architects seeking structural advice too late for optimal structural solutions, and the need for architects in
general to improve their focus upon collaboration. On the other hand architects are disappointed by engineers’ lack of both innovation and engagement with architectural design ideas. The paper concludes by discussing a range of approaches to engender better collaboration, stimulated in part by comments from a subsequent and less formal survey of practitioners.
Specifying Steel Fibre Reinforced Concrete, Segmental Tunnel Linings
Abstract
In the UK and more recently in the US and Australasia steel fibre reinforced concrete (SFRC) is becoming the
material of choice for segmental tunnel lining projects. In 2008 there were two projects in New Zealand where
SFRC fibre only solutions were preferred over traditional reinforcing; The Hobson Bay Sewer and the Rosedale
Water Outlet. The challenge faced by engineers involved in designing these projects is to unambiguously specify the performance required by the SFRC so as to achieve in the finished structure the performance that was assumed for the design. New Zealand has not been remiss in making it possible to meet this challenge. Since 2006, design methods for SFRC have been available in NZS 3101:2006 Concrete Structures, Part 2, Appendix A to section C5. The documented test and design methods describe not only how the material properties are determined but provide guidance on the design strengths to be used in the ultimate and serviceability limit state for different Performance Classes. An identical approach to the use of strength grades for the specification of both steel and concrete. Clause C5.5 of NZS 3101 states: “The design properties of steel fibre reinforced concrete are dependant on the post cracking toughness of the composite material. The properties of the fibre, such as its aspect ratio (length/diameter), ultimate tensile strength and end anchorage have a significant influence on the performance of the fibre reinforced concrete. Different fibre properties will result in different fibre dose rates to meet specific design properties.”
This means that even fibres that look the same, but supplied from different sources, will give different properties to the fibre reinforced concrete. EN 14889-1 fibres for concrete, is a quality control performance based manufacturing standard for steel fibres. In order to comply with the standard, manufacturers have to declare a minimum fibre dosage to achieve a required post crack flexural strength in a reference concrete. As a design engineer if there is any doubt in your mind about the performance of a particular fibre type, ask the supplier to provide a copy of this information. It allows for complete transparency enabling you to compare the expected performance between the fibre types on offer.
In Europe the Performance Class concept for SFRC is now also being used as a Quality Control measure in the
manufacture of SFRC. There is a requirement that batching plants obtain certification that they can deliver
performance classes consistently, just as they deliver certified plain concrete grades under a quality controlled
certification scheme. There is also compulsory product certification for steel fibres (through EN 14889-1), only
products with CE marking can be sold in European member states, this ensures a minimum level of quality and
performance.
We currently have one component of the Performance Class concept in New Zealand through NZS 3101; perhaps the next stage is compulsory product certification for steel fibres combined with the implementation of certified grades for SFRC.
Note from the Editor
Abstract
5.-Note-from-the-Eidtor-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Tribute to Tom Paulay
Abstract
6.-A-Tribute-to-Tom-Paulay-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Comment on Balustrades in Relation to New Zealand Building Code
Abstract
7.-Comment-on-Balustrades-in-Relation-to-New-Zealand-Building-Code-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Identifying Heritage Value in URM Buildings
Abstract
A large number of the heritage buildings in New Zealand are constructed from unreinforced masonry (URM). These buildings were not designed to resist seismic loads and now pose the highest earthquake risk of any building type due to the inherent weakness of the material and several key structural deficiencies. Many of these buildings will require seismic retrofit in order to meet the requirements of The Building Act 2004. URM buildings are a salient part of the culture and landscape of New Zealand, and it is vital that their important aspects are identified prior to any strengthening work. This identification process will inform the selection and design of an appropriate seismic retrofit intervention and ensure that a solution which is sympathetic to the heritage and aesthetics of the building is achieved.
The primary aim of this article is to reconcile the engineering goal of seismic strengthening of at-risk heritage buildings with the architectural goal of ensuring that their historic and aesthetic qualities are retained. This article is intended to assist structural engineers in recognising the important heritage aspects of URM buildings, but it is emphasised that this is not a substitute for the engagement of a professional heritage consultant.”
8.-Identifying-Heritage-Value-in-URM-Buildings-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
SESOC Design Guide - Anchor Bolts for Steel Structures
Abstract
This paper has been prepared by SESOC for the guidance and assistance of its members. It deals with anchor bolts (historically called ‘hold down bolts’) that are cast into reinforced concrete foundations in order to ‘anchor’ steel structures to those foundations. The guide is of a general nature, explaining the manner in which anchor bolts behave and therefore should be designed, the materials and fabrication methods that should be specified and used in their manufacture, and common problems with design, manufacture, and installation.
The basic principles of structural action are described, with only a small number of relevant equations. Because of the infinite variety of foundation types, reinforcing arrangements, and edge distances, it is not possible to provide ‘equations’ to cover all situations. However, if the fundamental actions are understood and allowed for in the design of the bolt embedment and the foundation, a dependable anchorage can be achieved.
Design of Bolted Connections: A Comparison of a Proposal and Various Existing Standards
Abstract
The design of bolted connections in most international design standards is based on the computation of the resistance of assumed ductile failure modes, further modified for the potential occurrence of brittle failure modes. Lately, various design proposals have been presented to cover the ductile and brittle failure modes separately. A proposal for inclusion into the Canadian wood design standard is presented, and its predictions of resistance for connection configurations that have been tested are compared to predictions using the current Canadian and European design standards for connections.
10.-Design-of-Bolted-Connections-A-Comparison-of-a-Proposal-and-Various-Existing-Standards-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Assessing the Dimensional Stability of New Zealand Concrete
Abstract
Concrete is subject to deformation in service due to loading, material, and environmental effects. Elastic, drying shrinkage, creep, and thermal movements can be particularly important for larger structures such as bridges, where realistic prediction of deflections is important. Results from several years of testing of structural concrete from around New Zealand are presented, and guidance is given about selecting appropriate material properties for assessing deformation of concrete structures in the serviceability limit state.
A companion paper describes how deflections and stress levels can be assessed using these properties for proposed structures. Research findings indicate that while compressive strength can be controlled within a fairly narrow range, properties such as elastic modulus, drying shrinkage, and creep may vary significantly. In design, it is important to consider the significance of the likely variability of material properties on the performance of a proposed structure by carrying out analyses with a range of material properties.
11.-Assessing-the-Dimensional-Stability-of-New-Zealand-Concrete-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Analysis for Creep, Shrinkage and Thermal Effects in Concrete Structures
Abstract
Deformation of concrete elements due to heat of hydration, creep, and shrinkage can have significant effects on the performance of concrete structures. Typical problems include long-term increases in deflection, stress redistribution in sections, redistribution of structural actions, relaxation of structural actions induced by imposed displacements, and deformations associated with the heat of hydration. The basis of methods used for assessing actions induced by creep and shrinkage of concrete is described, and examples are provided to indicate the likely magnitude of these effects on the serviceability of structures.
12.-Analysis-for-Creep-Shrinkage-and-Thermal-Effects-in-Concrete-Structures-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Extended Direct Analysis of Steel Frames
Abstract
A method for Extended Direct Analysis of steel frames as part of the design process is described. Effects considered in this analysis include: thermal residual stresses; moment-axial force interaction (material nonlinearity);
member out-of-straightness; frame out-of-plumb; and statistical variation of properties. Local P-D and global P-D second-order (geometric nonlinear) effects are properly considered. The frame is satisfactory if it does not
become unstable under factored statically applied forces or exceed a defl ection limit state. A program developed to permit the type of analysis required is described, and an example is provided.
13.-Extended-Direct-Analysis-of-Steel-Frames-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Sustainable Durability Design
Abstract
Steel is one of the most sustainable materials on Earth. It is 100% reusable, recyclable, easy to use, and maintain. To complement the numerous benefits of steel and extend its life, suitable protective measures must be taken to ensure structural performance is not reduced over its design life. Corrosion protection systems have been used for decades, but recent advancements in coatings, the use of weathering steel, and improved durability design guidelines and quality control can extend the time to first maintenance and improve the sustainability of steel structures.
This paper looks at the various methodologies to improve sustainability by outlining the guidance available for sustainable durability design and provides a brief introduction to those systems.
14.-Sustainable-Durability-Design-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Update from Standards New Zealand
Abstract
AS/NZS 2754.1 Timber adhesives – new Interim Standard
Structural design actions – new Amendment
New BRANZ design tool – lintels and beams calculator
Cement & Concrete Association – 2008 RED Book
Amendment No. 1 to NZS 3116:2002 Concrete segmental and flagstone paving
Timber framed buildings
Revision of NZS 3122:1995 and NZS 3123:1974
Specification – Seismic performance of engineering systems in buildings
Code of Practice for concrete structures for the storage of liquid
Revision of NZS 3404 Steel structures – Phases 1, 2, & 3
15.-Update-from-Standards-New-Zealand-SESOC-Journal-Vol.22-No.2-Sep-2009.pdf
Tribute – John Rutledge
Letter to Editor re Coupled Shear Walls
Abstract
My memory is that ACI318-05-Chapter 21 devotes a few pages and provides quite explicit requirements for diagonal cages
Letter to editor re Replacing Steel with Plastic Fibres
Abstract
I am writing to you as a concerned professional engineer employed by a manufacturer and supplier
of steel and synthetic fibres used to reinforce concrete, who is alarmed with the marketing approach
of some suppliers of synthetic fibres; in particular the promotion of their use as a substitute for steel
mesh and/ or steel fibres in concrete elements.
Letter to Ed re Some Aspects of Structural Stability During_After Fire Introduction
Abstract
This letter has been prompted by my observation of designs which do not comply with the NZ Building
Code requirements for building structural performance during and after fire. there appear to be
some common misconceptions among designers on this topic and by some conflicting requirements
between relevant NZ Standards.
I have consulted a number of engineering colleagues, Professor Andy Buchanan of the University of
Canterbury and Carol Caldwell a consulting fi re engineer on this matter.
Letter to Editor Steel Fibre reinforcing in Concrete
Abstract
I am writing to SESOC to express my concern as a contractor, specialising in the design and
construction of slab on grade, over the information being supplied with steel fibre in the New Zealand
market.
Steel fibres are routinely being used as reinforcement for concrete slab on grade. However
engineers, ready mix concrete suppliers and construction companies such as ours are being offered
a wide range of steel fibres, typically with no sound data on their quality or performance in concrete.
Letter to Editor Re Industry Feedback regarding NZS3101:2006
Abstract
We would be interested in hearing from structural engineers of difficulties that they have experienced in interpreting and applying this Standard.
A Design Methodology For The Assessment and Retrofit Of Flexible Diaphragms In Unreinforced Masonry Buildings
Abstract
Unreinforced masonry buildings (URM) have historically performed poorly in large earthquakes.
Many URM building failures have been attributed to poor diaphragm performance and inadequate wall − diaphragm connectivity. This paper provides a brief introduction into URM buildings and their seismic behaviour. It then outlines a design methodology for the assessment and retrofit of flexible diaphragms in URM buildings with an accompanying design example. Recommendations for future research are also provided.
In-Field Simulated Seismic Testing of As-Built and Retrofitted Unreinforced Masonry Partition Walls Weir House Wtn
Abstract
Unreinforced masonry (URM) partition walls of William Weir House in Wellington were subjected to out-of-plane forces to investigate the as-built wall characteristic behaviour. The lateral load resisting system of the 1932 reinforced concrete building was scheduled to undergo seismic strengthening, and due to the absence of reliable wall out-of-plane assessment data, consulting engineers adopted an experimental proof-testing approach. A team of student researchers from the University of Auckland tested four URM partition walls by subjecting the walls to out-of-plane uniform pressure applied by means of a system of airbags. The testing included two mid-storey and two top-storey URM partitions, which had developed prior minor structural cracks. The full-scale in-situ testing confirmed that the precracked partitions had sufficient strength to resist the current New Zealand seismic demand, and the experimental programme resulted in substantial financial benefits for the client as none of the walls were identified as demolition or strengthening candidates. In addition to the as-built out-of-plane tests, two tests were conducted on partition walls retrofitted using near surface- mounted (NSM) fibre-reinforced polymer (FRP) strips. The results of the as-built and the retrofitted wall testing are reported, the wall behaviour is evaluated against the current seismic demand and the assessment results are compared with the New Zealand Society for Earthquake Engineering (NZSEE) recommendations
Potential Failure Modes Associated with Hollow-Core Floors and Seismic Actions
Abstract
In the last decade much has been learnt about the performance of hollow-core floors and this is reflected in the provisions in the current Structural Concrete Standard (NZS 3101:2006 with Amendment No. 2). This paper gives a brief comparison of the detailing of hollowcore floors, as specified by the Structural Concrete Standard, with practice based on earlier editions of the Standard. Problems that may arise where the detailing falls short of currently accepted practice are briefly described.
A number of different failure modes of hollow-core floors subjected to seismic actions, which have been observed in tests or predicted in analytical studies, are briefly outlined. The intention in writing this paper is to give structural engineers involved in assessing existing buildings with hollow-core floors or designing new hollow-core floors an over-view of potential problem areas. More detailed information on assessment and design of hollow-core floors is given in two proposed reports.
Opportunities in Large Timber Pole Construction from a Novel Full Strength Round Connection
Abstract
TTT Products Ltd developed the technology to quickly lathe 15 m long poles into “Unilogs” up to 480 mm in diameter. These lathed poles are widely used in retaining wall and structural applications. The development of 250 mm diameter connections that are capable of full axial strength for effective structural performance opens new opportunities for large scale round timber structures. As each pole is manufactured in a lathe, it is a simple operation to cut 4 annular grooves into the outside of both ends. A tubular steel connector, manufactured with raised annular bands on the inner surface to fi t the timber grooves, is clamped across the connection. The system modifies an existing tubular connection designed for manual erection of the towers in difficult terrain. Laboratory testing of the connection was undertaken for 1 and 3 annular bands and the results are compared with the full strength of 4 annular band connections used on site. The new connection performs well and failure occurred in timber bearing and/or compression at an average of 820 kN before the connection load decreased.
Splitting Of New Zealand Grown Radiata Pine due to Connections Loading Perpendicular to Grain Theory and Applications
Abstract
This paper reviews a number of existing simple analytical fracture mechanics models available for determination of the splitting resistance of timber beams loaded perpendicular to grain by connections. Special focus is on the so-called van der Put/Leijten model, which is now used in the European and Canadian timber design codes. The applicability of this model to a number of situations encountered in practical design is discussed, and an experimental investigation of splitting failures in New Zealand grown Radiata Pine is presented. Tests were conducted on so-called plate specimens made of sawn timber, glue-laminated timber, and laminated veneer lumber. The characteristic (5-percentile) value of the sought fracture property varies between 13.5 N/mm1.5 and 20.4 N/mm1.5 for the tested materials. These values are to be compared with a value of 14 N/mm1.5 used in the European timber design code.
World Conference On Timber Engineering 2010, 20-24 June, Riva Del Garda, Trentino, Italy
Abstract
The World Conference on Timber Engineering was held in Riva Del Garda a town on the edge of beautiful lake Lago de Garda nestled among the mountains in Northern Italy. The conference had a total of 652 delegates and 70 partners from 43 countries with 8% of the delegates from New Zealand and Australia. The New Zealand group presented 18 high quality papers and 5 posters.
We were particularly well represented by the Structural Timber Innovation Company (STIC) group and this has significantly raised the profile of New Zealand timber engineering internationally.
Suggested Changes To NZS 3101:2006 with Amendments 1 and 2
Abstract
NZS 3101:2006 Concrete Structures Standard is a design code published by Standards New Zealand. Since the publication of the second amendment to NZS 3101:2006 a number of questions about specific clauses in the standard have been sent to Standards New Zealand and members of the Standards committee. The authors have sighted these questions and believe that a number of changes should be considered to correct errors, simplify interpretation of clauses and prevent unintended consequences or clashes with other clauses.
The suggested changes, which are detailed below, are made by the authors and they have not been
considered by Standards New Zealand or the NZS 3101 Standards Committee.
Department Of Building And Housing Response To The Paper “Suggested Changes To NZS 3101_2006 With Amendments 1 And 2”
Abstract
This response comments on the paper by Richard Fenwick and Dene Cook entitled “Suggested Changes to NZS 3101:2006 with Amendments 1 and 2. I understand that the purpose of the paper was to elicit comments relating to the on-going development of the Concrete Design Standard. I know there has been concern expressed about the lack of a forum to discuss such issues and, to this end, the new SESOC forum for NZS 3101 at http://www.sesoc.org.nz/discussion_forum is a welcome initiative and its use is to be encouraged. It is important to understand that the suggestions put forward by Richard Fenwick and Dene Cook are only suggestions.
Sesoc Practice Guideline - Independent Review Of Structural Designs For Building Consent
Abstract
The objective of this SESOC Practice Guideline is to provide a framework for independent third party review of structural designs submitted for building consent. The target audience of this document is professional engineers who are involved in the practise of structural engineering design and design review. It is not intended to be prescriptive, or to be used by others as a basis for prescribing the required scope for structural design reviews. However, it will provide useful background
material to others including clients, regulators and building officials. It is hoped that this Guideline will lead to a simpler, safer, more reliable and more consistent approach being taken by structural engineering designers and design reviewers across New Zealand.
Earthquake Reconnaissance – Forensic Engineering On An Urban Scale
Abstract
On 30 September 2009 a Richter magnitude 7.6 earthquake occurred approximately 50 km offshore from the Indonesian city of Padang on the west coast of Sumatra. As part of an AusAID initiative, the authors spent eight days conducting detailed structural assessments of damage to school buildings and medical/hospital buildings in the greater Padang region under the jurisdiction of the Australia – Indonesia Facility for Disaster Reduction (AIFDR). Approximately 300 school and 100 medical buildings were assessed during this time. The procedure used for this ‘forensic engineering’ task on an urban scale, rather than individual building scale, is described. From the data collected, the authors were able to identify common structural defects as well as deduce systemic deficiencies in the overall design and construction process for the Padang region, with a summary of these observations presented.
Earthquake-Damaged Unreinforced Masonry Building Tested In-Situ
Abstract
In December 2007 a magnitude 6.8 earthquake had an epicentre located approximately 50 km from the city of Gisborne, New Zealand. This earthquake caused damage to a number of buildings in Gisborne, and in particular, to numerous unreinforced masonry buildings. One such building was damaged to the extent that significant post-earthquake repairs were necessary, and partial removal of two of the building’s gable ended walls was required. This reconstruction provided an opportunity for a team of researchers from the University of Auckland to conduct field tests on the building, allowing comparison with companion testing that had previously been undertaken in a laboratory setting. This field testing involved the extraction of clay brick and mortar samples, in-situ bed joint shear tests, diagonal shear tests on samples extracted from the gabled walls, an in-situ in-plane shear test and out-of-plane testing of a gable ended wall both in the as-built condition and after the installation of a near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) retrofit solution. Testing confirmed that the boundary conditions in real buildings can significantly affect experimental response, with vertical restraint resulting in a large increase in out-of-plane load capacity, and also confirmed that the near-surface mounted FRP solution is an excellent low invasive option for seismic strengthening of unreinforced masonry walls. Details of the history of
the building, and the methods used to undertake the field testing are reported, and experimental results are presented.
Out-Of Plane Strengthening Of Unreinforced Masonry Walls Using Near Surface Mounted Fibre Reinforced Polymer Strips
Abstract
The development of cost effective minimally-invasive seismic retrofit techniques is required for clay brick unreinforced masonry (URM) buildings because of their recognised poor seismic performance.
A laboratory-based experimental study with well defined but artificial boundary conditions, which utilises constituent construction materials that replicate the material properties of masonry found in historic URM buildings, is currently addressing this need. The purpose of this study is to investigate the performance of near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) strips as a seismic retrofit solution for out-of-plane lateral loading of the walls in URM buildings. In addition, five retrofitted URM walls located in four different buildings were tested in-situ by applying out of plane loading, to complement the laboratory-based study. Testing confirmed that the NSM CFRP retrofit technique is an excellent minimally-invasive and cost effective option for seismic strengthening of URM buildings. Provisional details of the design methodology for the NSM CFRP retrofit technique, and laboratory and in-situ test results are reported. Two recent projects that implemented the NSM CFRP technique are also briefly presented.
22 FEBRUARY CHRISTCHURCH EARTHQUAKE
Abstract
GREG McRae (University of Canterbury) has shared some questions with us regarding the 22 February earthquake which had a devastating effect on Christchurch. These questions need answering before we can move on with the reconstruction work with confidence. We also refer you to the SESOC website where you can comment online to a number of questions which require some healthy debate.
FORSYTH BARR STADIUM – DUNEDIN, NEW ZEALAND A NEW FULLY ROOFED RUGBY STADIUM FOR OTAGO
Abstract
Otago desired a new rugby stadium to replace the existing Carisbrook Park, colloquially known as “The House of Pain” due to the sometimes severe winter weather that could plague major tournaments. New Zealand Rugby Football Union winning the rights to the 2011 Rugby World Cup provided the catalyst for this project to get under way. To be constructed on a new site close to the city, the new stadium was to be fully roofed, but needed to avoid the costs associated with opening sections and the like. The solution developed was for a relatively low transparent roof angled for beneficial transmission of sunlight to the turf. The region is subject to significant wind, seismic actions and to sub-alpine snow fall. These factors lead to a challenging project. This paper describes those challenges and the solutions developed.
A PILOT SURVEY OF STRUCTURAL ENGINEERS’ PERCEPTIONS REGARDING SPECIFICATION OF LAMINATED VENEER LUMBER IN SINGLE-STOREY INDUSTRIAL BUILDINGS
Abstract
A pilot survey of Christchurch structural engineers was carried out between November 2009 and February 2010, to examine factors affecting the specification of laminated veneer lumber (LVL) for single-storey
industrial buildings. Single-storey industrial buildings were chosen for study because they are a significant proportion of the workload of most civil and structural engineering firms in Christchurch, the specification of materials is done by the engineer, and currently steel is the preferred structural material for this type of building.
RETROFIT TECHNIQUES FOR SEISMIC IMPROVEMENT OF URM BUILDINGS
Abstract
There are many complex considerations when seeking to seismically retrofit unreinforced masonry (URM) buildings. Strength requirements need to be evaluated, and the intrinsic strength of the existing materials should be maximised before adding any additional structure. Descriptions of current common techniques for improving the seismic response of URM buildings are outlined, and comments made as to their general appropriateness with regard to architectural and heritage principles. These techniques are explained and critiqued using examples to illustrate their merits or lack thereof.
TESTING AND SEISMIC RETROFIT OF 1917 WINTEC F BLOCK URM BUILDING IN HAMILTON
Lumantarna, Liam Wotherspoon and Jason M. Ingham
Abstract
Wintec F block is a two storey unreinforced masonry (URM) building constructed in 1917 with an architectural style termed “stripped classical”, that was assessed to be potentially earthquake prone according to the provisions of the Building Act 2004. Material testing and seismic assessment were conducted on the as-built structure and it was determined thatWintec F block had sufficient out-of-plane seismic strength for most of its walls, but that the building had insufficient in-plane seismic strength. Seismic improvement was proposed using a type of strain-hardening fibre reinforced shotcrete called Engineered Cementitious Composite (ECC) combined with steel reinforcement, and the building was strengthened to 100% of New Building Standard (NBS).
TENTATIVE SEISMIC DESIGN GUIDE- LINES FOR ROCKING STRUCTURES
Abstract
Many new and existing buildings have insufficient weight to resist overturning loads due to earthquakes without uplift. Previous versions of the New Zealand loadings code allowed simplified procedures for the design of rocking structures provided the ductility factor was limited to not more than two. The new loadings code, NZS 1170.5, removed this exemption and requires that a special study be performed whenever energy dissipation through rocking occurs. This paper presents a tentative design procedure intended to substitute for the special study required by the code.
The resistance function of rockingwallswas developed fromthe principles of engineering mechanics. The results from a series of time history analyses were used to develop a procedure to estimate maximum seismic displacements and empirical equations were derived to estimate the dynamic amplification of inertia forces. A substitute structure approach, using spectral displacements at an effective period calculated from the ductility factor, provided accurate predictions of the displacements from more sophisticated nonlinear analyses.
Four example designs were completed and the predicted response compared to time history results. The procedure provided a satisfactory estimate of response for regular structures, but it was less accurate where torsional effects were significant.
DESIGN OF FLOORS CONTAINING PRECAST UNITS IN MULTI-STOREY BUILDINGS
Abstract
As a result of research carried out in the last decade methods of detailing hollow-core and other forms of precast units in floors have been developed to overcome a number of weaknesses, which have been observed in structural tests and predicted in analytical studies. This work has lead to a number of changes being introduced into the Structural Concrete Standard, NZS 3101: 2006 with Amendment 2. The intent behind this paper is to identify and describe the specific aspects that should be addressed by structural designers for floors containing precast units, and to identify the relevant clauses in the Structural Concrete Standard. In addition guidance is given on aspects of behaviour that are not currently covered by the Standard. The paper does not consider methods of assessing diaphragm forces induced in floors by seismic or wind forces.
SEISMIC BEHAVIOUR OF STEEL MOMENT FRAMES WITH AN INNOVATIVE SLOTTED-BOLTED CONNECTION IN NEAR FIELD EARTHQUAKES BASED ON ENERGY
Abstract
Input energy and the ratio of hysteretic to input energy could be regarded as criteria to evaluate the performance of a structure during a seismic event. With regard to the significance of employment of slotted bolted connections in seismic design of steel moment frames, a new type of them has been introduced. Subsequently, the seismic performances of steel moment frames with/without the proposed connection subjected to near field earthquake excitations have been compared by means of energy concepts. Nonlinear dynamic analyses were made using three far field and three near field records through PERFORM platform. Moreover, the effects of the number of stories and bays as well as Peak Ground Acceleration (hereafter PGA) of earthquake record were studied. The results show that the performance of steel moment frames with the proposed connection subjected to near field as well as far field earthquakes are more dependable compared to those of customary steel moment frames on the basis of energy criteria.
Letter to the Editor_Travel to IDEERS Seismic Design Competition in Taiwan
Abstract
First and foremost, we would like to extend our thanks to the Structural Engineering Society for providing sponsorship for our team to attend the 2010 postgraduate IDEERS seismic design competition in Taiwan. Without your generous support we would not have been able to attend the competition, from which we have all increased our earthquake engineering knowledge.
Letter to the Editor_Boundary Wall Surcharges in Auckland
Abstract
I am responding to your editorial in the March 2010 SESOC journal. In this journal you wrote a short dissertation on boundary walls whereby you queried a number of issues surrounding the design of boundary walls. The following is my understanding of the situation.
22 February Christchurch Earthquake_Questions Regarding the Design Process
Abstract
Greg McRae (University of Canterbury) has shared some questions with us regarding the 22 February earthquake which had a devastating effect on Christchurch. These questions need answering before we can move on with the reconstruction work with confidence. We also refer you to the SESOC website where you can comment online to a number of questions which require some healthy debate – Editor.
Forsyth Barr Stadium – Dunedin, NZ_A New Fully Roofed Rugby Stadium for Otago
Abstract
Otago desired a new rugby stadium to replace the existing Carisbrook Park, colloquially known as “The House of Pain” due to the sometimes severe winter weather that could plague major tournaments. New Zealand Rugby Football Union winning the rights to the 2011 Rugby World
Cup provided the catalyst for this project to get under way. To be constructed on a new site close
to the city, the new stadium was to be fully roofed, but needed to avoid the costs associated with opening sections and the like. The solution developed was for a relatively low transparent roof angled for beneficial transmission of sunlight to the turf. The region is subject to significant wind, seismic actions and to sub-alpine snow fall. These factors lead to a challenging project. This paper describes those challenges and the solutions developed.
A Pilot Survey of Structural Engineers’ Perceptions Regarding Specification of Laminated Veneer Lumber in Single-Storey Industrial Buildings
Abstract
A pilot survey of Christchurch structural engineers was carried out between November 2009 and February 2010, to examine factors affecting the specification of laminated veneer lumber (LVL) for single-storey industrial buildings. Single-storey industrial buildings
were chosen for study because they are a significant proportion of the workload of most civil and structural engineering firms in Christchurch, the specification of materials is done by the engineer, and currently steel is the preferred structural material for this type of building.
The survey was designed to answer the following questions:
1. What are engineers’ perceptions regarding specification of LVL in single-storey industrial buildings?
2. What barriers prevent increased use of LVL in this application?
3. How do engineers rate LVL compared with steel on factors which determine usage?
Retrofit Techniques for Seismic Improvement of URM Buildings
Abstract
There are many complex considerations when seeking to seismically retrofit unreinforced masonry (URM) buildings. Strength requirements need to be evaluated, and the intrinsic strength of the existing materials should be maximised before adding any additional structure. Descriptions of current common techniques for improving the seismic response of URM buildings are outlined, and comments made as to their general appropriateness with regard to architectural and heritage principles. These techniques are explained and critiqued using examples to illustrate their merits or lack thereof.
Testing and Seismic Retrofit of 1917 Wintec F Block URM Building in Hamilton
Abstract
Wintec F block is a two storey unreinforced masonry (URM) building constructed in 1917 with an architectural style termed “stripped classical”, that was assessed to be potentially earthquake prone according to the provisions of the Building Act 2004. Material testing and seismic assessment were conducted on the as-built structure and it was determined that Wintec F block had sufficient out-of-plane seismic strength for most of its walls, but that the building had insufficient in-plane seismic strength. Seismic improvement was proposed using a type of strain-hardening fibre reinforced shotcrete called Engineered Cementitious Composite (ECC) combined with steel reinforcement, and the building was strengthened to 100% of New Building Standard (NBS).
Tentative Seismic Design Guidelines for Rocking Structures
Abstract
Many new and existing buildings have insufficient weight to resist overturning loads due to earthquakes without uplift. Previous versions of the New Zealand loadings code allowed simplified procedures for the design of rocking structures provided the ductility factor was limited to not more than two. The new loadings code, NZS 1170.5, removed this exemption and requires that a special study be performed whenever energy dissipation through rocking occurs. This paper presents a tentative design procedure intended to substitute for the special study required by the code.
The resistance function of rocking walls was developed from the principles of engineering mechanics.
The results from a series of time history analyses were used to develop a procedure to estimate maximum seismic displacements and empirical equations were derived to estimate the dynamic amplification of inertia forces. A substitute structure approach, using spectral displacements at an effective period calculated from the ductility factor, provided accurate predictions of the displacements from more sophisticated nonlinear analyses.
Four example designs were completed and the predicted response compared to time history results. The procedure provided a satisfactory estimate of response for regular structures, but it was less accurate where torsional effects were significant.
Design of Floors Containing Precast Units in Multi-Storey Buildings
Abstract
As a result of research carried out in the last decade methods of detailing hollow-core and other forms of precast units in floors have been developed to overcome a number of weaknesses, which have been observed in structural tests and predicted in analytical studies. This work has led to a number of changes being introduced into the Structural Concrete Standard, NZS 3101: 2006 with Amendment 2. The intent behind this paper is to identify and describe the specific aspects that should be addressed by structural designers for floors containing precast units, and to identify the relevant clauses in the Structural Concrete Standard. In addition guidance is given on aspects of behaviour that are not currently covered by the Standard. The paper does not consider methods of assessing diaphragm forces induced in floors by seismic or wind forces.
Seismic Behaviour of Steel Moment Frames with an Innovative Slotted-Bolted Connection in Near Field Earthquakes Based on Energy
Abstract
The steel moment frame with fully restrained (FR) connections is a very popular type of seismic load resistance system worldwide. Several post-earthquake reconnaissances have revealed some weaknesses associated with welded FR connections. The great expense which needs to be spent on the repair of such systems is one of their main drawbacks. This leads to the idea of “damage avoidance design” to become more highlighted among structural engineering communities.
Moreover, observed responses of the damaged steel frames in the 1994 Northridge and the 1995 Hyogoken Nanbu earthquakes show that the connection’s behaviour has switched from initially rigid to semi-rigid during ground motion. On the other hand, the overall Abstract Input energy and the ratio of hysteretic to input energy could be regarded as criteria to evaluate the performance of a structure during a seismic event. With regard to the significance of employment of slotted bolted connections in seismic design of steel moment frames, a new type of them has been introduced. Subsequently, the seismic performances of steel moment frames with/without the proposed connection subjected to near field earthquake excitations have been compared by means of energy concepts. Nonlinear dynamic analyses were made using three far field and three near field records through PERFORM platform. Moreover, the effects of the number of stories and bays as well as Peak Ground Acceleration (hereafter PGA) of earthquake record were studied. The results show that the performance of steel moment frames with the proposed connection subjected to near field as well as far field earthquakes are more dependable compared to those of customary steel moment frames on the basis of energy criteria.
The Future is Multi-storey Buildings Utilising Composite Materials
Abstract
Letter to the Editor
It is disturbing to note that in his recent opinion piece, the former Minister for Agriculture and
Fisheries and MP for Christchurch, the Hon Jim Anderton continues his one-sided campaign to rebuild the multi-storied buildings in the Christchurch CBD in wood. He notes in his opinion piece that his views have been labelled as “ridiculous and stupid” by the Canterbury President of the Master Builders’ Federation.
Jim Anderton cites new research by Professor Andy Buchanan of the University of Canterbury which positioned engineered timber construction as a viable alternative to concrete and steel in multi-storey buildings. It is disturbing because some claims made in the research, particularly on sustainability, cannot in the foreseeable future be met. There are also concerns over long term structural performance due to dimensional changes in the timber. HERA pointed this out to both
Jim Anderton and Prof. Buchanan when the research was first published, and more importantly, that multi-storey timber buildings have not gained a significant mainstream following either here or overseas due in part to these unresolved concerns. Rushing forward building designs without these issues being fully addressed is unlikely to provide real benefits for the people or the economy of Christchurch.
BRANZ Funds Research to Investigate Structural Design of Buildings for Fire
Abstract
Letter to the Editor
Every year BRANZ expends considerable time and effort to consult widely with the building and construction industry in New Zealand so as to help inform the BRANZ annual Building Research Levy investment process. A significant proportion of this investment is targeted at the specific issues that the industry expresses concern about, but there is also a general expectation that a portion of the funding will be spent on future-focussed research that will help the industry deal with issues that can be described as being “over the horizon”.
One such current area of research is that relating to the design of structures in fire. The BRANZ Fire and Structural Engineering Team is part way through a three year project…
Combined Reinforcement – Practical Experiences
Abstract
Concrete is a brittle material and cracking is normal. In fact, in order to take account of the reinforcing effect of bar or mesh the cracked section is used in the design of concrete structures. If these cracks are controlled within specified levels they are not detrimental to the integrity of the structure and do not affect its serviceability. This control is generally met by providing a minimum percentage of steel reinforcing.
NZS 3106:2009 Design of concrete structures for the storage of liquids provides a procedure on how to calculate crack widths in reinforced concrete, taking into account expected stress distribution and the age of concrete when this cracking may occur.
Combined Reinforcement – Practical Experiences Gerhard Vitt
Abstract
Adding steel fibres to concrete very positively affects both crack development and cracking process itself. But in the past, steel fibres were hardly being used in combination with traditional concrete reinforcement. Nowadays combined reinforcement is becoming more and more common, at least in Western Europe. Several research projects have been carried out to derive design procedures for combined reinforcement. The post crack strength of fibre concrete may be taken into account both for serviceability and ultimate limit state. Numerous projects have been carried out. A few of them will be presented in this paper, giving insight into why combined reinforcement was chosen.
Performance of Timber Structures in the Christchurch Earthquakes
Abstract
This paper is a review of the performance of timber buildings in the 2010 and 2011 Christchurch earthquakes, most being from the earthquake of 22 February 2011. This includes engineered timber buildings using glulam and LVL. Domestic house construction is not included except for a few special cases.
Steel Building Damage from the Christchurch Earthquake Series of 2010_2011
Abstract
This paper presents preliminary field observations on the performance of selected steel structures in Christchurch during the February 22nd, 2011, Magnitude 6.3 event. In the downtown area of Christchurch, this event was considerably more severe than that from the September 4, 2010, Darfield earthquake. Focus is on performance of eccentrically braced frames, concentrically braced frames, moment resisting frames, and industrial storage racks. With a few notable exceptions, steel structures performed well during this earthquake, to the extent that inelastic deformations were approx 50% less than what would have been expected given the severity of the recorded strong motions. Some hypotheses are formulated to explain this satisfactory performance.
These structures have not visibly suffered further damage in the June 6th or June 13th earthquakes so this paper has been extended in coverage to the full damaging earthquake series of 4 September and 26 December 2010, 22 February, 6 June and two on 13 June 2011. The main focus is on the 22 February event which was significantly more intense.
Performance of Unreinforced Stone Masonry Buildings during 2010_2011 Canterbury Earthquake Swarm and Retrofit Techniques for their Seismic Improvement
Abstract
The sequence of earthquakes that has greatly affected Christchurch and Canterbury since September 2010 has again demonstrated the need for seismic retrofit of heritage unreinforced masonry buildings. Commencing in April 2011, the damage to unreinforced stone masonry buildings in Christchurch was assessed and recorded with the primary objective being to document the seismic performance of these structures, recognising that they constitute an important component of New Zealand’s heritage architecture.
A damage statistics database was compiled by combining the results of safety evaluation placarding and post-earthquake inspections, and it was determined that the damage observed was consistent with observations previously made on the seismic performance of stone masonry structures in large earthquakes. Details are also given on typical building characteristics and on failure modes observed. Suggestions on appropriate seismic retrofit and remediation techniques are presented, in relation also to strengthening interventions that are typical for similar unreinforced stone masonry structures in Europe.
Performance of Unreinforced Clay Brick Masonry Buildings during The 22nd February 2011 Christchurch Earthquake
Abstract
In the early morning of 4th September 2010 the region of Canterbury, New Zealand, was subjected to a magnitude 7.1 earthquake. The epicentre was located near the town of Darfield, 40 km west of the city of Christchurch. This was the country’s most damaging earthquake since the 1931 Hawke’s Bay earthquake (GeoNet, 2010). Since 4th September 2010 the region has been subjected to thousands of aftershocks, including several more damaging events such as a magnitude 6.3 aftershock on 22nd February 2011. Although of a smaller magnitude, the earthquake on 22nd February produced peak ground accelerations in the Christchurch region three times greater than the 4th September earthquake and in some cases shaking intensities greater than twice the design level (GeoNet, 2011; IPENZ, 2011). While in September 2010 most earthquake shaking damage
was limited to unreinforced masonry (URM) buildings, in February all types of buildings sustained damage. Temporary shoring and strengthening techniques applied to buildings following the Darfield earthquake were tested in February 2011. In addition, two large aftershocks occurred on 13th June 2011 (magnitudes 5.7 and 6.2), further damaging many already weakened structures. The damage to unreinforced and retrofitted clay brick masonry buildings in the 4th September 2010 Darfield earthquake has already been reported by Ingham and Griffith (2011) and Dizhur et al. (2010b). A brief review of damage from the 22nd February 2011 earthquake is presented here.
President's Report
Note From the Editor
Letters to the Editor
Design on Conventional Structural Systems Following the Canterbury Earthquake - A SESOC Guidance Note
L'Aquila Earthquake Italy 2009
Abstract
A significant earthquake of 6.3 Mw took place in L’Aquila, 110 km Northeast of Rome on 6th April 2009 and located in the Abruzzo region. L’Aquila then had a population of 73,000 and suffered many deaths during the event which also made 65,000 people homeless. Buildings constructed of stone rubble masonry and more recently reinforced concrete frame with brick masonry infill were often badly damaged or destroyed. This article details the resultant damage and also shows various methods for shoring.
The Coy Mistress - A Review of Masonry Behaviour
Abstract
Reproduced with thanks and approval from IStructE and Dr Bill Harvey (author)
Seismic Resistance of New Zealand Brick Veneer
Abstract
Recent full-scale cyclic and shake tests by the author showed that modern, well-constructed, single and two-storey brick veneer clad New Zealand houses will perform very well under in-plane seismic load. Separate out-of-plane shake table tests showed that veneer shedding is unlikely from design-level seismic shaking.
The performance of brick veneer construction in recent New Zealand earthquakes is discussed.
The compressive and bond strengths of a wide range of brick veneer mortar mixes was measured both on-site and in the laboratory. A selection of these mixes was used to construct brick veneer walls which were later tested under out-of-plane seismic shaking. By examining the mortar properties which gave good wall performance, critical mortar properties to ensure good seismic performance were determined.
Recommendations are made to masonry standards so that this will be achieved on-site.
Test Results for Extracted Wall-Diaphragm Anchors from Christchurch Unreinforced Masonry Buildings
Abstract
Test results are presented for wall-diaphragm plate anchor connections that were axially loaded to rupture. These connection samples were extracted post-earthquake by sorting through the demolition debris from unreinforced masonry (URM) buildings damaged in the Christchurch earthquakes. Unfortunately the number of samples available for testing was small due to the difficulties associated with sample collection in an environment of continuing aftershocks and extensive demolition activity, when personal safety combined with commercial activity involving large demolition machinery were imperatives that inhibited more extensive sample collection for research purposes.
Nevertheless, the presented data is expected to be of assistance to structural engineers undertaking seismic assessment of URM buildings that have existing wall-diaphragm anchor plate connections installed, where it may be necessary to estimate the capacity of the existing connection as an important parameter linked with determining the current seismic capacity of the building and therefore influencing the decision regarding whether supplementary connections should be installed. The performance of brick veneer construction in recent New Zealand earthquakes is discussed. The compressive and bond strengths of a wide range of brick veneer mortar mixes was measured both on-site and in the laboratory. A selection of these mixes was used to construct brick veneer walls which were later tested under out-of-plane seismic shaking. By examining the mortar properties which gave good wall performance, critical mortar properties to ensure good seismic performance were determined. Recommendations are made to masonry standards so that this will be achieved on-site.
Seismic Analysis of a Low-Damage Precast Wall with End Columns (PreWEC) Including Interaction with Floor Diaphragms
Abstract
The 2010/2011 Canterbury earthquakes have demonstrated that low-damage structural systems should be adopted to improve the seismic performance of concrete buildings and to reduce the economic and social impact of building damage in future earthquakes. One such low-damage structural system is selfcentering precast concrete walls that utilise jointed construction and unbonded post-tensioning. A new low-damage concrete wall system that uses this self-centering design is PreWEC, which consists of a precast wall with end columns. The PreWEC system was designed to overcome the deficiencies of previous low-damage wall systems by increasing the moment capacity in a cost effective manner, so that the PreWEC system is comparable to traditional reinforced concrete construction in addition to providing superior seismic resilience.
It is important that when a building is constructed using a low-damage wall system, its seismic performance, including the self-centering capability, is not compromised by damage caused to other structural elements when the building is subjected to an earthquake input motion. Similarly, it is important to avoid damage occurring during excitation that arises from interaction between the wall system and other structural elements. Experimental and analytical validation of the PreWEC system is summarised in addition to details of analytical studies that were performed to examine the interaction between the PreWEC wall, the floor diaphragms and gravity columns, as well as the seismic response of a prototype building that included PreWEC walls. Recommendations are presented to improve the seismic design practice for low-damage concrete buildings with specific consideration to the wall-to-floor interaction.
Standards NZ and DBH Updates
News From The Regional Structural Groups
Treasurer's Report to Management Committee Meeting 20 March 2012
Obituary (Ken McIntosh)
President's Report
Abstract
A report from SESOC Management Committee President, John Hare
Note from the Editor
Abstract
A note from SESOC Journal Editor, Stewart Hobbs
Letters to the Editor
Abstract
ALERT - Tension Cable and Rod Connectors
Wind Design Calculations per NZS 3604
CPEng: A Mark of Quality?
Abstract
The Licensed Building Practitioner scheme has recently been introduced in response to concerns over the quality of work undertaken across a broad range of professionals in the construction industry. As structural engineers, our quality and experience is measured by attaining Chartered Professional Engineer (CPEng) status. But just how well can the quality of our engineers be determined by the current New Zealand CPEng examination process? This paper highlights the disparity in examination requirements for the professional engineering qualification between The United States of America, the United Kingdom, and New Zealand. Weaknesses in the current CPEng assessment procedure are discussed along with possible improvements to the process.
A Review of the Suitability of Fibre Reinforced Concrete for Structural Applications in New Zealand
Abstract
The introduction of design methods for steel fibre reinforced concrete in the most recent revision of the New Zealand Concrete Structures Standard has made it easier for engineers to use the material in structural applications. However, there are concerns that SFRC is being recommended for applications for which it is not appropriate. The purpose of this report is to guide engineers on the suitability of SFRC for structural applications. The report is structured into sections discussing each application in turn, with discussion based on review of relevant research, existing examples of the application, and where possible design methods. In addition to determining applications for which SFRC is suitable, a number of recommendations are made for extension or revision of the SFRC design methods in the New Zealand Concrete Structures Standard.
A number of appendices are included at the end of the report. These provide additional information including an overview of fibre reinforced concrete classification and details regarding test methods for SFRC.
Seismic Design of Plasterboard Wall Bracing Systems
Abstract
The performance of plasterboard bracing elements during the Canterbury earthquakes and recent experimental testing has brought into question assumptions that are currently made in the seismic design and analysis of houses. This paper highlights and addresses shortcomings in current design procedures. The cyclic response of several plasterboard bracing walls is considered and interpreted. The dynamic energy dissipating or damping potential of plasterboard walls is shown to be limited, indicating that the use of current NZS1170.5 reduction factors, used in NZS3604, may not be appropriate. The experimental response of the bracing walls is modelled using finite element models that are subjected to 15 earthquake records, compatible with New Zealand Standards (NZS1170.5). It is demonstrated that current design approaches are non-conservative, resulting in excessive lateral displacements and failure to satisfy accepted seismic performance criteria. New force-reduction factors for the seismic design of plasterboard bracing walls are determined. Finally, a revised house design procedure is proposed.
New Low Damage Timber Frame Solution for Multi-Storey Office Type Buildings
Abstract
The focus of seismic design is shifting from providing for life safety only to also minimising damage to the building. A brief review of passive structural control methods is provided followed by a description of friction sliding connections and rocking lateral load resisting systems. A gravity rocking moment connection with friction energy dissipation is proposed for office type timber multi-storey buildings. Preliminary testing of a 1:20 scale model has shown excellent low-damage performance with high energy dissipation and good self-centring characteristics.
Seismic Retrofit of Light-Weight Timber Building with Soft First Story
Abstract
It has been observed that building structures with the first story of relatively low stiffness compared to the upper stories has the potential to develop significant deformation at the first story during earthquakes. Engineers have been aware of the phenomenon since the 1920s (Nishkian 1927, Snyder 1927, Martel 1927). It has been generally accepted (Chopra 1973) that such arrangements should be avoided due to high ductility demand.
Seismic Resilience Foundation System for Residential Dwellings and Possible Construction Techniques
Abstract
A seismic resilience foundation system for residential dwellings shall need to provide protection against ground motion induces damages, liquefaction and tsunami. As such it is desirable that the system has the lateral force resisting properties of high integrity, ductility, bending moment capacity and buoyancy. The construction techniques to be utilized to realize the design are segmental construction, post tensioning and securing voids to create buoyancy. The construction of the segments could be executed by the precast method or by preplaced aggregate grout construction technique.