SESOC

Journals Abstracts

These are short abstracts of the material printed in our journal which is published twice annually. The Journal covers items of interest to structural engineers, including but not limited to: technical papers, project reports, materials information, code reviews.

Journal: Vol 22 No. 1 2009

 

Title
Letter to Editor Re: B2 Durability – A Complex Mosaic of Liability and Risk Vol.22 No.1 2009
Author/s

Maurice Quinn P.Eng Ontario
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.
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Title
Letter to Editor Re An update to the ‘Seismic Retrofit Solutions’ project Vol.22 No.1 2009
Author/s

Jason Ingham
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.
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Title
Introduction To Precast Double Tee Support Systems Study Vol.22 No.1 2009
Author/s

John Hare
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.
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Title
Precast Double Tee Support Systems Vol.22 No.1 2009
Author/s

John Hare, Richard Fenwick, Des Bull, Richard Built (SESOC Sub Committee)
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.
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Title
Design Considerations For Green Roofs In New Zealand: A Case Study Vol.22 No.1 2009
Author/s

Stuart J Oliver, Richard Cooper
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.
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Title
Sustainability Briefing – Green Roofs Vol.22 No.1 2009 (Reproduced By Permission Of The Structural Engineer Volume 87 Issue (1) January 2009)
Author/s

Istructe Sustainable Construction Panel
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.
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Title
Structural Implications Of Green Roofs, Terraces And Walls Vol.22 No.1 2009
Author/s

Mikaël Gartner (Reproduced by permission of the SEAOSC Sustainable Design Committee)
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.
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Title
Development Of A Seismic Retrofit Model For The Ideers Competition Vol.22 No.1 2009
Author/s

Dmytro Dizhur, Charlotte Knox, Samuel Green, Ronald Lumantarna, Quincy Ma
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.
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Title
An Investigation Of Structural Engineer-Architect Collaboration Vol.22 No.1 2009
Author/s

A.W. Charleson, S. Pirie
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.
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Title
Specifying Steel Fibre Reinforced Concrete, Segmental Tunnel Linings Vol.22 No.1 2009
Author/s

Jeff Novak (Abstract By Alan Ross)
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.
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