Single storey precast panels out of plane parts loading for seismic assessment of existing building  

Hi

We are seeking clarification on the correct procedure to analysis existing precast concrete panels for out-of-plane actions (for a seismic assessment of an existing building), for a single storey warehouse building to the minimum design standards.

We have analyzed a single storey simple warehouse type building (designed circa 2016 and built circa 2017) and our assessment has been peer reviewed by a reviewer who disagrees with our approach to analyze the precast concrete panels. We have not been able to get agreement on a very fundamental design philosophy.

Our understanding is that the design loads of a single storey pin based concrete panel (supported on the foundations) spanning to a waler beam at the top of the panel, its connections, waler beam and its connections need to be analyzed to equation 8.2 (1) in section 8 of NZS1170.5. We have essentially used the same procedure outlined in the sesoc paper (Southwick, 2017). The panels are approximately 10-13m tall. 3 sides of the warehouse are singly reinforced concrete panels and the fourth is a combination of concrete panels and steel cross braces. Cross braces roof diaphragm is present. This is basically the entire bracing system. Plan dimensions are 60m x 45m approximately 13m heigh at the ridge apex and 10m at the sides.

The review engineers agree that the panels should be treated as a part, but the first paragraph of section 8.2 refers them back to section 5 of NZS1170.5 and hence believe section 5 can be used to analyze the panels and wailing beam for out of plane actions as they are ground supported. Their reasoning that the part (the panel) is supported directly on the ground floor therefore section 5 can be used (regardless of whether they rely on support from the building at roof level for out-of-plane lateral stability). Therefore using section 5 to determine the demand calculations is the minimum design requirement and can be used for a seismic assessment of an existing building.  Section 12.11.1 of ASCE7-22 has also been provided by the reviewer to support this, however we do not believe this is appropriate as in the case of this building the connections of the wailing beam are expected to fail first, hence the building has not been detailed appropriately to allow yielding with the reduction modification factor of this equation.

We have provided the following information to support assessing the panels to Equation 8.2(1):

Determination 2013-057

SESOC Journal Paper (Southwick,2017)

SESOC Interim guidance

NZSEE C5 2018 version section C5.6.4

BRANZ Design Guide 2007 Slender precast concrete panels with low axial load

TS1170.5 Draft for comment and commentary 

All of which have been dismissed in one way or another.

Our opinion is that if the panels (and associated connections) are analyzed to section 5, this will lead to an assessment that is below the minimum design standards. With regards to ASCE7-22 we believe this is incorrect to do as that part of the code assumes the building is designed to meet other design aspects of ASCE7-22. So it is incorrect to use one section of the American code to justify demand calculation for a building in NZ which has been designed to NZ codes (without showing it meets US design procedures).

We have also looked at the new TS1170.5 draft and commentary and it appears that there is no longer the statement about parts directly supported on ground but rather a modified Chi for floor height coefficient for single storey structures at roof level. If we use these values with NZS1170.5 accelerations we get a very similar result to used in our assessment.