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BC Update: No.35 - Review of Design and Construction of Slender Precast Concrete Walls

15 Dec 2005: The Report to the Department of Building and Housing, Review of Design and Construction of Slender Precast Concrete Walls is now available from the Department’s website.

The Report has been distributed to design engineers, territorial authorities, contractors, precast concrete manufacturers and representative organisations. A limited number of hard copies are also available from the Department by calling 0800 242 243.

In the mid-1990s demand grew for larger and higher industrial and commercial single-storey buildings with precast panels. The development of new types of slender precast concrete wall (SPCW) panel has raised concern in the design profession about the behaviour of these wall panels in earthquakes and fires.

The Building Industry Authority commissioned the review that has resulted in the recently published Report. The Report investigates a number of issues and makes recommendations. The Department has reviewed the Report and supports some of the recommendations, and is already acting on others.

A summary of the key issues covered in the Report are:

  • a review of current design and construction practice
  • the identification of various structural systems employing SPCWs
  • concerns in the design profession about panel slenderness and the lack of definitive guidelines on maximum height to thickness ratios of SPCW panels. Recent research into buckling under in-plane seismic loads has resulted in a maximum ratio limit of 75 being incorporated into the draft Concrete Standard DZ 3101. Publication of this document as NZS 3101 is anticipated in late 2005 and will be reviewed by the Department with the intention of citing it as part of the Verification Method B1/VM1.
  • concern about behaviour of SPCW panels during fire. Recent research has resulted in the publication of the Cement and Concrete Association of New Zealand (CCANZ) design method for SPCW panels in the draft Information Bulletin IB 82, Slender Concrete Walls. The Department supports the use of this design method and notes CCANZ is preparing a computer program version of the design method.

Further recommendations from the Report and some of the Department’s responses are:

  • cantilever foundations: the Report recommends against the use of two details used in cantilever foundations for SPCW panels. It also recommends against the use of ‘drill-in’ fixings (eg, expanding or chemical anchors) to connect eaves beams to SPCW panels. The Department supports these recommendations and intends to issue a practice advisory as guidance to good detailing practice in accordance with section 175 of the Building Act 2004.
  • construction standards: the Report recommends that building consent authorities require PS3 producer statements from contractors certifying that buildings have been built in accordance with the drawings and specification. The Department supports this recommendation as one way a building consent authority can satisfy itself on reasonable grounds that the work will comply with the Building Code.
  • observation of construction: the Report recommends that building consent authorities require engineer observation and PS4 producer statements to address some industry concern about low standards of construction of SPCW buildings associated with ‘unsupervised’ construction. The Department supports a greater level of construction supervision particularly for critical aspects and therefore supports this recommendation as one way a building consent authority can satisfy itself on reasonable grounds that the work complies with the Building Code.
  • building consents: the Report notes that many building consent authorities issue building consents on the basis of producer statements and design reviews. The Report supports this system provided that an audit process is in place using appropriately qualified people, such as qualified engineers, to check specific applications. It recommends that the audit sample is selected using experienced engineering judgement and not just based on a random statistical selection process. The Department supports this advice to building consent authorities.