The Seismic Capability of Curtainwalls

Designing and Assessing Curtainwalls in New Zealand and Australia

Overview

Authors

Photo of Peter Lalas MIEAust CPEng NER APEC Engineer IntPE(Aus)

Peter Lalas MIEAust CPEng NER APEC Engineer IntPE(Aus)

Principal Facade Engineer

Janus Facades Pty Ltd

peter@janusfacades.com


Keywords


Abstract

The testing of aluminum/glass curtainwalls for seismic capability, mainly inter-story drift, has been carried out on many curtainwalls over the last 20 years in New Zealand. This paper considers that curtainwalls can be designed to resist any earthquake, when the value of expected displacements is known.

In New Zealand there is no statute requirement to seismic test facades, despite the recent earthquakes in Christchurch, Wellington and Kaikoura and continuing daily earthquakes of magnitude 2 to 3. There is also no New Zealand requirement to seismic test windows, cladding or skylights. Curtainwalls are seismically tested in a laboratory only if required by the Facade Specification.

Curtainwall engineers do not have the information to analyze a building structure to determine realistic seismic displacements. Reliance is placed on the Building Structure Engineer who usually only quotes Code values. Most Australasian building structures are concrete. The structural engineer designs to the concrete structures Standard which indicates that beam deflection is span/500. This figure is passed on usually without any analysis of the project structure. The curtainwall can be designed to whatever figure is given, but these figures tend to be inaccurate and over-conservative.

Eq-Assess is the de-facto standard in New Zealand for the analysis of the seismic capability of existing structures including facades. The part of Eq-Assess which refers to curtainwalls is based on stick curtainwall technology which is typically not applicable in New Zealand, Australia or Asia.

Introduction

Recent earthquakes in Christchurch, Wellington and Kaikoura in New Zealand have highlighted the requirement for buildings and their components to not collapse, thus endangering their occupants and people in their

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Background; Current Design and Testing of Curtainwalls in New Zealand

The author has assessed several buildings in Christchurch following the severe February 22, 2011 earthquake. This was a magnitude 6.3 earthquake, resulting in 182 deaths and widespread damage estimated at

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Eq-Assess analysis of a stick and Unitized curtainwall

The following deformation-based analysis compares the seismic % NBS of a stick curtainwall with a unitized curtainwall. The capacity of the curtainwall to accept inter-storey drift is compared with the

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Conclusion and Future Work

Curtainwall designers/engineers can design a unitized curtainwall with joints to match any seismic requirement, but they must be given realistic expected displacements by the building Structure Engineer. If these numbers

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Rights and Permissions

The photographs used in this paper were taken by the author except for Figure 1 which is available in the common domain.

AAMA CW-DG-1-79 Curtainwall Design Guide

Alcan Architectural Systems manual; St Kilda Suite; Alcan Technical Data 1985

Chris Arnold, FAIA, RIBA Building Systems Development Inc “Seismic Safety of the Building Envelope”; Richard A. Behr (editor), 2004. “Architectural glass to resist seismic and extreme climatic events” Updated: 11-10-2016

AS/NZS 4284; 2009 Australian / New Zealand Standard “Testing of building facades

New Zealand Building Code, Clause B1 structural adequacy Acceptable Solutions and Verification Methods for New Zealand Building Code Clause B1 Structure

NZS 1170.5:2004 Structural design actions - Part 5:Earthquake actions - New Zealand

Provides procedures for the determination of earthquake actions on structures in New Zealand. Appendices cover aspects of ultimate limit state design and the requirements for material specific structural design standards that are able to be used in conjunction with NZS 1170.5.

BRANZ (Building Research Association of New Zealand) “Evaluation Method EM7 Performance of mid-rise cladding systems” (version 2, May 2019)

Richard A. Behr (editor), 2004. “Architectural glass to resist seismic and extreme climatic events” Updated: 11-10-2016 Woodhead Publishing ISBN 978-1-84569-369-5 (book) Woodhead Publishing ISBN 978-1-84569-685-6 (e-book)

Eq-Assess; “The Seismic Assessment of Existing Buildings; Technical Guidelines for Engineering Assessments”; July 2017; Section C10 secondary Structural and Non-Structural Elements; Part C10.6.8 Curtain wall framing systems.