More resilient wall building structures

Abstract

This project addressed a gap in knowledge regarding the seismic resilience of multi-storey buildings in Aotearoa New Zealand. Reinforced concrete structural walls are one of the most common and effective means of protecting buildings against earthquakes. To be effective, structural walls need to be 1) proportioned appropriately for the building, 2) constructed on a sturdy foundation, and 3) soundly connected to that foundation. But currently New Zealand standards allow a reinforcement configuration for connecting reinforced concrete structural walls to their foundations called “staggered lap splices”. However, this configuration is not permitted in concrete walls designed to sustain large lateral deformations during earthquakes in highly seismic regions of other countries such as the USA and Japan.

Staggered lap splices were thought to be an improvement over other reinforcement configurations (e.g. non-staggered lap splices) that were already known to be vulnerable to losses of lateral load resistance at relatively small lateral deformations during earthquakes compared to design expectations. New Zealand design practice does not permit non-staggered laps near critical sections of RC walls expected to sustain large lateral deformations, and the staggering laps were perceived as a way to improve the deformability of walls with lap splices. But staggered lap splices have never been experimentally tested in walls to confirm improved resilience. The experiments completed in this project were the first full-scale tests of reinforced concrete structural walls with staggered lap splices in the world.

Six reinforced concrete structural walls, each approximately eight meters tall, were tested at the University of Canterbury’s Structural Engineering Laboratory. Four walls had staggered lap splices designed to be compliant with the current version of New Zealand’s concrete structures standard. One wall had non-staggered lap splices, which is not currently permitted in New Zealand design practice. The final wall tested an alternative method of connecting walls to their foundations, namely the mechanical coupling of vertical reinforcement. Experiments recorded how damage might accumulate during an earthquake, how walls deformed under intense loading, and the ultimate strength and deformability of the walls.

Walls with staggered lap splices were observed to be as or even more vulnerable to losses of lateral load resistance at lateral deformations lower than expected in design than walls with non-staggered lap splices are. The experimental results suggest the permissibility of including “staggered lap splices” in the design practice of reinforced concrete structural walls expected to sustain large lateral deflections during earthquakes should be comprehensively reviewed.

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