Controlled Rocking Heavy Timber Walls for Regions of Low To Moderate Seismicity

Abstract eng:
Controlled rocking heavy timber walls (CRHTW) have been developed and implemented in New Zealand using PrestressedLaminated (Pres-Lam) timber products to resist large seismic loads and minimize structural damage. Controlled rocking walls are designed to rock on their foundation in response to seismic loads, and this rocking behaviour is controlled with posttensioning (PT) and supplemental energy dissipation. The CRHTW offers environmental and economic benefits that could also be realized in lower seismic hazard regions like Eastern North America and Europe. For these regions, the reduction or omission of PT or energy dissipating elements could simplify design and construction, and the application of Cross-Laminated Timber (CLT) could increase the appeal of this structural alternative. However, the performance of such a simplified CRHTW made of CLT has not previously been evaluated. Furthermore, although previous CRHTW studies have shown that higher mode effects can increase the shear and moment demands above the design levels, these higher mode effects have not been studied for CLT CRHTW without supplemental energy dissipation. This paper addresses these questions by first presenting the design and analysis of a prototype simplified CRHTW, considering the low-to-moderate seismic hazard of Ottawa, Canada. The design process considers capacity design of the CRHTW by applying two recently-proposed methods for estimating higher mode effects. A numerical model of the design is developed and subjected to non-linear time history analyses (NLTHA) with twelve ground motions that are representative of the design hazard with a 2% probability of exceedance in 50 years. The NLTHA results show that, despite the omission of supplemental energy dissipation, the wall’s peak displacements are only 0.63% of the wall height, interstorey drifts are significantly below the 2.5% limit, and the maximum shear and bending moment demands are 45% and 70% of capacity, respectively. Of the two methods considered for predicting the peak forces caused by higher mode effects, one is accurate to within 30% and the other to within 15%, both without any empirical calibration.

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