A Three-dimension Model for Slow Hybrid Testing of Retrofits for Soft-story Wood-frame Buildings

This paper will present a new 3D seismic analysis package developed for analyzing the collapse mechanism of soft-story wood-frame buildings. This new seismic analysis package is developed as part of the on-going NSF funded NEES-Soft project. The objective of the NEES-Soft project is to reduce the seismic collapse risk of older wood buildings with soft-story deficiency. The project objective is being accomplished through a combination of numerical modeling and experimental testing. The NEES-soft experimental program includes shake table testing of a full-scale four-story building, slow hybrid-testing of a full-scale three-story building, real-time hybrid testing of a three-story shear wall with a fluid damper and quasi-static testing of a knee-brace retrofit. The 3D analysis program is developed specifically to model all these tests and to provide a better understanding of the collapse mechanism of soft-story wood buildings. While various numerical models have been developed over the years to allow researchers to analyze the seismic performance of wood buildings, these models are formulated based on small rotation theory; hence may not be suitable for studying the collapse which is a large deformation problem. Understanding the collapse mechanisms is essential for formulating retrofit options to mitigate the seismic risk.

The new dynamic analysis package for wood buildings will allow improved predictions of the seismic performances over a wide range of seismic loading conditions, namely from small deformation all the way to collapse. In addition, this new dynamic analysis package can also be used to perform both slow and real-time hybrid tests. The focus of this presentation will be on the application of the 3D model for slow hybrid test. The slow hybrid test is used to study the effectiveness of different retrofits used for strengthening the soft first story. The retrofit options considered in NEES-Soft include inverted moment frame, steel moment frame, cross-laminated timber, viscous fluid damper, shape memory alloy and knee-brace. Over strengthening the first story will result in damages propagate to the upper stories instead of in the first story. In the slow hybrid test, the second and third stories are physical structure while the first-story (i.e. the soft-story) is being numerically analyzed with different retrofits. This hybrid test setup allows the evaluation of different retrofits without having to physically re-construct the first story. The effectiveness of different retrofits can be determined or quantified by examining the damages occur in the physical second and third stories. The formulation of the 3D model and the application of this new analysis package for slow hybrid testing of the three-story wood building will be discussed. Preliminary results of the slow hybrid testing will also be presented.

Researchers should cite this work as follows:

• Weichiang Pang; Ershad Ziaei; Xiaoyun Shao; John van de Lindt; Mikhail Gershfeld; Michael Symans; Elaina Jennings (2014), "A Three-dimension Model for Slow Hybrid Testing of Retrofits for Soft-story Wood-frame Buildings," https://datacenterhub.org/resources/12821.

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