Experimental investigation of long term and lateral load behavior of CLT shear walls for mid-rise wood buildings

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University of Alabama Libraries

There is a recognized need for tall building (8-20 story) construction in the United States due to growing population in the urban areas. In addition, there is a significant emphasis placed by the communities on sustainability. Wood is a sustainable construction material with a negative carbon footprint in comparison to steel and concrete, which are the traditional building materials used predominantly in tall buildings. Traditional Light Wood Frame Shear Wall system used in residential building construction in the U.S. cannot be used to construction tall building as it fails to provide necessary strength and stiffness. Mass timber panel such as Cross-Laminated Timber has been recognized as a promising building construction material in recent times and has been used in hundreds of building mostly in low seismic regions. However, to realize an all wood tall building in high seismic areas, lateral load resisting system (LLRS) using CLT needs to be developed and characterized before its implementation into building construction. This research focusses on addressing some of the issues in developing a robust LLRS using unbonded post-tensioned rocking CLT wall system for high seismic application. The parameters that affect the behavior of this system such as the compression, moisture diffusion and creep behavior of CLT material were studied by conducting laboratory testing. The performance of CLT rocking wall system was investigated through laboratory testing of four full scale specimens using different wall dimensions and detailing to gain a thorough understanding of this system behavior under reverse cyclic loading. The results show that this system can provide full recentering up to 3% drift with limited sustained damage at the rocking toes and limited energy dissipation capability. The rocking wall system can be designed as a robust LLRS but can be further improved by incorporating external energy dissipating elements into the system. To improve the system performance by including damping in the rocking wall system, o-connector and LiFS are used to connect two rocking walls. The coupled walls still provide the recentering while reduces the seismic displacement demand resulting from higher damping. Tests and finite element analysis of o-connectors were carried to understand its force-displacement behavior and energy dissipating capacity under reverse cyclic load. Design equations based on the test and FEA results are proposed. Laboratory tests were conducted on two CLT-LiFS hybrid walls in addition to component level tests on LiFS and CLT-LiFS connection. A load transfer mechanism in CLT-LiFS hybrid wall is proposed and used with a simplified calculation procedure to predict the force-displacement behavior of hybrid wall. The study shows that the analysis procedure predicts force capacity within 20% of the test results and can be conservatively used for practice. The test results show that the hybrid wall system has improved energy dissipation capacity while providing almost full recentering at 4% drift. The CLT building performance can be improved and the cost associated with LLRS may be reduced by taking into account the beneficial effect of non-rectangular shear walls (such as T-wall, I-wall). Non-rectangular walls can be achieved by connecting them at web-to-flange interface with high stiffness connections. Also, a high stiffness wall-to-foundation connection which can transfer the high base shear to foundation needs to be developed. Two connections, one for web-to-flange interface and another for wall-to-foundation interface, is developed by using grouted shear key incorporating ultra-high performance concrete and self-tapping screw. Laboratory tests on these two connection show that the connections have very high stiffness (4 times) compared to traditional bracket type ones and they have high strength as high as 3 to 4 times.

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Civil engineering