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Optimized seismic design and dynamic response analysis of mass timber rocking wall lateral system
Huang, Da
Huang, Da
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2023
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Abstract
As societal expectations for urban development move towards a more resilient and sustainable focus, renewable construction materials are gaining more attention in the past decade and for the foreseeable future. One of the most well-known environmental challenges facing society today is greenhouse gas emissions, specifically carbon dioxide. The building and construction industry is one of the largest contributors to global carbon dioxide emission, which occurs during the construction and occupancy life cycle of buildings. Timber is considered as a sustainable and carbon-friendly solution for building systems due to its renewable nature and the potential ability to store carbon long term.
Mass timber is a family of engineered wood products that are produced from smaller timber components joined together using glue or mechanical connectors. Utilizing mass timber floor system with glulam gravity frame gives the possible solutions to create tall timber buildings with flexible floor plan applications. Mass timber gravity system can be combined with traditional steel and concrete lateral systems. But there are benefits to exploring a lateral system made also out of mass timber products. Firstly, this will enable a more streamlined construction process because the construction will only require a timber construction crew. Secondly, past studies revealed that a new type of lateral resisting system called mass timber rocking walls can potentially improve the resilience of the building during earthquakes. This system utilizes mass timber products as wall panels and unbonded post-tension bars to tie the rocking panel to the foundation. The rocking wall lateral system can achieve a ductile response and assure recentering capability. Energy dissipation devices such as U-shaped flexural plates (UFPs) are used as supplement dampers to dissipate energy and reduce accelerations. The use of replaceable dampers also allows localized damage to specific components that can be replaced after large seismic events.
In this thesis, a simplified numerical model for dynamic response prediction of mass timber building with PT rocking wall system was developed and validated with shake table test data. The concept of the simplified model is to concentrate the nonlinearity of that system into a few nonlinear rotational springs and represent rocking wall panel with elastic lumped mass spring series to reduce the computational cost. The simplified numerical model was first validated using the data from the NHERI TallWood 2-story tests conducted in 2017. Then the author expanded the simplified modeling concept using SAP2000 for the 10-story mass timber building which will be tested in spring 2023. Another 2D analytical model of the 10-story mass timber building is also developed to consider torsional responses.
An optimized performance-based seismic design (PBSD) frame is developed by expanding the existing PBSD framework through an automated procedure to obtain optimized design solutions utilizing Genetic Algorithms (GA). While simplified models are much more computationally efficient than traditional FEM models, a large amount of simulation needed for optimized PBSD using GA still needs hours of simulation to complete. To enable a more reasonable time frame for the proposed PBSD optimization, a generalized artificial neural network (ANN) model was trained using simplified mechanical models and replaced the nonlinear time history simulation process in the GA search for optimized PBSD. A web-based automatic design application as well as a MATLAB program was developed to enable the selection of rocking wall key design parameters based on the tools developed in this study.
The author also actively participated in the collaborative research and development effort that leads to the testing of the NHERI TallWood 10-story building. Relevant research and design work conducted by the author as part of the testing project is also presented here.
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