Browsing by Author "Gao, Zhenjia"

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    Computational framework for the analysis of hybrid masonry systems using an improved non-local technique
    (2014-12-05) Gao, Zhenjia; Stanciulescu, Ilinca; Padgett, Jamie; Lou, Jun; Willam, Kaspar
    Hybrid masonry structures combine the ductility of steel components with the shear strength of reinforced masonry panels. The goal of this research is to provide a sound basis for the design of an optimal type of hybrid structure that can be implemented as a new lateral-force-resisting system in high seismic regions. The most challenging part in the hybrid structure simulation is to capture the behaviour of concrete under different loading scenarios. This thesis sets up a computational framework for the analysis of hybrid masonry systems using an improved non-local technique, including the contributions such as: adopting the consistent linearisation technique to improve the computational efficiency of the non-local one-scalar damage model; presenting a new way to calibrate parameters in the tension damage law in the two-scalar damage model by correlating them to the ones in the one-scalar damage model; designing a data structure to save the domain information for each material point in order to apply the non-local technique; proposing an automatic parameter calibration procedure based on the Nelder-Mead simplex method for the two-scalar damage model utilizing the global system testing data; proposing and identifying the internal variable to be non-localized to enhance a new damage model to obtain the mesh regularization solution. Finally, this thesis performs a system-level numerical study of the energy dissipation mechanisms of hybrid masonry structures under cyclic loading. The numerical studies extrapolate test data to a wider range of structural configurations in terms of various connector strengths and different masonry panels to maximize seismic energy dissipation. This work also investigates the influence of the load transfer mechanism on the lateral strength, stiffness, energy dissipation capacity and deformation pattern of the hybrid system. Findings from the numerical studies performed in this work confirm the feasibility of using hybrid structures in high seismic areas.
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    Systematic Calibration of Model Parameters Based on Large-Scale Experiments on Hybrid Masonry Walls
    (American Society of Civil Engineers, 2016) Gao, Zhenjia; Stanciulescu, Ilinca
    Hybrid masonry is a relatively new type of structural system that benefits from the ductility and ease of construction of steel frames and from the in-plane strength and stiffness of reinforced masonry panels. Finite element analyses of hybrid masonry systems employ complex models, such as the two-scalar continuum damage model, to capture the propagation of damage through the masonry panels. Such formulations rely on several constitutive parameters but no simple experiments exist that can be used to decouple their effect and calibrate them independently. This paper proposes a method to calibrate the masonry parameters using experimental data from global system testing. Steel components are described by an elastoplastic model with kinematic hardening whose constitutive parameters are easily calibrated. A parameter calibration procedure for the damage model parameters based on the behavior of the base wall of a two-story hybrid system in global testing is proposed. In order to reduce the number of calibrated parameters, two constraints are applied to the compressive range of the constitutive law, requiring that for that range the stress-strain curve is similar to that of concrete. The effectiveness of these two constraints in finding an optimized set of parameters more efficiently is then verified by using uniaxial compression test data. An automatic calibration procedure of the remaining parameters is proposed based on the Nelder-Mead simplex method. It is demonstrated through numerical experiments that the models with calibrated parameters can accurately capture the behavior of hybrid masonry systems.
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    Through-bolt push out effects on the behavior of hybrid masonry systems
    (Elsevier, 2015) Nistor, Mihaela; Gao, Zhenjia; Stanciulescu, Ilinca
    This paper provides specifications necessary for designing hybrid masonry systems that resist through-bolt push out effects. Hybrid masonry is a relatively new structural system that can be used in seismic areas and comprises masonry panels connected to frames through steel plate connectors. However, masonry break-out at the connection between the steel plates and the masonry panel requires further analysis to better understand the load transfer mechanism of the hybrid masonry system. Therefore, we use a computational framework to model the hybrid masonry that uses a typical plasticity model with hardening for the steel components and a nonlocal two-scalar damage model that accounts for tension and compression for the masonry panel. Based on parametric studies conducted using this framework we provide recommendations for the through-bolt location and for the reinforcement percentage and location within the masonry panel to achieve best results in the load transfer mechanism of the hybrid masonry system during a seismic event.