Main Thrusts

Research Interests

• Smart structural materials and systems

• Small- and large-scale experimental testing and numerical simulation of structures under extreme loading

• Design of multi-hazard resilient structures using advanced materials

• Hybrid simulation methods for structural performance assessment

• Non-linear finite element modeling and seismic assessment of reinforced concrete structures

SMA-Based Active Confinement Technique for Seismic Rehabilitation of RC Columns

Shape memory alloy (SMA) is a class of smart material that exhibits unique thermomechanical behaviors associated with phase transformation between two crystal structures (i.e., martensite and austenite). At a temperature below M_f (martensite finish temperature), SMA remains in its martensite phase and experiences large residual strain when unloaded after being excessively deformed. When the SMA is heated above A_f (austenite finish temperature), it transforms into austenite phase and recovers its original shape, a phenomenon known as shape memory effect. If the SMA is restrained from recovering its original shape, a large recovery stress (prestress) would develop in the material. The application of active confinement using SMA takes advantage of the thermally triggered recovery stress of the prestrained SMA. Concrete actively confined by the SMA shows much enhanced compressive behavior in terms of both strength and ductility. The SMA-based active confinement technique is effective in inducing ductile response from RC columns with insufficient transverse reinforcement.

Development of a New Type of Hybrid Simulation Framework - MTI Simulation

The concept of material testing integrated simulation method (MTI) simulation initiated from an idea to combine experimental testing into numerical simulation for the performance evaluation of a structure. While the overall structure is numerically modeled in an analysis platform, one or more materials which exhibit complex behaviors can be replaced by physical specimens and tested in the laboratory. The responses of the test specimens will be incorporated in the analysis platform by continuously providing realistic material behavior in place of the existing material models for all corresponding regions/components of a structural system. This method is quite effective in simulating structures with a number of critical regions/components subjected to different demand levels (e.g. plastic hinges in multiple bridge columns).

MTI simulation can be applied to study the seismic response of a RC bridge column based on the following assumptions: (1) Response of flexural-dominant RC components can be numerically approximated by using a fiber-based beam-column element where the uniaxial stress–strain relationship of each individual fiber whether concrete or steel fibers determines the sectional response. (2) Complex or highly nonlinear behavior which requires extensive numerical simulation is typically concentrated in a relatively localized region of the column such as the plastic hinge region.

Seismic Safety Evaluation of Base Isolation Tables