S. H. Lo

Experimental Study of Moderately Reinforced Concrete Beams Strengthened with Bolted-Side Steel Plates

Existing reinforced concrete (RC) beams can be effectively strengthened by attaching steel plates to the side faces of the beams using anchor bolts. The performance of this type of beam, bolted side-plated (BSP) beams, is mainly controlled by the degree of partial interaction at the steel-concrete interface. In this study, a total of seven moderately reinforced BSP beams with different steel plate depths and various bolt spacings were tested. Their behaviours were compared to the available test results for lightly reinforced BSP beams obtained by other researchers. The results show that moderately reinforced RC beams are more effective in increasing the flexural strength and ductility capacity using deeper steel plates than the use of a greater number of anchor bolts. It was also found that the longitudinal and transverse slips were controlled by both the stiffness ratios of the steel plates to the RC beam and the force-slip response of the anchor bolts.

Protecting underground tunnel by rubber-soil mixtures

This paper presents a promising earthquake protection method by placing rubber-soil mixtures (RSM) around underground tunnels for absorbing vibration energy and exerting a function similar to that of a cushion. The validity of the method will be demonstrated by numerical simulations using various recorded earthquake ground motions. The use of scrap tires as the rubber material can provide an alternative way of consuming huge stockpiles of scrap tires from all over the world. Moreover, the low cost of this proposed method can greatly benefit developing countries where resources and technology are not adequate for earthquake mitigation using welldeveloped, yet expensive, techniques.

Geotechnical seismic isolation system - Experimental study

In this study, an experimental investigation program on a newly proposed seismic isolation technique, namely “Geotechnical Seismic Isolation (GSI) system”, is conducted with an aim of simulating its dynamic performance during earthquakes. The testing procedure is three-fold: (1) A series of cyclic simple shear tests is conducted on the key constituent material of the proposed GSI system, i.e., rubber-sand mixture (RSM) in order to understand its behavior under cyclic loadings. (2) The GSI system is then subjected to a series of shaking table tests with different levels of input ground shakings. (3) By varying the controlling parameters such as percentage of rubber in RSM, thickness of RSM layer, coupled with the weight of superstructure, a comprehensive parametric study is performed. This experimental survey demonstrates the excellent performance of the GSI system for potential seismic hazard mitigation.

3-D CONVOLUTIONAL PERFECTLY MATCHED LAYER MODELS FOR DYNAMIC SOIL-STRUCTURE INTERACTION ANALYSIS IN THE FINITE ELEMENT TIME-DOMAIN

The perfectly matched layer (PML) has been employed as a very efficient absorbing boundary condition for solving elastodynamic problems in bounded domains by using the finite difference method. However, in the finite element time domain (FETD), the application of PML formulations usually involves a mixed scheme with velocity/displacement and stresses as unknowns to avoid temporal convolution operations, which could lead to an increase in computational costs especially when three-dimensional (3-D) simulations are used. This paper presents the preliminary research on 3-D convolutional PML models for dynamic soil-structure interaction (SSI) analysis in FETD with displacements as the only unknowns. The variational formulation is derived for the use of finite element method (FEM) to discretize the problem domain, which avoids tricky coordinate transformation and requires minor modification of existing displacement-based finite element software. The stability and efficiency of the proposed formulation are first demonstrated by relevant 3-D benchmark examples even with small bounded domains. Numerical results are also presented for the classical SSI problem of a building with rigid footing on layers on a half-space.