Seismic evaluation of traditional timber framed masonry systems using shake table tests and finite element modelling

摘要

The superior performance of timber-framed structures in prior earthquakes has led to their increasing popularity in seismically active regions since past few decades. These structures correspond to the local seismic cultures developed by local people using local materials to resist earthquakes. However, there is a lack of experimental research that aims to characterise the behaviour of timber-framed masonry structures when subjected to seismic hazards, despite their outstanding features and ease of construction. The present study describes a set of experiments conducted on a prototype single-story, single-room timber frame structure filled with dry stack masonry, using a shake table with half-scale dimensions. The present study examined three distinct models, one featuring a bare timber frame without a diaphragm, the other a bare timber frame with a diaphragm and the third one incorporating a timber frame infilled with dry stack masonry. The dynamic characterization of the models was carried out under white noise base excitation. Additionally, the seismic behaviour of the timber frame with infill was investigated by subjecting it to a ground motion of increasing intensity. The study evaluated the dynamic characteristics of the system including natural frequency, damping ratio, mode shapes, and stiffness degradation. The observed results indicate a reduction in frequency to 30% and a degradation in stiffness to 48% when subjected to shake table motions up to a peak ground acceleration of 0.45 g. Sensors and instrumentation were strategically placed to capture the dynamic response of the structure in terms of peak accelerations at the sill, lintel, and roof levels. Acceleration amplification factors of both in-plane and out-of-plane walls are presented based on the measurement of the acceleration response from the floor to the roof level. The amplification of acceleration response was found to be higher for out-of-plane walls, with a value of 300%, as compared to in-plane walls, which exhibited a lower amplification value of 100%. Experimental findings substantiate that these building systems provide efficient seismic resilience. Furthermore, for interpretation of the dynamic characteristics mostly the mode shapes, an analytical model of the timber-framed masonry is developed in ABAQUS software and the results from finite element analysis fared reasonably well with the experimentally evaluated values.