This paper presents experiments and in-depth analysis of the imaging of surface acoustic waves by means of the photoelastic effect. Gigahertz surface acoustic waves, generated by optical pump pulses in a thin gold film on a glass substrate, are imaged in the time domain by monitoring ultrafast changes in optical reflectivity. We demonstrate how images of the in-plane acoustic shear strain component can be obtained by measurements with two different optical probe pulse polarizations incident from the substrate side.

A vertical irregularity setback in reinforced concrete (RC) building affects its performance and response especially subjected to earthquake ground motions. It is necessary to understand how the seismic damage is established due to setbacks and avoid damage concentration on the irregularity section. The objective of this study is to propose a formula to estimate the damage distribution along the height of the setback building from a geometric measure of the degree of irregularity. First, previous experimental tests for two types of setback buildings, a towered and a stepped setback frames, were analyzed to verify the accuracy of the frame analysis. The results of the frame analysis considerably matched the experimental test results. Furthermore, to study the relationship between the degree of setback and the distribution of damage, a parametric study was conducted using 35 reinforced concrete setback frames, consisting of models with stepped setback type and towered setback type with different degrees of setback. The inelastic dynamic analyses of all the frames under three earthquake ground motions were conducted. The irregularity indices proposed in literature were adopted to express the degree of setback and the structural damage was expressed by the Park–Ang damage index. Using nonlinear regression analysis, formulas to estimate damage index ratio between two main structure parts (tower and base) from setback indices were proposed. Finally, the proposed formula was applied to the experimental test results to confirm its validity.

During the 2011 Great East Japan Earthquake, high-rise buildings in Tokyo, Nagoya and Osaka swayed vigorously and caused damage to non-structural elements such as with the falling of ceiling panels. Those cities are located near deep layers of sediment and such conditions can create long period ground motions of low frequency even when far from the epicenter of an earthquake. These low frequency waves can travel backwards and forwards through the sediment upon meeting hard obstacles like rock, creating ground movement that resonates with tall structures causing them to sway and topple. In this report, the performance of high-rise buildings during the 2011 Great East Japan Earthquake is presented first. Then, the safety of high-rise buildings with long period ground motions in a massive earthquake that may arise in the future is discussed.  Index Terms-high-rise building, long period earthquake Earthquake

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