Rocking motion is sensitive to the boundary and initial conditions of a rocking structure, making experiments nonrepeatable. Thus, the claims that numerical rocking motion models are not only inaccurate but that all rocking structures behave unpredictably. Hence, rocking is not used as a seismic design approach. This paper revisits the issue of rocking motion unpredictability. Seismic behavior of structures is inherently stochastic, because the loading is stochastic. Therefore, the question of interest is not whether models can predict the seismic response to a single ground motion, but if the statistical characteristics of the ensemble of responses to a set of ground motions that define the seismic hazard can be predicted. For this purpose, a rocking podium, which is a three‐dimensional structure comprising an aluminum slab supported by four tubular steel columns, was tested on a shake table excited by two sets of 100 consistently generated ground motions. It was found that the cumulative distribution function (CDF) of the experimentally obtained displacements is statistically stable. Next, a blind prediction contest was organized. The contestants were invited to predict the CDFs of the slab lateral displacement. They were able to predict the slab displacement CDF relatively well. Both finite element and discrete element modeling approaches were used, but no clear pattern emerged as it was found that the performance of either approach depends on the input parameters used and the assumptions made. It was also observed that the contestants who did not use Rayleigh damping in their models produced better predictions.

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A conventional direct shear apparatus (DSA) has been modified to improve its articulation by moving the point of shear load application to the sample centre. Jewell's symmetrical arrangement has been adopted for a 100 mm square shearbox, resulting in increased dilation rate and reduced rotation. Testing using coarse Leighton Buzzard sand has enabled the performance of the modified DSA to be optimised by exploring different test configurations. Optimum results were obtained with a substantial initial gap between the shearbox frames of 5D 50 , the use of thin rubber edging strips to contain the sand, and the omission of grid plates at the sample boundaries. Upper-frame rotations persist during testing, but have almost no effect on measured parameters. A framework of relationships between parameters measured in a direct shear test ((ö9 ds ) p , ł p and (ö9 ds ) ld ) and relevant plane strain parameters ((ö9 ps ) p and ö9 crit ) is set out, based on Rowe's flow rule and Davis's (1968) relation. Stroud's simple shear apparatus (SSA) data for coarse Leighton Buzzard sand have been examined and shown to fit Rowe's flow rule. The output from the modified DSA also fits these relationships well, and shows good internal consistency. A simple relationship enables modified DSA peak direct shear friction angles to be converted into plane strain friction angles. Large displacement direct shear friction angles for the modified DSA are related to critical state friction angles by tan(ö9 ds ) ld sin ö9 crit .

Shaking table testing is a common experimental method in earthquake engineering for performance assessment of structures subjected to dynamic excitations. As most shaking tables are driven by servo hydraulic actuators to meet the potentially significant force stroke demand, the review is restricted to hydraulic shaking tables. The purpose of the control systems of hydraulic shaking tables is to reproduce reference signals with low distortion. Accurate control of actuators is vital to the effectiveness of such apparatus. However, the system dynamics of a shaking table and the specimens to be tested on the shaking table are usually very complex and nonlinear. Achieving the control goal can prove to be challenging. A variety of closed- and open-loop control algorithms has been developed to solve different control problems. With the focus placed on the control schemes for hydraulic shaking tables, the paper reviews algorithms that are currently used in the testing industry, as well as those which are the subject of academic and industrial research. It is by no means a complete survey but provides key reference for further development.