After the 1995 Kobe earthquake in Japan, the National Research Institute for Earth Science and Disaster Prevention (NIED) constructed a new large-scale shaking table as a facility for three-dimensional earthquake damage testing, called E-Defense. The facility was completed in March 2005. E-Defense has the unique capacity to experiment with life-size buildings and infrastructural systems in real earthquake conditions, and is intended to be the ultimate verification tool. The current paper describes the specification of the facility, features of the control system, and some experimental results of the control performance tests. It also describes major ongoing projects at E-Defense.

Abstract:Large-scale shake table tests were conducted at E-Defense, Japan, to examine the 4 dynamic response of a steel concentrically braced frame. The specimen was a single-bay, single-5 story frame with a pair of square-HSS braces placed in a chevron arrangement. The gusset plates 6 connecting the brace to the framing elements were provided with an elliptic fold line to 7 accommodate out-of-plane rotation of the brace in compression. The specimen was subjected 8 repeatedly to a unidirectional ground motion with increasing magnitude until the braces buckled 9 and eventually fractured. The bracing connections performed as intended; the gusset plates 10 folded out-of-plane and no crack was observed in the gusset plate or in the critical welds. 11Consequently, the test results demonstrated excellent performance of the bracing connections. 12Elastic deformation of the beam prevented the braces from developing their full tensile strength. 13Yielding in the middle of the beam, which was predicted by monotonic loading analysis, did not 14 occur. The specimen response was reproduced by a numerical model using fiber elements. This 15 model was able to predict the occurrence of brace buckling and fracture and thereby, accurately 16 trace the dynamic behavior of the frame. 17

E‐Defense, which is operated by the Japanese National Research Institute for Earth Science and Disaster Resilience, currently contains the world's largest 3‐dimensional shaking table (size: 20 × 15 m, maximum loading capacity: 12 000 kN). This facility has already implemented over 80 full‐scale or large‐scale experiments since its operation commenced in 2005. During these research activities, E‐Defense has encountered many challenges in the successful execution of various types of experiments within the designed experimental capacity and under the guidance of safe operational management. The experience gained in the past years using E‐Defense has led to the accumulation of knowledge on loading/shaking techniques, measurements for large‐scale specimens, table maintenance and operation, safety management, and specimen construction. This article highlights the major technical issues that have been encountered during the operation of E‐Defense and introduces the solutions that have been achieved. This is followed by brief summaries of some of the major experiments conducted since E‐Defense was commissioned.

Summary Nonlinear signal‐based control (NSBC) is very powerful for controlling structural systems with parameter variations and has the advantage that the controllers can be designed using classical control theory and expressed by transfer functions. This report describes the first application of NSBC to shake table tests with nonlinear specimens and compares the performance of NSBC with that of a basic control approach that relies on the inverse transfer function of the controlled system. NSBC and the basic approach were numerically applied to shake table tests to excite a nonlinear single‐degree‐of‐freedom system with earthquake acceleration motion, considering the nonlinear specimen characteristics and estimation errors associated with the table dynamics. NSBC achieved excellent control with near 100% accuracy, whereas the basic approach provided insufficient control. Although inaccurate estimation of the pure time delay in the controlled system causes instability at the practice of NSBC, proper design of the nonlinear signal feedback controller prevented instability. In experimental examinations, controllers for the two approaches were designed on the basis of the table dynamics with/without a specimen, which were preliminarily identified by performing tests using a random wave with small amplitude excitations. With no specimen present, both approaches yielded the expected acceleration motion on the table with high accuracy. However, with the specimen present, only NSBC successfully achieved excellent control of the shake table with near 100% accuracy, whereas the basic approach did not because of the specimen nonlinearity. These results numerically and experimentally demonstrate the efficiency and practicality of NSBC for shake tables supporting nonlinear structures.

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