Keiichiro Suita

E-Defense Tests on Full-Scale Steel Buildings Part 2 - Collapse Experiments on Moment Frames

A major research project on steel buildings utilizing the E-Defense three-dimensional shake table facility is underway in Japan. It involves several studies on moment frames, innovative methods for new or existing buildings, protective systems, and nonstructural elements. As one of the studies, a challenging seismic experiment to simulate collapse of a full-scale bulding comprising the moment frame will be conducted in September 2007. Collapse is defined as the state where the structure loses its ability to sustain gravity loads. To-date, only a few full-scale tests have been conducted for the multi-story steel moment frames, and none of those simulated collapse. Two decades ago, a 6-story moment frame was pseudo-dynamically tested by static actuators simulating severe earthquakes. Recently, a 3-story moment frame including exterior walls was tested up to an overall drift angle of 1/15 rad, by static loads to reflect the effects of the ground motion that is greater than considered in the current seismic codes. These full-scale tests employed quasi-static loading, since a dynamic loading facility capable of much more realistic simulations was not available. The E-Defense shake table which commenced operation in 2005 is capable of subjecting a full-scale structure to the strongest ground motion recorded in the world. With a 12,000 kN specimen placed on 15m x 20m table, the table can produce a maximum velocity of ±2.0m/s and a maximum displacement of ±1.0m. With the E-Defense shake table, we have the first opportunity ever to simulate the behavior of full-scale structures up to collapse, and to obtain detailed response data. This paper outlines the test plan of collapse simulation, as well as technical issues being addressed during the process of test preparation.

EFFECT OF COLUMN BASE BEHAVIOUR ON THE SEISMIC RESPONSE OF STEEL MOMENT FRAMES

The plastic deformation behaviour of embedded-type column bases was experimentally examined. The primary parameters were width-to-thickness ratio and axial load ratio, and results showed significant strength deterioration induced by local buckling that was largely affected by the test parameters. Analytical models of the test specimens were developed. The developed models were applied for nonlinear dynamic analysis of low- and mid-rise steel moment frames. The analysis results showed the importance of considering deterioration behaviour of column bases as it significantly affected the response and the collapse limit. Large dependency of the collapse limit on the width-to-thickness ratio of the column in addition to the strength itself is also noted from the analysis.

TEST ON REINFORCED COLUMN BASES AND PLASTIC DEFORMATION CAPACITY

A standard base plate connection is commonly adopted for column bases of low-rise steel structures. In most practical design, the column bases are likely covered by shallow concrete slab to hide the bolted base plate and level the slab. Cyclic loading tests are conducted, and the effects of thickness and shape of slab are investigated with reference to the standard base plate connection. That experiment showed that shallow embedded-type column bases strength and stiffness was better than exposed-types. But its strength decreased at large deformation area. So we reinforce the column base with steel bars because we intend to prevent its strength from decreasing. The test show that the covering slab and steel bars contributes to both the initial stiffness, ultimate strength and strength decreasing.

Comparison of Seismic Design Codes for Steel Buildings in Japan and the United States

This is a preface to six papers, which conducted a thorough comparative investigation on seismic design codes for steel building structures in Japan and the United States. The study is associated with the globalization of earthquake resistance technologies. The working group organized by the Subcommittee of Steel Connection of the Architectural Institute of Japan surveyed codes and associated regulations proposed by SAC Joint Venture of the United States after the Northridge Earthquake. Similarities and differences of the current Japanese design are examined for steel and electrode materials, design of beam-to-column connections and column bases connections, and the scheme of the seismic design oriented toward performance based design.