A Research on Steel Frames Having Large Elastic Deformation Capacity

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This paper is aimed to study the cyclic behavours of high strength steels with weld connection. Many fractures in or near the welds of bottom flange of beams connected to the columns had been observed in the investigations after Northridge Earthquake of USA (1994) and Hyogoken-Nanbu Earthquake of Japan (1995). Although in principle the high strength steels are assumed to be used below the yield point (within elastic range) in the damage tolerant structures, it is still necessary that the inelastic cyclic behaviors of high strength steels should be studied experimentally in case of extreme large earthquake. The most critical reason to result in the fracture at beam ends is the concentration of inelastic strain which is greatly influenced by the welding defective, heat affect and stress gradient. In this experimental study, a large number of test specimens with weld connection using 4 kinds of high strength steels and 2 kinds of plain strength steels had been manufactured. Tension and compression cyclic loading was carried out controlled by the measured displacement. It was found that the inelastic deformation capacity of high strength steels was dramatically reduced due to the influence of weld connection. Unfortunately, some of specimens were broken in brittle during the cyclic loading experiments. Although it is no problem for high strength steels with weld connection to be used in the elastic range, further detailed researches and advanced technologies should be necessary before the high strength steels could be put into the use of seismic structures if the plastic deformation of high strength steel is expected.