Deformation Capacity of Flange-Welded Web-Bolted Moment Connection Under Cyclic Loading

Abstract eng:
Recent advances in seismology have enabled the precise prediction of long-period ground motions produced by oceantrench earthquake, such as the Nankai trough earthquake in Japan. Long-period ground motions cause significant cyclic deformation to moment connections in the plastic range, which may lead to fracture. Most steel buildings in Japan are constructed using rolled hollow section columns and wide flange beams, and beam flanges are connected by CJP groove weld and a beam web is connected by bolts to column. If the web-bolted connection has insufficient flexural strength, as commonly designed in early days, deformation capacity of the moment connection decreases and possibility of fracture will increase. In the previous researches, deformation capacity under cyclic loading was usually estimated by Miner rule based on the concept of fatigue. However, previous experimental studies indicated that Miner rule is inaccuracy of estimation. The objective of this study is to investigate the effect of flexural strength of beam web connection on deformation capacity before fracture of beam flange due to cyclic loading. Two types of moment connections using weld access hole details, one is flange-welded web-bolted moment connection and the other is flange and web-welded moment connection, were prepared for test specimens. Three types of cyclic loadings, i.e. constant amplitudes, two-step constant amplitudes and random amplitudes were tested. Deformation capacity was compared by constant amplitude cyclic loading with respect to loading amplitudes. From the relationship between loading amplitude and the number of cycles until fracture, deformation capacity of web-welded specimens is larger than that of web-bolted specimens and the difference becomes obvious at larger loading amplitude. From the comparison of the bending moment carried by the beam flange and the beam web, the bending moment carried by the beam flange is larger after slippage of the bolted web connection. The fracture of moment connection under varying amplitude loading was estimated. In previous research, we conducted varying amplitude loading tests for welded moment connections and proposed a method to estimate deformation capacity using the formulated crack propagation at the weld considering the effect of loading amplitude and welding details. In this study, a total four cyclic loading tests by two kinds of two-step amplitude, i.e. increasing amplitude and decreasing amplitude, and a total of four cyclic loading tests by two kinds of random amplitude simulating seismic responses by longperiod ground motion were conducted. From the results of two-step amplitude loading tests, it is shown that the deformation capacity under decreasing amplitude loading is larger than increasing amplitude loading and this phenomenon is estimated by the proposed estimation method. From the results of random amplitude loading tests, it is also shown that the proposed estimation method well evaluate the instant of fracture and the accuracy of the method is better than Miner rule.

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