A Research on Steel Frames Having Large Elastic Deformation Capacity

本文旨在研究高强度钢焊接连接的循环行为。在1994年美国北岭地震和1995年日本小古根-南部地震后的调查中，发现梁与柱连接的底部翼缘焊缝处或焊缝附近有许多裂缝。虽然原则上假定高强钢在容损结构中使用于屈服点以下（弹性范围内），但仍有必要对高强钢在特大地震作用下的非弹性循环行为进行试验研究。导致梁端断裂的最关键原因是非弹性应变集中，而非弹性应变集中受焊接缺陷、热影响和应力梯度的影响较大。在本次试验研究中，制作了大量采用4种高强度钢和2种普通强度钢进行焊接连接的试件。在实测位移的控制下进行拉压循环加载。结果表明，由于焊缝连接的影响，高强度钢的非弹性变形能力显著降低。不幸的是，在循环加载试验中，一些试件出现了脆性断裂。虽然焊接连接的高强钢在弹性范围内使用是没有问题的，但如果期望高强钢的塑性变形，在将高强钢投入到地震结构中使用之前，还需要进一步的详细研究和先进的技术。

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.