A Research on Steel Frames Having Large Elastic Deformation Capacity

研究了高强度钢焊接接头的循环疲劳性能。在1994年美国北岭地震和1995年日本兵库县南部地震后的调查中，发现了许多位于柱梁下翼缘焊缝处或焊缝附近的裂缝。尽管在损伤容限结构中，原则上假定高强钢在屈服点以下（弹性范围内）使用，但仍有必要对高强钢在大震作用下的非弹性循环性能进行试验研究。非弹性应变的集中是导致梁端断裂的最主要原因，而非弹性应变的集中受焊接缺陷、热影响和应力梯度的影响很大。本试验采用4种高强度钢和2种普通强度钢制作了大量的焊接试件。拉伸和压缩循环载荷进行控制的测量位移。结果表明，由于焊缝连接的影响，高强钢的非弹性变形能力大大降低。但在循环加载过程中，部分试件发生了脆性断裂。虽然采用焊接连接的高强度钢在弹性范围内使用是没有问题的，但如果要使高强度钢产生塑性变形，还需要进一步的深入研究和先进的技术才能将其用于抗震结构。

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.