中文摘要：

为了预判高性能H型钢梁发生整体失稳的时机以及论证加载过程中使用侧向支撑的必要性,通过运用能量法推导了无侧向支撑条件下任意两点对称集中荷载作用时H型钢梁在弹性阶段整体失稳的理论公式,并结合有限元模型对公式进行了验证,发现理论值与有限元值相对误差在3.5%以内,表明公式具有较高的精度。运用该公式以及现行《钢结构设计规范》（GB50017-2003）分别计算了名义屈服强度分别为460,550,690 MPa的高性能H型钢梁临界弯矩。计算结果表明,在跨中未设置任何侧向支撑的情况下进行两点对称加载,3种钢梁都会在弹塑性阶段发生整体失稳现象,且其临界弯矩约为0.75倍极限弯矩。由此建议使用侧向支撑对钢梁进行约束,以期达到极限抗弯强度。

英文摘要：

In order to predict the timing of the occurrence of the steel girder overall instabili- ty and demonstrate the necessity of using lateral support during the loading process, the theoretical formula of the lateral-torsional buckling of the H-shaped steel girder in the elastic stage is derived by the energy approach under the condition of no lateral bracings at any 2-point symmetrical transverse loading. Combined with the finite element model to verify the formula, it is found that the relative error between theoretical values and numerical values is less than 3.5 %, which indicates that the formula has a high precision. This formula and the current＂Design code for steel structures＂（GBS00017-2003） are conducted to calculate the critical moment for high performance H-shaped girders, whose nominal yield strength are respectively 460 MPa, 550 MPa, 690 MPa. The calculation results show that when two symmetrical loading is carried out, without any lateral bracings in the middle span, overall instability phenomenon of the three kinds of steel girder will appear in the elastic-plastic stage and the critical moment is about 0.75 times of the ultimate moment. It is recommended to use the lateral bracings on the steel girder to carry out the constraint, which is expected to achieve the ultimate flexural strength.