【作者】 朱群红；

【导师】 童根树；

【作者基本信息】 浙江大学 ， 结构工程， 2004， 硕士

【摘要】 本文首先对腹板的高度线性变化的变截面工字钢梁的剪切中心位置进行研究分析，发现只要保持截面的其他尺寸不变，每个截面的剪切中心连线仍是一条直线，弯扭失稳是以截面剪心的位移为准的，因此仍可以取传统的直线坐标系统。 其次，本文通过对大量不同截面尺寸的双轴对称和单轴对称简支等截面梁在不等端弯矩作用下的情况进行有限元分析后，发现我国规范提供的等效弯矩系数公式β_b=1.75-1.05k+0.3k²≤2.3（k=M₀/M₁）精度欠佳，尤其用在双轴对称截面梁产生异向曲率时过分保守，丧失了经济性。本文根据有限元计算结果重新提出β_b的计算公式，且在计算单轴对称等截面梁时，认为拟合公式的适用范围在-I_yB/I_yT≤k≤1内的误差较小，对双轴对称截面则自动退化到-1≤k≤1。 最后，考虑变截面梁的楔率影响，按能量法推导了上述情况下梁的临界荷载公式，保留公式形式，用有限元结果进行计算机回归分析，调整公式中的各项系数，得到物理意义明确，且形式与等截面梁一致，并便于在工程设计应用的梁平面外弹性弯扭屈曲临界荷载表达式，发现拟合公式比《门式刚架轻型房屋钢结构技术规程CECS102：2002》中公式精度高，并且将CECS102：2002中的公式与《钢结构设计规范》（GB 50017-2003）中对等截面钢梁的稳定系数公式进行对比，发现CECS102：2002中所提供的计算变截面梁平面外屈曲临界荷载公式的不足之处，并指明了该公式不合理的原因。更多还原

【Abstract】 At first, this thesis studied the position of shear center of tapered I-beam. If only the web is linearly varied along the member, and the other dimensions are kept constant, and it can be shown that the shear center axis of the tapered I-beam is still a straight line. Flexural-torsional buckling may be still studied using the shear center line as a reference axis to define the lateral displacement and the rotation.Secondly, the elastic lateral buckling of simple supported I-beams with doubly-symmetrical and mono-symmetrical cross-sections under moment gradient isinvestigated by FEA method, it is found that the formula for betab (equivalent momentcoefficient) currently used in Steel Structures Code is not accurate enough in some cases, e.g. when beams are bent in double curvature. An improved design formula is proposed on the basis of results of FEA. Furthermore, we thought the application tomono-symmetry section should be confined and -1≤k≤1 todoubly-symmetry section.At last, considering the effects of taper ratio, we derived critical load of tapered I-beam by energy method. Using the formulation thus obtained, but adjusting the coefficients in this formulation based on the results of FEA, we obtained a new formula for the Critical moment for lateral-torsional buckling of tapered I-beams, it has a similar formulation as those for beams with constant cross-sections,, with clear meaning and easy to application in practice. We found the precision of the new formula is better than CECS 102:2002. Moreover, we point out the formula in CECS 102:2002 not to be exact because it considered the monosymmetry twice.更多还原