众所周知,在钢吊车梁的设计中,一般循用双向弯曲公式进行强度计算,而对弯曲扭转产生的扇性正应力忽略不计。这一假定对具有制动结构的吊车梁是符合实际的,但对不带制动结构的单轴对称工字形梁则不然。因为前者在梁的上翼缘平面外有足够刚度,扇性惯性矩相应地增大,扇性正应力因之减小,后者适得其反。如对承受起重量 It is well known that in the design of steel crane girders, the strength calculation is usually performed using the bidirectional bending formula, and the fan-shaped normal stress generated by the bending and torsion is neglected. This assumption is realistic for a crane beam with a braking structure, but not for uniaxially symmetric I-beams without a braking structure. Because the former has sufficient rigidity outside the plane of the upper flange of the beam, the fan-like moment of inertia increases accordingly, and the fan-shaped normal stress decreases. The latter is counter-productive. If it is to withstand the weight