桥式起重机主梁是由左右腹板与上下盖板组成的箱形结构。为提高刚性,梁内设有大小隔板。由于焊缝大部分集中在梁的上部,焊后引起下挠变形。但技术要求两根主梁装焊成桥架后,应具有L/1000的上挠值(L——起重机跨度)。为此,常采用腹板预制上拱度的方法,即在备料时,预先使腹板具有大于L/1000的上挠值f预(图1)。 Bridge crane girder is a box-shaped structure composed of left and right webs and upper and lower cover. In order to improve the rigidity, the beam is provided with a size partition. As most of the weld concentrated in the upper part of the beam, causing the next after welding deformation. But the technical requirements of the two beams installed into the bridge after the bridge, should have L / 1000 on the value of the deflection (L - crane span). For this reason, the method of preloading cambering by webs is often used, ie the web is prefabricated with an upwelling value f greater than L / 1000 (Fig. 1) at the time of preparation.