The essential problem in the process of technological prestressing is the imperfection of web sheets. These elements made of relatively large sheets (about 2 meters high) show significant imperfections of the shape and flatness. Initial deflections have the value equal several times the web thickness, but they tend to grow in the process of straightening. Such a case can particularly occur when stresses that compress the shield of the web sheet between diaphragms are close to the critical buckling stress. Experiments were carried out in a real object. The box girder having I I .Om span and 1.8 m in its height was prestressed by welding the straps on the bottom flange and on the web in the vicinity of the bottom llange. Results of performed investigations are the subject of the paper.

The shear lag effect of the steel box girder section in a self-anchored suspension bridge was investigated in this study. Finite element analysis software Midas Civil was used to discretize the girder under analysis into space plate elements and establish a plate element model. The law of shear lag in the longitudinal direction of the girder in the construction and completion stages was determined accordingly. The shear lag coefficient appears to change suddenly near the side support, middle support, side cable anchorage area, and near the bridge tower support of the steel box girder under the imposed load. The most severe shear lag effect is located near the side support and near the side cable anchorage area. Steel box girder sections are simulated before and after system conversion to analyze the shear lag coefficient in the bridge construction stage. The results show that the shear lag coefficient markedly differs before versus after system conversion due to the different stress mechanisms. The finite element analysis results were validated by comparison with the results of an analysis via analogous rod method.

Inclinedweb box girders are widely used in urban areas because of their attractive appearance. However, there are few studies on the vehicle shear force distribution of this type of bridge. In this study, we established 62 three-dimensional finite element models in which the shear force of each web of the box girder can be extracted; furthermore, we investigated the shear force distribution law in webs of the box girder under live loads, including single-chamber and multichamber inclined web box girders. The main parameters studied include the number of vehicle lanes and chambers, slope of the inclined webs, and support conditions. The results reveal that an uneven distribution of web shear force exists in both the single-chamber box girder and multichamber girder under live loads, and the maximum value of the vehicle shear force distribution factor is greater than the average shear value shared by all webs. Therefore, the uneven distribution of shear force in the webs of the box girder cannot be ignored under eccentric vehicle loads. These values greatly exceed the safety factor of 1.15 that is used in conventional calculations.