Shear Lag Effects on Typical Box-Girder Bridge and Tall Building

In typical box-girder bridge. axial force transferred between web and flange by shear. for box-girder with a wide flange. a large part of the flange will not be connected directly to the web.

This will cause a high stresses concentration in a connected part of the flange while the remaining part of the flange is not fully stressed as shown in figure 1-C. this will result in distortion in parts of the flange. as a result plane section will not remain plane after loading and stress distribution in the flange is not uniform. in some.

Moreover, there is a tendency for longitudinal in-plane displacements of bride deck away from the flange/web connection to lag behind those parts of the bridge in close vicinity to the flange/web connection. 

Shear lag effects will cause a high concentrated area in the connection part between web and flange. these effects will be very serious and effective in case of the wide flange. therefore it should be considered in the design of the box-girder bridge.

Figure 1

For a tall building like the one showed in figure 2. under the effects of a moment resulted from lateral loads such as wind or earthquake load. the tall building will act as a cantilever. the theoretical stress distribution will be similar to figure 2-A. however, the actual stress distribution will be similar to that shown in figure 2.

Columns located at the corners will be subjected to higher stress concentrations while the columns located at the center will receive fewer stresses. these loads and stress will be transferred from building  web to flanges. the connection between web and flange will be fully and highly stressed while unconnected part will not be fully stressed as shown in figure 2-B.

These will result in a concentration of stresses in part of the building. this should be considered in the design to avoid unwanted stress concentration 

Figure 2

Leave a Comment