Abstract: In general, codes and regulations consider seismic
loads only for completed structures of the bridges while, evaluation
of incomplete structure of bridges, especially those constructed by
free cantilever method, under these loads is also of great importance.
Hence, this research tried to study the behavior of incomplete
structure of common bridge type (box girder bridge), in construction
phase under vertical seismic loads. Subsequently, the paper provided
suitable guidelines and solutions to resist this destructive
phenomenon. Research results proved that use of preventive methods
can significantly reduce the stresses resulted from vertical seismic
loads in box cross sections to an acceptable range recommended by
design codes.