Composite construction is normally warranted when the cast-in-situ construction is very different, if not possible, more over composite construction is an automatic choice when the quality construction is not assured at site and speed of construction is decisive factor. So that the members are made some place else like factories or industry and then shifted to the site.
Advantages of Composite
The advantages in using pre-stressed pre cast concrete beams with cast in situ slab in composite construction are as follows:-
- Appreciable saving in cost of steel in composite member as compared to fully pre-stressed cast in situ members.
- The pre-stressing can be in stages; this would facilitate providing only the required pre-stress to take care of service loads.
- In many cases, precast pre-stressed units serve as supports and dispense with the formwork required for placing the cast-in-situ concrete.
- Easy and fast execution of work is possible particularly in bridge construction when normal traffic cannot be disturbed for long.
- Proper utilization of properties of concrete in the composite member, such as use of high strengthconcrete in the pre cast pre-stressed unit a part of which become the tensile zone after the composite action is established and use of medium strength concrete in the insitu portion which form the compression zone of the composite member.
- Possibility o fuse of different materials like light weight concrete for the cast-in-situ portion resulting in the reduction of dead load of the structure which would load to overall economy.