The primary aim of all structural design is to insure that the structure will performs satisfactorily during its design life. Specifically, the design must check that the structure is capable of carrying the loads safely and that it will not deform excessively due to the applied loads. This requires the designer to make realistic estimates of the strengths of the materials composing the structure and the loading to which it may be subjected during its design life. Furthermore, the designer will need a basic understanding of structural behavior. The designer must make an assessment of the future likely level of loading, including self-weight, to which the structure may be subjected during its design life. Using computer methods or hand calculations the design loads acting on individual elements can be then be evaluated. The design loads are used to calculate the bending moments, shear forces and deflections at critical points along the elements. Finally, suitable dimensions for the element can be determined.
Building structure is a structure which is composed of both structural and nonstructural elements. The primary purpose of structural members is to build up and maintains its shape under a considerable load action to have adequate stability strength and stiffness. Not only safety but it also fulfills the requirement of serviceability as well as it should be economical. Regarding safety it requires that the strength of the structure should be adequate for all the loads which are reasonably considered.
When we come to the serviceability, it requires that all kinds of loads likely to occur during use, everything should be satisfactory, for example excessive deflection should be adequately small; vibration should be within the tolerable limit, the maximum width of crack also should not be greater than the specified limit etc. The structure also should be economical keeping its safety against to collapse