The Structural system is defined as an assembly of interrelated or interdependent elements which forms a complex structure designed and built for resisting different loads on the structure. It is a set of elements unified whole for serving a common purpose. The elements of a structural system can be related to bones of one’s body. If bones are weak and not properly aligned and integrated one’s body would not be able to take the load of the body. In the same way, if the structural system is not proper than it would not be able to take loads. A building can also be understood as a physical embodiment of a number of systems and subsystems integrated with each other forming building as a whole.
The structural system for a building particularly consists of a stable assembly of structural elements designed and constructed to support and transit applied loads safely to the ground where in its each member has a unique behaviour under the applied loads. Structural Systems Function is to resist loads acting on a structure and provide a skeleton in the building which encloses and subdivides space in order to provide a protected environment.
The structural System as a whole is divided in into different systems:
01. Load Bearing System
02. Framed System
03. Shell System
04. Strut and Tie
All the Structural Systems have different advantages and disadvantages. So depending upon the condition the proper structural system has to be chosen by the Structural Engineer. The chosen structural system must possess the following properties:
- State of Equilibrium
- Adequate Strength
- Geometrical Stability
- Adequate Rigidity
The Structural System can further be categorized between Substructure and Superstructure.
It is the portion of a structural system that is below the ground level. It includes foundations, columns, walls below ground level, basement slabs, bridge piers and abutments, base of retaining wall. The purpose of this substructure is to support superstructure and transfer the load coming from superstructure to ground below.
It is the portion of a structural system above the ground surface and visible after completion of the project. It includes beams, slabs, columns, domes, shells and walls above ground, steel frames, bridge deck, wall of retaining wall etc. The portion of the structural system which serves the purpose of the system comes under superstructure.
Also know: Difference between Column and Shear wall
In the substructure one of the most important elements is the foundation. This foundation system must be designed to transmit the loads from the superstructure structural system directly to the ground in such a manner that settlement of soil for the completed building will be within acceptable limits.
In most buildings, the superstructure structural system consists of floor and roofs, horizontal members that support them and vertical members that support the other components. The superstructure structural system is designed to transmit its loads to the foundation system in the manner anticipated in the design of the foundations.
The superstructure of the building is loaded with different loads and different loading conditions. Due to these different loadings instability of the structure may occur.
One way to provide lateral stability is to incorporate in the system the diagonal members called bracing.
By providing bracing, columns and beams work together to carry the lateral loads downward.
Another way is to rigidly connect beams to columns to prevent a change in the angle between the beams and columns, thus making them work together as a rigid frame to resist lateral movement.
Another method is to provide long walls known as shear walls in two perpendicular directions. Lateral forces on the building can be resolved into forces in each of these directions. The walls then act like vertical beams (cantilevers) in transmitting the forces to the foundations.
So from all the above discussion it is seen that it is also important to protect the structural system against damages, especially from the fire. For fire protection, bracing can be encased in fire-resistant floors, roofs or walls. Similarly, columns can be encased in walls and beams may be encased in floors. Or fire-resistant materials, such as concrete, mineral fiber or plaster may be used to box in the structural members.
It is the choice of a right structural system which will and renders the optimum use of the building at an optimum cost. One has to choose the right structural system striking balance between its intended use and functions and of course the cost associated with it. Space i.e. volume, height, column or obstruction free area i.e. long span/short span etc will decide the right structural system. And having chosen the right structural system, it is the structural/geometrical configuration of placing all structural elements, which will yield the most economical design i.e. optimum cost of the building.