Both, braced frame and moment resisting frame are used in the construction of structures which are subjected to lateral loads such as wind and seismic forces. This is particularly obvious for very tall structures where the lateral forces are the most important design consideration.
In braced frames, the beams and columns are generally arranged in an orthogonal pattern in both, the elevation and on the plan. The structural members are joined using a pinned connection which does not transfer moments.
In moment resisting frames, the structural members are joined together using rigid joints which transfer moment. So, the moment resisting frame depends on the joints to transfer lateral loads to the foundation.
Both, braced frame and moment resisting frame perform the same function which is resisting lateral loads and providing stability, but different mechanisms are used in each system. That is why it is important to know the difference between these structural systems.
Table 1: Difference Between Braced Frame and Moment Resisting frame
|Braced frame||Moment resisting frame|
|Pin connection is used to form the beam-column joints.||Rigid connection as shown in Fig. 1 is used between beams and columns.|
|The connection does not transfer moments.||Moments are transferred through the connection.|
|It depends on the bracing system, as shown in Fig. 2, to transfer lateral loads to the foundation. horizontal and vertical bracing systems are used.||It relies on the rigid connection to transfer lateral loads to the foundation.|
|The analysis of braced frame structure is easy and simple.||The analysis of the connection is fairly complex.|
|It is not labor intensive.||It is substantially labor intensive.|
|Cost-effective due to pinned connection which is simple to analyse and easy to construct.||Expensive to construct.|
|Provides good stabilization to the structure.||The method of stabilization is not as good as braced frames.|
|Braced frame system is mostly used in the construction of steel and timber structures.||Reinforced concrete structures inherently employ moment resisting frame.|
|Beams and columns are analyzed under vertical loads only, assuming the bracing system supports all lateral loads.||Beams and columns are analyzed under axial loads and moments.|
|As a minimum, three vertical planes of bracing are needed, to provide resistance in both directions in plan and to provide resistance to torsion about a vertical axis.||All connection are rigid.|
|It has less deformation capacity and more stiffness compared to moment resisting frames.||Moment resisting frames have more deformation capacity and less stiffness compared to braced frames.|