Braced Frames

Braced Frame is a common system employed to resist the significant lateral loads where when tall structures are exceptionally subjected to brace the frames, bracing can occur within a single bay inside the internal bays or along the external bays or it can span the entire face of a structure on perimeter. The advantages of braced frames from a structural engineering standpoint are enormous. Braced frames carry the lateral forces in an axial manner with tension and compression, rather than through the bending of elements which is quite inefficient from flexibility point of view. The separation of the lateral system from the gravity system being concentrate at some points gives further advantages during the design phase. This allows the lateral system to be separate , therefore permits for repetition in-floor systems and column sections. With minimal frame action and mostly axial deformation, minimal moments in the columns and girders result from the applied lateral loads compared to a moment frame. This in turn leads to cheaper girder-column connections. Among all Bracing Systems, two of them are normally widely used by the designers, namely, the cross Concentric Bracings System and the Eccentric Bracing System. These are explained further in detail as follows: Concentrically Braced Frames Steel Concentrically Braced Frames (CBFs) are assumed and recommended to be strong, stiff and ductile. The quality of the seismic response is determined by the performance of the brace. For achieving a good performance from a CBF, the brace must behave as a structural fuse thus should fail prior to any other component of the frame. The frame remains stable and resist gravity loads and withstand aftershocks without collapse. Braced Frames of structural members consists of a theoretical point of view, maybe connected to each other by means of simple flexural hinges. The resistance to horizontal forces, the most common type of braced frame is the concentric cross brace. The restricted space may have an effect on the mechanical and plumbing distribution as well as any architectural soffit details. The structural engineer needs to be able to provide this type of information to the architect to avoid potentially costly field revisions during construction. With this design approach, only half of the members are active when the lateral loads are applied. The adjacent member within the same panel is considered to contribute no compressive strength. Utilizing tension only members makes very efficient use of the structural steel shape and will result in using the smallest members such as wind or seismic, is achieved by means of braces, which essentially work in tension or compression.