COMPARATIVE STUDY OF CONCENTRIC AND ECCENTRIC BRACING SYSTEM FOR LATERAL LOADS ON HIGH RISE IRREGULAR STEEL BUILDING

The resistance to the lateral loads from wind or from an earthquake is the reason for the evolution of various structural systems. Because, when a high-rise or any multi-level structure is subjected to lateral or tortional deflections under the action of seismic loads; the resulting oscillatory movement can induce a wide range of responses in the building. As a result, lateral stiffness is a major consideration in the design of tall buildings. In addition to this, many existing steel buildings and reinforced concrete buildings for which the poor lateral stiffness is the main problem; need to be retrofitted to overcome the deficiencies to resist the lateral loading. Lateral load resisting systems are structural elements providing basic lateral strength and stiffness, without which the structure would be laterally unstable. The unstable nature of structure is solved by appropriate provision of bracings systems. Bracing system is a structural system which forms an integral part of the frame. Thus, such a structure has to be analyzed before arriving at the best type or effective arrangement of bracing. Bracing is a highly efficient and economical method of resisting lateral forces in a frame structure because the diagonals work in axial stress and therefore call for minimum member sizes in providing the stiffness and strength against horizontal shear. Different literature review indicate that there is enough research on braced frame but mostly it is either experimental study or Finite element analysis of single bay regular two storey frame. Some macro model studies have been also done but limited to five to fifteen storey 2D frame steel building. So in this study, Earthquake analysis is done on G+25 steel building making T plan with 3D modeling (i.e. high rise framed building) in seismic zone IV (Adama City) for seismic ,dead and live loads to see the effect on both conditions i.e. with and without different bracing. Bracing structures are widely utilized in steel buildings to increase the resistance of the overall structural systems. But the resistance capacities of bracings are different for different orientation of bracing systems. Previous studies said that X bracing performs better than any other concentrically bracing type. But their criteria of measurement are not stipulated clearly. To minimize such set back, this study considers the weight of the bracing assumed to be a constant parameter for all selected bracing type. The building has been modeled and analyzed using ETABS software making 15 horizontal bays of width 4 meters, and storey height of 4m due to lateral earthquake as per Ethiopian Building Code of standard