Estimation of Axial Force Demand on Beams of Braced Frame in EBF Systems
The axial force in the link beams of an eccentrically braced frame (EBF) plays a significant role in determining the shear capacity of the link beam, which is a ductile member of the frame. However, incorrect estimates of the axial force in the braced bay beam can result from inaccurate diaphragm models and simplified linear analyses, leading to improper design and potentially significant damage during an earthquake. Additionally, beams outside the link area also experience significant axial force, but this factor is often neglected in the seismic design of structures. In order to address these issues, a simplified method has been developed to estimate the axial force in the link beams and beams outside the link area of EBF systems. This method takes into account the distribution of earthquake load along the length of the frame and the equilibrium of the structure at the ultimate capacity of the EBF link beam. The proposed method was tested using linear and non-linear numerical analyses, and was found to be accurate with an average error of less than 10% compared to the results of the non-linear analyses. The most effective variables in determining the axial force of the beams include the frame's geometry, the placement of the bracing bay, the type of frame connections, and the sections of the link beams and braces. Frames with simple connections tend to have a greater amount of axial force in the beams compared to other connection configurations.
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