Prediction of lateral stiffness and fundamental period of concentrically braced frame buildings

Abstract

In this paper, a simple hand calculation method to predict lateral stiffness and fundamental period of concentrically braced frame buildings with either fixed or pin base, which can also be used for unbraced frame buildings, is theoretically derived. To verify the reliability of the developed equations, the estimated lateral stiffness and fundamental periods are compared with the corresponding values obtained from pushover and Eigenvalue analyses for a wide range of low to medium rise buildings (i.e. up to ten storeys) with varying geometrical configurations. Systematic investigation of parameters affecting the fundamental period of frame buildings is also carried out. Although the basic formulation considers X and chevron brace configurations explicitly, its applicability to other types of brace configurations is also investigated. The suitability of the proposed equation for the braced frames with linear variation of section properties along the building height and pin beam-column connections is also scrutinized. Reliability of the developed hand calculation method is verified using the experimental test and numerical analysis results available in the literature. Finally, a flowchart and two worked examples are provided to explain the sequence of steps to calculate the fundamental period of concentrically braced frame buildings.