A Comparison of Optimized Nonlinear Time History Analysis and the Equivalent Lateral Forces Method for Brace Design A Comparison of Optimized Nonlinear Time History Analysis and the Equivalent Lateral Forces Method for Brace Design
Current design specifications for BRBF's are based on inelastic design spectra and approximate formulas for the determination of natural period. These spectra are used to obtain seismic base shear, and the distribution of equivalent lateral forces. Yielding and drift criteria are then used to determine brace areas. This design procedure is referred to throughout the thesis as the "Equivalent Lateral Force Procedure" (ELF).
The thesis compares results from the NTHO and ELF procedures for a variety of BRBF's and levels of seismicity. The ELF procedure is judged against the more accurate NTHO procedure, and BRBF's are identified where the ELF procedure produces unconservative and excessively conservative designs.
Since the NTHO procedure is more computationally expensive than the ELF procedure, design charts are developed for quickly sizing brace areas for a variety of BRBF's based on the NTHO procedure. Among the conclusions at the end of the thesis is the surprising result that the design charts show a near linear variation of brace area from story to story.
School:Brigham Young University
School Location:USA - Utah
Source Type:Master's Thesis
Keywords:braced frames buckling restrained nonlinear time history optimization genetic algorithm
Date of Publication:08/07/2007