Seismic response factors of code-designed high-rise buildings using 3D non-linear analysis
Creators: name: Hussain, Nadeem
Publisher: name: University of British Columbia
Year: 2024

description: Despite the recent initiatives and developments in building design provisions using performance-based design, practicing engineers frequently adopt force-based design approaches irrespective of the structural system or building irregularity. Modern seismic building codes adopt the concept of simplifying the complex nonlinear response of a structure under seismic loading to an equivalent linear response through elastic analytical procedures using seismic design response factors. Previous studies also adopted different methodologies for quantifying the seismic response factors. This study initially presents a systematic review of the response factors used with linear analytical procedures recommended by modern building design provisions using SDOF and MDOF systems covering previous analytical, experimental and hybrid works. Limitations and gaps are identified from the previous works with 94% on 2D analysis, 92% on regular low-rise buildings and a mere 15.4% of earlier research on shear walls considering mostly unidirectional seismic loading. This comparative review highlighted the need for future research to calibrate seismic response factors to achieve more economical designs with consistent safety margins for different structural systems and irregularities using 3D bidirectional seismic loading. This study thus assessed the force-based seismic design approach of building codes in which the elastic seismic forces and deformation demands are adjusted through the response modification coefficients to arrive at an economical design under the design earthquake. Toward this objective, four multi-storey steel buildings of 8 to 20 storeys are designed using different standards. Additionally, nine high-rise (RC) structures of 40 to 60 storeys are designed in detail to ensure fair assessment of code-recommended coefficients. Three-dimensional (3D) inelastic analyses are performed for the 13 benchmark buildings using detailed fibre-based models. ISAs and MBIDAs under 26 strong ground motions are conducted to assess the seismic design coefficients. For MSBs, the results revealed a safety margin of 42% to 54% on the R coefficients specified in the design codes. For RC high-rise buildings, the observed overstrength factors for regular and irregular buildings range between 2.62 and 2.98, reflecting the code conservative value of 2.5. The deflection amplification coefficients (Cd) exhibit a 14% to 25% safety margin and validate the design code approach for assigning equal or lower Cd factors than the response modification coefficients (R). The safety margins for the R coefficients ranged from 42% to 63% for the bearing wall buildings and between 7% to 21% for dual structures. The fragility functions derived using MBIDA results and damage state probabilities confirmed the satisfactory seismic performance of the 13 benchmark structures at different intensity levels. The outcomes of the current study suggest the potential of increasing the R coefficients for MSBs and RC-bearing wall buildings initially by 10% and by 5% for dual RC buildings, resulting in more cost-effective designs for steel and RC high-rise buildings without compromising safety.