Consideration of strength-stiffness dependency in the determination of lateral load pattern

• Published in: Soil dynamics and earthquake engineering (1984) Vol. 137; p. 106287
• Main Authors: Ghaderi, Parham, Khosravi, Horr, Firoozjaee, Ali Rahmani
• Format: Journal Article
• Language: English
• Published: Barking Elsevier Ltd 01.10.2020; Elsevier BV
• Subjects: Aircraft accidents & safety; Algorithms; Building codes; Computer applications; Cost analysis; Damage patterns; Dependence; Design; Ductility; Earthquake damage; Earthquakes; Frame design; Frames; Ground motion; Knots; Lateral load pattern; Lateral loads; Load distribution; Multistory buildings; Nonlinear analysis; Nonlinear dynamic analysis; Nonlinear dynamics; Optimization; Optimum strength distribution; Seismic activity; Seismic design; Seismic design codes; Stiffness; Strength; Strength-stiffness dependency; Uniform damage; Uniform ductility; Vibration mode; Strength-stiffness dependency; Lateral load pattern; Seismic design codes; Uniform ductility; Nonlinear dynamic analysis; Optimum strength distribution; Uniform damage
• ISSN: 0267-7261; 1879-341X
• DOI: 10.1016/j.soildyn.2020.106287

The lateral load pattern used in design can significantly influence the distribution of strength and stiffness and consequently the distribution of damage along the height of the structure. The distribution patterns provided in seismic design codes are primarily derived from the fundamental elastic mode of vibration without considering the inelastic behavior of structures. This code-based load pattern causes concentrated damage in some stories, while leading to inefficient use of materials in other stories. Therefore, recent studies have employed optimization algorithms to develop lateral load patterns that achieve a uniform distribution of damage over all stories. These algorithms usually determine the distribution of strength along the height to achieve a particular ductility, while the stiffness is assumed to be constant. This assumption is contrary to the strength-stiffness dependency in steel or RC elements, hence causing some errors in the proposed load patterns. This paper presents an innovative algorithm to consider strength-stiffness dependency in the development of a lateral load pattern used for the design of moment frames. The proposed algorithm is implemented in MATLAB with supplementary OpenSees codes called in for nonlinear dynamic analysis. To reduce the computational cost of the nonlinear dynamic analysis during the optimization process, original n-bay frames are represented by simplified single-bay frames. The algorithm is implemented 800 times for 5 multi-story building models, 4 target ductility level, and 40 earthquake ground motions, with each implementation requiring a large number of trial and error iterations. The analysis results are processed to achieve two new lateral load patterns, which are evaluated using three original frames subjected to different ground motions. The results demonstrate that the moment frames designed by the proposed load patterns exhibit a more uniform distribution of ductility along the building height compared to the structures designed by the previously proposed lateral load patterns. [Display omitted] •The strength-stiffness dependency is considered in the determination of lateral load pattern.•A new innovative algorithm is proposed to consider strength-stiffness dependency.•Two new lateral load patterns are proposed and evaluated.•The proposed lateral load patterns lead to a more uniform distribution of ductility.