“…This is a major advantage compared to evolutionary algorithms, which are certainly more accurate in exploring the entire search space but also more computationally expensive due to the large number of iterations involved. In previous studies (Mohammadi et al 2019;Nabid et al 2020) it was demonstrated that the proposed UDD approach leads to optimum design solutions of comparable accuracy to genetic algorithms using thousands of iterations, thus showing high computational efficiency and simplicity.…”
Section: Effect Of Convergence Factormentioning
confidence: 95%
“…In line with other studies from the literature Sorace and Terenzi 2008), the efficiency of a damper optimisation methodology can be assessed based on energy dissipation criteria. An energy based UDD methodology was recently adopted by Nabid et al (2020) for the optimisation of friction dampers in RC structures. In the quoted study, the slip forces of friction dampers were redistributed with the aim to obtain a more uniform height-wise distribution of energy dissipation capacity under a design earthquake.…”
This paper presents a practical multi-level performance-based optimisation method of nonlinear viscous dampers (NVDs) for seismic retrofit of existing substandard steel frames. A Maxwell model is adopted to simulate the behaviour of the combined damper-supporting brace system, with a fractional power-law force–velocity relationship for the NVDs, while a distributed-plasticity fibre-based section approach is used to model the beam-column members thus incorporating the nonlinearity of the parent steel frame in the design process. The optimum height-wise distribution of the damping coefficients of NVDs satisfying given performance requirements is identified via a uniform damage distribution (UDD) design philosophy. The efficiency of the proposed multi-level performance-based design optimisation is illustrated through nonlinear time-history analysis of 3-, 7- and 12-storey steel frames under both artificial and natural spectrum-compatible earthquakes. Sensitivity analysis is performed to investigate the effects of initial height-wise damping distribution, convergence factor and uncertainty in design ground-motion prediction on the optimisation strategy. The efficiency of the final optimum design solution is also investigated by using drift-based, velocity-based, and energy-based UDD approaches to identify the most efficient performance index parameter for optimisation purposes. It is found that regardless of the selected performance parameter, the optimum damping distribution identified by the proposed methodology leads to frames exhibiting lower maximum inter-storey drift, local damage (maximum plastic rotation) and global damage index compared to an equal-cost uniform damping distribution. However, using drift-based UDD approach generally results in a better seismic performance. It is shown that the proposed UDD optimisation method can be efficiently used to satisfy multiple performance objectives at different intensity levels of the earthquake excitation, in line with performance-based design recommendations of current seismic codes. The proposed method is easy to implement for practical design purposes and represents a simple yet efficient tool for optimum seismic retrofit of steel frames with NVDs.
“…This is a major advantage compared to evolutionary algorithms, which are certainly more accurate in exploring the entire search space but also more computationally expensive due to the large number of iterations involved. In previous studies (Mohammadi et al 2019;Nabid et al 2020) it was demonstrated that the proposed UDD approach leads to optimum design solutions of comparable accuracy to genetic algorithms using thousands of iterations, thus showing high computational efficiency and simplicity.…”
Section: Effect Of Convergence Factormentioning
confidence: 95%
“…In line with other studies from the literature Sorace and Terenzi 2008), the efficiency of a damper optimisation methodology can be assessed based on energy dissipation criteria. An energy based UDD methodology was recently adopted by Nabid et al (2020) for the optimisation of friction dampers in RC structures. In the quoted study, the slip forces of friction dampers were redistributed with the aim to obtain a more uniform height-wise distribution of energy dissipation capacity under a design earthquake.…”
This paper presents a practical multi-level performance-based optimisation method of nonlinear viscous dampers (NVDs) for seismic retrofit of existing substandard steel frames. A Maxwell model is adopted to simulate the behaviour of the combined damper-supporting brace system, with a fractional power-law force–velocity relationship for the NVDs, while a distributed-plasticity fibre-based section approach is used to model the beam-column members thus incorporating the nonlinearity of the parent steel frame in the design process. The optimum height-wise distribution of the damping coefficients of NVDs satisfying given performance requirements is identified via a uniform damage distribution (UDD) design philosophy. The efficiency of the proposed multi-level performance-based design optimisation is illustrated through nonlinear time-history analysis of 3-, 7- and 12-storey steel frames under both artificial and natural spectrum-compatible earthquakes. Sensitivity analysis is performed to investigate the effects of initial height-wise damping distribution, convergence factor and uncertainty in design ground-motion prediction on the optimisation strategy. The efficiency of the final optimum design solution is also investigated by using drift-based, velocity-based, and energy-based UDD approaches to identify the most efficient performance index parameter for optimisation purposes. It is found that regardless of the selected performance parameter, the optimum damping distribution identified by the proposed methodology leads to frames exhibiting lower maximum inter-storey drift, local damage (maximum plastic rotation) and global damage index compared to an equal-cost uniform damping distribution. However, using drift-based UDD approach generally results in a better seismic performance. It is shown that the proposed UDD optimisation method can be efficiently used to satisfy multiple performance objectives at different intensity levels of the earthquake excitation, in line with performance-based design recommendations of current seismic codes. The proposed method is easy to implement for practical design purposes and represents a simple yet efficient tool for optimum seismic retrofit of steel frames with NVDs.
“…A previous study indicated that the frame deformation depends on the column and beam strength distribution along the height of the structures (Wongpakdee and Leelataviwat, 2017). To obtain uniform damage, the strength distribution can be adjusted or an optimization method (Nabid et al, 2020) could be applied to yield a more uniform DI along the height.Figure 19.Energy dissipation distribution at the 500-year and 2500-year return period levels.…”
Section: Performance Evaluation Of Example Structuresmentioning
A buckling-restrained knee-braced frame (BRKBF) is an efficient structural system utilizing short buckling-restrained braces (BRBs) as knee bracing elements. Because of the shorter yielding core length compared to those of conventional BRBs, one of the key parameters concerning the performance of this system is the low cycle fatigue cumulative damage of the BRBs. This paper presents a seismic design method considering the cumulative damage, performance evaluation, and collapse assessment of 3-story, 6-story, and 9-story archetype BRKBFs. An energy-based plastic design method was utilized to design the example frames. The frames were then evaluated by nonlinear static analysis and multiple-stripe analysis (MSA). The results indicated that BRKBs were able to accommodate seismic motions with limited damage. The validity of the design methodology considering cumulative damage was also confirmed.
“…Du et al 4 established the geometric parameter optimization model of the reverse toggle brace viscous damper and proposed a virtual viscous damper model with an additional damping ratio, based on which a viscous damper priority placement analysis method was developed. Nabid et al 5 developed a practical energy‐based optimization method for reinforced concrete frame structures equipped with friction‐based energy dissipation dampers.…”
Installing passive energy dissipation dampers in the main structure is an effective way to reduce structural seismic response. The traditional optimal design of passive energy dissipation systems requires a massive nonlinear time history analysis, which is an extremely inefficient process and, as a result, limits its application in practice. In this paper, an efficient optimal design method for dampers is proposed based on the inelasticity‐separated finite element method (IS‐FEM) and genetic algorithm. The IS‐FEM is a novel efficient structural nonlinear analysis method that can avoid the real‐time updating and decomposition of the structural global stiffness matrix in a traditional structure analysis and only requires a small‐scale Schur complementary matrix representing local nonlinear behavior being decomposed per iteration. To make the IS‐FEM available for the analysis of structures equipped with an energy dissipation system, the inelasticity‐separated governing equations of displacement‐based dampers are derived first. Then, an improved constrained optimal genetic algorithm based on population feasibility is presented to enhance the searching ability near the feasible domain boundary. Finally, an efficient damper optimization design method is proposed by combining the developed genetic algorithm with the proposed IS‐FEM‐based analysis procedure for passive energy dissipation structures. The accuracy and efficiency of the proposed method are verified by designing a set of metallic yield dampers to retrofit a steel structure.
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