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This paper presents a novel descent algorithm based on the step-by-step iterative principle, applied to the optimum design of steel frames. The search consists on finding the direction which decreases the structural weight most quickly. As the design problem includes discrete variables, the optimum is found by evaluating the structural weight gradient step by step. The step size is controlled in such a way that convergence towards infeasible or suboptimal solutions is avoided. By properly choosing the initial solution, it is possible to increase the efficiency and the convergence speed of the algorithm. Many strategies, for the choice of initial design point, by making use of engineering intuitions or using optimized design obtained by other algorithms are discussed. Furthermore, it is confirmed in this study that the proposed algorithm can be used to improve optimum designs found by metaheuristic algorithms. The optimization results, relative to several weight minimizations problems of benchmark planar steel frames designed according to Load and Resistance Factor Design, American Institute of Steel Construction (LRFD-AISC) specifications, are compared to those obtained by different optimization methods. The comparison proves the efficiency and robustness as well as the prompt of convergence of the proposed descent algorithm developed in this paper.

The present research aims to study the influence of the soil–structure interaction (SSI) and existence or absence of masonry infill panels in steel frame structures on the earthquake-induced pounding-involved response of adjacent buildings. The study was further extended to compare the pounding-involved behavior versus the independent behavior of structures without collisions, focusing much on dynamic behavior of single frames. The effect of SSI was analyzed by assuming linear springs and dashpots at the foundation level. The infill panels were modeled using equivalent diagonal compression struts. The steel frames were assumed to have elastic–plastic behavior with 1% linear strain hardening. The dynamic contact approach was utilized to simulate pounding between the adjacent buildings. Nonlinear finite element analysis was performed for two adjacent multi-story structures with four different configurations representing cases that can exist in reality. The seismic response of the studied cases generally emphasized that ignoring the soil flexibility and/or the contribution of the infill panels may significantly alter the response of adjacent structures. This may result in a false expectation of the seismic behavior of buildings exposed to structural pounding under earthquake excitation.

In this paper, a new design-driven hybrid optimization algorithm called guided evolution strategy (GES) is proposed for a reliable and rapid optimum design of space steel frames. The rationale behind the proposed GES algorithm is to improve convergence characteristics of the evolution strategies (ESs) optimization method by guiding search process according to the satisfaction/violation of strength constraints in a previous design. This is referred to as guided mutation, which is introduced as an auxiliary tool to a stochastic mutation scheme for accelerating the convergence speed of the optimization algorithm. The efficiency of the GES algorithm is investigated and quantified using design examples where sizing optimization of two space steel frames are achieved under strength and displacement constraints imposed according to ANSI/AISC 360-10 (Specification for structural steel buildings, ANSI/AISC 360-10, Illinois, 2010) and ASCE/SEI 7-10 (Minimum design loads for buildings and other structures, ASCE/SEI 7-10, Reston, 2010) design specifications. The solutions produced to these design examples with the GES algorithm are compared to those of some selected metaheuristic search techniques in terms of accuracy of the obtained solutions as well as speed of convergence to the optimum designs. It is shown that the GES algorithm has improved search abilities with respect to other employed techniques.

Traditional structural design involves drawing recognition, repeated modeling, parameter tuning, and numerous mechanical analyses by skilled designers, which is time-consuming and inefficient. To address those problems, a two-stage automatic structural design of the steel frame based on expert experiences is proposed. In the first stage, from the computer-aided design plain drawing, semantic features (walls and openings) and geometrical information of architectural elements are extracted by a layer classification method. The segmentation of rooms is conducted by an enclosed region detection method and the connectivity graph is generated using the connected component analysis method. Based on expert experiences considering both structure and architectural function requirements, the structural member configuration and the floor load distribution are automatically established to obtain the parametric structural model. In the second stage, a modified particle swarm optimization (MPSO) based on expert experiences is proposed for single-objective structural optimization according to the design codes. Then based on MPSO, a hierarchical multi-objective optimization method is adopted to obtain more available solutions with different economic benefit and redundant safety. The results show that the proposed two-stage structural design framework is fully automatic and highly efficient. It integrates parametric modeling and structural optimization, and also enables effective transfer of different data items including architectural plan and structural model. It provides a guideline to automatic structural design of steel frames.

Traditional center brace steel frame structural systems typically focus on refining the member cross-section size in the brace arrangement and optimization analysis. However, they often overlook the critical aspects of brace location and overall structural performance that are inherently interconnected. This study highlights the impact of different brace arrangement locations on the structural performance. Consequently, by employing the fundamental principle of maximum structural stiffness and a derived theoretical model of a simplified optimized arrangement, we proposed a novel method for optimizing the arrangement of center braces. This resulted in significant enhancements in the mechanical properties of the steel frame brace structural system compared with traditional approaches. It elucidated the intrinsic connection between the positional parameters of the center brace and the lateral resistance performance of each story and derived a theoretical formula validated through 190 ABAQUS finite element analysis models. Building on this foundation, this study further analyzed the factors influencing the lateral resistance performance within the frame brace system. A simplified mechanical model of the center brace steel frame structure was established, along with an explanation of the brace optimization principles using the basic brace unit. The static and dynamic performances of structures featuring optimal brace arrangements were thoroughly examined to understand their impact on the overall lateral performance and yielding mechanisms. Additionally, the dynamic response of the structures following the implementation of optimal brace arrangements was studied to explore the relationship between brace location and seismic performance.

A new method is presented for an application of the Gaussian mixture model (GMM) to a multi-objective robust design optimization (RDO) of planar steel frame structures under aleatory (stochastic) uncertainty in material properties, external loads, and discrete design variables. Uncertainty in the discrete design variables is modeled in the wide range between the smallest and largest values in the catalog of the cross-sectional areas. A weighted sum of Gaussians is statistically trained based on the sampled training data to capture an underlying joint probability distribution function (PDF) of random input variables and the corresponding structural response. A simple regression function for predicting the structural response can be found by extracting the information from a conditional PDF, which is directly derived from the captured joint PDF. A multi-objective RDO problem is formulated with three objective functions, namely, the total mass of the structure, and the mean and variance values of the maximum inter-story drift under some constraints on design strength and serviceability requirements. The optimization problem is solved using a multi-objective genetic algorithm utilizing the trained GMM for calculating the statistical values of objective and constraint functions to obtain Pareto-optimal solutions. Since the three objective functions are highly conflicting, the best trade-off solution is desired and found from the obtained Pareto-optimal solutions by performing fuzzy-based compromise programming. The robustness and feasibility of the proposed method for finding the RDO of planar steel frame structures with discrete variables are demonstrated through two design examples.

This paper presents the fragility assessment of non-seismically designed steel moment frames with masonry infills. The assessment considered the effects of multiple earthquakes on the damage accumulation of steel frames, which is an essential part of modern performance-based earthquake engineering. Effects of aftershocks are particularly important when examining damaged buildings and making post-quake decisions, such as tagging and retrofit strategy. The procedure proposed in the present work includes two phase assessment, which is based on incremental dynamic analyses of two refined numerical models of the case-study steel frame, i.e. with and without masonry infills, and utilises mainshock-aftershock sequences of natural earthquake records. The first phase focuses on the undamaged structure subjected to single and multiple earthquakes; the effects of masonry infills on the seismic vulnerability of the steel frame were also considered. In the second phase, aftershock fragility curves were derived to investigate the seismic vulnerability of infilled steel frames with post-mainshock damage caused by mainshocks. Comparative analyses were conducted among the mainshock-damaged structures considering three post-mainshock damage levels, including no damage. The impact of aftershocks was then discussed for each mainshock-damage level in terms of the breakpoint that marks the onset of exceeding post-mainshock damage level, as well as the probability of exceeding of superior damage level due to more significant aftershocks. The evaluation of the efficiency of commonly used intensity measures of aftershocks was also carried out as part of the second phase of assessment.

In engineering practice, creating window openings in partition infill walls is a common requirement for infilled frames. However, the intervention of infill walls may interrupt the desired cyclic behavior of the infilled frame, and worst yet, the inevitable window opening might further aggravate such negative interaction. To protect the openings from the detrimental multiple diagonal struts mechanism of the traditional infill wall with a window opening under lateral loadings, this research presents a novel infill wall system with a window opening for semi-rigid steel frames. Three half-scaled specimens are subjected to quasi-static cycle tests: a bare steel frame, a steel frame infilled with a traditional infill wall with a window opening, and a precast infill wall with a window opening and sliding joints in a steel frame. Experimental results show that the proposed infill system with a window opening can release adverse crack development or opening deformation of the window opening by mitigating the detrimental multiple diagonal struts effect in conventional infill walls with window openings under lateral loadings. In this way, the developed infilled frame exhibits similar cyclic behavior to the designed bare steel frame with higher energy dissipation capacity. Furthermore, parametric analysis results reveal that the friction factor of the sliding joints has a significant effect on enhancing the bearing capacity of the proposed infill system, while the change of opening sizes and locations of the window opening has negligible impact on the cyclic behavior of the developed infill system.

This study explores seismic performance of steel frame buildings with SMA-based self-centering bracing systems using a probabilistic approach. The self-centering bracing system described in this study relies on superelastic response of large-diameter cables. The bracing systems is designed such that the SMA cables are always stressed in tension. A four-story steel frame building characterized until collapse in previous research is selected as a case-study building. The selected steel frame building is designed with SMA bracing systems considering various design parameters for SMA braces. Numerical models of these buildings are developed by taking into account the ultimate state of structural components and SMA braces as well as the effect of gravity frames on lateral load resistance. Nonlinear static analyses are conducted to assess the seismic characteristics of each frame and to examine the effect of SMA brace failure on the seismic load carrying capacity of SMA-braced frames. Incremental dynamic analyses (IDA) are performed to compute seismic response of the designed frames at various seismic intensity levels. The results of IDA are used to develop probabilistic seismic demand models for peak inter-story and residual inter-story drifts. Seismic demand hazard curves of peak and residual inter-story drifts are generated by convolving the ground motion hazard with the probabilistic seismic demand models. Results show that steel frames designed with SMA bracing systems provide considerably lower probability of reaching at a damage state level associated with residual drifts compared to a similarly designed steel moment resisting frame, especially for seismic events with high return periods. This indicates reduced risks for the demolition and collapse due to excessive residual drifts for SMA braced steel frames.

This study proposes a novel external steel-frame system equipped with viscoelastic nodal dampers for improving the seismic performance of reinforced concrete (RC) structures. The nodal dampers utilize viscoelastic materials to dissipate seismic energy through hysteretic shear deformation, thereby reducing the dynamic response of the main structure. An external steel frame is connected to the original RC frame through these dampers, forming an integrated load-bearing and energy-dissipating system. A series of shaking table tests were conducted on two models: the original RC frame and the retrofitted structure incorporating the external steel frame with viscoelastic nodal dampers. The tests investigated the acceleration and displacement responses under different seismic excitations, with peak ground accelerations ranging from 0.2 g to 1.0 g. The results demonstrate that the proposed system significantly enhances stiffness and energy dissipation capacity, effectively reducing floor acceleration and inter-story drift. Under moderate earthquakes, the external steel frame increases the overall stiffness, while under strong ground motion, the viscoelastic nodal dampers dominate energy dissipation. The maximum reduction in acceleration response reached 64%, and inter-story displacement was reduced by up to 52.4%. These findings confirm the system’s ability to provide both seismic strengthening and damping, offering a practical and sustainable solution for the seismic retrofit of existing RC structures.