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Structural health monitoring (SHM) and Non-destructive Damage Identification (NDI) using responses of structures under dynamic excitation have an imperative role in the engineering application to make the structures safe. Interpretations of structural responses known as inverse problems are emerging topics with a large body of works in the literature. They have been widely solved with Machine Learning (ML) techniques such as Artificial Neural Network (ANN), Deep Neural Network (DNN), Adaptive Network-based Fuzzy Inference System (ANFIS), and Support Vector Machine (SVM). Nonetheless, these approaches can precisely predict the inverse problems of civil structures (e.g., truss or frame systems) with low damage levels, which have to wait until the structures reach certain damage or deteriorate level. The issue is related to the fact that most of the real structures have very low damage levels during their routine maintenances and usually be neglected due to limitations of the current techniques. This paper proposes a combination of Particle Swarm Optimization and Support Vector Machine (PSO-SVM) for damage identifications. The proposed approach is inspired by the effective searching capability of PSO, which can eliminate the redundant input parameters and robust SVM technique to classify damage locations effectively. In other words, natural frequencies and mode shapes extracted from the numerical examples of truss and frame structures are used as input parameters in which the redundant parameters might lead to reduction of the accuracy in the predicting models. The proposed PSO-SVM shows superior accuracy prediction in both damage locations and damage levels compared to the other ML models. It also substantially outperforms other ML models through validated cases of low damage levels.

In the present article, an advanced charged system search (ACSS) algorithm is designed for optimizing the large-scale frame structures using box-shaped sections for columns. The proposed ACSS is an extended version of the charged system search (CSS) which is a metaheuristic algorithm that uses the electrostatics and Newtonian laws of mechanics under the conditions of the Coulomb law. Two large-scale 3D frames with 1026 and 1935 components are optimized using AISC-LRFD to show the efficiency of using the box-shaped sections. Overall performance of the ACSS algorithm with box-shaped sections is compared to those of the upper bound strategy for integrated versions of the standard Big Bang Big Church algorithm and two of its newly developed variants. The results show the successful performance of using steel box-shaped columns in comparison to the frames with I-shaped sections. The numerical results show that the ACSS is efficient and robust compared to its standard version.

In the present paper, Fragility Curves (FCs) of Reinforced Concrete (RC) building types with moment-resisting frame structure representative of the existing Italian building stock have been derived through an analytical approach. The proposed methodology is based on Non-Linear Dynamic Analyses encompassing all the steps required to bring about reliable as well realistic fragility results. First, prototype building types have been selected by considering the main attributes affecting the seismic vulnerability of existing RC buildings, that is: age of construction (i.e. ‘50 s, ‘70 s and ‘90 s), number of storeys (i.e. 2, 4 and 6 storeys), arrangement in elevation of infills (i.e. Bare-, Infilled-, Pilotis-frame) and design level (i.e. seismic or gravity loads). A simulated design has been used for detailing the building types at hand, whose non-linear dynamic response has been computed by using a large set of signals. The signals have been purposely selected in order to approach the elastic design spectra provided in the Italian seismic code for different return periods, being able to take into account also record-to-record variability and soil-amplification effects. A specific relationship between the considered engineering demand parameter (i.e. inter-storey drift ratio) and all damage levels proposed in the EMS-98 scale have been defined on the basis of empirical data and expert judgement. A set of FCs in terms of peak ground acceleration are finally derived and compared to point out the role of the considered vulnerability attributes.

In this essay, the progressive collapse resistance of the reinforced concrete wall-frame structures was evaluated with and without considering the soil–structure interaction. The vulnerability of the frames against progressive collapse was investigated with the middle column removal scenario from the first story, based on the sensitivity index. To evaluate the effects of soil–structure interaction, the wall-frame structures along with the soil (hard soil) and foundation were simultaneously modeled in FLAC software and compared with the frames in Seismostruct software. The results showed that the sensitivity index decreased by considering the soil–structure interaction in the wall-frame structures. Afterward, a parametric study of the structures (foundation thickness) and substructures (soil types, soil densities, soil saturation conditions and soil layers) was performed. The results showed that with an increase in thickness of the foundation, the sensitivity index increased, and therefore, the condition of the structure would be more critical against progressive collapse. It was found that high groundwater levels in the subsoil can reduce its bearing capacity and lead to the damage to the structure. In addition, it was determined that by changing the substructure soil type from type 4 (Clay-MC) to type 1 (Rock), the use of layer 1 (SM) and layer 2 (SM-CL/ML (Very hard clay)-SM), and the soils with high density, the condition of the structures is better to prevent progressive collapse.HighlightsProgressive collapse was studied in RCSWs frames considering soil–structure interaction.A parametric study of structure and substructures was done on progressive collapse.Vulnerability of frames for progressive collapse was assessed by sensitivity index.

The simple lateral mechanism analysis (SLaMA) is an analytical method to assess the force–displacement capacity curve of Reinforced Concrete (RC) structures composed of frames, cantilever walls or dual wall/frame systems. The current version of the method was proposed in the 2017 New Zealand guidelines for the seismic assessment (NZSEE in New Zealand Society for Earthquake Engineering, the seismic assessment of existing buildings—technical guidelines for engineering assessments, Wellington, 2017). Regarding frame structures, the possible influence of infill walls is currently considered locally with checks on the RC members. However, it is universally known that infills have a major effect on the global capacity curve of the frame. In this paper, a comprehensive SLaMA method for infilled frames is proposed, which allows considering the influence of the infills on the global force–displacement curve without any numerical algorithm. The extended SLaMA method is herein formalised and it is validated in a companion paper (part 2) through an extensive parametric analysis. The extended SLaMA is based on the possibility to separately calculate the base shear contributions of the frame and the infills, in turn based on global equilibrium considerations. Such considerations also allow defining a novel procedure to post-process the results of pushover or time-history analyses where infills are modelled as diagonal struts, or to interpret experimental tests. This allows, within a single numerical analysis, to decouple the frame and infills contributions to the base-shear capacity. The decoupling procedure is herein demonstrated for an ideal two-storey, one-bay masonry-infilled frame with different infills configurations.

In the recent two decades, the progressive collapse of reinforced concrete (RC) frame structures attracted unprecedented research interests in the structural engineering community. Experiments are regarded as an essential method in this field since actual cases can barely provide sufficient and effective data to support rigorous research. In this paper, prevailing experimental assumptions and configurations among over 100 series of experiments are quantitatively revealed by a bibliometric collection based on systematic search in an academic database. Since numerous experiments have been reported on the progressive collapse of RC frame structures, this paper subsequently presents a state-of-the-art review summarizing both experimental consensuses and controversies constituted by three main aspects: (a) static mechanisms, (b) dynamic behavior, and (c) threat-dependent research. The significance of secondary mechanisms, existing problems of dynamic effects, and potential flaws of the threat-independent assumption are discussed in detail with experimental findings. Future needs are emphasized on research targets, correlations between experiments and design, dynamic effects, threat-dependent issues, and retrofitting. These recommendations might help researchers or designers realize a more reliable and realistic progressive collapse design of RC frame structures in the future.

Numerous seismic damage investigations have demonstrated that reinforced concrete (RC) frame structures tend to exhibit a Strong-beam Weak-column failure mechanism, which contradicts the intended Strong-column Weak-beam design philosophy. To explore the underlying causes of this discrepancy and identify effective strategies to enhance the realization of the Strong-column Weak-beam behavior, the mechanical performance of RC frames with varying axial compression ratios and beam-end reinforcement ratios was analyzed using the finite element analysis software ABAQUS. Key structural characteristics of failure modes, such as deformation patterns, concrete tensile damage distribution, stress distribution in slab reinforcement, concrete compressive strain in columns, plastic hinge distribution, and structural displacement ductility were examined. The results indicate that merely reducing the amount of reinforcement at beam ends has limited effectiveness in altering the failure mode and improving displacement ductility, even reduce the amount of top reinforcement at beam end to 33 % of designed quantity which is below the minimum value specified in structural design codes, the failure mode and ductility of the RC frame still cannot be substantially improved. Whereas lowering the axial compression ratio significantly enhances structural performance, when the high axial compression ratio is adjusted to a low one, for instance, from 0.9 to 0.3, the ductility of the frame structure is significantly improved, and the plastic hinge at the column end of the upper floor is successfully shifted to that beam end. Furthermore, the influence of the monolithic slab on the failure behavior of RC frames is twofold: it not only involves the contribution of slab reinforcement parallel to the beam ribs, but also stems from the presence of the monolithically cast slab-beam-column system, which improves the overall structural integrity performance. Moreover, to better measure the participation effect of the cast-in-place floor slab and reflect the potential participation capacity of the monolithic slab, the calculation formulas for the bending resistance reserve of the exterior and interior the middle frame were respectively proposed. This formula breaks through the rigid limitation of the 6 times of the slab thickness (6 ) as the width of the beam end flange suggested by the code, and better estimates the participation effect of the cast-in-place floor slab.

For stiffness design optimization of composite frame structures, one of the major problems when using fiber winding angles as design variables directly is the lack of convexity of the objective function, which may lead to different local optima depending on initial designs when a traditional gradient-based optimization algorithm is applied. Therefore, the present paper adopts a gradient-based two-step optimization scheme to cope with the difficulty and search for a better optimal design of composite frames in which the fiber winding angles are taken as design variables. To realize the two-step optimization scheme, the equivalent stiffness parameters of a composite beam with circular cross-section are derived in explicit expressions and used to force the convexity of the design optimization of the composite frame. The stiffness matrices are linearly expressed in terms of the stiffness parameters, which guarantee the convexity of the design variable feasible region in the stiffness parameter space. The equivalent stiffness parameters are adopted to keep invariance of physical quantities between fiber winding angle and equivalent stiffness parameter spaces. In the two-step optimization scheme, the minimum identification problem with the constraint that the objective function at the new starting point is less than or equal to the previous objective function at the optimum point in fiber winding angle space is established. Then, the two-step optimization scheme can be implemented in the fiber winding angle and structural equivalent stiffness parameter spaces, respectively, until the minimum identification problem is not possible to identify a new starting point. The proposed two-step optimization scheme for composite frames fully takes advantage of the stiffness parameters in convexity and fiber winding angles as practically physical quantities, respectively. The sensitivity information of the objective function with respect to fiber winding angles and equivalent stiffness parameters is derived by the analytical sensitivity analysis method. Numerical examples show that the two-step optimization scheme can effectively force convexity of the optimization model and help to eliminate the initial design dependency. The effectiveness of the proposed two-step scheme is further verified through the particle swarm optimization (PSO) algorithm which is an evolutionary algorithm with global optimization capability.

In this study, the method of inscribed hyperspheres (IHS) is presented and applied for the optimal design of 2-D steel moment frame structures. The weight of the structures, which is a function of the design variables (cross-sectional areas), is optimized subject to stress, displacement, size limits, and the variables’ linkage constraints. The IHS approach is employed to find the acceptable centers. The basic idea of this method is to inscribe the largest possible sphere in a closed space that has been created by the objective function and linearized constraints in each step. The obtained results were presented in discrete and continuous variables and compared to the results reported in the literature. This comparison showed the efficiency of this method. Also, a new mixed method of combining the optimality criteria (OC) method and the IHS method is presented in this study. It was observed that the number of iterations needed to reach the optimal solution using this new method is less than that of the above two methods when used individually, and the problem is converged to the optimal answer with extremely low iterations.