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The main aim of this study is to derive a simple design procedure to determine the required sizes of vertical shear links and eccentric steel braces for the seismic retrofitting of an existing reinforced concrete frame structure with in-elevation irregularities due to setbacks designed for gravity load only. The proposed procedure distributes the vertical shear links and eccentric steel braces over the height of the structure to dissipate seismic energy away from the main structural members without any numerical iterative strategy. In fact, the capacity curve through the extension of the improved upper-bound pushover analysis method, adapted to the frame structures with setbacks, and the capacity spectrum method are the only required input parameters. A six-story RC frame structure with a towered type of setback at the second story is used in a numerical investigation to assess the effectiveness of the proposed design procedure. The structure has to be retrofitted to withstand the seismic demand imposed by the current Algerian seismic design code in a high-risk area. Nonlinear time-history analyses of original non-retrofitted and retrofitted frames are carried out considering a set of seven artificially generated records for obtaining the mean value of structural responses, which corresponds to the specified seismic demand. The results show that the proposed simplified design procedure is effective in significantly reducing both global and local seismic demand parameters and in avoiding structural instability due to the formation of a column-hinging mechanism, which has occurred at the second story where the setback is located.

Current seismic analysis contemplates the simultaneous use of the orthogonal components of an earthquake in order to determine the structural stresses closer to reality. This has led to these components being combined considering a fraction of them, as applying them completely would lead to excessively conservative results. However, their application is carried out considering that the direction of the components coincides with the orientation of the orthogonal axes that define the resistant structure. The assumption takes on special importance when it comes to establishing performance demands on a structure based on nonlinear time-history analysis. To establish the proportional relationship between the seismic components, the angle of incidence is used, which is one of the imponderable variables of an earthquake. In this investigation, a group of reinforced concrete structural archetypes with various typologies and regularity in plan is presented, which allow the effect of the angle of incidence in determining the maximum displacement demands to be studied. To study the response, a set of strong earthquakes recorded in Chile is used, obtaining the angle of incidence that produces the maximum displacement demands through interstory drift and roof displacement. A statistical analysis is also carried out in which the influence of the angle of incidence that produces the maximum response is studied.

This paper presents a displacement-based seismic design method for building structures equipped with viscoelastic dampers (VEDs) featuring strong nonlinear characteristics. First, major insights from recent analytical and experimental research on this type of VEDs, including their behavior and sources of nonlinearity, are briefly introduced. Then, a simplified response spectra-based method for estimation of the peak seismic response of the structure without and with VEDs is proposed. Here, the undamped and damped structures are reduced to equivalent single-degree-of-freedom (SDOF) systems through linearization procedures. The simplified analysis method allows for the assessment of the effects of VEDs on the structural response through a set of analytical expressions formulated in terms of two parameters controlling the design of the dampers: (1) the VED design strain; and (2) the stiffness ratio of the dampers to the main structure. In the displacement-based design procedure proposed here, the VED design strain is obtained from response history analyses of the base frame, whereas the stiffness ratio is determined through iterative calculations based on the simplified analysis method. Then, the design parameters are extended to the multi-degree-of-freedom (MDOF) system of the actual structure and VEDs are sized at each story. Finally, verification of the design layout is done through nonlinear time-history analysis. The use of time domain analysis procedures and simplified analysis tools to find the design parameters of the dampers provide the proposed methodology with a balance between accuracy and effectiveness. To illustrate the design process, the paper concludes with a design example of supplemental VEDs for the seismic retrofit of a 7-story reinforced concrete frame building.

To improve the computational efficiency of global sensitivity analysis (GSA) for complex structures, this study proposed a new importance analysis method (IE) based on the low deviation sequences and orthogonal polynomials to study the influence of parameters’ uncertainty on three structural seismic demands. A comparative investigation utilizing nonlinear time history analysis for these seismic demands was conducted using OpenSEES. The variance-based importance analysis method and the Tornado graphic sensitivity analysis method were employed to validate the accuracy of the proposed approach. The results regarding the order of importance are nearly consistent across methods, demonstrating the effectiveness of our proposed method. Notably, the sample size required by this new method is only 1024 to achieve reliable results, which is significantly lower than existing sampling methods that necessitate thousands of samples for effective importance analysis; thus, enhancing overall efficiency. Furthermore, the findings indicate that the influence of representative value of gravity load ( M s ) on seismic demands is relatively substantial, whereas the influence of modulus of elasticity of concrete ( E c ) is comparatively minor.

To better predict the responses of tall buildings in regional seismic simulation, a nonlinear multiple degree-of-freedom (MDOF) flexural-shear (NMFS) model and its associated parameter calibration method are proposed. The model has such advantages as (1) representation of the nonlinear flexural-shear deformation mode of tall buildings, (2) a high computational efficiency, (3) convenient parameter calibration, and (4) the ability to output the inter-story drift of each story. The characteristics of the nonlinear lateral flexural-shear deformation mode of tall buildings are appropriately considered in the NMFS model. The accuracy of the inter-story drift prediction is far superior to the traditional nonlinear MDOF shear (NMS) model. The computing efficiency is also remarkably improved and the speed-up ratio is greater than 30,000 by comparing to the corresponding refined finite element (FE) model. The parameters of the building models can be conveniently and efficiently calibrated using the widely accessible building attribute data from GIS. More specifically, only the descriptive information (i.e., structural height, year of construction, site condition and structural type) of each building is required to perform such calibration. Two representative tall buildings and a residential area with tall buildings are selected to demonstrate the implementation and advantages of the proposed NMFS model. Outcomes of this work are expected to provide a useful reference for future work on regional seismic loss estimations of tall buildings.

This study presents a comprehensive probabilistic evaluation of seismic response prediction methods for horizontally curved reinforced concrete (RC) bridges under bidirectional earthquake excitations with varying incident angles. A total of 14 bridge models—comprising both straight and curved configurations with different abutment conditions—were subjected to over 4,000 nonlinear time history analyses using 22 far-field ground motion records rotated across 13 angles from 0° to 180°. Seismic responses, including column drifts and abutment displacements, were assessed in global, local, and vectorial directions. A definition for “real” responses, representing resultant displacements independent of orientation, was proposed to capture maximum structural demands. The influence of horizontal curvature, abutment boundary conditions, and ground motion directionality on seismic performance was systematically examined. Results show that neglecting incident angle variability leads to underestimation of displacement demands by up to 25%. The study further evaluates the reliability of conventional combination rules—100/30, 100/40, and SRSS—in predicting maximum seismic responses. A new probabilistic framework was adopted to evaluate the likelihood of exceedance associated with the predicted structural responses under each combination rule. Findings indicate that while the 100/30 rule may be suitable for straight bridges, it underperforms for highly curved configurations. The SRSS rule consistently offers more accurate estimates, particularly when real responses are used as the benchmark. The study highlights critical limitations in existing design practices and provides targeted recommendations for selecting appropriate combination rules based on bridge geometry and abutment type, contributing to more reliable seismic design and assessment of irregular RC bridges.

From a tectonic perspective, Türkiye is a geographical region known for its high seismic activity, with some of the most active faults in the world. On February 6, 2023, two consecutive earthquakes with magnitudes of Mw 7.7 and Mw 7.6 struck Kahramanmaraş within a remarkably short time span of 9 h. This event stands out as a rare and unprecedented tectonic occurrence in terms of seismicity and tectonic activity over the past 100 years. The impact of these two major earthquakes on the region's reinforced concrete structures was significant, resulting in severe damage and the collapse of numerous buildings. It is of utmost importance to investigate and examine the design flaws and underlying factors that contributed to the damage observed in the reinforced concrete structures affected by these earthquakes. Such research will not only contribute to the improvement of structural design, seismic regulations, and quality control measures during construction but also enhance our understanding of earthquake engineering. In this study, an in-depth field investigation was conducted on reinforced concrete structures in Hatay, one of the regions most affected by the Kahramanmaraş earthquakes. The damages occurring in the buildings were documented through a detailed field survey and analyzed. A total of 540 reinforced concrete structures in the Hatay region were extensively examined, and the damages that occurred in these structures were photographed and interpreted to understand their underlying causes. Subsequently, based on the findings from the field investigation, a structural model was designed that incorporated the most significant design and construction errors responsible for the damages observed in the 540 examined structures. The devised model was subjected to static push-over analysis and nonlinear dynamic analysis using the SAP2000 finite element software, and the results obtained were interpreted.

Nonlinear dynamic properties of soil crucially influence structural responses during seismic events, highlighting the interdependence between soil and structural behavior. Incorporating soil-structure interaction (SSI) significantly increases structural vulnerability, especially in irregular conditions, compared to traditional fixed-base structures. Despite the emerging construction of reinforced concrete structures with floating columns in urban areas, their seismic performance, particularly when considering soil-structure interaction, remains largely unexplored. Therefore, this study aims to investigate the structural seismic response of mid-rise reinforcement concrete structures with and without floating columns situated on multilayered soil deposits, incorporating the effects of SSI. The nonlinearity of the soil materials was modeled using an isotropic hardening elastoplastic hysteretic constitutive model. A three-dimensional numerical investigation, employing finite element nonlinear time history analysis, was conducted to study seismic responses of structures under different configurations and base conditions. The results were presented as the ratio of structural responses with soil-structure interaction to fixed-base responses subjected to earthquake events. Structures with floating columns exhibited 1.43 times higher peak lateral storey displacement and 55% higher inter-storey drift ratio compared to those without, considering soil-structure interaction. The analysis results demonstrated a decrease in base shear values of up to 35% when accounting for SSI effects.

The resilience of cities has received worldwide attention. An accurate and rapid assessment of seismic damage, economic loss, and post-event repair time can provide an important reference for emergency rescue and post-earthquake recovery. Based on city-scale nonlinear time-history analysis (THA) and regional seismic loss prediction, a real-time city-scale time-history analysis method is proposed in this work. In this method, the actual ground motion records obtained from seismic stations are input into the building models of the earthquake-stricken area, and the nonlinear time-history analysis of these models is subsequently performed using a high-performance computing platform. The seismic damage to the buildings in the target region subjected to this earthquake is evaluated according to the analysis results. The economic loss and repair time of the earthquake-stricken areas are calculated using the engineering demand parameters obtained from the time-history analysis. A program named, “Real-time Earthquake Damage Assessment using City-scale Time-history analysis” (“RED-ACT” for short) was developed to automatically implement the above workflow. The method proposed in this work has been applied in many earthquake events, and provides a useful reference for scientific decision making for earthquake disaster relief, which is of great significance to enhancing the resilience of earthquake-stricken areas.

This paper presents numerical simulations within the frame of the project SERA—AIMS (Seismic Testing of Adjacent Interacting Masonry Structures). The study includes blind pre-diction and post-diction stages. The former was developed before performing the shaking table tests at the laboratory facilities of LNEC (Lisbon), while the latter was carried out once the test results were known. For both, three-dimensional finite element models were prepared following a macro-modelling approach. The structure consisted of a half-scaled masonry aggregate composed by two units with different floor levels. Material properties used for the pre-diction model were based on preliminary tests previously provided to the participants. The masonry constitutive model used for the pre-diction study reproduced classical stress–strain envelope, whereas a more refined model was adopted for the post-diction. After eigenvalue analysis, incremental nonlinear time history analysis was performed under a unique sequence based on the given load protocol to account for damage accumulation. In the post-diction, the numerical model was calibrated on the data recorded during the shaking table tests and nonlinear dynamic analysis repeated under the recorded accelerogram sequence. The interaction between the two units was simulated through interface elements. Moreover, the timber floors were accounted following different strategies: not modelling or considering nonlinear wall-to-floor connections. Advantages and disadvantages are then analysed, comparing the pre-diction and post-diction results with the experimental data. Numerical results differ from the experimental outcomes regarding displacements and interface pounding, although a clear improvement is visible in the post-diction model.