Payam Tehrani

Elastomeric composite material exhibit a highly nonlinear mechanical response that varies significantly with the applied deformation mode, particularly under large strain conditions. This behavior makes the selection of an appropriate hyperelastic constitutive model essential for achieving reliable numerical predictions. In this study, the uniaxial tensile and compressive behaviors of elastomeric composite material are experimentally investigated and subsequently reproduced through finite element simulations conducted in Abaqus software. Several commonly used hyper elastic strain-energy formulations, including Ogden models of different orders and Reduced Polynomial models, are identified using experimental stress–strain data and systematically compared. The results show that although lower-order models can represent the initial stiffness with reasonable accuracy, they fail to adequately describe the response at large deformations. Among the examined formulations, the sixth-order Ogden model provides the closest agreement with experimental results in tension, accurately capturing the pronounced strain-stiffening behavior observed at high stretch levels. In contrast, the second-order Reduced Polynomial model offers superior performance in compression by effectively reproducing both the initial softening response and the subsequent stiffness increase associated with material densification. These findings confirm the strong dependence of hyper elastic model performance on deformation mode and demonstrate that different constitutive formulations may be required for tensile and compressive loading conditions. The results provide practical guidance for the numerical modeling and design of sandwich structures incorporating elastomeric composite material cores.

The influence of soil-foundation-structure interaction (SFSI) on seismic performance continues to be extensively investigated, yet limited attention has been given to reinforced concrete (RC) dual systems comprising shear walls and moment-resisting frames. This research explores the effects of SFSI on seismic demand distribution between these components across varying building heights and soil conditions. Three RC structures (5-, 10-, and 15-story) were designed per ASCE 7–22 and ACI 318 − 19 for soil types C and D accounting for both fixed-base and flexible-base scenarios, resulting in 12 cases. Inelastic time history, incremental dynamic analysis (IDA), and pushover analyses were conducted using OpenSees. Key response parameters, including capacity curves, inter-story drifts, plastic hinge rotations, and damage distribution, were evaluated, and collapse fragility curves were developed. Results indicate that SFSI increases plastic hinge rotations by up to 65% on soil type D and 36% on soil type C, with the greatest effects in shorter buildings. Although SFSI had minimal impact on taller structures at the design-level earthquake, IDA results reveal a substantial increase in collapse probability at high seismic intensities due to excessive displacements and amplified P-Delta effects. SFSI reduced collapse resistance margins by up to 35%, highlighting deficiencies in current design codes. These findings underscore the necessity of incorporating SFSI effects in seismic design to enhance the accuracy of seismic demand assessments and improve safety, particularly for RC dual systems on softer soils.

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.

Buildings and other human-made structures can exhibit various irregularities due to environmental factors or architectural considerations. These irregularities can alter the structural response to applied forces, leading to the concentration of seismic demands in specific elements, such as shear walls or braces, which may result in irreparable damage or even collapse. As a result, understanding and considering these effects is essential in the analysis and design of irregular structures. While most research on irregularities in height has focused on setback structures, this study investigates the seismic behavior of RC buildings with geometric irregularities in shear wall height. The seismic response and collapse capacity of buildings with varying levels of irregularity are evaluated in comparison to regular structures to assess the impact of these irregularities on structural capacity. The results imply that when this type of irregularity occurs at higher elevation levels, it has minimal impact on the seismic behavior and, in some cases, may even enhance it. However, when the irregularity spans multiple stories and originates from lower elevation levels, its impact becomes significant, leading to substantial increases in structural responses and a higher probability of collapse. Furthermore, it was demonstrated that present seismic standards are ineffective in providing accurate predictions of the seismic behavior of RC shear wall structures exhibiting this type of irregularity. Consequently, this study proposes a new index, ∅_v, which accounts for the vertical position of wall width reduction, addressing a critical gap in current seismic design provisions for these types of structures. Finally, recommendations were provided to improve the existing seismic codes.

Near-field (NF) and far-field (FF) ground motion records were used to develop seismic fragility curves at different damage states for a multi-span reinforced concrete bridge using incremental dynamic analysis (IDA). The use of different methods for the prediction of the fragility curves, including truncated IDA, was also investigated. The results indicated that the median spectral acceleration causing different states of earthquake damage was lower for the NF records than for the FF records. In other words, the studied bridge was more vulnerable when subjected to NF records. The significantly larger probabilities of failure at different damage states, especially at the bar buckling damage state, for the case of NF records was attributed to the significantly larger variability of the results compared with the case of FF records. The results also showed that the probability of failure at different damage levels was relatively low for the case of the FF ground motions. It was also found that truncated IDA could be used to predict the fragility curves with sufficient accuracy for the cases studied.

Seismic design codes have imposed some limitations on the maximum subtended angle of curved bridges and allow engineers to analyze and design them using an equivalent straight bridge. This paper investigates these limitations and evaluates the AASHTO code recommendations regarding the prediction of the seismic responses of curved bridges using an equivalent straight bridge for bridges with different abutment properties at different seismic hazard levels. In this regard, the seismic responses of 21 horizontally curved and straight RC four-span bridges with different abutment types are investigated. In 7 bridge models, soil-abutment-bridge interaction is neglected, while in the rest of the bridge models, the seat-type abutments with the participation of the nonlinear backfill soil, gap, and abutment piles are used in structural modeling. First, nonlinear static (pushover) analyses are carried out to evaluate the overall behavior of the bridges with different abutment configurations in the two perpendicular principal directions. Subsequently, nonlinear time history analyses are performed to predict the seismic response of bridge elements, including column drifts and deck displacements at the place of the abutments in the radial and tangential directions at different seismic intensity levels, including the design basis earthquake (DBE) and maximum credible earthquake (MCE) excitation levels. In addition, the actual maximum displacements of the components of the bridges (i.e., the total absolute displacements) were also predicted and evaluated for different cases. It was found that the abutment properties and boundary conditions had a significant effect on the seismic response assessment of curved bridges compared to straight bridges, while such parameters are not currently considered by the design codes. The results also indicated that by increasing the seismic intensity level, more limitations should be imposed on the use of the equivalent straight bridges.