The present study is the first to investigate the effect of plate skew angle and crack parameters on the buckling of cracked CNT-reinforced composite skew plates. A MATLAB code, developed within the extended finite element method (XFEM), analyzes the buckling stability of various cracked CNT-reinforced composite skew plate models under different in-plane loading and boundary conditions. The analysis considers varying plate skew angles, crack lengths, and crack locations. The effect of single-walled carbon nanotube (SWCNT) volume fraction and dispersion, modeled using the Eshelby-Mori-Tanaka homogenization scheme, on critical buckling is also examined. Results indicate that the buckling capacity of cracked CNT-reinforced composite skew plates is significantly affected by not only the skew angle and boundary conditions of the plate but also by the length and location of the crack. Moreover, the agglomeration of CNTs reduces the effective stiffness and buckling capacity.

Steel plate shear walls (SPSWs) nowadays are accepted as an efficient lateral force-resisting system, especially for high-rise structures, because of their large initial stiffness and high level of energy absorption. There are different types of SPSWs based on their infill plate type. Cellular solid shear walls (CSSWs) are innovative steel shear walls filled with cellular solids. CSSWs can be useful for special architectural designs because of their unique appearance and openings. Whereas many studies have been reported on the SPSWs, there is a shortage of studies about CSSWs. This study presents the results of a detailed, numerical parametric analysis of triangular and quadrilateral CSSWs under monotonic loading in terms of their shear capacity, initial stiffness, and ductility, and also compares them with SPSWs. The investigated parameters are the size of cells, the cellular solid depth, and the cell wall thickness. The study results indicate that at the same capacity, the quadrilateral cellular solids are far lighter than triangular ones, making the quadrilateral CSSWs more suitable for use. In addition, the findings reveal that the performance of CSSWs is good enough to be used as a lateral force-resisting system in buildings. Finally, a practical procedure for the strength capacity of CSSWs based on the theoretical strip model is proposed.

This paper presents an investigation into the compressive buckling stability of cracked carbon nanotube reinforced composite (CNTRC) skew plates, employing a computational approach based on the extended finite element method (XFEM). The core objective of this research is to accurately determine the critical buckling load and mode shape of these complex nanocomposite structures under compressive loads. Crucially, the influence of center and off-center cracks on the compressive buckling behavior of skew plates has not been handled in previous literature. Initially, the effective mechanical properties of the nanocomposite material are accurately estimated using the Eshelby-Mori-Tanaka homogenization scheme, which accounts for the dispersion of CNTs. Subsequently, an eigen-buckling analysis is performed on numerical models of the cracked CNTRC skew plates utilizing the XFEM method, implemented within a custom computational code developed in MATLAB. This study systematically examines the influence of key parameters on the critical buckling coefficient and mode shape, specifically focusing on the volume fraction and agglomeration state of the CNTs, the length and position of the crack, various boundary conditions, and the skew angle of the CNTRC skew plates. The main finding is a clear correlation between geometry and stability: the buckling coefficient significantly increases with an increasing skew angle, highlighting the structural benefits of tailoring the geometry. Moreover, the investigation confirms that the crack's length and position profoundly affect the compressive buckling capacity, providing crucial insight into fracture-induced instability. This work improves upon existing models by integrating the complexities of material heterogeneity (CNTs), geometric anisotropy (skew angle), and structural defects (cracks) within a robust XFEM framework.

In the present research, an attempt was made to improve the behavior of T-stub connections by providing stiffener details for these joints and then investigating the effect of using the proposed stiffener on the joint with non-rolled tee profiles. In this regard, five full-scale experimental samples were constructed and tested. The first sample was considered a control sample, which was designed and manufactured based on the regulations. The next two samples were constructed with rolled tee sections using proposed stiffeners of different thicknesses. In the next two specimens, the T-stub connection was constructed using the non-rolled tee sections, and in one of the specimens, the proposed stiffener was used. The tests were performed under quasistatic cyclic loading, and based on their results, the seismic parameters of ultimate strength, effective stiffness, ductility, and energy dissipation capacity were evaluated. The results of connections with rolled tee sections indicated that the proposed stiffeners increased ultimate rotational strength by up to 13.8%, effective stiffness by 92%, energy dissipation capacity by 67%, and ductility by 58%. Adding stiffeners to non-rolled tee sections boosted rotational strength by 12%, stiffness by 117%, ductility by 59%, and energy dissipation by 62%, significantly improving T-stub connection behavior.

Over the past few years, the development of Elliptic and Quasi-X bracing systems has introduced innovative approaches to structural reinforcement. While Elliptic Braced Resisting Frames (ELBRFs) have been extensively studied in both single-story and multi-story configurations, empirical data on Quasi-X Braced Resisting Frames (QXBRFs) remain limited. This gap has raised concerns about the reliability of numerical simulations for QXBRFs. To address this, the present study experimentally investigates the seismic behavior and failure mechanisms of multi-story QXBRFs, comparing their performance with ELBRFs. By providing experimental data for multi-story QXBRFs, this study contributes to the validation of numerical models and a deeper understanding of their seismic properties. Laboratory tests are conducted using 1/6-scale, single-span, four-story models of both ELBRF and QXBRF under cyclic quasi-static loading. Various seismic performance indicators—including stiffness, ductility, strength, failure modes, and energy dissipation—are assessed. In addition, nonlinear finite element method (FEM) analyses benchmark the seismic performance of QXBRFs against ELBRFs and traditional X-braced frames under similar loading conditions. The results confirm the seismic behaviors and failure patterns observed in the experimental tests. Findings indicate that incorporating elliptic and Quasi-X braces into moment frame systems significantly enhances seismic performance. The yielding of these braces delays column failure, allowing the structure to withstand substantial nonlinear deformations before collapse. In both systems, yielding initiates in the lower stories and progresses upward, eventually affecting the columns. However, QXBRFs exhibit more pronounced strength degradation at higher displacements compared to ELBRFs. These results highlight the effectiveness of these bracing systems in improving structural resilience and safety during earthquakes. Moreover, the response modification factors for ELBRFs and QXBRFs are calculated as 7.3 and 6.8, respectively. The theoretical predictions from numerical models closely align with experimental findings, reinforcing confidence in the design and application of these bracing systems for seismic resistance.

The finite point method (FPM) is a numerical, mesh-free technique for solving differential equations, particularly in fluid dynamics. While the FPM has been previously applied in solid mechanics to analyze plates under in-plane loading, there remains a notable scarcity of research exploring the out-of-plane analysis of elastic plates using this method. This study thoroughly investigates the elastic FPM analysis of thin plates subjected to transverse loadings, focusing specifically on various boundary conditions (BCs). Boundary conditions represent a significant challenge in the out-of-plane analysis of thin plates within the FPM framework. To address this challenge, the approach incorporates additional nodal points positioned close to each boundary node, supplementing the points distributed throughout the plate’s interior and along its edges. The strong form of the governing equation is employed for the interior points, while the analysis also includes the scenario of a plate resting on boundary columns. Both distributed and concentrated external loads are examined to provide a comprehensive understanding of the behavior under different loading conditions. Furthermore, the optimal placement of the extra boundary nodes is briefly discussed, alongside a focus on the number of nodes within the finite point clouds. An appropriate range for this number is proposed, although the determination of the optimal distance for the extra boundary nodes and the ideal number of cloud points is earmarked for future research. The contribution of this work is to enhance the understanding of the FPM in the context of thin plates, particularly concerning the critical influence of boundary conditions.

Previous experimental studies have effectively demonstrated the remarkable efficiency of the stiffened channel link in connecting circular columns and I -shaped beams. This research aims to present design criteria and assess the seismic properties of this specific connection type through numerical modeling. Various parameters, including stiffener type and geometric properties of the stiffened channel element, were duly taken into account. The findings from over 136 nonlinear finite element analyses (FEAs) reveal that the recommended detailing scheme reliably satisfies all the regulations specified for rigid beam -to -column connections in special moment frames.

Previous earthquake experiences have shown that conventional yielding dampers designed for an earthquake intensity cannot perform adequately at higher intensity levels. This paper addresses this issue by proposing a two-level yielding configuration for knee-braced steel frames having an innovative deformation-controlled ring damper (CRD). The proposed configuration includes a knee element damper (KED) and a CRD with a deformation-control device. In weak or moderate earthquakes, the CRD serves as the primary energy absorber. In contrast, in higher-intensity earthquakes, the deformation of the CRD is controlled and the KED acts as a secondary fuse for energy dissipation. In this study, four traditional ring dampers with different geometric properties and two CRD were experimentally tested and their numerical models in Abaqus were successfully verified. The results demonstrated stable and asymmetric hysteretic curves with satisfactory ductility and energy absorption of the ring dampers. Additionally, the CRD revealed a proper control of deformation. Subsequently, a previously tested knee-braced frame specimen with the common ring damper was numerically modeled. After verifying the validity of the model, the behavior of a typical knee-braced frame equipped with a deformation-controlled multi-ring damper (CRD-KBF) was investigated and compared with a common KBF and ring-braced frame (RBF). The obtained results confirmed the expected two-level yielding behavior of the proposed configuration. The numerical analyses demonstrated higher ductility and energy dissipation capacity of the CRD-KBF compared to the other frames.

In recent decades, researchers have evaluated the seismic performance of the innovative Elliptic-Braced Resisting Frames (ELBRFs) only in single-story single-span configurations. Although numerical studies have investigated the behavior of multi-story ELBRF configurations, the lack of laboratory data has cast doubt on the reliability of these numerical results. To address this gap in knowledge, this article evaluates the seismic performance and failure mechanisms of multi-story ELBRFs through a laboratory program and compares them with a developed type of this bracing system known as Mega Elliptic-Braced Resisting Frames (MELBRF). The key contribution of this research is the provision of laboratory test data for multi-story ELBRF and MELBRF systems, which can be utilized to validate numerical models and investigate their seismic characteristics. In this study, laboratory tests are used to examine the cyclic behavior and to calculate parameters such as strength, ductility, stiffness, energy dissipation, seismic performance, and failure modes in multi-story specimens. To this end, an experimental test of a 1/6 scale single-span four-story ELBRF specimen and a two-span four-story MELBRF specimen under cyclic quasi-static loading was conducted. Next, the seismic behavior of the proposed specimens is compared with other types of bracing systems such as X-, V-, Inverted-V, Two-Story X-, and Two-tiered diagonal braced frames in a story-base model under cyclic quasi-static loading through nonlinear FEM analyses. The results indicated that the yielding of elliptic braces would delay the failure mode of adjacent elliptic columns and thus help tolerate significant nonlinear deformation to the point of ultimate failure. The response modification factor in ELBRF and MELBRF is 7.3 and 6.5, respectively. Symmetrical behavior, high energy absorption, appropriate stiffness, and high ductility in comparison with conventional systems are some of the advantages of the proposed systems.

The process used to produce nanosheets may cause damage such as cracks in them. These cracks can adversely affect the buckling capacity of nanosheets. The main contribution of this research endeavor is to extend the previous studies on undamaged nanosheets to the cracked ones concerning the size-dependent effect. On the nanoscale, the assumption of material continuity, which is the fundamental assumption in classical continuum mechanics, is not valid. In this case, nonlocal non-classical theories are employed to analyze nanosheets. The present paper examines the nonlocal buckling of cracked graphene sheets under uniaxial and biaxial loads. To this end, the governing equations are developed based on the first-order shear deformation theory and using Eringen's nonlocal elasticity theory. Moreover, cracked nanosheets with various boundary conditions are analyzed via the extended finite element method. The variables under study are the small scaling parameter, crack length, nanosheet dimensional parameters, and support conditions. The results indicate that while the small scaling parameter reduces the critical buckling capacity of nanosheets, the presence of a crack in the nanosheet and the increase in its length intensify the nonlocal effect. In addition, as the aspect ratio of the nanosheet increases from one, the nonlocal effect decreases gradually. The small-scale effect increases by constraining the edges of the cracked nanosheets.

Steel plates have traditionally been the reinforcement of choice for conventional elastomeric bridge bearings. In addition, these bearings are often employed under fixed boundary conditions (bonded application) as seismic isolators. The main objective of this study is to develop a new type of elastomeric bearing with improved lateral flexibility and superior seismic isolation efficiency. The new bearing is a partially bonded mesh-reinforced (MR) elastomeric bearing. MR bearings employ high-strength steel mesh reinforcement layers instead of steel-reinforcing plates. Additionally, the bearing is utilized in a partially bonded application; that is, only a limited region at the central portion of the bearing contact surfaces is bonded to the top and bottom supports. Given this specific boundary condition and the bending flexibility of the mesh reinforcement layers, the MR bearing experiences lateral rollover deformations under shear loads. During lateral rollover deformation, the upper and lower surfaces of the bearing partially roll off the contact supports. This experimental study compared the cyclic lateral responses of bonded plate-reinforced (PR) bearings (as reference bearings) and their partially bonded MR-bearing counterparts. The elastomer material properties and geometrical characteristics of the two bearing types were identical. The experimental results suggest that partially bonded MR bearings are feasible, perform more flexibly in the lateral direction, and exhibit greater energy-dissipation capability than PR bearings. This study focuses on a new type of elastomeric bridge-bearing isolator designed to be more flexible horizontally and better at absorbing the input energy of earthquakes. The new bearing isolator was constructed using laminated rubber material layers that were bonded to high-grade steel mesh reinforcement layers instead of conventional steel plates. The mesh reinforcement is rigid when stretched in a flat direction; however, it can bend easily. The bearing isolator was only partially bonded to its supports, which allowed it to deform more freely in the horizontal direction. During horizontal deformation, the upper and lower surfaces of the bearing partially roll off the contact supports. In this study, the new bearing type was compared with the conventional (steel plate reinforced) type, and it was found that the new bearing type is more effective at absorbing seismic excitations and can provide greater flexibility in the horizontal direction. This new bearing type is called a partially bonded mesh-reinforced elastomeric bearing.

In the present study, the sound transmission loss (STL) through the air-filled rectangular double-walled cross-ply fiber metal laminated (FML) nanoplates under simply supported and clamped boundary conditions is studied using the nonlocal strain gradient theory (NSGT) and third-order shear deformation theory (TSDT). NSGT is complemented with hardening and softening material effects, which can significantly enhance the accuracy of small-scale results. The sound velocity potential and Hamilton's principle are employed to derive the coupled size-dependent vibroacoustic equations. The Galerkin method is exploited to solve vibroacoustic equations and obtain the STL. The developed solution is examined in terms of its accuracy and precision via a comparison with other available data in existing research. The effects of different parameters such as boundary conditions, nonlocal and strain gradient parameters, lay-ups, incident angles, and acoustic cavity depth on the STL through the double-walled FML nanoplates are investigated.

With the growing use of functionally graded (FG) microplates in structural acoustic metamaterials for aerospace and automotive applications, accurate modeling of sound transmission loss is critical for effective vibration and noise control engineering. In this study, a theoretical model is formulated based on the first-order shear deformation theory (FSDT) to estimate sound transmission loss (STL) through air-filled rectangular double-walled FG microplates with simply supported boundary conditions. The microplates are subjected to a nonlinear thermal environment, and the modified strain gradient theory (MSGT) is employed, incorporating three material length scale parameters to account for the size effect. The material properties are temperature-dependent and vary across the thickness following a power-law distribution. Size-dependent coupled vibroacoustic equations are derived utilizing the sound velocity potential, normal velocity continuity conditions, and Hamilton's principle, and are subsequently solved using the Galerkin method. Comparative analysis is performed by contrasting the results obtained from the MSGT model with those from the modified couple stress theory (MCST) and classical continuum theory (CCT) models, allowing for the assessment of the accuracy and precision of the proposed solution. Additionally, the influence of various parameters, such as gradient index, length scale parameters, temperature variation, incident angles, and acoustic cavity depth, on the STL is investigated. Key findings demonstrate that in the stiffness-controlled region, length scale parameters significantly enhance STL, while power-law index and temperature variation reduce it.

In recent decades, various strategies have been employed to enhance the seismic resilience of structural systems in the event of earthquakes. One such innovative method is the elliptic-braced moment-resisting frame with a rotational friction damper (ELBRF-RFD), which serves as a displacement-restraint bracing technique connecting the elliptic brace to the upper beam. To design an ELBRF-RFD based on contemporary guidelines, for the first time, this study introduces the quantification of seismic performance factors (SPFs) through incremental dynamic analysis (IDA). The research then proceeded to design 3-story, 5-story, and 7-story archetypes in type II soil using the presumed SPFs. A comparative analysis was conducted with inverted-V braced frames equipped with rotational friction dampers (CBF-RFDs). The performance of each archetype was evaluated through nonlinear static pushover analysis (NSPA) and IDA, employing 15 earthquake records from the past and using the OpenSees software. For the response modification factor, suggested values of 11.2 (allowable stress method) and 7.8 (ultimate limit state methods) were identified. Furthermore, the collapse probability of archetypes was determined by employing fragility curves and considering sources of uncertainty.

The present study proposes a new system for preventing local buckling in reduced beam sections (RBSs). The proposed method is called the "hybrid-sandwiching system". In this approach, high-strength grout sandwiches an RBS part of a beam with the help of steel strips and high-strength bolts. Two T-shape specimens representing a beam-to-column connection were tested under displacement-controlled cycling loading. One specimen includes the conventional RBS and the other includes the proposed hybrid-sandwiched RBS. The experimental results of the specimens showed that the specimen with hybrid-sandwiched RBS experienced a considerable rotation up to a drift angle of R = 7% without any buckling in the web and flanges. However, in the specimen with conventional RBS, the flanges were buckled, and consequently, a significant strength degradation was observed at a drift angle of R = 4%. The experimental results confirmed that the hybrid-sandwiching system not only provides great ductility for RBSs but also does not disturb the basic role of the RBSs in moving the location of the flexural plastic hinges away from the columns' faces. In addition to experimental investigations, the finite element models (FEMs) of the specimens were conducted and validated with experimentally-obtained results. A series of FEMs was also carried out to verify the influence of hybrid-sandwiching systems on RBSs with different sizes.

This paper is presented to study the free vibration analysis and optimization of CNT/polymer/fiber laminated truncated conical panels. Each layer of the panel is composed of a polymeric matrix reinforced with oriented fibers along with uniformly distributed and randomly oriented agglomerated carbon nanotubes (CNTs). The panel is modeled based on the first-order shear deformation theory (FSDT) and the effective mechanical properties are estimated using the Eshelby-Mori-Tanaka approach, Hahn's homogenization method, and the rule of mixture. The governing equations are derived utilizing Hamilton's principle and are solved numerically via the differential quadrature method (DQM). An optimization problem is provided via particle swarm optimization (PSO) and the optimum orientations of the fibers and best values of weight fractions of the CNTs and fibers are found to increase the fundamental frequency and reduce the relative cost of such structure. It is concluded that the optimum design of the panel is strongly affected by the chirality of the CNTs and the boundary conditions.

Concentrically braced frames (CBFs) collapse mainly because of soft story formation at one or a few stories in which excessive brace buckling occurs. This study provides an intuitive understanding of the collapse mechanism of CBFs with 3–18 stories subjected to mainshock-aftershock sequences. Such understanding will support development of design methods that preclude low-capacity collapse modes specially under multi-shock excitations. This paper assesses the collapse mechanism as a stage in which the imposed seismic energy fails to dissipate and eventually leads to uncontrolled kinetic energy. The investigation focuses on the role and distribution of the various energy measures and different dissipating mechanisms throughout the structures. The employed structural models simulate softening-induced dynamic instability by modeling various inelastic damage modes including buckling of the brace members. Collapse mechanism is identified for various combinations of the utilized mainshock-aftershock pairs that are gradually scaled following the IDA process. The distribution of input and dissipated energies along various stories reveals the role of upper stories in damping the imposed energy. Furthermore, the similarity between the height profile of the residual drifts and the story imposed energies highlights the characteristic of the structures in adapting their drift response to a mode with the highest energy absorption.

This paper presents the buckling analysis of cracked CNTRC plates under shear loading using XFEM, focusing on the existence of the off-center cracks as the novelty of the research. For this purpose, the equivalent mechanical properties of the nanocomposites are calculated using the Eshelby-Mori-Tanaka homogenization scheme. The CNTs are assumed to be randomly oriented, experiencing the null, partial and complete agglomeration. The numerical models of the cracked CNTRC plates with center and off-center cracks are created using a calculation code prepared in MATLAB. The effect of volume fraction (VCNT = 0.0, 0.05, 0.1, 0.15, 0.20) and agglomeration of CNTs, crack length (0.0 <= a* <= 0.8), location of the crack (0.0 <= ey* <= 0.9 and 0.0 <= ex* <= 0.6), boundary conditions (SSSS, CCCC, CFCF, CSCS) and aspect ratio of cracked CNTRC plate (L* = 0.5, 1.0, 2.0) on the critical buckling coefficient and mode shape is investigated. The results show that the critical buckling mode shape is affected by the interaction effects of various cracking parameters. In addition, the CNT parameters, including the volume fraction and agglomeration, significantly affect the shear buckling capacity of the cracked CNTRC plates.

In the concept of conventional structural design, the general assumption is that the structure is fixed at its base, while the fact is that the supporting soil medium allows for some general motions of the foundation due to its flexibility. Regardless of stiffness of structure’s frames, this phenomenon results in a subsequent increase in natural period of the system and alters the overall expected response. Moreover, considering soil–structure interaction (SSI) in dynamic analysis of a building structure may result in producing an additional motion of the structure due to rocking motion of the building. The main purpose of the current study is to explain how the mechanism of the effect of rocking motion on the behavior of a steel plate shear wall (SPSW) structure. In this order, the SSI phenomenon is studied and explained in a typical mid-rise steel plate shear wall frame resting on shallow foundation. The SSI effects on the inelastic responses of such a frame due to El Centro 1940 earthquake were examined in detail using a direct method, and also, the results were compared to those for the fixed base frame. Then, a procedure is presented to clarify how SPSW behavior could be influenced by rocking component. Here, two site conditions were considered (typical stiff and soft soil deposits). The results indicated that the SSI greatly affects the seismic performance of the SPSW structure in terms of the seismic story shear forces, displacements and story drifts.

Extensive research has been carried out on steel moment frames to improve the cyclic performance of seismic resisting connections with Reduced Beam Section (RBS). The lateral-torsional buckling and reducing of the flexural resistance of the beam are the disadvantages of conventional RBS connections with radial cutting in the flange. Therefore, some researchers have suggested the reducing of the web in lieu of the flange as an effective strategy to prevent these phenomena. The present study aims to investigate the cyclic behavior of the reduced web section (RWS) connections with vertical-slits (VS) as a cost-effective alternative with multiple design parameters through an experimental and numerical study. Two full-scale specimens of the bolted end-plate VS-RWS connection were experimentally tested under the SAC cyclic loading to evaluate the performance of connections, and then in order to obtain proper ranges for the geometric design parameters, a parametric study was carried out using the verified numerical models. The parameters consist of the distance between the column face and the beginning of the reduced region, the length of the reduced region, as well as the depth and width of the vertical-slits. Based on the results, the appropriate ranges for the geometric parameters of VS-RWS have been recommended. In order to obtain the story drift of the frame caused by the VS-RWS beam flexural deformation using the conjugate beam method, the original VS-RWS was replaced with an equivalent constant-cut reduced beam section (CC-RBS). At last, a step-by-step design procedure for VS-RWS connections was provided according to AISC-358.