This study presents a new way to improve masonry wall behavior. Masonry structures comprise a significant part of the world’s structures. These structures are very vulnerable to earthquakes, and ...their performances need to be improved. One way to enhance the performances of such types of structures is the use of post-tensioning reinforcements. In the current study, the effects of shape memory alloy as post-tensioning reinforcements on originally unreinforced masonry walls were investigated using finite element simulations in Abaqus. The developed models were validated based on experimental results in the literature. Iron-based shape memory alloy strips were installed on masonry walls by three different configurations, namely in cross or vertical forms. Seven macroscopic masonry walls were modeled in Abaqus software and were subjected to cyclic loading protocol. Parameters such as stiffness, strength, durability, and energy dissipation of these models were then compared. According to the results, the Fe-based strips increased the strength, stiffness, and energy dissipation capacity. So that in the vertical-strip walls, the stiffness increases by 98.1%, and in the cross-strip model’s position, the stiffness increases by 127.9%. In the vertical-strip model, the maximum resistance is equal to 108 kN, while in the end cycle, this number is reduced by almost half and reaches 40 kN, in the cross-strip model, the maximum resistance is equal to 104 kN, and in the final cycle, this number decreases by only 13.5% and reaches 90 kN. The scattering of Fe-based strips plays an important role in energy dissipation. Based on the observed behaviors, the greater the scattering, the higher the energy dissipation. The increase was more visible in the walls with the configuration of the crossed Fe-based strips.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Shape memory alloys (SMAs) have been widely used in civil engineering applications including active and passive control of structures, sensors and actuators and strengthening of reinforced concrete ...(RC) structures owing to unique features such as the shape memory effect and pseudo-elasticity. Iron-based shape memory alloys (Fe-SMAs) have become popular in recent years. Use of iron-based SMAs for strengthening RC structures has received attention in the recent decade due to the advantages it presents, that is, no ducts or anchor heads are required, friction losses do not occur and no space is needed for a hydraulic device to exert force. Accordingly, Fe-SMAs embedded in a shotcrete layer have been used for pre-stressing RC beams at Empa. The aim of this study is to present an approach to model and analyze the behavior of RC members strengthened and pre-stressed with Fe-SMA rebars embedded in a shotcrete layer. The lack of research on developing finite element models for studying the behavior of concrete structures strengthened by iron-based shape memory alloys is addressed. Three-dimensional finite element models were developed in the commercial finite element code ABAQUS, using the concrete damaged plasticity model to predict the studied beams’ load–displacement response. The results of the finite element analyses show a considerably good agreement with the experimental data in terms of the beams’ cracking load and ultimate load capacity. The effects of different strengthening parameters, including SMA rebar diameter, steel rebar diameter and pre-stressing force level on the beam behavior, were investigated based on the verified finite element models. The results were compared. The load-displacement response of an 18-m concrete girder strengthened and pre-stressed with iron-based SMA bars was examined by the developed finite element model as a case study.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
From past earthquakes, it has been found that the large residual displacement of bridges after seismic events could be one of the major causes of instability and serviceability disruption of the ...bridge. The shape memory alloy bars have the ability to reduce permanent deformations of concrete structures. This paper represents a new approach for retrofitting and seismic rehabilitation of previously designed bridge columns. In this concept, the RC bridge column was divided into three zones. The first zone in the critical region of the column where the plastic hinge is possible to occur was retrofitted with near-surface mounted shape memory alloy technique and wrapped with FRP sheets. The second zone, being above the plastic hinge, was confined with Fiber-Reinforced Polymer (FRP) jacket only, and the rest of the column left without any retrofitting. For this purpose, five types of shape memory alloy bars were used. One rectangular and one circular RC bridge column was selected and retrofitted with this proposed technique. The retrofitted columns were numerically investigated under nonlinear static and lateral cyclic loading using 2D fiber element modeling in
software. The results were normalized and compared with the as-built column. The results indicated that the relative self-centering capacity of RC bridge piers retrofitted with this new approach was highly greater than that of the as-built column. In addition, enhancements in strength and ductility were observed.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Nowadays, steel plate shear wall is considered as a suitable system for conventional lateral load resisting systems, because of high post buckling strength, significant ductility, stable hysteresis ...characteristics and high initial stiffness. Although early experimental and analytical research on steel shear wall clarified various aspects of seismic behavior of such system, but still several issues such as deterioration behavior of the system require more investigation on the subject. Like any other structures, in order to investigate the performance of steel plate shear wall (SPSW) comprehensively, its nonlinear behavior should be assessed in a wide range. In this study, based on the modified Ibarra–Krawinkler deterioration model, new equations are proposed in order to provide an acceptable prediction of nonlinear cyclic behavior of one-story SPSWs with hinged-joints. For this purpose, a number of 60 SPSWs were numerically modeled and analyzed and the modified Ibarra–Krawinkler deterioration model parameters were calibrated and pertinent parameters were identified. Then, using statistical regression analysis, the behavioral equations are presented; in which displayed an acceptable level for prediction of cyclic performance of SPSW system.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Steel plate shear walls usually do not satisfy the strong-column weak-beam design criteria, leading to larger column sections. On the other hand, rigid frame structures are typically constructed in ...low-rise to mid-rise buildings built in locations prone to strong earthquakes due to their high flexibility and cost-effective solutions. Overcoming these restrictions to the SPSW system, this paper is dedicated to employing a semi-rigid connection that dissipates energy well and reduces the forces applied to the structure. By using a semi-rigid connection in an adjacent span to the SPSW, the actual flexural capacity of the beam end decreases and, subsequently, improves the performance of the structure in terms of the of the strong-column weak-beam criteria. Thereupon, the impact of the semi-rigid connections on steel frames with SPSWs as a sideway resisting system can be assessed by implementing a numerical study. In this paper, a new methodology for modelling semi-rigid joints is used considering five connections with different moment capacities. Moreover, the influence of three different circular diameters on the behavior of the perforated SPSWs was investigated. To fulfil these purposes, nonlinear dynamic analysis was conducted to assess the reliability of 5-, 10-, and 15-story frames resisted with SPSWs and semi-rigid connections subjected to actual ground motion records. A total of 45 frames were modelled and the obtained results were compared with reference benchmarks. The outcomes of the studies show good agreement with design building code requirements. In addition, the reliable performance of the structure under seismic loads is evaluated. According to the results of the parametric study, the presumed allowable drift leads to obtaining the optimum moment capacity of connection for each model and illustrates the applicability of a new structural system consisting of SPSWs and semi-rigid connections simultaneously.
The hybrid steel frame is a new laterally resistant steel frame composed of rigid and semi-rigid connections. The objective of this study is to select a hybrid frame with an appropriate seismic ...performance based on a multi-criteria decision-making approach. The seismic performance of different patterns and positions of semi-rigid connections within the selected frames is examined. Static, cyclic and nonlinear dynamic analyses are conducted on the selected frames. The Analytic Hierarchy Process is then used to evaluate the performance of the frames. The results indicate that the hybrid frame can offer an enhanced performance in comparison with rigid frames if the hybrid frame is well proportioned.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Field evidence of recent earthquakes shows serious bridge damages due to the direct compression or tension in the columns and some flexural and shear failures caused by the variation in axial force ...of the columns. These damages could not be produced solely by the horizontal seismic excitations; the vertical component of the earthquake is involved. This paper presents a numerical study highlighting the presence of vertical seismic excitation. Nonlinear time history analyses are conducted on detailed three-dimensional models of multi-span simply supported and multi-span continuous bridges using a suite of representative ground motions. The results showed the significant influence of vertical excitation on the bridge responses. Therefore, it is imperative to include more efficient criteria to upgrade the design codes and extend practical techniques that consider and cope with the structural effects of vertical ground motion along with the horizontal excitations.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Vertical component of seismic excitations tremendously affects the performance of bridges during the earthquakes. Several conducted studies identified the lack of engineering attention to the ...vertical seismic excitation as the main reason of various considerable bridge damages during the past earthquakes. Thus, in this article, an innovative system with superelastic properties is proposed for retrofitting and also new design of the bridges which can simultaneously mitigate the effects of vertical and horizontal seismic excitations. In order to investigate the efficiency of the new system, an evaluation is performed through many nonlinear time history analyses on a three-dimensional model of a detailed multi-span simply supported bridge using a suite of representative ground motions of the bridge region. The analyses are conducted separately on the pertinent issues that affect the performance of the new proposed system. As a part of the study, to identify the sensitivity of the new system and evaluate the overall seismic performance, several assessment parameters are utilized. The results show that the proposed system is efficient for reducing bridge responses as well as improving nonlinear performance of the columns during vertical and horizontal seismic excitations.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
Superelastic shape memory alloys (SMAs) have the potential to create a spontaneous recentering mechanism on the connections of a structural system under seismic actions, which results in mitigation ...of the damage in the main structural members. In this article, innovative types of steel beam-to-column moment connections incorporating SMA bolts and plates are introduced and studied through a numerical approach. First, SMA bolted end-plate connection model is produced and analyzed by means of the finite element method to validate the numerical analysis against the prior experimental results. Then, the performance of eleven different end-plate moment connection models subjected to cyclic loading is investigated. By selecting the lower values for the moment capacity based on bolts strength in comparison to the flexural resistance of the beam, the plastic hinge is transferred from the beam section to the beam-column interface. Hence, employing superelastic materials at the connection interface could be potentially effective in providing the desired self-centering effect in the connection. To this end, the impact of utilizing superelastic SMA bolts and end-plates instead of using the conventional structural steel on the overall cyclic response of the connections is evaluated in this study. Results show that extended end-plate connections equipped with SMA bolts and end-plates, if properly proportioned and detailed, not only exhibit a clear reduction in the residual drifts after a seismic event, but also can meet the ductility requirements with good energy dissipation and sufficient stiffness.
This paper presents a numerical study on two innovative classes of beam-to-column connections equipped with superelastic shape memory alloy (SMA) tendons as recentering elements and shear tabs or web ...hourglass steel pins (WHPs) as supplementary energy dissipating and shear resisting components. First, the finite element model of the shear tab connection with SMA tendons is produced and analyzed to validate the numerical analysis against the prior experimental results. Then, special cast high strength brackets are proposed to incorporate SMA tendons in the connections. Afterwards, a parametric study is performed considering the effects of shear tabs' presence, SMA tendons' initial prestress, shear tab bolts' initial prestress, coefficient of friction between shear tab and beam web, length/arrangement of SMA tendons and brackets, and shear resisting mechanism of the connection. Finally, additional class of SMA-based connections equipped with hourglass steel pins passing through the beam web is introduced, studied under cyclic loads, and examined when subjected to high levels of shear force demand. Results show that incorporating shear tabs and WHPs in the SMA-based connections, if properly designed and installed, not only improves their energy dissipation capability, but also can enhance their moment capacity, initial stiffness, and shear resistance, with no negative effect on the recentering ability.
•Two innovative types of SMA-based connections with web energy dissipating devices are introduced.•Finite element models are validated against prior experimental results.•Special cast brackets are proposed to incorporate SMA tendons in the connections.•Parametric studies are performed to investigate the parameters affecting the behavior of the connections.•The proposed connections are examined under high shear force levels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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