Experimental and analytical study on the behavior of steel plate shear walls with box-shaped columns under cyclic loading

Steel plate shear walls are lateral load resisting systems consisting of vertical steel plate infills connected to the surrounding beams and columns. One of the parameters affecting the behavior of steel plate shear wall system under lateral load is characteristic of surrounding members. Since there are lots of experimental and analytical studies on steel plate shear walls with I-shaped surrounding members, this research is an experimental study carried out on a one-third scale steel plate shear wall system with box-shaped columns along with further analytical studies. The objectives were to calculate the stiffness, strength and energy dissipation capacity of the specimen and compare them with a very similar system constructed with I-shaped columns. Cyclic loading protocol of ATC-24 was used for test. Obtained experimental results showed a good conformity between box and I-shaped specimens. It is shown that the system can provide good initial stiffness and high ultimate capacity and remain intact under seismic effects. Some analytical studies on failure modes of system with box-shaped columns were also conducted using finite-element software confirming that the columns bottom connections and their flange buckling at that point are one of the most common modes of failure and a triangular reinforcing plate at that point can improve columns connection behavior effectively

Lateral capacity and seismic characteristic of hybrid cold formed and hot rolled steel systems

This thesis addresses the application of hybrid cold-formed steel (CFS) - Hot-Rolled Steel (HRS) structures, as a new lateral force resisting system for light weight steel framed buildings in seismic regions. The study considers hysteretic behaviour, as well as maximum lateral load resisting capacity through comprehensive testing and advanced numerical analyses. The study identifies the advantages and disadvantages of the proposed hybrid system and provides in depth knowledge about performance characteristics of this innovative structural system, in order to facilitate the use of this system in earthquake-prone regions. The project is divided into three main parts: experimental, numerical and analytical studies. A comprehensive literature review is performed as a part of this study, in order to discover the existing gaps in the current knowledge regarding the structural performance of CFS structures and the methods for lateral performance enhancement. The literature review suggests that although CFS walls are not new, and have been used as non-structural components for many years, their application as main load-bearing structural frames is relatively new. That is, appropriate guidelines that address the seismic design of CFS structures have not yet been fully developed in the literature. In addition, the lateral design of these systems is not adequately detailed in the available standards of practice. There have been several attempts to improve the seismic performance of such structural system by different bracing or sheathing configurations. However, there is minimal background information available on hybrid systems such as hot rolled-cold formed structures. In this study, a series of CFS-HRS hybrid shear walls are constructed in order to investigate the lateral behaviour of the walls with different configurations to obtain the optimum combination of HRS and CFS. Different configurations are considered to provide the most efficient load transfer pattern from cold formed steel part of the wall to the Hot Rolled section, which is responsible for withstanding the lateral loads. The CFS part is aimed to transfer lateral loads to HRS part without any internal local failure. The ideal failure condition is the HRS yielding. Therefore, the optimum rigidity of the HRS part is of great importance to prevent any local failure happening prior to reaching the maximum lateral capacity of the HRS. For each experimental specimen, the hysteretic envelope curve is plotted, and different characteristics are evaluated. Since the failure mode of such systems is very complicated, the test results will provide the possible failure modes to be utilised for any further investigation or any optimisation analysis in numerical and analytical studies. In addition, Non-linear finite element (FE) analysis is employed using the ABAQUS software [1], in order to investigate the seismic performance of the proposed hybrid shear walls in multi-storey light steel frames. The nonlinear analysis accounts for different structural characteristics, including material non-linearity, geometric imperfection and residual stresses. The numerical models are verified based on experimental test results. The principal objective of this part of the study is aseismic optimisation of the proposed hybrid system and finding the corresponding dimensions and configurations to improve the strength and stiffness to achieve the objective. Using the hybrid wall panel system, a 4-storey building in an earthquake prone region is designed as per the relevant codes of practice. For the designed 4-storey building, the CFS part of the panel only bears the gravity loads, while a hot rolled steel collector transfers the lateral load to the HRS part acting as the main lateral load resisting system. Finally, the building is designed using different lateral load resisting systems and the results are compared with those from the proposed hybrid system in terms of cost. Furthermore, based on the real failure mode shapes obtained from test specimens, a Finite Strip Method program is developed to evaluate the elastic buckling mode shapes of a single stud with an arbitrary section detail. The code is helpful for design of CFS studs as explained in Chapters 3 and 5

Seismic retrofitting of substandard frame buildings using steel shear walls

The use of steel shear panels represents an effective strategy to enhance the seismic performance of substandard framed buildings not designed to resist earthquakes. The seismic response of framed structures equipped with steel walls can be predicted using finite element models with accurate shell elements for representing the steel panels. However, such a detailed numerical description requires significant computational resources, especially for nonlinear dynamic analysis of large retrofitted buildings with steel infill plates. Besides, the design of steel shear walls for seismic retrofitting has been addressed mainly by trial-and-error methods in previous research and practical applications. Therefore, there is a clear need for more simplified and efficient numerical models for accurate simulations of steel shear walls under earthquake loading and enhanced seismic retrofitting design procedures with automatic selection of the retrofitting components. In this research, an 8-noded macroelement formulation is first proposed incorporating six nonlinear springs with asymmetric constitutive relationships. To improve the macroelement performance, material parameters are calibrated via genetic algorithms (GAs) based on the numerical results from validated shell element models. Subsequently, simple functions for macroelement material parameters in terms of steel plate geometrical properties are determined using multiple linear regressions. Applications to numerical examples have confirmed the accuracy and computational efficiency of the proposed macroelement with calibrated material properties. An improved optimal seismic retrofitting design procedure utilising steel shear wall macroelements is developed based on the capacity spectrum method. The proposed approach regards the selection and design of infill plates as a multi-objective optimisation problem with constraints solved by GA procedures. Nonlinear regression for equivalent viscous damping of steel shear walls is also carried out to determine the hysteretic damping ratio as a function of plate dimensions and drift demand. Afterwards, the proposed optimal design strategy is applied to the seismic retrofitting of a deficient 4-storey RC frame building. Seismic assessment is finally conducted for the retrofitted structure, where a significant enhancement of the seismic performance is observed.Open Acces

Hybrid cold-formed steel structural systems for buildings

Cold-formed steel (CFS) shear walls or strap-braced walls are the primary lateral load resisting components in light-weight steel framed (LSF) structures. Despite the increasing demand on the application of CFS systems in mid-rise construction, the relatively low lateral load resistance capacity of these systems has remained one of the major obstacles for further growth, as this low resistance becomes problematic in their use in cyclonic wind regions or highly seismic zones. In this thesis, in order to address this issue, a new Hybrid CFS wall composed of CFS open sections and square hollow sections (SHS) is developed and investigated. The proposed hybrid system is suitable for light-weight steel structures for mid- to high-rise construction, due to its satisfactory lateral load resistance. The thesis presented provides the results of the study which contains experimental and numerical investigation as outlined in the following. In the first stage of this study, a comprehensive literature review was conducted to reveal the existing gaps in the previous studies on CFS structures under lateral loads. In the second stage, a series of full-scale experimental tests were performed on seventeen hybrid CFS wall panels in order to investigate their lateral performance, shear resistance, failure modes and energy absorption. In the third stage of this thesis, a comprehensive study was performed on the theories and applications of the numerical models for analysis of the lateral behaviour of CFS wall systems during the past several decades, and all existing numerical methods for simulating the behaviour of CFS shear walls were accordingly classified. In stage four of this study, proposed hybrid wall panel was further developed, and twenty new wall configurations were evaluated using non-linear finite element analysis, aiming to further investigate the seismic performance of CFS hybrid walls. Finally, in the last stage, a sustainability analysis was performed which could be of interest to all stakeholders including owners, builders and investors, when assessing the potential use of hybrid CFS systems, in particular for mid-rise buildings

Effects of Aspect Ratio and Plate Thickness on the Behavior of Unstiffened Steel-Plate Shear Walls with Pinned and Rigid Connections

Unstiffened steel plate shear walls (SPSWs) have been in use mostly in recent years. In this numerical study, the buckling behavior of a single-storey single-bay unstiffened SPSW with two pinned and rigid beam-column connections under lateral loading is investigated. The SPSW had different wall aspect ratios (L/h=1, 1.5, 2, 2.5, and 3) and infill plate thicknesses (tw= 3, 5, and 7 mm). Their effect on the buckling behavior of SPSW was examined using buckling analysis in ABAQUS software. Results indicated that with the increase of infill plate thickness, the lateral resistance of unstiffened SPSW system increases, but by increasing wall aspect ratio, its resistance decreases. In both connection designs, the model with L/h=1 (square-shaped model) showed better ductility and higher stiffness and strength in all three thicknesses. Maximum shear stress responses of SPSW models showed that in pinned design with L/h=1, the most change in shear stress values was 8% when infill plate thickness reached from 5 to 7 mm; while for rigid connection, it was reported as 7% when it increased from 3 to 5 mm. This indicates that in rigid connection, increasing the infill plate thickness has less effect on the increase of lateral resistance. By examining the performance of rigid and pinned beam-to-column connections with different wall aspect ratio and infill plate thickness, it was found out that maximum shear stress in rigid connection increased by 11% compared to pin connection. It was concluded that an optimum unstiffened SPSW model had a wall aspect ratio of 1 and infill plate thickness of 7 mm

Experimental and Numerical Research on Steel Plate Shear Wall with Infill Plate Connected to Beam Only

Steel plate shear walls consist of thin infill steel plates attached to beams, called (horizontal boundary elements, HBEs), and columns (vertical boundary elements, VBEs) in structural steel frames. The thin unstiffened web plates are expected to buckle in shear at low load levels and develop tension field action, providing ductility and energy dissipation through tension yielding of the web plate. HBEs are designed for stiffness and strength requirements and are expected to anchor the tension field formation in the web plates. VBEs are designed for yielding of web plates and plastic hinge formation at the ends of the HBEs. This design approach may result in very large demand on boundary frame members, especially VBEs in most cases. Several methods such as using LYP, perforating the infill plate and omitting connection of infill plate to columns have been proposed to reduce the moment and axial force demands on the VBEs. Study the behavior of steel plate shear walls omitting the connection of infill plate and columns is the main purpose of this research. A classic analysis base on PFI method along with quasi static cyclic experimental study has been performed in order to investigate the behavior of such a system. The results of the experimental study are used to verify numerical models. Behaviors of proposed system (overall capacity and initial stiffness) were compared with those of the conventional SPSWs. Results show that both parameters are reduced in comparison to the conventional SPSWs

Experimental Study of the Resistance of Expanded Metal Panels Submitted to Cyclic Shear Tests

Experimental and theoretical study of expanded metal panels (EMP) has shown that they are useful for seismically retrofitting reinforced concrete moment resisting frames (RC-MRF). Although this product has merit of strength and ductility, it is at present only used for non-structural applications. There is no guidance existing to help the engineers determine the mechanical properties or to indicate in which field of the structures this product can be used. With the aims at providing quantitative data for these purposes and at introducing a simplified model of EMP working in shear, description and comparison of the results of 22 monotonic and cyclic experiments of 4 profiles of EMP in small and large scale is presented. Numerical approach with FINELG, a nonlinear finite element code developed at University of Liege, is used to calibrate and simulate the tests. A good correlation between tests and numerical simulations is observed