Investigation of the behavior of stiffened steel plate shear walls with Finite element method

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1 Technical Journal of Engineering and Applied Sciences Available online at TJEAS Journal /67-73 ISSN TJEAS Investigation of the behavior of stiffened steel plate shear walls with Finite element method Masoud Ghaderi 1, Hossein Ghaffarzadeh 2, Nima Moslemi 3 1. Department of Civil Engineering, Germi Branch, Islamic Azad University, Germi, Iran Ghaderi.masoud64@gmail.com 2. Assistant Professor, Faculty of Civil Engineering, University of Tabriz 3. Department of Civil Engineering, Germi Branch, Islamic Azad University, Germi, Iran ABSTRACT: Steel plate shear walls have been used in reinforced and unreinforced which is new resistant system against lateral loads of wind and earthquake. In recent decade, this system has been considered by researcher. According to the optimal performance of this type of lateral load system such as high stiffness, great ductility and energy dissipation capacity, it could be used in structures retrofitting. In this paper an unreinforced steel shear wall has been modeled by ABAQUS software and its result has been compared with experimental models. Stiffness and resistance of samples have been studied after verification of numerical modeling, behavior of reinforced steel shear walls and effect of stiffeners arrangement on parameters strength, stiffness and ductility has been investigated. Keywords: Steel Plate Shear Walls, Stiffeners, cycle loading, Non-Linear Analysis, ultimate strength, INTRODUCTION Steel plate shears walls, have been used in various buildings as a resistance system against lateral load specially force of the earthquake since It seems first building that used in steel shear walls was a Twenty-storey Nippon Steel Building in Tokyo. In third high building in Tokyo name Shinjuku Nomura, height of 211meters and 51 floors from ground level and height of 27.5 meters and 5 floors in underground, steel plate shear walls have been used in central core (which is around elevator, stairs, facility risers) in order to avoid use of concreted shear wall. Stiffer has been used in mentioned steel plate shear walls in order to prevent buckling of steel plate. Stiffer on one side has been welded vertically and one the other side welded to steel plate horizontally. For building the thousand-room hotel placed in Dallas, the designer used steel shear walls in order to resistant lateral forces especially wind (sabouri,g.2001). As it been seen it figure1, steel plate shear walls forms from steel plate are surrendered by columns and beams. Steel shear walls act like cantilever girder which columns are as flange, floors beams are as stiffer and steel palate are as web of it. In this system unlike girders that because of weakness of its flanges have no useful role in force resistance, in steel shear walls columns have great role in bearing load because of their strength. The likeness of shear walls to reinforced girder in web have caused that the researches which have done in girders field are the basis of studies about steel plate shear walls. Figure1. Similar shear walls with steel girder The system of steel plate shear walls had a good performance in experimental studies and Northridge, America and Kobe, Japan strong earthquakes.therefore its application in making new buildings and also strengthen the

2 existing buildings are being increased rapidly. The application of this system, have decreased the use of steels in steel frame toward steel moment frame about 50% (sabouri, G, 2001). Because of the great performance of un-stiffened shear walls, most of researches have been done on such type of walls. On the other hand, because welding stiffer to steel plate is time-consuming and expensive, in the short span and if the opening is no used, the steel plate would be used without stiffer. But it has no good performance in large spans un-stiffened steel plate shear walls and creates overall buckling in throughout walls. To prevent buckling of steel plate, improvement of Hysteresis curve and increasing energy absorption are two common methods. One is using of high thickness of steel plate and the other is using of stiffer. The first method is totally uneconomical and costly because improving hysteresis curves of mentioned walls requires that the thickness of steel plate would be increased. The second method which would be achieved by reinforce the steel plate via stiffer, is totally effectively and economically. With stiffening the steel plate, the hysteresis curves could be converted from S shape to spindle in steel plate shear walls. Thus, with increasing the area under the mentioned curves the amount of energy absorbed will be increase and improve the steel shear walls behaviors (sabouri, G, 2001). Steel plate shear walls have better performance than all properties concentric bracing systems (CBF) and Eccentric braces (EBF) in terms of operational, functionality and behavior. This system has better performance than X shape bracing system in terms of stiffness and considering the possibility of opening in every location is the best bracing system. The system behavior in plastic scope and its amount of absorbing energy has better performance than bracing systemand in this system because of the material and connections variety, moderate stress is better than other systems resistant to lateral loads. System behavior is better especially is plastic area too. Using of concrete shear walls in metal construction causes the strains, stresses and inappropriate deformations because of using of different materials at the interface between the wall and frame. Also, steel shear walls compared with concrete shear walls has lesser weight so less force is applied to the columns and foundations and construction bear lesser lateral forces (sabouri,g,2001) STUDIES ON THE STEEL PLATE SHEAR WELL In 1998, an experimental sample has been studied in 1:2 scale sizes by Driver and et al. In this samples the four-storey that has been shown in figure2, lateral loading has been done in level floors and constant axial load has been applied to the columns. Increasing lateral load till twentieth cycle, the experiment was stopped because of failure Connection in left column of the plate. Figure 2. Specimen tested by Driver et al Figure 3. Hysteretic loops of samples tested by Driver et al. 68

3 As it has been shown in figure3 this sample has been resistant to 8.5 times of yield displacement. So its coefficient ductility is 8.5 (Driver,R.G, 1998). 3. Verification of Steel plate shear wall modeling in ABAQUS software The term finite element first is introduced by Clough for solving elasticity problem in However, the first person that used this method in solving Torsion issues was Courant (1943). In this method overall the geometric model has been divided to Smaller components called element. Each element itself has nodes that are allocated input (loading and boundary conditions) and output (results). Finite element method is a numeral method that is base on the experimental results. So the issue that needs to be considered is reliability of this method in term of accuracy and perfectness of the results. For verification of steel shear walls modeling results in ABAQUS software, Driver and et al sample has been choose that has been studied in figure2. Sections used in the modeling, span and height model (figure2) and finite element sample model have been shown in figure4 too (Alinia.M.M, 2001). Figure4. The finite element model, the method of loading and boundary conditions Cyclic loading is applied to sample (fig.5). Hysteresis curve also has been shown in figure 6. As it has been shown in figure3 displacement that has been given from results is 8.5. In modeled sample of ABAQUS software, as hysteresis curve shows, ductility coefficient has been calculated as follow: 73 max 8.59 y 8.5 Figure 5. Cycling Load on samples according to ATC-24 Figure 6. Hysteretic loops of samples by numerical analysis It has been shown that ductility coefficients obtained from both methods are in good agreement with each others. Figure 7 shows the Von Mises Stress Contours. The ultimate shear walls resistance in experimental sample is 2500 KN and numeral sample is 2584 KN that has very well Conformity with experimental results. In both laboratory and numerical models, there was 69

4 Tech J Engin & App Sci., 4 (2): 67-73, 2014 some reduction in the resistance the system. The reason of the small difference between the results is incomplete effect of it. In modeled sample by ABAQUS software the initial curvature of the plate has been done by applying perpendicular to the load plate. This event influence the initial shape of steel plate in numeral model but yet it far from reality a little. The difference between the results of the two methods cannot be solely attributed to modeling errors because there are also the usual experimental errors. Figure 7.Von Misses Stresses Contours 4. Stiffer effect on steel plate shear walls study In this season some frame sample with stable span and height and various stiffer orders have been applied in ABAQUS under static and cyclic loading. It important to say that in this study plate order is shown with H (horizontal) and V (vertical). For example, H2V3 demonstrate that stiffened shear plate walls are horizontal with 2 stiffer and vertical with 3 stiffer which all of stiffer have been placed in one side of steel plate. The characteristics of studied steel plate in this season (width and height of span and thickness of plate) and characteristics of beam and column (fig8) and characteristics of used material for beams, column, stiffer, and steel plate have been shown in table 1. These used materials have been considered equal. 5m 3m t=7mm L80x80x8) Stiffer section ( Column section Beam section Figure8. Sections for the Specimen Table1. Materials for the Specimen Plate Beam, Column Stiffer 0 (kg / cm 2 ) E(kg / cm 2 ) x x106 Also the connection of beam and column is rigid and plate is connecting to frame rigid. Because of facing of incomplete issue, lateral curvature of plate is applied as first incomplete in numeral model. This task could be done by applying a little load vertically or could make a small initial deformation according to one of the buckling mode of the plate (usually the first buckling mode) obtained from the Eigen value buckling analysis of the plate. In this study first method has been used and a small load is perpendicular to the plate in desired location (Alinia.M.M, 2001) NON-LINEAR STATICS AND CYCLIC ANALYSIS OF SAMPLES In this season, un-stiffened sample has been Non-linear static analysis by ABAQUS then cyclic analysis has been done based on ATC-24 loading pattern. Von Mises stress contours is given in (Fig.9). As can be seen in this figure, yielding has been started from the section that has been found on the diagonal 70

5 tension specimens. In the corners of the panel and mounting plate to the beam and column there was a stress concentration. Minimum and maximum amount of tension has been demonstrated in fig.9 (ATC,1992) Figure 9. Von Misses Stresses Contours of un-stiffened samples The Hysteretic loops of samples obtained applying cyclic loading. Using hysteresis cycle could obtain ductility coefficient, Ultimate strength and stiffness sample. For analyzing the impact of stiffer on parameters, more over unreinforced sample, 13 samples of various stiffer orders have been studied that has been shown in table 2. Table 2. Ductility coefficient, stiffness and ultimate strength of Specimen Ultimate Percentage of stiffness Percentage of sample ductility strength increase kg increase strength ( ) (kg) strength mm H0V0 H1V0 H1V1 H1V2 H1V3 H2V0 H2V1 H2V2 H2V3 H3V0 H3V1 H3V2 H3V3 H4V % 0.85% 22.16% 29% 17.5% 21.59% 6.91% 9.2% 0.7% 1.29% 7.46% 8.4% 13.9% % 12.28% 15.06% 24.9% 4.6% 14.41% 16.76% 22.63% 9.23% 18.49% 13.78% 29.94% 33.97% INVESTIGATION OF SAMPLES RESISTANCE PARAMETER In this season both of non-linear static and cyclic analysis of sample has been used and ductility coefficient, stiffness and their resistance have been obtained from hysteresis curves then have been compared and summarized in a bar plot. Figure 10 shows ductility coefficient diameter, figure 11 shows the bar plot of sample strength variations and figure 12 demonstrates variation of sample stiffness. According to figure 10, the conclusion is that most of sample coefficient ductility is 6. Therefore it can be considered 6 force efficient plasticity of reinforced steel plate shear walls. Figure10. Ductility coefficient of samples According to the bar plot (figure 11), maximum strength related to sample H1V3 with 29% of increasing strength and minimum resistance related to sample H3V0 with 0.7% of increasing resistance to unreinforced sample. In this part we confirm the best performance of H1V3 in term of increasing strength. 71

6 Figure 11. Variation of the percentage increase in the samples strength According to the bar plot (figure 12) which shows the percentage of stiffness increase of all samples, the best performance of H1V3 in rate of stiffness has been approved, however increasing stiffness in H3V3 was more than H1V3. But considering other effective parameter on steel shear wall such as ductility coefficient, ultimate strength, energy absorption, economical, the advantage of H1V3 is obvious. Hysteretic loops of sample H1V3 has been shown in figure 13. Figure 12. Variation of the percentage increase in samples stiffness Figure13. Hysteretic loops of sample (H1V3) CONCLUSION In this study, the finite element ABAQUS software has been used for analyzing the stiffer effect on steel plate shear wall. For verification of modeling, an experimental sample that its results were available has been modeled and compared with experimental results. Non-linear static analysis has been done on sample for investigating the behavior of stiffened steel shear wall and yield point displacement system has been obtained, then according to ATC-24 loading model, a cycle analysis has been done and hysteresis curves has been obtained. The parameter of resistance such as ductility coefficient, ultimate strength and stiffness has been obtained from hysteresis curves. Graphs comparing changes of resistance parameter of steel plate shear wall parameter has been shown in figures Considering the high resistance of steel plate and using its post-buckling resistance, the thickness of plate even in high steel shear wall and large shear forces was little. In other word, the steel plate was thin. Unstiffened steel shear panel had very flexible behaviors and had been buckled in initial loading process. As a result, it didn t have high energy absorption capacity and compression has been seen in hysteresis curves. Because of soon buckling in un-stiffened samples especially in thin plate, the use of stiffer in steel panels is the best method for preventing of hysteresis curves compression and increase of the area under the curves (increase of energy absorption capacity). According to the analysis, changing the stiffer orders is not significant change in the coefficient ductility of stiffened steel plate shear walls and 6 could consider for all of stiffened steel plate shear walls. According to analysis results, the compression can be prevented in hysteresis curves of steel plate shear walls by stiffener and deforms these curves from S shape to spindle shape. According to studies results, stiffening of steel shear walls would cause increasing in strength and stiffness of sample toward un-stiffened sample. 72

7 The results of non-linear static and cyclic analysis demonstrated that the samples which had one horizontal and three vertical stiffer had the most increase of ultimate strength and stiffness. The dimensions of the studied source in this paper were 115cm (width) and 150cm (height). REFERENCES Sabouri,G Lateral Load Resisting Systems An Introduction To Steel Plate Shear Walls. Anghizeh Publication, Tehran, Iran. Driver, R.G., Kulak, G.L., Elwi, A.E., Kennedy, D.J.L Cyclic tests of four-story steel plate shear wall. J. Struct. Eng. 124 (2): Khlkhali,2010. Finet Element Analysis with ABAQUS. Puplication of the Dibagaran artistic and cultural institute. Dibagaran Tehran publishing co. Alinia, M.M., Dastfan, M Cyclic behavior, deformability and rigidity of stiffened steel shear panels. Journal Of Constructional Steel Research. 63: