Abstract
JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 2021, VOL. 20, NO. 1, 44–60 https://doi.org/10.1080/13467581.2020.1816547 BUILDING STRUCTURES AND MATERIALS A study on Static behavior of New Reinforced concrete column-steel beam Composite Joints a,b b b b Yuhong Ling , Jinghang Xu , Zhenhai Guo and Xingui Wen a b State Key Laboratory of Subtropical Building ScienceGuangzhou, South China University of Technology, Guangdong, China; School of Civil Engineering and TransportationGuangzhou, South China University of Technology, Guangdong, China ABSTRACT ARTICLE HISTORY Received 26 October 2019 Through Experiment, we study the aseismic behavior of inserted reinforced concrete column- Accepted 26 August 2020 steel beam (RCS) composite joints. In order to design an RCS with endplate combination joint, we analyze simulation test joints on a basis of the static load test combining with finite element KEYWORDS software ABAQUS. The numerical simulation results and the contract test results which include Reinforced concrete column; finite element simulation of load–displacement curve of bending moment–rotation curve and steel beam; RCS composite the components of yield sequence are basically the same as the experiment results. This joint; seismic behavior uniformity verifies the reliability to use numerical simulation upon such problems. To compare with the ordinary reinforced concrete structures, the new type of inserted RCS composite joints is safer, and it presents a better seismic performance under the static load of the beam end. After we use numerical simulation to study the influential factors of six kinds of RCS combina- tion of static performance including the axial compression ratio, steel insert length, the thickness of endplate, the ratio of the width of column section and beam section, the column concrete grade and four kinds of joint structure, we found that it does not only well perform on mechanical aspect but also is simple and convenient on the structure and construction of RCS composite nodes. 1. Introduction understandings and researches on the working perfor- mance of RCS composite structures. China’s composite In the early 1980s, American researchers proposed structure industry-standard Code for Design of a new structural system. It is a frame structure con- Composite Structures (JGJ 138–2016) (2016) (former sisting of referred to as the RCS composite struc- Technical Specification for Steel-Reinforced Concrete ture. Different materials are adopted in beams and Composite Structures (JGJ 138–2001) (2001)) has columns so that they can fully take advantage of decided the formation to connect steel-reinforced con- steel and concrete (Griffis 1992). If using different crete columns and steel beam regulations, but it does materials is not the case, then the rationality and not specifically explain the case of the column as economy will be reflected in material selection. a reinforced concrete column. Other than this problem, Many scholars inside and outside the country another issue is the impossibility to directly apply for- have done a lot of research on the RCS composite eign research results in China since the Chinese design frame. Li, Li, and Jiang (2012), Alizadeh, Attari, and system is different from that of foreign countries. Thus, Kazemi (2015), Nguyen, Nguyen, and Le et al. it is urgent to study the RCS composite structure. Since (2016), Mirghaderi, Bakhshayesh Eghbali, and the RCS composite joint is the pivotal force transmis- Ahmadi (2016), and so on have all carried out sion component of the combined structure, then it is tests on different types of RCS composite joints necessary to start researching RCS composite joint at and have proposed a variety of new joint forms first. Liu et al. (Yang et al. 2013), Lai (Chuangui 2016), with excellent seismic performance. Men et al. (Jinjie, Liquan, and Runrun et al. 2014; Jinjie, In recent years, some large-scale stadiums and exhi- Peng, and Zhifeng 2015), Xiong et al. (Liquan, Xin, and bition halls in China have begun to adopt the RCS Xianzhi et al. 2017) have carried out experiments and composite frames such as the Qinyang Middle School simulations of a variety of RCS composite nodes. In Gymnasium in Meijiang District of Meizhou City and addition, Ling et al. (Yuhong, Jianjia, and Hongwei the Meizhou World Merchants Center. In China, how- et al. 2016a) propose a new type of penetration joint ever, there are only some industrial buildings and light- of steel secondary beam and concrete main beam, duty houses have adopted RCS composite structures which is welded with anchor endplate at the end of (Guoliang et al. 1996). Here still remains insufficient steel secondary beam and fully penetrated into the CONTACT Yuhong Ling 3134587566@qq.com School of Civil Engineering and Transportation South China University of Technology, Guangzhou 510640, China Picture Number: TU398 Article Number: A © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the Architectural Institute of Japan, Architectural Institute of Korea and Architectural Society of China. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 45 Table 1. Concrete material properties (N/mm ). Compressive strength Specimen Strength grade of Measured Average number concrete value value SK1 C30 26.4 28.5 SK2 C30 28.4 SK3 C30 30.8 Table 2. Material properties of steel and reinforcement (N/mm ). Yield strength Ultimate strength Steel type Property f f y u 6 mm steel plate Q345 403 593 10 mm steel plate Q345 423 578 C 8 reinforcement HRB400 408 610 C 16 reinforcement HRB400 455 640 C 20 reinforcement HRB400 452 631 Figure 2. A well-made test joint. concrete main beam. The test results show that the (unit: mm). The distance from the joint to the loading upper flange of the secondary steel beam can yield in point is l = 1500 mm, the steel is made of Q345 steel, tension, which can give full play to the bending capa- and four transverse stiffeners are set according to the city of the secondary steel beam, and the joint has specifications (to meet the requirements of the speci- better deformation capacity. fication high-thickness ratio. At the same time Set the On this basis, this paper discusses the designa- stiffeners at the point of concentrated force). Besides, tion of a plug-in RCS composite joint with an end- the hole is opened at the corresponding position of plate. The steel beams of this joint are directly the steel beam to make the column stirrups pass inserted into the concrete column. The column stir- through the steel beam web. rups pass through the holes, the steel beam, then The section size of the column is 400 × 400 and through the hoops on the steel beam web. An the column length is 2 m. The joint is located in the endplate is placed at the end of the inserted steel middle of the column and the thickness of the beam, and the static behavior is studied through protective layer is 20 mm. C30 concrete and experiments. Besides, six factors that affect the sta- HRB400 reinforcement are used. The material prop- tic performance of the RCS composite joint are erties of specimens are shown in Tables 1 and 2. studied by finite element simulation. An RCS com- According to the principle of the strong column and posite joint with good mechanical performance, weak beam, strong joint and weak component, the simple structure and convenient construction is moment design value of the column at the joint selected. meets the requirements of Code for Seismic Design of Buildings (GB 50010–2010) (GB 50011-2010 2016), taking 2 times the yield bending capacity of the 2. Experiment design steel beam. The axial force at the top of the column 2.1. Joint design is an axial force with a 0.3 axial compression ratio, and the reinforcement of the column is calculated The steel beam is welding I-beam, the section accordingly. h1× b1× t1× b2× t2× tw = 400 × 120 × 10 × 120 × 10 × 6 Figure 1. Test RCS composite joint sample diagram. 46 Y. LING ET AL. Figure 3. Loading device. In addition, to prevent the steel beam from being pulled out and to increase the stiffness of the joint, an endplate is welded to the end web of the steel beam joint. The height of the endplate is the same as the height of the steel beam; the width is the same as the width of the flange of the steel beam, and the thick- ness of the endplate is the same as the thickness of the stiffener. To prevent the concrete at the lower flange of the steel beam from being locally crushed during load- ing, we place 2C20 at the lower flange of the steel beam near the edge of the column. The length of the steel bar is 200 mm, which is the No. 4 steel bar in Figure 1(a) shown in the joint schematic. Figure 2 shows a well-made test joint. 2.2. Test loading and measurement The test was conducted at the Structural Laboratory of Figure 4. Schematic diagram of displacement meter. South China University of Technology. The schematic Figure 5. First crack on concrete column. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 47 the column top and bottom adopt the flat-plate hinge support to simulate the force of the frame beam and column. To prevent the buckling of the steel beam during the loading process, the lateral support is used to limit the out-of-plane displacement of steel beams. During the test, a constant vertical axial force was applied to the top of the column using a jack, and a vertical load was applied at the free end of the steel beam using an MTS servo loading system. In this paper, the steel beam insertion surface is called the right side of the column. During the test, the axial force of 0.3 axial compres- sion ratio should be used, and the column top shaft pressure is loaded to a predetermined value in 7 times where each stage is 100 kN, and then the top load should keep stable, finally, the steel beam load is applied. For the convenience of test control, referring Figure 6. First crack on left side of concrete column. to the US specification, the loading mode of the steel beam adopts displacement control, 1 mm per stage, at least 3 minutes after each stage of loading. And 4 mm diagram and field diagram of the test loading device for each stage after yielding until damage (Wei 2010). are shown in Figure 3. According to the relevant litera- The test contents include column top axial force and ture (Xian, Yan, and Wei et al. 2007), the method beam end load, steel bar and steel beam strain, beam adopts the scheme that the beam end is loaded, and Figure 7. The final cracks of the concrete column. 48 Y. LING ET AL. Figure 8. Steel beam failure phenomenon diagram. 3. Test results and analysis 3.1. Test phenomenon 140 At the beginning of loading, the load–displacement W1 curve changes in a straight line. When the beam end W6 displacement is loaded to 18 mm, the first crack appears at the front and back of the column at the same time. The front crack starts from the lower flange of the steel beam insertion surface (the tensile flange). It firstly extends to the cylinder angle at about 45°, then horizontally extending to the center of the front as shown in Figure 5. When the loading is continued to the beam end displacement of 20 mm, cracks also 0 appear on the left side of the column, and the crack 0 20 40 60 80 position is on the upper side extending vertically displacement(mm) downward as shown in Figure 6. When the beam end displacement is loaded to 22 mm, a new oblique crack Figure 9. Loading versus displacement. appears on the left side. The angle between the long side of the beam is about 60°, and the remaining cracks have a certain degree of extension. The maximum 1.0 crack width is 0.14 mm at this time. When the beam Rigid node end displacement is loaded to 26 mm, there is a crack k=3.57 0.8 Semi-rigid node from the upper right to the lower left in the upper center of the front center about 45° from the long side of the column. The left and back cracks extend, and on 0.6 the right side of the insert extends two new cracks k=25 Dimensionless corner1 from the tension flange appear, one up and one Dimensionless corner2 0.4 down, currently the largest crack is still on the front Dimensionless corner3 and the crack width is 0.2 mm. When the beam end k=0.5 0.2 displacement is loaded to 30 mm, a new one from the Flexible node upper right to the lower left appears in the lower part of the front center, and the crack is about 30° from the 0.0 0.0 0.2 0.4 0.6 0.8 1.0 long side of the column. The other cracks have a certain extension, and the maximum crack width is Dimensionless corner θ 0.22 mm. When loaded to 42 mm, a small piece of Figure 10. Dimensionless bending moment–rotation curve. peeling happens on the right side of the insertion face near the tensile flange. When the displacement of the beam end is loaded to 46 mm, the original crack end loading point displacement and corner of beam extends. The maximum crack width is 0.36 mm on the and column, and concrete column crack. Figure 4 is front side. Currently, the load–displacement curve is a schematic view showing the arrangement of the dis- still rising. When the displacement is 80 mm, the load– placement meter. Load(K N ) D im e n s io n a l b e n d in g m o m e n t M JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 49 Figure 11. The arrangement of endplate strain rosette. Figure 13. Load endplate principal stress curve. Figure 12. Load endplate principal strain curve. test safety issue, the test has been stopped. The steel beam and the concrete column are well anchored displacement curve increases with a smaller amount during the whole test. There is no steel beam is pulled but it still rises. The ultimate load has not been reached out. The final cracks on the concrete surface are shown but the steel beam is flexed by the compression flange, in Figure 7, and it can be seen from Figure 7(e) that and the deformation is large. The web near the com- there is no obvious crack at the left side of the concrete pression flange also has a large bulge. To ensure the column, indicating that the endplate has no prying 50 Y. LING ET AL. Figure 16. ABAQUS global model. Figure 14. Stress–strain curve of concrete under uniaxial ten- sion and compression. Figure 17. Meshing. Figure 15. Stress–strain curve of steel. the load increases, the displacement growth rate of the action. The deformation of the steel beam is shown in curve W1 is significantly higher than the curve W6 Figure 8. because the steel beam produces a bending deforma- tion after entering the yielding stage. When the load is 148.8kN, the steel beam is yielded by the compression 3.2. Steel beam displacement analysis flange, but the load–displacement curve of the beam Based on the experimental data, a load–displacement end has no obvious inflection point. Besides, it is still curve is plotted as shown in Figure 9. At the beginning rising steadily which indicates that the failure type is of the loading, the two curves are straight lines. The a ductile failure. In engineering, this kind of joint is ratio of the slopes is about 5 which is approximately relatively safe. equal to the ratio of the distances of the two displace- ments to the joints. This indicates that the bending deformation of the steel beam itself is small at the 3.3. Joint stiffness analysis beginning of loading. The deformation of the steel beam is mainly caused by the relative rotation The stiffness type of the joint is generally judged by the between the steel beam and the concrete column. As moment–rotation curve. In this test, two methods are JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 51 classification standard in the European Eurocode3 specifi - cation (Eurocode 3 1992). According to formula (1) and formula (2), the dimensionless rotation angle θ and the dimensionless bending moment M are calculated, respec- tively. According to the relevant provisions of the European Eurocode3 specification , for the lateral displace- ment frame, when the slope of the dimensionless moment–rotation curve of the joint is less than 0.5, the joint is hinged; when θ is less than or equal to 0.0267 and the slope of the curve is greater than 25, or when θ is greater than or equal to 0.0267, and less than or equal to 0.12 and the slope of the curve is greater than 3.57, the joint is connected; if the slope of the curve is in the rest range, the joint is considered as a semi-rigid joint. θ ¼ θ=θ Figure 18. Beam end load versus displacement curve. M ¼ M=M In formula: θ is relative angle of the beam and column; θ is ultimate plastic angle of steel beam, θ = M L /EI ; p p p b b M is the actual bending moment of the joint; M is the full-section plastic bending capacity of steel beams. According to the above formula, we draw the dimensionless bending moment–rotation curve of the test joint, the boundary line between the hinge and the semi-rigid joint, the semi-rigid joint and the just joint in the figure. As shown in Figure 10, it can be judged that the joint is semi-rigid. 3.4. Strain distribution of endplate The endplate and the steel beam web are in a complex Figure 19. Dimensional bending moment versus turn curve. stress state. To reflect the stress situation accurately, three-dimensional strain rosette is arranged on the end- used to measure the relative rotation angle of beams plate and the steel beam web in the test, as shown in and columns. The first method uses the displacement Figure 11. Each strain flower is composed of three strain gauges W4 and W5 to determine the rotation angle of � � gauges, and the strain ε , ε and ε in three direc- 0 45 90 the column, and the displacement gauge W6 measures tions can be measured. According to the knowledge of the steel beam. To subtract the rotation angle of the material mechanics, the main strain and main stress steel beam from the rotation angle of the column, we curves of the three strain flowers on the endplate can obtain the relative rotation angle 1 of the beam and be obtained, as shown in Figures 12 and 13. It can be column. The second method uses the displacement seen from the main strain curve that the main strain 3 of gauges W7 and W8. According to the cosine theorem, strain rosette 48–50 located at the upper part of the the relative rotation angle of the beam and column can endplate is larger, and there is an obvious decrease after be obtained. The displacement meter W7 measures reaching the yield load of the steel beam, which should the relative rotation angle 2 of the compression flange be caused by the reduction of the binding on the core and the column. The displacement gauge W8 is mea- area of the joint after the steel beam yielding. In addi- sured as the relative rotation angle 3 of the tensile tion, the value of the main stresses of strain rosette flange and the column. 51–53 and strain rosette 54–56 are very small, while The joint type of the experimental RCS combined joint the maximum value of the main stress of strain flower is judged by the unsupported frame beam-column joint 48–50 in the upper part of the endplate is compressive 52 Y. LING ET AL. Figure 20. Mise stress cloud of finite element analysis process. stress, and the compressive stress exceeds the yield load μ ¼ θ =θ u y of the endplate, which proves that the upper part of the endplate is involved in restraining the deformation of According to the test results of this test, the rela- the concrete, and the endplate plays the role of pre- tive rotation angle of the joint at yield θ is venting the steel beam from being pulled out. 0.02 rad. Since the displacement of the test to the beam end is 80 mm and the relative rotation angle is 0.08 rad, the joint still does not reach the failure state, so the RCS composite joint of this test can be 3.5. Joint ductility analysis calculated. The ductility coefficient is greater than 4, which is safer than the general reinforced con- According to the literature, the corner ductility coeffi - crete structure. cient is used to judge joint ductility (Augusti 1996), The above test shows that the joint is a semi- which is the ratio of the relative rotation angle at the rigid joint. To enhance the rigidity of the joint and time of joint failure θ to the relative rotation angle at make it convenient to design the joint according the time of yield θ . Equation (3) is the calculation to the just-connected joint in the high-intensity formula. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 53 Insert 200 Insert 250 Insert 300 Insert 350 0 20 40 60 80 100 displacement(mm) 1.0 Rigid node 0.8 k=3.57 Semi-rigid node 0.6 k=25 Insert 200 0.4 Insert 250 Insert 300 Insert 350 0.2 k=0.5 Flexible node 0.0 0.0 0.2 0.4 0.6 0.8 1.0 Dimensionless corner θ Figure 21. Influence of steel beam insertion length on static performance of joints. 4. Numerical simulation research 4.1. Numerical simulation reliability verification 4.1.1. Building model Figure 20. (Continued). The ABAQUS finite element software is used to simulate the RCS combined joints. According to area, we consider adding structural measures to the previous research of the RCS beam-beam improve the joint stiffness. In this paper, the finite joints (Yuhong et al. 2016b), the relevant para- element numerical simulation will be used for meters of the ABAQUS model were determined. further study. The concrete column and steel beams are made Table 3. Influencing factors and parameters chosen. Influencing factor Parameters Steel Beam Insertion Length 200, 250, 300, 350 (mm) Endplate Thickness 0, 6, 9, 12, 15 (mm) Joint- Extended-End- Z-axial Y-axial Width:120, Z-axial Height:400, 500, 600, 700, 800, 1200 (mm) Structural Plate Y-axial Z-axial Height:400, Y-axial Width:120, 180, 240, 300 (mm) Vertical-Steel Column Set on the upper and lower flanges of the steel beam insertion end, the height of the steel column: 200, 400, 600, 800 (mm), refer to 22a) U-Shaped-anchor Set on the web of the steel beam insertion end, refer to 23a) stud Set on the upper and lower flanges of the steel beam insertion end, refer to 24a) L o a d (K N ) D im ensional bending m om ent M 54 Y. LING ET AL. Figure 22. Simulation analysis of steel beam insertion length. of C3D8R solid elements, and the reinforcement is columns. Depending on the actual situation, made of T3D2 truss units. The constitutive relation there will be some relative displacement between of concrete material is plastic damage model, steel beam or endplate and concrete, therefore which uses isotropic elastic damage, isotropic ten- the TIE command cannot be used. Actually, the sile and compressive plastic theory to simulate the interaction is determined by tangential friction. inelastic behavior of concrete. It is assumed that According to the correlation in the literature (Zhifeng 2014), the friction function uses the concrete shows softening after tensile crack- a penalty function with a friction coefficient of ing, and hardening before softening after com- 0.2, and the normal direction is defined as a hard pressive failure. In this paper, the reinforcing bars contact and allows separation after contact. The are all three grades of steel, so the constitutive grid size of the concrete column is 40 mm, and relation of reinforcing bars is a double diagonal the grid size of the steel beam is 30 mm. The grid model. Steel beams adopt the same constitutive is further refined in the core area of the joint. relation as steel bars. The model is suitable for Figure 16 shows the boundary conditions and high strength reinforcement without obvious flow loading mode of the model, and Figure 17 shows amplitude. Figure 14 is the stress–strain curve of the mesh division of the model. concrete under uniaxial tension and compression, and Figure 15 is the stress–strain curve of steel. For interface interactions, the contact between the 4.1.2. Comparative analysis of numerical steel plates is based on the TIE command. The simulation results and test results steel beams or endplate inserted into the concrete Figures 18 and 19 are the comparison of the beam end column interacts with the concrete of the load–displacement curve and the dimensionless JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 55 load–displacement curves obtained from the test results. The non-dimensional bending moment–rota- tion curve obtained by numerical simulation is slightly larger than the experimental value, which may be caused by the error of the measurement method. The 100 pointer of the displacement gauge is perpendicular to the compression flange of the steel beam during the Endless plate End plate thickness 6 test. During the loading process, as the steel beam is End plate thickness 9 bent, there will be a certain relative sliding between the End plate thickness 12 displacement meter and the steel beam and the finite End plate thickness 15 element simulation leads to fixed vertical displacement of the joint, resulting in some difference between the 0 20 40 60 80 100 two measurements. However, it can be seen from the displacement(mm) figure that the overall difference between the two is small, and the finite element simulation results can reflect the actual bending moment–rotation change of 1.0 the joint within the error tolerance. Rigid node In summary, it can be proved that the finite element 0.8 k=3.57 Semi-rigid node simulation method used in this paper can accurately simulate the stress of the RCS composite joint. 0.6 Therefore, the finite element simulation method of k=25 this paper can be used to further study the static Endless plate 0.4 performance of RCS composite joints. End plate thickness 6 End plate thickness 9 0.2 End plate thickness 12 k=0.5 4.1.3. Stress analysis End plate thickness 15 Flexible node In the test, only the strain gauge is arranged on part of 0.0 the position, and the distribution of strain and stress at 0.0 0.2 0.4 0.6 0.8 1.0 part of the position can be obtained, while the finite Dimensionless corner θ element simulation can obtain the distribution of Figure 23. Influence of endplate thickness on static perfor- strain and stress at any position of the model, and mance of joints. obtain its development rule in the whole process of loading. The following treatment of ABAQUS obtained bending moment–rotation curve obtained by numer- the Mise stress nephogram of the model, i.e. the fourth ical simulation and experiment. intensity equivalent stress. It was assumed that shape It can be seen from the figure that the numerical change energy density was the factor causing material simulation results are consistent with the beam end yield and the material state could be judged. Figure 24. Simulation analysis of endplate thickness. Dimensional bending moment M Load(KN) 56 Y. LING ET AL. Figure 25. Effect of extended endplate on static performance of joints. Figure 20 is the Mise stress cloud map of the 4.2. Factors affecting static performance of joints finite element analysis process. As can be seen 4.2.1. Influencing factors research from the figure, the yield of the joint occurs first For the study of factors affecting the performance of at the compression flange of the steel beam near joints, consider the following three types: (1) steel beam the joint in the extension section. With the increase insertion length, referencing steel reinforcement and of load, all the tensile and compression flanges considering the different depths of the steel beam yield, and then the web of the steel beam in the inserted into the column, it will affect the rotation of joint area begins to yield until the complete yield. the joint; (2) the thickness of the endplate, the endplate When the beam end displacement is loaded to the plays a role in preventing the steel beam from being maximum test displacement of 80 mm, yield occurs pulled out, the thickness of the endplate will affect the within a small range of the upper endplate. This is performance of the joint; (3) in terms of joint construc- basically the same as the yield of the tested tion, the extended endplate and the vertical-steel col- component. umn are considered to transmit the joint force to the In conclusion, it can be proved that the finite outside of the joint; the U-shaped anchor and the stud element simulation method used in this paper can can also strengthen beam-column constraints. simulate the stress of RCS composite joints more To study the influence of the above three factors on accurately. Because of the high cost and low effi - the static performance of the joint, the numerical simu- ciency of experimental research, the finite element lation method described above is used along with the simulation method in this paper can be used to application of experimental joint as a basic model, and further study the static performance of RCS compo- the control variable method is used for research. The site joints. research parameters are shown in Table 3. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 57 respectively, 200 mm, 250 mm, 300 mm and 350 mm. Figure 21 shows the load–displacement curve, bend- ing moment–rotation curve and dimensionless bend- ing moment–rotation curve of joints under different insertion lengths. Figure 22 is the nodal stress nepho- gram at 20 mm beam end displacement under differ - ent steel beam insertion lengths. With the increase of the insertion length of steel beam, the load–displace- ment curve of the joint keeps rising, the yield strength of the joint keeps increasing, and the rigidity of the joint keeps increasing. After the insertion of 300 mm, the increase of the insertion length will reduce the rising trend of the curve. Considering that the insertion length of steel beam is too long, it will affect the continuity of concrete and the bearing capacity of the column, it is recommended to take 300 m as the insertion length of the steel beam in the project m. That is 3/4 of the column section width. 4.2.3. Endplate thickness To study the influence of endplate thickness on the mechanical properties of RCS composite joints, five ABAQUS models were designed. The endplate thick- ness was 0 mm (without endplate), 6 mm, 9 mm, 12 mm and 15 mm, respectively. Figure 23 shows the load–displacement curve, bending moment–rotation curve and dimensionless bending moment–rotation curve of joints under different endplate thickness. Figure 24 is the stress nephogram of the joint without endplate and the joint with endplate thickness of 6 mm when the beam end displacement is loaded to 100 mm, respectively. It can be seen that increasing the endplate can share part of the stress in the joint area and reduce the web stress in the joint area, which means the endplate can effectively improve the mechanical performance of the joint, but the thickness of the endplate increases without significant changes in the curve, indicating that the thickness of the end- plate has little impact on the performance of the joint, and the optimal thickness can be the same as the thickness of the stiffener. 4.2.4. Joint-structure It can be seen from section 3.2.3 that the effect of increasing the endplate on the mechanical perfor- mance of the joint is very significant. On this basis, four kinds of RCS composite joints with different Figure 26. Effect of vertical-steel column on static perfor- mance of joints. construction forms are designed in this section, including extended endplate joint, vertical-steel col- umn joint, U-shaped anchor joint and stud joint. 4.2.2. Steel beam insertion length Eighteen finite element models are established to To study the influence of steel beam insertion length study the influence of joint construction on the static on the stress performance of RCS composite joints, performance of RCS composite joints, which are four finite element models are established. The length shown in Figures 25–28. From the above results, the of the steel beam inserted into the concrete column is, Z-direction height of the extended endplate is better 58 Y. LING ET AL. Figure 27. Effect of U-shaped anchor bars on static performance of joints. than the extended Y-direction height in improving 4.2.5. Optimized RCS composite joint the performance of the joint. But since the concrete According to the research results of the influencing shear capacity of the joint domain itself is strong, the factors, the factors that can improve the performance overall performance of the joint is not improved of the joints are combined. Considering the integrity much after the expansion of the endplate; the verti- of the joints, an RCS composite joint is preferred, and cal-steel column can improve the strength and rigid- the schematic diagram is shown in Figure 29(a). The ity of the joint, but the extent of the increase is not load–displacement curve of the optimized joint and obvious. After the U-shaped anchor is added, the the dimensionless bending moment–rotation curve strength and stiffness of the joints are improved, are compared with the basic joints, as shown in and the joint performance of the two rows of anchor Figure 29(b). ribs is better than that of one row of anchor ribs. The It can be seen from the figure that the load–displa- U-shaped anchor ribs strengthen the connection cement curve of beam end and the dimensionless between the steel beam and the concrete and pre- moment–rotation curve of the optimized joint are vent the steel beams from being pulled out and greatly improved compared with the basic joint. The destroyed; studs can increase the strength and stiff - yield load of a joint is 207.5kN, which is 44.1% higher ness of the joints, especially for the increase of joint than the basic joint, and the initial slope of the dimen- stiffness, and the lifting effect is more obvious than sionless bending moment–rotation curve is 3.14, other structural measures. which is 48.8% higher than the basic joint. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 59 Figure 28. Effect of studs on static performance of joints. element simulation method can be used to 5. Conclusion study such problems. Through the above research, the following conclusions (3) The six factors that affect the performance of the joints can be drawn: are studied by numerical simulation. According to the research results, the optimal values of the factors and (1) During the test, the steel beam is anchored the optimal structure of the joints are given. well without being pulled out. The test joint (4) According to the research results of the influential destruction begins with the compression factors, a RCS composite joint is preferred under yielding of the flange of the steel beam of the situation where the best value of each para- the outrigger, which belongs to destruction. meter is applied. With the structure of expanded According to the European Eurocode3 specifi - endplate and the welding stud, the inserted length cation, the joint is a semi-rigid joint. The duc- of steel beam takes 3/4 of the section width of the tility coefficient of joint rotation is greater column, and the ratio of the beam-column section than 4, which is higher than that of the ordin- width is 7/20, the yield strength of steel beam is ary reinforced concrete structure, and the increased by 44.1%, and the initial slope of the safety evaluation is higher. dimensionless bending moment–rotation curve is (2) The finite element simulation method used in 48.8% higher than the base joint. The joint has this paper can accurately simulate the stress of a high bearing capacity, high rigidity, simple struc- RCS composite joints. Therefore, the finite ture and convenient construction. 60 Y. LING ET AL. Sections of a New Type of Composite Structure [D]. Quanzhou: Huaqiao University. Eurocode 3. 1992. “Design of Steel Structure.” In ENV, 1993- 1-1. Brussel, Belgium: Commite European de Normalesation (CEN). GB 50011-2010. 2016. Code for Seismic Design of Buildings [S]. 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Runrun, et al. 2014. “Analysis on General Detailing Requirements and Failure Modes of RCS Composite Joints [J].” Structural Engineer, no. 5. Li, W., Q. N. Li, and W. S. Jiang. 2012. “Parameter Study on Composite Frames Consisting of Steel Beams and Reinforced Concrete columns[J].” Journal of Constructional Steel Research 77 (none): 145–162. doi:10.1016/j.jcsr.2012.04.007. Liquan, X. et al. 2017. “Research on Restoring Force Behaviors of Reinforced Concrete Column and Steel Beam Composite Joints [J].” Architectural Structure, 47 (23): 72–79. Mirghaderi, S. R., N. Bakhshayesh Eghbali, and M. M. Ahmadi. 2016. “Moment-connection between Continuous Steel Beams and Reinforced Concrete Column under Cyclic loading[J].” Journal of Constructional Steel Research 118: 105–119. doi:10.1016/ j.jcsr.2015.11.002. Nguyen, X. H. et al. 2016. “Experimental Study on Seismic Performance of New RCS Connection[J].” Structures 9: 53– Wei, L. 2010. Experimental Study on the Mechanical Behavior of New Type All-bolts Connections of Concrete-filled Square Tubular Column and Steel Beam [D]. Hebei: Hebei University of Technology. Figure 29. Optimized RCS composite joint. Xian, L., X. Yan, M. Wei, et al. 2007. “Experimental Research on Seismic Behavior of Reinforced Concrete Column-to-steel Beam Joints with Bolted End-plate [J].” Journal of Hunan Disclosure statement University: Natural Science 34 (2): 1–5. No potential conflict of interest was reported by the authors. Yang, L., G. Zixiong, D. Jingzhou, and H. Qunxian. 2013. “Experimental Study on Seismic Behavior of Prefabricated RCS Frame Jointswith Different Failure Mechanisms [J].” Journal of Civil Engineering 46 (3): References 18–28. Alizadeh, S., N. K. A. Attari, and M. T. Kazemi. 2015. 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Journal
Journal of Asian Architecture and Building Engineering
– Taylor & Francis
Published: Jan 2, 2021
Keywords: Reinforced concrete column; steel beam; RCS composite joint; seismic behavior
