NUMERICAL ANALYSIS OF THE SEISMIC PERFORMANCE OF STEEL FRAMES INFILLED WITH COMPOSITE PANELS

Transcription

1 1NCEE Tenth U.S. National Conference on Earthquake Engineering Frontiers of Earthquake Engineering July 21-25, 214 Anchorage, Alaska NUMERICAL ANALYSIS OF THE SEISMIC PERFORMANCE OF STEEL FRAMES INFILLED WITH COMPOSITE PANELS Hetao Hou 1, Jian Zhou 2, Minglei Wu 3, Haining Liu 2, Jingjing Li 2, Zhonglong Lv 2 ABSTRACT In order to study the seismic performance of steel frames with sandwich composite panels (SCP), three one-bay and one storey specimens were tested under cyclic loading. Seismic behaviors were evaluated in line with the failure mode and damage process of the specimen. According to the test data, hysteretic loops, skeleton curves, curves of strength degradation, curves of stiffness degradation, ductility index and viscous damping coefficient were obtained. It was recognized that the failures of panels mostly occurred around the embedded parts, and SCP exhibited a better integration than traditional walls. The initial lateral stiffness of steel frame infilled with SCP increased due to the existence of panel. Moreover, Finite Element Analysis (FEA) study was also carried out by using ABAQUS. Four main influential parameters, including panel thickness, axial load ratio of column, stiffness of SCP and steel frame, slenderness ratio of column were considered. Analysis results showed that the existence of SCP improved the initial lateral stiffness and ultimate strength of steel frame. Moreover, axial compression ratio of column, stiffness of connection and slenderness ratios of column also played important roles in the seismic performance. Finally, the suggestions for seismic design were put forward based on the test data and FEA results. 1 Associate Professor, School of Civil Engineering, Shandong University, Jinan 2561, P.R.China 2 Graduate Student Researcher, School of Civil Engineering, Shandong University, Jinan 2561, P.R.China 3 Assistant engineer, Shandong Engineering Consulting Institute, Jinan 251, P.R.China Author Hetao Hou, Jian Zhou, Minglei Wu, Haining Liu, Jingjing Li, Zhonglong Lv. Numerical analysis of the seismic performance of steel frames infilled with composite panels. Proceedings of the 1 th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK, 214.

2 1NCEE Tenth U.S. National Conference on Earthquake Engineering Frontiers of Earthquake Engineering July 21-25, 214 Anchorage, Alaska NUMERICAL ANALYSIS OF THE SEISMIC PERFORMANCE OF STEEL FRAMES INFILLED WITH COMPOSITE PANELS Hetao Hou 1, Jian Zhou 2, Minglei Wu 3, Haining Liu 2, Jingjing Li 2, Zhonglong Lv 2 ABSTRACT In order to study the seismic performance of steel frames with sandwich composite panels (SCP), three one-bay and one storey specimens were tested under cyclic loading. Seismic behaviors were evaluated in line with the failure mode and damage process of the specimen. According to the test data, hysteretic loops, skeleton curves, curves of strength degradation, curves of stiffness degradation, ductility index and viscous damping coefficient were obtained. It was recognized that the failures of panels mostly occurred around the embedded parts, and SCP exhibited a better integration than traditional walls. The initial lateral stiffness of steel frame infilled with SCP increased due to the existence of panel. Moreover, Finite Element Analysis (FEA) study was also carried out by using ABAQUS. Four main influential parameters, including panel thickness, axial load ratio of column, stiffness of SCP and steel frame, slenderness ratio of column were considered. Analysis results showed that the existence of SCP improved the initial lateral stiffness and ultimate strength of steel frame. Moreover, axial compression ratio of column, stiffness of connection and slenderness ratios of column also played important roles in the seismic performance. Finally, the suggestions for seismic design were put forward based on the test data and FEA results. Introduction In spite of comprehensive literatures on steel frame, sandwich composite panels (SCP) are seldom taken into consideration in current design [1][2][3]. Although composite panels are nonstructural elements, the lateral stiffness, ultimate strength and energy dissipation capacity of the steel frame could be greatly improved. The sandwich composite panels not only have the effect of maintenance and separation, but also participate in the force against earthquakes. A composite structural system consisting of semi-rigid steel frames infilled with composite panels was presented. The objective of this paper is to report an experimental investigation and finite element analysis on steel frame infilled with SCP. Experimental Research 1 Associate Professor, School of Civil Engineering, Shandong University, Jinan 2561, P.R.China 2 Graduate Student Researcher, School of Civil Engineering, Shandong University, Jinan 2561, P.R.China 3 Assistant engineer, Shandong Engineering Consulting Institute, Jinan 251, P.R.China Author Hetao Hou, Jian Zhou, Minglei Wu, Haining Liu, Jingjing Li, Zhonglong Lv. Numerical analysis of the seismic performance of steel frames infilled with composite panels. Proceedings of the 1 th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK, 214.

3 Description of specimen In the experiment, three specimens were manufactured and tested to investigate the performance of infilled frame under cyclic loading [4][5]. The frame was a one-bay, one-storey steel frame. The columns for specimen were H-shaped steel sections of HW mm, meanwhile, the beam was H-shaped steel section of HN mm. The characteristics of test specimens are summarized in Table 1. SF1 and SF2 are shown in Fig. 1 and 2, respectively. SF3 was a pure steel frame. The beam-to-column joints of the specimens were end-plates. The connection between the frame and SCP was achieved by using a steel plate with an elliptic hole Φ22 4mm that was welded on the column flange or beam flange. The horizontal section of SCP was shown in Fig. 3. The beam-column joint is shown in Fig.4. A bolt that was drawn into the embedded part in the SCP is shown in Fig.5. Fig. 1 Dimension of SF1 Fig. 2 Dimension of SF2 Fig. 3 Horizontal section of SCP

4 Fig. 4 Joint detail Fig. 5 Detail of connection between column/beam and SCP Experimental set-up and testing procedure With the purpose of loading the specimens, the closed-loop servo-hydraulic system was utilized in test. The cyclic static displacement was imposed in the plane of the SCP at the center line of the beam, and the column base was assumed fixed. No axial load was applied on the specimen. The test data were recorded by Portable Data Collection System. In line with ATC-24 guidelines for cyclic testing of steel frame, model installation of experiment is shown in Fig.6 [6]. The testing procedure was made and strictly followed as shown in Fig.7. Suffice to note that the loading history was divided into elastic and inelastic cycles ?/mm Loading Step Fig. 6 Model installation Fig. 7 Loading procedures Experimental Results As can be seen from the experiment phenomenon, when the steel frame was subjected to a horizontal load, the bolt slipped in the hole, the mutual interaction was built [7][8]. The steel frame resisted the load in cooperation with SCP, the initial lateral strength and stiffness raised. With the increasing of load, diagonal cracks around the embedded parts appeared on the surface of SCP, and then long cracks were observed in the middle of SCP as shown in Fig.8. The observation was significantly different from the previous literatures, in which the infilled wall, such as brick infill, and masonry infill, generated large diagonal cracks across the wall. Therefore it was seen that, as a precast concrete member, SCP showed a better integration than traditional walls. When the displacement increased from moderate level to high level, cracks around the embedded parts tended to dilate, as shown in Fig.9; namely cracks widen from cyclic loading

5 along crack surfaces. As soon as cracks appeared, the forces transmitted from steel frame to SCP were concentrated on the cracked region, followed by concrete spalling with the ongoing displacement, as shown in Fig.1. Local buckling was observed on the top flange of beam, shown in Fig.11. In the experiment, neither the connecting plate nor the embedded parts failed to keep working. Test results showed that adequate detailing and proper construction of connection between steel frame and SCP was achieved. Fig. 8 Cracks at top corner Fig. 9 Cracks at bottom corner Fig. 1 Spalling at bottom corner Fig. 11 Local bucking of beam Numerical Analysis Model and Material Properties Numerical analysis was carried out using finite element software ABAQUS. Three-dimensional shell element S4R was applied to steel column, steel beam, connecting plate and SCP. Steel wire of SCP embedded in the concrete was defined by element rebar. A simplified numerical model was built as illustrated in Fig.12. Beam-column joints were shown in Fig.13. The bolt in the endplate was defined with a nonlinear spring element. The cyclic static displacement was imposed in the plane of the SCP at the center line of the beam.the column base was assumed fixed. Fig. 12 FEA model Fig. 13 Beam-column joint In the numerical analysis, true stress and strain of steel was necessary, which is shown in Table 2. The concrete was defined as smeared plasticity. The cube compressive strength of concrete cubes (15mm 15mm 15mm) was tested at an average value of 32.N/mm 2, the elastic modulus was N/mm 2.

6 Table 2 True stress and strain of steel True Stress (Mpa) True Strain Numerical analysis results Based on the implicit algorithm, SF2 was calculated by ABAQUS, deformed models of FEA and test are shown in Fig 14 and 15, respectively. Fig. 14 Deformed model of FEA Fig. 15 Deformed model of test As can be seen from the experiment phenomenon, when the specimen was subjected to a horizontal load, the distribution of the stress was around the diagonal area. With the increasing of load, diagonal cracks around the embedded parts appeared on the surface of SCP, and then long cracks were observed in the middle of SCP. From the stress distribution of steel frame in numerical result, maximum value appeared in the top and bottom flange of beam. However, the stress of column was small. These analysis results agreed with test data. From the whole deformation, relative displacement between steel frame and SCP could not have a good consistency due to the spring connection. Whereas, it has a good agreement with test data. SCP yielded prior to steel frame Test FEA 3 2 Test FEA Force/kN Force/kN Displacement/mm DIsplacement/mm Fig. 16 The envelope curves of SF2 Fig. 17 The skelton curves of SF2

7 The envelope curves of test specimen and FEA are shown in Fig. 16, skeleton curves in Fig. 17. As shown in Fig.16, the envelope curves include two main portions, the positive loading portion showed no obvious strength degradation of the specimen, furthermore, the lateral strength of steel frame even keeped increasing till the end of test. It revealed that although member damage occurred, such as beam buckling and concrete spalling, the specimen still maintained bearing capacity, which was achieved by the success of connection between the frame and SCP. It could be concluded that column connection was more effective to integrate the steel frame and SCP. In Fig. 17, Comparison was made between the test data and numerical analysis results, and a good agreement could be found with a deviation. Deviation maybe caused by the difference of damage factor between positive and negative loading, and the slip between SCP and steel frame. Parametric Analysis Thickness of SCP, axial load ratio, connection stiffness and slenderness ratios of column were considered to evaluate the influence on the seismic behavior of the whole structural system. In this model, a typical steel frame with the size of 3.3m 4.5m was studied. The columns for specimen were H-shaped steel sections of HW mm; meanwhile, the beam was H- shaped steel section of HN mm. The thickness of SCP was 15mm, composited with a 6mm insulation layer unchangeably and two concrete wynthes on both sides connected by steel slice. The axial and shear stiffness of the connection between SCP and steel frame was N/m and N/m, respectively. The stiffness of beam-column joint was N/m. The Effect of SCP Thickness To study the effect of SCP thickness on the seismic behavior of the whole structural system, thickness of 12mm, 15mm and 18mm were conducted. In Fig. 18, skeleton curves illustrated clearly that the lateral load maintained the same level approximately with increase in SCP thickness. The contribution of SCP was ignored with certain connection stiffness consistently. As shown in Fig.19, stiffness degration, K, was generally higher in the steel frame infilled with SCP compared to the pure steel frame. With a slight increasing of displacement, the lateral stiffness decreased sharply, and the drastic descending trend extended to the relative displacementδ/δ y =1.5. In Fig. 2, strength degradation, λ i, increased slightly at the ultimate state. As shown in Fig. 21, there was no significant improvement in energy-absorption. The stress of SCP reduced 3% significantly and a later destruction was observed with increase in SCP thickness.

8 Force/kN mm 15mm 12mm 18mm K(kN/mm) mm 15mm 12mm 18mm Displacement/mm Fig. 18 Skeleton curves Fig. 19 Stiffness degradation curves? i 1 mm-n mm-p 15mm-N 15mm-P 12mm-N 12mm-P 18mm-N 18mm-P N*m mm 15mm 12mm 18mm Fig. 2 Strength degradation curves Fig. 21 Energy-absorption curves The Effect of Axial Load Ratio The effect of axial load ratio was investigated, five axial load ratios of,.2,.4,.6,.8 were conducted. In Fig. 23, it was illustrated clearly from skeleton curves that the lateral load decreased proportionally with increase in axial load ratio. As shown in Fig.24, stiffness degration, K, also decreased with increase in the axial load ratio. The lateral stiffness decreased sharply, with a slight increasing of displacement, and the drastic descending trend extended to the relative displacementδ/δ y =1.5. In Fig. 25, strength degradation, λ i, increased slightly at the ultimate state. Shown in Fig. 26, the capacity of energy-absorption decreased 5% proportionally Force/kN -2 K(kN/mm) Displacement/mm Fig. 23 Skeleton curves Fig. 24 Stiffness degradation curves

9 ? i 1 -N -P.2-N.2-P.4-N.4-P.6-N.6-P.8-N.8-P N*m Fig. 25 Strength degradation Fig. 26 Energy-absorption curves The Effect of Connection Stiffness Four connection stiffness of N/m, N/m, N/m, N/m were conducted to investigate the influence of connection stiffness on seismic behavior. As shown in Fig. 29, a higher lateral load was observed with increase in the connection stiffness. However, the increasing stress in SCP obviously led to a prior destruction. No more contribution was found when the connection stiffness exceeded N/m. It could be concluded that reasonable connection stiffness played an important role in resisting the cyclic load E6 2.9E7 2.9E8 2.9E9 2 Force/kN Displacement/mm Fig. 29 Skeleton curves The Effect of Slenderness Ratios Column sizes HW , HW and HW were conducted to investigate the effect of slenderness ratios on the steel frame infilled with SCP. The slenderness ratios of steel column were 16, 19 and 24, respectively. As shown in Fig. 3, the lateral load increased 3% with decreased in slenderness ratio. In Fig. 31, the initial lateral stiffness increased 3% smartly due to the decrease in slenderness ratio. As shown in Fig. 32, strength degradation increased slightly at the ultimate state. As shown in Fig. 33, there was a significant improvement in energy-absorded.

10 Force/kN -2 K(kN/mm) Displacement/mm Fig. 3 Skeleton curves Fig. 31 Stiffness degradation curves ? i 24-N 24-P 19-N 19-P 16-N 16-P N*m Fig. 32 Strength degradation curves Fig. 33 Energy-absorption curves Conclusions The following conclusions could be obtained from the observations and analysis on the conducted experiment and FEA on the steel frames infilled with SCP: (1)Test results showed that the lateral stiffness and ultimate strength of steel frame increased owing to SCP, and SCP yielded prior to steel frame. The main failure modes of steel frame infilled with SCP included the concrete spalling around the embedded parts, and the local buckling of beam flange. Comparison was made between test data and numerical analysis results, and a good agreement could be found with a deviation. Deviation maybe caused by the difference of damage factor between positive and negative loading, and the slip between SCP and steel frame. (2) Finite element analysis was carried out using ABAQUSl. The contribution of the different SCP thickness was insignificant under the same connection stiffness, the stress of SCP reduced significantly with increase in SCP thickness. The later stiffness and energy-absorbed capacity reduced with increase in axial load ratio. A higher lateral stiffness was observed with increase in the connection stiffness. The lateral stiffness and energy-absorbed capacity decreased with increasing slenderness ratio. Acknowledgements

11 This paper was supported by the Natural Science Foundation of Shandong Province, China (ZR211EEM23) and the Graduate Education Innovative Projects of Shandong Province, China (SDYC116). References 1. Hetao Hou, Canxing Qiu, Jing-feng Wang and Guo-Qiang Li. An experiment study on sandwich composite panel infilled steel frames. Advanced Steel Construction 212; 8(3): (In Chinese) 2. Hou He-tao, QIU Can-xin, LI Guo-qiang, WANG Jing-feng. Cyclic test on steel frames with energy-saving sandwich composite panels. Engineering Mechanics 212; 29(19): (In Chinese) 3. Hou He-tao, MA Ke-feng, LI Guo-qiang, CHEN Lu. Experimental investigation on the flexural behavior and dynamic response of the composite sandwich panels with truss shear connectors. Journal of Guangxi University 211; 36(1): (In Chinese) 4. Li Guo-qiang, ZHAO Xin, SUN Fei-fei, GAO Wen-li, YANG Zun-quan, JIN Shi-wen. Shaking table study on a full scale model of wall panel and their connections of steel frame residential building systems. Earthquake Engineering and Engineering Vibration 23; 23(1): (In Chinese) 5. PENG Xiaotong, GU Qiang, LIN Chen. Hysteretic behavior analysis of steel frame-reinforced concrete infill wall structure with semi-rigid jonits. Journal of Building Structures 29; 3(1): (In Chinese) 6. ATC-24. Guidelines for cyclic seismic testing of components of steel structures. Redwood City CA: Applied Technology Council, FANG Youzhen. Hysteretic Behavior of Composite Steel Frame (Weak axis of Column) with PR connection 一 Reinforced Conerete Infill Shear Wall Struetural System under Cyclic Loading. Xi an University of Architecture & Technology 26. (In Chinese) 8. Rassati GA, Hajjar JF, Schultz AE. Cyclic analysis of PR steel frames with composite reinforced concrete infill walls. Advances in Structures 23; 1(2):