International Journal for Research in Technological Studies Vol. 1, Issue 8, July 2014 ISSN (online):

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1 International Journal for Research in Technological Studies Vol. 1, Issue 8, July 2014 ISSN (online): Structural Performance of Multistory RC Frame and Dual System under Lateral Loading Dr.G.Nandini Devi Associate Professor in Civil Engineering Sree Sastha Institute of Engineering and Technology, Chennai, Tamilnadu, India Abstract Experimental investigations were carried out on reinforced cement concrete frames (representing a fivestorey building in quarter-scale) three bay conventional frame (bare frame) and three bay framed shear wall (dual frame with shear wall in middle bay). The frames were tested by subjecting them to static cyclic lateral loading. Their strength, load-deflection behaviour, stiffness, ductility characteristics, energy dissipation characteristics, rupture characteristics and moment-curvature relationships were studied. The results have been compared and the advantages of shear wall and its performance are presented in this study. The analytical studies were carried out using finite element software ANSYS and SAP2000Nonlinear. The experimental and the analytical results were compared. Keywords: - concrete, reinforced concrete, ductility, ductility factor, energy dissipation, frame - wall system, pushover analysis I. INTRODUCTION High rise buildings provide a decent shelter with minimum possible area of land for the maximum possible requirements at a reasonable cost. Reinforced concrete (R.C.) is a popular material for building construction in India because it is cheaper than structural steel. The damages and failures that have occurred to high-rise buildings subjected to seismic excitation has led to a demand for increased knowledge of the seismic behaviour of such structures in order to establish adequate seismic design criteria. The trend today in high-rise architecture is to have a free-form shape that fulfils the dual function of creating an exciting exterior and at the same time provides more percentage of interior spaces. Moment-resisting frames are structures having the traditional beam-column framing. They carry the gravity loads that are imposed on the floor system. The floors also function as horizontal diaphragm elements that transfer lateral forces to the girders and columns. In addition, the girders resist high moments and shears at the ends of their lengths, which are, in turn, transferred to the column system. As a result, columns and beams can become quite large. Dual systems have a complete space frame that supports vertical loads and combine moment-resisting frames with either shear walls or braced frames to resist lateral loads. In this system, a central core or dispersed shear walls interact with the remaining beam-column or slab-column framing in the building via rigid floor diaphragms as shown in Figure 1. No consistent and widely accepted practical design methods and tools are available for shear walls. Chandrasekaran et al (2006) have developed pushover analysis procedure. With the increase in the magnitude of monotonic loading, weak links and failure modes in the multi-storey RC frames can be usually identified. The major focus of study was to bring out the superiority of pushover analysis method over the conventional dynamic analysis method recommended by the code. The results obtained from the numerical studies showed that the response spectrum method underestimates the response of the model when compared with modal pushover analysis. Fig. 1: Transfer of Lateral Forces in uilding Kadid et al (2008) have evaluated the performance of framed buildings under future expected earthquakes using a non linear static pushover analysis. Three framed buildings with 5, 8 and 12 stories were analyzed. The results obtained show that properly designed frames will perform well under seismic loads. The pushover analysis was a relatively simple way to explore the non linear behaviour of buildings. The results obtained in terms of demand, capacity and plastic hinges gave an insight into the real behaviour of structures. Panneton et al (2006) have studied an eight-storey RC shear wall building to evaluate the impact of new requirements. Static and modal analyses were conducted according to the 2005 NCC procedures, and three-dimensional dynamic inelastic time history analysis was performed using three earthquake records. Youssef elmouden et al(2007) summarized the results of an investigation on post peak modeling and nonlinear performance prediction of RC structural walls. All essential characteristics of the hysteretic behaviour of the walls, including strength degradation, stiffness degradation, pinching and slippage, bond slip effect, inelastic shear deformation mechanisms and confinement effects, are explicitly modeled analytically and experimentally. The analysis was, generally, in good agreement with experimental results and show that the model proposed can be reliably used for performance predictions of RC structures. Kien Vinh Duong et al (2007) have studied RC structures that were built approximately 40 years ago or earlier, and some recently built without adequate consideration for shear-critical behavior under seismic conditions. JurajKrálik and JurajKrálik Jr (2009) have presented the results of experimental and numerical analysis of the seismic resistance of a RC coupling system considering the plastic capacity. The experience from dynamic analysis of a hospital structure in accordance with standard requirements is presented. Dynamic parameters of the building structure are checked by experiment and the Copyright IJRTS 19

2 calculation model is modified on the basis of the experiment. The nonlinear analysis of the coupling system was realized in the program CRACK under system ANSYS for Kupfer s failure condition and Červenka s model of the concrete strength reduction. validated in the laboratory. There is a need to investigate the behaviour of these systems, to quantify their behaviour, validate and improve models of their behaviour, and to determine whether current code provisions properly indicate the relative performance of these systems. II. NEED FOR THE PRESENT WORK The large number of publications available on shear wall structures indicates the importance of these structures in the field of multi-storey building construction and the consequent interest evinced by the structural engineers in trying to understand the behaviour of such structures. Still the behaviour in the inelastic range, the dynamic responses etc. of the shear wall structures are yet to be investigated. From literature review, it has been noticed that a lot of research work was carried out on R.C. shear wall both analytically and experimentally. Though analytical work on framed shear wall was considerable but only a few experimental studies were conducted on multi-storey framed shear wall subjected to lateral loads. No testing of a dual system, which is commonly regarded as being superior to the other frame systems, is known to have been undertaken. The actual performance of these systems has not been Details eams x Columns (for first and second storey) x Columns (for third, fourth and fifth storey) x Shear wall Table 1 Model Dimensions with Reinforcement Details Flexural Size in mm Reinforcement x 0 in which x on either side act as boundary element III. EXPERIMENTAL INVESTIGATION OF RC FRAME AND RC DUAL FRAME A. Specimen Details The experimental investigation consists of testing one-fourth scaled models of three bay five storey reinforced concrete frame without shear wall (RC bare frame) and with shear wall (RC dual frame) in middle bay under static earthquake type lateral cyclic load. The three load points were located at the 5 th, 3 rd and 1 st storey level in line with the beams. The load points roughly simulate the equivalent static seismic load in the frame (Santhakumar 1974). Model dimensions withreinforcement details are given in Table 1. The details of the sections and reinforcement details are shown in Figure 2 for RC bare frame and Figure 3 for RC dual frame respectively. 8 mm 2 nos., both at top and bottom 10 mm nos., 3 nos. on either side 10 mm nos., 2 nos. on either side 8 mm nos., 8 nos. on either side Shear Reinforcement 6 mm legged at 30 mm c/c nea junction region and 60 mm c/c at middle region. 6 mm legged at 40 mm c/c at junction region and 80 mm c/c at middle region. 8 mm legged at 200 mm c/c throughout entire height. For boundary elements, 6 mm legged at 40 mm c/c at junction region and 80 mm c/c at middle region. 60mm c/c 60mm c/c 60mm c/c C2 C2 650 C2 C2 650 C2 C mm C1 C mm C1 C1 60mm c/c 60mm c/c s 60mm c/c s C2 C2 650 C2 C2 650 C2 C mm C1 C mm C1 C mm dia 6 nos 6mm dia lateral ties Section C1C1 10mm dia 4 nos 6mm dia lateral ties Section C2C2 8mm dia 4 nos 6mm dia lateral ties Section 10mm dia 6 nos 6mm dia lateral ties Section C1C1 10mm dia 4 nos 6mm dia lateral ties Section C2C2 8mm dia 4 nos 6mm dia lateral ties Section 6mm dia lateral ties 8mm dia 16 nos in 2rows Section SS All dimensions are in millimeters Fig. 2 Schematic Diagram of Reinforcement Details of RC are Frame All dimensions are in millimeters Fig. 3 Schematic Diagram of Reinforcement Details of RC Dual Frame Copyright IJRTS 20

3 International Journal for Research in Technological Studies Vol. 1, Issue 8, July 2014 ISSN (online): During the experiment, to measure longitudinal steel strains by DEMEC gauges in the reinforcements of beams, columns and shear walls mild steel studs, cut from 8 mm diameter plain round bars, were welded to the longitudinal bars of beams, columns and shear walls. The studs were cut to the correct length so that they were flush with outer surface of concrete. Rubber tubes of correct size were introduced on the stud before concreting to isolate the studs from concrete, and later removed after final setting of concrete.. Concreting And Curing For mixing of concrete, an electrically operated concrete mixer was used and the concrete was placed immediately after mixing. Needle vibrator of 20mm diameter was used for compaction of concrete. The casting was done at a stretch. Twelve numbers of bolt holes of 50mm diameter were provided in the footing portion of the frame at the same locations as that in foundation block. Companion specimens such as cubes, cylinders and prisms were cast for frames. The specimen was covered with wet gunny bags to enable curing. C. Lifting And Erection Of Specimens The frame was lifted using overhead crane and moved towards the foundation block on the test floor. The frame was fastened securely to the chain block of the moving crane near the centre of gravity of the specimen after covering the beam column junctions with gunny bags to avoid even minor damages. The foundation portion of the test specimen was inserted in the gap between the two webs of the foundation block. The bolts in the foundation block were inserted before the crane was released. Suitable scaffolding arrangement at suitable levels on both sides of the specimen was done, which acted as a platform for preparation of specimen for testing and for taking measurements of strain and displacement during testing. D. Foundation lock Details A pre-cast foundation block available in the Structural Engineering Laboratory of Coimbatore Institute of Technology, Coimbatore was used for fixing the specimen for testing. It was cast earlier in such a way that the same unit could be used for testing any number of frames. The main reinforcement for the footing consists of 10 numbers of 16mm diameter HYSD bars both at top and bottom level and held in position by shear reinforcement of 8mm diameter HYSD bars placed at mm intervals. The foundation block had twelve numbers of bolt holes of 50mm diameter to enable the fixing of frame specimens to be tested. The fixity of foundation block was obtained by fastening the foundation block with the structural test floor by twelve numbers of 50mm diameter rods. E. Experimental Setup The models were tested as vertical cantilevers at the base under a cyclic loading program. The schematic diagram of test set-up is presented in Figure 4. The test setup consists of the following: 1. Loading arrangement 2. Instrumentation for measuring deflection during test. 3. Arrangement for taking measurement of strains on steel and concrete. 4. Measurement of rigid body displacement during test. Load cells which were calibrated earlier through proving rings were used to measure the applied load as the load was static lateral cyclic and also checked with the pressure gauges which were attached to hydraulic jacks. For the application of load through jacks, two numbers of hand operated oil pumps were used. One pump was used for forward loading and other pump was used for applying load in the reverse direction, if needed. The lateral movement of the test frames at the ultimate load stages was avoided by providing suitable guides using mild steel pipes FOUNDATION LOCK 2. PUSH PULL JACK 3. FRAME FOR TEST 4. STEEL STAND TO HOLD LVDT 5. JUNCTION OX FOR PUSH 6. JUNCTION OX FOR PULL 7. OIL PUMP UNIT 8. STRONG TEST FLOOR 9. REACTION FRAME 10. LVDT TO MEASURE DISPLACEMENT 11. DEFLECTOMETER Fig. 4 Schematic Diagram showing complete Test Setup F. Instrumentation for the Measurement of Deflection LVDT (Linear Variable Differential Transformer) of least count 0.01mm was used for measuring deflections at all storey levels. LVDTs were connected to slotted angles that were in turn connected to the fixed type of steel reaction frame available in the laboratory. For top storey, mm LVDT was used to measure deflection and 50mm LVDT was used for the other four storey. If needed, LVDT s were removed and resetting was done to ensure correct measurement of deflection. G. Strain Measurement The steel studs, which were provided on the main steel reinforcement of beams, columns and shear wall before casting the frame, were attached with DEMEC (pellets) points using araldite. Also the DEMEC points were fixed to the beams, columns and shear wall faces at selected salient positions to measure the surface strain in concrete during testing of the frame. Due to availability of strain gauges, mm strain gauges were used to measure strain for beams, mm strain gauges were used for columns and 200mm strain gauges were used for shear walls. Proper attention was paid to ensure that strain was measured at exact points though different strain gauges were used. H. Testing Of Frames The effectiveness of instrumentation set up and the loading were checked in the beginning by loading and unloading the frame with small loads (of the order of 0.5 kn at all the three load points) till all the readings were repeatable. are and dual frame models were subjected to static lateral cyclic loading. Cyclic loading is the forward loading and unloading. A pre-determined level of static lateral cyclic loads was applied to the frame. The loading sequences in the Copyright IJRTS 21

4 beginning, for all the frames were almost same. The load increment for each cycle was 2kN (incremental base shear was 6kN) at the initial stages i.e., before initial cracking, 6kN (incremental base shear was 18kN) in the later cycles i.e., after the first cracking and during final loading, i.e. near final collapse. The deflections at all storey levels were measured at each increment or decrement of load. The strains in steel and concrete were monitored at maximum load of each cycle and at unloading conditions of frame (i.e. when the load is released fully) during all cycles of loading. For each loading stage, the readings on deflectometers placed on test floor and the readings for the rotation of foundation block were recorded. The formation and propagation of cracks, hinge formation and failure pattern have been recorded. The load cycles were continued till final collapse of the frame had occurred. The time taken for completing one cycle of loading was about two hours and around 8 to 10 days of continuous testing for each specimen was required. IV. FINITE ELEMENT ANALYSIS USING ANSYS In the present work, the behaviour of reinforced concrete frame specimens have been studied using ANSYS software to find the deflected shapes and stress distribution in the frame and shear wall. Non linear behaviour and material property of R.C. elements have been considered in the Finite Element Analysis (FEA). The frame elements have been modeled in 3D as solid elements and Non-linear Finite Element Analysis has been carried out based on the following assumptions: 1. The shear wall material is isotropic. 2. The reinforcement is assumed to be smeared throughout the element. 3. The concrete material is assumed to be initially isotropic. 4. The tensile strengths of concrete are taken to be 0.1 times their corresponding compressive strengths. A. Characteristics of the SOLID65 Element (3D Reinforced Solid) SOLID65 is used for the three-dimensional modeling of solids with or without reinforcing bar (i.e. rebar). The solid is capable of cracking in tension and crushing in compression. SOLID65 allows the presence of four different materials within each element; one matrix material (concrete) and a maximum of three independent reinforcing materials. The most important aspect of this element is the treatment of non-linear material properties. The concrete is capable of cracking (in three orthogonal directions), crushing, plastic deformation and creep. The rebars are capable of tension and compression, but not shear. They are also capable of plastic deformation and creep. The geometry, node locations, and the coordinate system for this element are shown in Figure 5. The element is defined by eight nodes and the isotropic material properties. The element has one solid material and up to three rebar materials. Rebar specifications include the material number, the volume ratio and the orientation angles ( and ). The rebar orientations can be graphically verified. Whenever the reinforcement capability of the element is used, the reinforcement is assumed to be smeared throughout the element. Fig. 5: SOLID65 3-D Reinforced Concrete Solid Element. Structural Modelling The frame was modeled in 3D using eight node solid elements. The reinforced cement concrete members of the frame namely, columns, beams and shear wall have been modeled using SOLID65 element (3-D Reinforced Concrete Solid) available in the element library of ANSYS software. SOLID65 has three degrees of freedom at each node: translations in the nodal x, y, and z directions. To account for rotational degrees of freedom, thickness of SOLID65 element was considered as 50mm thick so that for 50mm thick, element rotation was neglected whereas as structural; element rotation will be taken into account. The isometric view and front view showing rebars of the models of bare frame and dual frame are shown in Figure 7 and Figure 8 respectively. Nonlinear material properties have been assigned to the elements. Additional concrete material data, such as shear transfer coefficients, tensile stresses and compressive stresses are input in the concrete data table. Typical shear transfer coefficients range from 0.0 to 1.0, with 0.0 representing a smooth crack (complete loss of shear transfer) and 1.0 representing a rough crack (no loss of shear transfer). This specification may be made for both the closed and open crack. In the present analysis, the shear transfer coefficient for an open crack was assumed as 0.3 and that for closed crack was assumed as 0.7. If cracking occurs at an integration point, the cracking was modelled through an adjustment of material properties, which effectively treats the cracking as a smeared band of cracks, rather than discrete cracks. The tensile and compressive stresses for concrete are given as per the test results of the companion specimens corresponding to the specified frame model. Load has been applied as pressure equivalent to that of ultimate load and nonlinear analysis was done. Pressures may be input as surface loads on the element faces. Positive pressures act into the element. For example, the ultimate load of reinforced concrete bare frame was 63.3kN. It was applied as surface load of magnitude equal to 6330kN/sq.m [(63.3/2*0.1*0.05) = 6330kN/sq.m]. Copyright IJRTS 22

5 International Journal for Research in Technological Studies Vol. 1, Issue 8, July 2014 ISSN (online): Fig.7: Finite Element ANSYS Model Reinforced Concrete are Frame V. FINITE ELEMENT ANALYSIS USING SAP2000 NONLINEAR Pushover analysis is a static, nonlinear procedure in which the magnitude of the structural loading is incrementally increased in accordance with a certain predefined pattern. With the increase in the magnitude of the loading, weak links and failure modes of the structure are found. The loading is monotonic with the effects of the cyclic behavior. The ATC-40 and FEMA-273 documents recommend pushover analysis. A. Nonlinear Static Pushover Analysis Nonlinear static pushover analysis is a very powerful feature offered in the nonlinear version of SAP2000. In addition to performing pushover analyses for performance-based seismic design, this feature can be used to perform general nonlinear static analysis. Two types of nonlinear behaviour i.e. material nonlinearity and geometric nonlinearity can be considered in a nonlinear static pushover analysis. 1) Load Control Two distinctly different types of control are available for applying the load. Fig. 8: Finite Element ANSYS Model - Reinforced Concrete Dual Frame 2) Force control: The full load combination is applied as specified. Force control should be used when the load is known (such as gravity load), and the structure is expected to be able to support the load. 3) Displacement control:a single Monitored Displacement component (or the Conjugate Displacement) in the structure is controlled. The magnitude of the load combination is increased or decreased as necessary until the control displacement reaches a value that you specify. Displacement control should be used when specified drifts are sought (such as in seismic loading), where the magnitude of the applied load is not known in advance, or when the structure can be expected to become unstable.. Procedure The following general sequence of steps is involved in performing a nonlinear static pushover analysis: 1. Create the model similar to any other analysis. Here material nonlinearity and pushover analysis results are restricted to frame elements, although other element types may be present in the model. Copyright IJRTS 23

6 2. Define the static load cases, if any, that are needed for use in the pushover analysis (Define > Static Load Cases). 3. Define any other static and dynamic analysis cases. 4. Define the pushover load cases (Define > Static Pushover Cases). 5. Define hinge properties, if any (Define > Hinge Properties). 6. Assign hinge properties, if any, to frame elements (Assign > Frame > Hinge). 7. Run the basic linear and dynamic analyses (Analyze > Run). 8. If any concrete hinge properties are based on default values to be computed by the program, concrete design has to perform to determine reinforcing steel. 9. If any steel hinge properties are based on default values to be computed by the program for Auto-Select frame section properties, steel design has to perform and accept the sections chosen by the program. 10. Run the pushover analysis (Analyze > Run Static Pushover). 11. Review the pushover results (Display > Show Static Pushover Curve), (Display > Show Deformed Shape), (Display > Show Element Forces/Stresses > Frames...) C. Structural Modeling The frame was modeled using frame sections. The reinforced cement concrete members of the frame namely, columns, beams and shear wall have been modeled using frame sections available in the element library of SAP software. Reinforcements are included by selecting material type as concrete. Nonlinear material properties have been assigned to the elements. eams were assigned M3 and V2 hinges at both ends and columns were assigned PMM hinges at both ends. As shear walls can be modeled as strut elements with possibilities of forming axial hinges, it was modeled with P hinges. The isometric view and front view of SAP models of reinforced concrete bare frame and dual frame are shown in Figure 9 and Figure 10 respectively. Loads were applied as horizontal nodal loads at 1 st, 3 rd and 5 th storey level as similar to experimental investigation. Fig. 9: Finite Element SAP Model are Frame VI. ANSYS 2D ANALYSIS AND RESULTS A. RC are Frame The reinforced cement concrete members of the frame namely, columns and beams have been modelled using EAM23 2-D Plastic eam. EAM23 is a uni-axial element with tension-compression and bending capabilities. The element has three degrees of freedom at each node: translations in the nodal x and y direction and rotation about the nodal z-axis. The element has plastic, creep, and swelling capabilities. ANSYS 2D model is shown in Figure 11 (a). The deflected shape of bare frame at ultimate load is Fig. 10: Finite Element SAP Model Dual Frame also shown in Figure 11(b). Ultimate base shear obtained from ANSYS-2D analysis was 186.0kN and ultimate deflection was mm.. RC Dual Frame The reinforced cement concrete members of the frame namely, beams, columns and shear wall have been modelled using EAM23 2-D Plastic eam. ANSYS 2D model of dual frame is shown in Figure 12(a). The deflected shape of frame at ultimate load is also shown in Figure 12(b). Ultimate base shear obtained from ANSYS-2D analysis was 283.0kN and ultimate deflection was mm. Copyright IJRTS 24

7 International Journal for Research in Technological Studies Vol. 1, Issue 8, July 2014 ISSN (online): (a) ANSYS 2D Model (b) Deflected shape Fig.11: ANSYS 2D Model of are Frame (a) ANSYS 2D Model (b) Deflected shape Fig.12: ANSYS 2D Model of RC Dual Frame VII. COMPARISON OF PERFORMANCE OF FRAMES: F AND DF UNDER LATERAL LOADING The observations were critically evaluated to study the performance of the frames in the following aspects. Load Carrying Capacity Load-Deflection ehaviour Deflection Profile Stiffness Characteristics Ductility Characteristics Energy Dissipation Capacity Rupture Characteristics A. Loading and Load-Deflection ehaviour The lateral load simulating earthquake load was applied at the 1 st, 3 rd and 5 th storey level using double acting hydraulic jacks. The load increment for each cycle was 2kN (incremental base shear was 6kN) at the initial stages i.e., before initial cracking and the load increment was 6kN (incremental base shear was 18kN) in the later cycles i.e., after the first cracking and same increment was adopted during final loading for post ultimate study. The deflections at all storey levels were measured using LVDT at each increment or decrement of load. The strain in steel and concrete were measured using DEMEC points at maximum load of each cycle and at unloading conditions of shear wall (i.e. when the load is released fully). The formation and propagation of cracks, hinge formation and failure pattern have been recorded. The deflectometer readings for calculating error due to rigid body rotation of foundation block were also recorded. The cracking load for bare frame (F) was 10.9kN (base shear, 32.8kN) and that for dual frame (DF) was 41.40kN (base shear, 124.2kN). The ultimate base shear of bare frame was 189.9kN and for dual frame, the ultimate base shear was 316.8kN. The dual frame was capable of withstanding 1.67 times load than that of the bare frame, which clearly indicates that the larger load capacity of the dual frame, when compared with the bare frame was due to the contribution of the shear wall. The ratio of crack load to ultimate load of bare frame and dual frame was and respectively as shown in Figure ASE SHEAR in kn Ultimate Crack F DF Fig. 13: Ratio of Crack Load to Ultimate Load of are Frame and Dual Frame Copyright IJRTS 25

8 Experimental cyclic ase Shear Vs Top Storey Deflection Diagram of are Frame was shown in Fig. 14. The maximum top storey deflection measured for the two frames F and DF, corresponding to their ultimate load were mm and 48.4 mm respectively as shown in Fig ASE SHEAR in kn Fig. 14: ase Shear Vs Top Storey Deflection Diagram of are Frame F 320 ARE FRAME 280 DUAL FRAME ASE SHEAR in kn = TOP STOREY DEFLECTION in mm Fig. 15: Comparison of ase Shear Vs Top Storey Deflection The prediction of top storey deflection of frames by the finite element analysis yielded results close to that of experimental value as shown in Figure 16. The predicted value of top storey deflection of bare frame and dual frame at the ultimate load from ANSYS analysis was 89.18mm and mm respectively. The value of top storey deflection of bare frame and dual frame at the ultimate load from SAP2000nonlinear analysis was mm and mm respectively. The deflected shape of the finite element model of bare and dual frame is a replica of that due to experimental investigation. It has been also observed that the theoretically predicted ultimate load values using finite 18 DUCTILITY FACTOR: Ductility factor for 12th cycle = µ 12 = 12/ y = 108.6/26.53= where, y is the first yield deflection. Cumulative Ductility factor = µn = 1n n/ y where 'n' is the load cycle number for which cumulative ductility factor is calculated TOP STOREY DEFLECTION in mm element analysis compares well with the experimental data for both the frames ASE SHEAR in kn Fig. 16: ase Shear Vs Top Storey Deflection of Dual Frame. Deflection Profile EXPERI MENTAL ANSYS- 3D TOP STOREY DEFLECTION in mm The Figure 17 shows a plot of experimental deflection profile along the height at different stages of loading. It has been observed that deflection of dual frame at ultimate load and at failure was very less when compared to bare frame. At their ultimate load, the deflection of the dual frame was 32.68% of deflection of the bare frame. The deflection of the dual frame at collapse was 24.87% of deflection of the bare frame. The drift in percentage of the bare frame at ultimate and collapse was 3.9 and 13.4 respectively. The drift in percentage of the dual frame at ultimate and collapse was 1.3 and 3.3 respectively. The inter-storey drift observed in bare frame and dual frame was 0.77% and 0.25% respectively. It has been noted that the drift % of dual frame was less even at collapse i.e. the inter-story deflection of frame was less. Fig. 17: Experimental Deflection Profiles of Frames C. Stiffness Degradation The stiffness of the dual frame during the first cycle of loading (initial stiffness) was 80.8kN/mm whereas for bare frame it was 10.3kN/mm. The initial stiffness of the dual frame was 7.84 times higher than that of the bare frame at initial stage of loading. This increase in stiffness is due to the contribution of shear wall. The comparison of stiffness Copyright IJRTS 26

9 degradation of the dual frame Vs roof drift ratio in % up to ultimate load is shown in Figure 18. The stiffness of the dual frame during the service load (50% of the ultimate load) was 16.9kN/mm whereas for bare frame it was 1.6kN/mm. The dual frame is times stiffer than bare frame at their corresponding service load. Stiffness degradation curve of both the frames were deeper at initial cycles of loading as most concrete cracking and bond slip initiation occurred in the early stages of the test. And stiffness degradation rate was less in the later cycles of loading. On comparison of the stiffness of the two frames at service load, it can be understood that the dual frame can be used for a larger service load. In general, all the frames show considerable degradation in stiffness in the early cycles of loading i.e. before 0.5% drift because most concrete cracking and bond slip initiation occurred in the early stages of the test and stiffness degradation rate was less in the later cycles of loading. For comparing the stiffness of three frames, code preferred roof drift for bare frame 0.6% is used. At code specified drift limit, the stiffness of bare frame, shear wall and dual frame is 4.08 kn/mm, 3.2 kn/mm and 14.73kN/mm respectively STIFFNESS, kn/mm EXPERIMENTAL ANSYS (unit top) ROOF DRIFT RATIO in % Fig. 18: Stiffness Degradation of the Dual Frame Vs Roof Drift Ratio in % D. Ductility Factor and Cumulative Ductility The ductility factor of the dual frame was during the first cycle of loading and it was during the last cycle of loading. The ductility factor of the bare frame was during the first cycle of loading and it was during the last cycle of loading. The cumulative ductility for dual frame was and that for bare frame was at their corresponding final cycle of loading. The dual frame showed 3.5 times better cumulative ductility than bare frame. Drift ratio of dual frame at ultimate load was and of bare frame at ultimate load was At ultimate load, global ductility of dual frame was 8.07 and of bare frame were Response reduction factor (R) based on equal energy concept is 2.82 for bare frame and 3.89 for dual frame. ased on equal maximum deflection assumption, R is found to be for bare frame and 8.07 for dual frame. E. Energy Dissipation Capacity During the first cycle, the dual frame dissipated kNm energy whereas the energy dissipated by the bare frame was kNm. And during collapse, the energy dissipated by the bare frame, shear wall frame and dual frame was 7.243kNm, 8.256kNm and 3.163kNm respectively. The cumulative energy dissipation capacity of dual frame was kNm and that for bare frame was kNm at their corresponding final cycle of loading. The cumulative energy dissipation capacity of dual frame is 0.38 times less than that of bare frame. F. Cracking ehaviour and Mode of Failure In the case of bare frame (F), the first crack was initiated in the second storey of middle beam at the base shear of 32.8kN in 6 th cycle. Further, with the increase of load, new cracks developed in the other storey columns. All the beams were found to be cracked near the junction of beam and column. The formation of hinge was reached by fracture of the tension reinforcement in beams. After all the floor beams plastified, the first storey left column, middle left column steel yielded and crushing of concrete took place in first storey right column, middle right column. Hinge mechanism was also observed in upper end of third storey column. All the beam and column reaches failure stage. The frame failed at the ultimate load stage by forming panel mechanism. In the case of dual frame (DF), the first crack was initiated in the third storey of left beam and right beam near column junction with the corresponding base shear was 124.2kN in 21 st cycle. Hinge formation was observed in the bottom of first storey left boundary element of shear wall. All the beams were found to be cracked near the column junction. Separation crack (flexural crack) was appeared between shear wall and foundation. All the beam ends near shear wall and beam junctions found to be cracked. Flexural crack width in shear wall increased when the load was increased further and further. The formation of plastic hinges in the floor beams were observed after severe cracking of shear wall in the ground storey. First storey left column, first storey right column and first storey right boundary element were found to form hinge mechanisms. Crack formed between shear wall and foundation expanded further and other flexural cracks were formed in first storey shear wall which expands further. The frame failed at the ultimate load stage by failure of first storey left boundary element of shear wall (two of four main rebars of LE1, two were split). The formation of flexural hinges at salient locations i.e. at junction of left side beams and columns was also observed. Figure 19 shows bare frame at initial stage and at failure and Figure 20 shows dual frame at initial stage and at failure. Copyright IJRTS 27

10 International Journal for Research in Technological Studies Vol. 1, Issue 8, July 2014 ISSN (online): efore Testing Fig. 19: Reinforced Concrete are Frame At Failure efore Testing Fig. 20: Reinforced Concrete Dual Frame VIII. FINITE ELEMENT ANALYSIS USING ANSYS A. Deflection The top storey deflection of bare frame and dual frame was found to be 89.18mm, 37.71mm and mm from ANSYS 3D model. The theoretical value obtained from At Failure ANSYS was 39.78% and 12.56% less from experimental values for F and DF respectively. The deflected shape of ANSYS model of F and DF is shown in Figure 21. Fig. 21: Deflected Shapes of F and DF at Ultimate Load Copyright IJRTS 28

11 International Journal for Research in Technological Studies Vol. 1, Issue 8, July 2014 ISSN (online): Stress Flow Pattern In bare frame, first, second, third storey beams has high compressive stress. Middle columns experiences high compressive stress up to third storey. First storey right column also has high compressive stress. In dual frame, all structural elements have low compressive stress. Presence of shear wall in dual frame reduces high compressive stress in beams and especially in columns proving that shear wall absorbs major portion of lateral load applied to the structure. Figure 22 shows stress flow pattern of F and DF. C. Principal Tensile Contours These distributions help to identify the hinging locations. In bare frame all beams and first storey columns show hinge formation whereas in dual frame beams and columns show no hinge formations and only first storey shear wall have hinge location. All the beams, columns and shear wall except first storey experiences very less tensile stress in the dual frame. In the dual frame, the first storey shear wall have hinge location and experienced less tensile stress whereas in shear wall frame major portion of first storey and Fig. 22: Stress Flow Patterns of F and DF at Ultimate Load near loading point of third storey experienced high tensile stress when compared to dual frame. The principal tensile strain and compressive strain contours of dual frame was also found to be less as the corresponding tensile and compressive stresses were less when compared to other two frames. The strain contour was found as a replica of the observation of strain measurements in the experimental study. Figure 23 shows Principal Tensile Contours of F and DF. Fig. 23: shows Principal Tensile Contours of F and DF at Ultimate Load IX. FINITE ELEMENT ANALYSIS USING SAP 2000 NONLINEAR A. Deflection The top storey deflection of bare frame, shear wall and dual frame was found to be mm and 42.75mm from SAP push over analysis. The theoretical value obtained from SAP was 14.6% and 11.67% less from experimental values for bare frame and dual frame respectively. The deflected value from push over analysis was found to be close to the experimental value. 1) Hinge Identification In bare frame, there are totally 70 hinges. It has been noted that first hinge is formed in first storey left beam and first storey right beam at the extreme column junction. At failure, all the beams of the frame reached failure stage. All the first storey columns near foundation end and all the third storey columns at its upper end also reached failure stage at the final stage. The inter storey drift up to third storey was large and for third to fifth storey, it was less. First storey columns and first, second beams have high shear force at the ultimate load. It has been also noted that the applied load is concentrated in the middle two columns than the extreme columns. Copyright IJRTS 29

12 In dual frame, there are totally 42 hinges. It has been noted that first hinge is formed in first storey left boundary element and same was observed during experimental investigation. When load was applied to dual frame, it has been noted the applied load was taken by shear wall therefore formation of first hinge. At failure, all left beams except first storey reaches maximum stage (C) whereas all right beams are in immediate occupancy (IO) stage below life safety level. First storey left boundary element has reached failure stage and first storey right boundary element has reached maximum limit (C). Yield hinge () was also noticed in first storey left column base, first storey and second storey right column base. At ultimate load, first storey left boundary element reaches failure and during experiment out of four rebars of first storey left boundary element, two rebars were split thereafter the frame not taking load. From shear force diagram, it is seen that shear force is concentrated in first storey left column, left and right boundary element. All the beams have less shear force. In general, the formations of hinges in the dual frame were satisfactory. Figure 24 shows SAP Model of F at First Hinge Formation and at Failure and Figure 25 shows SAP Model of DF at First Hinge Formation and at Failure. Fig. 24: SAP Model of F at First Hinge Formation and at Failure Fig. 25: shows SAP Model of DF at First Hinge Formation and at Failure The performance of the frames is given in Table 2. Table 2 Experimental and Analytical Results for the Frames F and DF Frame F DF Cracking ase Shear (kn) 32.8kN 124.2kN Ultimate ase Shear (kn) 189.9kN 316.8kN Crack to Ultimate Load ratio Top-storey deflection (mm) at Ultimate Load mm 48.4 mm Top-storey deflection (mm) at failure mm mm First yield deflection ( y) 33 mm 6 mm Drift % (= ( /H)*) at Ultimate Load Drift % (= ( /H)*) at Collapse Load Experimentally observed initial stiffness 10.30kN/mm 80.8kN/mm Stiffness at the cracking load 2.4kN/mm 19.9kN/mm At service load (50 % of ultimate load) 1.6kN/mm 16.9kN/mm Stiffness at collapse 0.5kN/mm 3.0kN/mm Theoretical stiffness from ANSYS-3D (applying unit load at top) 8.92kN/mm 72.88kN/mm Global ductility at Ultimate Load Copyright IJRTS 30

13 Ductility during first cycle of loading Ductility during last cycle of loading Cumulative Ductility Drift Ratio at Ultimate Load Response Reduction Factor, R i. the equal energy concept ii. the equal maximum deflection response Energy Dissipation during first cycle of loading kNm kNm Energy Dissipation during last cycle of loading 7.243kNm 3.163kNm Cumulative Energy Dissipation Capacity kNm kNm Deflected Shape of ANSYS Model mm mm Experimental Top Storey Deflection mm 48.4 mm % Difference 39.78% 12.56% Deflected Shape of SAP2000 Model mm 42.75mm X. INTERACTION OF SHEAR WALL AND FRAME From the finite element analysis using SAP2000NL, the shear force in the structural elements of the frame namely, beams, columns and shear wall was obtained. The comparison of the shear force in the left column of the bare frame and the dual frame at 189.9kN (Ultimate load of F) is shown in Figure 26. The shear force comparison in the right column of the bare frame and the dual frame at 189.9kN (Ultimate load of F) is shown in Figure 27. Figure 28 shows comparison of the shear force in the beams of the bare frame and the dual frame at 189.9kN (Ultimate load, F). % Difference 14.6% and 11.67% Fig. 27: Shear Force in Right Column of F and DF at 189. (Ultimate ase Shear of F) Fig. 26: Shear Force in Left Column of F and DF at 189.9kN (Ultimate ase Shear of F) The sum of the shear force at the bottom of the left column and the right column of the dual frame have experienced only 22.26% and 19.25% times the corresponding shear force of the bare frame at 189.9kN. The sum of the shear force at the bottom of the left column and the right column of the dual frame was only 69.0% and 63.55% times the corresponding shear force of the bare frame even at 66.8 % higher load. The shear force for beams of the dual frame was 40.6% times the bare frame of the first storey and was 12.4% times the bare frame of the fifth storey. In the dual frame, the presence of the shear wall reduces the member forces for about less than 50% when compared to the bare frame. Fig. 28: Shear Force in eams of F and DF at 189.9kN (Ultimate ase Shear of F) XI. CONCLUSIONS: From experimental investigation carried out on multi-storey reinforced concrete shear wall and on dual frame to static cyclic loading, it was found that boundary elements were the positions of hinge locations. The work reveals the percentage error between the predicted and experimentally observed values of strength, stiffness and ductility to describe its structural behaviour. Copyright IJRTS 31

14 1. For F, it was observed that the estimated ultimate load ANSYS analysis was found to be 2.05% less than the experimental ultimate load. The predicted initial stiffness was 13.4% less from ANSYS than the experimental observed stiffness. The experimentally calculated global ductility of bare frame was 49.6 % higher than the assumed value. 2. For DF, it was observed that the estimated ultimate load ANSYS analysis was found to be 10.7% less than the experimental ultimate load. The theoretical initial stiffness from ANSYS was 9.8% less than the experimentally obtained stiffness. The global calculated global ductility of dual frame was 80 % higher than the assumed value. 3. The shear force at the bottom storey columns of dual frame have experienced only about 20% of the shear force in bare frame. The shear force in columns at the bottom storey of dual frame was about only 65% of the shear force in bare frame even at 66.8 % higher load. The shear force for beams of the dual frame was 40.6% times the bare frame of the first storey and was 12.4% times the bare frame of the fifth storey. In the dual frame, due to the presence of shear wall the moment frame forces were reduced for about 50% less when compared to the bare frame. The sequence of formation of hinges during experiment seems to match with Push over analysis 4. About % of deflection of bare frame was controlled due to the presence of shear wall as its lateral rigidity is high. 5. From push over analysis using SAP2000Nonlinear, the drifts could be predicted and the predicted drift in percentage is 14.6 % and % less when compared to the experimentally obtained drift for F and DF. 6. The ultimate base shear carried by the DF was 1.67 times higher than that of the F. The initial cracking load of DF was 3.79 times greater than that of the F.This higher load carrying capacity is due to the contribution of the shear wall which is absent in bare frame and moment redistribution of beam-column elements which is absent in shear wall. 7. In general, global ductility of DF was 1.8 times higher than that of F. 8. The push over analysis of SAP model of the frames yielded good results and can be used. As push over analysis can be done only on frame elements, shear wall frame can be modeled as equivalent strut model with frame elements available in software with axial hinges in boundary element. Test results showed that the shear wall failed at the base due to shear and that the pushover test provides a simplified representation of the cyclic test. The predicted cracking would be more if the effect of stiffness degradation due to cracking was considered. [2] IS: (1993), Ductile Detailing of RC Structures Subjected to Seismic Forces, ureau of Indian Standards, New Delhi [3] IS: 1893-Part 1 (2002), Criteria for Earthquake Resistant Design of Structures (Fifth Revision), ureau of Indian Standards, New Delhi [4] IS: 456 (2000), Code of Practice for Plain and Reinforced Concrete, ureau of Indian Standards, New Delhi [5] KadidA. and oumrkik A. (2008), Pushover Analysis of Reinforced Concrete Frame Structures, Asian Journal of Civil Engineering (uilding And Housing), Vol. 9, No. 1, pp [6] Kien Vinh Duong, Sheikh S.A. and Vecchio F.J. (2007), Seismic ehavior of Shear-Critical Reinforced ConcreteFrame: Experimental Investigation, ACI Structural Journal, Vol. 104, No. 3. [7] Naveed Anwar (2007), ehavior, Modeling and Design of Shear Wall-Frame Systems, Asian Center for Engineering Computations and Software, ACECOMS, AIT, Thailand. [8] SAP2000Nonlinear Version 12 Reference Manual.Yaw-Jeng Chiou, Fu-Pei Hsiao, Wei-Tsung Lee, Maw-ShyongSheu and Yuh-Wehn Liou (2000), Earthquake Resistance Experiment and Failure Evaluation for Frame-Shear Wall of School uildings, National Cheng Kung University, Tainan, Taiwan. [9] Youssef elmouden and PierinoLestuzzi (2007), Analytical Model for Predicting Nonlinear Reversed Cyclic ehaviour of Reinforced Concrete Structural Walls, Engineering Structures, Vol. 29, Issue 7, pp [10] Kien Vinh Duong, Sheikh S.A. and Vecchio F.J. (2007), Seismic ehavior of Shear-Critical Reinforced ConcreteFrame: Experimental Investigation, ACI Structural Journal, Vol. 104, No. 3. [11] Panneton M., Léger P. and Tremblay R. (2006), Inelastic Analysis of a Reinforced Concrete Shear Wall uilding According to The National uilding Code Of Canada 2005, Canadian Journal of Civil Engineering, Vol. 33, No. 7, pp [12] JurajKrálik and JurajKrálik Jr (2009), Seismic analysis of reinforced concrete frame-wall systems considering ductility effects in accordance to Eurocode, Engineering Structures, Vol.31, Issue 12, December, pp REFERENCES [1] ANSYS Version 10 Classic Reference Manual.Chandrasekaran S. and Anubhab Roy (2006), Seismic Evaluation of Multi-Storey RC Frame Using Modal Pushover Analysis, Nonlinear Dynamics, Vol. 43, No. 4, pp Copyright IJRTS 32