INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 4, No 3, 2014

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1 INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 4, No 3, 2014 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN Structural behaviour of hybrid fibre reinforced concrete exterior Beam- Column joint subjected to cyclic Muthuswamy K.R 1, Thirugnanam G.S 2 1- Head of Department / Civil Engineering, Sakthi Polytechnic College, Erode, Tamilnadu, India 2- Professor and Head / Civil Engineering, Institute of Road and Transport Technology, Erode, Tamilnadu, India krmuthuswamy@gmail.com doi: /ijcser ABSTRACT Beam-column joints in a multistory reinforced concrete framed structure take an important role in the structural integrity of the building. Pertaining to these areas, a high percentage of transverse hoops in the core of joints are much needed to meet the requirement of strength, stiffness and ductility. A provision of high percentage of transverse hoops is certainly cause congestion of steel which results in construction difficulties. The usage of fibre reinforced concrete in beam-column joints can be an alternative solution for minimizing the congestion of transverse reinforcement. Main objective of this study is to identify the potential of hybrid fibre reinforced concrete (HFRC) as a ductile material which can be used for the construction of beam-column joints. One fifth scale model of an exterior beam-column joint made of conventional concrete and fibre reinforced concrete has been selected as test specimen for this experimental study. The specimens were subjected to cyclic. Such various parameters that load carrying capacity, load-deflection behavior, ductility, energy absorption, stiffness and failure patterns of the joints have been studied. The experiment results of beamcolumn joint with fibre reinforced concrete are compared with the beam-column joints which are made of conventional concrete. From the test results, it is found that the beam-column joint with HFRC results to 50% increase in ductility and 80% increase in energy absorption capacity in comparison with conventional concrete. HFRC in beam-column joint may be used to resist the earthquake in any seismic prone area. Key words: Fibre Reinforced Concrete; Hybrid fibre; Beam-Column joint; Ductility; Energy absorption; Stiffness. 1. Introduction The behaviour of reinforced concrete which resists framed structures in recent earthquakes all over the world has alerts poor performance of beam column joints. Simple beam-column joints become less efficient structurally as a result of strong wind, earthquake, or explosion. Fiber Reinforced Concrete has potential application in building frames due to its high seismic energy absorption capability and relatively simple construction technique. Beam-column connections with high performance fibre reinforced cement composites including polyethylene fibres have unbreakable strength, deformation capacity, and damage tolerance (Parra-Montesinos et. al, 2005). It is known that steel fibers bridging across the cracks in the concrete mix and increase the joint strength (Filiatrault et. al, 1994). While ductility, stiffness and strength could be definitely increased by using steel fibre reinforced concrete, it gets decreasing the stirrups in the joint and confinement regions of the column and beam. The usage of steel fibre reinforced Received on December, 2013 Published on February

2 concrete can reduce the cost of steel reinforcement and difficulties in its placing (Gencoglu and Eren, 2002, Ganesan et. al, 2007). Steel fibre reinforced concrete along with silica fume as partial replacement of cement gives significant improvements in strength properties due to synergistic influence of silica fume and fibre reinforcement (Ghugal and Bhalchandra, 2009). Hybrid fibre reinforced concrete of polyolefin steel combine enhances the flexural strength and ductility performance of reinforced concrete beams (Eswari et. al, 2008). Provision of Hybrid fibre reinforced concrete made of steel and polypropylene fibre in the beam-column joint region exhibits enhanced strength, deformation capacity, energy dissipation capacity and damage tolerance and may replace part of ties in columns by steel and synthetic fibres and thereby reducing the cost of construction (Perumal and Thanukumari, 2010). The main objective of this research focuses whether hybrid fibre reinforced concrete would be a suitable material for beam-column joints with high ductility, and energy absorption capacity for structures constructed in active seismic zones or not. 2. Materials and methods 2.1 Materials used Ordinary Portland cement (OPC) grade 53cement was used for the experiment study. Local river sand possesses specific gravity of 2.65 conforming to grading zone II and coarse aggregate having specific gravity of 2.70 conforming to well graded aggregate of maximum size of 12.5mm as per I.S: was used. Silica fume was added as partial replacement of cement at 7.5% by weight of cement in order to improve the performance of concrete (Muthuswamy and Thirugnanam, 2009). A super plasticizer was added with dosage of 1% by weight of cement. The round crimped steel fibres with optimum proportion of 1% by volume of concrete having an aspect ratio of 60 was used in this work (Muthuswamy and Thirugnanam, 2010). The alkali resistant glass fibre with optimum proportion of 0.03% by volume of concrete having filament diameter 14microns, 12mm length and aspect ratio 857 was used for this work (Chandramouli et. al, 2010). M30 grade concrete mix was designed as per I.S: and the mix proportion arrived was 1:1.22:2.60 with water cement ratio Design and casting of specimens A multibay, multistory reinforced concrete building (Ground floor + 4 storeys) located in a place under the seismic Zone III (as per Indian standard) was analyzed using STADD pro software. The frames were designed for seismic load according to IS: 1893 (Part-I)-2002 and detailed as per IS: The frame was reduced to one-fifth scale model to suit the arrangement and test facilities. A typical exterior Beam Column joint was selected as test specimen for the present experimental study. A prototype frame with beam dimensions of 305 x 460mm including slab thickness of 110mm and column dimensions of 305 x 460mm. For the test model the dimension of the beam was fixed as 120mm x 170 mm in cross section and 450mm long, and column sizes were 120mm x 230 mm and 600mm high. Three types of reinforced cement concrete exterior beam-column joints, one without fibre, one with steel fibre and one with hybrid fibre (steel+glass) were cast to study the behavior of the beamcolumn joints under seismic type. Figure 1shows the reinforcement details of beamcolumn joint. Concrete mix grade M30 was used to prepare the concrete specimens as per the mix design. The concrete was placed in the mould in layers and compacted by tamping such that no voids 263

3 were present in the concrete. The specimens were de-molded after 24 hours and cured under water for 28 days. The specimens were white washed, and horizontal and vertical lines were drawn at 50mm and 100mm intervals respectively in order to facilitate the monitoring of crack patterns during testing. Figure 1: Ductile detailing of Beam - Column Joint as per I.S: Test setup and instrumentation The specimen was tested in a structural engineering laboratory. Figure 2(a) and 2(b) shows the test setup used for forward and reverse cyclic. An axial load of 100kN corresponding to approximately 0.1fck compressive stress has been applied on the column in order to simulate the effect of axial load during the seismic load. The transverse was applied on the tip of the beam. The transverse was gradually applied in the increments of 0, 3, 6, etc. upto the maximum load level in that particular cycle. The was withdrawn at the same interval and the corresponding deflections were noted. Figure 2(a): Test setup for Forward cyclic load 264

4 Figure 2(b): Test setup for Reverse cyclic load This sequence is referred to as forward cyclic. Then the was applied at the bottom of the tip of the beam and the upward deflections were noted upto the maximum load in that cycle and un was done as stated before. This sequence is referred to as reverse cyclic. One forward cycle and one reverse cycle put together forms one complete cycle of giving hysteresis loop of load deflection curve. A hydraulic jack was used to apply the axial load to the column. To record the load precisely a proving ring was used. The load was applied gradually in forward and reverse directions to obtain cyclic on the specimens. The deflection was measured at each increment/decrement at the free end tip by using a dial gauge. Figure 3 shows the load sequence diagram for the HFRC beam-column joint. 3. Results and discussion Figure 3: Load sequence diagram of HFRC beam-column joint Three sets of beam-column joints namely conventional RCC, SFRC and HFRC joints were tested to study the behaviour under cyclic. The parameters such as load carrying 265

5 capacity, load deflection behavior, ductility, energy absorption and stiffness degradation were calculated. The results are presented in Tables 1 and 2. S. No Table 1(a): Experimental results of RCC Beam - Column joint Cycle No Max Load in KN Max deflection in mm Ductilit y factor Relative Energy Absorption KN-mm Stiffnes s KN/mm Forward cycle Reverse cycle S. No S. No. Table 1(b): Experimental results of SFRC Beam - Column joint Cycle No Max Load in KN Max deflection in mm Ductilit y factor Relative Energy Absorption KN-mm Stiffnes s KN/mm Forward cycle Reverse cycle Cycle No. Table 1(c): Experimental results of HFRC Beam - Column joint Max Load in kn Max deflection in mm Ductility factor Relative Energy Absorption knmm Stiffness kn/mm Forward cycle Reverse cycle

6 Table 2: Cumulative ductility factor and cumulative energy absorption Cumulative Energy Absorption KNmm Cumulative Ductility factor Cycle No RCC SFRC HFRC RCC SFRC HFRC Load carrying capacity The first crack was observed during the 6th cycle at the load level of 29kN. As the load level gets increased, series of cracks developed. The ultimate load carrying capacity of the HFRC beam-column joint was 36kN recorded at the end of the 8th cycle. The first crack load capacity of the beam-column joints RCC, SFRC and HFRC were observed as 18kN, 24kN and 29kN respectively. The ultimate load capacity of the beam-column joints RCC, SFRC and HFRC were observed as 27kN, 33kN and 36kN respectively. The first crack load capacity of HFRC joint is 61% and 21% more than that of conventional RCC joint and SFRC joint respectively. The ultimate load carrying capacity of HFRC joint is 33% and 9% more than that of conventional RCC joint and SFRC joint respectively. Figure 4 shows a comparison of first crack and ultimate load values. 3.2 Load-Deflection behaviour Figure 4: Comparison of Load carrying capacity Figure 5 shows the load deflection diagram for the HFRC beam for 1 to 9 cycles. The deflection observed was greater than that obtained in the previous cycles. The comparison of 267

7 the maximum load in each cycle and the corresponding maximum deflection of all the beamcolumn joints are clearly indicated in Figure 6. Figure 5: Load Deflection diagram of HFRC Joint 3.2 Ductility Figure 6: Equivalent Static load Vs Max. deflection Ductility of a structure is its ability to undergo deformation beyond the initial yield deformation, while still sustaining load. Ductility factor is defined as the ratio of the maximum deflection at any load level to the first yield deflection. Cumulative ductility up to any load point is defined as the sum of the ductility at maximum load level attained in each cycles up to the cycle considered. The first yield deflection was noted from the loaddeflection diagram assuming it as a bilinear diagram. The ductility values and cumulative ductility values are tabulated as given in Table 1 and 2. The ductility factor was 0.92 for the conventional RCC beam-column joint, 1.10 for SFRC joint and 0.81 for HFRC joint during the first cycle of. The cumulative ductility values were for RCC joint, for SFRC joint and for HFRC joint respectively. Figure 7 compares the cumulative ductility of all the beam-column joints. During the final stages of the cumulative 268

8 ductility values of HFRC and SFRC beam-column joints were higher than that of conventional RCC joint which is an essential requisite for beam-column joints in seismic region. Figure 7(a): Variation of Cumulative Ductility factor 3.3 Energy absorption Figure 7(b): Comparison of Cumulative Ductility factor When the beam is subjected to cyclic, some energy is absorbed in each load cycle which is as much equal as to the work in straining or deforming the structure to the limit of deflection. The energy absorption capacity was calculated as the area under the hysteresis loop of the load deflection diagrams. The cumulative energy absorption capacity of the beamcolumn joint was obtained by adding the energy absorption capacity of the joint during each cycle considered. The energy absorption and cumulative energy absorption values are calculated and shown in Tables 1&2. The relative energy absorption capacity was 10.5kNmm for the conventional RCC, 17.22kN-mm for SFRC and 7.38kN-mm for HFRC beamcolumn joint during the first cycle of. The cumulative energy absorption was 269

9 319.5kN-mm for conventional RCC, kN-mm for SFRC and kN-mm for HFRC beam-column joints respectively. Figure 8 compares the cumulative energy absorption capacity of all the beam-column joints. The total energy absorbed by the HFRC and SFRC beam-column joints were respectively 1.8 and 1.7 times higher than that of conventional RCC beam-column joint. Figure 8(a): Variation of cumulative energy absorption 3.4 Stiffness degradation Figure 8(b): Comparison of cumulative energy absorption Stiffness is defined as load required for producing unit deformation in a member. The slope of the tangent drawn to each cycle of the hysteric curve at a load of 0.75 times the maximum load was measured as stiffness. Stiffness of the HFRC beam-column joint decreases slowly when the load increases. The stiffness values for the joints are tabulated as given in Table 1. Figure 9 shows the variation of stiffness degradation with load cycles (Forward & Reverse cycles). The values of stiffness of HFRC joints are more than that of conventional RCC and SFRC joints. The rate of stiffness degradation of HFRC is low in comparison with other types. 270

10 3.5 Behavior and mode of failure Figure 9: Variation of stiffness with load cycle Figure 10 shows the failure pattern of RCC, SFRC & HFRC beam-column joints. As the load increases, the width crack also increases. The concrete was crushed and spalling down. In case of RCC joint the failure occurred at the junction of beam and column by yielding of beam reinforcement after forming plastic hinge in the beam region. In case of SFRC and HFRC joints the failure occurs after the formation numerous cracks in the beam region and crushing at the junction of beam and column. Figure 10(a): Closer view of failure pattern of RCC Beam-Column joint Figure 10(b): Closer view of failure pattern of SFRC Beam-Column joint 271

11 4. Conclusions Figure 10(c): Closer view of failure pattern of HFRC Beam-Column joint The results from this research aimed at development of beam-column joints with higher ductility and energy absorption capability for the structures constructed in active seismic zones through the use of hybrid fibres have been reported. Based on the experimental results the following conclusions are drawn. 1. The use of hybrid fibre in the RCC beam-column joint results in 61% increase in first crack load and 33% increase in ultimate load. 2. The cumulative ductility of HFRC beam-column joint has been increased to an amount of 1.5 times when compared with that of conventional RCC beam-column joint. 3. The cumulative energy absorption capacity of HFRC beam-column joint was 1.8 times that of conventional RCC beam-column joint. 4. The rate of stiffness degradation of HFRC joints is low when compared to conventional RCC joint. The addition of Hybrid fibres improves the initial stiffness of a joint. 5. The presence of hybrid fibres helps in reducing the crack width and causes lesser damages to the FRC beam-column joints than that of conventional RCC joint. 6. The failure of SFRC and HFRC joints occurred after the formation numerous cracks in the beam region and crushing at the junction of beam and column. The mode of failure of FRC joint is more ductile than RCC joint. In general, the hybrid fibre reinforced concrete for beam-column joints is highly advisable and recommended for cyclic when compared to beam-column joints with mono fibre (Steel fibre) and without fibres. 5. References 1. Gustavo J. Parra-Montesinos, Sean W. Peterfreund and Shih-Ho Chao, (2005), Highly Damage-Tolerant Beam-Column Joints Through Use of High-Performance Fibre- Reinforced Cement Composites, ACI Structural Journal, 102(3), pp

12 2. Andrew Filiatrault, Karim Ladikani and Bruno Massicotte, (1994), Seismic Performance of Code-Designed Fibre Reinforced Concrete Joints, ACI Structural Journal, 91(5), pp Mustafa Gencoglu and Ilhan Eren, (2002), An Experimental Study on the Effect of Steel Fiber Reinforced Concrete on the Behavior of the Exterior Beam-Column Joints, Turkish Journal of Engineering & Environmental Sciences, 26, pp Ganesan, N., Indira, P.V. and Ruby Abraham, (2007), Steel Fibre Reinforced High Performance Concrete for Seismic Resistant Structures, Civil Engineering and Construction Review Journal, December 2007, pp Yuwaraj M. Ghugal and Surekha A. Bhalchandra, (2009), Performance of Steel Fibre Reinforced High Strength Silica Fume Concrete, Civil Engineering and Construction Review Journal, October 2009, pp Eswari, S., Raghunath, P.N. and Suguna, K., (2008), Ductility Performance of Hybrid Fibre Reinforced Concrete, American Journal of Applied Sciences, 5(9), pp Perumal, P. and Thanukumari, B., (2010), Seismic performance of hybrid fibre reinforced Beam Column joint, International Journal of Civil and Structural Engineering, 1(3), pp Muthuswamy, K.R. and Thirugnanam, G.S., (2009), An Experimental Study on High Performance Concrete with Silica Fume and Fly Ash as Partial Replacement Of Cement, National Conference on Recent Advances in Concrete, Steel and Composite Structures, IRTT, Erode, pp Muthuswamy, K.R. and Thirugnanam, G.S., (2010), Performance of Steel Fibre Reinforced High Performance Concrete, National Conference on Emerging Trends in Civil Engineering, KSRCE, Thiruchengode, India, pp Chandramouli, K., Srinivasa Rao, P., Panneerselvam, N., Seshadri Sekhar, T. and Sravana, P., (2010), International Journal of Mechanics and Solids, 5(1), pp Indian standard code of practice for specification for coarse and fine aggregate from natural sources of concrete, I.S: , Bureau of Indian Standards, New Delhi, India. 12. Indian standard code of practice for recommended guidelines for concrete mix design, I.S: , Bureau of Indian Standards, New Delhi, INDIA. 13. Indian standard code of practice for criteria of earthquake resistant design of structures Part-1, General provisions and buildings, I.S: , Bureau of Indian Standards, New Delhi, India. 14. Indian standard code of practice for ductile detailing of reinforced concrete structures subjected to seismic forces, I.S: , Bureau of Indian Standards, New Delhi, India. 273