BEHAVIOR OF EXTERIOR R.C BEAM COLUMN JOINT WITH STRENGTHENED CONCRETE AND DIAGONAL CROSS BRACINGS

International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 04, April 2019, pp. 701-710. Article ID: IJCIET_10_04_074 Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=04 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication Scopus Indexed BEHAVIOR OF EXTERIOR R.C BEAM COLUMN JOINT WITH STRENGTHENED CONCRETE AND DIAGONAL CROSS BRACINGS Nandhigam Vijayaprasad M.E Student, Department of Civil Engineering, Chandigarh University, Mohali, Punjab Aditya Kumar Tiwary Assistant Professor, Department of Civil Engineering, Chandigarh University, Mohali, Punjab ABSTRACT Reinforced concrete moment resisting structures everywhere throughout the world is in necessity of quick actions for overhauling their execution level to survive the seismic loading impacts. Failure of beam column junctions are identified as the central cause of failure in moment resisting frames during seismic loads. Successful and economical techniques are required to improve joint structural properties and ductility of structures. In present work the seismic behavior of beam column joints with Diagonal cross bracings and strengthened concrete is contemplated. Performance of beam column joints with reinforcement specifications as per IS 13920:1993 and IS 456:2000 along with diagonal cross bracings, strengthening of concrete by using glass fibers and GGBS are studied in this exertion. The outcomes in this study illustrates that the provision of additional diagonal cross bracings and strengthening of concrete shows improvement in structural properties like load carrying, energy dissipation capacities and ductility which eventually improves the seismic behavior of beam column joints. Keywords: Beam-column Joints, Glass Fibers, GGBS, Diagonal cross bracings, Seismic Performance Cite this Article: Nandhigam Vijayaprasad and Aditya Kumar Tiwary, Behavior of Exterior R.C Beam Column Joint with Strengthened Concrete and Diagonal Cross Bracings, International Journal of Civil Engineering and Technology, 10(4), 2019, pp. 701-710. http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=04 http://www.iaeme.com/IJCIET/index.asp 701 editor@iaeme.com Behavior of Exterior R.C Beam Column Joint with Strengthened Concrete and Diagonal Cross Bracings 1. INTRODUCTION While constructing R.C structures in regions of low to medium seismicity Structural Engineers neglect about seismic impact. Ongoing seismic tremors have exhibited that when the beams and columns in a R.C structure not able to withstand to these seismic loads, the rectitude of the entire structure is endangered if the joints, where these individuals are associated fizzle. Bar segment joints are defenseless to disappointment sooner than the adjoining members because of the annihilation of joint zone. The performance of beam column junctions is affected if it is not properly designed. The examination with supposition of joint being inflexible neglects to think about the impacts of high shear forces created inside the joint. The behavior of beam column joint region under seismic impacts has been an examination point since a long time. Previous works related to this study are reported in literature. K.R. Bindhu.et.al. researched on a six storeyed building situated in zone –III where an exterior R.C beam column joint at transitional storey is depicted as per latest codal provisions from IS 1893 and IS 13920. These were tested under two different axial cyclic loads in which two specimens are detailed as per IS 456 and SP 34 and other two specimens under IS 13920. Tensile cracks are formed on all the specimens at interface of the beam and column which shows that strong column and weak beam state and the joints have some hairline cracks which exhibits the shear –resisting capacity of joints [1]. AnusreeLal regarded joint as a structural member where the bending moments and shear forces are large enough when compared to other elements. Considering the exterior joints is one of the failure zones, a G+2 building is prototyped in STAAD Pro VSi where the joint is modelled in ANSYS where the maximum deformation noted as 0.48 mm and shear stress is 4.27MPa which is in the allowable limit [2]. Francesca Feroldi.et.al. stated that moment rotation behavior of the joints is strongly influenced by the plates and bolted connections. The initial stiffness for each type of connection is determined in the experimental program where as numerical studies on pultruded plates and c-shape FRP profiles of bolted connections states that they have strong effect on the ultimate moment and rotation which is related to ultimate strength [3]. Flora Flaeschini main objective is to influence the joints by using recycled concrete which contains Electric Arc Furnace (EAF) slag. Using EAF slag helps in obtaining high load carrying capacity in the joints than the conventional concrete [4]. Ninik Catur Endah Yuliati.et.al. stated that collation between monolithic and non-monolithic BCJs where deflection and static load capacity of joints are evaluated. The monolithic BCJ is conventionally casted where non-monolithic specimens are casted with and without notch. A similar performance of monolithic and non-monolithic notch in terms of structural behavior is observed [5]. 1.1. Notation 𝑓𝑐𝑘 𝑓𝑜 ∈𝑜 𝐸𝑐 𝐸𝑜 R ∆𝑈 ∆𝑦 S1 Characteristic compressive strength of concrete. Maximum stress. Strain for maximum stress. Modulus of elasticity of concrete. Ratio of maximum stress to strain at maximum stress. 𝐸 Parameter depending on the shape of the stress- strain curve= 𝐸𝑐 𝑜 Ultimate displacement. Yield displacement. BCJ with reinforcement as per IS 456 and M40 concrete. http://www.iaeme.com/IJCIET/index.asp 702 editor@iaeme.com Nandhigam Vijayaprasad and Aditya Kumar Tiwary S2 BCJ with reinforcement as per IS 456 and strengthened concrete. S3 BCJ with reinforcement as per IS 456 with diagonal cross bracings and M40 concrete. S4 BCJ with reinf. as per IS 456 with diagonal cross bracings and strengthened concrete. V1 BCJ with reinforcement as per IS 13920 and M40 concrete. V2 BCJ with reinforcement as per IS 13920 and strengthened concrete. V3 BCJ with reinforcement as per IS 13920 with diagonal cross bracings and M40 concrete. V4 BCJ with reinf. as per IS 13920 with diagonal cross bracings and strengthened concrete. 2. EXPERIMENTAL PROGRAM 2.1. Compressive strength and Split tensile strength of concrete M40 grade concrete mix design was done conferring to Indian standard code of practice IS 10262:2009 where OPC 53 grade cement, aggregate of 20mm size and sand of zone –II is used. To obtain best mix proportion, cement is partially replaced with GGBS with a varying percentage of 0%,30%,40% and 50%. For each proportion of mix, an electro chemical resistant glass fibre of 0%,0.33% and 1% is added to the total volume of concrete, where the workability for all proportions ranges from 100 to 150 mm. The compressive and split tensile strength results of concrete are given in Table 1. The finalized concrete mix of M40 contains GGBS of 40%which is replaced by cement and Glass fibres of 0.33% to the volume of concrete. Table 1 Compressive strength and Split tensile strength values of Concrete GGBS % Glass fiber % 0 30 40 50 0 0.33 1.0 0 0.33 1.0 0 0.33 1.0 0 0.33 1.0 Compressive strength 7 Days (N/mm²) 28 Days (N/mm²) 32.30 49.60 37.30 60.66 36.59 58.03 33.34 54.73 38.5 66.93 37.77 64.03 33.72 57.395 38.94 70.19 38.2 67.15 33.04 53.66 38.16 65.63 37.434 62.732 Split tensile strength 28 Days (N/mm²) 5.39 9.26 10.49 5.77 9.91 11.23 6.48 11.13 12.62 5.51 9.47 10.73 2.2. Reinforcement detailing of joints The design of reinforcement for exterior beam column joints are done according Indian standards IS 456:2000 [6] and IS 13920:1993 [7] where diagonal cross bracings are used in joint sections as shown in Fig 1 and Fig 2. Two specimens are casted according to IS 456 with and without diagonal cross bearings and are compared based upon their structural performance. Another two exterior beam column joints with respect to with and without diagonal cross bracings were also casted which are conforming to IS 13920 and are evaluated based on their high load carrying capacity. http://www.iaeme.com/IJCIET/index.asp 703 editor@iaeme.com Behavior of Exterior R.C Beam Column Joint with Strengthened Concrete and Diagonal Cross Bracings Figure 1 Reinforcement of R.C exterior BCJ as per IS 456:2000 with and without bracing Figure 2 Reinforcement of R.C exterior BCJ as per IS 13920:1993 with and without bracings 2.3. Testing setup The R.C exterior BCJ which is designed and casted as per Indian standards of IS 456:2000 without bracings were tested under a 200 tones capacity loading frame, in which the end conditions of the exterior beam column specimens were fixed on bottom side and hinged on top side of the column as shown in Fig 3. The load cell was placed on the hydraulic jack from a distance of about 100 mm from the cantilever end of the beam. The load is applied gradually as cyclic loading until the failure modes are formed where the deflection in the joints are noted with the help of linear variable differential transducers (LVDT’s) which is fixed at the edge of beam at the loading point. Figure 3 Schematic diagram of test setup and Experimental test setup http://www.iaeme.com/IJCIET/index.asp 704 editor@iaeme.com Nandhigam Vijayaprasad and Aditya Kumar Tiwary 4. ANALYTICAL MODELLING 4.1. Material properties Finite element analysis was adopted to study the Non-linear behavior of the BCJs in this study. The ABAQUS/ Standard (ABAQUS, version CAE 2017) was used for the analysis. The beam column joint was modeled with solid 3D elements 8-node linear brick (C3D8R), Two node linear 3D truss element (V3D2) were taken for modelling steel reinforcement. Concrete behavior was modeled by a plastic damage model. Two failure modes, tensile damage and compressive damage were assumed in this model. Concrete damage plasticity model in ABAQUS CAE 2017 was used in simulation of concrete behavior of beam column joint. The average compressive strength of controlled and strengthened test specimens after 28 days is 49.6 MPa and 70.19 MPa, the tensile strength of test specimens after 28 days is 5.39 MPa and 11.13 MPa. These compressive and tensile strengths are utilized to find the stress strain performance of concrete. The Modulus of elasticity and poisons ratio for concrete used are 35.2 GPa, 41.98 GPa and 0.2 respectively. The Modulus of elasticity and poisons ratio for steel used are 210 GPa and 0.3 respectively. The stress strain behavior of concrete follows the simplified form of equations given by Desayi and Krishnan [8] and Carreira and Chu [9]. 𝑓 𝑓𝑜 = 𝑅( ∈ 𝜖𝑜 1+(𝑅−1)( ) , Where R = ∈ 𝛽 ) ∈𝑜 𝐸𝑐 𝐸𝑜 , 𝛽= 𝑅 ( 𝑅−1 ) By using the simplified form of Desayi and Krishnan and Carreira and Chu equations the Stress (vs) Strain curves of compressive and tensile behavior of concrete are plotted as shown in Fig 4. Concrete damage plasticity parameters adopted for present work are given in Table 2. 80 Stress (MPa) Stress (MPa) 15 10 5 60 40 20 0 0 0 0.001 0.002 0.003 0.004 0.005 0.006 0 0.007 0.001 0.002 with replacement 0.003 0.004 0.005 0.006 Strain Strain without replacement without replacement With replacement Figure 4 Stress (vs) Strain curve for tension and compression Table 2 Concrete damage plasticity parameters Dilation angle 31 Eccentricity 0.1 𝒇𝒃𝒐 /𝒇𝒄𝒐 1.16 K 0.6667 Viscosity parameter 0 4.2. Modeling in ABAQUS The BCJs were modeled in ABAQUS CAE 2017 software by means of the above type of elements and material properties [10]. Two groups having a total of eight beam column joints are modeled in Abaqus. An axial load is made to act on the column with fixed support at bottom and hinged support at top. On the beam a load is applied from a distance 100 mm from the cantilever end. The models are analyzed with cyclic loading. The reinforcements are as shown from Fig 5. http://www.iaeme.com/IJCIET/index.asp 705 editor@iaeme.com Behavior of Exterior R.C Beam Column Joint with Strengthened Concrete and Diagonal Cross Bracings Figure 5 Reinforcement as per IS 456 and as per IS 13920 with and without bracing 5. RESULTS AND DISCUSSION 5.1. Validation of Analytical results with Experimental results Ultimate load and deflection of casted BCJ with reinforcement details as per IS 456 :2000 are obtained as 39.38 kN and 25.9 mm respectively. Ultimate load and deflection results obtained from ABAQUS are 42.9 kN and 27.88 mm. The variation in results of load and deflection are 8.93% and 7.645%. The variation between experimental and analytical results are within the acceptable limits. 5.2. Load and deflections of Beam column joints The Yield load, Ultimate load, Yield displacement and Ultimate displacements of the BCJs of the two groups attained from Finite Element analysis by using ABAQUS CAE 2017 software. The obtained results are given in Table 3 and the load deflection curves are shown in Fig 6. Table 3 Load and Displacements of Beam Column Joints Specimen Yield Load (kN) S1 S2 S3 S4 V1 V2 V3 V4 5.18 6.30 6.85 7.14 5.92 6.23 8.42 9.36 Ultimate Load (kN) 42.9 48.6 53.2 56.4 44.6 51.5 56.9 61.3 Yield Displacement (mm) 8.68 8.48 7.96 7.78 7.92 7.75 6.94 6.74 Ultimate Displacement (mm) 27.88 29.8 32.5 36.8 32.9 36.4 39.6 41.8 70 Load (kN) 60 50 40 30 20 10 0 0 5 10 15 20 25 30 35 40 45 Displacement (mm) S1 S2 V1 V2 S3 S4 V3 V4 Figure 6 Load vs Displacement curves http://www.iaeme.com/IJCIET/index.asp 706 editor@iaeme.com 50 Nandhigam Vijayaprasad and Aditya Kumar Tiwary 5.3. Effect of strengthening of concrete and provision of diagonal cross bracings Two group BCJs are modelled using ABAQUS with reinforcement detailing as per IS 456 and IS 13920 with and without strengthening of concrete and also with and without provision of diagonal cross bracings. The support conditions and Loading conditions are kept same for all the modelled specimens so as to find out the variations in different parameters. The results for two groups of beam column joints obtained are shown from Fig 7 to Fig 14. Figure 7 Strain vectors, Stresses in reinforcement, Displacement and Mises Stresses in S1 Figure 8 Strain vectors, Stresses in reinforcement, Displacement and Mises Stresses in S2 Figure 9 Strain vectors, Stresses in reinforcement, Displacement and Mises Stresses in S3 Figure 10 Strain vectors, Stresses in reinforcement, Displacement and Mises Stresses in S4 In Group-1 beam column joints the Mises stresses are decreasing from S1 as 10.68% ,20.05% ,23.52% for specimens S2, S3, S4 respectively. Variation in displacements for http://www.iaeme.com/IJCIET/index.asp 707 editor@iaeme.com Behavior of Exterior R.C Beam Column Joint with Strengthened Concrete and Diagonal Cross Bracings specimens S2, S3, S4 from S1 are 15.32 %, 17.86%,19.36% decrease respectively. The strain decrement for specimens S2, S3, S4 compared to S1 are 70.2%,71.23%, 75.88% correspondingly. Figure 11 Strain vectors, Stresses in reinforcement, Displacement and Mises Stresses in V1 Figure 12 Strain vectors, Stresses in reinforcement, Displacement and Mises Stresses in V2 Figure 13 Strain vectors, Stresses in reinforcement, Displacement and Mises Stresses in V3 Figure 14 Strain vectors, Stresses in reinforcement, Displacement and Mises Stresses in V4 For Group-2 beam column joints the Mises stresses are decreasing from V1 as 11.14% ,32.28% ,43.52% for specimens V2, V3, V4 respectively. Variation in displacements for specimens V2, V3, V4 from V1 are 17.74 %, 35.4%,37.2% decrease respectively. The corresponding strain decrement for specimens V2, V3, V4 compared to V1 are 78.9%,79.6%, 81.4%. http://www.iaeme.com/IJCIET/index.asp 708 editor@iaeme.com Nandhigam Vijayaprasad and Aditya Kumar Tiwary 5.4. Energy dissipation capacity The Force-Displacement hysteretic loops for beam column joint modelled specimens of two groups are obtained from ABAQUS CAE 2017. The capacity to dissipate energy of all the BCJs was obtained from the enclosed area of the load deformation curves. The Energy dissipating capacities for different BCJs are represented in the Fig 15. Beam column junctions with additional diagonal cross bracings shows better energy dissipation compared to the beam column junctions with conventional reinforcement. Column axial load helps in dissipating the energy for beam column joints with diagonal cross bracings. V4 V3 V2 V1 S4 S3 S2 S1 S1 S2 S3 S4 V1 V2 V3 V4 5.7 6.2 ENERGY DISSIPATION KN-MM 8 3877.24 2269 2065.3 3728.64 2591.8 1792.8 1214.28 0 2000 4000 5304.48 6 4 2 4.73 4.15 4.69 4.08 3.21 3.51 0 6000 DUCTILITY FACTOR Figure 15 Energy dissipation capacity and Ductility Factors of Different Beam column Joints 5.5. Ductility factor Ductility is very important property for any structural element, as it is the ability for any structural member to endure deformation preceding the yielding limit with out trailing much of its strength. Ductility factor is used to scale the ductility in any structural member. Generally, it is defined as the ratio of deflection caused at ultimate point to the deflection at yielding point. Ductility factors for different specimens are represented in Fig 15. Ductility Factor, 𝜇∆= ∆𝑈 ⁄∆𝑦 The ductility factor of S2, S3, S4 has a respective increment of 9.35%,27.1%,47.4% compared to specimen S1 in Group-1 and similarly for specimens V2, V3, V4 has an increment of 13%,37.35%,49.4% compared to specimen V1. Hence the provision of diagonal cross bracings improves the ductile property of the structural member. 6. CONCLUSIONS In this paper R.C exterior BCJs are analyzed using Finite element analysis software ABAQUS and following conclusions are obtained from this work. • In loading condition, reinforcement at beam column junction are under maximum stresses. The stresses in reinforcement are decreasing from S1 as 10.68% ,20.05% ,23.52% for specimens S2, S3, S4 and stresses are decreasing compared to V1 as 11.14% ,32.28% ,43.52% for specimens V2, V3, V4. Provision of diagonal cross bracings helps in reducing the stresses by transferring stresses uniformly to above and below column reinforcement. • The strain decrement for specimens S2, S3, S4 from S1 are 70.2% ,71.23%, 75.88%, similarly for specimens V2, V3, V4 compared to V1 are 78.9% ,79.6%, 81.4%. The diagonal cross bracings reduce the diagonal cracks in beam column joint and thus reducing the distortion of BCJs and maintaining structural integrity. • One reason for failure of BCJs is the loss of grip on reinforcement bars by concrete due to its limited strength. In this study with addition of GGBS and Glass fibers, concrete http://www.iaeme.com/IJCIET/index.asp 709 editor@iaeme.com Behavior of Exterior R.C Beam Column Joint with Strengthened Concrete and Diagonal Cross Bracings • • strength is increased by 41.51% with respect to conventional concrete and it was perceived that Strengthening of concrete helps in improving the BCJ structural performance. Ductility factor of S2, S3, S4 has a respective increment of 9.35%,27.1%,47.4% compared to specimen S1 and similarly for specimens V2, V3, V4 has an increment of 13%,37.35%,49.4% compared to specimen V1. From this work it was observed that by providing diagonal cross bracings and strengthening of concrete increases energy dissipating capacity and ductile property of beam column joints. BCJs with diagonal cross bracings and strengthened concrete exhibits better performance compared to BCJs with conventional reinforcement detailing and conventional concrete. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] Bindhu, K. R., P. M. Sukumar, and K. P. Jaya. "Performance of exterior beam-column joints under seismic type loading." ISET Journal of Earthquake Technology 46.2 (2009): 47-64. Anusree Lal.” Analysis of Exterior Beam Column Joint Using ANSYS.” International journal of science and research. Vol. 5, no. 7 (2016), pp. 2013–16. Feroldi, Francesca, and Salvatore Russo. 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