STRENGTHENING OF REINFORCED CONCRETE WIDE BEAMS USING STEEL PLATES WITHIN SHEAR ZONE

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 12, December 2018, pp , Article ID: IJCIET_09_12_092 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed STRENGTHENING OF REINFORCED CONCRETE WIDE BEAMS USING STEEL PLATES WITHIN SHEAR ZONE Dr. Ra'id Fadhil Abbas Civil Dep., Eng. College, Mustansiriyah Univ., Baghdad, Iraq Dr. Wisam Hulail Sultan Civil Dep., Eng. College, Mustansiriyah Univ., Baghdad, Iraq L. Jasim Jarallah Fahad Civil Dep., Eng. College, Mustansiriyah Univ., Baghdad, Iraq ABSTRACT The research involves experimental study for strengthening of R.C. wide beams using steel plates that are externally bonded on surface of beam sides under shear effect. Nine beams of mm were tested. The parameters of the study were plating ratio (ratio of plates area to side area of the beam within shear zone) (0 %, 33 % and 55 %), shear span to effective depth ratio (a/d) (2.5 and 4.2) and type of concrete (NSC and HSC). The results indicated that the presence of steel plates improves the shear cracking load (PR) and the ultimate shear capacity (Pu). The percentage of improvement in Pcr and Pu is larger as a /d increases and as compressive strength decreases. The improvement in Pu ranges from 8 % to 22 % for beams of 33 % plating and from 15 % to 33 % for beams of 55 % plating. Presence of steel plates in shear zone has not significant effect on load deflection response except at the advanced stages of loading where they make the response slightly stiffer. Strengthening by external steel plates reduces width of main failure crack and changes its pattern.the failure in some cases is accompanied with splitting some plates from the concrete surface. Increasing a/d ratio results in reducing Pcr and Pu, the effect for a/d ratio is smaller as ratio of plating is larger. Also, increasing a/d ratio makes the load deflection response softer especially in advanced loading stages. Using HSC improves Pcr and Pu, the effect is smaller as ratio of plating is larger. Using HSC improves the load deflection response and makes it stiffer especially in advanced loading stages. Keywords: wide beam, high strength concrete, shear, steel plates, bond, shear span to depth ratio editor@iaeme.com

2 Dr. Ra'id Fadhil Abbas, Dr. Wisam Hulail Sultan and L. Jasim Jarallah Fahad Cite this Article: Dr. Ra'id Fadhil Abbas, Dr. Wisam Hulail Sultan and L. Jasim Jarallah Fahad, Strengthening of Reinforced Concrete Wide Beams Using Steel Plates Within Shear Zone, International Journal of Civil Engineering and Technology, 9(12), 2018, pp INTRODUCTION AND RESEARCH SIGNIFICANT Wide beams or thick slabs are characterized by their large width which approximately equivalent to twice of their depth at least [1] [2]. Using wide beams is popular in one-way R. C. joist floors for constructional and architectural advantages [3]. They are frequently used as economical transfer elements where the total structural depth must be kept to a minimum. When wide beams are used, the time savings in construction due to the simplicity of formwork and reinforcement placement can significantly enhance the cost effectiveness of the overall project [4]. Also, wide beams are useful to reduce reinforcement congestion in column strip of flat slab system and for more controlling on deflection and cracking requirements in addition to their role in provision appropriate punching shear strength for this system without using drop panel nor increasing slab thickness. In this types of beams, shear effects are mainly controlling in failure of them and determination of their ultimate capacity, also their shear behavior is fairly different from shear behavior of ordinary beams because of smallness of depth to width ratio of this type of beams in comparison with the ordinary beams. Therefore, most researches that concern to this topic were concentrated on shear capacity of wide beams through determination the effective width used in computing concrete shear strength and role of stirrups in increasing the total shear strength through numerous published studies [1] [5] [4] [6] [7]. Sometimes, it is needed to increasing ultimate shear capacity and improving cracking behavior of R.C. beams so that they are adequate to carry the addition loads not account in their design or for more safety or to treatment the lack of control quality [8]. For this purposes, steel plates may be used as a technique to strengthen the structural members or to repair the damaged members through connecting the plates on surfaces of beams using adhesive materials or bolts [9] [10]. The adhesive provides a shear connection between the concrete and the plates to makes them behaves as composite member [11]. This type of strengthening is popular because of its availability, cheapness, isotropic material, easy to work, high ductility and high fatigue strength [12]. Many researchers studied the benefit of using the steel plates in improvement the shear behavior of ordinary beams with different techniques for connection way. The studies showed a good improvement can be obtained when this type of strengthening is used [13] [14]. The current study investigates the effect of using steel plates bonded on sides of beams within shear zone on behavior and shear capacity of R.C. wide beams with varying shear span to effective depth ratio and concrete strength type. 2. EXPERIMENTAL PROGRAM The experimental program consists of testing nine simply supported R.C. wide beams. All beams have an overall length of 1200 mm, a width of 220 mm and a depth of 110 mm (effective depth equals 90 mm). The parameters of the study are ratio of plates area to side area for beam within shear zone (the distance between load and support positions), shear span to effective depth ratio (a/d) and concrete compressive strength (f, ). All beams are longitudinally reinforced by 5 φ 10 mm at bottom layer and 2 φ 4 mm plain bars at top layer. All beams were editor@iaeme.com

3 Strengthening of Reinforced Concrete Wide Beams Using Steel Plates Within Shear Zone not transversely reinforced (without stirrups). Details of the beams and parameters of the study are illustrated in Table 1. Table 1. Detail s of the tested beams Beam Name a / d Strength type Ratio of covering plates B1 2.5 Normal 0 B2 2.5 Normal 33 % B3 2.5 Normal 55 % B4 4.2 Normal 0 B5 4.2 Normal 33 % B6 4.2 Normal 55 % B7 2.5 High 0 B8 2.5 High 33 % B9 2.5 High 55 % The main parameter is ratio of covering plates. Two ratios were used: 33 % and 55 %. The first ratio was made through bonding plates at 75 mm c / c between them (3 plates for beams of a/d = 2.5 as in B2 and B8 and 5 plates for beams of a/d=4.2 as in beams B5). While the second ratio was made through bonding plates at 45 mm c / c between them (5 plates for beams of a/d = 2.5 as in B3 and B9 and 8 plates for beams of a/d = 4.2 as in beams B6). Details of plates connected to beams sides are shown in Fig. 1. Figure 1. Details of steel plates externally bonded on beam sides 3. MATERIALS AND MIX PROPORTIONS Ordinary Portland cement (type I) and natural fine aggregate (sand) with 4.75 mm maximum size and crushed coarse aggregate (gravel) with 10 mm maximum size are used to produce the concrete used for casting beams of the study. Also, super plasticizer admixture were used to reduce water to cement ratio, then to get high strength concrete. Table 2 shows amounts of materials for one cubic meter of concrete for normal and high strength concrete mixes. The quantities were taken from some previous studies [15-17] with slight modifications editor@iaeme.com

4 Dr. Ra'id Fadhil Abbas, Dr. Wisam Hulail Sultan and L. Jasim Jarallah Fahad Table 2. Quantities of materials for one cubic meter of concrete Material Cement Sand Gravel Water Super plasticizer Normal Strength Conc. 400 kg 600 kg 1200 kg 200 liter High Strength Conc. 550 kg 700 kg 1000 kg 155 liter 10 liter 4. STEEL REINFORCING BARS Deformed steel bars are used in this work with nominal diameters of 10 mm for longitudinal reinforcement in tension side (bottom side) and plain bars of diameter 4 mm are used for longitudinal reinforcement in compression side (top side). Longitudinal reinforcement are connected to make cages of the specimens as shown in Fig. 2. The concrete cover for reinforced bars was 10 mm from all sides. The laboratory tensile tests on bars showed that the average yield stress for 10 mm bar was 576 MPa. Figure 2. Steel reinforcement cage 5. HARDENED MECHANICAL PROPERTIES RESULTS Table 3 shows test results of mechanical properties for hardened concrete. These properties are concrete compressive strength (fʹc), splitting tensile strength (ft) and modulus of rupture (fr). Each value presented in this table represents the average value of three specimens. Table 3. Tests results of mechanical properties for hardened concrete fʹc (MPa) f t (MPa) f r (MPa) Normal Strength Conc High Strength Conc STRENGTHENING TECHNIQUE Steel plates were used in this research for strengthening the wide beams by bonding plate pieces on two sides of the beams within shear zone. The dimensions of the plates were 110 mm height, 25 mm width and 1.25 mm thickness. The plates were bonded on the concrete using adhesive material (Sikadur 31 DW) with thickness about 2 mm. This material has adhesive strength about 3 N/ mm 2 at 7 days curing and at temperature 23 C and tensile strength about 23 N/ mm 2 at 14 days curing at the same temperature. The tests on beams were performed after two weeks from completing process of gluing the plates. Fig.3 and Fig.4 show pieces of plates and way of bonding them on beams sides. Yield tensile strength of the plates was 432 MPa according to the laboratory tests editor@iaeme.com

5 Strengthening of Reinforced Concrete Wide Beams Using Steel Plates Within Shear Zone 7. TESTS AND MEASUREMENTS OF BEAMS All beams were tested using a hydraulically universal testing machine of 3000 kn capacity under monotonic loads at the Structural Laboratory of the college of Engineering at Mustansiriyah University as shown in Fig.5. The beams are supported at distance of 1100 mm between supports. The load was applied by two line loads through two steel rods. The distance between the support and the load positions (shear span) is 225 mm for a/d = 2.5 and 375 mm for a/d = 4.2. Central vertical deflection is measured using dial gauge of (0.01 mm) accuracy as shown in Fig RESULTS OF TESTED BEAMS Table 4 summarizes results of first shear cracking load (Pcr), ultimate load (Pu), ratio between the two loads and percentages of increasing in them due to using steel plates. Beam Name a / d, MPa Table 4 Experimental results of tested beams Increasing in P cr Covering plates ratio P cr (kn) P u (kn) Increasing in P u P cr / P u B B % % % 0.4 B % % % 0.39 B B % % % 0.32 B % % % 0.33 B B % 33 3 % 77 8 % 0.43 B % % % editor@iaeme.com

6 Dr. Ra'id Fadhil Abbas, Dr. Wisam Hulail Sultan and L. Jasim Jarallah Fahad 9. DISCUSSION OF RESULTS 9.1. Failure Modes and Crack Pattern Fig.7 shows modes of failure and crack pattern for all tested beams. It is noted that all beams are failed in shear by diagonal splitting mode. The main crack is wider and more pronounced as a/d increases. Also the propagation of the main crack is more sudden in case of HSC beams. Presence of external steel plates reduces width of main failure crack and changes its pattern. In some beams, the main crack propagates between the plates especially in case of beams of 33 % plating as in beams B2 and B8. While in other beams, the main crack intersects the plates and causes splitting some plates from the concrete due to failure in bonding of adhesive material as shown in B3, B5, B6 and B9. The last picture of Fig.7 shows sample for splitting of plates from concrete surface. Splitting of plates indicates that the plates did not reach to its yielding stress. Figure 7 Pictures of failure modes and crack pattern 9.2. Effect of Steel Plates From Table 4, it is noted that the using steel plates to strengthen the concrete wide beams results in improvement in shear cracking capacity (Pcr) and this improvement is larger as ratio of editor@iaeme.com

7 Strengthening of Reinforced Concrete Wide Beams Using Steel Plates Within Shear Zone plating increases. This role is due to carrying these plates apart of shear stresses caused in beam, therefore, the stresses in concrete decreases and this results in delaying in appearance of the first shear crack. The percentage of increasing in Pcr due to presence of steel plates is larger as a /d increases and as compressive strength decreases. Maximum increasing in Pcr was 29 % in case of 55 % plating when a/d = 4.2 for NSC beam. Using steel plates improves the ultimate shear capacity (Pu) of the beams. The improvement is larger as ratio of plating increases. Presence of steel plate prevents the extending of main failure crack and thus it delays causing shear failure to upper load. The percentage of improvement in Pu due to presence of steel plate is larger as a /d increases and as compressive strength decreases. The improvement ranges from 8 % to 22 % for beams of 33 % plating and from 15 % to 33 % for beams of 55 % plating. Maximum increasing in Pu was 33 % in case of 55 % plating when a / d = 4.2 for NSC beam. Also steel plates slightly reduces the ratio (Pcr / Pu) for all types of beams as shown in Table 4. Fig.8 shows effect of steel plate s ratio on load- deflection response. It is concluded that presence of steel plates in shear zone has not significant effect on this response for all both types of concrete and for both values of a/d. The reason of this behavior because the side plates have very small influence on flexural rigidity due to their small effect on increasing moment of inertia where their positions were designed to improve the shear capacity rather than flexural capacity. The curves of beams are generally close to them with varying ratio of plating especially in earlier stages of loading. In advanced stages of loading, the curve is slightly stiffer with increasing ratio of platting due to the role of plates in arresting propagation of cracks and delaying occurrence of the failure. Also, the plates result in higher deflection at ultimate load. Figure 8 Effect of platting ratio on load deflection response 9.3 Effect of Shear Span to Depth Ratio (a/d) Table 5 shows effect of shear span to depth ratio on shear cracking capacity (Pcr) and ultimate shear capacity (Pu). It is noted that increasing a/d ratio results in reducing Pcr and Pu. Increasing editor@iaeme.com

8 Dr. Ra'id Fadhil Abbas, Dr. Wisam Hulail Sultan and L. Jasim Jarallah Fahad a/d ratio causes increasing the bending moment within shear zone and this leads to increasing tensile stresses on it, then the first crack appears at lower load and the failure occurs at lower ultimate load. Increasing a/d ratio causes reduction in Pcr ranges from 23 % to 31 % and in Pu ranges from 10 %to 18 %. This effect for a/d ratio is smaller as ratio of plating is larger. Therefore, maximum effect for a/d ratio is in case of non-plated beams (31 % reduction in Pcr and 18 % reductions in Pu). Plating case Table 5. Effect of a/d on Pcr and Pu a /d = 2.5 a /d = 4.2 Reduction in P cr (kn) P u (kn) P cr (kn) P u (kn) P cr Reduction in P u Non-plated % 18 % 33 % plated % 12 % 55 % plated % 10 % Fig. 9 shows effect of a/d ratio on load deflection response. It is concluded that increasing a/d ratio makes the response softer, i.e increasing this ratio leads to increase in deflection value. With progressing the loading, the difference in deflection values becomes larger. Generally. This effect for a/d ratio decreases with increasing plating ratio. Figure 9. Effect of a/d ratio on load deflection response editor@iaeme.com

9 Strengthening of Reinforced Concrete Wide Beams Using Steel Plates Within Shear Zone 9.4 Effect of Concrete Compressive Strength (, ) Table 6 shows effect of increasing concrete compressive strength (, ) on shear cracking capacity (Pcr) and ultimate shear capacity (Pu). It is noted that increasing (, ) improves Pcr and Pu. Increasing (, ) cause increasing in concrete ability to resist tensile stresses in shear zone and this leads to delaying appearance of first shear crack and makes the failure occurs at upper ultimate load. Increasing (, ) causes improvement in Pcr ranges from 32 % to 42 % and in Pu ranges from 22 % to 30 %. Generally, this effect for (, ) is smaller as ratio of plating is larger. Therefore, maximum effect for (, ) is in case of non-plated beams (42 % increasing in Pcr and 30 % increasing in Pu). Table 6. Effect of, on P cr and P u Plating case Normal strength High strength improvement in improvement P cr (kn) P u (kn) P cr (kn) P u (kn) P cr P u Non-plated % 30 % 33 % plated % 23 % 55 % plated % 22 % Fig. 10 shows effect of increasing (, ) on load deflection response. It is concluded that increasing (, ) makes the response slightly stiffer, i.e. increasing it leads to reducing in deflection value. With progressing the loading, the difference in deflection values becomes larger. Generally. This effect for (, ) is approximately similar for all values of plating ratio. Also, it leads to larger deflection at failure. in Figure 10 Effect of (, ) on load deflection response 10. CONCLUSIONS 1-All tested beams were failed in shear by diagonal splitting mode. Presence of external steel plates reduces width of main failure crack and changes its pattern. In case of low plating ratio, editor@iaeme.com

10 Dr. Ra'id Fadhil Abbas, Dr. Wisam Hulail Sultan and L. Jasim Jarallah Fahad the main shear crack propagates between the plates while in case of high platting ratio, the main crack intersects the plates and causes splitting some plates from the concrete surface due to failure in bonding of adhesive material. 2- Using steel plates in strengthening the beams results in improving shear cracking capacity (Pcr). The percentage of increasing in Pcr is larger as a/d increases and as compressive strength decreases. Maximum increasing in Pcr was 29 % in case of 55 % plating when a/d = 4.2 for NSC beam. 3- Using steel plates improves the ultimate shear capacity (Pu) of the beams. The percentage of improvement in Pu is larger as a /d increases and as compressive strength decreases. The improvement ranges from 8 % to 22 % for beams of 33 % plating and from 15 % to 33 % for beams of 55 % plating. 4- Presence of steel plates in shear zone has not significant effect on load - deflection response for both types of concrete and for both values of a/d. In advanced stages of loading, the curve is slightly stiffer with increasing ratio of plating due to the role of plates in arresting propagation of cracks and delaying occurrence of the failure. 5- Increasing a/d ratio causes reduction in Pcr ranges from 23 % to 31 % and reduction in Pu ranges from 10 % to 18 %. This effect for a/d ratio is smaller as ratio of plating is larger. 6- Increasing a/d ratio makes the load - deflection response softer especially in progressing loading stages. This effect for a/d ratio decreases with increasing plating ratio. 7- Using HSC in wide beams improves Pcr and Pu. Increasing (, ) from 33.8 to 64.1 causes improvement in Pcr ranges from 32 % to 42 % and in Pu ranges from 22 %to 30 %. Generally, this effect for (, ) is smaller as ratio of plating is larger. 8- Increasing (, ) makes load deflection response stiffer especially at advanced stages of loading. Generally, the effect for (, ) is approximately similar for all values of plating ratio. 9- Although the small depth of R.C. wide beams in comparison with ordinary beams, it is useful using steel plates to improve shear behavior of these types of beams in cracking and ultimate stages through connecting it on sides of beams within shear zone using good bonding material or bolts for connecting them to concrete surface. REFERENCES [1] S. E. Mohammadyan Yasouj, A. K. Marsono, R. Abdulah, and M. Moghadasi, Wide beam shear behavior with diverse types of reinforcement, ACI Structural Journal, 112 (2), 2015, [2] J. H. Haido and I. H. Musa, Cracking strength of steel fiber reinforced concrete shallow wide beams under impact actions, International Journal of Scientific & Engineering Research, 4 (4), 2013, [3] A. B. Shuraim and A. I. Al-negheimish, Design consideration for joist floor with wide shallow beams, ACI Structural Journal, 108 (2), 2011, [4] E. G. Sherwood, A. S. Lubell, E.C. Bentz, and M.P. Collins, One-way shear strength of thick slabs and wide beams, ACI Structural Journal, 103 (6), 2006, [5] M. Said, and T.M. Elrakib, Enhancement of shear strength and ductility for reinforced concrete wide beams due to web reinforcement, HBRC Journal, (9), 2013, [6] E. M. Lotfy, H. A. Mohamadien, and H. M. Hassan, Effect of web reinforcement on shear strength of shallow wide beams, International Journal of Engineering and Technical Research, 2 (11), 2014, editor@iaeme.com

11 Strengthening of Reinforced Concrete Wide Beams Using Steel Plates Within Shear Zone [7] E. O. L. Lantsoght, C. V. D. Veen, A. D. Boer, and J. C. Walrvan, Influence of width on shear capacity of reinforced concrete members, ACI Structural Journal, 111 (6), 2014, [8] M. Z. Jummat and Md. Ashraful alam, Strengthening of reinforced concrete structures, Overview Paper, Civil Eng. Department, University of Malaya, 50603, Kuala Lumpur, 1-4. [9] B. Sevim, Structural strengthening behavior of beam using steel plates, International Journal of scientific research and management, 5(2), 2017, [10] K. S. Swetha and R. M. James, Strengthening of R.C. beam with web bonded steel plates, International Journal of Engineering and Techniques, 4(3), 2018, [11] D. K. Eberline, F. W. Klaiber and K. Dunker, Bridge strengthening with Epoxy bonded steel plates, Transportation Research Record 1180, Bridge Engineering Center, Iowa State university, [12] E. M. Lotfy and W. Elkamash, Numerical study of R.C. beams strengthening by external steel plates, American Journal of Engineering research, 6(3), 2017, [13] K. A. Mosher and A. H. H. Hasson, Strengthening of reinforced concrete beam in shear zone by compensation the stirrups with equivalent external steel plates, Journal of Babylon University, 24(3), 2016, [14] S. A. Bhagat and J. P. Bhusari, Improving shear capacity of R.C. beams using epoxy bonded continuous steel plates, International Journal of Advanced technology in Civil Engineering, 2 (1), 2013, [15] M.H., Mohammed, Behavior of steel fiber reinforced self-compacting concrete slabs under one-way bending, Eng. & Tech. Journal, 33(6), 2015, [16] W. H. Sultan and R. F. Abbas, effect of longitudinal hollows on behavior and capacity of high strength reinforced concrete one way slabs, Civil and Environmental research, 9 (12), 2017, [17] H. I. Al Shaikhli and Kadhim Naief Kadhim "Development An Equations For Flow Over Weirs Using Mnlr And Cfd Simulation Approaches"(IJCIET), Volume 9, Issue 3, March 2018, pp editor@iaeme.com