FLEXURAL STRENGTHENING OF REINFORCED CONCRETE BEAM WITH FERROCEMENT

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1 FLEXURAL STRENGTHENING OF REINFORCED CONCRETE BEAM WITH FERROCEMENT S. P. Shang*, Hunan University, China L. O. Zeng, Hunan University, China H. Peng, Hunan University, China 28th Conference on OUR WORLD IN CONCRETE & STRUCTURES: August 2003, Singapore Article Online Id: The online version of this article can be found at: This article is brought to you with the support of Singapore Concrete Institute All Rights reserved for CI Premier PTE LTD You are not Allowed to re distribute or re sale the article in any format without written approval of CI Premier PTE LTD Visit Our Website for more information

28 th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 28-29 August 2003, Singapore FLEXURAL STRENGTHENING OF REINFORCED CONCRETE BEAM WITH FERROCEMENT S. P. Shang*, Hunan University, China L. O. Zeng, Hunan University, China H.

2 28 th Conference on OUR WORLD IN CONCRETE & STRUCTURES: August 2003, Singapore FLEXURAL STRENGTHENING OF REINFORCED CONCRETE BEAM WITH FERROCEMENT S. P. Shang*, Hunan University, China L. O. Zeng, Hunan University, China H. Peng, Hunan University, China Abstract Ferrocement is a type of thin layer to reinforce concrete construction, where usually hydraulic cement is reinforced with layers of continuous and relatively small diameter steel wire mesh. Recently ferrocement technology is becoming more and more attractive in housing construction. This paper deals with the response of ferrocement thin plates reinforced with wire meshes as flexural strengthening material for reinforced concrete beams. Experiments in the study involve testing of 16 RC beams strengthened in flexure with ferrocement and 2 control specimens without being strengthened. Strengthening results of ferrocement reinforced with U-shape (ferrocement cast onto the tension face and two profile faces) have been analyzed. Mid-span deflection, crack width and strains in the steel are measured during the course of the tests. Performance of the tested beams is presented and discussed in this paper. The test results confirm that ferrocement contributes greatly to increase of the flexural capacity, raise of crack-resisting capacity and improvement of the bending stiffness of RC beams. This paper uses nonlinear analysis method to obtain the whole load-deflection curves for RC beams. The theoretical curves show a good agreement with the experimental curves of the tested beams. Keywords: R C beams; Ferrocement; Strengthening; Flexural strength; Nonlinear analysis 1. Introduction Deterioration of reinforced concrete structures due to corrosion of the steel rebars or continual upgrading of service lodas (increase of the traffic load on bridges for example) has resulted in a large number of structures requiring repairing or strengthening. A number of techniques have been used in the past. In the case of concrete structures, these techniques include: strengthening with steel reinforcing plate, bonding with carbon fiber and strengthening with prestressed. These methods have showed that post build strengthening can be successfully achieved and is usually feasible and economical. Recently, Ferrocement technology is becoming more and more attractive in housing construction, which is made of high grade mortar reinforced with layers of fine steel wire meshes[1 l. The use of precast ferrocement elements in construction will reduce the cost and labor force substantially. With the industrialized building systems, the components can be mass-produced and hence, the method reduces the overall construction time. Principal advantages of ferrocement over FRP sheets include fireproof without epoxy-bonded and flexibility in its use. Another significant advantage of this repair technique is that overall repair cost in terms of labor, material and equipment is low and can offset the high material cost. A global perspective of research on ferrocement has recently been 501

3 presented. The work of Logan[2] et al. dealt with flexural strengthening with ferrocement. The results show that ferrocement has obvious effects on raising the load-bearing capacity and crack-resisting capacity. The model for the contribution of composites to flexural capacity is based on methods used for conventionall~ reinforced concrete. Basnnbnl ] et al. tested retangular beams using ferrocement, and observed that beams exhibited superior cracking behavior, increased rigidity and had enhanced structural capacity. However, ductility was reduced. Ong[4] et al. investigated the flexural behavior of retangular beams strengthened with 20-mm-thick ferrocement laminates. Methods of attachment of the ferrocement laminate using epoxy resin dahesive, anchor bolts, and power-driven concrete nails were examined. The strengthened beams show greater stiffness, higher ultimate flexural capacity, and reduced crack spacings and widths at all load levels. In another study, P.Paramasivam[5] et al. carried out an extensive series of experiments on RC T-beams strengthened with ferrocement laminates attachment to the tension face. The results show that use of closely spaced shear connectors and proper surface preparation leads to improved serviceability and flexural capacities. Mothana Ahmed AI-Kubaisy[6] et al. carried out an experimental investigation to furnish additional information on the flexural behavior of ferrocement-strengthened RC beams. In that study, it can be seen that strengthening or repairing with ferrocement applied to the tension face can significantly increase the ultimate strength of RC beams, and reduce the crack width and spacing. This study focuses on the application of ferrocement in the strengthening of reinforced concrete beams with U-shape (ferrocement cast onto the tension face and two profile faces) strengthened form. Total pieces of 18 specimens have been studied and their results have been analyzed and reported. Performances of the beams were compared and assessed with particular emphasis on cracking behavior, mid-span deflection, and ultimate strength capacity. Compared with the conventional reinforced concrete, ferrocement is reinforced in two directions; therefore, it has homogenous-isotopicproperties in two directions. Compared with the specimens without being strengthened, the strengthened specimens are significant in reduction of crack spacing and crack width, prevention of cover spalling even at large deflection, increase of the toughness, and considerable improvement in flexural capacity. 2. Experimental Program A total of eighteen reinforced concrete beams (100 x 180 x 2200-mm) were cast in the laboratory with the reinforcement. The beams were divided into two series, labeled A and B. Series A consisted of thirteen beams. In these beams, the bottom flexural reinforcement consisted of three 8-mm-diameter bars providing a total cross section of 151-mm 2. Series B consisted offive beams. This series consisted of three 10-mm-diameter bars providing a total cross section of 256-mm 2. All beams were reinforced with two 6-mm-diameter bars top. Stirrups made of 4-mm-diameter rods were used at a spacing of 100-mm in series A and 80-mm in series B to provide adequate shear reinforcement. Fig 1 shows the test arrangement and reinforcement details. The beams were cast in molds made of steel plate sides. Three 150mm concrete cubes and four 70mm mortar cubes were cast with each beam determining the compressive strength of the concrete and ferrocement mortar, respectively. P/2 1(j4~~;u{J1 Il ~ >I':)<-_~>~~~~~~~~~~~~+'_-_-_-_-_-_2""'2_.j<-0_-0_-~_-~_+._.-_-_-_-_-_-~_-_-_-_-_-J_>:_>I'--- ~ ~ l j100 I I 3<,610 I Fig 1. Geometric Details and Configuration of Test Beams Ferrocement was cast onto the tension face and two profile faces of the beams, and which is called U-shape. Square welded wire mesh was used to strengthen the beams. There were two kinds of steel wire mesh, which were different in the diameter of the wire. The wire mesh details are shown in Table 1. Thickness of the ferrocelllent laminate was 20mm, as seen in Fig 2(a). Denotation of cross section can be seen from Fig 2(b). 502

$5 303 371 Modulus of Elasticity (MPa) 1.8x10 5 1.8x10 5 Mo ar o co,- o ~=~C\I 20 20 H 100 H (a) 1 ~l~ ~0//; v~~ [j~~; ~~ ~;0. /' "'-.. I /i "--- b Asml Wire mesh Asm L-.!l-l As I I Fig 2.$

4 Table 1-Wire Mesh Properties Wire Diameter Mesh Name (mm) Weld mesh Weld mesh Aperture Yield Stren- Ultimate Str- (mm) oth (MPa) enoth (MPa) Modulus of Elasticity (MPa) 1.8x x10 5 Mo ar o co,- o ~=~C\I H 100 H (a) 1 ~l~ ~0//; v~~ [j~~; ~~ ~;0. /' "'-.. I /i "--- b Asml Wire mesh Asm L-.!l-l As I I Fig 2. Typical section of beams (b) h Table 2 gives the details of the tested beams. The varying parameters were determined by the layers of wire meshes, diameter of wire meshes and compressive strength of mortar. A1 and 81 were the control specimens, to which no ferrocement strengthening was applied. All beams were simply supported over a 2000mm and tested under monotonic loading. The load was applied using a 32-ton oil jack and spread into two point loads on the beams. The oil jack was placed under the mid-span of the beams. Three dial gauges were installed at two load points and mid-span of the beams to measure the deflections. Cracks were carefully observed and measured with the aid of a magnifying glass. To facilitate crack detection, the beams surfaces were painted white. Table 2-Detail of Test Beams Flexural Mortar Cube Concrete Series Beams Weld Mesh No. No. Reinforcement Mesh Name No. Strength Cube Strength Diameter (mm) (MPa) (MPa) A A2 8 Weld mesh A3 8 Weld mesh A4 8 Weld mesh A5 8 Weld mesh A6 8 Weld mesh A A7 8 Weld mesh A8 8 Weld mesh A9 8 Weld mesh A10 8 Weld mesh A11 8 Weld mesh A12 8 Weld mesh A13 8 Weld mesh Weld mesh B Weld mesh B4 10 Weld mesh B5 10 Weld mesh Results And Discussion Generally, the structural behavior of the strengthened beams is similar to the control beams. Failure in both cases was typical tension failure. Experimental results obtained from the tests for all the beams are summarized in Table 3. The table gives the loads at first cracking, at yielding of flexural reinforcement and at ultimate of beams. In Table 3, R1 is the ratio of the strengthened beam's first 503

5 cracking load to control beam's first cracking load, and R2 is the ratio of the strengthened beam's ultimate load to control beam's ultimate load. From table 3, it can be seen that strengthening the beams with ferrocement laminate improves the flexural strength by 18% to 68% in series A, and by 34% to 46% in series B, respectively. The results show that ferrocement has the obvious effects on raising the load-bearing capacity. Cracking load of beams in series A varied 1.25 and 2.25 times of that of the control beam. In series B, results of ferrocement-strengthened beams show that first-crack loads increase by 33% to 67% compared with control beam. In Fig 3, it is shown that the crack width and spacing of strengthened beams with U-shape ferrocement were reduced. "Ii a bl e 3-S ummary 0 f test resu I ts Beams No. First Cracking Yielding of Flexural Ultimate Load R1 Load (kn) Reinforcement Load(kN) (kn) R2 A A A A A A A A A A A A A A1 AS A6 Fig 3. Modality of some beams A7 504

6 Load-Deflection Curves for beams are shown in Fig. 4. The figure shows that mid-span deflection for all strengthened beams was lower than that of the control beams at given loads. And slope of curve for ferrocement-strengthened beams was smaller than that of the control beams. It is shown that ferrocement contributes greatly to improvement of the bending stiffness of RC beams ::::. ~ o...i 25 --A1 --A2 --A A5 230,._" -A.--A6.!o:: I~::. ~~ ~ -.-A7 9/ ~ ~~. ~~ Z'i._.,IV " / ~ / Il 5 :0",. yy /-, O+-~~~--~---.~--r-~-r~ o A1 ---A ~"~~~ " '" fy".~_.-. ~ ::::. -A.--A "0 f /~~ ----Y- A13 tl$ r 0 20.:I...I Iii J.,f,/ t //,l;./ 10 5, Fig !o:: :;30 f'. ~ , A-83.A.--4~ --82 ~...,A.----.~ / /-"'.- f i e ~25...I tv " ~ l I..' 15 ~", 'f' 10 'I ~ 5 if 0 0 l",'d I -span 10 D e 1m ectlon. 20( mm f5 Load-Deflection Curves of Some Beams 4.Non-linear analysis Ferrocement beams are more likely to be over-reinforced, and the reinforcement is more evenly dispersed as compared with conventionally reinforced beams[21. This paper uses nonlinear analysis method to obtain the whole load-deflection curves for RC beams. It is computed using the following assumptions: 1. The stain of reinforced, wire mesh and concrete are based on plane deformation assumption. Strains were assumed to be linearly distributed 2. No slid between concrete and steel 3. The bending stiffness of RC beam is the same along the lognitudinal direction of beam 4. Wire mesh stress-strain relationship is asm=esm'esm (Esm S Esm,u), a sm =fsy (los S loy) 5. Steel stress-strain relationship is as=es'es (EsSEy)' as = fy (los >Ey) 6. Concrete stress-strain relationship is a e = 2[(~)_(~)2] ao (0 SEe S Eo), a e =a O (Eo SEe S Eeu) Eo Eo where Eo=0.002, Ee,u = The ferrocement onto the two profile faces uses the coefficient of fj, whose expression is fj = 0.8~ from this study. b The analysis is outlined below: 505

7 h Ee he W enee <EO' E=-X a = ao[2(~) - (~)2] = ao[2(~x) - (~X)2] Eo Eo EOhe heeo Fe = foe abl dx =bifoe 00 [2(~x) -(~x)2]dx =biao(ehe _ e;he) eohe eohe eo 3e5 From equilibrium of internal forces, it can be got: L N = 0 =>Fe = E sesas + {3E smesmasm From plane deformation assumption, the following expressions are gained: _Ee = he ho -he Ee he h -he Es ho -he =>Es =TEe' Esm = h -he =>Esm = he Ee The calculating as follows: when E < Eo E < fy e 's E s b ( Eehe E;he) E A {3 E A lao = Es s s + Esm sm sm Eo 3Eo b1ao(se -3so)h; -3s;(EsAs + f3esmasm)hc +3s;(hoEsAs + f3hesmasm) = 0 From above two equations, it can be got: - B +.J B 2-4AC h = c 2A 2AhO + B -.JB2-4AC E s = _ B +.J B 2 _ 4AC e C (1) when fy ee > EO,Es < Es b100he - b1a O sohc = EsEsAs + {3E smesmasm 3s c b 1 a O(3Ee -eo)he 2 +3ec(EsAs + f3esmasm)he - 3Ec(hoEsAs + f3hesmasm) = 0 From above two equations, it can be got: e s - B +.J B 2-4 AC 2A (2) 2 Ah 0 + B -.J B 2-4 AC = --""'------,=====-- e C - B +.J B 2-4 AC 506

8 when b (Echc _ E;hc) = Eo 3Eo From above equation, it can be got: e6 (fyas + Pf syasm ) he when fy E >Eo,E >-, c s Es (3) b10 ohc - b10 0 E ohc = fyas + PfsyAsm 3e c From above equation, it can be got: 3E c (fyas + f3fsy A sm ) h = ---" '--- c b 1 o O ( 3E c - 3Ec) From (1)-(4), the relationship between mid-span deflection and load is clear. From Fig. 5, it can be seen that the theoretical curves show a good agreement with the experimental curves of the tested beams, especially before flexural reinforcement yielded Z.~ z,.~ :::.. 20.~----.~ :::.. 25.c'-"~/-- \ "0 r( -. "0 co.. co i 0 J! A...J,...J ~ / 01.. / II II.. -A--- 1 A2-Experimental result. -A--- 5 A4-Experimental result 5 I ---A2-Theoretical result --- A4-Theoretical result Z Z.- e :::.. r e :::><.., :::.. " p.-./' ~ ~~~\, 15 " Ii co.1.( "0 // 0 co ( '&-6...J Jt J 20 I J 10 if i A5-Experimental result 10 ". ---A7-Experimental result 5 : ---A5-Theoretical result 5 f --- A7-Theoretical result o o~~~~~~~~~~ o Fig. 5 Theoretical Load-Deflection Curves of Some Beams 507

9 Calculation An experimental investigation has been carried out to provide information on the flexural behavior of RC beams strengthened with U-shape ferrocement. From the study, the following conclusions may be drawn: 1. Strengthening with U-shape ferrocement applied to the tension face and two profile faces can significantly increase the ultimate strength of RC beams. 2. Results show that ferrocement has obvious effects on raise of crack-resisting capacity, increase of the number of cracks, and decrease of the crake width. 3. Ferrocement contributes greatly to improvement of the bending stiffness of RC beams. At given loads, the mid-span deflection for strengthened beams was lower than that of the control beams. 4. Increasing the surface steel wire mesh increases the load at which the first cracks occur, increases ultimate load, and increases bending stiffness of RC beams. 5. Through nonlinear analysis method to obtain the whole load-deflection curves for RC beams, the theoretical curves agree well with experimental curves of the tested beams. References [1] ACI Committee. "A Guide for the Design Construction and Repair of Ferrocement". ACI Structural Journal, 1988, 85(3): [2] Logan D. and Shah S.P.,"Moment Capacity and Cracking Behaviour of Ferrocement in Flexure".Journal of the American Concrete Institute, 1973,70(12): [3] Basaunbull A, Gubati A, AI-Sulaimani, et al. "Repaired Reinforced Concrete Beams". ACI Material Journal, 1990,87(4): [4] Ong, K. C., Paramasivam, P. & Lim, C.T.E. "Flexural strengthening of reinforced concrete beams with using ferrocement laminates". J.Ferrocement, 1992,22(4): [5] Paramasivam P, Ong K C G, Lim C T E. "Ferrocement Laminates for Strengthening RC T-beams". Cement & Concrete Composites, 1994, 16(2): [6] MothanaAhmed AI-Kubaisy, Mohd Zamin Jumaat. "Ferrocement Laminate Strengthens RC Beams". Concrete International, 2000, 22(6): Notation b =the width of cross section b 1 = the width of cross section after strengthened h =the height of cross section hi = the height of cross section after strengthened he = the compressive depth of cross section a o =the maximal compressive stress of concrete E 0 = the maximal compressive strain of concrete when a = a 0 Ee =the given compressive strain of concrete Fe =the composition of forces of compressive concrete Asm = the area of steel wire mesh on tension face Asm 1 = the area of steel wire mesh on two profile faces Esm =the stains of steel wire mesh E sm =the modulus of steel wire mesh elasticity As = the area of steel tension reinforcement E s =the strains at which tension reinforcement yielded E s =the modulus of tension reinforcement elasticity 508

Strengthening of Predamaged Reinforced Concrete Beams by Ferrocement Plates

Strengthening of Predamaged Reinforced Concrete Beams by Ferrocement Plates Research Article International Journal of Current Engineering and Technology ISSN 2277-4106 2012 INPRESSCO. All Rights Reserved. Available at http://inpressco.com/category/ijcet Strengthening of Predamaged