INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET)

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1 INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET) International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 ISSN (Print) ISSN (Online) Volume 4, Issue 6, September October 2013, pp IAEME: Journal Impact Factor (2013): (Calculated by GISI) IJARET I A E M E BEHAVIOR OF TIMBER BEAMS PROVIDED WITH FLEXURAL AS WELL AS SHEAR REINFORCEMENT IN THE FORM OF CFRP STRIPS Javaid Ahmad 1, Dr. Javed Ahmad Bhat 2, Umer Salam 3 1 Graduate Student, National Institute of Technology, Srinagar 2 Associate Professor, National Institute of Technology, Srinagar 3 Graduate Student, National Institute of Technology, Srinagar ABSTRACT The aim of current study is to investigate the effect of tensile and shear reinforcement in the form of Carbon Fiber Reinforced Polymer (CFRP) composites on flexural behavior of timber beams. Five beams with cross section of 70mm x 120mm were tested, where one served as control beams (without CFRP strengthening). Timber species used in this study was Cedrus Deodara (Deodar). An experimental investigation was conducted on the behavior of FRP-reinforced wood section. The strength of timber beams was significantly improved upon combined flexural and shear strengthening with maximum percentage increase being 71.43%for Deodar beams. This study, in turn, led to an empirical procedure based on modification factors, suitable for application in the design of FRP reinforcement of existing timber beams under different configuration of strengthening materials applied. Keywords: Retrofitting, Fiber Reinforced Polymers, Flexural Strengthening, Timber Failures, Shear Strengthening, Ductility Index, Flexural Rigidity. 1. INTRODUCTION Rehabilitation of deteriorated civil engineering infrastructure such as buildings, bridge decks, beams, girders, marine structures, roads etc. has been a major issue in last decade. The deterioration of these structures might be due to aging, poor maintenance, corrosion due to unfavorable environmental conditions, poor initial design or construction and accidental situations like earthquakes. The need to upgrade the deteriorated civil engineering infrastructure is necessitated due to the ever increasing demand e.g. unprecedented loads on buildings which have not been considered in design and likewise. New technology options in rehabilitation are being developed from polymers, metals, ceramics and composites of these materials and some of these high performance materials are already being utilized in construction. While the concept of composites has been in existence for 153

2 several millennia, the incorporation of fiber reinforced polymer (FRP) is less than a century old. These composites combine the strength of fibers with the stability of polymer resins. Market penetration of timber and fiber composites within the construction industry will ultimately be determined by final cost. CFRP is more expensive. However, material cost alone is not the prime consideration for many applications using these materials. It is important to consider the total built cost rather than just comparing the material component costs with traditional materials but the costs of design, manufacture, fabrication and erection need to be considered as well. Building owners, when looking at new construction, have not given a great deal of consideration to long term rehabilitation methods, costs or effects on projected service. Although research has been done to strengthen timber using FRP, but the comprehensive analysis and design are not established in detail. This is one of the reasons why the application of FRP to timber is very limited. In the plate bonding or externally bonded technique, the FRP is situated on the external tensile surfaces of the concrete beam to improve the flexural strength or on the vertical surfaces of the beam to increase its shear capacity (Allbones, 1999) [3]. Arduini and Nanni (1997) have investigated plates in the form of flexible carbon FRP sheets, to be externally bonded to the concrete surfaces. The strengthening technology consisting of externally bonded CFRP sheets to concrete is easy to perform and significant improvement was found for ultimate load capacity and to a lesser extent in flexural stiffness. [5] Plevris and Triantafillou (1992) provided an analytical study of the short-term flexural behavior of timber beams and beam-columns reinforced on the tension face only with epoxy-bonded unidirectional CFRP sheets. This work demonstrated that even a small amount of fibers, as low as 1% of the cross-sectional area, of thin carbon FRP bonded to timber beams could result in a strength increase on the order of 60%. [18] There was another research done by Fiorelli and Antonio (2002) to evaluate the structural behavior of timber beams strengthened with FRP. The research was focused on the experimental and theoretical analysis of timber beams of the species Pinus Caribea Hondurensis which were reinforced with GFRP and CFRP fabrics. The results of this research showed that the flexural stiffness (EI) determined experimentally was greater than the theoretical values. These values are in favor of structural safety. It shows that the increase of stiffness varied from 15% to 29% for beams strengthened with glass and carbon fabric. The use of FRP provides better results in load capacity and in the vertical displacement of the beam. [9] Gentile et al. (2002) have investigated creosote-treated sawn Douglas Fir timber beams strengthened with GFRP bars. The beams were obtained from a dismantled bridge that was in service for over 30 years and were tested to obtain initial stiffness before strengthening. The percentage reinforcement ratios were between 0.27 and 0.82%. The results have shown that the failure mode has changed from brittle tension to compression failure. The flexural strength increased by 18 to 46%. [10] Buell and Saadatmanesh (2005) have conducted research on creosote-treated solid-sawn Douglas Fir strengthened with bidirectional CFRP fabric. The results show that applying carbon fabric to the timber beams provides significant increase in the bending and shear capacity, and nominal increase in the stiffness of the beams. The ultimate bending strength was increased between 40 to 53% and the horizontal shear strength was increased between 36 to 68%. [6] The present study focuses on application of pre-fab CFRP strips for flexural and shear strengthening of timber beams. The strips or plates are attached to beams by means of specified adhesive. The flexural tests are carried out on timber beams strengthened with CFRP in varying proportion with an object of studying the improvement in load carrying capacity, modulus of rupture, flexural rigidity and ductility of these beams. However, the scope of this study is limited to seasoned dry timber only which infers the applicability of research findings to beams used in dry condition or in the interior of structure. 154

3 The timber species used in this research is Cedrus Deodara commonly known as Deodar. It is being widely used in upper northern region (primarily Jammu and Kashmir) of India for structural purposes due to its prime availability in this region. Besides, this it is having good mechanical properties as compared to other timber species found in northern region of India. Having been widely used in structures constructed decades ago, it has become necessary to rehabilitate the timber structures which have suffered damage. Leaving the application of conventional rehabilitation techniques aside, we are left with application of fiber composites as best alternatives for rehabilitation of these structures. So, research has been conducted at National Institute of Technology, Srinagar (NIT Srinagar) to study the feasibility of utilizing CFRP for rehabilitation or design of new structures using Deodar. 2. METHODOLOGY This section describes features of beam specimens, beam designation, loading equipment, instrumentation and testing schemes. In the present study, ten timber beams were prepared for testing among which eight beams were strengthened using CFRP Plates of different widths. The beams without strengthening served as control beams and used as reference level for checking improvement in properties of strengthened timber beams. As already mentioned timber species utilized for beams is Cedrus Deodara. The ultimate tensile strength and modulus of elasticity of specimens of Deodar were observed to be 35 MPa and 10 GPa respectively. The typical geometry and testing arrangement is shown in Fig1. 480mm P P 480mm 70mm 120mm 1524mm CFRP Strip Shear Reinforcement Fig 1: Flexural Test Loading Arrangement The properties of materials used are summarized in Table 1 whereas beam designations are shown in Table 2. Table 1: Material Properties Property Deodar CFRP Ultimate tensile strength, N/mm 2 Ultimate tensile strain, % Tensile modulus of elasticity, KN/mm

4 Beam Designation Width, mm Control Beam - D - FPD-S FPD-S FPD-S FPD-S Table 2: Beam Designation Flexural Reinforcement Shear Reinforcement Thickness, Area of Depth, Thickness, mm CFRP, mm mm % Span of Beam, m B f = 30mm B f = 40mm B f = 50mm B f = 70mm A CFRP = 0.36% A CFR RP = 0.47% A CFRP = 0.59% A CFR RP = 0.83% Fig 2: Graphical representation of Beam cross-sections Reinforcement was used in the form of CFRP strips of varying widths applied on the bottom face and sides of the beams using adhesive(fig 2). The CFRP sheets were supplied by GSP Superb Technology (India), a New Delhi based supplier who imports it from Korea. The mechanical properties of CFRP are shown in Table 1. Strengthened beams were provided with a single strip of CFRP of thickness 1mm and different widths in all specimens varying from 30mm to 70mm. The tests were carried on beam models in a loading frame of capacity 500KN. Prior to testing dial gauges were set up at mid span and two alternate points. The loading was applied by means of hydraulic jack till failure and deflections were noted every 4KN interval load. The failure pattern was studied for each beam discussion regarding which is given afterwards. Fig 3 shows schematics of flexural testing. (a) Front View (b) Side View Fig 3: Testing Arrangement 156

5 3. RESULTS AND DISCUSSIONS The results from laboratory testing for the strengthened beams are compared with control beam (un-strengthened) in order to study the behavior of strengthened timber beams in terms of load carrying capacity, bending strength, stiffness and ductility. In addition, the modes of failure for all beams have been studied and discussed. 3.1 Unstrengthened Beam An unstrengthened timber beam (Deodar) was tested under two point loading. This is to determine the initial bending stiffness whilst in the elastic zone. The Deodar Control beam started to behave non-linearly when the load was 16.6 kn and the corresponding deflection was 10.5 mm. The failure load was 29.05KN for Deodar Control Beam. Any non-linearity in the behavior of timber beam was due to plasticity in the compression zone and the level of plasticity will determines whether the beam fails in compression or otherwise. Fig 4shows load versus deflection at mid-span of control beam for every 4 kn load interval. It is clear that all beams exhibited linear elastic as expected. The gradients of the lines were determined from which the stiffness of the beams can be calculated. This was done so that the uniformity of initial stiffness could be judged. Table 3 contains other properties of control beams. Moreover, Fig 5 shows failure pattern of control beam Load, KN Control Beam Deodar Midspan Deflection, mm Fig 4: Load Deflection Curve for Control Beams Table 3: Control beam test results Deodar Control Beam Failure Load, P u, KN Maximum Midspan Deflection, δ u, mm 23 Flexural Rigidity, EI, KNm Modulus of Rupture, N/mm

6 Fig 5: Failure Pattern of Control Beam 3.2 Strengthened Beams The beams were tested under two point loading until failure. For comparison purposes, the results of load-deflection curves for all beams are plotted. Main discussion from curves focuses on load carrying capacity, bending strength, stiffness and ductility of the strengthened beams relative to the un-strengthened beams (control beams). In addition deflection, crack patterns and failure behavior are also discussed. In general, all control beams and strengthened beams behaved linearly elastic initially and as the load increased, the flexural cracks increased in number, width, and depth, and the beams tend to behave non-linearly until failure. There are some slight drops observed in some of the curves as a result of internal cracking of the beam, which is hardly recognized through the observation with eyes and ears. All figures clearly indicate that all the strengthened beams have higher ultimate load carrying capacity than control beam. When there is significant failure, the corresponding load will be taken as ultimate load carrying capacity. Besides that, the strengthening beams with FRP also enhance the flexural stiffness. In other words, the strengthened beams experienced lower deflection than the un-strengthened control beam at the same load level. This low deflection phenomenon is desirable in the aspect of serviceability limit state in design to ensure comfortability of timber structures. In timber design, generally the deflection will govern the design. Beams were strengthened using CFRP plates with of thicknesses 1mm and four different widths i.e. 30, 40, 50 and 70 mm. The span of Deodar beams was 1.524m. In this study, the same control beam was used for comparison. The beams were tested and the graphs of load versus midspan deflection were plotted in Fig Load, KN Midspan Deflection, mm Control Beam Deodar FPD-S-30-1 FPD-S-40-1 FPD-S-50-1 FPD-S-70-1 Fig 6: Load Deflection curves for Deodar beams strengthened using CFRP 158

7 The behavior exhibited by beams under combined flexure-shear tests is similar to that of beams provided with only tension reinforcement but these differ in the level of improvement in terms of strength stiffness and ductility. It is observed that providing flexural and shear reinforcement does not improve the behavior to the desired level as observed in earlier tests. Beam FPD-S-30-1 starts to behave non-linearly when the load was 14.11KN and corresponding mid span deflection was 8.78mm. This point was the limit for proportionality and then beam shows non-linear behavior where from the stiffness decreased gradually. When the load was increased to kn, the mid span deflection was mm, beam stopped to take any extra load, however no de-bonding occurred. Beyond 39.01KN, the load decreased abruptly. A tensile crack occurred with impressions on CFRP strip acting as shear reinforcement. Shear cracks were restrained by virtue of shear reinforcement. In fact, this beam failed in tension. The CFRP plate was not ruptured indicating that the yield or ultimate stress was not reached. For beam FPD-S-40-1 the proportionality limit was 16.6 kn which was slightly higher compared to beam FPD-S This beam has shown good performance at the beginning of the testing where the slope of the curve was greater than the slope for beam FPD-S-301. When the load was increased to kn, there was large deflection of 29.1mm in the beam and failure took place. It is very common to timber beams that when the beam fails in tension, the compression fiber fails too and vice versa due to large deflection. Thus, by increasing the CFRP area, it helps the beam to reduce the serious crack but the strengthened area was not sufficient to prevent the beam from tension failure. When compared to FPD-40-1 the failure load was 41.5KN. The increase in load capacity in FPD-S-40-1 was due to presence of shear reinforcement which prevented the shear cracks and thus increased the load capacity. In this case the main function of CFRP plate as shear reinforcement was to prevent shear cracks and that of CFRP plate as tension reinforcement was to share the stress at the tension fiber and reduced the deflection and to delays the formation of tensile crack. In this test, the beam failed in tension. There was no de-bonding of the plates. When the beam was strengthened with more area of CFRP plate such as beam FPD-S-50-1, the load-carrying capacity was increased to 49.8KN. The cracks occurred at the beam corner at midspan where the maximum bending stress occurred. Corners or edges are weak zone for timber beams. Hence, the cracks were considered not serious because the main timber fibers were not cracked. The beam failed at the ultimate load 49.8KN. At failure, de-bonding occurred between CFRP plate and the beam surface. It seems that the maximum tensile and compressive capacity of timber was fully utilized. The tensile strength of CFRP plate was too high relative to the tensile timber capacity, hence the CFRP plate was not fully utilized. Beam FPD-S-70-1 was strengthened using wider and thicker section where the cross section dimension was 70 mm by 1 mm. The proportionality limit was kn. The beam started to crack when the load reached at 33.2 KN, however the cracks were prevented to propagate to wider area by the help of CFRP plate and shear reinforcement. The tensile cracks were small and only the bottom layer at midspan was affected. The total failure occurred at the ultimate load of 41.5 KN. It very obvious that the compression zone has reached it ultimate capacity. Any CFRP area of more than 0.59% of beam cross section will not give enhancement to the ultimate capacity unless the compression zone is strengthened. Thus, when the beam was strengthened using more area or wider plate, the ultimate load as well as the slope of load-deflection curve was increased and the failure mode was changed from tension to compression. The application of CFRP plate as shear reinforcement in addition to tension reinforcement gives advantage where failure occurs due to shear cracks. Besides, the presence of shear reinforcement increases the load carrying capacity relative to beams with tension reinforcement alone. 159

8 3.2.1 Effects on Load Carrying Capacity The load carrying capacity of all beams is shown in Table 4. The strengthened beams have greater load carrying capacity when compared to control beam only up to a limit beyond which it decreases. Generally, the ultimate and service load carrying capacity was increased as the percentage of CFRP increased up to CFRP area of 0.59%. The ultimate load was increased significantly when the percentage of CFRP plate was 0.36%. This percentage was considered small when compared to beam cross section but the strength achievement was very encouraging where the increase in ultimate load was 34.28%. The highest increment for ultimate load among these beams was 71.43% i.e. when the beams were strengthened using 0.59% of CFRP. Table 4: Load carrying capacity of Deodar beams provided with flexural and shear reinforcement Beam Ultimate Midspan Increase in Area of Load Deflection, Load CFRP P (%) u δ u Capacity (KN) (mm) (%) Control Beam- D FPD-S FPD-S FPD-S FPD-S To get a better and clearer understanding regarding this relationship, ultimate loads were plotted against percentage area (tensile reinforcement) of CFRP as shown in Fig 7. The relationship is not linear. When the beam was strengthened using more than 0.59% CFRP, it would not enhance the load carrying capacity as the compression zone has achieved maximum capacity. Thus, it can be concluded that the beam experiences over-reinforced if the percentage of CFRP is greater than 0.59%. This is clearly shown by the curve in Fig Load, KN Load Vs CFRP Area Tensile Reinforcement Area, % Fig 7: Load Vs Area of tension reinforcement These results indicate that beams were over reinforced beyond FPD-S The increases the load carrying capacity for this beam was 71.43%. In summary, the load carrying capacity of the strengthened Deodar beams increases between % to 71.43%, when the CFRP area is between 160

9 0.36% to 0.59%. Beyond CFRP area of 0.59% the beams showed decrease in load carrying capacity owing to compression failure of over reinforced section Effects on Flexural Rigidity (EI) The flexural rigidity of beams strengthened using CFRP plate are tabulated in Table 5. Generally, the flexural rigidity was increased as the percentage of CFRP plate increased up to a limit. It seems that strengthening using wider plate was efficient to enhance the stiffness. The effect of plate width can be confirmed by comparing beams FPD-S-30-1, FPD-S-40-1, FPD-S-50-1 and FPD- S Wider plate is more effective to prevent the initial crack at bottom layer because most of the tensile cracks started at the unstiffened portion. The flexural rigidity of the beams could be increased to 65% for Deodar, when the timber beams were strengthened using CFRP plate of area of 0.36%. Table 5: Effect of CFRP area on flexural rigidity of Deodar beams provided with flexural and shear reinforcement Beam Flexural Percentage of Increase in Rigidity, Modification CFRP Area, EI, EI, Factor % KNm 2 % Control Beam-D FPD-S FPD-S FPD-S FPD-S Fig 8 shows the relationship between the flexural rigidity and the area of CFRP plates. The graph shows that there is decrease in flexural rigidity of beam when the area of CFRP exceeds 0.36%. It is observed that there is a limiting value for the elasticity after certain area of CFRP which pertains to optimum value for CFRP area Flexural Rigidity, EI, KNm Flexural Rigidity Vs Tensile Reinforcement Tensile Reinforcement, % Fig 8: Flexural Rigidity Versus CFRP Area 161

10 3.2.3 Effects on Ductility Beam FPD-S-50-1 was taken as a typical example for discussion of ductility. The Loaddeflection curve for the beam is shown in Fig 9. From the curve, the maximum elastic load and ultimate load, and the corresponding deflections were determined y = -3E-07x 6 + 4E-05x x x x x R² = Load, KN FPD-S-50-1 Poly. (FPD-S-50-1) Midspan Deflection, mm Fig 9: Load Deflection Curve for the beam FPD-S-50-1 In this study none of the CFRP plate has yielded because the yield strain for CFRP is higher than the yield strain of the timber. Hence the compressive zone of the timber will reach its yield point before CFRP. From the curve, the elastic deflection, and the ultimate deflection were e = mm, and u = mm, respectively. The curve was very smooth exhibiting no sudden crack or crush occurred. The total failure occurred when the deflection at mid-span was mm which is considered high. This value provides good performance in the ductility point of view where the people will have ample time to escape from the building before collapse. Using the same procedures mentioned earlier, the ductility indices were calculated based on energy methods and the summary of the results is shown in Table 6. Table 6: Ductility Index for Deodar beams provided with flexural and shear reinforcement Beam CFRP Energy Ductility index Area, % Elastic Ultimate Based on Energy W e W tot Nm or J Nm or J Control Beam - D FPD-S FPD-S FPD-S FPD-S The polynomial regression equations for the other beams are shown in Table 7. There was significant increase in ductility when the timber beams are strengthened using CFRP plates. Even 162

11 after ultimate failure, the beams still held together. By taking control beam as a reference, the highest ductility index based on energy method was 5.47 where the percentage increase was %. From these results, there is a relationship between the CFRP area and the ductility index. The relationship is shown graphically in Fig 10. The curves indicate that ductility index increases nonlinearly as the area of CFRP plates increased. When the area of CFRP is about 0.59%, we get maximum value for the ductility index and any increases in CFRP area beyond this value will not improve the ductility. 6 5 Ductility Index Ductility Index Tension Reinforcement, % Fig 10: Ductility index Vs Tension reinforcement Table 7: Polynomial Regression Equations of load deflection Curves of Beams Deodar Beams Control Beam-D y = x x x ; [R² = ] FPD-S-30-1 y = -9E-05x x x x x x ; [R² = ] FPD-S y = -5E-06x x x x x ; [R² = ] FPD-S y = -5E-07x 6 + 6E-05x x x x x ; [R² = ] FPD-S y = -7E-07x 6 + 8E-05x x x x x ; [R² = ] 4. CONCLUSIONS I. In general, the percentage increase in load carrying capacity in all these beams was found to be more than that in beams provided with flexural reinforcement only. II. The maximum increase in load carrying capacity was 71.43% when area of tensile reinforcement was 0.59%. III. The balanced reinforced occurred when the CFRP was about 0.59%. 163

12 IV. Ductility index obtained from energy method was observed to vary in the range for Deodar beams. V. The failure mode was debonding of CFRP plate in some cases. VI. Combined flexure-shear reinforcement is effective as compared to flexural reinforcement alone. VII. All beams in this study did not fail due to peel off and also no de-bonding occurred between CFRP plate and the bonding agent and between bonding agent and timber substrate because the bonding length for all beams (1.5 m) was sufficient. VIII. When FRPs were bonded to the timber, randomization of defects (e.g., timber knots and drying cracks) reduces the variability of properties and consequently increases the tensile strength. Other effect was that the "bridging effect" exerted by the FRP composite skin on the bonded timber also increases the tensile strength. IX. Although steel bars or plates are still used for strengthening works, but if high strength, modulus and ductility of FRP are used, the FRP could be the right choice provided the overall price is considered. 5. REFERENCES [1] A Borri, Dr M Corradi, Andrea Grazini (2003), FRP Reinforcement of Wood Elements Under Bending Loads. [2] Alann André and Robert Kliger, (2009), Strengthening Of Timber Beams Using Frp, With Emphasis On Compression Strength: A State Of The Art Review. The second international conference of International Institute for FRP in construction for Asia-Pacific Region. [3] Allbones, C. (1999). The Use of Pultruded Composites in the Civil Engineering and Construction Industry.Proceedings of Composites and Plastics in Construction Nov. Watford, UK, pp (5) 1-3. [4] A Yusof and A. L. Saleh, (2010), Flexural Strengthening Of Timber Beams Using Glass Fibre Reinforced Polymer Electronic Journal of Structural Engineering [5] Arduini, M. and Nanni, A. (1997).Behaviour of Precracked RC beams Strengthened with Carbon FRP Sheets. Journal of Composites for Construction. Vol. 1, pp [6] Buell, T. W. and Saadatmanesh, H. (2005). Strengthening Timber Bridge Beams Using Carbon Fiber. Journal of Structural Engineering. [7] Chaallal, O, Nollet, M. J. and Perraton, D. (1998). Shear Strengthening of RC Beams by Externally Bonded Side CFRP Strips. Journal of Composites for Construction. Vol. 2, pp [8] Dagher, H. J. and Altimore, F. M. (2005).Use of Glass-Fiber-Reinforced Polymer Tendons for Stress-Laminating Timber Bridge Decks.Journal of Bridge Engineering.Vol 10, pp [9] Fiorelli, J. and Dias, A. A. (2002). Evaluation of the Structural Behaviour of Wood Beams Reinforced With FRP. The 7th World Conference on Timber Engineering, WCTE Broughton, J. G. and Hutchinson, A. R. (2001).Effect of timber moisture content on bondedin rods.journal of Constr. and Building Materials. [10] Gentile, C., Svecova, D. and Rizkalla, S. H. (2002). Timber Beams Strengthened with GFRP Bars: Development and Applications. Journal of Composites for Construction. [11] Grace, N. F., Soliman, A. K., Abdel-Sayed, G.And Sale, K. R. (1998). Behaviour and Ductility of Simple and Continuous FRP Reinforced Beams. Journal of Composites for Construction. Vol. 2, pp [12] Halliwell, S. M. and Moss, R. (1999).Polymer Composites in Construction the Way Ahead.Proceedings of Composites and Plastics in Construction Nov. Watford, UK, pp (30)

13 [13] Horyna, T. Foschi, R. O. and Ventura, C. E. (2001).Response of Timber Bridge to Traffic Loading.Journal of Bridge Engineering.Vol 6, pp [14] Humphreys M.F, Francey K.L (2005), An investigation into the rehabilitation of timber structures with fiber composite materials. [15] Keble, J. (1999). Alternative Structural Strengthening with Advanced Composites. Proceedings of Composites and Plastics in Construction Nov. Watford, UK, pp (18) 1-8. [16] Kirn, Y. and Davalns, J. F. (1997). Delamination buckling of FRP layer in laminated wood beams. Journal of Composite Structures. Vol 37, pp [17] Micelli, F., Scialpi, V. and La-Tegola, A. (2005).Flexural Reinforcement of Glulam Timber Beams and Joints with Carbon Fiber-Reinforced Polymer Rods. Journal of Composites for Construction. [18] Plevris, N. and Triantafillou, T. C. (1992).FRP-Reinforced Wood as Structural Material. Journal of Materials in Civil Engineering [19] Plevris, N. and Triantafillou, T. C. (1995). Creep Behavior of FRP-Reinforced Wood Members. Journal of Structural Engineering [20] Radford, D. W., Goethem, D. V., Gutkowski, R. M. and Peterson, M. L. (2002). Composite repair of timber structures. Journal of Constr. and BuildingMaterials.Vol 16, pp [21] Saadatmanesh, H. and Malek, A. M. (1998). Design Guidelines for Flexural Strengthening of RC Beams With FRP Plates. Journal of Composites for Construction. Vol. 2, pp [22] Serrano et.al (2007), Technical Report, Design of safe timber structures. [23] Tingley, D. A., Gai, C. and Giltner, E. E. (1997). Testing Methods to Determine Properties of Fiber Reinforced Plastic Panels Used for Reinforcing Glulams. Journal of Composites for Construction. [24] Triantafillou, T. C. (1997). Shear Reinforcement of Wood Using FRP Materials. Journal of Materials in Civil Engineering.Vol 9, pp [25] ACI 440 (2002), Guide for the design of externally bonded FRP systems for strengthening concrete structures. [26] FIB Bulletin 14 (2001), Externally bonded FRP reinforcement in RC structures. [27] Italian National Research Council (2004).CNR-DT 200/2004. Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Existing Structures. Rome, Italy. [28] Dr. Salim T. Yousif, New Model of CFRP-Confined Circular Concrete Columns: Ann Approach, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 3, 2013, pp , ISSN Print: , ISSN Online: [29] A.S Jeyabharathy, Dr.S.Robert Ravi and Dr.G.Prince Arulraj, Finite Element Modeling of Reinforced Concrete Beam Column Joints Retrofitted with GFRP Wrapping, International Journal of Civil Engineering & Technology (IJCIET), Volume 2, Issue 1, 2011, pp , ISSN Print: , ISSN Online: [30] Javaid Ahmad, Seismic Evaluation & Retrofit Assessment of Jlnm Hospital, Rainawari Srinagar, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 4, 2013, pp , ISSN Print: , ISSN Online: [31] Shaikh Zahoor Khalid and S.B. Shinde, Seismic Response of FRP Strengthened RC Frame, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012, pp , ISSN Print: , ISSN Online: [32] Wani Ahmad and Javed Ahmad Bhat, Pre-Tensioned Precast Elements as a Replacement to Wooden Bracings in the Armature Cross Wall System: An Abstract Attempt to Revive the Forgotten Heritage, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012, pp , ISSN Print: , ISSN Online: