Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : CFRP

Punching Shear Resistance of Reinforced Concrete Flat Slabs Strengthened by CFRP and GFRP: A Review of Literature

Hadi N. G. Al-Maliki; Ali Al-Balhawi; Asma M. Ali

Engineering and Technology Journal, 2021, Volume 39, Issue 8, Pages 1281-1290
DOI: 10.30684/etj.v39i8.2011

Flat reinforced concrete (RC) slabs or plates are still widely used in buildings and are most popular in single or multiple story floor construction systems. This is due to the ease and speed of implementation as well as the continuous smoothness that is provided in relation to the locations of members. Flat slab systems have an inadequate shear strength in both directions. Thus, they are subjected to a shear failure at their intersections with columns, which results in the collapse of a larger part of the structure. Shear failure occurs due to many reasons including changing the functions of the facility, the technical errors in the design and implementation procedures, an increase in the load, deterioration of materials, and poor quality. The carbon fiber reinforced polymer (CFRP) sheets/strips and glass fiber reinforced concrete polymer (GFRP) are used as a composite section formulated when there is a structural deficiency. Strengthening by using CFRP and GFRP provide an improvement in the punching shear resistance in both directions as well as flexural strength, ductility, and hardness. They are more suitable for a practical use as a substitute for other costly and difficult approaches such as increase the cross-sectional area of columns and so on. This paper reviews the up to date studies of enhancing the shear resistance of flat slabs by CFRP/GFRP and discusses the used materials for strengthening flat slabs and the used methods, which are used to implement these materials. Also, a summary for the cited studies are stated and the possible future works are suggested.

Retrofitting of SCC Deep Beams With Circular Openings Using CFRP

Nabeel A. Al-Bayati; Dhiyaa H. Mohammed; Nawfal A. Abdul Jabbar

Engineering and Technology Journal, 2021, Volume 39, Issue 7, Pages 1092-1104
DOI: 10.30684/etj.v39i7.74

The main objectives of this study are: encouraging the production and use of  self-compacting  concrete,  use  of  materials  which  are  lightweight,  easy to  use,  and  highly  efficient  in  the  retrofitting  of  reinforced  concrete buildings. Six deep beams specimens (L= length of 1400mm, h= height of 400mm,   and   b=   width   of   150mm)   were   cast   using   self-compacting concrete.  The  location  of  the  openings  is  in  the  middle  of  assumed  load path.  Five  patterns  were  adopted  to  arrange  carbon  fiber  reinforced polymer (CFRP) strips. The cylinder compressive strength of the concrete was  approximately  equal  for  all  beams  and  was  about  (44  MPa)  at  28 days  age.  All  the  beams  have  the  same  steel  reinforcement  for  shear  and flexure. There have been many tests for fresh and hardened concrete. The reinforced  concrete  deep  beams  were  tested  up  to  (60%)  of  the  ultimate load of control beams to simulate degree of damage, and then released the load. After that,the beams were retrofitted using (CFRP) strips, and then the beams were tested to failure. The study was focused on determining the vertical mid-span deflection, ultimate load, the load that causes first shear and flexural cracks, and mode of failure. Theresults showed that, the best increase in the ultimate failure load was (27.27%) and achieved using the inclined  strips  pattern  and  the  pattern  of  vertical  and  horizontal  strips together.  Reduction  in  the  deflection  values  for  the  retrofitted  beams compared  to  the  control  beam  by  about  (12-13%)  due  to  restrictions imposed by CFRP strips and the epoxy.

Flexural Behavior of RC Beams Strengthened by NSM-CFRP Laminates or Bars

Ikram A. Saeed; Riadh Al-Mahaidi; Tareq S. Al-Attar; Basil S. Al-Shathr

Engineering and Technology Journal, 2018, Volume 36, Issue 4A, Pages 358-367
DOI: 10.30684/etj.36.4A.1

The strengthening and enhancing the structures represents an important aspect in the construction industry due to the growing need to increase the tolerability of origin to a specific level and within the required rehabilitation and maintenance work. This paper assessed the performance and effectiveness of the Near Surface Mounted (NSM) strengthening technique for the reinforced concrete beams. Three (140x260x2700 mm) reinforced concrete beams were strengthened in flexure with NSM strengthening systems using Carbon Fiber Reinforced Polymer (CFRP) strips, bars, and cement-based adhesive as a binding materials. The flexural behaviour of the beams was evaluated by testing the specimens under three-point loading to failure. The structural performance, deflection, ductility, stiffness, and modes of failure of the tested beams are presented and discussed in this paper. The test results indicate that using NSM-CFRP strips and bars is practical and significantly improves the stiffness and increases the flexural capacity of reinforced concrete beams. The strength increments were 48, 42, and 15 percent recorded with CFRP bars, rough strips, and smooth strips respectively. The deflection of the strengthened beams was reduced by about 66, 48, and 58 percent for CFRP smooth strips, rough strips, and CFRP bars respectively, compared with the control beam due to the increased stiffness of the strengthened beams.

Effect of Wetting and Drying Cycles on Behavior of Concrete Externally Strengthened with CFRP Laminates

D.H. Mohammed; T.S. Al-Attar; H.A. Dawood

Engineering and Technology Journal, 2017, Volume 35, Issue 7, Pages 675-684
DOI: 10.30684/etj.35.7A.2

This study describes an experimental work that was made to evaluate the effect of wetting and drying cycles on the behavior of concrete specimens externally strengthened with CFRP laminates. The experimental work included testing of twenty-three concrete specimens externally strengthened with CFRP laminates in different positions, with two compressive strength levels. The experimental variables considered in the test program include, compression strength of concrete, number of carbon fiber reinforced polymer (CFRP) strip layers, using CFRP strips throughout the total length of the specimen or within the middle third, and the number of wetting and drying cycles. The testing program included compression strength test, four-point flexural test, direct tension test, single and double face shear tests. The experimental results show that the increasing time of exposure to wetting and drying cycles lead to a significant increase in compressive strength, increasing the cracking loads which reached up to 22%., and decreasing the ultimate load carrying capacity.

Effect of Shear Span-Depth Ratio on Shear Strength of Porcelanite Lightweight Aggregate Reinforced Concrete Deep Beams Strengthened by Externally Bonded CFRP Strips

K.F. Sarsam; N.A.M. Al-Bayati; A.S. Mohammed

Engineering and Technology Journal, 2017, Volume 35, Issue 3, Pages 267-275
DOI: 10.30684/etj.35.3A.12

This paper presents an experimental investigation of structural behaviour of reinforced concrete deep beams strengthened in shear by CFRP strips. The experimental program consisted of fabricating, casting and testing of nine identical porcelainte lightweight aggregate reinforced concrete deep beams. Three of the tested deep beams were unstrenghtened to serve as reference beams, while the remaining beams were tested after being strengthened using CFRP strips in two different orientations (vertical and horizontal). The locally available natural porcelanite aggregate is used to produce lightweight aggregate concrete. The beams were designed to satisfy the requirements of ACI 318M- 14 building code. In order to insure shear failure modes, adequate flexural steel reinforcement were provided. Effect of three different values of shear span to effective depth ratio (a/d =1.0, 0.8, 1.2) were selected. All beams have been tested as a simply supported beams subjected to two concentrated points loading. The beam specimens were tested up to failure under monotonic loads. The experimental work showed that the failure load increases as the shear span to effective depth ratio deceases. As the shear span to effective depth ratio decreased from 1.0 to 0.8, the percentage of increase in the ultimate load was about 24%. In addition, the diagonal compression strut crack of unstrenghtened control beams was changed to several diagonal cracks at mid depth within the shear span of the strengthened beams and exhibited more ductile failure mode.

Improving the Strength of Steel Perforated Plate Girders Loaded in Shear Using CFRP laminates

May J. Hamoodi; Waeel Sh.Abdul-Sahib; Ihsan K.Abed

Engineering and Technology Journal, 2015, Volume 33, Issue 9, Pages 2119-2129

The structural behavior of perforated composite web plate girders under shear loading is studied. Five steel plate girders have been tested. Two of them are reference girders, not perforated and perforated. The perforated webs in the three other girders are strengthened with carbon fiber reinforced polymer (CFRP) laminates in different patterns. The diameter of the central circle opening is 300 mm, where is 60% of the web depth. It is found from the experimental work that the ultimate shear load for the perforated composite web plate girder is higher than the reference perforated girder in a range of 100% to 134% depending on the orientation of the fiber in CFRP laminates. Through the experimental results, new formulas are presented to predict the ultimate shear load of perforated strengthened steel girders by CFRP laminates. A nonlinear finite element analysis is carried out for the tested plate girders using the package software program (ANSYS V.14.5). The analytical results contain the distribution of VonMises stresses, which is useful to have a better understanding to the results obtained from the experimental tests.

Behavior of Corbels Strengthened with Carbon Fiber Reinforced Polymers (CFRP) – Numerical Study

Sameh Badry Tobeia

Engineering and Technology Journal, 2014, Volume 32, Issue 10, Pages 2394-2407
DOI: 10.30684/etj.32.10A.7

In this paper, a numerical modeling performed to study the effect of carbon fiber reinforced polymers (CFRP) as a shear strengthening of corbels. In this study a theoretical simulation is achieved with reinforced concrete corbels, several CFRP strengthening positions has been studied with different shear span – effective depth ratio (a/d) of (0.5,0.6&0.7). The numerical model, by using program (ANSYS 12.1) verified by compare its results with the experimental results. It was found that the position and the amount of (CFRP) as well as the vary of (a/d) ratio, have a great effects on the ultimate load capacity of corbels. Where, the ultimate load capacity increase as the amount of (CFRP) increased in certain positions of corbels, with regards the vary in (a/d) ratio.

Punching Shear Resistance of Reinforced Concrete Flat Plate Slabs Strengthened with CFRP

Eyad K. Sayhood; Mohammed J.Hamood; Aseel A. Abdul Ridha

Engineering and Technology Journal, 2014, Volume 32, Issue 2, Pages 511-529
DOI: 10.30684/etj.32.2A.16

The purpose of this study is to present a model suitable for analyzing reinforced concrete (RC) slabs strengthened with Carbon fiber reinforced polymer (CFRP) failing in punching shear using the finite element method. a nonlinear three-dimensional finite element analysis has been used to conduct an analytical investigation on the overall behavior of reinforced concrete slabs strengthened with CFRP strips. ANSYS (version 11, 2007) computer program is utilized.The 8-node isoparametric brick elements in ANSYS are used to represent the concrete, the steel bars and CFRP strips are modeled as axial members discrete within the concrete brick elements by assuming perfect bond between the concrete and steel and between the concrete and CFRP strips. The numerical analysis incorporates material nonlinearity due to concrete cracking in tension, nonlinear stress-strain relations of concrete in compression, crushing of concrete and yielding of steel reinforcement. Also, the evaluation of the CFRP strips enhancement in shear strength of RC slabs is investigated.
Different types of RC slabs strengthened with CFRP strips have been analyzed. Available experimental results are chosen to check the validity and the accuracy of the adopted models. In general, a good agreement is obtained between the finite element and the experimental results. The maximum percentage difference in ultimate load-carrying capacity is 8.83%. Several parametric studies have been carried out to investigate the effects of some important material parameters on the behavior of strengthened RC slabs. These parameters are the concrete compressive strength, the concrete tensile strength, the number of layers of CFRP strips, the configuration of CFRP strips and the effect of diagonal stirrups of CFRP.

Strengthening of Continuous Reinforced Concrete Beams by Cfrp Laminates

Sabih Z. Al-Sarraf; Hisham Al-Hassani; Ali S. Al-Jebouri

Engineering and Technology Journal, 2013, Volume 31, Issue Issue 2 A, Pages 330-344
DOI: 10.30684/etj.31.2A.10

Experimental investigations of the behavior of reinforced concrete three-span continuous beams with 1200 mm length for each span, with cross-section 120 mm width and 180 mm depth strengthened by CFRP in flexure case of beams have been presented. The experimental program consisted of nine RC beams, which were strengthened at some locations with CFRP laminates and carefully designed to fail in flexure. The results show that the use of external CFRP laminate connected to the beams could enhance the ultimate flexural load capacity up to 102.88%.

Influence of Anchorage on the Behavior of CFRP RC Beams in Flexure

Samir F. Dawood; Sabih Z. Al-Sarraf

Engineering and Technology Journal, 2010, Volume 28, Issue 9, Pages 1836-1853

This research study involves experimental and theoretical investigations of the
behavior of flexural debonding of carbon fiber reinforced polymer (CFRP) laminates
with steel anchorages. A total of nine reinforced concrete beam specimens with cross
section of (150mm width by 250mm height and 2000mm length) were investigated in
this study to observe the flexural strength of each one. Eight beam specimens were
strengthened with CFRP laminates and one beam specimen was tested without
strengthening. The experimental results showed that the use of CFRP strips as external
strengthening has significant positive effect on ultimate loads, crack patterns and
deflections. The percent of increasing of the ultimate load capacity can be increased by
about 65% when using two layers of CFRP strips instead of one layer. The ultimate
load is increased by about 118% for the beams strengthened with bonded CFRP and
external anchorage with respect to the reference beam. Three-dimensional nonlinear
finite element analysis (i.e. ANSYS - version 9.0 computer program ) is used to
investigate the performance of reinforced concrete beams strengthened with CFRP.
The comparison between the numerical and the experimental results asserted that good
validity of the numerical analysis and the methodology developed in this study.