Saleh H. Alsayed

Performance of glass fiber reinforced plastic bars as a reinforcing material for concrete structures

Abstract The increasing use of fiber reinforced plastic (FRP) bars to reinforce concrete structures necessitates the need for either developing a new design code or adopt the current one to account for the engineering characteristics of FRP materials. This paper suggests some modifications to the currently used ACI model for computing flexural strength, service load deflection, and the minimum reinforcement needed to avoid rupturing of the tensile reinforcement. Two series of tests were conducted to check the validity of the suggested modifications. The first series was used to check the validity of the modifications made into the flexural and service load deflection models. The test results of the first series were also analyzed to develop two simple models for computing the service load deflection for beams reinforced with glass FRP (GFRP) bars. The second series was used to check the accuracy of the modification suggested into minimum reinforcement model. Test results of the first series indicate that the flexural capacity of the beams reinforced by GFRP bars can be accurately predicted using the ultimate design theory. They also show that the current ACI model for computing the service load deflection underestimates the actual deflection of these beams. The two suggested models for predicting service load deflection accurately estimated the measured deflection under service load, and the simpler of the two pertains better predictions than those of the models available in the literature. Test results of the second series reveal that there is an excellent agreement between the predicted and recorded behavior of the test specimens, which suggests the validity of the proposed model for calculating the required minimum reinforcement for beams reinforced by GFRP bars.

Experimental and Numerical Study for the Shear Strengthening of Reinforced Concrete Beams Using Textile-Reinforced Mortar

In this paper, the effectiveness of textile-reinforced mortars (TRMs), as a means of increasing the shear resistance of reinforced concrete beams, is experimentally and numerically investigated. Textiles comprise of fabric meshes made of long woven, knitted or even unwoven fiber rovings in at least two (typically orthogonal) directions. Mortars—serving as binders—may (or may not) contain polymeric additives usually used to have improved strength properties. These TRMs may be considered as an alternative to fiber-reinforced polymers (FRP), providing solutions to many of the problems associated with application of the latter without compromising much of the performance of strengthened members. In the present study, a new type of textile (basalt-based textile) was used as strengthening material. Two different mortar types’ viz. cementitious and polymer-modified cementitious mortars were used as binding material for the textile sheets. The studied parameters also included the number of textile layers as well as the orientation of the textile material. The experimental program comprises of testing two control beams which were intentionally designed to be deficient in shear, in addition to testing eight beams which were externally upgraded by TRM sheets for enhancing their shear capacity. On the basis of the experimental response of reinforced concrete members strengthened in shear, it is concluded that textile-mortar composite provides substantial gain in shear resistance; this gain is higher as the number of layers increases. With higher number of layers, textile with 45° orientation along with polymer-modified cementitious mortar provides the highest shear strength enhancement. Nonlinear finite-element (FE) analysis was also carried out on the tested beams using LS-DYNA, which is transient nonlinear dynamic analysis software. The numerical analysis carried out involved case studies for TRM modeled, with and without mortar. Good agreement was achieved between the experimental and numerical results especially for the ultimate load carrying capacity for the case of FE models incorporating mortar. The study was extended numerically to include additional cases of TRM-strengthened specimens with more number of TRM layers as well as a case of FRP-strengthened specimen.

Flexural behaviour of concrete beams reinforced with GFRP bars

Abstract This study presents the results of the comparison made between the predicted and the measured load-deflection relationships for 12 concrete beams reinforced either by steel or glass fibre reinforced plastic (GFRP) bars. The numerical part of the study was carried out using: (i) the computer model which accounts for the actual properties of the composite constituents developed as part of this study, (ii) the ACI load-deflection model, and (iii) the modified load-deflection model available in the literature for beams reinforced by FRP bars. The last two models were implemented on a spreadsheet. The deflection limit and the ultimate strength of concrete were the control parameters in design of the test beams. The computer model provides an accurate prediction of the measured service and full load-deflection curves. The errors in prediction of service load deflection and ultimate flexural strength are less than 10% and 1%, respectively. In the case of GFRP reinforced beams, the service load deflection predicted by the ACI model is in error by 70%, while that predicted by the modified model is in error by less than 15%.

Seismic Response of FRP-Upgraded Exterior RC Beam-Column Joints

Shear failure of exterior beam-column joints is identified as the principal cause of collapse of many moment-resisting frame buildings during recent earthquakes. Effective and economical strengthening techniques to upgrade joint shear resistance and ductility in existing structures are needed. In this paper, efficiency and effectiveness of carbon fiber-reinforced polymer (CFRP) sheets in upgrading the shear strength and ductility of seismically deficient exterior beam-column joints have been studied. Four as-built joints were constructed with nonoptimal design parameters (inadequate joint shear strength with no transverse reinforcement) representing preseismic code design construction practice of joints and encompassing most of existing beam-column connections. Out of these four as-built specimens, two specimens were used as baseline specimens (control specimens) and other two were strengthened with CFRP sheets under two different schemes (strengthened specimens). In the first scheme, CFRP sheets were epo...

Ductility of Concrete Beams Reinforced with FRP Bars and Steel Fibers

A total of 18 concrete beams were tested to study the influence of adding steel fibers (SF) to concrete mix on the ductility of concrete beams reinforced with fiber reinforced plastics bars (FRP beams). The main variables in the study were the type and volume fraction of the steel fiber. The study also investigated the accuracy of an available model, developed originally to predict the flexural strength of concrete beams reinforced with SF and steel bars (SF-steel beams), after modification in estimating the flexural capacity of the fibrous FRP beams (SF-FRP beams). The results indicate that the ductility of FRP beams is less than 50% of that of the respective steel beams. The results also reveal that the ductility of SF-FRP beams is directly related to the fiber content. In addition, the test results show that inclusion of 1% of hooked SF can improve the ductility of FRP beams to be the same as that of the steel beams. Furthermore, comparison between the predicted and measured flexural capacity of SF-FRP beams shows that the modified model can predict the measured results within a reasonable accuracy.

Effect of blast loading on CFRP-Retrofitted RC columns - a numerical study

This study aims to investigate the effect of blast loads generated as a result of explosive charges on the existing exterior RC circular columns of a typical building in the city of Riyadh. A procedure has been developed for evaluating the dynamic characteristics of the circular column with and without retrofitting. A wide range of parametric studies have been performed as part of this investigation to examine the effects of stand-off distance, charge weight and the presence of CFRP retrofitting on the level of damage to the RC column. The nonlinear finite element analysis was carried out using LS-DYNA software with explicit time integration algorithms. Different charge weights of 100, 200, 500 and 1000 kg equivalent weight of TNT at stand-off distances of 1, 4 and 15 m were considered. Results described in this paper indicate that CFRP strengthening could be an effective solution to limit the damage caused by moderate explosions. The stand-off distance was found to play a very important role in mitigating the adverse effects of a blast. The results also indicate that the maximum lateral deflection experienced by the column decreased exponentially with the increase in the stand-off distance and also decreased for the columns strengthened with CFRP, compared with the unstrengthened columns.

Seismic Behavior of As-Built, ACI-Complying, and CFRP-Repaired Exterior RC Beam-Column Joints

In this paper, the efficiency and effectiveness of carbon-fiber-reinforced polymer (CFRP) sheets for upgrading the shear strength and ductility of a seismically deficient exterior beam-column joint were studied and compared with an American Concrete Institute (ACI)-based design joint specimen. One as-built joint specimen, representing the preseismic code design and construction practice for joints and one ACI-based design joint specimen, satisfying the seismic design requirements of the current code of practice were cast. The as-built specimen was used as baseline (control) specimen. These two specimens (i.e., the as-built control and the ACI-based specimens) were subjected to cyclic lateral load histories to induce damage equivalent to damage expected from a severe earthquake. The damaged control specimen was then repaired by filling its cracks with epoxy and externally bonding CFRP sheets to the joint, the beam, and part of the column regions. This specimen was identified as the repaired specimen. The repaired specimen was subjected to a similar cyclic lateral load history, and its response history was recorded. The response histories of the as-built control, the repaired, and the ACI-based design specimen were then compared. The test results demonstrated that externally bonded CFRP sheets can effectively improve both the shear strength and the deformation capacity of seismically deficient and damaged beam-column joints to a state comparable to the ACI-based design joint.

Tensile properties degradation of glass fiber-reinforced polymer bars embedded in concrete under severe laboratory and field environmental conditions

This paper presents the test results of an experimental study to investigate the durability of newly developed glass fiber-reinforced polymer bars. The main objective of this study is to investigate any degradation in the tensile properties of the glass fiber-reinforced polymer bars using accelerated aging methods. Glass fiber-reinforced polymer bars were embedded in concrete prisms and exposed to several environmental conditions for 6, 12, and 18 months. The environments included exposure to tap water and seawater at two temperatures (room temperature and 50°C), seawater dry/wet cycles and alkaline solution at 50°C. In addition, two typical field conditions of the Kingdom of Saudi Arabia (Gulf area and Riyadh area) were included. The performance of the glass fiber-reinforced polymer bars was evaluated by conducting tensile tests on the bars extracted out from the concrete prisms after exposure to different conditions. In addition, scanning electron microscope was used to investigate the degradation mechanism of the bars. After 18 months of exposure, test results showed that both the tap water at 50°C and the alkaline solution at 50°C had the maximum harmful effect on the tensile strength of glass fiber-reinforced polymer bars. The two field conditions showed almost no degradation in the tensile properties of the tested bars.

Numerical Investigations on the Seismic Behavior of FRP and TRM Upgraded RC Exterior Beam-Column Joints

AbstractIn this paper, a detailed procedure for nonlinear finite-element analysis of fiber reinforced polymer (FRP) and textile reinforced mortar (TRM) upgraded reinforced concrete (RC) beam-column exterior joints is presented for predicting their seismic performance under simulated earthquake loading. The finite-element (FE) model was developed using a smeared cracking approach for concrete and three-dimensional layered elements for the FRP and TRM-composites. The results obtained from FE analysis were compared with the test results. The tests were conducted on four as-built exterior beam-column joint specimens under simulated seismic loads. Out of these four specimens, one specimen was tested as a control specimen and the other three were tested after strengthening with TRM, carbon FRP, and glass FRP sheets, respectively. The FE results were compared with the test results through load-displacement behavior, ultimate loads, and crack pattern. Comparison of FE results with the experimentally observed resp...

CONCRETE COLUMNS REINFORCED BY GLASS FIBER REINFORCED POLYMER RODS

A total of 15 concrete columns were cast and tested to investigate the influence of replacing longitidunal and/or tie steel bars by an equal volume of amount of glass fiber reinforced polymers (GFRP) bars on the behavior of concrete columns. The columns were subjected to concentric monotonic axial loading. The concrete block for all columns was 459X250X1200 mm. The results indicated that replacing the longitudinal steel bars by GPRP bars reduced the axial capacity of the column by 13%. The results also showed that regardless of the type of the longitudinal bars, replacing the steel ties by GFRP ties reduced the axial capacity of the column by 10%. However, the study revealed that replacing the steel ties by GFRP had, up to about 80% of the ultimate load, no influence on the load axial shortening curve. Furthermore, the results indicated that the currently used ACT formula to estimate the axial capacity of the column overestimated the actual capacity of the column reinforced longitudinally and or transversely by GFRP bars.