54 research outputs found
Performance of glass fiber reinforced plastic bars as a reinforcing material for concrete structures
No full textThe 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.King Abdulaziz City for Science and Technology
(KACST), funded the research project AR-14-35 entitled "Glass Fiber Reinforced
Plastic Rebars: Properties and Applications in Concrete Structures."Corresponding Author:
Prof. Saleh Hamed Alsayed
Civil Engineering Deparatment, College of Engineering, King Saud University, P.O. Box 800
Riyadh-11421, Saudi Arabia.
Email: [email protected]
Sensitivity of compressive strength of HSC to hot-dry climate, curing regimes, and additives
No full textSeventy 152 mm (6 in.) concrete cubes and fifteen 152 × 305 mm (6 × 12 in.) cylinders of high-strength concrete were cast and tested. The influence of different curing methods on reducing the deleterious impact of adverse climatic conditions on the compressive strength was evaluated. Other variables considered in the study were the shape of the specimens. addition of silica fume, type of curing compound, curing period, and replacement of superplasticizer by retardant and plasticizer. It was found that, for concrete tested 28 days after casting, treatment with resin compound applied to the exposed surface of the specimen provided better protection to concrete than intermittent spraying of water. However, intermittent spraying of water with and without burlap covering also provided an acceptable means of protecting concrete against adverse climatic conditions. It was also found that adding 10 percent of silica fume to the concrete mix may increase the compressive strength of the concrete by 25 percent without influencing its sensitivity to hot weather effects. Conversely, replacing superplasticizer by an equivalent quantity of retardant and plasticizer (based on equal concrete slump) reduced the compressive strength by about 10 percent, but the concrete became less sensitive to adverse climatic conditions. Furthermore, for concrete tested 90 days after casting, it became visible that concrete cured by intermittent spraying of water with burlap covering had a higher compressive strength than that cured by water spraying with no burlap covering
Influence of superplasticizer, plasticizer, and silica fume on the drying shrinkage of high-strength concrete subjected to hot-dry field conditions
No full textThe effects of adding condensed silica fume (10% of cement weight) on the concrete mix, and those of adding either superplasticizer or plasticizer on the drying shrinkage (DS) of 12 high-strength concrete prisms exposed to either controlled laboratory or hot-dry field conditions, were monitored for over 3 years. The results indicate that for specimens cured under controlled laboratory conditions, inclusion of silica fume in the concrete mix reduces the 3-year DS by 25%, the induced shrinkage stress by 36% and the first month rate of DS by 21%. The corresponding reduction in the 3-year DS, the induced shrinkage stress, and the first month's rate of DS for the counterpart specimens cured under hot-dry field conditions are 13%, 26%, and 24%, respectively. The results also show that for specimens cured under laboratory conditions, replacing the superplasticizer by plasticizer increases the 3-year DS by 21%, the induced shrinkage stress by 27%, and the first month's rate of DS by 32%. The corresponding increase in the DS, the induced shrinkage stress, and the first month DS for the counterpart specimens cured under the hot-dry field conditions are 27% and 34%, and 35%, respectively. Furthermore, test results indicate that the range of the maximum recorded DS strains in 3-year exposure period is between 450 to 650 μm/m and is dependent on the concrete content of admixtures. On the other hand, depending on the curing conditions, 75 to 80% of the 3-year DS occurs within the first 3 months of exposure. © 1998 Elsevier Science Ltd
Efficienty of CFRP sheets in upgrading and/or strengthening square reinforced concrete columns
No full textStrengthening and/or upgrading reinforced concrete columns through utilization of composite sheets is now receiving wide acceptance worldwide. The technique is simple to use and has many advantages over other available methods. However, limited data is available about its efficiency in confining non-cylindrical shape columns. In this paper, the influence of using different schemes of wrapping of carbon fibre reinforced polymer (CFRP) sheets on the behaviour of reinforced concrete columns with and without utilizing
mechanical anchoring system is reported. The columns were 300 × 300 mm in cross section and 2005 mm in height and were subjected to incremental monotonic loading until complete failure. Test results indicated that the horizontally aligned CFRP sheets had more contribution to enhancing the ductility of the columns than the strength whereas the vertically aligned sheets had more contribution to increasing the column's ultimate capacity. The results also showed that both ductility and strength of the wrapped columns can be significantly increased by utilizing mechanical anchoring system that reduces the
distance between the unsupported nodal points for the sheets.Corresponding Author:
Prof. Saleh H. Alsayed, Civil Engineering Department, Department of Civil Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia. Email: [email protected]
Ductility of concrete beams reinforced with FRP bars and steel fibers
No full textA 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
A Numerical Model for Predicting the Behavior of Rehabilitated and/or Strengthened RC Beams
No full textThe work presented herein uses the compatibility of deformations, equilibrium of forces, and a more rational stress-strain relationship for concrete in compression to suggest a numerical model that is capable of estimating, for any load level, the forces, moments, stresses, strains, and curvatures of the reinforced concrete beams before and after repairing, upgrading and/or strengthening. The model considers the variation of stresses, strains, and curvatures along the length of the beam. It also accepts different material properties, cross sectioal shapes, and loading and reinforcement configurations. Further, it takes into account effects of shrinkage and creep on the deflection and the strain of concrete and internal and external reinforcement. Thus, it can be used with different techniques that are available for rehabilitation and/or strengthening of reinforced concrete beams.The analytical prediction using the proposed model was checked against the published experimental data and found in good correlation with the corresponding measured results. It also accorded better prediction than other models available in the literature.It is believed that availability of such a model is of great value to the structural engineer especially through the design and decision process. It can be used to evaluate the strength and serviceability criteria of the existing damaged or undamaged structure. Then, if needed, the model can be utilized to help in selecting the type and size of the material that best fulfills the conditions to rehabilitate and/or strengthen the structure. This will, of course, influence the work strategy and may lead to appreciable saving in both time and cost
Effect of curing conditions on strength, porosity, absorptivity, ans shrinkage of concrete in hot and dry climate
No full textThis study is concerned with the effect of intermittent wet and dry curing methods on the strength, modulus of elasticity, porosity, absorptivity, and shrinkage of the concrete. The study was carried out in field conditions that are characterized by hot air temperature, low relative humidity, large diurnal variations, direct solar radiation, and relatively high wind speed. It was found that intermittent wet curing methods are suitable in the aforesaid severe conditions with regard the strength and the durability of the concrete. However, as far as the rate of shrinkage after stopping the curing process is concerned, neither the intermittent wet curing nor the dry methods are an acceptable technique of curing. Therefore, other methods to reduce the rate of shrinkage were advised. Further, and based on the results of this study, some recommendations about using the design guidelines that were formulated on the basis of experimental results carried out in relatively cold and humid climate conditions were discussed. © 1994
Shrinkage of fibre and reinforced fibre concrete beams in hot-dry climate
No full textThe influence of steel fibre inclusion on the shrinkage of 16 full-size plain and reinforced concrete beams was assessed. Shrinkage measurements, at three levels over the depth of the beams, were carried out for 200 days. Half of the beams were cured in a controlled laboratory environment and the other half cured under hot, dry and windy climatic conditions. Test results show that under laboratory curing conditions adding 1% by volume of steel fibres reduced the ultimate shrinkage at the top, mid-height, and bottom of the plain concrete by 16, 23, and 28%, respectively. However, in the reinforced concrete beam the presence of longitudinal reinforcement rendered it less significant. Under the uncontrolled severe curing environment, the addition of 1% by volume of fibres produced a reduction of 30% in shrinkage at the bottom level of both the plain and the reinforced concrete beams. At the top level, however, the geometry constraints and the compaction techniques influenced the fibre contribution to shrinkage. © 1994
Ductility of concrete beams reinforced with FRP bars and steel fibers
No full textA 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
Stress-strain relationship of normal, high-strength and lightweight concrete
No full textA simple mathematical model to generate a full spectrum (ascending and descending portions) of the stress-strain curves for normal, high-strength and lightweight concrete is suggested. The only parameter needed to run the model is the ultimate compressive strength of the concrete. The model was deduced by considering the average values of series of test results obtained for specimens tested under various conditions. It provided a good prediction of experimental results available in the literature. When compared with other models, it gave better predictions
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