33 research outputs found
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]
Non-linear finite element analysis for RC elements subjected to in-plane loads
No full textCivil Engineering Department, College of Engineering, King Saud University.
Riyadh, 11421, Saudi ArabiaA non-linear iterative solution of finite element formulation implemented a 486 personal computer for predicting the cracking shapes and their propagation in reinforced concrete elements subjected to in-plane stresses is presented. The model is based on a smeared crack representation and a plane stress state simulation. It considers the influence of concrete tension stiffening after cracking, compressive stress degradation due to cracking, and single and double crack conditions. The reliability of the model is checked against the experimental results for specimens that were tested by the author as well as those tested by other researchers. Comparisons of the results show that the proposed model predicts the measured results with an overall average error of 2% and a coefficient of variation of 1.48. This work forms an effective tool for investigation of inelastic behavior of a concrete and reinforcing bar composite
Influence of severe hot-dry climate on the mechanical properties of fibrous reinforced concrete beams
No full textThis paper presents the results of the work carried out to study the influence of curing environment and steel fiber volume fraction on the flexural strength, flexural rigidity, flexural toughness, and ductility of fibrous reinforced concrete (RC) beams. A total of twenty simply supported beams were tested. Ten of the twenty beams were cured under controlled laboratory conditions and the other ten were cured under severe hot dry climate (SHDC) characterized by their intense heat, Iow relative humidity, direct solar radiation, and large diurnal variations of daily temperatures. Tests were carried out 28 and 90 days after casting. Test results show that for non fibrous RC concrete beams the adverse effects of SHDC have more influence in reducing the flexural toughness than the flexural strength. On the other hand, test results indicate that under any of the two curing environment considered in this study, the flexural strength, flexural rigidity, flexural toughness and ductility of the fibrous RC beams are in direct proportion with the fiber content. Moreover, the results reveal that the enhancements in these engineering properties due to the steel fiber addition are not affected by the above described severe field conditions. Furthermore, inclusion of steel fibers in concrete helps, to some extent, in reducing the adverse effects of SHDC on the properties of concrete
Flexural deflection of reinforced fibrous concrete beams
No full textThe results of tests on 10 reinforced concrete beams with and without steel fiber reinforcement are presented. A simple empirical equation to estimate deflection of the reinforced concrete beams is derived from the test observations. The model accounts for the aspect ratio and the volume fraction of the steel fibers. The mean and the coefficient of variation of the ratio of the measured to the calculated deflections, for the design-to-cracked moment ratios in the range of 1 to 4.5, are 99 and 8.2 percent, respectively. The model also well estimated the deflections measured by other researchers
Ductility of Concrete Beams Reinforced with FRP Bars and Steel Fibers
No full text 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. </jats:p
Durability of Glass Fiber Reinforced Plastic Bars
No full textA total of 112 specimens of E-glass fiber reinforced plastic
(GFRP) rebars with 12.7 mm in diameter were used to investigate the
effect of alkalinity concentration and moist curing temperature on
their tensile strength and weight. The main variables in the study
include alkalinity (NaOH) concentration (0, 5 and 20 g/l), moist
curing temperature (21±1 and 40 ±1 °C), GFRP rebar conditions
(coated or uncoated with cement paste) and immersion period (1, 4, 8
and 12 months).
The test results indicate that alkaline solution and temperature
may cause great loss to the tensile strength of the GFRP rebars and, in
general, that loss is in direct proportion with the moist curing
temperature, alkalinity concentration and the immersion period. These
same factors also affect, although to a much less extent, the weight
reduction of the GFRP rebars.
The results also reveal that under normal temperature and
drinking water temperature conditions, the presence of cement paste
around the GFRP rebars plays a paramount factor in deteriorating the
rebars. However, under high moist temperature, the temperature
becomes the controlling factor in deterioration process of the rebars.King Saud University
Riyadh, Saudi Arabi
Strength, water absorption and porosity of concrete incorporating natural and crushed aggregate
No full textThis paper presents the results of an extensive experimental program which was carried out to study the influence of Riyadh area aggregates on the compressive strength, water absorption, and porosity of the concrete. Parameters involved were crushed washed aggregate, natural unwashed aggregate, and four different water cement ratios. Natural aggregates are characterized as porous limestone rocks with high water absorption, low bulk specific gravity, excessively dusty degraded, and contain large quantities of very fine sand. Test results indicate that with proper selection of mix proportions and adequate compaction both aggregates can be used to produce concrete with ultimate compressive strength that is usually specified for most concrete structural applications. Results also indicate that the natural aggregate concrete has less compressive strength, less porosity and higher water absorption compared to that of concrete made with crushed aggregate. This is true for 0.4,0.45,0.5, and 0.55 water cement ratios
Influence of chemical and mineral admixtures and curing regimes on the engineering characteristics of HSC subjected to hot-dry field conditions
No full textThe short and long time effects of different curing regimes and inclusion of chemical and
mineral admixtures on the strength and drying shrinkage of high strength concrete (HSC)
exposed to hot-dry field conditions were examined. A total of 70 compressive strength
specimens and 34 drying shrinkage specimens were considered in the study. The main
variables in the study include curing regimes and period, concrete mixes and curing
environment.
The results indicate that under hot dry field conditions, inclusion of silica fume (SF) and
superplasticizer in the concrete mix greatly improve the 28-day and 90-day compressive
strength of the concrete and particularly when the concrete casting is followed by curing
with intermittent spraying of water. The results also reveal that the rate and the 5-year
maximum recorded drying shrinkage strains of the HSC subjected to hot-dry field
conditions are lower for specimens cured with intermittent spraying of water with or
without burlap covering. Furthermore, the test results show that inclusion of
superplasticizer and silica fume reduce the drying shrinkage of the HSC
Strength, Water Absorption and Porosity of Concrete Incorporating Natural and Crushed Aggregate
No full textThis paper presents the results of an extensive experimental program which was carried out to study the influence of Riyadh area aggregates on the compressive strength, water absorption, and porosity of the concrete. Parameters involved were crushed washed aggregate, natural unwashed aggregate, and four different water cement ratios.Natural aggregates are characterized as porous limestone rocks with high water absorption, low bulk specific gravity, excessively dusty degraded, and contain large quantities of very fine sand.Test results indicate that with proper selection of mix proportions and adequate compaction both aggregates can be used to produce concrete with ultimate compressive strength that is usually specified for most concrete structural applications. Results also indicate that the natural aggregate concrete has less compressive strength, less porosity and higher water absorption compared to that of concrete made with crushed aggregate. This is true for 0.4, 0.45, 0.5, and 0.55 water cement ratios
Upgrading and/or strengthening of rectangular columnsusing FRP fabrics prediction model
No full textA simple modification to the currently utilized ACI model to estimate the axial capacity of rectangular reinforced concrete (RC) columns wrapped with FRP fabrics (sheets) is suggested. The modification accounts for the presence of longitudinally and transversely aligned FRP fabrics around the perimeter of the columns. The suggested model is based on the analyses of the experimental data available in the literature. Comparisons between the measured and estimated axial capacity of FRP wrapped columns show that the contribution of FRP fabrics in the column carrying capacity can be reasonably estimated using the modified model
