Alfarabi Sharif

Strengthening of Initially Loaded Reinforced Concrete Beams Using FRP Plates

In this study, the reinforced concrete (RC) beams are initially loaded to 85% of the ultimate flexural capacity and subsequently repaired with FRP (fiber reinforced plastic) plates, bonded to the soffit of the beam. The plate thickness is varied to assess the premature failure initiated at the plate curtailment zone due to the high concentration of shear and peeling stresses. Different repair and anchoring schemes were conducted in an effort to eliminate such failures and insure ductile behavior. The results indicated that the flexural strength of the repaired beams is increased. The ductile behavior of the repaired beams is inversely proportional to the plate thickness. The use of an I-jacket plate provided a proper anchorage system and improved the ductility of beams repaired with plates of large thickness.

Comparison of properties of steel slag and crushed limestone aggregate concretes

Abstract Steel slag is produced as a by-product during the oxidation of steel pellets in an electric arc furnace. This by-product that mainly consists of calcium carbonate is broken down to smaller sizes to be used as aggregates in asphalt and concrete. They are particularly useful in areas where good-quality aggregate is scarce. This research study was conducted to evaluate the mechanical properties and durability characteristics of steel slag aggregate concrete in comparison with the crushed limestone stone aggregate concrete. The durability performance of both steel slag and crushed limestone aggregate concretes was evaluated by assessing water permeability, pulse velocity, dimensional stability and reinforcement corrosion. The results indicated that the durability characteristics of steel slag cement concretes were better than those of crushed limestone aggregate concrete. Similarly, some of the physical properties of steel slag aggregate concrete were better than those of crushed limestone aggregate concrete, though the unit weight of the former was more than that of the latter.

Sulfate resistance of plain and blended cements exposed to varying concentrations of sodium sulfate

Concrete deterioration due to sulfate attack is the second major durability problem, after reinforcement corrosion. This type of deterioration is noted in the structures exposed to sulfate-bearing soils and groundwater. Though concrete deterioration due to sulfate attack is reported from many countries, the mechanisms of sulfate attack have not been thoroughly investigated, particularly the effect of sulfate concentration and the cation type associated with the sulfate ions on concrete deterioration. This study was conducted to evaluate the performance of plain and blended cements exposed to varying concentrations of sodium sulfate for up to 24 months. Four types of cements, namely Type I, Type V, Type I plus silica fume and Type I plus fly ash, were exposed to five sodium sulfate solutions with sulfate concentrations of 1%, 1.5%, 2%, 2.5% and 4%. These concentrations are representative of the sulfate concentration in highly saline soils. The sulfate resistance was evaluated by visual examination and measuring the and reduction in compressive strength. The maximum deterioration, due to sulfate attack, was noted in Type I cement followed by silica fume and Type V cements. The performance of Type V, Type I plus silica fume and Type I plus fly ash was not significantly different from each other. The enhanced sulfate resistance noted in the Type I cement blended with either silica fume or fly ash indicates the usefulness of these cements in both sulfate and sulfate plus chloride environments.

Flexural behavior of precracked reinforced concrete beams strengthened externally by steel plates

This paper presents comprehensive data and their interpretation on the plate bonding repair technique in terms of effects of plate thickness and end anchorage on ductility, ultimate load, and mode of failure. Reinforced concrete (RC) beams were preloaded to 85 percent of their ultimate capacity and subsequently repaired by bonding steel plates of different thicknesses with and without end anchorages. Anchor bolts were used for end anchorages. The repaired beams showed higher strength than the original beams, provided the plates did not exceed a certain limiting thickness. Increasing the plate thickness changed the mode of failure of the repaired beams from flexural to premature failure, developed due to shear and/or tearing of the plate, causing a reduction in ductility. End anchorages to the bonded plates could not prevent the premature failure of the beams but improved ductility with decreasing significance as the plate thickness increased, and yielded a marginal improvement in ultimate strength. A procedure for designing the bonding plate to avoid premature failure is suggested.

The effect of thermal cycling on the durability of concrete made from local materials in the Arabian Gulf countries

Abstract This paper presents results of a study on the effect of heating/cooling cycles on the durability of concrete made from available limestone aggregates in the Arabian Gulf countries. The coefficients of thermal expansion of three different limestone rocks, mortar and concrete were determined. Specimens of limestone rocks, mortar and concrete were heated in a temperature controlled oven to 80°C for 24 hours and then cooled in the oven to room temperature for another 24 hours. After 30, 60 and 90 cycles, specimens were tested for compressive and flexural strengths, pulse velocity and permeability. The test results indicate that the experimentally determined values of the coefficient of thermal expansion vary from 5.07 to 9.99 × 10 −6 /°C and that the limestone rocks tested are thermally anisotropic. Also, it is indicated that heating/cooling of concrete affects its durability performance as it loses up to 27 and 32% of its compressive and flexural strength, respectively. For all tested specimens, the greatest loss of strength is observed after 30 cycles.

PEELING AND DIAGONAL TENSION FAILURES IN STEEL PLATED R/C BEAMS

Abstract This paper focuses on the design of an experimental investigation motivated by the need to identify various independent modes of failure of steel plated R/C beams. Parameters controlling the various failure modes are identified, and an elaborate testing program confirms existence of peeling failure and flexural failure in addition to isolation of a diagonal tension mode of failure. An expression is proposed to predict ultimate capacity of steel plated R/C beams prone to fail by diagonal tension.

EFFECT OF HOLIDAYS AND SURFACE DAMAGE TO FBEC ON REINFORCEMENT CORROSION

Abstract This study was conducted to evaluate the effect of holidays and damage to fusion bonded epoxy coating (FBEC) on reinforcement corrosion in chloride-contaminated concrete. The effect of these parameters on the corrosion of FBEC bars was compared with corrosion of mild steel by measuring the corrosion potentials and corrosion current density at regular intervals. The corrosion current density measurements indicated that the defect-free FBEC bars were in a passive condition in the concrete specimens with up to 2% chloride by weight of cement. The long-term maintenance-free performance was not assured in the concrete specimens with chloride concentration of 1% and above and made with FBEC bars having >1% surface damage or with 3 holidays per linear foot. The long-term performance of FBEC bars with up to two pinholes (ASTM A 775 limit) was satisfactory in the concrete specimens with up to 2% chlorides, by weight of cement. Furthermore, surface damage to FBE coating is more critical compared to holidays, from the point of view of corrosion of FBEC bars, in chloride-bearing concrete.

Loss of Punching Capacity of Bridge Deck Slabs from Crack Damage

Field observation of punching-type failure of deck slabs in girder-slab bridges that were repetitively subjected to overweight vehicles has led to a study of punching of reinforced concrete slabs with the object of observing the detrimental influence of crack damage, if any, on the punching resistance. Crack damages, geometrically modeled as a flaw, was introduced in the test panels by embedding metallic inserts in the shape of conical frustrums. It has been observed that the punching capacity is impaired by the flaw if the geometrical configuration of the flaw bears a critical orientation with regard to the load.

Effect of thermal variations on bond strength of fusion-bonded epoxy-coated bars

Fusion-bonded epoxy coating is extensively used to enhance the corrosion resistance of reinforcing steel. The bond strength between these bars and the concrete is expected to be less than that of the uncoated bars and it may be further impaired due to prolonged exposure to thermal variations. This investigation was conducted to evaluate the effect of thermal variations, simulating the changes in the night to day temperature, on the bond strength of fusion-bonded epoxy-coated steel reinforcement. The pull-out specimens, prepared using bars of two different sizes and two coating thickness, were exposed to thermal cycling. The critical and ultimate bond strength of the fusion-bonded epoxy-coated bars were compared with that of the uncoated bars. The results indicated a reduction in the critical bond strength between concrete and the fusion-bonded coated bars. Furthermore, the difference between the critical bond strength in the coated and uncoated bars decreased with increasing thermal cycles, indicating that thermal variation has a greater effect on bond strength than the coating thickness.

Use of CFRP to Maintain Composite Action for Continuous Steel–Concrete Composite Girders

AbstractThe loss of composite action at the negative moment region for a continuous composite girder reduces the girder’s strength and stiffness. This paper presents an experimental investigation into the use of carbon fiber–reinforced polymer (CFRP) to maintain the composite action at the negative moment region of continuous composite girders. This is achieved by bonding CFRP sheets to the top of a concrete slab at the negative moment region. Six two-span continuous composite girders were tested. CFRP sheet thickness was varied to assess its effect on girder behavior. The girders were designed to have full composite action between the concrete slab and the steel girder. Moment capacity at the positive and negative moment regions was evaluated experimentally and theoretically. A plastic analysis was conducted to evaluate the ultimate capacity of the girders. Finite-element modeling evaluated girder performance numerically. The experimental results confirmed the effectiveness of CFRP sheets in maintaining ...