Sameer Hamoush

Out-of-plane behavior of surface-reinforced masonry walls

Abstract This paper presents the results of an experimental program designed to evaluate the out-of-plane shear strength of masonry wall system; and to evaluate of the influence of the area of externally bonded FRP composites on the shear strength of the system. Eighteen compact masonry wall panels (3′×2′×8″, 900×600×200 mm) were tested for static out-of-plane loads. Nine panels were reinforced by one layer of WEB ‘S-Glass’ fiber-reinforcing system attached to the tension side of the wall, while the remaining nine were reinforced with two layers of composite overlay on the tension side. The influence of the overlays embedded length (the distance between the support and the overlays end) on the shear strength was also investigated. The variables evaluated included three layout configurations and two reinforcement ratios. Three different distances between the overlay end and the adjacent support were tested, 0, d /4 ( d is the block unit thickness) and d /2. Both one and two layers of WEB fibers were used and three specimens were evaluated for each variable. An MTS machine was used to test each panel under four-point load conditions. The failure loads, mid-span deflection, fiber-end slippage and failure modes were recorded. Based on the results of the experimental program, it appears that the out-of-plane shear strength of the concrete masonry wall systems is constant over the range of variables tested. The measured shear strength of the masonry wall specimens evaluated in this program indicates that the code defined shear strengths may not be as conservative as assumed.

Variation of the fracture toughness of concrete with temperature

Abstract This paper presents an experimental investigation on the variation of residual fracture toughness of concrete with elevated temperatures. A total of 80 beams 150 × 150 × 750 mm were tested under three-point bending, half of which had a 25-mm initial notch at mid-span and the rest of which had a 60-mm initial notch. The temperatures used in the study were 50, 100, 150, 200, 250 and 300 °C. The study also includes cyclic heating effects where the specimens were subjected to cycles of heating and cooling. In each cycle, the specimens were placed in a furnace preheated to the desired temperature for 24 h and then removed and left to cool for another 24 h. The process was repeated for the desired number of cycles. The results show that the residual fracture toughness of concrete decreases with the increase in temperature. The results also show that the fracture toughness is further reduced with the increase of number of heating and cooling cycles.

Bond shear modulus of reinforced concrete at high temperatures

The effect of fire and high temperature on the behavior and properties of concrete has drawn considerable attention. In this work an experimental program is used to determine the effect of high temperature on the interfacial bond shear modulus between concrete and reinforcement. Steel bars of different diameters were embedded in concrete cylinders for a depth less than that required for total development to assure failure by loss of bond. Specimens were then kept in an oven for different time durations and different temperatures. Specimens were then cooled by either keeping cylinders at room temperature or immersing them in water. The pull-out test was applied, and loads and displacements were recorded. Results from the pull-out test were then used along with an analytical model to calculate the bond shear modulus. The analytical model is based on the physical representation of the pull-out test, assuming linear elastic behavior of both steel and concrete.

The fracture toughness of concrete

Abstract Analytical modeling and experimental testing are used to evaluate the fracture toughness of plain concrete. The analytical modeling of the fracture toughness considers both the opening of the crack due to the applied external loads and the closing of the crack due to the interlock pressure of the aggregate. Superposition in the linear elastic theory is used to find the mode I stress intensity factor for the opening of the crack. A new line integral is developed in this paper to avoid the non-linearity at the crack processing zone due to the closing pressure. The new line of integration is evaluated in conjunction with the plane stress finite element technique. Data from experimental testing of notched beam specimens are used as an input for the analytical modeling. The developed fracturing criterion is shown to be independent of the length of the crack, it is only a function of the aggregate size and gradation. For given aggregates sizes in the concrete mix, the developed criterion is shown to be a material property.

RESIDUAL FRACATURE TOUGHNESS OF CONCRETE EXPOSED TO ELEVATED TEMPERATURE

This paper uses an analytical-experimental model to evaluate the residual fracture toughness of concrete exposed to elevated temperatures. In addition to the basic model of traction-free cracks, this analytical model also accounts for the closing pressure at the crack extension zone of notched concrete beam specimens. The stress beyond the tip of the crack extension zone is considered plastic with a magnitude equal to the modulus of rupture of the concrete. The crack opening displacements, failure load, initial crack length, and deflection at failure loads obtained from tests are incorporated in the analytical model to evaluate the concrete toughness. A total of 45 6 x 6 x 30-inch (150 x 150 x 750-mm) three-point-bent beam specimens with a central notch were tested. Each set contained three beams, and each was tested under ambient temperature conditions to validate the developed analytical model. The remaining 36 specimens were tested after they were exposed to one cycle of heating and air-cooling to room temperature. Temperatures considered were 50, 100, 150, 200, 250, and 300 C and were maintained for 24 hours.

A mixed-mode crack analysis of rectilinear anisotropic solids

Abstract A simple numerical method is presented for analysing the mixed mode of rectilinear anisotropic solids. The method is formulated on the basis of a finite element and the crack closure integral approach in conjunction with fundamental relationships in fracture mechanics. A simple and efficient solution procedure is developed involving only the known auxiliary solution for evaluating the strain energy release rate. The finite element solution converges to an accurate solution for small crack extensions. Numerical examples are presented to demonstrate the accuracy of the proposed approach.

Analytical Study of Reinforced Concrete Beams Strengthened by FRP Bars Subjected to Impact Loading Conditions

Civil engineers have considered Fiber Reinforced Polymer (FRP) materials to enhance the performance of structural members subjected to static and dynamic loading conditions. However, there are some design limitations due to uncertainty in the behavior of such strengthened members. This fact is particularly important when considering the complex nature of the nonlinear behavior of materials, the impact loading conditions and geometry of the members having FRP systems. In this research, a new analytical model is developed to analyze structural members strengthened with FRP systems and subjected to impact loading conditions. ABAQUS based finite element code was used to develop the proposed model. The model was validated against nine beams built and tested with various configurations and loading conditions. Three sets of beams were prepared and tested under quasistatic and impact loadings by applying various impact height and Dynamic Explicit loading conditions. The first set consisted of two beams, where one of the beams was reinforced with steel bars and the other was externally reinforced with GFRP sheet. The second set consisted of six beams, with five of the beams were reinforced with steel bars and one of them wrapped by GFRP sheet. The last set was tested to validate the response of concrete beams reinforced by FRP bar. In addition, beams were reinforced with glass and carbon fiber composite bars tested under Quasi-Static and Impact loading conditions. The impact load was simulated by the concept of a drop of a solid hammer from various heights. The numerical results showed that the developed model can be an effective tool to predict the performance of retrofitted beams under dynamic loading condition. Furthermore, the model showed that FRP retrofitting of RC beams subjected to repetitive impact loads can effectively improve their dynamic performance and can slow the progress of damage.

STRENGTH OF CONCRETE REINFORCED WITH TREATED FEATHERS

Two methods of feather treatment were investigated in this work. In the first method a water-repellent agent was used and in the second method feathers were impregnated with a blocking agent followed by a water-repellent agent and the alkalinity of the matrix was also reduced. Flexural, tensile and compressive strengths were then evaluated at different ages and for different volumetric feather ratios. This method of treatment improved the compressive, tensile and flexural strengths of concrete compared with untreated-feather-reinforced concrete.

Fracture Model to Predict Stress Intensity in Fiber Reinforced Concrete

A fracture model is developed to predict the stress-intensity factor of fiber reinforced cementitious composites. The model accounts for the fiber bridging over the crack faces in the crack-tip zone. The proposed model is based in the superposition technique in fracture mechanics in conjunction with an existing pullout model for the fiber pulling out of the concrete. The proposed fracture model assumes that the final slip distance of the fibers equals the final crack-flange opening displacement. In this model 2 basic steps are used in the solution procedure. The first step ignores the contribution of the fiber and finds the crack-flange displacement at the location of the fibers. The second step finds the crack-flange displacement due to one unit of force at each fiber location.