A. Ghani Razaqpur

Finite element modeling of coupled heat transfer, moisture transport and carbonation processes in concrete structures

Carbonation is one of the many reasons of reinforcement corrosion in concrete structures. Due to the coupling effects of moisture, heat and carbon dioxide transport in concrete, the modeling of this problem is a rather challenging task. A nonlinear finite element approach is adopted here for tracing the spatial and temporal advancement of the carbonation front in concrete structures with and without cracks. A two-dimensional Windows-based finite element computer program, called CONDUR, is developed and the results obtained from the program are compared with available experimental data. The program is designed to be flexible and comprehensive in its scope.

Exact analysis of beams on two-parameter elastic foundations

Abstract Efficient beams on two-parameter elastic foundation finite elements have recently been developed. The stiffness matrix and nodal loud vector of these elements have been derived on the basis of the exact displacement function obtained from the solution of the governing differential equation. Most of the existing elements are, however, either limited to certain combinations of beam and foundation parameters, or provide only the solution of the homogeneous form of the governing equation. In this paper a new finite element is derived which eliminates these limitations. The stiffness matrix, nodal load vector and shape function of the clement are derived using the differential equation of a beam on a two-parameter elastic foundation. The complete solution of the equation corresponding to the most common types of load is also presented. This permits the determination of the deflections and internal forces anywhere along a simple or continuous beam on two-parameter foundations.

Proposed Shear Design Method for FRP-Reinforced Concrete Members without Stirrups

An improved method for evaluating the shear resistance of fiber-reinforced polymer (FRP) reinforced concrete members without stirrups is presented. The effects of shear and moment interaction at section and of member sizeon its shear strength are considered. For beams with a span-depth ratio (a/d) less than 2.5, the effect of shear transfer by arch action is taken into account. Following the traditional ACI approach, the concrete contribution is defined as a function of the square root of concrete strength, but the contribution from the aggregate interlock mechanism is expressed as a function of the cubic root of the axial rigidity of longitudinal reinforcement. The member size effect on its shear strength is also considered. The predictions of the proposed method are in better agreement with available experimental data than those of any of the current shear design methods for FRP-reinforced concrete structures.

Shear Strength of FRP Reinforced Concrete Members with Stirrups

AbstractThe mechanisms of shear transfer in fiber-reinforced polymer (FRP) reinforced concrete members with shear reinforcement are discussed, and it is explained how these were used to derive the shear design provisions of the Canadian standard for design and construction of building structures with FRPs. Subsequently, the accuracy of these provisions and the validity of their underlying assumptions are assessed by comparing the predicted shear strengths of over three hundred FRP-reinforced beams with their corresponding experimental values. Although the focus of the paper is mainly on beams with FRP shear reinforcement, for completeness beams with and without shear reinforcement are analyzed. It is determined that the mean and standard deviation of the ratio of the test to predicted shear strength of the beams without shear reinforcement are 1.16 and 0.24, respectively, whereas those of beams with shear reinforcement are 1.15 and 0.23. The strengths of these beams are also computed using the recommendat...

Shear Strength of Fiber-Reinforced Polymer Reinforced Concrete Beams Subject to Unsymmetric Loading

This study is concerned with the determination of the effects of shear span-to-depth ratio (a/d) and beam depth, or size, on the concrete contribution to the shear resistance of beams longitudinally reinforced with carbon fiber-reinforced polymer (CFRP) bars. One of the distinguishing features of the study is the unsymmetrical nature of the applied load, which creates two distinct a/d ratios in the same beam and allows the effect of the a/d ratio on shear strength to be clearly seen. Six simply supported large size CFRP reinforced concrete beams without shear reinforcement were tested, each under a single concentrated load. The test variables were the a/d ratio, varying from 1.0–11.5, and the beam depth varying from 200–500 mm. All the beams failed in shear, but the failure load and location for some of these beams could not be predicted by the shear design recommendations of American Concrete Institute (ACI) Committee 440. The reason is that these recommendations do not account for the effects of a/d and beam size on shear strength. Suggestions are made for the inclusion of these parameters in the shear design equations.

Experimental Performance of Steel Beams under Blast Loading

In this study, the dynamic response of typical wide-flange steel beams was experimentally evaluated under blast loading. A total of 13 beams were field tested using live explosives, where the charge size ranged from 50 to 250 kg of ammonium nitrate-fuel oil mixture, and the ground stand-off distance was from 7.0 to 10.3 m. Blast wave characteristics, including incident and reflected pressures, were recorded. In addition, time-dependent displacements, accelerations, and strains at different locations along the steel members were measured, and the postblast damage and mode of failure of the test specimens were observed. The blast load characteristics were compared with those obtained using the Technical Manual UFC 3-340-02 results. The displacement response results were used to validate the results obtained from a nonlinear dynamic analysis based on a single degree-of-freedom (SDOF) model. Results showed that the UFC 3-340-02 pressure predictions compare reasonably well with the measured pressure in the positive phase in terms of both the peak pressure and overall time variations. The SDOF model predicted the maximum displacements of beams in the elastic range reasonably well, but it overestimated them in the plastic range.

CFRP Anchor for Preventing Premature Debonding of Externally Bonded FRP Laminates from Concrete

AbstractTo delay or prevent debonding of externally bonded fiber-reinforced polymer (FRP) laminate from concrete substrate, a new carbon FRP (CFRP) anchor is developed. The monolithically built anchor comprises two legs and a wide head plate, with the legs inserted into adhesive-filled drilled holes in the concrete and the head plate bonded to the surface of the FRP laminate and the adjacent concrete. Full-scale reinforced concrete T-beams were strengthened in flexure with different amounts of CFRP laminate and tested in four-point bending. The anchor number and spacing were varied to find the most effective configuration. It was determined that the configuration involving nearly uniform spacing of the anchors along the laminate and the placement of the laminate strips between the anchor legs were most effective to allow beams with up to eight plies of the laminate to fail by rupture of FRP rather than debonding. When comparing the efficiency factor of the proposed anchor with those of other anchors repor...

Behavior of Beams Strengthened with Novel Self-Anchored Near-Surface-Mounted CFRP Bars

A commonly observed failure mode in laboratory tests involving surface bonded fiber-reinforced polymer (FRP) laminates or near-surface-mounted (NSM) bars is premature delamination, that is, the separation of the FRP from the substrate well before the FRP reaches its ultimate strain capacity. To delay the onset of delamination and to ensure that the NSM FRP reinforcement continues to contribute to member strength after partial delamination, a new self-anchored carbon fiber-reinforced polymer (CFRP) bar was developed and tested for this investigation. This bar is made with a series of monolithic spikes that can be anchored deep inside the concrete. In addition to cutting grooves into the concrete cover for the placement of the primary reinforcing bar, holes are drilled deep into the concrete to insert the spikes. To test the performance of this bar, six large, simply supported, reinforced, concrete beams were retrofitted with NSM bars and tested in four-point bending. Two beams were strengthened with NSM ba...

A new CFRP anchor for preventing separation of externally bonded laminates from concrete

Twelve identical concrete prisms were strengthened with Carbon Fibre-Reinforced Polymer (CFRP) laminate strips on two opposite faces and the laminates were anchored using the newly developed CFRP π-anchor. Prisms were tested in tension to investigate the effectiveness of the anchor to possibly delay delamination and/or to prevent the complete separation of the laminate from the prism. The salient feature of the anchor is its wide head to resist high interfacial shear stresses and its shanks that were inserted in predrilled holes to provide mechanical anchorage and to resist pull-out. The anchor doubled the tensile load-carrying capacity, effectively delayed delamination and prevented the CFRP laminate from full separation. Furthermore, the strengthened prisms experienced noticeable deformation.

Use of polymer grids for short- and long-term crack control in concrete slabs

Abstract Shrinkage cracks in Portland cement concrete can cause serious problems when cracked reinforced concrete is subjected to corrosive agents such as salts. The seepage of salty solutions through the cracks into the reinforcing steel can lead to corrosion of the steel and ultimately failure of the structure. This paper presents the results of an extensive experimental investigation designed to evaluate the potential of using polymer grids to minimize shrinkage cracks and their subsequent effects on corrosion of steel reinforcement. The investigation consisted of a short-term and a long-term programme. In the short-term programme, 120 × 600 × 2000 mm concrete slabs were subjected to drying shrinkage. In the long-term programme, 100 × 500 × 3200 mm concrete slabs were loaded and unloaded under severe conditions of deicing salt applications. The test results showed that the use of polymer grids can minimize shrinkage cracking. Also, in the occurrence of a crack, the presence of polymer grids as secondary reinforcement resulted in controlling the crack width.