Arockiasamy, Madasamy

This thesis presents the experimental and analytical investigation of fiber (steel and Kevlar) reinforced concrete (FRC) to determine its fracture mechanic properties especially the J-integral. The freeze-thaw durability of fiber reinforced and air-entrained concrete is also investigated. The fiber reinforced concretes were found to have a much greater flexural strength and toughness compared to plain concrete. The compressive strength was found to decrease with the addition of fibers and air-entrainment. In all cases the addition of 1.0% or more fibers prevented catastrophic failures. The mixing and setting of FRC requires a rigorous procedure which must be followed to achieve a homogeneous matrix.

The feasibility of the use of double-tee beams in a bridge system is examined by conducting tests on a 1:3.5 scale model of a two-span transversely and longitudinally post-tensioned continuous double-tee beam system. Constant amplitude fatigue loading was applied on the model at typical locations simulating HS 20-44 AASHTO truck loading. The behavior of the bridge system was evaluated in terms of deflections, wheel load distributions, crack growth and patterns with increasing number of cycles of fatigue loading. A finite element analysis of the bridge system was done using plate and beam elements and results compared with experimental values.

Durability of concrete bridge decks reinforced with conventional structural steel is a major concern in aggressive environments. To address this problem, there have been efforts, in recent years, to develop and evaluate alternatives to conventional steel. One alternative is fiber reinforced polymer (FRP) composite reinforcement. FRP composites have been used successfully in many industrial applications. This thesis investigates short-term mechanical properties of FRP rebars as reinforcement for concrete bridge decks and discusses results of extensive laboratory tests. Four test methods (tension, flexure, shear and bond) are developed and test protocols are proposed for adoption by AASHTO.

Flexible plastic and metal pipes are increasingly being used for drainage and storm sewers. When flexible pipes are buried at shallow depths, the pipe behavior will not depend on the dead load pressure above the crown, but rather on the live load pressure (vehicle load). Field tests were designed to evaluate the performance of large diameter flexible pipes of 36 in. (915 mm.) and 48 in. (1050 mm.) under shallow burial depths subjected to the actual vehicle loading. The test pipes included high-density polyethylene (HDPE) pipes, polyvinyl chloride (PVC) pipes, steel pipes and aluminum pipes. AASHTO standard pipe installation procedures were followed and pipes subjected to vehicle loads simulating the effect of HS 20-44 trucks. Measurements of interior pipe-wall strains, soil pressures at different depths and pipe deformations were taken to determine the influence of surface vehicle loads. Results of field tests are compared with those based on theoretical analyses.

Integral construction is being used to reduce the maintenance cost and avoid problems associated with bridge deck joints. Continuous deck jointless bridges with joints only at abutments and integral bridges with no joints at abutments are two major types of integral constructions being adopted. Integral abutment bridges accommodate superstructure movements without conventional expansion joints. The current practices adopted by various state departments of transportation are evaluated to arrive at a rational design procedure for integral abutment bridges. An illustrative numerical design example of an integral abutment bridge is presented with emphasis on the pile-soil interaction, temperature, creep and shrinkage effects and varying soil strata. Important design parameters are identified concerning the selection and design of pile, use of predrilled hole, the type of fill in the predrilled hole, elevation of water table, soil type, and pile orientation. The effect of these parameters are analyzed using LPILE and FB-Pier computer programs.

This study presents the experimental and theoretical studies on debond of carbon fiber laminates bonded to concrete, which aids in understanding the mechanics of the repaired damaged prestressed concrete girders with externally bonded carbon plates. The bond strength of carbon plate specimens bonded to concrete is determined experimentally by the debond test. The initial crack is introduced in the specimens at one location, namely the plate/adhesive interface. The fracture toughness for debonding is evaluated and expressed as the critical strain energy release rate. A finite element analysis was performed to evaluate the compliance and stress distribution in the debond test specimens.

One of the major problems the construction industry faces today is corrosion of reinforcing and prestressing steel, which significantly affects the durability of concrete structures. Fiber reinforced plastics (FRPs) are highly regarded as prospective replacement for steel in prestressed concrete structures under corrosive environment. This investigation was conducted to establish the feasibility of using Carbon Fiber Composite (CFC) cables as reinforcing/prestressing elements in concrete bridge structures. Besides investigating durability of CFC cables and pretensioned concrete beams with CFC cables in adverse environments (alkali and seawater), flexure and shear tests were performed on single Double-Tee beams, together with service load behavior, fatigue strength and ultimate load capacity tests on a half scale model Double-Tee girder bridge system prestressed with CFC cables. Exposure to seawater and alkali environments has no adverse effect on the strength of the CFRP tendons as well as the pretensioned beams with CFRP. Based on the flexural strength tests on Double-Tee beams, the bond between CFRP tendons and concrete is satisfactory. The Double-Tee bridge system exhibited good fatigue resistance and adequate ductility under ultimate load conditions. The ultimate load capacity of the bridge is approximately three times the service load corresponding to two HS20-44 trucks and equals 2.4 times the first crack load. Finite element analyses were carried out to predict elastic deformations and collapse load of the Double-Tee bridge prestressed with CFC cables. Feasibility of using CFC cables in bridge structures is assessed based on the experimental and analytical parameters such as deflections, strains, crack distributions and crack widths.

One of the major problems the construction industry faces today is low corrosion resistance of reinforcing and prestressing steel, which significantly affects the durability of concrete structures. Theoretically Advanced Composite Materials (ACM) can successfully be used in concrete structures, in lieu of steel, as reinforcing and/or prestressing elements, owing to high tensile strength, immunity towards corrosion, low Young's modulus, light weight and high fatigue resistance. Very little experimental and performance data are available on the properties of ACM and their application in concrete structures. Thus, to ensure safety of the structures, accurate assessment and continuous performance monitoring of the ACM together with the structure have to be made with an option of active and/or passive structural control. This investigation is aimed to establish the feasibility of using Aramid Fiber Reinforced Plastic (AFRP) cables as reinforcing/prestressing elements in concrete bridge structures. Besides investigating the durability of the AFRP cables in adverse environments (alkali and seawater), static and ultimate load tests were performed on a Double-Tee beam and three rectangular beams together with static, fatigue and ultimate load tests on a half scale model Double-Tee bridge system prestressed with AFRP. The AFRP specimens exposed to alkali and seawater for 900 hours retained 88% of the average failure strength of control specimens. Large deformations at ultimate conditions and good fatigue resistance were observed in the experimental studies. A computer code, FRPFLEX, was developed to perform flexural analysis of beams prestressed/reinforced with the ACM. An incremental, stiffness augmented non-linear analysis was performed using grillage analogy to assess static flexural behavior of Double-Tee bridge system. Analytical results showed good correlation with experimental findings. An active deformation/vibration control model is suggested, which can be incorporated in prototype bridges for safety and performance data evaluation. Feasibility of the use of the AFRP cables in bridge structures is assessed based on the experimental and analytical parameters such as deflections, strains, crack distributions, crack widths and energy considerations.

The effects of various nonuniform stress fields on the stress intensity factors for the semi-elliptic surface crack (three-dimensional problem) in a finite plate are determined using the weight function approach. The formulation satisfies the linear elastic fracture mechanics criteria and the principle of conservation of energy. Based on the knowledge of stress intensity solutions for the reference load/stress system, the expression for the crack opening displacement function for the surface crack is derived. Using the crack opening displacement function and the reference stress intensity factor, the three-dimensional weight functions and subsequently the stress intensity solutions for the surface crack subjected to nonuniform stress fields are derived. The formulation is then applied to determine the effects of linear, quadratic, cubic, and pure bending stress fields on the stress intensity factor for the surface crack in a finite plate. In the initial stage of the study a two-dimensional problem of an edge-crack emanating from the weld-toe in a T-joint is considered. The effect of parameters such as plate thickness, weld-toe radius, and weld-flank angle on the stress intensity factor for an edge-crack is studied. Finite element analyses of the welded T-joints are performed to study the effects of plate thickness, weld-toe radius and the weld-flank angle on the local stress distribution. The ratio of plate thickness to weld-toe radius ranging from 13.09 to 153.93, and the weld-flank angles of 30, 45, and 60 degrees are considered in the analyses. Based on the results from FEM analyses, a parametric equation for the local stress concentration factor and a polynomial expression for the local stress distribution across the plate thickness are derived using the method of least squares and the polynomial curve-fitting technique.