Arockiasamy, Madasamy

The flexural behavior of rectangular concrete beams strengthened with externally bonded Carbon Fiber Reinforced Plastic (CFRP) laminates was studied by varying the number of plates bonded to their bottom tensile face. The increases in strength and stiffness of the beams provided by the bonded plates, over control beam without CFRP plates, were evaluated. Failure loads of the beams were determined by the ACI strain compatibility method using a FORTRAN software developed for this purpose. The predicted collapsed load agrees reasonably well with the actual failure load. Precracked solid and voided slab bridge models retrofitted with varying number of CFRP laminates were used to evaluate their contribution to the flexural resistance. The increases in strength and stiffness of the retrofitted slabs were based on the deflections, strains and crack patterns at ultimate load. Theoretical analyses to predict the load-deflection behavior of the precracked sections were performed using PCFRAME software. The predicted values agree reasonably well with the experimental results.

Nonlinear finite element analyses of the reinforced rectangular beams, prestressed solid slab and prestressed voided slab retrofitted with CFRP laminates are carried out using the software ANSYS(version 5.0) on the Sunwork station. The computer analyses are based on the proposed stress-strain relationship considering the effects of tensile stress on both elastic modulus and maximum compressive stress of concrete. Several assumptions are made in predicting the loss of tensile strength due to crack, confinement due to the laminate bonding, tensile strength due to the prestress force, failure pattern due to the concentrated stress adjacent to the loading point and concrete crushing due to large compressive strain. A subroutine is developed using macro commands of ANSYS. In this research, Branson's equation or Ie procedure is assumed in the prediction of deflection of retrofitted concrete members. The modifications needed due to laminate bonding are the cracking moments of inertia (Icr) of the beams or slabs bonded with CFRP laminates, which are included in the analysis.

The feasibility studies on the use of non-metallic continuous fiber reinforcement in reinforced and prestressed concrete structures are presented herein. Experimental results from studies on relaxation, bond and transfer length of Carbon Fiber Composite Cables (CFCC) are presented followed by results of flexural load tests on concrete beams reinforced and prestressed with CFCC. Durability of the CFCC is another prime concern, and hence part of the study also focuses on establishing the durability of the CFCC exposed to aggressive environments like alkali solution and sea water. The basic mechanics that govern the structural behavior of the beams, provide important insight into the potential that CFCC has to offer.

The automation of retaining structure selection and design by utilizing artificial intelligence tools is presented herein. The study involved the development of a microcomputer based expert system, RESTEX (REtaining STructure EXpert). The modules of the expert systems RETAININGEARTH, with M.1 knowledge base, and REFLEXYS have been updated and the resulting RESTEX modules are written in C using Exsys Professional for high speed and efficient utilization of memory. RESTEX is an interactive menu-driven system consisting of modules for Structure Selection, Preliminary Design, Soils Classification, Stability Analysis, and Reinforcement Design. The system is capable of performing selection, analysis, and design of gravity walls, cantilever walls, counterfort walls, reinforced earth, gabion, cantilever and anchored sheet piles.

The automation of bridge strength evaluation by utilizing artificial intelligence tools is presented herein. The study involved the development of a microcomputer based expert system, REX (Rating EXpert). REX is an interactive menu-driven system combining the expert system shell EXSYS, the Grillage program 'BRIDGES', and various other pre- and post- processing devices. The system is capable of analyzing and assessing the load carrying capacity of solid and voided slab, and AASHTO girder and slab bridges.

Reinforced and prestressed concrete bridges are subjected to non-linear temperature
variations leading to complex thermal stresses which vary continuously with time. Though
these stresses are often comparable with those produced by live and dead loads, little
guidance is given in bridge design codes on how these stresses are accurately computed.
The objective of this project is to study the response of Florida bridges in the extreme
thermal environment The project is divided into the following four tasks
i) Computer modeling of the bridge and estimation of the thermal response.
ii) Field measurements of temperatures in typical bridges.
iii) Comparison of observed and estimated data.
iv) Suggestions and/or revisions to the existing thermal stress allowances in the code.
A computer software FETAB was used to model and analyze the thermal response
of several bridge cross sections. Two single cell box girder bridges, located at the 1-595
and US-441 interchange, Fort Lauderdale, were instrumented with thermocouples and
vibrating wire strain gages. The predicted temperature variations were found to compare
fairly well with those measured in the field. Though the analytical values vary a little from
the actual field data, emphasis was given to gain insight into the problems associated with
the thermal effects in concrete bridges. Suggestions were made for revision of existing
design code provisions for improved design of bridges.

The behavior of a precast single-cell segmental box bridge with external post-tensioning is studied based on a 1:3.5 scale model of the Long Key bridge in the Florida Keys. Constant amplitude fatigue loading was applied on the model at a critical location simulating HS20-44 AASHTO truck loading. The performance of the bridge model was evaluated in terms of deflections, strains in concrete and across the joints, and behavior of joints between the segments with increasing number of cycles of fatigue loading. Thermal response of the bridge model was also studied using finite element analysis and the predicted temperature distributions were compared with the experimental values.

This thesis describes the development of a microcomputer based prototype expert system, RETAININGEARTH, for the selection and design of earth retaining structures. RETAININGEARTH is an interactive menu-driven system and consists of two modules--the selection module, SELECTWALL and the design module. SELECTWALL is developed using the rule-based M.1 knowledge engineering shell and it makes a choice of the most appropriate retaining structure from a list of ten typical walls. The design module consists of five independent design programs which performs detailed designs of the concrete gravity and cantilever walls, gabions, reinforced earth and sheetpile structures. The SELECTWALL and the design module are linked by the M.1 external code EXT through a control program CALL. All the design procedures are coded using the C programming language.

This thesis presents a procedure for the selection and design of retaining walls using an expert system. The selection part is formulated in the form of production rules by OPS5, a programming language for production systems, and the design part is written in the procedural language, BASIC. Nine different types of retaining walls are incorporated in the knowledge base of the selection part, and three types of walls in the design part of the expert system. The selection and design parts are combined using OPS5 support routines.

The feasibility of the use of precast prestressed concrete multi-box beams with transverse post tensioning is examined for a medium span bridge system based on analytical and experimental studies on a 1:2.5 scale model. Constant amplitude fatigue loading was applied on the model at typical locations simulating HS20-44 AASHTO truck loading. The performance of the bridge system was evaluated in terms of deflections, strains in the concrete, wheel load distribution, and behavior of longitudinal joints with increasing number of cycles of fatigue loading. A grillage analysis of the bridge system was carried out to predict the elastic behavior and the cracking moments and the results compared with the experimental values.