This study investigates the feasibility of strengthening reinforced concrete beams with epoxy-bonded Glass-Fiber-Reinforced-Plastic (GFRP) plates. The composite plate is epoxy-bonded to the tension flange of the beam to increase its stiffness and strength. Seven rectangular and one T-beam, retrofitted with composite plates, were tested to failure under symmetrical 4-point bending. The load versus deflection and the load versus strain in the composite plate, steel rebar and the extreme compression fiber of concrete were measured and plotted for the midspan section throughout the entire range of loading up to failure. Analytical models based on the equilibrium of forces and compatibility of deformations were developed to predict the stresses and deformations of the beam in the linear and nonlinear regions. The predicted and measured results correlated well. The analytical models were used in a parametric study to investigate the effects of design variables such as, plate area, plate strength and stiffness, reinforcement ratio, etc., on the moment-curvature relationships of typical rectangular and T cross sections.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

No description available.

The main objective of this research is to estimate the sizes of riprap (loose rock) on highway or railroad embankments approaching bridges, that would be stable in major floods. Two assumptions about the flow direction were made: one horizontal to the bridge abutment and the other normal to the projection of the bridge abutment. Three dynamic conditions of stability of riprap were observed and classified as shaking, some movement, and large movement (washing out). Shaking is the most conservative criteria for design because it indicates more stability than is necessary, requires larger rock, and is less cost efficient. Some movement suggests a conservative design criteria and is the most desirable because it requires smaller riprap and is therefore less expensive. Large movement or washing out means the least stable condition; it may leave the structure as well as human lives exposed to danger.

This thesis is a contribution to the existing knowledge of the nature of the scour hole around bridge piers. The analysis is based on the fictitious, long contraction concept developed by Dr. Emmett M. Laursen. This concept and its equation has been used herein to determine the size of rip-rap particles which will reduce the local scour at bridge piers. Evaluation of the parameters involved in it is required for sizing the rocks in a prototype. Values such as approach velocity, water depth, average diameter of the rip-rap particles in the scour, and geometry of the pier are among the values to be known. Both a graphic and an analytical procedure are proposed as a means to find the size of particles to be used as protection. The discussion and conclusions derived from this investigation will be of great help to civil engineers working in the field of river engineering.

Hydrodemolition is the use of a high pressure water-jet to remove concrete. It is a new method of concrete removal which is becoming increasing specified by state Departments of Transportation for bridge rehabilitation work. The technical, financial and contractual aspects of using hydrodemolition are examined and a brief explanation of salt induced concrete deterioration in bridges is presented. Interviews were conducted with state DOT engineers, general contractors, specialty hydrodemolition subcontractors and hydrodemolition equipment manufacturers. These interviews identified problems encountered with using hydrodemolition. Possible solutions to these problems are presented. These possible solutions are based on both suggestions made by the persons interviewed and the author. / Master of Science

Due to the increasing rate of deterioration of concrete bridges caused by exposure to chlorides, it has become apparent that effective protection methods need to be employed which will prevent chlorides from reaching critical contamination within the life of the structure. One method of protection is the application of concrete surface sealers which form water-resistant barriers and reduce chloride intrusion. It is imperative to know how effective sealers are and how long sealers retain their effectiveness in order to plan reapplication and estimate life cycle costs for comparison to other maintenance activities. This research was conducted to predict the service life of concrete sealers for both horizontal and vertical bridge components. As a secondary goal, the use of a rapid, non-destructive Surface Absorption Test (SAT) was investigated as a possible substitute for analyzing the condition of sealers. This was done by comparing SAT results with the standard concrete sampling and chloride analysis technique typically employed. Four sealers were applied to horizontal laboratory specimens (slabs), vertical laboratory specimens (wall sections), and bridges (high-volume and moderate-volume). Control sections were also included in all specimen types. The laboratory specimens were exposed to a 3% NaCl solution for 30 1-week cycles, each cycle being three days of exposure and four days of air drying. Background chlorides and the chloride ion profiles were determined after 10, 20 and 30 cycles of saltwater exposure. The surface absorption test was conducted at various intervals throughout the cycles. The surface absorption test was also used to attempt to measure the traffic wear effect on the field specimens. The results indicate that the two epoxies exhibited very little effectiveness in preventing chlorides from entering the concrete. The silane and siloxane sealers performed much better in the laboratory settings, retaining over 90% reduction of chlorides throughout the test period. A service life model which includes laboratory performance and considers application exposure conditions is suggested. It has been discovered that, at present, surface absorption testing may be used on a limited basis to obtain results which indicate sealer effectiveness, but only if the testing occurs under extremely limited or controlled environments. / Master of Science

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Humanities, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND HUMANITIES. / Bibliography: leaves 115-118. / by Susan Kay Jackson. / B.S.

Following results over recent years, this thesis enhances the problem of minimizing a cost functional defined on a state trajectory of an autonomous switched dynamical system. The cost functional traditionally used, is augmented with explicit costs on the switching times and the final time is set by a constraint as opposed to being given. An equation for the gradient of the cost functional is derived and an algorithm is proposed for computing local minima. The algorithm is based on existing steepest descent methods including the Armijo procedure and gradient projection. A matlab implementation of the algorithm is developed in order to solve optimal problems that can be modelled with costs on or between the switching times. An existing problem, the motivation for this research, where repairs on a bridge is to be optimized, is provided and solved.

In 1991, seven corrosion inhibitors, surface applied liquids and concrete admixtures, were identified as promising for the repair of reinforced concrete structures subject to chloride induced corrosion. Small scale (1 ft.²) reinforced concrete specimens were cast to evaluate the inhibitors effectiveness. A treatment matrix was established to evaluate the inhibitors performance on three ranges of corrosion activity and evaluate the effect of application time and drying. Corrosion rate measurements taken with a linear polarization device were used to monitor the inhibitors effectiveness. The effect of the admixtures on the concrete properties, and the effect of the surface applied inhibitors on the overlay bond strength were evaluated. Rapid freeze-thaw tests were conducted to estimate the durability of the inhibitor modified concrete. Three combinations of inhibitors were identified for large scale testing after ten months of accelerated chloride exposure. The larger specimens, removed from an actual bridge deck, were treated to test the effective inhibitors field application techniques. Service life estimates were made for the two combinations of inhibitors which were most effective to aid the engineer in assessing the inhibitors cost effectiveness. / Master of Science