Sandepudi, Krishna Srinivasa.

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.

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.