Date of Graduation

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor

Micah Hale and Cameron D. Murray

Committee Member

Omar Manasreh

Second Committee Member

Canh N. Dang

Third Committee Member

Gary Prinz

Keywords

bridge girder, camber, deflection, creep, shrinkage, modulus of elasticity, prestress losses, prestressed concrete, prestressing strand

Abstract

Many precast, prestressed concrete girders have camber less or higher than the design values. This discrepancy between the design and the actual camber creates construction problems when installing the cast-in-place concrete deck. The objective of this research was to improve the accuracy of estimating long-term camber, deflection, and prestress losses of precast, prestressed concrete girders.

The experimental program consisted of measuring concrete properties and performing field measurements of camber, deflection, and prestress losses for girders in Arkansas. The investigation involved testing nine full-scale girders from two prestressed concrete plants that regularly supply concrete girders to bridge projects in Arkansas. The girders included AASHTO Types II, III, IV, and VI. Prestress losses were monitored for the nine girders. However, camber and deflection were measured for a total of 87 girders.

Field measurements and laboratory testing showed that the current method that the ARDOT uses overestimates camber, specifically in the AASHTO Type II and III girders. Field measurements indicated that the design erection camber was greater than the average measured camber by 67%, 128%, 61%, and 25% for the AASHTO Type II, III, IV, VI girders, respectively. The overestimation in camber was mainly attributed to the actual concrete compressive strength at release being greater than the specified compressive strength as high as 73% for some girders. It was also determined that the 2014 AASHTO LRFD Refined Method for estimating prestress losses overestimated the total prestress losses at the time of deck placement for the AASHTO Type II and III girders.

Available for download on Wednesday, April 26, 2023

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