Providing the minimum flexural reinforcement requirements for concrete girders specifies that additional reserve capacity is provided over the flexural cracking limit state. This ensures that collapse will not occur upon flexural cracking. The AASHTO LRFD Bridge Design Specifications (2017) for the minimum flexural reinforcement requirement are experimentally based on research from 1962 and did not include segmental girders, which were not prevalent at the time. Furthermore, there has not been research regarding the minimum flexural reinforcement for segmental girders. There is also research suggesting that scale effects have an influence that was not captured in previous experimental programs. This thesis is completed to evaluate the minimum flexural reinforcement in concrete girders as part of the National Cooperative Highway Research Program (NCHRP) 12-94 project. The details of the construction of the reinforced concrete and pretensioned girders are presented. Experimental results and commentary of the testing on two reinforced concrete and three pretensioned girders have been documented. Further study was completed with the design and analytical study of segmental girders on important parameters used in deriving the minimum flexural reinforcement requirements regarding the AASHTO LRFD Bridge Specifications (2017).
The overstrength moment ratio required through the AASHTO LRFD Bridge Specifications (2017) has been clarified, which allows for an adequacy evaluation for minimally reinforced girders. Through the experiments, it is shown that the full-scale girders perform adequately, despite having the minimum or less than minimum flexural reinforcement. There is also further evidence provided for a decreasing modulus of rupture value for an increasing beam depth. The bond condition of the reinforcement is shown to be a significant factor and the overstrength moment ratio remains close to one for unbonded external segmental structures, despite substantially varying the amount of prestressing steel. Girders with bonded reinforcement achieve much higher overstrength moment ratios than girders with unbonded tendons and behave more similarly to pretensioned girders. Additionally, bonded reinforcement experiences local debonding which allows for greater ductility in the structures
