Shear repair methods for conventionally reinforced concrete girders and deep beams

by Howell, Daniel A.

Many conventionally reinforced concrete deck girder bridges (RCDG) and their intermediate supporting bent caps were designed during the Eisenhower interstate era of the 1950’s with the AASHO design equations at the time, which subsequently place higher demand on the concrete. The referenced components may exhibit diagonal cracking due to the initial design assumptions, increased traffic volume and truck weights, as well as temperature and shrinkage affects. Action is needed as these structures approach the end of their useful design life. Wholesale replacement is not economically feasible; therefore, repair may provide a more attractive alternative to maintain operational safety and freight mobility.

The current research program builds on previous work at OSU, which focused on estimating unrepaired specimen capacity, to include various repair methods. The experimental program included full scale testing of specimens with vintage 1950s details, reinforcing steel, concrete strength/composition, and flexural cutoffs details. Repairs included externally applied steel stirrups, supplemental internal stirrups, externally applied carbon fiber reinforced plastic (CFRP), carbon fiber tape utilized in a near surface mount application, and longitudinal post tensioning (bent cap specimen only). All specimens were initially loaded under quasi-static force control to produce diagonal cracks in the specimen then repaired and tested to failure.

Ultimate specimen capacity was compared against that predicted from those available in the literature (where applicable), international codes, sectional Modified Compression Field Theory (MCFT) analysis, Modified Zararis Mechanical Model (bent caps only), Strut-and-Tie methods (bent cap only), and nonlinear finite element analysis (NLFEM).

Results indicate the repair methods increased the member strength and the predicted member strenths compare well to certain international codes, sectional MCFT analysis, and nonlinear FEM element analysis. Some repair techniques such as surface mounted CFRP produced disparate outcomes for different specimen types. The NSM repair technique requires additional research to draw general conclusions. Longitudinal post tensioning compared well with the Modified Zararis method. STM methods form a very conservative lower bound for design and are thus not suggested for base specimen capacity prediction in a retrofit analysis. Design recommendations for the deep beams are not provided, as there is not sufficient data to support general conclusions.