This research investigates the potential of a new technique designated as Partially Embedded Bars (PEB) for shear-strengthening of existing reinforced concrete (RC) bridge girders. In this
technique, shear strengthening is achieved by inserting steel or FRP bars into holes bored through
a partial depth of the girder cross-section and then bonded with an epoxy adhesive. The PEB
approach is a modification of an existing retrofit technique, referred to as Deep Embedment (DE)
or Embedded Through Section (ETS) technique. Experimental studies by previous researchers
have been limited to the DE or ETS method wherein steel or CFRP bars are inserted through the
full depth of the RC girder, which can be time-intensive (since access to the bottom of the bridge
is necessary) and uneconomical. In addition, most of the reported studies are limited to small-scale
testing or comprise configurations that do not resemble typical highway bridges or Caltrans
practice.
A preliminary exploratory experimental program is first carried out comprising pull-out
testing to examine the several options that exist to implement the PEB approach – both in terms of
the strengthening bar material type (steel or FRP) and the type of bonding material (epoxy or grout)
to be used to anchor the bar into the girder web. The pull-out test campaign comprising thirty
rectangular concrete blocks with embedded uncoated traditional Steel (Grade 60 ksi), uncoated
High Strength Steel (HSS) Grade 80 ksi, and sand-coated and smooth carbon fiber reinforced
polymer (CFRP) bars bonded with either epoxy or grout was performed to determine the most
effective strengthening material option. Findings from the direct pull-out testing revealed that the
specimens with sand-coated CFRP bars bonded with the epoxy performed remarkably better than
the specimens with other strengthening materials.
Next, an experimental program comprised of three-point load bending testing to failure of full-scale RC T cross-section girders strengthened in shear was carried out. The tested girders
represent an existing prototype bridge from the Caltrans bridge inventory. The girders were
strengthened in shear with the PEB technique utilizing CFRP bars and epoxy adhesive using two
options. The primary goal of the first option was to evaluate the effectiveness of the PEB method
as a shear-strengthening technique, whereas the second option investigated the effect of increasing
the shear reinforcement ratio on the shear capacity gain associated with employing the PEB
method. Results from the two tests demonstrated that the PEB method is an effective shear-strengthening
technique. An increase of 53% and 30% was observed in the shear capacity of the
strengthened specimen compared to the control specimen. Results from the second test revealed
that increasing the shear reinforcement ratio has an adverse effect on the shear strength gain
associated with utilizing the PEB technique.
Finally, the experimental testing was supplemented with numerical simulations to provide
additional insight into the shear capacity gain as a result of implementing the PEB method.
Observations of the two tests were supported by the three-dimensional nonlinear finite element
modeling (FEM) which resulted in good correlations with global and local behaviors of the
experimentally tested girders. The validated model can be utilized to generate a parametric study
that can eventually lead to the development of a step-by-step design guideline to help bridge
engineers estimate the gain in shear capacity of RC girders strengthened with the PEB method.