PhD thesis,
Flexural Strengthening of Reinforced Concrete Beams With Mechanically Fastened Fiber Reinforced Polymer Strips
University of Wisconsin В– Madison, (2002)
Abstract
The purpose of this research was to study a new method of flexurally
strengthening reinforced concrete beams. The proposed method uses
multiple mechanical fasteners unlike current practice, where a fiber
reinforced polymer (FRP) strip is attached to the beam with an adhesive.
In order to study the method of strengthening beams by mechanically
attaching FRP strips, construction engineering, material engineering,
and structural engineering research areas were addressed. Coupon
tests were performed on the material components. Custom FRP strips
were designed specifically for use with mechanical fasteners. Behavior
of connections with single and multiple fasteners were examined experimentally,
and small-scale beam tests were conducted to examine the feasibility
of the overall method and to further identify factors affecting the
structural behavior of the strengthened beam. Large-scale experiments
were conducted in order to examine the behavior of larger beams with
the custom strips. Parameters such as fastener spacing, pre drilling
pilot holes and edge distance were examined in these tests. To further
increase
the understanding of the method, an analytical model was developed
and predictions obtained by analysis were compared to the experimental
results. The analytical model was developed to consider the unique
factors that affect the strength of a beam with a mechanically fastened
strip; the fastened connection strength, the total number of fasteners
required to develop the strength of the strip, and the distance between
the last fastener and the support. Issues of strip termination were
examined both experimentally and analytically.
The research results showed that longitudinal moduli and strength
results for the custom strips closely matched the target design values.
Small-scale beams were successfully strengthened using a mechanically
fastened FRP strip, and showed increases of yield and ultimate moment
capacities of 34.2 and 24.8 percent over the unstrengthened control
beams. Large-scale beams with mechanically fastened custom FRP strips
showed increases of 21.6 and 20.1 percent in the yield and ultimate
moments over the unstrengthened control beams. Large-scale beams
not only achieved levels of strengthening comparable to the adhesively
bonded method, but the fastened method resulted in strengthened beams
with a gradual failure mode, as opposed to the sudden failure mode
of the adhesively bonded beams. The FRP strip attachment with mechanical
fasteners was completed in less time than it took to attach the FRP
strips with an adhesive.
Analytical and experimental investigations have shown that reinforced
concrete beams can be flexurally strengthened by mechanically attaching
a custom FRP strip. With special attention given to material and
construction considerations, this method has the potential of providing
a strengthened member with a gradual failure mode, as opposed to
the sudden failure mode exhibited by current adhesively bonded methods.
