Reinforced Concrete
One of the earliest studies into the development of the new repair technique investigated
the flexural behavior of reinforced concrete rectangular beams with epoxy bonded
Fiber Reinforced Polymer (FRP) laminates. The primary area of interest was the magnitude
of increase in strength and stiffness of the beams provided by the bonded laminates.
The effectiveness of external reinforcement was assessed in terms of deflection,
cracking and ultimate load. Deflections, strain distributions, crack development
and modes of failure were evaluated for a series of many full scale test beams with
varying amounts of FRP laminates.
The beams were tested under four-point static loading to ultimate failure. Strains,
deflections, cracking and the applied load were recorded at every load increment.
On approaching the ultimate capacity, the load was then released slowly and strain
and deflection data were recorded. Crack patterns were plotted at each load step
up to ultimate.
An important variable was the number of applied laminates. All the strengthened
laminated beams failed by concrete crushing with a significant increase in the flexural
capacity. Beams with three FRP laminates exhibited a considerable increase in flexural
capacity and ductility.
The stress-strain relationship for the FRP laminate is linear up to fracture, however,
the beams exhibited substantially large deflections beyond the yield stress of the
steel reinforcement. Hence, through proper design, FRP laminates can be used as
an effective external reinforcement.
Strains in the concrete and FRP laminates are much reduced with the increasing number
of laminates. At any applied moment, the laminated beams exhibited smaller strain
values than the control beam, indicating an enhanced concrete confinement due to
the applied FRP laminates.
Theoretical analysis using computer software developed by SDR was used to predict
the structural behavior of the beams. The program considers non-linear material
properties and is capable of analyzing reinforced or prestressed concrete beams
subjected to external loads. The stress-strain relationship of concrete, steel and
FRP laminates can be input directly into the program.
Additionally, a loading history can be applied to the structure that matches the
exact test conditions. The actual material properties at the end of each load step
are recalculated and used in the analysis for the next loading phase.
The nonlinear finite element program was used to model the behavior of all test
specimens. In all cases the theoretical results agreed closely with the test results.
Experimental and theoretical results generally indicated that the flexural strength
of deficient beams is significantly increased. The results showed that for fully
wrapped rectangular members, flexural strength gain could increase up to 70% depending
on the number of applied CFRP layers.
This finite element software has been further calibrated and refined through extensive
testing of different structural members to yield accurate predictions.
Computer modeling procedures have been developed in which an accurate representation
of the existing member can be created, and the best configuration and quantity of
the FRP can be determined.
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