17-01-2013, 03:35 PM
STREGTHEIG OF RC BEAMS WITH PREFABRICATED RC RECTAGULAR CROSS-SECTIOAL PLATES
STRE.pdf (Size: 2.21 MB / Downloads: 102)
Abstract :
The topic of this study is to strengthen cracked beams with prefabricated RC
rectangular cross-sectional plates. The damaged beams were repaired by epoxy based
glue. The repaired beams were strengthened using prefabricated RC rectangular crosssectional
plates. The strengthening plates were bonded to the bottom face of the beams
by anchorage rods and epoxy. The strengthened beams were incrementally loaded up to
maximum load capacities. The experimental results were satisfactory since the load
carrying capacities of damaged beams were increased approximately 47% due to
strengthening. The post-elastic strength enhancement and the displacement ductility of
all the beams are researched during the experiments. The experimental program was
supported by a three-dimensional nonlinear finite element analysis. The experimental
results were compared with the results obtained from the beam modeled with ANSYS
finite element program.
INTRODUCTION
Beams and columns of buildings or bridges that have been built long time ago or
damaged due to an earthquake or other reasons are usually strengthened. In
strengthening of beams, increasing the depth of a beam with a bonding plate is
frequently used. For this reason, various techniques are proposed. The techniques used
commonly in literature are to strengthen a beam by bonding steel plates [1, 2, 3].
Swamy et al. [4] researched the effect of glued steel plates on the first cracking load,
cracking behavior, deformation, serviceability, and ultimate strength of RC beams.
Adhikary and Mutsuyoshi [5] studied RC beams strengthened in shear with web-bonded
continuous steel plates. Su et al. [6] investigated ductility performance of concrete
beams under different bolt-plate arrangements. Instead of a steel plate, a FRP plate is
also used in literature [7, 8, 9, 10, 11, 12]. Ceroni [13] researched RC beams externally
strengthened with Carbon Fiber Reinforced Plastic (FRP) laminates and Near Surface
Mounted (NSM) bars under monotonic and cyclic loads.
EXPERIMETAL PROGRAM
Test setup
All beams were incrementally loaded up to maximum load capacities in order to define
the load–displacement relationship. A single point bending test setup was adopted, as
shown in Fig. 1. The beams were simply supported with the clear distance of 1800 mm
between the supports and loaded at mid-span. Load was applied by a 250 kN hydraulic
jack in the vertical direction. Mid-span displacements of beams were measured with the
help of a linear variable displacement transducer (LVDT). The beam was incrementally
loaded up to the failure under load control. For each increment of the load, the
displacements were measured by the help of LVDTs placed at mid-span.
Bonding procedure
The strengthening plates were bonded to the bottom face of the repaired beams by Hilti
and anchorage rods. Before the anchorage rods of 10 mm in diameter and 200 mm in
interval were applied, the holes of 12 mm in diameter on the bottom faces of the beams
and strengthening plates were opened. These holes were filled by “Hilti”. The
anchorage rods were driven about 150 mm into the holes, as seen in Fig.2, Fig.3.
FIITE ELEMET METHOD
In order to compare the experimental results, a nonlinear finite element model with
ANSYS [20] was used to determine the ultimate load capacity of the beams. The
properties and geometric characteristics of the beam in the nonlinear finite element
model were taken the same as in the tested beams. Material properties of concrete and
steel reinforcement in nonlinear finite element analysis are given below.
Concrete
In this study, Hognestad concrete model was used due to lack of confinement for the
concrete [21]. The stress-strain values obtained from this model were used in the
definition of the multilinear isotropic model. In the Hognestad concrete model, the part
of stress strain curve until to the peak considered to be parabolic in the second degree;
and the downward part considered to be linear. In the model, the formula for the
parabola of the curve until the peak is given in Eq.(1) and for the maximum deformation
in Eq.(2).
CONCLUSION
There are several strengthening methods found in the literatures which use FRP plates
or steel plates. But, corrosion is important problem for steel plates. Although FRP plates
are safe and light in weight, fire and freeze-thaw are important problems for them.
Moreover, strengthening with FRP and steel plates, the structure does not get extra
strength against lateral loads.