Recent earthquakes have demonstrated that most of the reinforced concrete
structures were severely damaged during earthquakes and they need major repair works.
Beam column joints, being the lateral and vertical load resisting members in reinforced
concrete structures are particularly vulnerable to failures during earthquakes. The existing
reinforced concrete beam-column joints which are not designed as per code IS
13920:1993 must be strengthened since they do not meet the ductility requirements. The
finite element method (FEM) has become a staple for predicting and simulating the
physical behavior of complex engineering systems. The commercial finite element
analysis (FEA) programs have gained common acceptance among engineers in industry
and researchers. The details of the finite element analysis of beam column joints
retrofitted with glass fiber reinforced polymer sheets (GFRP) carried out using the
package ANSYS are presented in this paper. Three exterior reinforced concrete beam
column joint specimens were modeled using ANSYS package. The first specimen is the
control specimen. This had reinforcement as per code IS 456:2000. The second specimen
which is also the control specimen. This had reinforcement as per code IS 13920:1993.
The third specimen had reinforcement as per code IS 456:2000 and was retrofitted with
glass fiber reinforced polymer (GFRP) sheets. During the analysis both the ends of
column were hinged. Static load was applied at the free end of the cantilever beam up to a
controlled load. The performance of the retrofitted beam-column joint was compared
with the control specimens and the results are presented in this paper.
Key words: Beam column joint, Retrofitting, FRP sheets. The techniques of using fiber sheets for strengthen the beam column joints have a number of favorable characteristics such as ease to install, immunity to corrosion and high strength. The simplest way to strengthen the joints is to wrap fiber sheets in the joint
region in two orthogonal directions. Many fiber reinforced polymer sheets are available the market for strengthening reinforced concrete members .Glass fiber reinforced
polymer sheets are commonly used for retrofitting the structural elements.
The beam column joint considered for analysis consists of a cantilever portion and
column portion as shown in Figure 1.a and Figure 1.b. The column had a cross section of
200 mm x 200 mm with an overall length of 1500 mm and the beam had a cross section
of 200 mm x 200 mm and the length of the cantilevered portion was 600 mm. The control
specimens were designated as C1 and C2. C1 had reinforcement as per code IS 456-2000
and C2 had reinforcement as per code IS 13920-1993. The specimen retrofitted with glass
reinforced polymer sheet was designated as C3 which had reinforcement as per code IS
456-2000. The column portion was reinforced with 4 numbers of 12mm diameter Fe 415
rods and the beam portion was reinforced with 2 numbers of 16 mm diameter Fe 415 rods
each in the tension and compression zones. The lateral ties in the columns of the
specimens C1 and C3 were 6 mm diameter Fe 250 bars with the spacing of 180 mm c/c
as per code IS 456:2000, clause 26.5.3.2(c). Beam had vertical stirrups of 6 mm diameter
Fe 250 bar at 120 mm c/c as per code IS 456:2000, clause 26.5.1.6. The development
length of the tension and compression rods in beam were also provided as per clause
26.2.1 of code IS 456:2000. For the specimen C2, the lateral ties in the columns consisted
of 8 mm diameter Fe 415 bar at 75 mm c/c for the central distance of 1100 mm as per
code IS 13920:1993, clause 7.4.6 and 6mm diameter Fe250 bars at 100 mm c/c for the
remaining length of the column. Beams had vertical stirrups of 6 mm diameter Fe 250 bar
at 40 mm c/c. up to a distance of 340 mm from the face of the column as per code IS
13920:1993, clause 6.3.5 and 6 mm diameter Fe250 bar at 80 mm c/c for remaining
length of the beam. The development length of the beam rods were also provided as per
code IS 13920:1993, clause 6.2.5. M25 grade concrete was adopted. 13920:1993
Meshing was done for both control and retrofitted specimens using ANSYS. Both ends of
the column were hinged. The concrete was modeled using Solid 65 element. The
reinforcement was modeled using Link 8 element. The wrapping was modeled using
Solid 45 element. The static load was applied at the free end of the cantilever beam at a
regular load interval of 5 kN for the control and retrofitted reinforced concrete beam
column joint models. The performance of the retrofitted beam column joint specimen was
compared with the control beam-column joint specimens
NON LINEAR MODELING OF THE BEAM-COLUMN JOINTS
Non linear analysis was done for three beam column specimens using the
software ANSYS. A transverse static was applied at the free end of the beam to develop a
bending moment at the joint. The load was increased in steps till a controlled load of 22
kN. The deflection at the free end of the cantilever beam was noted. The deflections of
the specimen C1 were found to be 12.5 mm for the load of 15 kN, 35 mm for the load of
20 kN, and 56 mm for the load of 22 kN. The same procedure was repeated for the
specimen detailed as per code IS 13920-1993 and for the retrofitted specimen. Figure 3a,
Figure 3b, and Figure 3c show the typical views of the deflected control and retrofitted
specimens. Figure 4 shows the load deflection curve for the control and retrofitted
specimens. Table 1 shows comparison between the deflections and energy absorption
capacity of the control and retrofitted specimens.
DISCUSSION OF THE RESULTS
It can be found from the Table 1 that the deflection of the beam column joint
specimen detailed as per code IS 13920-1993 is 19.64 % less than that of the specimen
detailed as per code IS 456-2000 and deflection of the beam column joint specimen
retrofitted with glass reinforced polymer sheet was 42.85 % less than that of the
specimen detailed as per code IS 456-2000.The energy absorption capacity of the
specimen beam column joint specimen detailed as per code IS 13920-1993 is 15.93 %
more than that of the specimen detailed as per code IS 456-2000 and energy absorption
capacity of the beam column joint specimen retrofitted with glass reinforced polymer
sheet was 34.22 % more than that of the specimen detailed as per code IS 456-2000.
CONCLUSIONS
Based on the ANSYS modeling and analysis carried out on the control and retrofitted beam
column joint specimens using GFRP sheets, the following conclusions were drawn:
• The deflection of the beam column joint specimen detailed as per code IS 13920-1993
was found to be 19.64 % lower than that of the specimen detailed per code IS 456-
2000.
• The deflection of the beam column joint specimen retrofitted with GFRP sheet reduced
the deflection about 42.85 %.when compared with the deflection of specimen detailed
as per code IS 456-2000.
• The energy absorption capacity of the beam column joint specimen detailed as per code
IS 13920-1993 was found to be 15.93 % higher than that of the specimen detailed per
code IS 456-2000.
• The energy absorption capacity of the beam column joint specimen retrofitted with
GFRP sheet increased about 34.22 %.when compared with the energy absorption
capacity of specimen detailed as per code IS 456-2000.
No comments:
Post a Comment