Civil Engineering Reference
In-Depth Information
Table 10.3
Major design parameters of column specimens
Specimen
Prestressing force (kN,
f
pu
,
f
c
A
g
)
ED bar ratio (%)
ED bar detail Bar diameter (mm)
C5C
1042, 0.5, 0.072
0.5
16
C8C
1042, 0.5, 0.072
1.0
25
The specimens were modeled using the finite element mesh illustrated in Figure 10.17. The
two flange sides of the bridge piers which carry the bending moment, are subjected mainly to
compression and tension. They are modeled as nonlinear beam-column elements with fiber
sections. The two web sides of the bridge piers which are parallel to the bending direction
and thus resisting the shear force, are modeled by PCPlaneStress Quadrilateral elements. The
cap beam on the top of the column is defined as a rigid body in the finite element model. The
prestressing tendons in the center of the specimens were modeled separately using nonlinear
beam-column elements consisting only of fibers of TendonL01 material.
The boundary condition and load pattern in the finite element model were defined according
to the test condition, as shown in Figure 10.17. The axial loads acting on the columns were
applied as vertical nodal forces on the cap beam. The prestressing force was applied as a
vertical nodal load acting at the top and bottom of the column. The direction and magnitude
of the axial loads and the prestressing remain constant in the analysis. The horizontal forces
were changed according to the displacement control scheme.
The analysis procedure was separated into two steps. In the first step, the axial loads were
applied to the columns using load control by 10 load increments. In the second step, the
axial loads were kept constant and the reversed cyclic horizontal loads were applied by the
predetermined displacement control on the drift displacement. The common displacement
increment used in the analysis was 1.0 mm. The nodal displacement and corresponding
horizontal forces were recorded at each converged displacement step, and the stress and strain
of each of the elements were also monitored.
The SCS calculated load-drift relationships for the two specimens are compared with the
experimental results in Figures 10.18 and 10.19. It can be seen that the finite element analyses
successfully predicted the load-drift characteristics of the specimen, including post-cracking
stiffness, yield drift, ultimate strength, and energy dissipation. As observed in the experiment,
the finite element analysis could predict the specimens reaching its peak load in the 3% drift
loading cycle. The strength degradation in the post-peak region was also well predicted in the
analyses, both in the positive and the negative directions. The nearly flat-top envelopes of the
specimens (a typical behavior of the flexure mechanism) was also predicted by the analyses.
Table 10.4
Material properties of column specimens
Prestressing steel
ED bar
Concrete
compressive
strength (MPa)
Yield strength
(MPa)
Ultimate
strength (MPa)
Yield strength
(MPa)
Ultimate
strength (MPa)
Specimen
C5C
55
1670
1860
434
653
C8C
30
1670
1860
434
653
