Earthquake Engineering Research - HKU Libraries - The University ...

304
concrete frames as documented in literature (Kowalsky et al. 2000). The program was
then used to evaluate the ability of concrete bridges to withstand seismic disturbance.
VALIDATION
The dynamic tests of a prestressed lightweight concrete bridge model specimen were
conducted at the University of California - San Diego (Kowalsky et al. 2000). The
dimensions and configuration of the specimen are shown in Fig. 5. The columns were
circular RC columns with 203 mm -diameter cross section. The girder was 381 mm x381 mm
square PC girder. A total prestress force of 445 kN was applied through four 15 mm
Dywidag bars. It was a shake table experiment; the specimen was subjected to a
predetermined ground motion, A mass block of 11643 kg was attached to the girder.
The fiber discretization of the cross sections of the fiber element model is shown in
Fig. 6. Since only two-dimensional analysis is needed, concrete of the cross section is
divided into layer fibers. Seven and six control sections for girder and columns are used
respectively. The material parameters used in the analysis are as indicated in Tables 1 and
2. The prestress forces were simulated with two horizontal concentrated nodal forces at
the two end nodes of the girder. The prestressing tendons were modeled by the offset
stress and strain with offset yielding strength due to the pretension. It was reported in
(Kowalsky et al.2000) that the strength of the steel was increased by strain rate and an
average yield stress enhancement of 13% was applied to their section analysis with better
agreement with experiment. Thus the average yield stress enhancement of 13% of steel
was also Mowed in the fiber element analysis.
Table 1 Analytical material parameters of steel
/,(MPa)
Hardening Ratio
Es(MPa)
dsu
Main Bar (DIORebar)
514.15
0.006
200000
0.09
Tendon (offset values)
419.88
0.0123
186000
—
Table 2 Analytical material parameters of concrete
/'c(MPa)
do
/«,(MPa)
dm
Unconfined
35.5
0.004
15
0.02
Confined
36
0.0048
16
0.023