Numerical methods in bridge structure analysis - Computational Analysis and Design of Bridge Structures - page 88

3.3.4 A simple example of creep analysis
A three-span continuous bridge that is built span by span will be used as an
example here to illustrate the concrete creep behavior and the application
of time incremental analysis method. The example has three equal spans
with a span length of 30 m (Fan 1998). The first construction stage is the
casting of the first 36-m girder segment with the support of falseworks (first
span plus 6-m cantilever). The falseworks are removed after the concrete is
cured for one week. The second stage is to cast the next 30-m girder seg-
ment. After the concrete is cured for the same number of days (one week),
the last 24-m segment is cast as the last stage. The bridge is completed after
the last segment is cured for one week. The structural weight is 100 kN per
meter. In this model 3D frame elements are used.
Figure 3.13 shows moment distributions after the bridge is built when
creep effects are not considered. The moments at the first and second
interior bearings are −4,928 and −7,005 kN-m respectively. For compari-
son, both would be −9,000 kN-m if the three-span bridge is built all at
once. Figure 3.14 shows the final moment distributions eight years after
the bridge is built. Due to creep effects, moments at the interior bearings
become −8,283 and −8,926 kN-m, respectively, revealing the tendency of
concrete creep that the internal forces distributions would eventually be

−7005

−4928

−4066

−3738

−2267

−1800

−1528

−87 1

0 −5 0

610

928

1595
3662
5329

1855

2348 2332

2471
4542
6214
7485
8357 8828 8899 8571 7842

3257 3317

437 5040 5302 5163 4625

3686

4265

5185

5798

6714 659 7463

7930 7997 766 6931

Figure 3.13 Moment distribution of a three-span continuous bridge built span by span,
without consideration of concrete creep considered (kN-m).

−8926

−8283

−6084

−5526
−3169
−1212
344

−5531

−4931

−3641

−2536

−1979

−1598

0 44 0

58
2253

573

1287

1501 2258 2616 2573 2130

2204

2247

2725

4009

4095
5543
6591

4048
5443

4477

5414

5829

6438 7034 7229 7024 6419

7238 7486 7334 6782

Figure 3.14 Moment distribution of a three-span continuous bridge eight years after
built span by span, with consideration of concrete creep considered (kN-m).