Structural Engineering:
Moving Load Tests of Full-Scale RC Girders to Failure
Continually varying moment and shear interactions especially
those observed near continuous support locations can not be adequately produced
with stationary loading conditions. To address these conditions, a unique
loading system was developed to produce varying shear-moment interactions.
The moving load testing system was used to test four full-scale CRC girder
specimens constructed with 1950’s design details and construction practice.
A combination of live (moving) and superimposed dead (stationary) loads were
applied to the test specimens. The magnitude of live load was increased until
failure of the specimen was achieved.
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| Fig. 1. Moving load testing frames. |
Fig. 2. Moving load assembly and telescoping push-pull
cylinders. |
Conclusions
A research program was conducted to evaluate structural performance
of simulated RCDG bridge girders subjected to moving loads. A unique moving
loading system and testing methodology were developed to test four full-scale
CRC girder specimens. The specimens represented 1950’s design and construction
practice and were subjected to continually varying shear-to-moment ratios
from the moving load apparatus. Based on the laboratory tests, the following
conclusions are presented:
- CRC girders subjected to moving loads exhibited different cracking patterns
than those subjected to stationary loading. Cracks on girder specimens
subjected to moving loads tended to be more vertically oriented, more
widely spaced, and crossed concrete compression struts.
- Application of laboratory moving loads produced load histories at critical
sections in CRC girders that are more reflective of those for in-service
bridge girders subjected to moving vehicle loads than those produced by
stationary loading.
- The major component of crack motion for girders subject to stationary
loading is transverse to the crack. By comparison, moving loads produced
longitudinal motions along diagonal cracks that were equal to or greater
than the observed transverse motion. The almost circular crack motions
produced during load passage may enhance aggregate interlock at diagonal
cracks during the compression phase. However, repeated loading over time
may wear the crack faces and reduce force transfer effectiveness across
the crack interface.
- Moving loads produced strain reversals in the stirrups, with strain
magnitudes less than the static dead load strain. This increases the magnitude
of the stress range for fatigue considerations as compared with stationary
loading and may also result in increased bond deterioration rates under
repeated loading.
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