Abstract:
This thesis studies the dynamic responses of moving vehicle loads. This response is
measured for both transverse stresses and deformations in the cantilever slab adjacent to
the main deck of concrete highway bridges. The whole analytical process regarding this
investigation is based on finite element analysis. A finite element model to analyze the
cantilever three-span box girder bridge has been developed using shell element. A
vehicle is simulated according to the HS20-44 truck design loading contained in the
AASHTO specifications and vehicle load is applied at various points on the vehicle
path. A step by step full transient dynamic analysis has been performed. Parameters like
vehicle speed, span length, width of the cantilever part and damping condition are
included in the investigation with a systematic approach. Span length variation is done
with appropriate slab thickness and deck height for being realistic practice. Dynamic
amplification factors (DAF) are evaluated at various points along the middle span of the
bridge. From the numerical results, it has been found that dynamic amplification factor
is critical at the piers rather than mid span or other part of the span. The effects of
vehicle speed, span length and cantilever slab width on dynamic amplification factor
were significant. But the variation of the DAF with respect to those parameters is rather
arbitrary. Again, it was also found that 0% damping caused abnormally high value,
whereas, 2.5% and 5% damping gave closely similar values which was more realistic.
Based on the overall findings, DAF value for vertical deflections of the cantilever part
of deck slab is recommended as 1.7 near pier and 1.64 near midspan i.e. recommending
70% and 64% impact increment near pier and midspan over static results calculated for
deflections. Again, for stresses in the transverse direction DAF value is suggested as
1.91 near pier and 1.78 near midspan i.e. recommending 91% and 78% impact
increment near pier and midspan over static results calculated for stresses.
