huangyhg

cast-in-place bridge abutment
i'm currently designing a bridge abutment for a pre-engineered steel bridge.
i have done similar designs in the past.
the bridge is a 40'x16' single span with one fixed bearing and one expansion bearing.
a colleague advised me that i should design the abutment stem assuming that the bridge superstructure provides lateral support.
through my research and study i have found that if a bridge has a fixed bearing at one end and an expansion at the other both abutments should be designed as free cantilevers. is this correct?
should the stem deflection be calculated to determine adequate stiffness? if so, where could i find a good reference outlining this procedure?
thank you for your time,
wyoming e-i-t
a few thoughts for your consideration......
for non-integral systems such as yours it is not common practice to utilize the bridge superstructure as lateral (longitudinal) support.
a common controlling load case for abutment designs is the construction case, when the abutment is partially or completely backfilled with a construction surcharge but without the superstructure dead load. this typically controls the sliding check and possibly the stem reinforcing.
another thought to consider is the appropriate earth pressure (active or at-rest) to use for the abutment design. a very stiff abutment system and/or restraint provided by the superstructure could result in higher at-rest earth pressures that should be accounted for in the design.
ditto. also, you can check with the superstructure designer to see if the superstructure design did consider the abutment load, but i doubt it does.
ps, i've worked on many designs for "pre-engineered" bridges and none of the superstructure designs considered any abutment loads.
far from providing support to the bridge, the superstructure actually passes on the braking forces to the abutments.
ciao.
thanks for all the feedback!
i too have designed many of these types of bridges. just design the abutments as cantilever stems using a suitable active soil pressure and some surcharge if appropriate. i only allow that passive pressure which is in front of footing. i also assume over time that the so called expansion end will not be fully sliding in future years due to dirt and lack of maintenance. consequently, i assume that 15% of the thermal force in the longitudinal direction will act horizontally at the bridge seat. the abutment should be designed for this force as well.
good luck

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