Distribution of longitudinal forces in a railway pile bent bridge 2

[BrAB2]

Hi,

I am a new bridge engineer who is working on a design of a replacement of an existing bridge with a 3 span pre-stressed concrete box beam superstructure supported by a 3 pile bent with concrete caps at the end and interior bents. I have been asked to use standard pile bent superstructure and substructure drawings for a railway to see if a 3 pile substructure will work with longer spans. The pre-stressed concrete spans have a 1/2 in. elastomeric pads and longitudinal restraint brackets welded to the underside of the box beams and placed 1/4" away from the side of the cap. My question is how should I consider the load path he distribution of the longitudinal forces to the substructure if there is no contact of these restraint brackets with the cap. Bearing pad friction from temperature forces appear to be a lot larger than the longitudinal forces so these forces may not make it into the substructure.

Any suggestions feedback would be helpful.

Thanks!

 

[SlideRuleEra]

1) My question is how should I consider the load path he distribution of the longitudinal forces to the substructure if there is no contact of these restraint brackets with the cap.

2) Bearing pad friction from temperature forces appear to be a lot larger than the longitudinal forces so these forces may not make it into the substructure.

1) 100% of longitudinal forces are transmitted into the substructure by friction between beams/neoprene pad/pile cap. This assumes there is an air-gap at both ends of each beam in addition the the gap between the restraint brackets and the cap.

2) Forces (longitudinal in this case) do not just "vanish" because of thermal expansion/contraction forces... think "statics". You may want to review how elastomeric bearing pads absorb shock and allow movement.

http://www.SlideRuleEra.net

 

[oldestguy]

brAB2 this is your lucky day. You probably won't find another engineer here with more experience in this subject.