Modelling an Integral Abutment Bridge

[X-Wing]

Gooday Fellows!

What is the correct (or the most likely the close one to represent) way to model a bridge with integral abutments? Bridges with no joints, and practically the end diaphragm on abutments are to be poured monolithic with the backwalls?

Thanks!

 

[A4North]

It should be modelled as a rigid frame.

 

[X-Wing]

Ah so it means that the abutments should be modeled with the copings and shafts with soil springs with support at the bottom, not just simply a support representing the abutment, it that correct? Thanks!

 

[Qshake]

The modeling of the integral abutment depends on what the goal of the analysis is. If you're simply developing a model for live load response across the bridge, it's normal practice to consider the integral abutment, founded on steel piling) as a simple support with no moment resistance in the longitudinal direction. Not only is this normal practice but it is conservative for the design of the superstructure elements. It's also a likely situation since the stiffness differential at the concrete diaphragm/beam to pile will result in the pile providing the little displacement and rotation to develop a "pin" connection. Especially if the pile are turned on their weak axis for the longitudinal direction. This detail wtih the pile weak axis is used by many US DOTs.

Most DOTs have details to account for the moment that is developed at the integral abutment. Additional reinforcing is provided from the slab down the back of the abutment. This has become standard practice.

If your abutment is founded on drilled shafts, then a split analysis analysis should be considered. One for the superstructure with the abutment pinned and another for the substrucure with the abutment fixed for frame action. This will provide the most conservative results for both siutations, deisgn of the superstructure and design of the substructure.

If you are analyzing the integral abutment alone or as part of the bridge for earthquake analysis then a more detailed model of the integral abutment is warrented. Keeping in mind that more detailed doesn't always mean a 3D brick element FEA. It may mean incorporating all the necessary stiffness elements and then condensing them to a point on a frame element. This method has been used successfully for years.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[X-Wing]

Thanks sir! That pretty sums up what I need, do you have links or particulars on how or details of DOT integral abutments?

Very Truly Yours,

- andru18

 

[X-Wing]

FOLLOWUP QUESTION:

Does the requirement of "No Seismic Analysis for Single Span Bridge are required" also applies for single span integral bridges?
If not, so it is necessary to to a seismic design?

Very Truly Yours,

- andru18