Integral End Bents Analysis and Design

[Fercho2006]

Does anybody could share the methodology for IEB's analysis and design? How LL is applied? Is it designed as a continuous beam? What is effective d? Thanks.

Note: IEB's subject to vertical loads only

 

[Qshake]

IEB are designed very conservatively by some and by others not so conservatively.

Most designs that I've seen only assume the bearing beam to provide the real structural capacity and the diaphragm to be just another load but no additional structural capacity. Most beams are designed using 4-#6s or even 4-#8 but rarely anything more. In many cases, the beams are generally about 3.5' deep and 2.5-3.0' in width.

For live load, the maximum number of axles are placed based on lane configuration and any live load reduction applied based on multiple lanes. The rear axle is always assumed to be on the centerline bearing and you must include the reactions of the other axles in the span.

To determine the number of pile there is no need to distribute the load to the girders, just use the total load. However, for the beam flexure most designs will assume simple shear distribution to the girders. With the diaphragm in place this isn't exact behavior but it represents one simple and conservative way. The other is to simply total the live load and make a uniform load of it.

I doubt you don't have any lateral loads, you're just making a simplifying assumption which is typical. Otherwise you can have both longitudinal and transverse loading for IEB.

Regards,
Qshake

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[jimaitken]

As Q-Shake said design methodology varies. Refer to you state DOT for guidance.

The MassHighway bridge design manual has some good guidence on the design and detailing of integral abutments . Try this link:

http://www.mhd.state.ma.us/default.asp?pgid=content/bridgeman_new02&sid=about

Remember to consider the bridge skew, horizontal alignment(curvature), and roadway grade when designing integral abutments.

It is important the abutments are not too stiff. To ensure that expansion at the bridge ends can occur design the foundation piles to allow for more deflection than normal (h-piles aligned along the weak axis). Stiffness is also a consideration when designing for seismic/ dynamic loading.
Semi integral abutments can eliminate the need for the more flexible foundations since the beams are supported on expansion bearings, but stiffness is still a consideration and the back wall cannot be so large that the soil pressure does not allow the bridge to expand.