How to calculate parapet loading for bridge when equal distribution not possible?

[DK1614]

I am reviewing the parapet loading requirement for a steel girder concrete deck bridge and had a question regarding load distribution.

Reviewing the uniform application of dead load requirement in AASHTO (Section 4.6.2.2.1 and Section 4.6.1.2.4b), the parapet loading will not be equally distributed among all the girders since the bearing lines of the curved girders that I am designing are skewed more than 10 degrees from radial.

AASHTO only says to use engineering judgement if the criteria for equal distribution is not satisfied.

Has anyone come across this situation before? How much additional parapet loading should be added to the exterior girder, if any?

Is the lever rule a way to designate loading for such a case?

 

[MIKE_311]

This article is saying that you cant use approximate methods to do the analysis and that you need to use a refined analysis method, e.g. FEA. Doing an FEA will distribute the parapet to load to the girder based on the models stiffness.

You need to follow 4.6.3.

 

[DK1614]

I do not have a FEA software that can do this analysis. Is there a manual way around it, or ca this be approximated?

 

[MIKE_311]

Its a curved girder and AASHTO is telling you that your bridge is outside the criteria for using approximate methods.

Section 4.6.4 gives options for refined methods. You can do a grillage analysis but you would need to somehow approximate the forces in cross frames/diaphragms, which are primary members in a curved bridge.

 

[DK1614]

Ok, I understand. Thank you.