Using sidewalks and barriers in bridge model

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dgeorgiu
Using sidewalks and barriers in bridge model

I'm modeling a bridge configuration that consists of 3 girders with a sidewalk above the 1st two girdes and a traffic barrier at the interior edge of this sidewalk, limiting the standard HL93 vehicle loading to the 3rd, or last, girder. Because I've included this barrier, vehicle LL should not be applied to the 1st two girders. When I run the analysis I notice that the same moment demand from LL+IM design is in all three girders. Since the vehicle is only allowed to travel over the 3rd girder, why do the 1st two girders see the same level of demand? Is there a certain setting that I should apply to prevent this from happening?

Rick Brice
At some time in the future,

At some time in the future, the bridge could be reconfigured allowing live load to be applied to all girders. For instance, the sidewalk and interior railing could be removed and the bridge widened (See LRFD 2.5.2.7). It is prudent to design all the girders for the HL93 loading. This is a standard design policy and is built into PGSuper.
 
If you think it is virtually inconceivable that the bridge will be reconfigured, you can remove the live load from any girder by setting its live load distribution factor to zero. To accomplish this, select Loads | Live Load Distibution Factors. In the Live Load Distribution Factors dialog, select "Directly Input Live Load Distribution Factors", and code in the factors you want to use.
 
Also, consider that even though some of the girders are not directly under the traffic lane, the live load distributes through the deck and diaphragms and is typically carried by several adjacent girders.
 
Let us know if you have any more questions.
 
Rick
 
Richard Brice, PE
Software Applications Engineer
WSDOT Bridge and Structures Office

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