Pedestrian Live loads on sidewalks

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Daniel R.
Pedestrian Live loads on sidewalks

When pedestrain live loads are combined with vehicular live loads PG super gives you three options. Can you explain the difference between these two options (2. envelope pedestrian live loads WITH vehicular live loads) and (3. Apply pedestrian live loads CONCURRENTLY with vehicular live loads). For option 3. are the vehicular live loads placed on the sidewalk with pedestrain live loads at the same time?

Pickings
You are exactly right. For

You are exactly right. For the envelope method, PGSuper will take the worst case of the pedestrian and vehicular live load response at each location and apply it to a given limit state combination. The concurrent method applies the sum of the pedestrian and vehicular load responses.

Richard Pickings, P.E.
BridgeSight Inc.

B
Pedestrian Live Load Only

Is there a way to take only the pedestrian live load only for the girders under the sidewalk? Looking for the LLDF for the interior girders if there is no lane where the sidewalk is. My case is that the bridge has a 16' sidewalk with 2 exterior girders under the sidewalk. How I'm reading AASHTO it says to take the design lanes from curb to curb, but it appears PGSuper is taking the calculation of lanes from barrier to barrier, even with the sidewalks. For my example, the number of lanes should be 5, but PGSuper is taking the number of lanes as 7. Is there an option to manually change the number of design lanes?

B

Rick Brice
There are provisions in

There are provisions in AASHTO that say the bridge needs to be designed for possible future configurations. A 16' sidewalk could easily be removed and turned into a vehicular lane in a future reconfiguration of the bridge - See 3.6.1.6. Hence there are 7 design lanes.

AASHTO is not clear regarding line girder analysis with live load distribution factors in combination with pedestrian live load. C3.6.1.1.2 provides some guidance for treating PL as "one loaded lane" for multiple presence factor. Applying the logic of this commentary to the distribution factors, the simultaneous application of PL and LL+IM for a "two or more loaded lane" case will always govern. Some feel this is overly conservative so PGSuper has the "envelope" option.

You can also define your own live load distribution factors. Using LLDF of 0.0 for girders supporting sidewalks will effectively eliminate LL+IM responses for those girders.

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