Currently working on a load rating

[ATHS]

Currently working on a load rating job. Using SAP to do a 2d model of the girder and then calculating capacities separately to determine the RFs. How do you load the exterior girder with sidewalk on it? AASHTO doesn't clearly specify anything about the loading to be used here. Attached is portion of section view showing exterior and First Interior girder. What loading would I take on these two girders ?

 

[BridgeSmith]

You would load the sidewalk with the pedestrian live load (75psf) and consider it as a loaded lane.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[bridgebuster]

I agree with BridgeSmith. However, you should check with your client. For NYSDOT we would check for the truck on the sidewalk without ped loads. This would be an operating rating condition.

 

[BridgeSmith]

For NYSDOT we would check for the truck on the sidewalk without ped loads.

Just curious, does that apply with or without a crash-worthy traffic barrier/railing between the roadway and sidewalk? We only do that if there isn't a traffic railing.

That's only for rating, though. For design, we always consider a possible future condition where the sidewalk is removed and that part of the bridge carries vehicle traffic. Well actually, in most cases, as a easy and conservative approach, we just leave the sidewalk DL and add vehicle traffic loading.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[ATHS]

@bridgebuster & bridgesmith - Would I use single lane loaded distribution factors to determine the pedestrian live load forces on exterior girder?

 

[BridgeSmith]

Calculating distribution factors for the sidewalk ped load seems like the hard way to get the load on the girder for it, but I guess you could. You'd have to convert your ped load to an equivalent axle line load (loading of a longitudinal line of truck axles), and then calculate the distribution factor for the equivalent line of trucks.

Since the ped load is just a uniform load over a specific width that does not move within a lane, like the truck loads are assumed to, I would think it would be much easier to just apply the ped load to the deck as a transverse continuous beam supported by the girders, and calculate the reactions at each girder.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[bridgebuster]

Rod - for us load rating and design are a little different. In the design world, the fascia girder would be designed for truck load, regardless of the sidewalk. In the load rating world, the truck would also go on the sidewalk. If there's a permanent barrier we would assume it doesn't exist unless there's a rating problem with the rating. In that case we would go to the ped load.

 

[ATHS]

@ Bridgesmith, thank you for the response. To get clarification, Do yo mean to use the girder reaction due to pedestrian load as a UDL on the beam to determine the forces effect due to pedestrian load along the beam ?

 

[BridgeSmith]

Do yo mean to use the girder reaction due to pedestrian load as a UDL on the beam to determine the forces effect due to pedestrian load along the beam ?

Well, not exactly. It's applied to produce critical load effects in the same way as a vehicular lane load. For instance, when calculating force effects at the middle of a span, you would load that span, but not the adjacent spans. For calculating force effects at an interior support, you would load the 2 adjacent spans.

Rod Smith, P.E., The artist formerly known as HotRod10