I am using the Substructure module of LEAP Bridge Concrete.
According to AASHTO LRFD, you can't have a truck on both the approach slab and on the deck, but you can have a lane load on both.
When generating live loads for an abutment, there are two check boxes to include live loads on an approach slab. One box is for truck loads and one box is for lane loads.
When I click either of the boxes for truck or lane load, i would expect it to create a force and moment under the "Cap/Stem Loads" for at least some of the auto generated live loads, but it doesn't seem to. When I auto generate a future wearing surface load using DW on the approach slab, it does create a force and moment under the "Cap/Stem Loads."
I am wondering if the boxes for the truck and lane load on the approach slab are working at all and if so how can i tell?. I am also wondering if by clicking the button for the truck load on the approach slab, will it make sure that there isn't a truck load on the deck for the same auto generated live load case?
Thanks,
Rob
I tested this issue and these are my findings.
1)In the first trial I modeled a stem wall abutment with No Approach slab and for LL load case I generated only the Design truck + Lane load.
2) The program generated the Design truck and lane load reactions on the bearing.
3) In the second trial I added a Approach slab in the same model and for LL load case I selected the Design truck + Lane load and also in the same dialog box I checked the Truck load and Lane load option under Include Approach slab and then I generated the loads.
4) The program generated the Design truck and lane load reactions on the bearing . When I checked the reactions the Design truck lane load reactions remained the same and there was increase in Lane load reactions .
Based on my findings it looks like the program is considering the additional lane load reactions on the bearing due to approach slab.
Please see the attached screenshots for more information.
Why does the approach slab lane load go to the bearings, but the approach slab and backwall dead loads becomes a "Cap/Stem Load" ?
Also, why does the truck load not affect the live load reactions? (I think I'm going to answer my own question.) Is it because the truck load on the deck controls over the truck load on the approach slab? I was playing around with the approach slab length and when I increased it to 99 feet, the truck load on the approach slab did show up. So i took it a step further and shortened the deck length to 10 feet and it became evident that the truck load on approach slab was controlling in this (unrealistic) scenario.
Thanks
Has there been any updates on this? I'm on v20, and I can verify that both truck and lane loads change when using the "include approach slab" check box; however, the difference in lane load reaction makes no sense to me. I'm getting a 15.5k difference with 1 loaded lane and an 18ft approach slab on two otherwise identical models. I can't see how you can get 15.5k out of an 18ft long lane on the approach slab. I also cannot precisely verify truck loading without knowing truck position, but the truck reactions are at least a little closer to reasonable.
Ryan, The way LEAP does approach slab reactions is if you select "Compute Continuous Reaction" and "Include Approach Slab" when auto generating the live load then LEAP considers the approach slab to just cantilever off the end of the abutment. So for your example you would have your main spans and then an 18 foot cantilever off the back of the abutment. A 15 kip lane load reaction does sound like what you would get from running an analysis like LEAP does it for the above analysis choices.