Braking force distribution on bridge deck 1

[AnaThompson]

What would be the most accurate way to distribute braking force longitudinally on a concrete bridge deck. I have a conventional bridge, with one segment over several spans, ending with a fixed bearing at the abutment. AASHTO is giving a way to distribute the braking force only transversely, but not longitudinally. Is it OK to assume that the whole braking force will be taken by the anchor bolts on the fixed bearings at the abutment and none by the expansion bearings. Also, in case of a fixed bearings at both ends of a span, what would be appropriate to use- half of the braking force for each fixed bearing?

 

[ishvaaag]

From what I read two months ago in the magazine Hormigón y Acero, the usual thing is to provide a single point along the bridge segment taking all the braking force, selected on the basis of how easy is to pass the load to the ground. Normally that was at 1 abutment, but in some cases it was at 1 intermediate support of gothic arch directrix. This in spite of the length of the segment/bridge being in one case astounding and leading to huge reaction forces for the composite section of the deck.

I assume that the forces from braking with integral abutments must be taken as resulting from the analysis of the bridge ..., what may involve a range of behaviors just in case, even when you are quite sure of what to expect.

 

[jorton]

In general, the load will be distributed based on the relative stiffnesses of the supports. If there is only one line of "fixed" bearings then I would design that bent for the full longitudinal load. In reality some of the load will also go to the other bearing lines. Steel bearings corrode and lock up. Elastomeric bearings all resist some shear before whatever is "fixing" them is engaged (say a pin or anchor bolts). Even bearings with ptfe have some friction. I would design these other bents for a portion of the load based on the relative stiffnesses of the bearings and bents. A span with fixed bearings at each end would be treated in the same manner. Fixing both ends of the span will have other implications with regards to temperature and shrinkage if applicable.

 

[AnaThompson]

Thank you for the replies, guys.
This was what I was thinking to use- distribute the braking force according to the stiffness of the bents. And yes, in the case of a span with both fixed ends there was a problem with temperature, creep and shrinkage. This was the reason I wanted to make sure I'm being accurate in accounting for the braking force and everything else along the C.R.L.

 

[Darkangel24]

Hello All,

I have a same question about braking force distribution but in my case, its a 2 span bridge with Expansion Joints at the abutments and all the bearings are elastomeric. Currently i have distributed the moment caused due to the longitudinal braking force equally to the abutment and the pier, but in actuality, the abutment with pile connection stiffness would be greater than the pier column connection(but due to presence of elastomeric bearings used on abutments and pier shouldn't the forces be equally distributed), SO i am thinking the percentage of moment distributed would be respective of its element stiffness. I am not sure if i should use equally distributed forces or determine the stiffness and then distribute the forces?

Sorry for posting in an existing thread, seemed relevant