Design Guidelines for bridge expansion joints 5

[EngRabih]

Please I need design guidelines for the bridge expansion joints

 

[civilperson]

They are unnecessary for bridge lengths up to 1100' if designed for axial stresses. Expansion joints are maintenance headaches and often the cause of premature failure.

 

[parapetguy]

Most joints are proprietary and are not "designed" but selected; the exception being fingerplates. Strip seals, compression seals and modular joints are proprietary and often can be found on a state DOT approved materials list.
Take a look at several state DOT bridge design manuals and you will be able to find an appropriate joint type. For most short bridges, a strip seal will be approriate.

The previous post by civil person stated that joints are not needed up to 1100 feet. Tennessee has some long bridges without joints but this is not the norm. Most states limit expansion length to around 400 feet and limit the skew to 30 degrees. The bridge also requires special detailing to allow flexibility in the substructure to accomodate the thermal movements. If you are interested in eliminating joints, do a search for the proccedings from the jointless bridge conference held in Baltimore a couple years ago.

 

[kelowna]

Most designers will specify only movement ranges and the contractor will buy a proprietory joint from a supplier.
All countries have expansion joint requirements in one or other code. In the USA and Canada, each State/Province do too. The joint manufacturer will be able to say if they comply with the specific requirements of the country/province/state.
I could not agree more, expansion joints are a pain in the neck, but they are also necessary. 1100 feet are 335 meters, with thermal coeficient of 12E-6, and a temperature range of 50 degrees you have an expansion of 200 mm. If you do not install an expansion joint those 200 mm are either going to cause a lot of stresses or a lot of cracks. That is without talking about braking forces, settlements, bearing movements,...

 

[bridgebuster]

http://www.wbacorp.com/Products/Products.aspx#3

 

[civilperson]

The unrestrained expansion of 1100 feet is as stated by kelona, the concrete cross section can easily handle the thermal stresses of increased temperatures if restrained between abutments. The 50 degree cited is an increase of 875 psi (assuming 3,500,000 psi=Ec).

 

[graybeach]

EngRabih,
Here in the US, many DOTs have specific guidelines for expansion joints. Only certain bridges are allowed to be designed integral or jointless. For these, we take the expansion back to a pavement joint off the bridge. We allow piles to move in their holes, and do not generally design the superstructure for axial constraint due to temperature change. This would be a huge force compared to the force required to deform the backfill.

 

[kelowna]

I find this topic very interesting, although we left EngRabih question aside.
As I said, I do not like expansion joints, but I think that they are a necessary evil. Any bridge can be designed to take the additional axial loads, I would be more concerned about the abutments being able to provide that restraint and the approaches performing well. Even if you design for axial loads, some movement is bound to take place, and the ciclic load might cause trouble.
On the other hand I have never worked on an integral bridge and obviously Civilperson has had successfull projects with them. Maybe it is time I re-think my approach. Could more people comment on their experience/oppinion/approach to this issue?

 

[RME1]

In the UK, you are required to consider integral abutments for any span <60m (if HA is the client). Over 60m you are free to put in expansion joints if you wish, but I have seen integral bridges up to 100m.
Over 60m I think you need pretty large abutments to withstand the expansion forces. If you go for a flexible pile solution, you can struggle with horizontal movement at the ends of the bridge

 

[civilperson]

The "sleeper slab" used on bridges in the SouthWest US builds a bottom slab continuous with the highway and a top slab as part of the bridge/abutment. This takes the movement out of the bridge and puts it in the 30' portion outside the abutments. This design also has seismic applications when the superstructure is cabled to the deadman anchor of the sleeper slab.

 

[shin25]

I have been working on a segmental bridge. This bridge is 645 m long, nine span continuous and has expansion dams only at the start and at the end of the bridge. Of course, ertain bearing systems have been designed to accomodate the movement due to creep, shrinkage and temperature.

 

[Zambo]

shin25,

on a prestressed bridge of 645m the movement due to shrinkage and creep and the max movement due to temperature differential will be considerable (I guess over 300mm). Either the columns will deflect or there will be sliding bearings. Sounds as if in your case sliding bearings have been used. Perhaps a couple of expansion joints and the remaining piers designed as built-in would have been an economic solution

 

[shin25]

Zambo,

Out of eight piers two are fixed and the rest are expansion type, which allow movement.

 

[Dinosaur]

I still don't understand how you can accommodate thermal effects in a 645 m bridge without finger joints or modular expansion joints. What I understand to be an expansion dam would never handle this.

 

[shin25]

As I have mentioned before not all the piers fixed (only the center two are), most of them are expansion type. So, not the whole 645m should be considered for temp. deformation.

 

[graybeach]

shin25,
If you only have expansion dams at the two ends with 645 m of structure between, how do you avoid considering the entire length for temperature deformation?

 

[shin25]

To begin with, half of the deformation will go in each dam. Also, the length of the bridge that is covered by fixed bearing is not going to contribute to the deformation.

 

[graybeach]

Even with half the deformation going to each dam, you are still considering the entire length. Now, whether the portion of the bridge between the fixed supports contributes depends on the stiffness of the piers. A superstructure in axial deformation could be hundreds of times stiffer than a pier in bending, so the superstructure will ignore the pier and do what it wants.