Location of point of zero thermal movement for bridge decks 2

[VoyageofDiscovery]

Does any one know how this point is determined for various span configurations?

Thanks

VOD

 

[TTK]

Caltrans has a nice summary of this on their website:

http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/bridge-memo-to-designer/bmd.htm#sec7

 

[VoyageofDiscovery]

Thanks alot TTK,

Have you used this before?

I have a integral multi-span continuous for LL and SIDL sitting on expansion bearings at the piers.

The Caltrans example is for bridge columns fixed top and bottom.

In my case would it be fair to assume the point of zero movement to be midway along my deck, as long as my abutment stiffnesses are equal?

Regards

VOD

 

[TTK]

VOD,

What is your span arrangement (# spans and lengths)?

If your bridge is completely symmetrical and your abutment stiffnesses are equal and all of the pier stifnesses are equal to each other you can assume the point of zero movement at the center of the bridge.

The CALTRANS tabulated example is for "fixed-fixed" columns but the basic theory can be used for other types of conditions. It's just a simple stiffness approach where a Unit movement (say 1") is applied at each support and the corresponding force resistance is calculated based on the stiffness of the substructure unit.

What will you be using this "zero point" for in your integral bridge?

 

[VoyageofDiscovery]

My precast spans are 100',135'and 75' and are on elastomeric bearings at similar piers 36' high.

I am trying to determine the thermal and shrinkage movement and thus calculate the resulting force transfered to the piers via the bearings.

Regards

VOD

 

[TTK]

The method is approximate but you can still use it for your bridge.

Apply a "unit" displacement (say 1") to each substructure unit. Based on the stiffness and fixity of each substructure unit (cantilever column for piers) calculate the force generated.

Then just follow the tabulated CALTRANS example to determine the point of zero moment.

You know by inspection it is somewhere in the first half of span 2 but it will depend on the relative stiffnesses of the abutments (piles) and piers (columns).