Design Memorandum



TO:                  All Design Section Staff

FROM:            Bijan Khaleghi
DATE:             September 5, 2008
SUBJECT:       Maximum Superstructure Length


The following table provides guidance to preliminary design staff regarding maximum bridge superstructure length

beyond which the use of either intermediate expansion joints or modular expansion joints at the ends is required.

*      Based upon 0.16" creep shortening per 100' of superstructure length, and 0.12" shrinkage shortening
        per 100' of superstructure length.
**    Based upon 0.31" creep shortening per 100' of superstructure length, and 0.19" shrinkage shortening
        per 100' of superstructure length
*** Can be increased to 800' if the joint opening at 64F at time of construction is specified in the expansion
        joint table to be less than the minimum installation width of 1-1/2". This condition is acceptable if the
        gland is already installed when steel shapes are installed in the blockout. Otherwise (staged construction
        for example) the gland would need to be installed at temperatures less than 45F.


Background:

The above information is to provide guidance, at the preliminary plan stage, in determining abutment types,
bridge length and need for intermediate expansion joints or modular joints at the bridge ends.  Deviation from
the above limits requires consultation with the Bridge and Structures Office Bearings and Expansion Joints
Specialist, and approval of the Bridge Design Engineer.

If you have any questions regarding these issues, please contact Ralph Dornsife at 705-7199 or Bijan Khaleghi

at 705-7181.

cc:   Mohammad Sheikhizadeh, Bridge Construction - 47354

       F. Posner, Bridge and Structures 47340


Note:   If you would like a PDF of this design memo, click here.