Memorandum

TO:	All Design Section Staff
FROM:	J. Kapur
DATE:	August 16, 2002
SUBJECT:	Bridge Bearing Replacement Provisions

This design memo is intended to clarify the intent of Section 8.4.3.C.6 of the Bridge Design Manual.

All bridge bearings other than steel reinforced elastomeric bearings shall generally be designed and detailed to accommodate the installation and operation of hydraulic jacks to facilitate bearing replacement.  Steel superstructure bridges with steel reinforced elastomeric bearings shall also be designed and detailed to accommodate jacking and replacement of these bearings.

Some questions have arisen regarding the need to accommodate elastomeric bearing replacement at prestressed concrete girder bridge abutments.  End type "A" girders (having integral end diaphragms) need not be detailed to accommodate elastomeric bearing replacement.  End type "B" girders (having L-type abutments) shall be designed and detailed to accommodate elastomeric bearing replacement.  Specifically, girder stops and end diaphragms shall be detailed to accommodate the placement of hydraulic jacks.  The standard end diaphragms for long span girders may not have sufficient flexural and shear capacity for the jacking operations.  The designer shall check these and provide sufficient steel reinforcement to accommodate shear forces and moments induced by jacking operations (Girder end types "A" and "B" are depicted on BDM sheets 6.2-A1-5 and 6.2-A1-6).  Incidentally, intermediate piers having steel reinforced elastomeric bearings shall also be designed and detailed to facilitate bearing replacement.

Background

Girder end type "A" corresponds to bridges having integral end diaphragms over abutments.  These structures are relatively short (less then 400 feet).  Consequently, the elastomeric bearings are subject to smaller longitudinal shear distortions and rotations.  The likelihood of these bearings slipping out and requiring resetting or replacing is relatively minimal.

Girder end type "B" corresponds to bridges having L-type abutments.  These structures are generally longer that 400 feet or have large skew angles.  Consequently, they are subject to larger longitudinal shear deformations and rotations.  The likelihood of these bearings slipping out and requiring resetting or replacement is greater.  Simple modifications having minimal economic impact can be made to girder stops and/or end diaphragms to facilitate hydraulic jack installation and bearing replacement.

If you have any questions, please call Ralph Dornsife at (360) 705-7199.

JK: dsb

RJD