 |
Memorandum
|
| TO: |
Bridge & Structures Office Design Staff |
| FROM: |
J. Kapur |
| DATE: |
June 11, 2001 |
| SUBJECT: |
|
At its May 2001 meeting, the AASHTO Subcommittee on Bridges and
Structures voted to approve revisions to the Method A design criteria limiting rotational
capacities of steel reinforced elastomeric bearings.
These criteria are delineated in Chapter 14 of the AASHTO LRFD Bridge Design
Specifications. The new criteria are more
stringent and will bring consistency between Methods A and B.
Henceforth, all future designs using the Method A procedure
shall be based upon equations (a), (b), and (c) below.
These equations replace equations (14.7.6.3.5-1), (14.7.6.3.5-2), and
(14.7.6.3.5-3), respectively, in the second edition LRFD. These revisions will eventually be published and
disseminated in the 2001 Interim AASHTO LRFD Bridge Design Specifications.
(a)
Rectangular
shaped bearings
(b)
Rectangular
shaped bearings
(c)
Circular shaped bearings
Where:
n = the number
of interior layers of elastomer, where interior layers are defined as those layers that
are bonded on each face. Exterior layers are
defined as those layers that are bonded only on one face.
When the thickness of the exterior layer of elastomer is more than one-half
the thickness of an interior layer, the parameter, n, may be increased by one-half for
each such exterior layer.
hri =
the thickness of the ith elastomeric layer
All
other variables are as defined in Chapter 14 of the AASHTO LRFD Bridge Design
Specifications.
The MS Excel spreadsheets residing on
the drive \\Bolt\BridgeSW\Bearings for designing steel reinforced elastomeric bearings
using the Method A procedure have been revised to incorporate these changes.
If you have any questions regarding this issue, please contact Ralph
Dornsife at 705-7199.
JK:dsb
KNK/RJD
cc: J. Weigel, Bridge and Structures - 47340
F. Higgins, Bridge and Structures - 47340