Memorandum

The general guidelines for steel bolts have been revised to discourage the use of ASTM A449 anchor bolts in seismic applications.  A typical example is anchor bolts for a bridge bearing, fixed for transverse and/or longitudinal seismic loads.  Another example is an earthquake restrainer attached to an existing bridge with resin bonded anchors. 

A suitable anchor bolt specification is ASTM F1554 (AASHTO M314).  When these bolts are designed to resist seismic forces, the Plans or Special Provisions shall specify supplemental Charpy V-notch testing (minimum CVN toughness of 25 ft-lb at 40 degrees F).  The intent of this change is to safeguard against brittle failure under shock loading (fast fracture).  

Special Provisions for resin bonded anchors will also reflect this change.   Replace BDM page 7.1-5 with the attached page.

  Background:

On February 28, 2001, a 6.8 magnitude earthquake caused minor damage to many highway bridges in Western Washington.  One bridge to suffer damage was the bascule bridge over the Duwamish River, bridge number 99/530.   Anchor bolts for an approach span failed in a brittle manner.  A metallurgical examination was performed on the broken bolts.  It was determined that the bolts met all requirements of the ASTM A449 specification.  Also, microscopic examination of the threads and galvanizing did not find any signs of hydrogen embrittlement.  However, the Charpy V-notch test results were extremely low (3 ft-lb at 45 degrees F).  A449 anchor bolts are expected to have highly variable impact properties. 

  For this reason, an anchor bolt specification with more reliable and consistent impact properties shall be used for seismic applications.  Impact testing, per lot of bolts, will also be required. 

  If you have any questions regarding this design issue, please contact Nate Brown at 705-7219.

  JK:dsb

NSB

Attachment 

            cc:        J. A. Weigel, Bridge and Structures - 47340
                        E. H. Henley, Bridge and Structures - 47340
                        H. L. Coffman, Bridge Preservation - 47341
                        F. Higgins, Bridge and Structures - 47340
                        R. Lewis, Construction - 47354
                        Z. Fahoum, Bridge and Structures – 47340