Proceedings of the 21st Annual Members' Conference, 1996, San Francisco, CA, (DFI)
A Bracing System Subjected to Dynamic Loading
M. Dean Keller, PE & Pradip K. Khan, PE
As part of the seismic upgrade at the Los Alamos National Laboratory (LANL), it was necessary to provide horizontal support at the second floor level of the Chemistry and Metallurgy Research (CMR) building. A steel strut connected these points to an anchor at the ground line. Two methods of anchoring the strut at the ground were considered in this initial study (AGRA, 1994). One solution was a twelve-foot cube of concrete, equal in weight to the vertical upward force. That solution provided acceptable Demand/Capacity (D/C ) ratios. The other method considered was a four-foot diameter drilled caisson, thirty feet deep. The deflection at the second story support was too large, using this method, and second floor concrete members had D/C ratios greater than unity (overstressed). Using the cube as an anchor would cost in excess of $100,000 more than the estimated cost for the caissons. The caisson design is the subject of this paper. Although neither of the authors are geotechnical engineers, the senior author has 30 years experience working with the volcanic tuff in the Los Alamos area. Whenever unusual situations arose, the senior author worked in concert with geotechnical firms to arrive at reasonable engineering solutions. In the case of lateral loading on caissons in volcanic tuff, there was a steep learning curve for both the authors and for their geotechnical counterparts to measure and apply the known properties of the volcanic tuff. In this paper the knowledge gained during the development of the initial report and that learned to date will be shared.
|article #88; publication #18 (AM-1996)|