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Retrospective Seismic Strengthening of a LINAC Baseframe

M Szegedi*, P Rassiah-Szegedi , V Sarkar , Y Huang , H Zhao , L Huang , A Paxton , F Su , G Nelson , B Salter , University Utah, Salt Lake City, UT


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: We are located in a seismically active area with a high probability of being subject to a surface-faulting earthquake (magnitude 7 or higher). In our clinic, we recently started a set of linear accelerator replacement, all of which can use the existing base frame. Currently, our vaults have base frames installed before city seismic code changes (2012, 2015) became law (HB203, HB316). This means the new code requires implementation of base frame seismic upgrades during any LINAC exchange.

Methods: A new LINAC installation was conducted in 2017 after removal of a 13 year old linac. Based on the previous installation documentation it was concluded that the existing base frame does not fulfill current code requirements but met vendor specifications for a True beam LINAC and did not require replacement. The frame itself is structurally more rigid than floors typically installed hence the actual anchoring needed to be reevaluated. To facilitate this, we initiated a visual inspection of one bolt to verify existing anchoring and found that the total tensile and shear strength of the current exiting 9 bolts did not meet state regulations. Necessary static calculations were done to increase the load by adding additional bolts. New bolts would attach to the existing frame and welding pads and complement the already installed bolt pattern. After evaluation we chose to implement a 4-bolt pattern to raise the static load above state requirements.

Results: The custom modification to the existing base frame allowed us to comply with state regulation. These results are documented for future reference for other sites.

Conclusion: Retrospective strengthening of a LINAC base frame can be achieved by applying static-load calculations adjusted for the specific environmental conditions of the site. A delay of 3 weeks at minimum should be planned for implementation.


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