Challenge

February 2012 - A local hospital planned to add a new computed tomography (CT) scanner to the radiology department. A 9-foot by 48-foot mobile trailer unit was proposed in order to utilize the equipment ahead of constructing a permanent addition to the hospital. However, the trailer would have to be adequately secured with tie downs to prevent excessive movement created by uplift and lateral forces during moderate to high wind conditions. These tie downs had to be installed quickly and ahead of the planned safety inspection. If the deadline for installing the tie downs and anchoring the temporary structure was missed, the hospital would have to wait an additional three weeks for the next available round of inspections before they could begin handling patients. The mobile trailer unit was parked at the rear of the hospital within an area having both concrete and asphalt pavement. Above and below ground utilities were also known to exist within the areas of the proposed tie down installations.

Solution

Helical anchors were selected to provide the tie down support for the trailer. Four Model 150 (1.5-inch round corner square bar) anchors with 10”-12” double-helix lead sections were selected to support the design service tension load of 10 kips each. Pavement was saw cut and removed at each anchor location. The anchors were then installed vertically to a depth of 14 feet and to torque-correlated ultimate capacities greater than twice the design service load (FOS ≥ 2). The engineer of record approved relocating one of the anchors due to a below-ground concrete obstruction. The tops of the anchors were poured into concrete with the upper bolt hole left exposed above grade to provide an attachment point for the high strength aircraft cable. The four helical anchors were installed in one day.

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Project Summary

Structural Engineer: TKW Consulting Engineers

Certified Anchor Installer: N Square, Inc.

Products Installed: (4) Foundation Supportworks® Model 150 Helical Anchors, 10”-12” Double-Helix Lead Sections, Installed to a Depth of 14 feet, Design Service Load of 10 kips