Project Type: Evaluation, Design, Bid Assistance and Construction Administration

The Vital Structure: 

Davit Crane Base Modifications

Issue

During a roof replacement project, it was found that numerous anchor rods securing steel davit baseplates to the roof structure were defective. The bases are used to secure a davit crane and platform for window washing. The davit assembly base must be engineered to resist ultimate limit loads of 4,600 lb (axial) and 29,900 ft-lb (moment).

base modifications for project
load testing for Davit System Certification

Diagnosis

When anchor rod nuts were attempted to be loosened for removal of the davits for roofing purposes, Vital Structures and the fall protection contractor observed that the rods were rotating inside the concrete pier. Vital Structures concluded that the davit bases should be removed, and a new structural attachment of the bases to the roof structure should be designed and implemented.

 

 

 

Solution

Vital Structures visited the site with a Ground-Penetrating Radar (GPR) professional to locate reinforcing steel inside of the concrete piers. The schematic rebar layout was used to develop an approach of anchoring into the piers from the side, using a steel “cap” dropped over the pier, and design documents were prepared. Competitive bids were solicited for the project, and a thorough shop drawing preparation and review process was undertaken due to the varying reinforcing steel layouts in each of the eighteen (18) total davit bases. Vital Structures also provided engineering oversight of load testing and certification of the (44) davit bases on the building.

schematic rendering of proposed steel cap assembly

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