Description:

Steel framing and platform to support 30 ton derrick crane and 60 ton window washing unit. The framing is installed on the roof of the tower, at elevation 700 ft above street level.

The project is challenging due to limited roof space and fragile glass roof system, low capacity of existing columns, limited mode of construction and transportation of materials given the high elevation, and high wind condition.                                                                                                               

To minimize potential of overload at any individual column during crane lifting operations, column jacks and pressure gages are installed and continuously monitored at several building columns. The columns' pressures are then adjusted accordingly to "balance" the loadings during lifting. 

Existing fragile glass roof prevents the use of drilling or welding for new framing connections.  Pretensioned collar friction connections are used, instead.

Location: Seattle, WA

Architect: Zimmer Gunsul Frasca

Contractor: Andersen Construction Company