Two WOLFF 1250 B US luffing tower cranes are working side by side on the $4.3 billion UCSF Health Helen Diller Hospital in San Francisco, handling major structural lifts on a confined site while the neighbouring hospital remains fully operational.
It is the first time two WOLFF 1250 B US cranes have worked together on a US construction site. Each crane offers a maximum capacity of 40 tonnes in two-fall operation and can lift 19.7 tonnes at the tip of its 65-metre jib.
Positioned around the perimeter of the triangular Parnassus Heights site, the cranes stand approximately 85 metres freestanding despite tower footprints of just 3.3 x 3.3 metres. With their jibs raised, overall height eaches around 152 metres.
California’s seismic requirements, combined with local ground conditions and surrounding utilities, ruled out conventional foundations. Instead, both cranes were installed on specially engineered pipe piles and steel grillages.
The cranes have become the main material-handling system for the project, lifting structural steel, reinforcement and other construction materials. Among the heaviest components are 32-tonne steel box columns, which are occasionally raised from horizontal to vertical using both cranes in tandem.
Space restrictions were so severe that a mobile crane weighing approximately 38 tonnes also had to be lowered into the basement by the tower cranes because no access ramp could be provided.
“The construction site conditions here are significantly more challenging than on those projects in downtown San Francisco,” said Drew Szabat, Construction Manager for the UCSF Health Helen Diller Hospital project.
Working immediately beside operating rooms, emergency facilities and patient areas also requires strict controls on noise, dust, vibration and exhaust emissions. The cranes may only slew above existing hospital buildings with an empty hook.
Dismantling will present another unusual challenge. One WOLFF crane will remove the other – a procedure that required approval from Cal/OSHA three years before erection. The remaining crane will then be lowered to around half height before a 600-tonne mobile crane completes its removal in several phases in early 2029.
The 15-storey, approximately 83,600 m² hospital is scheduled for completion in 2030.
