Steel Construction Vol 40 no 6 - International Steel Structures | Page 12

SAISC PROJECTS

Arup

Webcor Builders

Arup

and isolator sizes for the project. Following the city’s successful

connections would yield, and replacing them would be difficult

commissioning of early prototype bearing testing, the team used

and expensive, resulting in significant downtime. In addition, floor

the prototype testing results to optimize the superstructure design.

accelerations in the base-isolated hospital are significantly reduced,

This strategy led to early procurement of the isolators and an early

which results in lower demands on the anchorage and bracing for

steel bid package, as well as significant cost and material savings

equipment and nonstructural elements.

when it came to the structural steel.
Compared with a conventional fixed-base design, the baseisolated
It’s also important to note the benefits that the project’s base-

design also used significantly less steel – as in 3,000 tons (the

isolated design has over a conventional fixed-base design, including

project used 8,500 tons of steel in all). A fixed-base design would

performing much better in a major earthquake, better protecting

have also required deeper columns and beams, thus limiting the

the building’s contents and allowing the superstructure to

space available for utilities and make coordination more difficult.

withstand maximum-considered-earthquake-level earthquakes

Base isolation allowed steel intermediate moment frames to be

and remain elastic. In a fixed-base design, the moment frame

used for the superstructure, and a fixed-base building would have
had to meet requirements for steel special moment frames, leading
to additional building costs.
Superstructure
The hospital has two distinct floor plans: a four-story rectangular

ABOVE LEFT: A triple-pendulum bearing was subjected to lateral displacement
during the prototype testing.
ABOVE CENTRE: The building is supported on 115 of these bearings, allowing it
to slide 30 inches in any direction.
ABOVE RIGHT: Prototype bearing testing early in the design phase.

podium and a five-story bed tower comprising two interlocking
circular cylinders bisected by a parallelogram core. The glazed
cylindrical tower houses the patient rooms and support spaces,
while the brick podium houses the diagnostic and treatment
departments. The framing system uses composite flooring
supported by steel beams and girders, which in turn are supported

BELOW LEFT: Overhead medical equipment is supported by a steel modular grid
hung from the floor beams above.

on steel wide-flange and built-up cruciform columns. As the

BELOW RIGHT: The new base-isolated building on the left serves as a
replacement of the original main hospital on the right.

tower, transfer beams of W36 sections are used at levels 2 and 3

Webcor Builders

10 Steel Construction Vol. 40 No. 6 2016

building transitions from the rectangular podium to the cylindrical
to receive the W10 columns supporting the inpatient beds and

Perretti and Park