Seton Women's Center
Austin, Texas
119,270 Sq. Ft.
$31.7M
2008

Architect: STG

When Seton Medical Center (Austin) wanted to construct a new Women’s Center on their 38th Street campus, they were faced with a shortage of available building space.  They decided to locate the building on the west edge of their property, over an existing inner campus drive that they wanted to keep.  Because the property line was skewed about 30 degrees relative to the existing hospital buildings, the new tower layout had to incorporate two sets of grid lines, one parallel to the existing hospital and one parallel to the property line.  To further complicate matters, the layout of the patient floor required the tower width to be greater than the available space, so the south end of the new five level tower had to project over the existing Emergency Department, which had to remain in 24-hour operation throughout construction.  Finally, the south half of the site was about 15 feet lower than the north half, and the hospital wanted to enter the existing building at the Ground (Basement) Level, which required demolition of an existing site retaining wall at one end and additional basement excavation throughout and immediately adjacent to the property line.  This further required construction of a new cantilevered basement wall, which supported the columns adjacent to the property line above the first elevated level, but had no lateral support there, because of the clearance requirements above the roadway.  Because the site soils and shales are quite expansive, this cantilevered basement wall had to be constructed on piers, rather than on a soil bearing spread footing, which presented significant problems with achieving sufficient sliding resistance of the foundation system.

A steel structure was selected to frame the tower and address some of these issues.  Because the tower was built over a roadway, the lowest floor above the roadway was at the second elevated level, or about 30' above grade, and shoring for cast-in-place concrete would have been prohibitively expensive.  In addition, the floor to floor heights of the existing hospital were short, and steel provided additional room for mechanical piping and ductwork above the ceiling (utilizing web penetrations for some ductwork).  Most importantly, steel structure enabled us to design a story height truss system at the top level, in the mechanical penthouse wall, from which we could hang the east side of the 3rd and 4th floors where they projected over the Emergency Department.  This system included a truss at the south end of the tower that cantilevered about 20 feet to pick up the south end of an 85 foot span truss along the east side.  Virtually all of the truss connections (internally and to each other and the supports) were bolted to facilitate erection and fit-up requirements.  Erection sequencing was critical to the successful installation of the trusses and they were designed to be very stiff in order to minimize after erection deflections which would impact multiple framing levels.

The tower’s second level almost aligns with the existing Emergency Department’s cast-in-place concrete roof structure, so the second level patient rooms in that area actually utilize the existing roof structure as their floor (with a small amount of insulation and topping to align with the rest of the tower second level).   A series of diagonal expansion joints are required to mate the skewed buildings together in this area.  Where the new tower connects to the existing patient tower, the existing building edge of the various floors is not always aligned.  In several places, cantilevered trusses were needed to extend the upper levels of the new tower over the lower level projections of the existing hospital.  This necessitated the installation of several horizontal expansion joints where the floor expansion joints were offset at different levels.

The tower frame is laterally braced with narrow, but heavy, chevron-braced frames, because the opportunities for continuous lateral bracing generally existed only around the elevators and stair wells which were not uniformly distributed in the building.  The entire building is sheathed in glass curtainwall and brick of two different sizes which had to be relieved at every floor.

Construction of the structure for Seton’s Women’s Center is nearing completion and appears ready to accommodate finish out and move-in.  It is a signature example of what can be achieved with creative collaboration between Datum and their architectural clients, in this case, STG Architects, to meet demanding project requirements.