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Foundation types may consist of shallow or deep options. Shallow options include isolated spread footings, which are independent footings
that are provided for each column, and strip footings, which feature a continuous strip of concrete that spreads the weight of a load-bearing wall
across an area of soil. These footings are typically located a couple feet below the first floor of the building. Deep foundation options are used when
the upper strata of soil are not suitable for shallow foundations. Options
include drilled piers (large-diameter, concrete-filled shafts with a cage of
reinforcement) or auger cast piles (smaller-diameter shafts installed with
high-strength cement grout using a hollow stem auger). Auger cast piles
are typically used in groups at each column and
interconnected with a concrete pile cap.
BECAUSE AS-BUILT
The second valuable pre-design investigation
INFORMATION IS
is an underground site utility survey, especially
on expansion projects where workers must conOFTEN INCOMPLETE OR
tend with existing underground utilities that
INACCURATE, SITE UTILITY
need to be either relocated or accommodated
SURVEYS ARE CRITICAL.
in the design. A site utility survey will assist the
design team in identifying which underground
utilities must be addressed since as-built information is often incomplete,
inaccurate, or nonexistent. When an unexpected underground storm or
sanitary line is discovered during construction, it can lead to redesign and
construction delays.
Third, if necessary, a shielding study for linear accelerator vaults is required to ensure the size and layout of the vault is adequate to limit radiation exposure to staff, patients, and the public. A shielding study provides
shielding barrier recommendations, such as the wall and roof thicknesses required. Shielding materials can consist of lead, normal weight concrete, heavyweight concrete, steel plates, composite materials, or other
options. This study is performed by a physicist and should be authorized
early to allow time for coordination with the vendor, physicist, and design team.
Finally, obtaining any available existing drawings early in the design is
important. Healthcare projects are often additions to existing facilities.
Reviewing the existing drawings allows the engineer to check the existing
structure for any new loads that will be added to the structure and identify
any potential conflicts with the existing structure. Some hospital facilities
may have a dedicated storage room for drawings, while others may have
digital copies or none at all. When existing drawings are not available, site
visits may be necessary before design begins.
C O L U M N C O N S I D E R AT I O N S

Columns are vertical structural members that support each floor of a
building. Coordinating column sizes and locations in the beginning stages
of the project can lead to a more economical design while maintaining the
flow of the space. For new additions, keeping the column layout in mind
when laying out programming space reduces the need to shoehorn columns into undesirable locations after the owner has already signed off on
the floor plans. Typical hospital column spacing may range from 30 to 35
feet, but longer spans are also possible. Using modular bay spacing and
keeping columns on the same grid lines as much as possible have proven
to be more cost-effective design solutions.
Because many healthcare projects are designed for future growth,
identifying the number of potential future floors and areas of expansion,
including operating rooms, mechanical rooms, and penthouses, is important to ensure the columns and foundations have enough capacity to

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handle those additions. The structural drawings
should include a key plan indicating the anticipated
growth.
In the case of vertical expansions or renovations,
the column locations are already set by the existing
structure, but it's important to recognize that the
actual column locations that were built won't exactly match the theoretical column locations on the
existing drawings because of permissible construction tolerances, which allow for inherent variances
in construction materials and workmanship skills.
In some cases, the actual column locations may differ by several inches in multistory hospitals, which
could lead to a column potentially encroaching into
a new corridor.
The American Institute of Steel Construction
(AISC) Code of Standard Practice requires the
contractor to survey locations of existing columns
prior to detailing or fabricating steel for a vertical
addition. The new column will need to be placed as
close to the as-built column line as possible because
the existing columns typically cannot support the
load from the new columns when they are offset by
more than one-quarter to one-half an inch.
On horizontal additions, the adequacy of the perimeter beams, columns, and foundations must be
checked if the new structure imposes additional
loads on the existing structure. Using expansion
joints for a horizontal addition will isolate the new
gravity and lateral loads from the original hospital.
When locating columns at an expansion joint, it's
beneficial to hold the columns back 8 to 10 feet from
the existing building and cantilever the framing to
the expansion joint to avoid potential conflicts between new and existing column footings or piers.
B E A M L AY O U T

After the columns are set, the beams, or horizontal
structural members supporting the weight of the
floor, can be located. Beam depths may vary considerably on a project depending on the distance
between columns and the loading that must be supported. The design team should discuss the anticipated structure depth so the floor-to-floor heights
and ceiling heights provide adequate clearance for
mechanical ductwork, piping, and electrical conduit in above-ceiling spaces.
Patient room layouts also should be reviewed
in relation to the beam locations. Toilet, sink, and
shower drains that penetrate the floor must not
pass through a steel beam or narrow concrete joist
because the structural capacity would be undermined. Floor penetrations in concrete beams can
sometimes be accommodated by widening the
beam or adding supplemental reinforcing bars in
the beam. If floor penetrations cannot be moved,

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Healthcare Design - April 2019

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