720
Design Rationale, Building Subsystems
721
STRUCTURE
Many of the reasons leading to particular details in the structural
subsystem of the Prototype Design are discussed in Section 310 of the
Design Manual. This section consists mainly of those discussions
considered too detailed to be included in the Design Manual.
721.1
CLEAR SPANS
721.1.1
Span Range
Before a basic framing system could be selected, it was determined that
the clear spans required in the Prototype Design would fall within the forty-
to sixty-foot range. This range was determined by identifying the
maximum and minimum spans necessary for an acceptable degree of
adaptability. (See Section 710.) The upper end of the range was also
influenced by issues of cost since spans over sixty feet would have
eliminated the more economical of the structural alternatives.
The clear spans in the Prototype Design are somewhat greater than those
commonly found in current VA hospitals, but less than the spans seen in
some recent projects, e.g., VA San Diego (80'0"); McMaster University
Health Sciences Center, Hamilton, Ontario (73'6").
721.1.2
Spans in Modular Lengths
The actual spans selected vary in 4'6" increments from 40'6" to 58'6".
These dimensions are based on the same module as the 22'6" bay width,
namely 4'6". In other words, the bay width is always equal to five modules
and the beam lengths range from nine modules to thirteen modules. An
18'0" cantilever extends the bay length by four modules.
The small increments in the beam length allow adjustment of building
width. Also, any number of bay widths above three can be matched in
length by some combination of modular spans. Thus even a change of
direction in framing can result in buildings with a simple configuration, as
illustrated by the following examples.
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