Building Design and Construction Handbook - Merritt - Ventech!

STRUCTURAL THEORY 5.123
� �
2 V t 2
xz 3
where V � unit shear force normal to middle surface.
5.15.5 Folded Plates
v � � z (5.177)
t /t 4
A folded-plate structure consists of a series of thin planar elements, or flat plates,
connected to one another along their edges. Usually used on long spans, especially
for roofs, folded plates derive their economy from the girder action of the plates
and the mutual support they give one another.
Longitudinally, the plates may be continuous over their supports. Transversely,
there may be several plates in each bay (Fig. 5.98). At the edges, or folds, they
may be capable of transmitting both moment and shear or only shear.
A folded-plate structure has a two-way action in transmitting loads to its supports.
Transversely, the elements act as slabs spanning between plates on either
side. The plates then act as girders in carrying the load from the slabs longitudinally
to supports, which must be capable of resisting both horizontal and vertical forces.
If the plates are hinged along their edges, the design of the structure is relatively
simple. Some simplification also is possible if the plates, though having integral
edges, are steeply sloped or if the span is sufficiently long with respect to other
dimensions that beam theory applies. But there are no criteria for determining when
such simplification is possible with acceptable accuracy. In general, a reasonably
accurate analysis of folded-plate stresses is advisable.
Several good methods are available (D. Yitzhaki, ‘‘The Design of Prismatic and
Cylindrical Shell Roofs,’’ North Holland Publishing Company, Amsterdam; ‘‘Phase
I Report on Folded-plate Construction,’’ Proceedings Paper 3741, Journal of the
Structural Division, American Society of Civil Engineers, December 1963; and A.
L. Parme and J. A. Sbarounis, ‘‘Direct Solution of Folded Plate Concrete Roofs,’’
EB021D, Portland Cement Association, Skokie, Ill.). They all take into account the
effects of plate deflections on the slabs and usually make the following assumptions:
The material is elastic, isotropic, and homogeneous. The longitudinal distribution
of all loads on all plates is the same. The plates carry loads transversely only by
FIGURE 5.98 Folded-plate structure.