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Folded plates :

the structural efficiency of plates can be increased by stiffening them with ribs,

thus removing some of the material from the neighborhood of middle plane ofthe plate and increasing its moment of inertia. The same result may also be

achieved by folding the plate. A sheet of paper, held along one side, cannot supportits own weight, because its minute thickness does not give a sufficient lever arm to

the bending stresses. Folding the paper sheet brings the material of the crosssection away from its middle plane, and increases the lever arm of the bending

stresses, which becomes comparable to the depth of the folded strips. In fact, themoment of inertia of two plates at an angle is equivalent to that of a rectangular

cross section beam with depth equal to the depth of the plates, and a width equal tothe combined horizontal widths of the two plates.

Folded plates are assemblies of flat plates rigidly connected together along their edges in such a wayso as to make the structural system capable of carrying loads without the need for additionalsupporting beams along mutual edges.

Folded plates spanning 100 feet or more may be made of wood steel, aluminum, or reinforcedconcrete. Reinforced concrete folded plates are particularly economical because their formwork may

be built of straight planks, or the concrete slabs may be prefabricated on the ground, lifted into place,and connected by welding the transverse bars at the folds and concreting the joints, thus eliminatingmost of the formwork altogether.

Types of folded plates :1- Prismatic : if they consist of rectangular plates.

2- Pyramidal : when non-rectangular plates are used.

3- Prismoidal, triangular or trapezoidal.

On the other hand, Folded plates can be classified as:1- single.

2- Multiple.

3- Symmetrical.

4- Unsymmetrical.

5- Simple.

6- Continuous.

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7- Folded plates with simple joints.

8- Folded plates with multiple joints.

9- Folded plates with opened cross sectional.

10- Folded plates with closed cross sectional.

Historical Review :

compatibility of deformations and the relative ridge displacement, but for construction of "n" numberof plates, Gruber's analysis requires the analysis of7n-5 simultaneously equations. . Big Trouble.

developed considerably simpler procedure that still take into consideration the

compatibility of deformations and the relative ridge displacement, but for "n" number of plates,Vlasov's analysis requires the analysis of2n simultaneously equations . Also still hard.

which the effect of ridge displacement was completely disregarded. but for "n" number of plates,analysis requires the analysis ofn-1 simultaneously equations.

and Pei solution, that take into account the ridge displacements. These attempts can be classified to :

Analytical methods.

Folded Plate Behaviors :Each plate is assumed to act as a beam in its own plane, this assumption is justified when the ratio ofthe span "length" of the plate to its height "width" is large enough.But when this ratio is small, the plate behaves as a deep beam.

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