FOLDED PLATES

Nikhita KhuranaPulkit Chawla

Tanvi Yadav Dhruv Khurana

INTRODUCTION• FOLDED PLATES is one of the

simplest shell structure.

• They are more adaptable to smaller areas than curved surfaces which require multiple use of forms for maximum economy.

• A folded plate may be formed for about the same cost as a horizontal slab and has much less steel and concrete for the same spans.

• Folded plates are not adapted to as wide bay spacings as barrel vaults.

SHELL STRUCTUREFOLDED PLATE

STRUCTURE

BAY WIDTH OF FOLDED PLATES

BAY WIDTH OF BARREL VAULT

DESCRIPTION

BEHAVIOUR

BEHAVIOUR• Each plate is assumed to act as a beam in its own

plane, this assumption is justified when the ratio of the 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.

• When the folded plate is that with simple joint , which mean that no more than 2 elements are connected to the joint.

• But when more than 2 elements are connected to the joint, it can be named as multiple joint. The width of any plate should not be larger than 0.25 its length to be considered to act as beam.

• Actions of Folded plate due to loads : 1) SLAB ACTION : loads are transmitted to ridges by the bending of plates normal to their planes.2) BEAM ACTION : Loads are transmitted through plates in their planes to diaphragms.

RIDGE

COMPONENTS• The principle components in a folded plate structure are illustrated in the sketch below. They

consist of, 1) the inclined plates, 2) edge plates which must be used to stiffen the wide plates, 3) stiffeners to carry the loads to the supports and to hold the plates in line, and 4) columns to support the structure in the air.

• A strip across a folded plate is called a slab element because the plate is designed as a slab in that direction.

• The span of the structure is the greater distance between columns and the bay width is the distance between similar structural units.

• If several units were placed side by side, the edge plates should be omitted except for the first and last plate.

• If the edge plate is not omitted on inside edges, the form should be called a two segment folded plate with a common edge plate.

• The structure may have a simple span or multiple spans of varying length, or the folded plate may cantilever from the supports without a stiffener at the end.

TAPERED FOLDED PLATES

Inclined plates

Edge plates

Stiffeners

Columns

Span

Bay width

THE PRINCIPLE OF FOLDING

STRUCTURAL BEHAVIOUR OF FOLDING

• The inner load transfer of a folding structure happens through the twisted plane, either through the structural condition of the plate (load perpendicular to the centre plane) or through the structural condition of the slab (load parallel to the plane).

• At first, the external forces are transferred due to the structural condition of the plate to the shorter edge of one folding element.

• There, the reaction as an axial force is divided between the adjacent elements which results in a strain of the structural condition of the slabs. This leads to the transmission of forces to the bearing.

FORMS OF FOLDED PLATE STRUCTURES

FORMS OF FOLDED PLATE STRUCTURES• By using folded structures different spatial

forms can be made.

• The straight elements forming a folded construction can be of various shapes: rectangular, trapezoidal or triangular.

• By combining these elements we get different forms resulting in a variety of shapes and remarkable architectural expression.

• Folded structures in the plane are the structures in which all the highest points of the elements and all the elements of the lowest points of the folded structure belong to two parallel planes.

• Frame folded structures represent constructional set in which the elements of each segment of the folds mutually occupy a frame spatial form. This type of folded structure is spatial organization of two or more folds in the plane.

• Spatial folded structures are the type of a structure in which a spatial constructive set is formed by combining mutually the elements of a folded structure.

FORMS OF FOLDED PLATE STRUCTURES• The shape of folded structures affects the transmission of load and direction of relying of folded

structures. Based on these parameters, folded plate systems are further classified into : 1. linear folded plate structure 2. radial folded plate structure3. spatial folded plate structure

LINEAR FOLDED PLATE STRUCTURE

RADIAL FOLDED PLATE STRUCTURE

SPATIAL FOLDED PLATE STRUCTURE

• Combined folded constructions are carried out over the complex geometric basis, formed by the combination of simple geometric figures, rectangles and semicircles on one side or both sides.

• This type of folded structure can be derived in the plane or as a frame (cylindrical) structure,

and represents a combination of folded structure above the rectangular base and ½ of the radial construction.

EXAMPLE OF A COMBINED FOLDED STRUCTURE FORMED

BY A CYLINDRICAL FOLDED STRUCTURE AND HALF OF

DOME STRUCTURE

TYPES OF FOLDED PLATE STRUCTURES LONGITUDINAL/ PRISMATIC FOLDING• Longitudinal folding is characterized through

uninterrupted and linked folding edges where parallel and skew up folds and down folds alternate.

• Single-layered longitudinal folding corresponds in their load bearing structure to a linear load bearing system whereas a double-layered folding with different directions of their folds can create the structural condition of the plate.

SPOT OR FACET FOLDING• Also called spot or facet folding, requires that several folds

intersect like a bunch in one single spot. This results in pyramidal folds with crystalline or facet-like planes.

• Facet folding can either be based on a triangular shape or on a quadrangular shape.

• A single or double-layered facet folding resembles the load bearing structure of a plate and can be compared to space frameworks

SKETCH PYRAMIDAL FOLDING

SKETCH LONGITUDINAL FOLDING

MATERIALS•Reinforced Cement Concrete•Steel Plate•Mixture of Concrete and lightweight terracotta tiles•Polymer mixture of concrete and fibreglass•Scored laminated timber sheets

EXAMPLE: SANTA CRUZ AIRPORT, MUMBAI•Prestressed concrete folded plates•Extremely light with concrete thickness of 200mm•An existing hangar at Santa Cruz Airport, Mumbai (Bombay), India, has been extended to accommodate additional aircraft and engineering facilities. •Contains 8 folds•62 m long cantilever of the new folded-plate roof• Measure152 x 60 m in plan, and is symmetrically divided by a longitudinal expansion joint•The 152 m length consists of two cantilevered roofs, each 62.3 m long, and a central roof 27.4 m long over the maintenance building.•Highest point of roof is 32.3m above ground•The transverse section of the folded plate consists of eight 7.6 m wide modules, each having a corrugated plate arrangement, with horizontal top and bottom plates inclined at 45° between the webs.

EXAMPLE: THE CHURCH OF NOTRE DAME, THE CITY OF ROYAN

•Walls can be designed and carried out as folded structures, since by folding we get a solid construction that can accept large vertical and horizontal impacts, which enables exceptional height of the wall fabric. •This type of folded structures, due to their geometry, provides an economical solution and the rational use of material when compared to the height of the building. •Walls made as folded structures can be materialized in reinforced concrete. •Facility constructed with this structure is the church of Notre Dame, the city of Royan, France, 1958, with the walls built in the form of folded in "V" shape of reinforced concrete. •Viable galleries, which have a constructive role of the diaphragm, are built on them

• since they are of concrete, such roofs have inherent resistance to fire, deterioration and to atmospheric corrosion.

• They allow large spans to be achieved in structural concrete. This allows flexibility of planning and mobility beneath.

• Where ground conditions require expensive piled foundations the reduced number of supporting columns can be an economic advantage.

• The plates are required to be thicker than the shells, and there are more firms who will tackle constructing them without excessive prices, increasing competition and sometimes making the cost more competitive than for cylindrical shells.

DISADVANTAGES• Skilled labor is required in the construction of curved shuttering.• Since concrete is porous material, concrete domes often have issues with sealing. If not

treated, rainwater can seep through the roof and leak into the interior of the building• Labor skilled in curved shuttering are very expensive• Skilled labor for folded plates are hard to find

ADVANTAGES

•Storage buildings•Swimming pools•Gyms•Airports etc.

USES

APPLICATION• Folded structures have found the application in

architectural buildings and engineering structures.

• Based on the position in the architectural structure, this type of construction can be divided into: roof, floor and wall folded constructions.

• The largest number of examples of folded structures are roof structures.

• The need for acquiring the larger range and more cost effective structure led to the emergence of this type of structure.

• The largest application of folded structures is in the formation of trapezoidal sheet.

• This type of folded structure can absorb and receive the load without introducing additional structure.

• Application of trapezoidal sheet, except as roofing, is in making the thermal insulation of roof and wall sandwich panels.