Folded Plates 1..

FOLDED PLATE

• AKSHATA MARATHE• APARNA PILLAI• DHANYA PODUVAL• KETKI MAHAJAN• RENUKA KULKARNI• NIKHIL NAIR

• RIA NAIR• VARUN MALHOTRA• VISHAL JP• VISHAL PANSARE• YAMENI

INTRODUCTION

FOLDED PLATES

• It is another form of stressed skin roof and is sometimes called folded slab construction.

• The fold may take the form of a pitched roof, monitor roof or a multifold roof in single or multiple bays with up stand or down stand diaphragms at the supports to collect and distribute the slabs to enable concrete to be introduced and vibrated openings or windows can be left in the upper surface form work and these will be filled in with slip in pieces after the concrete has been placed and vibrated.

PRINCIPLE Longer spans can be accommodated with relatively small increases in weight by enlarging the lever arm of the structure; the top and bottom chords of each slanted slab house the main reinforcements while the shear stresses are absorbed across the sloping sides. The folded plate acts as a beam and can support even greater loads. BASIC ELEMENTS :The principle components in a folded plate structure are - 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. 4. Columns to support the structure in the air.

CONCEPT

FOLDED PLATES

• Folded plate roof is the other form of stressed skin or membrane in, which the stiffness of the skin is, used to distribute the loading to the point of support and is sometimes called folded slab construction.

• The basic design concept is to bend or fold a flat slab so that the roof will behave as a beam spanning in the direction of the fold.

• It is an example of a 3-dimensional or space structure.

1. When a thin sheet of paper rests between two supports it will bend due to the fact that it has insufficient strength to carry its own weight.

2. If the same piece of paper is folded then it will be capable of supporting one hundred times its own weight.

3. If the load is increased past this point then the structure will fail and the folds will flatten out.

4. This problem can be rectified by using transverse stiffeners at the ends. The folded plate acts as a beam and can support even greater loads.

TYPES OF FOLDING

FOLDED PLATES

THREE SEGMENT FOLDED PLATE :-

• The end stiffeners are rigid frames rather than deep girders.

• The forces from the reactions of the sloping plates on these rigid frames will be quire large and at an outside column they will not be balanced by thrusts from the adjacent plates.

• The size of the frames may be reduced by using a steel tie between the tops of the columns which can be concealed in the fenestration.

• The dimensions of the plates are dependent on both the width of the barrel and on the span.

• The depth of the shell should be about 0.10 times the span and the maximum slope of a plate should not be greater than 40 degrees.

CANOPIES :-

• This folded plate has four segments. • A two segment structure is not desirable because it has

very little torsional resistance.• Stiffeners can often be hidden on the top surface so

they are not in evidence and the shell will appear to spring from the vertical column.

• At the wall of the building there should also be a stiffener hidden in the wall construction. Provision should be made for drainage of the center valley.

TYPES OF FOLDING

FOLDED PLATES

Z SHELL :-

• Dramatic architectural effect - if the structure can be shown by a cantilever projected out beyond the support.

• The windows are normally open to the north but most of the light is actually reflected south light.

• Each of the units has one large sloping plate and two edge plates arranged with space between the units for windows.

• Adjacent units should be tied together by structural window mullions.

• The spans are limited in comparison to the plates having a large number of units side by side.

EDGE SUPPORTED FOLDED PLATES :-

• The usual upturned edge plate can be eliminated and the roof structure can be made to appear very thin if the edge plate is replaced by a series of columns.

• The slab between columns must be designed as a beam and it may be convenient to extend the main roof slab as a cantilever canopy.

• The beam element that carries the load of the roof between columns will then be wider and windows under the slab will have the same function as in the previous examples of folded plates.

• The vertical columns in the end walls at the crown of the gable take the reactions of the plates , thus the horizontal ties may be eliminated.

TYPES OF FOLDING

FOLDED PLATES

FOLDED PLATE TRUSS

• There are horizontal ties across the width only at the ends of the building and the structure acts as an edge supported shell.

• The thrusts from the triangular crossed arches are carried lengthwise to the ends. The top chord of the inclined truss is formed by the ridge member.

• The bottom chords are the ties at the base of the side gables and the diagonals are formed by the sloping valleys at the intersection of the gables and the triangular plates.

• The top longitudinal compression member may require some additional thickness to form a compression member of sufficient size to carry the compression force.

WALLS CONTINUOUS WITH SHELL :-• In this structure the walls are of tilt-up concrete

construction; concrete is cast flat on the floor and raised into place by cranes.

• The walls are designed to be continuous with the roof plates.

• In this design, columns are not necessary at the junction of the individual side wall panels because the walls are braced at the top. Only a simple grouted key slot is provided.

• The tilt-up panels can serve as their own foundation walls so only a continuous footing pad is used with a notch to receive the tilt-up panel.

TYPES OF FOLDING

FOLDED PLATES

TAPERED FOLDED PLATES :-

• Folded plate structures may be built with tapered elements • Another possibility is to place the smaller depths all at one

end so that the entire structure forms a circular ring. • The height of the shells at the center of the span is the

critical dimension for bending strength. • Therefore, the structure is not very efficient and not suitable

for long spans because of the excess height required for the large ends.

• A folded plate may be used for walls as a thin structural element by casting each plate flat on the floor and grouting the joints full of concrete.

• A wall of this type can be made much thinner than a flat wall.

FOLDED PLATE RIGID FRAME :-

• An arch with straight segments is sometimes called a rigid frame.

• It is not as efficient as the curved arch because the bending moments are greater.

• Ties across the plates are required at the knees and at the crown in order to distribute the forces at the ends of each segment.

CONSTRUCTION METHOD

FOLDED PLATES

• If a flat slab is folded or bent, it can behave as a beam spanning in the direction of the fold with a depth equal to the rise of the folded slab.

• When loaded , compression and tension stresses will be set up at the top and the bottom of the section respectively.

• Each slab spans between the folds and must be thick enough to span this distance and to have sufficient stiffness, to distribute the loads longitudinally.

• End frames must be provided to collect the force in the slabs and transfer them to the supports.

DESIGN PRINCIPLE

FOLDED PLATES

• The base unit of a folded plate is assembled from a thin steel reinforced concrete or steel surface that is bent to increase its strength and allow it to span like a beam.

• Folded plates have the primary bending stresses across their inclined section with peak stress at the ridge. The depth of the plates’ fold is proportional to its resistance to bending.

• Folded plates can be made of reinforced concrete or the steel but then can also be made of a mixture of concrete and lightweight terracotta tiles, in order to reduce the overall weight , or lightweight polymer mixture of concrete and fibre glass.

• Scored laminated timber sheets can also be used, resulting in a much lower weight to span ratio.

• This distribution of load through the depth of the steel reinforcement concrete or steel section embeds the folded plate with an affective property of pleating and arching that remains consistent within any space it defines.

CONSTRUCTION METHOD

FOLDED PLATES

FOLDED PLATES WITH SIMPLE JOINT

• When the folded plate is that with a 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. But when more than2 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.

Perpendicular to the main span, the shell acts as short span plates in transverse bending.

In the main span direction, the shell develops membrane tension at the top and compression at the bottom, in analogy to a beam in bending.

COMPONENTS OF FOLDED PLATES

FOLDED PLATES

The principle components in a folded plate structure are as given below:1) The inclined plates2) Edge plates which must be used to stiffen the wide plates3) Stiffeners to carry the loads to supports and to hold the plates

in line4) 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 slab in that direction.

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

• The structure above is a two segment folded plate .

• If several units were placed side by side, the edge plates should be omitted except for the first and the 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 above may have a simple span, or multiple span of varying length, or the folded plate may cantilever from the supports without a stiffener at the end.

RIGID FRAME

PRISMATIC BARRELS

FOLDED PLATES

o The span and the width of each bay governs the overall depth. This should not be less than between 1/10th and 1/15 of the span , or 1/10th of the width , which is greater.

o The width of each slab is limited only by requirement of the lateral stiffness which dictate the thickness.

o There are various methods of retaining the folds in position at the points of support where the load is taken down to the foundations they are as follows:

• Lattice frame or a rigid frame• Upstand diaphragm beam • Down stand diaphragm beam• Hipped folded slab• Prismatic barrels• North light

NORTH LIGHT

CONSTRUCTION DETAILS

FOLDED PLATES

FOLDED PLATES

CONSTRUCTION DETAILS

APPLICATION OF FOLDED PLATES

The Riverside Museum, Glasgow

Used as Canopy

SunBow House, Los Angeles

St. Pius X Catholic Church.

FOLDED PLATES

• 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 the folded structures are used.

ADVANTAGES & DISADVANTAGES

FOLDED PLATES

1. Folded plates are ideally suited for a variety of structures such as factory buildings, assembly halls, godowns, auditorium gym large spaces requiring column free spaces.

2. Simple shuttering involving straight planks are required. moveable formwork can be done resulting speedy construction.

3. Folded plates can provide longer span giving column free areas.

4. The design components and the diaphragms are simple compared to shell roofing.

1. Shuttering is expensive. Centering is also costly. 

2. Mostly used for RCC roofing 

3. Thin sections --- strict supervision desired 

ADVANTAGES DISADVANTAGES

DESIGN CONSIDERATIONS

FOLDED PLATES

COMPONENTS OF FOLDED PLATES

FOLDED PLATES