Tensile Structures

Also includes…. Cable Stayed Structures Pneumatic Structures Tent Structures

The DefinitionTensile structures are characterized by the prevalence of tension force in their structural systems and by limitation of compression forces to a few support members. Thus these lightweight structures do not require the considerable amount of construction material to absorb the buckling and bending moments in compression members. Tensile structures were first seen in the earliest forms of shelter, such as the tent. However it was Vladimir Shukhov who pioneered the use of tensile structures in the late 19th & early 20th centuries by doing many shell tower and pavilions such as the Elliptical Pavilion of the Pan-Russian Exposition in 1896.Although we have been using tension in our structures for many centuries, it only recently has become a form of art .

Three types of structures…. Cable Stayed Structures Pneumatic Structures Tent Structures

Cable Strengthened Structures

A Detailed Study In Architectural Terms

The Intro….Cable-stayed structures support horizontal planes (bridge decks, roofs, floors) with inclined cables that are attached to, or run over, tower(s) Cable-supported roof structures have inspired people for many years. However, cables systems are still a relatively new form of roof construction. Prior to the 1950s, steel cables were used primarily for long-span bridge structures, not buildings. Advancements in the understanding and analysis of cable-roof structures culminated in buildings like the Olympic Roof project designed for the 1972 Olympics in Munich, Germany. Today, cables structures are recognized as innovative structural solutions that create dramatic forms while efficiently enclosing large-volume spaces and providing transparency and natural light.

Cable-Stayed Structures: A BriefCable-supported structures generally can be sorted into

two categories: Cable suspended structures, where draped cables are the main supporting elements of the

structure, and their curvature is a major factor in the load-

carrying capacity of the system; and cable-stayed structures, where cables

stabilize vertical or sloped compression members (usually called masts or

pylons) and serve as tension- only members. The term

“cable” generically is used to describe a flexible tension

member consisting of one or

more groups of wires, strands or ropes. A “wire” is a

continuous length of steel that typically has a circular cross section, and is cold-

drawn from a small-diameter steel rod. A “strand” is an assembly of wires formed helically around a central

wire in one or more symmetrical layers. A wire

“rope” is made from multiple wire strands that are twisted

about a central core. Wire ropes frequently are used in cable-suspended structures

because ropes are more flexible than strands.

Cable net structures are for covering large unsupported spans with considerable ease. The constructional elements are steel pylons, steel cable networks, steel or wooden grids, and roof coverings of acrylic glass or translucent, plastic reinforced sheeting. Cables are fastened into the edges of the steel network, and are laid over pin-jointed and usually obliquely positioned steel supports, and then anchored.

Cable Nets

Structural CharacteristicsThe cables of a cable-stayed structure work solely in tension. The cables must not only have sufficient capacity to carry the dead load, but must also have enough reserve capacity to carry the live load. Otherwise, the horizontal surface may suffer serious deformations. The horizontal surface must be sufficiently stiff to transfer and/or resist the lateral and torsional stresses induced by wind, unbalanced live loads, and the normal force created by the upward pull of the stays. The stays are usually attached symmetrically to the column or tower with an equal number of stays on both sides. This is so that the horizontal force component of the inclined cables will cancel each other out and minimalize the moment at the top of the tower or column.The horizontal surface (bridge deck, roof, etc.) usually acts as a simple beam, most commonly in the form of a truss or box beam. The box beam is advantageous because resists torsional forces well; however, it provides a greater surface area subject to the lateral forces of the wind. The towers are the first portion of the structure to be constructed. The section of the horizontal surface supported by the first stay is built next. In a similar fashion, the remaining pieces are connected until the horizontal surface is successfully completed and supported.

Structural CharacteristicsThere are two primary cable configurations: radial patterns and parallel systems (or harp). In the radial system, the upper end of all of the the stays attach to a single point at the top of the tower. The advantage to this system is that the maximum degree of inclination of the cables is achieved which creates nearly vertical forces exerted at the top of the tower. This minimizes the bending moment in the tower. In the parallel system of stays, each stay is parallel and thus connects to the tower at a different height. This creates large bending moments in the tower because the forces from the cables have larger horizontal components.

Structural Details

Benefits And Penalties

The Examples of such big roofs supported by cables are –

The Olympic Stadium,AthensBraga Stadium, Portugal The Olympic Roof, Germany The O2, UK The Olympic Park,Germany

• Can Meet a Wide Range of Functional Demands• Can Provide Column Free Space Increasing Internal Flexibility• Can Be Easily Extended• Can Lead to Reduced Structural Weight• Can Lead to Higher Design Costs• Increased Thermal Movement• Erection Requires Special Consideration• Increased Costs for Corrosion Protection

Olympic roof,MunichConstruction materials UsedMasts : SteelCable Nets : SteelMembrane Panels : Acrylic SheetsCovered Area : 74000 m2

The cable net as built, the nets are formed of crossed pairs of strands spaced 750 millimeters in both directions. This spacing remains constant regardless of net shape, all changes of plane in the double-curved surfaces being accommodated by changes in the strand intersection angles . Intersections joints were formed by an automatic process, aluminum clamps with central holes being pressed on to all strands at exactly 750-millimetre centers under a defined level of pre-stress.

The transparent roof covering was formed of 2.9 x 2.9-metre acrylic panels of 4 millimeter thickness, laid on the cable net and bolted to the intersection nodes. As the angles of intersection in the cable net change up to 6 degrees under load and temperature change,the rigid acrylic panels had to be flexibly connected to the net. This was done by supporting the panels on neoprene pesetals , allowing them to 'float', and sealing the joints between panels with a continuous neoprene profile clamped to the panel edges.

Olympic roof,Munich

Detail of how the acrylic plates are connectedwith each other . They are all framed in asteel square section and then connected witheach other using bolt connection .Also the each of the acrylic plate rest on thenet structure which is also made up of steelcables passing horizontallyas well as laterally. None of the joint iscontinues with each other In order to gainmore stable form .

Olympic roof,Munich

The Olympic Park,Munich

Construction materials UsedArch : SteelCable Nets : SteelMembrane Panels : Plastic SheetsTo enable the open ice-surface in the Olympic Park to be used all round the year, independently of the weather, a light roofing, naturally without supports, was required a steel-trussed arch of three chords. With a span of 100m and a height of roughly 19m at its apex, the arch is capable of transmitting any thrusts to two large concrete abutments. Two sets of cables hang in opposingcurves from the arch, stabilizing it by their anchorage and forming a net. These symmetrical nets of cable have a grid of 75 x 75 cm and support a wooden lattice, upon which is attached a translucent plastic sheeting.

The Olympic Park,MunichThe construction and form of the “hanging from the arch” correspond to that of the roof edge. A series of elliptically strung openings below the latticed arch .These are filled by "glass eyes” equipped with ventilators. The first ever in itself , horizontally barred glass "façade" which is able to participate in the formal changes allowed by the anchoring cables.

The Olympic Park,Munich

The Structural Details