KKSB 4143 ADVANCED CONSTRUCTION & MATERIAL TECHNOLOGYFORM-ACTIVE STRUCTUREAlif Arif Iskandar Abd Wahab | A126688 : UKM 2009/10

FORM-ACTIVE STRUCTURE

• Load is taken by the form or shape of the structure

• Non rigid, flexible matter shaped in a certain way and secured by fixed ends, can support itself & span space. The structure transmit loads only through simple normal stresses; either tension or through compression.

There are 4 types of form-active structural systems

FORM-ACTIVE STRUCTURE

Form-active structure

1. Cable

2. Tent

3. Pneumatic

4. Arch

SPAN – Cable and Tent Structures

FORM-ACTIVE STRUCTURE

50 ------------------ 500m

30 ------------- 250m

25 ----------- 200m

5 ---- 40m

20 ------ 100m

20 --------- 150m

SPAN – Pneumatic and Arch Structures

FORM-ACTIVE STRUCTURE

10 -------------------- 300m

20 -------- 120m

10 ----- 70m

15 -------- 100m

4 ----- 30m

10 ------------- 150m

1. Cable Structure

• Two cables with different points of suspension tied together form a suspension system. A cable subject to external loads will deform in a way depending upon the magnitude and location of the external forces. The form acquired by the cable is called the FUNICULAR SHAPE of the cable.

Transversely and uniformly loaded cable Cable with central point load

1. Cable Structure• The natural stress line of the form active tension system is the

funicular tension line.• Any change of loading or support conditions changes the form of

the funicular curve.• Form active systems because of their dependence on loading

conditions are strictly governed by the natural ‘flow of forces’ and hence cannot become subject to arbitrary free form design.

• Cables can be of mild steel, high strength steel, stainless steel, polyester or aramid fibers. Structural cables are made of a series of small strands twisted or bound together to form a much larger cable.

• Most tensile structures are supported by some form of compression or bending elements, such as masts, compression rings or beams.

1. Cable Structure• Redirection of forces

• Due to the horizontal force, the load will be moved away from the point of suspension

• The cable transmits the load to both sides and the form will follow the direction of stresses

• The cable changes its shape with each new loading condition

1. Cable Structure• Cable stress S and

horizontal thrust H are inversely proportional to its sag h. If the sag is zero, cable stress and horizontal thrust will become infinite, thus the suspension cable cannot resist the load

1. Cable Structure• Restraining systems for stabilization

of suspension points• Structures for suspension points

• Column with oblique cable

• Oblique column with cable

• Trussed pylon

• Fixed-end column

• Rigid frame

• Shear wall buttress

1. Cable Structure

Igus Headquarters, CologneGrimshaw & Partners

1. Cable Structure

INMOS Microprocessor Factory, NewportRichard Rogers + Partners

Ingalls Rink, Yale UniversityEero Saarinen

p85

1. Cable Structure

The rink employs an innovative structural system in which a 90 meter reinforced concrete arch, from which a cable net is hung, supports a timber roof. This causes a stable, double curvature form

2. Tent Structure• This form of construction has only become well understood

and widespread in large structures in the latter part of the twentieth century. In tents structure, the retaining cables provide pre-tension to the fabric and allow it to withstand loads.

• The majority of fabric structures derive their strength from their doubly-curved shape. By forcing the fabric to take on double-curvature, the fabric gains sufficient stiffness to withstand the loads it is subjected to (for example wind and snow loads). In order to induce an adequately doubly curved form it is most often necessary to pretension or prestress the fabric or its supporting structure.

• Tensile membrane structures are most often used as roofs as they can economically and attractively span large distances.

2. Tent Structure - forms• Exterior supports arranged

peripherally

• Interior arch arranged axially

• Interior support arranged centrally

• Exterior supports arranged centrally

• Exterior supports with hanger cables arranged centrally

• Exterior supports with load cables arranged centrally

• Interior supports with load cables arranged centrally

• Exterior supports for peripheral high points with hanger cable arranged centrally

2. Tent Structure• Tent systems for spanning

rectilinear solid substructures

2. Tent Structure

The roof covering the main stadium consisted of a PVC-coated polyester fabric suspended on hangers independent of the cable net. The supporting masts held the main cables in tension, thus providing the necessary support for hanging roof areas.

Olympic Park, MunichGunter Behnisch

Haj Terminal, JeddahSkidmore, Owings & Merrill

The form and height of the fabric roof units promote circulation of air from the open side of the support area up to and through the open steel tension ring located at the top of the roof unit. Mechanical fan towers placed intermittently between the columns enhance air circulation.

2. Tent Structure

3. Pneumatic Structure• Any structure that derives its structural integrity from the use of internal

pressurized air to inflate a pliable material (i.e. structural fabric) envelope, so that air is the main support of the structure.

• It is usually dome-shaped, since this shape creates the strongest structure for the least amount of material. To maintain structural integrity, the structure must be pressurized such that the internal pressure is equal to or exceeds any external pressure being applied to the structure (i.e wind pressure).

• Air-supported structures are secured by heavy weights on the ground, ground anchors, attached to a foundation, or a combination of these.

3. Pneumatic StructureThere are some advantages and disadvantages as compared to conventional

buildings of similar size and application.

Advantages:• Considerably lower initial cost than conventional buildings • Lower operating costs due to simplicity of design (wholly air-supported structures only) • Easy and quick to set up, dismantle, and relocate (wholly air-supported structures only) • Unobstructed open interior space, since there is no need for columns • Able to cover almost any project • Custom fabric colors and sizes, including translucent fabric, allowing natural sunlight in

Disadvantages:• Continuous operation of fans to maintain pressure, often requiring redundancy or emergency

power supply. • Dome collapses when pressure lost or fabric compromised • Cannot reach the insulation values of hard-walled structures, increasing heating/cooling costs • Limited load-carrying capacity • Conventional buildings have longer lifespan

BC Place Stadium, VancouverStudio Phillips Barrett

3. Pneumatic Structure

It is the world's largest air-supported domed stadium and can seat 60,000 in its mixture of permanent and portable light-blue plastic seats.

3. Pneumatic Structure

South Hook LNG Dome , South WalesTectoniks Ltd

The strength and portability of the buildings derive from their unique design and construction.  Each structure is typically comprised of two layers of a fire retardant composite textile connected together using formers of the same material.  The cavity formed between the layers is pressurised with air producing an extremely rigid structural element which allows large spans to be achieved whilst keeping the overall weight of the structure to a minimum.

Cutty Sark Enclosure, GreenwichGrimshaw & Partners

3. Pneumatic Structure (Trensairity)

The Project consists of the erction of a temporary enclosure which protects the restoration work. The Temporary enclosure is a self-supporting pneumatic structure made out of low-pressure airbeams.

Self-cleaning transparent ETFE membranes are spanning in long strips between the airbeams being fixed within the pressure profile that's attached to the airtube. A slender wire mesh underneath the membrane stabilises.

4. Arch Structure• A curved structure designed to carry loads across a gap

mainly by compression.

• The mechanical principle of the arch is precisely the same as that of the portal frame. The straight pieces of material joined by sharp bends are smoothened into a continuous curve. This increases the cost of construction but greatly reduces the stresses.

• The geometry of the curve further affects the cost and stresses. The circular arch is easiest to construct, the catenary arch (the theoretical shape a hanging chain or cable will assume when supported at its ends and acted on

only by its own weight) is the most efficient.

4. Arch Structure• The suspension cable is

able to develop only tensile stresses under its own weight

• The ‘cable’ turned upside down develops only compressive stresses of the same magnitude

4. Arch StructureGeometrical forms

4. Arch Structure

The vaulted construction of the hall consists of prefabricated elements which spring from in situ concrete abutments.

The units are of "ferro-cement" and have a length of approximately 15 feet and a width of 8 feet 3 inches. The thickness of the curved precast parts is less than 2 inches. This small thickness is achieved only by the increased rigidity through the corrugation and the transverse webs at either end. The individual units are joined by in situ concrete.

Exhibition Building, TurinPier Luigi Nervi

4. Arch Structure

Sultan Ahmed Mosque, IstanbulMehmet Aga

The Mosque of Sultan Ahmed, Istanbul, on a prominent site is distinguished by its six minarets. Four enormous piers dominate the interior and carry a dome which is buttressed by four subsidiary half-domes.

Form-active Structure?

Eco-Pavilion, ChicagoZaha Hadid

Hadid’s curvilinear pavilion will be constructed out of fabric stretched over an aluminum frame. The tent-like form has been designed to be collapsible and easily re-installed.