WHAT YOU NEED TO KNOW ABOUT A LONG SPAN ROOF

Introduction
Long span roofs are also referred to as roofs that exceed a 12 m span. Long span roofs can produce resilient, column-free interior areas. They can also decrease substructure expenses and production times. Long span roofs are usually observed in a broad variety of building varieties such as:

Manufacturing plants
Warehouses
Agricultural structures
Aircraft hangars
Workshops
City halls
Gymnasiums
Auditoriums

The primary function of a long span roof is comparable to that of traditional roofs. Their purpose is to protect a building’s contents from the weather. This limits the extent of fire damage and provides sound and thermal padding as well. However, because they are the primary structural system except for the boundary walls, they may end up also supporting access routes, building services, lifting equipment, electrical systems, etc.

Materials

Long span roofs generally are of different material types in general. Some of those include aluminum alloy, steel, reinforced and prestressed concrete, and timber. Steel is often favored due to its tremendous durability. Steel is also preferred because it discourages the spread of fire. The design of long-span steel and steel-concrete composite columns is generally carried out to comply with BS EN 1993, BS 5950, or BS EN 1994 standards.

Portal Frame

Portal frames are a class of structural frame distinguished by a beam or rafter, held at either end by columns. However, the connecting joints of the columns and beams are ‘rigid’ so that any warping movement gets shifted to the columns. What this means, is that the beam can decrease in sectional size to span large ranges.

Generally, the joint connecting the beam and the column is made ‘rigid’ by the attachment of a bracket, a haunch. )or by deepening the section where the joints meet.) Portal frames made from reinforced precast concrete, steel, or laminated wood are often referred to as ‘glulam’.

Pitched Truss

A pitched truss is a triangulated plane frame separated at appropriate centers. To limit spreading, the beams, which make up the top edge of the truss get attached at their bases by a tie member. Bases are then attached in the basic triangle by using struts and ties. Purlins are set between the trusses to attach roof coverings.

Pitched trusses provide encourage good rainwater runoff. They also provide generous daylight spread from roof lights and raised roof volume because of their shape.

Pitched trusses are usually made out of steel sections. They joine together with bolts or by welding them to cast plates called gussets. Steel truss segments are generally angled sections. This is because they are economical and can withstand both tensile and compression. Timber segments are sometimes used as well, joined with bolts and timber connectors.

Saw-Tooth Roof

A saw-tooth roof contains a series of ribs, with each individual pitch much steeper than the next. This pattern is comparable in form to a saw’s teeth. (hence the name) 

Saw-tooth roofs enable the fabrication of pitched roofs over a large span without forming a high apex. Surfaces face the north and are then glazed to allow sunlight into the building. For that reason, saw-tooth roofs are also recognized as ‘north light roofs’.

Saw-tooth roofs were first seen in manufacturing and industrial structures. This was before the invention of electrical light. Though no longer needed, engineers have started to bring them back because they offer environmental effectiveness. The fact that their form allows for very easy solar panel installs.

Trussed Rafter

A trussed rafter is also intended for extremely long spans ranging between 15-45 m in length. Trussed rafters are generally made from wood or steel, and spaced at the center to support purlins. Trussed rafters generally have low pitches as well. (to provide adequate rainwater runoff and provide reasonable sunlight range from roof lights.) Trussed rafters also offer the benefit of lessening roof volume and depth, increasing with the span of the roof.

Space Deck

A space deck is a modular architectural roofing system based on simplistic pyramidal units. They are generally manufactured with tubular diagonals. Then, attached by welding to a forming tray and apex boss. Single span designs can produce large clear spans; (up to 22 m) while two-way span designs can accommodate spans of up to 33 m.

The parts of a span deck can be quickly carried to the job site. After transport, they get constructed into beams. The entire The space deck is then built at ground level before getting winched into place on top of perimeter supports. Any lightweight architectural decking is suitable as a roof coating. Roof lights can are optionally installed onto the square top space deck sections.

Space Frame

A space frame is comparable in theory to a space deck. It has a more detailed layout and design flexibility than other methods. Space frames are a lightweight and rigid roofing system. They ate made up of a series of connectors that tie together the struts and bracing segments. They are very durable due to the rigidity of the triangle, with any stress transferred as stress and compression loads across the span of each chord. The majority of space frames get manufactured out of structural steel or aluminum alloy pipes.

Buckminster Fuller invented the method of using space frames during the 1960s for his geodesic dome buildings.

Fabric Structures

Structural fabrics like PVC polyester and PTFE glass are very strong. They can also span quite large distances with very little material. They are normally forced into place by bracing structures, pulled tight by cables, or filled with pressurized air. Generally, fabric structures are translucent in color, providing good natural sunlight.

Monitor Roofs

Monitor roofs are flat roofs with raised sections that are also referred to as ‘monitors’. They provide a balanced amount of sunlight from the monitor lights that are not influenced by the building’s direction. Monitor roofs are generally assembled with light long-span girders that support them.

Long span Arch

Shell roofs which also called Long span arches are fully self-supporting, requiring no trusses, frames, support posts, or purlins. They are an architectural curved skin coating applied in a designated shape and area. The forces inside the shell are compressive and the restraining edge beams are ductile.

Suspension Structures

Suspension structures are generally used where the main elements of a structure support the load. (chains, wires, cables, etc,) Suspension Structures are subject entirely to extension forces. Horizontal, (or plain) constructions use a wire fastener supports elements that bear the local strain. These are generally used in roofs and bridges.

Cable-stayed Structures

Cable-stayed structures are a structural design obtained from bridge building. In cable-stayed structures, a flat roof gets hung from above by steel cables hanging downward from masts that tower above roof level. The cables then act as suspension elements. This causes the roofing system to behave like a standard load-resisting unit; subjected to shears, moments, and other types of action. Even under the danger of wind uplift, because of the weight of the roof, suspending elements are expected to remain in tension.

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