Long Span Truss 5s245y

LONG SPAN BEAM

NAVREEN SAYYED 12arc 29

Long Span Beams Beams which exceeds 12m span are categorized as long span beams. Design of long span beams The use of long span beams results in a range of benefits : • Including flexible, • Column-free internal spaces, • Reduced foundation costs, and • Reduced steel erection times. • Many long span solutions are also well adapted to facilitate the integration of services without increasing the overall floor depth.

Stub girders

Types of Beams 1. 2. 3. 4. 5. 6. 7.

Parallel beam Composite beams with web openings Cellular composite beams Tapered girders Stub girders Haunched composite beams Composite trusses

Parallel beam

Composite beams with web openings

Tapered girders

Cellular composite beams

Haunched composite beams

Parallel beam approach

Composite beams with web openings Web openings are typically formed in beams to allow services to through the beam. This enables the structural and service zones to occupy the same space, thereby reducing the effective overall depth of floor construction for a given spanning capability. Openings may also be formed for aesthetic reasons, for instance with cambered beams used to a roof. Composite beams with web openings have been shown to be a cost effective solution for spans in the range 10 to 16 m. A particular type of composite beam with web openings is the so-called Cellular beam, which is formed in a specific way and therefore described separately . The alternative way of forming the web openings is simply to cut them into the plate used to form the web of a Plate girder, or the web of a Rolled section. The most appropriate solution to adopt depends on the size, shape and regularity of the openings, or more commercial drivers such as the method used by a preferred supplier.

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The parallel beam approach is effective for spans up to around 14 m. Floor grids comprise two layers of fully continuous beams running in orthogonal directions. Services running in either direction can be integrated within these two layers, so that services ing in any direction can be accommodated within the structural floor depth. A further benefit is that, being fully continuous, the depth of the beams themselves is reduced without incurring the expense and complexity of rigid, full strength connection.

Cellular composite beams Cellular Beams are a form of beam with multiple regular Web openings , formed by splitting two Rolled sections longitudinally, to form two Tee sections. The two Tees, which may not come from the same donor section are then welded together to form an I-section with web openings which have a characteristic shape (normally, but not necessarily, circular).

Although cellular beams have regular openings some of these may be in filled, and/or stiffening added to accommodate local features such as incoming beams or heavy point loads. Double (oval) openings may also be included to facilitate the age of larger service ducts • •

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Castellated or cellular beams are examples of longer span which have large, generally regular, openings within the web depth. These beams achieve the benefits of greater structural efficiency by increasing the section depth for a given use of steel, and provide multiple routes for services. Cellular beams have greater architectural appeal because of their apparent lightness and distinctive appearance in long span roofs and floors. In a castellated beam, the web of a rolled section is cut along the length of the beam in a hexagonal ‘wave’ form. The two pieces are separated, offset and then welded together to achieve a deeper section.

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Car Parks At nominally 16 meter spans under car park loadings a cellular beam is an extremely efficient structural member. In addition to its light weight, a cellular beam provides three significant benefits in car park construction: Pre-Cambers Cellular beams can be pre-cambered at no cost during production to offset a proportion of the dead-load deflection. Large cambers allow the natural drainage of surface water. Appearance & Personal Security The large web openings provide a light and airy interior to improve personal security, increasingly demanded by clients for modern parking areas. Smoke Ventilation Stricter health & safety regulation dictates the need to consider the problems of smoke ventilation. The regular web openings accelerate smoke dispersion compared to solid web beams

Curves Cellular beams are the perfect solution for curved roof applications, combining a considerable weight saving compared with plain sections and a low-cost manufacturing process. In many buildings, deg longer internal spans creates more Flexible space planning. A variety of structural steel systems may be used to provide either long span primary beams or secondary beams. These long span structure generally use the principles of composite construction to increase their stiffness and strength, and often provide for integration of services within their depth via openings in the webs of the beams.

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Step 1 Two beams are split, the first using A special top tee (Orange) and the Second using a special bottom tee Cut (blue). Step 2 A bottom tee is bent to the Required radius. Step 3 A top tee is curved and welded to The bottom tee. The process is repeated using the so far unused tees to create a pair of curves.

Tapered girders • •

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This type is more effective for span of 13- 20 M. It is designed to provide the required moment and shear capacity at all points along the beam This type is another solution that allows services to accommodate within the structural floor zone. It is also possible to form web openings in tapered girders in regions of low shear, towards mid-span They are another solution that allows services to be accommodated within the structural floor zone. The depth of the girder increases towards mid-span, where applied moments are greatest, and thereby facilitating hanging services under the shallower regions near the beam s

Spanning between 19m and 26m, the girders are an architectural feature with top boom channels and plated webs connected by countersunk bolts. The web plates are tapered from 1m at the center to 0.6m at the ends. Each beam was fabricated in two pieces with a central splice designed as a feature and also requiring countersunk bolts.

Stub girders • • •

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A big advantage of this option is that spans in excess of 20 m can be economically achieved. Services and secondary beams can through the gaps between the beam stubs, reducing overall construction depth. The stub girder comprises a bottom chord which acts in tension and a series of short beam sections(stubs) which connects the bottom chord to the concrete slab. Voids are created adjacent to stub for services. Stub girders are a Vierendeel form of truss, a rather exotic hybrid that can be thought of as lying somewhere between a solid web I-section and a truss

STUB GIRDER SYSTEM - A steel beam-and-girder system in which the floor beams sit on top of the main girders, rather than framing into them. Short lengths of stub girders the same depth as the floor beams are welded to the tops of the main girders to provide a connection to the slab for composite action. The advantages of the stub girder system are reduced weight of steel and reduced story height

Yale Art Gallery, 1951. Architect: Louis Kahn. The loft-style spaces with triangular concrete ceiling grid allow for flexible exhibition space

Haunched composite beams • Spans in excess of 20 m can readily be achieved. • Haunched beams are designed by forming a rigid moment connection between beam and column. • Haunches may be added at the ends of a composite beam to provide moment continuity. • The stiffness and strength of the connections mean that the rest of the span can be shallower, and services ed under it. • In buildings where the services are likely to need frequent replacement (for example in hospitals ), hanging the services under the beams rather than ing them through holes in the webs, or through a truss, can be advantageous. • Extra service zone is created beneath the beam between the haunches offers flexibility in service layout.

Composite trusses Composite trusses, which use the concrete slab as the upper chord in the final state, can achieve spans in excess of 20 m. This means they have been used when very long spanning capability was needed. The main disadvantages are that during the construction phase the truss may be rather flexible (laterally), and that in the final state the cost of fire protection can be high given the large number of surfaces to protect. Clearly one of the prices to pay for the spanning ability is that fabrication cost is higher than for a plain beam. Services can be ed through the gaps between the truss to reduce overall floor depth.

W e m b l e y S t a d i u m

BIBLOGRAPHY http://www.steelconstruction.info/Long-span_beams http://fgg-web.fgg.uni-lj.si/~/pmoze/ESDEP/master/wg08/l0410.htm http://www.newsteelconstruction.com/wp/carlisle-academy-provides-educational-boostfor-cumbria/ http://architectuul.com/architecture/view_image/yale-university-art-gallery/4167 http://www.ihsti.com/CIS/document/86056 https://www.metabunk.org/sk/20141021-132630-tpgh0.jpg https://www.google.co.in/search?q=structure+with+long+span+composite+truss&biw=1366 &bih=662&source=lnms&tbm=isch&sa=X&ved=0ahUKEwir8rWKzNTPAhWLqI8KHf9zAF8Q_ http://www.steelconstruction.info/Framing_schematics