2 DIMENSIONAL TRUSS : MATERIALS AND CONSTRUCTION 3

TRUSS

A Pratt truss – University of ManchesterModified Warren trusses – National

Composites Centre, Bristol

Long-span, curved roof trusses Robin Hood Airport, DoncasterBolted angles to form lightweight, long-

span trusses

Tubular trusses as an aesthetic feature in a single storey buildingDouble chorded heavy timber truss

with 80 foot clear span

The Bank of China Tower (abbreviated BOC Tower)

Designed by I. M. Pei and L.C Pei of I.M Pei and Partners, the building is 315.0 m (1,033.5 ft) high with two masts reaching 367.4 m (1,205.4 ft) high. It was the tallest building in Hong Kong and Asia from 1989 to 1992, and it was the first building outside North America to break the 305 m (1,000 ft) mark. It is now the fourth tallest skyscraper in Hong Kong, after International Commerce Centre, Two International Finance Centre and Central Plaza

an externally visible truss structure.

The HSBC Main Building, Hong

Kong, an externally visible truss structure.

The new building was designed by the British architect Lord Norman Foster and civil & structural engineers Ove Arup & Partners with service design by J. Roger Preston & Partners, and was constructed by Wimpey International. From the concept to completion, it took seven years (1978–1985). The building is 180 meters high with 47 storeys and four basement levels. The building has a modular design consisting of five steel modules prefabricated in the UK by Scott Lithgow Shipbuilders near Glasgow, and shipped to Hong Kong. About 30,000 tons of steel and 4,500 tons of aluminum were used.

Pre-fabricated steel bow string roof trusses built in 1942 for war department properties in Northern Australia.Roof truss in a side building

of Cluny Abbey, France.

A truss bridge is a bridge whose load-bearing superstructure is composed of a truss, a structure of connected elements forming triangular units. The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads. A truss bridge is economical to construct because it uses materials efficiently.

The inclusion of the elements shown is largely an engineering decision based upon economics, being a balance between the costs of raw materials, off-site fabrication, component transportation, on-site erection, the availability of machinery and the cost of labor. In other cases the appearance of the structure may take on greater importance and so influence the design decisions beyond mere matters of economics.

Little Belt: a truss bridge in Denmark

The Little Belt Bridge was built by Monberg & Thorsen. Construction of the bridge began in 1929 and it was opened for traffic on 14 May 1935. It is 1,178 metres long, 20.5 metres wide and 33 metres high, with a main span of 220 metres. On the bridge there are two railway tracks, two narrow lanes for cars to cross as well as a sidewalk for pedestrians. No mass machinery was used in the construction of the bridge at the time.

The truss may carry its roadbed on top, in the middle, or at the bottom of the truss. Bridges with the roadbed at the top or the bottom are the most common as this allows both the top and bottom to be stiffened, forming a box truss. When the roadbed is atop the truss it is called a deck truss (an example of this was the I-35W Mississippi River bridge). When the truss members are both above and below the roadbed it is called a through truss (an example of this application is the Pulaski Skyway)

I-35W Mississippi River bridge

The I-35W Mississippi River Bridge (officially known as Bridge 9340) was an eight-lane, steel truss arch bridge that carried Interstate 35W across the Saint Anthony Falls of the Mississippi River in Minneapolis, Minnesota, United States. During the evening rush hour on August 1, 2007, it suddenly collapsed, killing 13 people and injuring 145. The bridge was Minnesota's fifth busiest, carrying 140,000 vehicles daily. The NTSB cited a design flaw as the likely cause of the collapse, and asserted that additional weight on the bridge at the time of the collapse contributed to the catastrophic failure.

This image, from the National Transportation Safety Board's Office of Research and Engineering, shows a fracture in a gusset plate that played a key role in the collapse of the Interstate 35W bridge.

The Allan truss, designed by Percy Allan, is partly based on the Howe truss. The first Allan truss was completed on 13 August 1894 over Glennies Creek at Camberwell, New South Wales and the last Allan truss bridge was built over Mill Creek near Wisemans Ferry in 1929. Completed in March 1895, the Tharwa Bridge located at Tharwa, Australian Capital Territory, was the second Allan truss bridge to be built, the oldest surviving bridge in the Australian Capital Territory and the oldest, longest continuously used Allan truss bridge.

Bailey bridgeDesigned for military use, the prefabricated and standardized truss elements may be easily combined in various configurations to adapt to the needs at the site. In the image at right, note the use of doubled prefabrications to adapt to the span and load requirements. In other applications the trusses may be stacked vertically.

Parker (camelback) trussA Parker truss bridge is a Pratt truss design with a polygonal upper chord. A "camelback" is a subset of the Parker type, where the upper chord consists of exactly five segments. An example of a Parker truss is the Traffic Bridge in Saskatoon, Canada. An example of a camelback truss is the Woolsey Bridge near Woolsey, Arkansas.

Pratt trussA Pratt truss includes vertical members and diagonals that slope down towards the center, the opposite of the Howe truss. The interior diagonals are under tension under balanced loading and vertical elements under compression.

The Pratt truss was invented in 1844 by Thomas and Caleb Pratt. This truss is practical for use with spans up to 250 feet and was a common configuration for railroad bridges as truss bridges moved from wood to metal. They are statically determinate bridges, which lend themselves well to long spans. They were common in the United States between 1844 and the early 20th century. 

Warren truss

The Warren truss was patented in 1848 by its designers James Warren and Willoughby Theobald Monzani, and consists of longitudinal members joined only by angled cross-members, forming alternately inverted equilateral triangle-shaped spaces along its length, ensuring that no individual strut, beam, or tie is subject to bending or torsional straining forces, but only to tension or compression. This configuration combines strength with economy of materials and can therefore be relatively light.

Whipple truss

A Whipple truss is usually considered a subclass of the Pratt truss because the diagonal members are designed to work in tension. The main characteristic of a Whipple truss is that the tension members are elongated, usually thin, at a shallow angle and cross two or more bays (rectangular sections defined by the vertical members).

Vierendeel truss

The Vierendeel truss, unlike common pin-jointed trusses, imposes significant bending forces upon its members — but this in turn allows the elimination of many diagonal elements. It is a structure where the members are not triangulated but form rectangular openings, and is a frame with fixed joints that are capable of transferring and resisting bending moments. While rare as a bridge type due to higher costs compared to a triangulated truss, it is commonly employed in modern building construction as it allows the resolution of gross shear forces against the frame elements while retaining rectangular openings between columns.

Lenticular trussA lenticular truss bridge includes a lens-shape truss, with trusses between an upper arch that curves up and then down to end points, and a lower arch that curves down and then up to meet at the same end points. Where the arches extend above and below the roadbed, it is a lenticular pony truss bridge.One type of lenticular truss consists of arcuate upper compression chords and lower eyebar chain tension links. The Royal Albert Bridge (United Kingdom) uses a single tubular upper chord. As the horizontal tension and compression forces are balanced these horizontal forces are not transferred to the supporting pylons (as is the case with most arch types).

The Royal Albert Bridge is a railway bridge that spans the River Tamar in England, United Kingdom between Plymouth, on the Devon bank, and Saltash on the Cornish bank. Its unique design consists of two 455 feet (138.7 m) lenticular iron trusses 100 feet (30.5 m) above the water, with conventional plate-girder approach spans. This gives it a total length of 2,187.5 feet (666.8 m). It carries the Cornish Main Line railway in and out of Cornwall.

Assignment (2)Bridge long 15-20 cm, w 4 cm, h no more 10 cm