These bearings are seated over base, plates which distribute the load from the bridge onto the ground. The end posts at the end of the truss are supported on bearings. These chesses are seated over the road-bearers and as such are placed transversely. The wooden ‘chesses’ form the decking of the bridge. These road-bearers are welded together in groups of three for, the facility of easy construction and placed longitudinally. The ‘road-bearers’ are supported on the transoms. The cross-girders or ‘transoms’ are long RSJ resting on the bottom chord of the girders. Class 24, 40 and 70 correspond to IRC Class B, A and AA loading respectively. These vehicle classifications have also been included in the IRC Bridge Code. The load carrying capacity of Bailey bridges is designated as Class 3, 5, 9, 12, 18, 24, 30, 40, 50, 60 and 70 and corresponds to the load in tonnes approximately as the class number.Ī bridge of Class 3 can carry a jeep, Class 9 can carry a truck, Class 50 can carry a centurian tank moving on its own power and Class 70 can carry the same tank when carried over a trailer. Maximum span covered by this type of bridge is 61 metres.
‘Single double’ or ‘single tripple’ girder is unsafe and hence is never used. Heaviest girder is the ‘tripple tripple’ with three trusses side by side and three storeyed trusses. Similarly, ‘triple double’ indicates three trusses side by side having two storeys. This is the lightest truss having a span of 15.2 metres. In such designation, the first word indicates number of trusses side by side and the second word indicates number of panels one above the other.įor example ‘single’ indicates single miss one storeyed. The bridge is designated according to the number of trusses and storeys by which the bridge girders are formed. As the span increases, the panels are arranged both side by side or one above the other to increase the load carrying capacity. These panels are of welded construction and are pin-joined to adjacent panels. This is a steel truss bridge of ‘through’ type having steel panels of 3050 mm. These bridges are also used as semi-permanent and permanent bridges.
#Flow free bridges 6x6 13 portable
These are still available as Portable Steel Bridges manufactured by Garden Reach Shipbuilders & Engineers Ltd., Calcutta with some modification. The design shall be based on safe working stresses for tension, compression and bending as given in Table 18.1 for some Indian timbers commonly used.īailey bridges were designed during the Second World War and extensively used in military operation as temporary bridges. The salbullah piles shall be painted with two coats of hot coal tar before driving. The timbers used for bridge works shall be seasoned and treated with preservatives such as ASCU or creosote oil. 50 mm × 50 mm deck stiffeners are also fixed at the bottom of decking planks for the same purpose. thick timber planks are longitudinally placed on both sides of the centre line of the transverse deck for distribution of live loads (wheel loads) over a few decking planks. Wooden sleepers are used as wheel guards on both sides of the carriageway. While the decking planks are fixed on to the timber beams directly by nails, an intermediate packing timber piece is fixed by countersunk bolts over the RSJ for the facility of nailing the decking timber over this timber piece. channel is placed on the top of the piles and RSJ are seated on these channels. When RSJ used over double rows of pile trestle for longer spans, one m.s. Timber beams are used for 3.0 m span superstructure and these beams are seated on single pile trestle by m.s. 18.1 and double rows for 4.5 m and 6.0 m span as in Fig.
The piles may be in single row for 3.0 m span as in Fig. These driven depths shall be below the bed level taking into consideration of the possible scouring of the bed if any. diameter driven to 3.0 m for 3.0 m span bridges and 4.5 to 6.0 m for 4.5 m and 6.0 m span bridges. The pile trestle is composed of a cluster of piles usually 200 mm. Timber bridges are generally constructed on salbullah pile trestle as sub-structure and foundation and timber decking over timber beams or over RSJ as superstructure. Callender-Hamilton (Unit Construction) Bridge 4. This article throws light upon the five main types of low cost bridges.
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