This article highlights the five main types of low-cost bridges. The types are: 1. Timber Bridge 2. Bailey Bridge 3. Callender-Hamilton Bridge (Structural Unit) 4. Sidewalks 5. Submarine Bridges
Enter #1. wooden bridge:
Timber bridges are usually built on Salbullah pile trestles as substructure and foundation and timber decks on Timber beams or RSJ as superstructure. The pile rack is formed by a group of piles, normally 200 mm. The diameter increased to 3.0 m for 3.0 m span bridges and from 4.5 to 6.0 m for 4.5 m and 6.0 m span bridges.
These advance depths should be below the bed, taking into account possible bed erosion, if any. The piles can be single row for 3.0 m spans as shown in Fig. 18.1 and double row for 4.5 m and 6.0 m spans as shown in Fig. 18.2. For the 3.0 m span superstructure, wooden beams are used and these beams are mounted on monopile racks by m.s. Winkelstollen and St. Platina.
When using the RSJ on double rows of longer span pile supports, a m.s. The channel is placed on top of the stakes and the RSJ sits on these channels. While the deck boards are nailed directly to the wood joists, an intermediate joint is attached over the RSJ with countersunk screws to allow the deck wood to be nailed over this piece of wood.
Wooden sleepers are used as fenders on both sides of the track. Two 50 mm trajectories. To distribute traffic loads (wheel loads) to some deck planking, thick wooden planks are laid along both sides of the stern centerline. 50mm × 50mm deck supports are also attached to the bottom of the deck for the same purpose.
Timbers used for bridge work must be tempered and treated with preservatives such as ASCU or creosote oil. Salbullah piles should be painted with two coats of hot coal tar before driving. Design should be based on safe working stresses in tension, compression, and bending as indicated in Table 18.1 for some commonly used Indian lumbers.
Type 2. bailey bGrateful:
Bailey bridges were designed during World War II and were widely used as makeshift bridges in military operations. They are still available with some modifications as portable steel bridges made by Garden Reach Shipbuilders & Engineers Ltd., Kolkata. These bridges are also used as semi-permanent and permanent bridges.
It is a continuous steel truss bridge with 3050mm steel plates. in length and 1450 mm in height. These panels are of welded construction and are attached to adjacent panels. As the span increases, the panels are placed side by side or on top of each other to increase load capacity.
The bridge is named for the number of trusses and decks that make up the bridge's girders. With this designation, the first word designates the number of crosses next to each other and the second word designates the number of panels one above the other.
For example, "single" means a single void on a floor. This is the lightest truss with a span of 15.2 meters. Likewise, "double triple" denotes three crosses side by side with two floors. The heaviest beam is the “Triple Triple” with three side by side trusses and three story trusses. "Single-double" or "single-triple" carriers are not safe and are therefore never used. The maximum span of this type of bridge is 61 meters.
The load capacity of Bailey bridges is designated as Class 3, 5, 9, 12, 18, 24, 30, 40, 50, 60 and 70 and corresponds approximately to the load in tons as class number.
A class 3 jumper can carry a jeep, a class 9 can carry a truck, a class 50 can carry a self-moving Centurian tank, and a class 70 can carry the same tank when transported on a trailer. These vehicle classifications have also been included in the IRC Bridge Code. Classes 24, 40 and 70 correspond to the IRC load of classes B, A and AA respectively.
Crossbeams or "bolts" are long RSJs that rest on the bottom chord of the beams. "Road supports" are supported by sleepers. These deck beams are welded together in sets of three and placed lengthwise for ease of construction. Wooden chessboards form the deck of the bridge. These chess pieces are above the road supports and are therefore placed crosswise.
The end posts at the end of the truss are supported on bearings. These bearings sit on base plates that distribute the load from the bridge to the ground. If the bearing capacity of the floor cannot support the slabs, then they are laid on sleeper beds. When these bridges are built semi-permanently, the bearing plates are attached to the abutments.
Walkways with a width of 760mm for pedestrians can be provided on one side or both sides. These walkways are placed beyond the main beams with the help of walkway beams attached to the end of the crosspieces.
When these bridges are used as makeshift bridges in emergency situations, ramps are needed to bridge the gap between the carriageway and the carriageway, which is approximately 710mm above the bottom of the base plate. 3050mm and 6100mm ramps are available. The first is used to save small unevennesses and the second to save large unevennesses.
Bailey bridges can be built on temporary supports or maneuvered into position using a "launch nose" and some pulleys.
The launching point consists of the same bridge plates and is of such a length that when the complete bridge beam together with the launching point is moved over several rollers on one bank and the launching point is thrown towards the other bank, the stability of the entire unit is maintained without replacing the unit (Fig. 18.4). Some Kent bar loading can also be used for stability if needed.
When the launch tip reaches the opposite shore, the unit will continue to move until the ends of the bridge beam reach final position on the bearings. The toe and Kent bar are then removed and the bridge girder is jacked down and finally placed on bearings.
Bailey bridges can also be built by unskilled labor under the supervision of a trained engineer. The heaviest component, weighing 300 kg, can be carried by six men. All components of a Bailey bridge can be transported to the job site in standard 3-ton trucks.
Enter #3.Callender-Hamilton Bridge (assembly).:
The Callender-Hamilton Bridges were originally designed for the Army to transport military cargo. This type of bridge covers spans from 12.0 m to 42.0 m and, like the Bailey bridge, is a 'passage' type truss. Callender Hamilton Bridges are also used as semi-permanent or permanent bridges.
The basic element used in the construction of this type of bridge is an angle of 150 mm × 150 mm × 20 mm × 3.0 meters in length used as the top chord, bottom chord, and diagonals of the Warren truss, as shown in Fig. Figure 18.5.
The length of the upper and lower strings is 3.0 m, and as such the bridge can be built in multiples of 3.0 m. For spans from 12.0 m to 24.0 m, one truss is used on each side, but for spans longer than 24.0 m and up to 42.0 m, two trusses bolted in pairs are used on each side. The load capacity of these bridges ranges from an 18-ton vehicle to a 30-ton vehicle.
The trusses carry the crosspieces, which are 300 mm × 90 mm channels. Road beams supported on cross beams (see Fig. 18.5) are made of timber with a length of 3.0 m and a cross section of 250 mm × 125 mm and are attached to the cross beam with 20 mm. diameter screws.
The deck boards or chessboards have a length of 3.37 meters and a cross section of 250 mm x 100 mm. The hinges are also made of wooden profile (225 mm × 225 mm). The wooden cladding described above can be replaced by steel or reinforced concrete tubs, provided that the weight of the replacement cladding does not exceed 3.35 t per 3.0 m span.
Callender-Hamilton Bridges can be built using one of the following methods, depending on site conditions and the availability of labor and equipment:
i) On-site assembly using temporary intermediate supports.
ii) Lift and launch from shore to shore using the launch nose of the Bailey Bridge.
iii) lifting and stacking complete trusses, one at a time, from bank to bank using cranes, winches and slings (Fig. 18.6).
Enter #4. dams:
Dams are built under the following circumstances:
i) When the importance of the road is not very great and the stream carries little or no water during the dry season and little water discharge during the monsoon, except during floods.
ii) The flood discharge in the stream only flows for a short period, say 24 to 72 hours.
iii) On mountain roads where small streams cross the roads at regular intervals.
Low dams have their tops level with or slightly above the stream bed so that floodwater discharge can be channeled over them (Fig. 18.7). During the monsoon, traffic has to stop six to eight times for 24 to 72 hours during floods.
The streams on which these dams are built remain dry or carry very little flow during the dry season, and flood discharges to streams only flow for short periods of time, say 24 to 72 hours. To protect the dam slab from abrasion, fence walls or curtain walls are erected on the U/S and D/S sides.
The depth of the curtain wall on the D/S side is greater because the erosion is greater on the D/S side. In general, curtain walls are taken 1.5 to 2.0 meters for U/S side walls and 2.0 to 2.5 meters for D/S walls. High or aerated dams are built where water flows continuously throughout the year and flood discharges happen 6-8 times every 24-72 hours during monsoon.
The lower level of these openings is kept close to bed level, and the upper level of the dikes is maintained so that traffic is not interrupted for more than 15 to 25 days during the monsoon. The openings can be circular or rectangular, as shown in Fig. 18.8a left half and right half, respectively. An aerated dam with rectangular openings is shown in photo 5.
Barriers or curtain walls are provided on the upstream and downstream sides, as in a low-level dam. In addition, aprons are used in front of these dams up to the curtain walls to ensure a smooth flow of water through the openings. Usually there is a 2.0-2.5m skirt on the U/S side and a 3.0-4.5m skirt on the D/S side.
Type #5. diving jumpers:
A submersible bridge is a compromise between an aerated dam and a raised bridge. In the case of a vented dam, except for normal flow, all flood water, whether normal or high, will flow over the vented dam, and in the case of a high-level bridge, all floods, including the highest will flow over it. the bridge with some freeboards crosses below deck.
But with dip bridges, ordinary floods will go under the bridge deck, but large floods will go over the deck.
Therefore, for the same location, a shallow or level embankment, if any, will cause the most disruption to traffic, a high or airy embankment will cause the least disruption, and inclined bridges will cause the least disruption to traffic.
For this reason, sidewalks are used on hill roads, village roads and other municipal roads, while submersible bridges are generally used on large municipal roads with low traffic intensity when there is a need to achieve savings due to lack of money and the choice is between low-cost bridges or no bridges.
Submersible bridges are built with a full linear channel from coast to coast, with no channel restriction. Both banks must be protected, with the slope aligned with the platform used to protect the base pond. For diving bridges, the skirts for the U/S and D/S sides should be 6 meters and 9 meters respectively, for bulkheads they are 2.0 meters for the U/S side and 2.5 meters. for the D/S side.
The details of the dip bridges are more or less the same as for an aerated dam with rectangular openings, except that the openings in the dip bridges may be larger. Control/sentry points such as dams should be provided.
- The 9 main types of mobile bridges (with diagram)
- Continuous bridges: types, design and advantages