COMPONENT PART OF A BRIDGE
1. Superstructure
2. Bearings
3. Substructure components
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Component parts of a bridge
MATERIAL SPECIFICATION
CONCRETE
Type of cement used for preparation of concrete shall be any one as specified in C1.18.4.1 or IRC : 112-2011 and select one
All course and fine aggregate shall confirm to IS :383 and shall be tested to confirm to IS :2386 ( Part 1 to 4)
Water used for mixing and curing shall be as per the IRC:112- 2011
Concrete shall have minimum 28days characteristic strength on 150mm cubes
REINFORCEMENT
All reinforcement shall be high yield strength deformed bars with grade/designation. Fe 500/fe500D conforming to IS:1786 and which shall be manufactured from primary
FOUNDATION
Pile foundation
Bored cast in situ piles can be provided and socketed as required in to be hard rock.
Pile test load shall be 1.5 times pile working load.
The permissible tolerance for piles shall be such that the shift at platform level not exceeding 75mm and the tilt not exceeding 1 in 150.
SUPER STRUCTURE
The superstructure of bridge is consisting of deck slab, girder, truss etc. These component vary based on the type of bridge (steel/ concrete) superstructure of the bridge bars the load passing over it. This help in transmitting the force formed by the load to the below structure.
DECKS
The decking is considered as the road or the rail surface of the bridge .The decks are supported by the girder or huge beams that is in turn supported by the piers. The whole arrangement is supported with a deep foundation mainly piles and cap arrangement.
Deck
BEARING IN BRIDGES
Loads are received by decks are transmitted to substructure with the help of bearing
This transmission is very essential in situation were substructure is not designed to take the load action directly.
The bearing allows longitudinal movement of girder this movement is due to forces acting on longitudinal direction. The force due to moving loads and the variation in temperature are cause for longitudinal force.
Selection of bearing depends on:
Loads acting
The geometry
Extend of maintenance
Clearance available
Displacement
Rotation and deflection policy.
Availability
Preference of designer and cost criteria
The designer must consider the bearing arrangement in bridge construction as a separate system.
In most of construction bearing is selected in the last moment. This result in increase of maintenance in future which must be avoided.
Bearing of bridges
SUB STRUCTURE COMPONENTS
PIER
Vertical structure used to support deck and load transmission to underground soil through foundation.
These structure serve as supports at intermediate point.
Functions
a. Load transmission to foundation
b. Resistance to horizontal force
Normally pier are designed to resist vertical loads alone. In areas which lie in the seismic zone, it is recommended to design the pier for lateral loads also.
Piers are constructed using concrete. Steel column filled with concrete is used as new technology of pier construction.
Classification of pier.
a. Based on structural connectivity – Monolithic/cantilevered
b. Based on shape- Solid /hollow, Hexagonal, Round, Octagonal , Rectangular
c. Based on framing – Single/Multiple column bent, Hammer head or pier wall type.
Piers
ABUTMENT
Vertical structure used to retain the earth behind the structure.
DL and LL from bridge superstructure is supported by the bridge abutment
The design loads on the abutment is mainly depend on a. Type of abutment b. Sequence of construction
The abutments are primarily designed to resist the over turning and sliding.
It must overcome differential settlement and excessive movement caused due to lateral forces or loads.
Abutment
WING WALL
Constructed as an extension to abutment
This can be constructed either integrally or independent with the abutment wall.
The wing wall must consider two design loads
a. Earth pressure from backfill b. Hydraulic load from saturated soil
Wing wall
PARAPET AND HAND RAIL
Not an important structure but provided for safety concerns.
Provided above the deck.
Prevention of vehicle from falling of the bridge in to water body.
Parapet and Handrails
FOUNDATION
Constructed to transmit the load from piers, abutment, wing wall and returns evenly on the strata
The foundation for bridge is deep insufficient manner to avoid scouring due to water movement or to reduce the chances of under mining.
The most common type of deep foundation for modern bridge is piling
The piles used for bridge construction may be concrete, steel or timber.
Most common which is pre-cast concrete piles
Foundation
MATERIALS REQUIRED FOR BRIDGE CONSTRUCTION
STONE
The greaten old bridges of the Etruscans, the romans , the Fratres Pontifices of the middle ages (since about 1100) and of later master builders were build with stone masonry.
The arches and piers have lasted for thousands of years when hard stone was used and the foundations constructed on firm ground ; with stone, one can build bridges which are both beautiful, durable and of large span (up to 150m).
Unfortunately, stone bridges have become very expensive. Over a long period, however stone bridges which are well designed and well built, might perhaps, turn out be the cheapest, become they are long- lasting and need almost no maintenance over centuries unless, attacked by extreme air pollution.
Stone is now a days usually confined to the surfaces, the st0nes being preset or fixed as facing for abutments, piers or arches ; Of course , sound weather-resisting stone must be chosen, and fundamental rock like granite , gneiss, porphyry, diabase or crystalized lime stone are especially suitable.
Caution is necessary with sand stones, as only siliceous, sand stone is durable.
The choice of colors of the stone is also relevant.
Granite of a uniform grey color and sawn surface can look as dull as simple plain concrete.
A harmonious mixture of different colors and slightly embossed surfaces can look very lively, even when the masonry areas are extensive.
The surfaces can also be enlivened by bright or dark joint filling.
The size of the stone blocks and the roughness of their surfaces must be harmonised with the size of the structure, the abutments , the piers.
Coarse embossing does not suit a small pier thick and 5m heigh , but large sized a masonry is suitable for large arch bridges such as the Saalebrucke Jena or the Lahntalbrucke Limburg.
Granite masonry was preferred for piers of bridges across the river Rhine, because it resist erosion by sandy water much better than the hardest concrete.
REINFORCED AND PRE-STRESSED CONCRETE
Concrete is a construction material used in almost all construction works.
Have a dull grey color, usually concrete is not proffered in construction bridges like bridges but some of concrete bridges have turned out to be beauties, if someone knows the art.
Good concrete attains high compressive strength and resistance against most natural attacks though not against de-icing salt water, or CO2 and SO2 in polluted air.
However, its tensile strength is low, so is not permeable in areas of tensile stresses.
For tensile cement of concrete steel bars are embedded in to it.
STEEL
Steel has the highest and most favorable strength qualities and it is therefore suitable for the most daring bridges with the longest spans.
Normal building steel has compressive and tensile strength of 370 N/mm2.
A special merit of steel is ductility, before it breaks it deforms considerably.
For bridges high strength steel is often proffered.
For building purposes steel plates of 6 to 80 mm thick are used. High strength of steel allow small cross-section of beam or girders and therefore a low dead load of the structure.
Aluminum was occasionally used for bridges and the same form was used as for steel girder.
PROCEDURE FOR BRIDGE CONSTRUCTION
STEP: 1- THE FOUNDATION
The foundation have the function of distributing various loads in an efficient manner to the ground.
The functions can be of two types.
The superficial foundations-these foundations are preferred for bridges whose level is closed to that of ground because in this case structures are subjected to reduce constraints compare to the wind and their gravity.
Deep foundations-this type of foundation is most suitable when the bridge begins to gain height.
STEP: 2-CONSTRUCTION OFSUPPORT
The number of supports (abutment and pile) necessary for construction of bridge, they will all be mounted simultaneously on both sides of shores.
Usually made of concrete, these supports are either cast in place, or prefabricated in a factory and then assembled on sites.
STEP: 3-ASSEMBLY AND LAUNCHING OF THE SUPERSTRUCTURE
The final weight of the structure, the greater or smaller distance between each pile and the final aim of the structure , it is often impossible to use concrete for the construction of the deck which, over great distances , collapses even some times under its own weight and its traffic
Now, the use of elements of metal beams that are assembled together to form the structure of the deck.
STEP: 4 – POURING THE SLAB
The beams are equipped on factory with connectors that allow the steel structure to be bonded to the concrete slab of the latter.
Thus, once the beam is installed on their final supports we could lost formwork on them and reinforcement before pouring a layer of thickness about 25 cm which will be the slab of the structure.
STEP:5- FINISHES
On each shore a crane installs the beam elements which are then reconstituted by welding on site.
The deck can then be equipped with a launching nose, completed with ballast at the rear to prevent tipping.
Pushed on the piles generally using winches , cables and pulleys , the deck advances at a speed of about 9m/h; Also this solution can be supplemented by restraint systems to prevent runaway.
PRECAUTIONS
ACCESS EQUIPMENT
One of the biggest risks faced by bridge workers is falling from a higher level of a bridge to lower one.
This happens because workers use wrong equipment.
Bridge walkers-which can securely lower workers up to 20 feet below a bridge even if space is limited.
Hydra platform-able to move workers up to to 35 feet below a feet.
UBITs-highly flexible units that can lower workers almost 26 feet below bridge deck.
EYE AND FACE PROTECTION
Eye and facial injuries typically happens because foreign objects and particles enter the eye while welding, cutting, nailing or working with concrete.
Use appropriate eye or facial mask to protect face from liquid chemicals, acids and injurious light radiation.
FIRE BLANKETING
Serious injuries on bridge construction site happen when utility lines, tables and typing that cross them are damaged by construction equipment.
A fire blanket is sheet of fire retardant material that can be placed over a fir in order to smoother it
It’s considered the best way to control an electrical or other utility-related fir.
FOOT PROTECTION
In areas where there’s a danger of foot injuries due to falling or rolling objects
Doing work where it’s possible an object could pierce the sole of a shoe
In need of protection from an electrical hazard, such as a static discharge or electric shock
UNDER-BRIDGE PROTECTION
Bridge utility lines can be damaged by construction equipment, tampering weather incidence an natural disaster
These threats can lead to loss of utility service, expensive repair costs, injury or loss life
Protection under bridge (PUB) systems are caging units designed to protect vulnerable utility lines under bridges
They can help ensure on going utility service along with worker and the community
HIGH VISIBILITY SAFETY EQUIPMENT
People working on bridges and roadways are required to wear special colorful and reflective clothing
It makes workers visible to drivers in work zone, which helps prevent accidence before there accidents before they happened
HAND PROTECTION
Employs are required to make sure that workers use appropriate hand protection when they are exposed to:
Harmful substances
Sharpe object that could cause cuts or lacerations
Work that could lead to severe abrasions or punches
Heat or chemicals that could cause burns
Weather extremes
HEAD PROTECTIONS OSCHA
Requires that works on bridge sits where hard hats when:
Object could fall on them
They could bump their hair on fixed objects
They could came into contact with electrical hazards(a big risk for bridge utility works
SIGINAGE BARRIES
Something as simple as using adequate signage and appropriate barriers can provide a great amount of protection for workers on bridge construction sites
OSHA standards require that traffic control science, signels, barricades, or devices must be used to protect construction employees from traffic hazards , such as motorists inadvertently entering the work space or existing the highway in wrong place
SAFE VEHICLES
The vast majority of deaths that occur in bridge and road construction zones in the US happened because a worker is hit by a piece of construction equipment’s or other vehicle.
That’s way it’s critical that all vehicles used on- site have safety feature including :
Working headlights and beark lights
Audible horns
Back-up alarms
Safety glass with no distortions
Proper mirrors
EQUPIMENTS USED IN BRIDGE CONSTRUCTION
The construction of bridges is a highly skilled process.
In order for the design of the bridge to be carried out , special equipment must be used to complete the project due to the size and weight of the materials.
According to transportation research board website. International construction companies work together to design built and supply the correct and most equipment for bridge construction.
BRIDGEBUILDER.
The machine is light weight
Easy to assemble
Moves on fixed rails.
The bridge builder is used to move materials and construct the frames of concrete bridges
The machine is designed to be able to move and support any were from 100 to 400 tons of bridge building materials
GANTRY CRANE
Gantry cranes are used to cost effectively erect and build segmented bridges
The NRS web site explains that gantries are built either as overhead or under-slung machines in order to meet specific bridge construction needs.
Gantry cranes are simply very large cranes that are used to maneuver and quickly built a bridge 1 beam at a time.
The Gantries operate by using hydraulic cylinders to support the various bridge segments.
The overhead Gantries suspended and move segments through the use of specifically designed tension bars.
BEAM LAUNCHER
A beam launcher is used to position and install pre-cast concrete beams for bridges that are being built over a body of water or viaducts.
When building a bridge that is crossing unsteady ground or has high piers, the beam launcher is used to position the beams correctly and safely.
The two kinds of beam launchers include single box and twin-truss type.
The single box beam launcher is light weight and used for erecting pre- cast beams on tight horizontal alignments.
The twin-truss beam launcher is used worldwide for constructing large scale bridges.
STRADDLE CARRIER
A straddle carrier is used in place of gantry crane when heavy materials must be lifted at casting yards, factories, storage areas, ports and marinas.
The NRS website explains that gantry cranes are attached to fixed rails, while straddle carriers are built on tires with motorized wheels to make construction and material mobilization possible.
Astraddle carrier operates by using hydraulic systems, winches, ropes, and electric and hydraulic motors.