Types of Loads for Design of Bridge Structures

Here, the different types of load impacted in the bridge are as follows.

Dead load
Superimposed Dead Load
Live load
Impact load
Wind load
Channel Forces
Longitudinal forces
Centrifugal forces
Differential settlement
Shrinkage and creep
Earth pressure
Buoyancy effect
Effect of water current
Thermal stresses
Seismic loads
Deformation and horizontal effects.
Erection stresses
Prestress

1. Dead Load

The self-weight of the bridge components, often referred to as what is the dead load of a bridge or dead load bridge, is represented by the dead load. The deck slab, wearing coat, railings, parapet, stiffeners, and other utilities are among the bridge’s different components.

It is considered the initial computable design load when constructing a bridge design.

2. Superimposed Dead Load

Other permanent objects such as parapets and road pavement, also known as superimposed load or superimposed dead load examples, are called superimposed dead loads. These things are long-term, though they may be replaced during the structure’s lifetime.

It is determined as the product of volume and material density, just like self-weight.

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3. Live Load

The moving load on the bridge, a key component of types of loads on bridges and loads on a bridge, corresponds to the live load the entire length of the bridge.

Vehicles, pedestrians, and other moving loads are examples. Selecting one vehicle or a group of vehicles to construct a safe bridge is difficult.

In anticipation of any form of vehicle moving on the bridge, IRC proposed some fictional cars as live loads, which will provide secure outcomes.

The following are the several types of vehicle loadings:

IRC class AA loading.
IRC class A loading.
IRC class B loading.

3.1 IRC Class Aa Loading

This form of loading can be used to design new bridges, especially those with heavy loads, such as highway bridges, city bridges, and industrial bridges. Normally, the following sorts of vehicles are taken into account when loading a class AA vehicle.

Tracked type
Wheeled type

3.2 IRC Class A Loading

All permanent bridges must be designed with this type of loading in mind. It is handled as a conventional bridge live load. When designing a bridge for class AA loading, it should also be checked for class A loading.

3.3 IRC Class B Loading

This sort of loading is used to create temporary bridges such as Timber Bridges. It’s considered a light load.

4. Impact Loads

These sudden loads, part of the 7 types of loads on bridges, generated as the vehicle is travelling on the bridge, induce the impact load on the bridge.

Whenever the wheel is in movement, the live weight shifts from one wheel to the next, causing the impact load on the bridge.

An impact factor is used to calculate the impact loads on bridges. The impact factor is a multiplication factor that’s also depending on numerous elements such as vehicle weight, bridge span, vehicle velocity, and so on.

5. Wind Loads

The wind load, an important aspect of bridge loads, is also a significant consideration in bridge design. Wind load on short-span bridges can be insignificant. For medium-span bridges, wind loads should be taken into account while designing the substructure.

Wind load is taken into account when designing superstructures for long span bridges. The surface areas of all elements (including superstructure and substructure) as seen in elevation are considered the exposed zone of the bridge (i.e., perpendicular to the longitudinal axis).

AASHTO specifies the loading on a bridge due to wind forces based on a wind velocity of (160 km/h). This translates to an intensity of (2.40 kN/m²) for standard girder/beam bridges, with a minimum total force of (4.38 KN/m).

5.1 Wind Load on Structure

Transverse Loading = (2.40 kN/m² ).
Longitudinal Loading = (0.58 kN/m² ).

5.2 Wind Load on Live Load

Transverse Loading = (1.46 kN/m) .
Longitudinal Loading = (0.58 kN/m).

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6. Channel Forces

The loads exerted on a structure by water course-related features are known as channel forces. Stream movement, floating ice, and buoyancy are only a few examples of these forces. Substructure elements are predominantly affected by channel forces, which are equivalent to seismic forces.

7. Longitudinal Forces

Braking or accelerating a vehicle on the bridge causes longitudinal forces, addressing the question of which type of load is every bridge designed to carry. When a vehicle comes to an abrupt stop or accelerates, longitudinal forces are applied to the bridge structure, particularly the substructure. As a result, the IRC advises that 20 percent of the live load be treated as longitudinal force on bridges.

The longitudinal force is exerted above the deck surface (1.8 m). The assumption is that all travel lanes are travelling in the same direction. The influence of longitudinal forces (breaking force) on the superstructure is minor.

Substructure elements, on the other hand, are more severely damaged. The breaking force, like longitudinal earthquake forces, is resisted by the piers and/or abutments that support fixed bearings.

8. Centrifugal Forces

The movement of vehicles over curves, a load bridge consideration, will create centrifugal force on the superstructure if the bridge is built on horizontal curves.

As a result, in this scenario, centrifugal forces should be considered as well. Centrifugal force can be calculated by

C = ( W xV ²) / (12.7 R )

Where,

W = live load ( kN )
V = Design speed ( kmph )
R = Radius of curve (m).

The truck loading is used to calculate centrifugal forces rather than the lane loading.

In each design traffic lane, one standard design truck is put to generate maximum forces in the bridge.

Decks attached to the primary members of the superstructure (for example, a composite concrete deck integrated with steel girders using shear connectors) transmit centrifugal forces to substructure elements via secondary components and bearings at piers and abutments.

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9. Differential Settlement

In the case of continuous and simply supported bridges, support settlement causes additional design moments in the superstructure. The quantity of settlement determines the force intensity.

10. Shrinkage and Creep

Concrete beams that were pre-stressed showed signs of shrinkage and creep. This distortion may have an impact on bridge design. Furthermore, when considering the composite action of bridges, cast in-situ concrete set on a specific beam subjected to shrinkage comes into play.

It adds to the stress level. It will be necessary to detail reinforcements in order to avoid this consequence.

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11. Earth Pressure

The typical method of applying earth pressure to the bridge can be used. Surcharged loads must be considered for the design based on the location.

Coulomb’s method or any other applicable approach could be used to compute active, at rest, and passive pressure coefficients.

12. Buoyancy Effect

The buoyancy impact is taken into account for huge bridge substructures submerged in deep water. If the depth of submersion is low, the effect may be insignificant.

Bridges with submerged underwater components (e.g., piers) are susceptible to the effects of buoyancy. This is usually just an issue with very big hollow constructions.

On pier footings and piles, buoyancy may provide an uplifting force.

13. Effect of Water Current

When constructing a bridge across a river, a portion of the foundation will be submerged in water. Horizontal forces are induced by the water movement on the submerged section.

Water current forces are greatest at the top of the water level and zero at the bottom of the water level, or at the bed level.

The pressure by water current ( P ) = KW [V²/2g]

Where

P = pressure ( kN/m²)
K = constant (value depending upon shape of pier)
W = unit weight of water
V = water current velocity (m/s)
G = acceleration due to gravity (m/s²)

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14. Thermal Stresses

The temperature causes thermal stresses. Extremely high or low temperatures cause stresses in bridge elements, particularly around bearings and deck joints.

Because these strains are tensile in nature, concrete is unable to withstand them and cracks emerge.

Additional steel reinforcement perpendicular to the primary reinforcement should be installed to resist this. There are also expansion joints available.

15. Seismic Loads

When constructing a class a bridge in a seismic zone or earthquake zone, earthquake loads must be taken into account. During an earthquake, they produce both vertical and horizontal stresses. The amount of force applied is mostly determined by the structure’s self-weight.

Larger forces will be exerted if the structure’s weight is greater. Seismic forces are a significant loading factor that frequently influences bridge design in seismically active areas. The acceleration coefficient at the bridge site is used to determine the degree of seismic activity.

Structures with only an acceleration coefficient higher than 0.19 are thought to be in a seismically active location. These coefficient, as well as whether or not its bridge is categorised as essential, are being used to provide a seismic performance category to the bridge (SPC).

16. Deformation and Horizontal Effects

Changes in material characteristics, either internally or externally, cause deformation stresses. Creep, concrete shrinkage, and other factors could cause the change.

Temperature fluctuations, vehicle brakes, earthquakes, and other factors will all produce horizontal forces. As a result, in bridge design, these are also considered design loads.

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17. Erection Stresses

During the construction of a bridge, construction machinery causes erection tension. These can be thwarted by offering appropriate support to the members.

18. Prestress

While prestress is more of a means of resisting load than a loading, it is often more convenient to treat it as such for analytic purposes. The approach of equivalent loads can be used to deal with prestress, just as it can with temperature.

FAQ

Bridge Structures

There Are Six Basic Bridge Forms: the Beam, the Truss, the Arch, the Suspension, the Cantilever, and the Cable-Stay.

Wooden Arch Bridge

Sit stable. And line them up this way for the birth. Okay that’s the hud spike down okay so now that i have these holes in the next part is to get the baseboards in on either side here.

Metal Truss Bridge

Steel truss bridge. A steel truss bridge is a bridge composed of only trusses. If the span of the bridge is too large, there is a disadvantage that it takes a lot of time to manufacture the members, but it is a representative railroad bridge that has the advantage of having light members and it is easy to construct.

Prefabricated Pedestrian Bridges

The federal highway administration estimates that pedestrian bridges range from $150 to $250 per square foot, totaling a cost of approximately $1 million to $5 million per complete installation.

Steel Bridge Truss

Prefabricated Bridges Residential

The cost is $120 to $160/square foot for bridges with simple precast abutments. Small precast prestressed concrete girder bridges with integral decks come in a variety of configurations. Girder types include flat slabs, void decks, rib decks, deck bulb-tee girders, and others.

Bridge Joists

The term ‘bridging’ refers to a brace, or an arrangement of braces, that is fixed between floor or roof joists to keep them in place, prevent joist rotation, and distributing loads over more than one joist.
Bridging can help strengthen a floor and stop it from bouncing when occupants walk across it.

Beam Bridge

A beam or “girder” bridge is the simplest and most inexpensive kind of bridge. In its most basic form, a beam bridge consists of a horizontal beam that is supported at each end by piers. The weight of the beam pushes straight down on the piers.

Truss Bridge Designs

In this experiment we have tested which type of truss bridge is the strongest, yet uses the least amount of material. Two of the most used truss bridges are of the pratt and howe design. Through our experiment it was found that the bridge design that minimized the maximum compression force was the howe bridge.

Steel Truss Pedestrian Bridge

As a general rule, the truss depth should be no less than 1/20th of the bridge span but — except in extreme cases — shall not be less than 1/25th of the bridge span.

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Types of Loads for Design of Bridge Structures