The predominant action on highway bridges is gravity loads due to self-weight and the mass/dynamic effects of moving traffic. Other actions that are frequently considered are temperature loads, construction loads, snow loads, earthquake loads, and possible differential settlement of the foundation.
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What are the different types of load on a bridge?
Types of Loads for Design of Bridge Structures. Various design loads to be considered in the design of bridges are: Dead load. Live load. Impact load. Wind load. Longitudinal forces. Centrifugal forces.
What is an impact load on a bridge?
Impact Loads The Impact load on bridge is due to sudden loads which are caused when the vehicle is moving on the bridge. When the wheel is in movement, the live load will change periodically from one wheel to another which results the impact load on bridge. To consider impact loads on bridges, an impact factor is used.
What are the factors affecting the impact factor of a bridge?
25% up to 5m and linearly reducing to 10% from 5 m to 9 m. If the length exceeds in any of the above limits, the impact factor should be considered from the graph given by IRC which is shown below. For bed blocks, I f = 0.5 4. Wind Loads Wind load also an important factor in the bridge design. For short span bridges, wind load can be negligible.
What are Haha loads on bridges?
HA loads are uniformly distributed load on the bridge deck. These types of loads on bridges must be considered and it is an essential type of load that we must apply to the design.
What is a settlement load on a bridge?
When the soil beneath a structure settles unevenly, it is called settlement load. Structures will sink and change shape when they experience settlement load.
What is settlement and how can it affect a bridge?
bridges in the United States are affected by bridge approach settlement, or the “bump at the end of the bridge.” The difference in elevation between the approach pavement and the bridge deck results from a complex interaction between the bridge structure, backfill soils and foundation soils; poor drainage is one ...
What are the two types of loads on a bridge?
Dead and live weight are essentially vertical loads, whereas forces from nature may be either vertical or horizontal. Wind causes two important loads, one called static and the other dynamic. Static wind load is the horizontal pressure that tries to push a bridge sideways.
What are the seven different types of loads that can affect a bridge?
Various design loads to be considered in the design of bridges are:Dead load.Live load.Impact load.Wind load.Longitudinal forces.Centrifugal forces.Buoyancy effect.Effect of water current.More items...•
What are approaches on a bridge?
In many instances, the areas on either side of a bridge are shielded with a longitudinal barrier such as a W-beam guardrail. The connection between a guardrail and a concrete barrier is also known as a 'transition' or 'bridge approach' system.
What is approach length in bridge?
As per IRC recommendations, the minimum length of approaches at the ends of the bridge is 15 m. The approaches on either side of the straight bridge shall have a minimum length of 15 m and suitably increased where necessary to provide minimum sight distance.
What are the 3 types of loads on a bridge?
There are 3 kinds of forces that operate on any bridge: the dead load, the live load, and the dynamic load.
What are the 3 types of loads?
The loads in buildings and structures can be classified as vertical loads, horizontal loads and longitudinal loads.
What is the difference between a dead load and a live load?
The dead loads are permanent loads which result from the weight of the structure itself or from other permanent attachments, for example, drywall, roof sheathing and weight of the truss. Live loads are temporary loads; they are applied to the structure on and off over the life of the structure.
What two forces must be concerned with on bridges?
Two major forces act on a bridge at any given time: compression and tension. Compression, or compressive force, is a force that acts to compress or shorten the thing it is acting on. Tension, or tensile force, is a force that acts to expand or lengthen the thing it is acting on. As a simple example, think of a spring.
What are the 5 main bridge types?
There are five types of bridges, and these are, Girder, arch, cable, rigid framed and truss. Each has its unique features and uses. This is a bridge in its simplest and most common form. A log across a stream is an example of this structure.
How do you calculate live load on a bridge?
8:2519:49TUTORIAL: Simple Span Live Load - YouTubeYouTubeStart of suggested clipEnd of suggested clipThe moment and the way you do that is by keeping your cg. And the nearest axle equidistant from theMoreThe moment and the way you do that is by keeping your cg. And the nearest axle equidistant from the mid-span of your bridge.
What negative effect does a bridge have on the environment?
Bridges and culverts can potentially alter the flow regimes of the river thereby affecting water velocity, depth, depositional patterns and channel morphology. Theses changes in turn may increase the risk of flooding and erosion. Surface water quality could be affected by a number of factors during operations on site.
How construction of bridges affect the environment?
The bridge construction activities also have the potential to cause a temporary increase in suspended sediments. Aquatic habitat will be disturbed in the vicinity of the construction area. Aquatic life uses of this portion of the Nun River will be negatively impacted.
How can we design bridges to be safe?
For designing safe bridge structures, the engineering design process includes the following steps: 1) developing a complete understanding of the problem, 2) determining potential bridge loads, 3) combining these loads to determine the highest potential load, and 4) computing mathematical relationships to determine the ...
How do Bridges help the environment?
And when a concrete bridge has reached the end of its useful life, the concrete can be recycled by crushing it and using it as fill for roads. In addition to reducing waste in landfills, this approach reduces the need to mine and process new materials and limits pollution involved in transporting material to sites.
What is bridge traffic loading?
Bridge traffic loading is often governed by trucks whose weights are substantially in excess of the legal maximum. Bridge traffic loading is applied to notional lanes which are independent of the actual lanes. Eurocode normal loading consists of uniform loading and a tandem of four wheels in each lane.
What is settlement of supports?
Settlement of supports induce additional design moments in superstructure in case of continuous and simply supported bridges. The intensity of force depends on the amount of settlement.
What is superimposed dead load?
Superimposed dead loads are gravity loads that consist of other permanent items such as parapets and road surfacing and other non-structural and architectural attachments to the bridge. Such items are long term but might be changed during the lifetime of the structure. Similar to self-weight it is calculated as the product of volume and material density.
What is an imposed load?
Imposed traffic loads consist of those forces induced by road or rail vehicles on the bridge. Bridge traffic can be vehicular, rail or pedestrian/cycle or indeed any combination of these. Depending on the design code, the type and intensity of the design vehicle changes. For example, HL-93 is used in AASHTO design code.
What happens when the top of a beam heats up relative to the bottom?
If top of a beam heats up relative to the bottom, it tends to expand; if it is restrained, bending moment and shear force are generated. The effects of both uniform and differential temperature changes can be determined using the method of ‘equivalent loads’.
What is vibration in a bridge?
Where natural frequency is at a level which can be excited by wind or traffic, Vibration in the deck is be a problem, in slender bridges. This effect is usually considered using impact factor in the design.
Which direction do wind loads apply to bridges?
Depending upon the wind intensity and the exposed area, wind loads are applied to bridges in transverse, longitudinal and vertical directions.
What is impact load on a bridge?
The Impact load on bridge is due to sudden loads which are caused when the vehicle is moving on the bridge. When the wheel is in movement, the live load will change periodically from one wheel to another which results the impact load on bridge. To consider impact loads on bridges, an impact factor is used.
What type of load is used in the design of all permanent bridges?
This type of loading is used in the design of all permanent bridges. It is considered as standard live load of bridge. When we design a bridge using class AA type loading, then it must be checked for class A loading also.
What is buoyancy effect?
Buoyancy effect is considered for substructures of large bridges submerged under deep water bodies. Is the depth of submergence is less it can be negligible. 8. Forces by Water Current. When the bridge is to be constructed across a river, some part of the substructure is under submergence of water.
What causes longitudinal forces on a bridge?
The longitudinal forces are caused by braking or accelerating of vehicle on the bridge. When the vehicle stops suddenly or accelerates suddenly it induces longitudinal forces on the bridge structure especially on the substructure. So, IRC recommends 20% of live load should be considered as longitudinal force on the bridges.
What are moving loads?
The moving loads are vehicles, Pedestrians etc. but it is difficult to select one vehicle or a group of vehicles to design a safe bridge. So, IRC recommended some imaginary vehicles as live loads which will give safe results against the any type of vehicle moving on the bridge.
What is dead load?
1. Dead Load. The dead load is nothing but a self-weight of the bridge elements. The different elements of bridge are deck slab, wearing coat, railings, parapet, stiffeners and other utilities. It is the first design load to be calculated in the design of bridge. 2.
Why do bridges have thermal stresses?
Thermal stresses are caused due to temperature. When the temperature is very high or very low they induce stresses in the bridge elements especially at bearings and deck joints. These stresses are tensile in nature so, concrete cannot withstand against this and cracks are formed.
What is settlement in construction?
Settlement is thedownward movementof a footing, pavement, or structure due todeformations of the supporting soil or piles. Settlement can be initiated by a number of factors which include, but are not limited to:
What is permanent load?
Permanent loads, are those loads whichalways remain and acton a bridgethroughout its life.
What is temporary load?
Temporary loads are those loads which are placed on a bridge foronly a short period of time.
What is deformation load?
Deformation loads are those loads induced by the internal or external change in material properties or member geometry. Creep
What is a dead load in composite construction?
In composite construction superimposed dead loads are thoseloads placed on the superstructure after the deck has cured and begun to work with the primary members in resisting loads.
What is live load?
The term live load meansa load that moves along the length of a span.
What is superimposed dead load?
separate items such assidewalks, railings, parapets, signing, utilities, and the wearing surface. Superimposed dead load is part of the total dead load. It is separated from the rest of the dead loadsbecause it is resisted by a composite section, therefore cause less deflection and stressin the stringer than other dead loads.
What is live load?
Live load models are composed of a combination of double axle load (tandem system), that represent an idealized design truck, and uniform distributed loads that account for the effect of cars, smaller trucks or crowds of people.
How does the influence line work?
The influence line follows the profile of the deflected shape of a structure generated by releasing the restraint corresponding to the action and applying a unit displacement or rotation in the direction of the action.
Dead Load
IRC Class Aa Loading
- The wind load is also a significant consideration in bridge design. Wind load on short-span bridges can be insignificant. However, 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. Wind Loads on Bridges are an issue that needs to be add…
IRC Class B Loading
- Additional steel reinforcement perpendicular to the primary reinforcement should be installed to resist this. There are also expansion joints available. Bridge Thermal Stresses Seismic Loads When constructing 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. Th…
Impact Loads
- HA loads are loads that are evenly distributed across the bridge deck. These types of loads on bridges must be taken into account, and they are an important factor in the design. The HA loads that must be applied are determined by the bridge’s span. The uniformly distributed load can be evaluated using the procedure below. When the bridge span is s...
Different Settlement
- However, because of the variations in loads and ground conditions, there is a risk of varied settlements when there are shallow foundations. Erection Loads The type of the building has a big impact on the loads that need to be considered for erection. Furthermore, the construction sequence is an important issue to consider during the design process.In addition, BS 5400 Part …