Week 1 Challenge

1. Different type of foundation in bridges.

* Shallow Foundation.

* Depth Foundation.

i) Shallow Foundation:

* d≤b

* Depth of the foundation is lesser than or equal to its Breadth.

* Shallow Foundation is also called Open Foundation.

ii) Depth Foundation:

* d>b

* Depth of the foundation is greater than its Breadth.

* Depth Foundation is also called Deep Foundation.

Selection of type is made:

Shallow foundations are commonly used for projects that are smaller in size and lighter in weight. They are common when the lowest

finished part of the structure is less than six feet deep and the dirt around the project has sufficient bearing capacity.

Types of foundation in Shallow Foundation:

* Combined Footing

* Mat Footing

* Spread or Isolated Footing

* Strip Footing

* Strap or Cantilever Loading.

Deep foundations are a type of foundation that is used to transfer building loads further down the earth to utilize stable soil. This

process is utilized when the existing soil is not stable enough to handle a foundation. Deep foundations are essential for safety and maintaining the

integrity of a building.

Deep foundation is used

* Poor bearing capacity of Top soil.

* Liquefication of soil strata.

* Large Flactuations in subsoil water level.

* Presence of Canal or Deep drainage linear near the foundation.

* Structures near seashore or riverbed.

2.Components of a RCC girder bridge resting on open foundation:

The bridge structure consists of the following components:

1. Superstructure or decking component
2. Bearings
3. Substructure Components.

Superstructure Components of Bridges

The superstructure of the bridge structure consists of deck slab, girder, truss etc. These components vary based on the type of bridge (whether

concrete or steel or composite). Superstructure of the bridge bears the load passing over it. This helps in transmitting the forces formed by the

loads to the below substructures.

Decks

The decking is considered as the road or the rail surface of the bridge. The decks are supported by the girders or the huge beams that is in turn

supported by the piers. The whole arrangement is supported with a deep foundation mainly piles and cap arrangement.

Bearings in Bridges

The loads received by the decks are properly and safely transmitted to the substructure with the help of bearings. These are components of bridge

that enables even distribution of load on the substructure material. This transmission is very essential in situations where the substructure is not

designed to take the load action directly.

The bearings in bridges allows the longitudinal movement of the girders. This movement is created due to the forces acting on the longitudinal

direction. The forces due to the moving loads and the variation in temperature are the main causes for longitudinal forces. The selection of bearing

is dependent on certain parameters, which are: Loads acting, the geometry, the extent of maintenance, the clearance available, the displacement,

rotation and deflection policy, availability, preference of the designer, the construction tolerances, and the cost criteria. For the bridge design, all

the above-mentioned aspect is considered for the design and the choice of bearings. The designer must consider the bearing arrangement in the

bridge construction as a separate system. In most of construction practice, the bearing is selected or the decision for bearing is done in the last

moment. This results in increase of maintenance in the future, which must be avoided.

Substructure Components of Bridges

The components involved in substructure of bridges are:

1. Piers
2. Abutments
3. Wing Walls and the Returns
4. Foundation

Piers

The piers are vertical structures used to support deck or the bearings provided for load transmission to underground soil through foundation. These

structures serve as supports for the bridge spans at intermediate points. The pier structure has mainly two functions:

1. Load transmission to the Foundation
2. Resistance to the horizontal forces

Most of the cases, piers are designed to resist the vertical loads alone. In areas which lie in the seismic zone, it is recommended to design the pier

for lateral loads also. Most of the piers are constructed using concrete. Steel for the construction of pier is used in very few cases till now. Use of

composite columns i.e. steel columns filled with concrete is used as new technology of pier construction. The pier is a vertical member that resist

the forces by means of shear mechanism. These forces are mainly lateral forces. The pier that consist of multiple columns are called as bent.

Types of Piers in Bridge Construction

There are different types of piers based on the structural connectivity, the shape of the section and the framing configuration.

• Based on the structural connectivity, the pier can be classified as monolithic or cantilevered.
• Based on the shape of the section pier can be classified as solid or hollow, hexagonal, round or octagonal or rectangular.
• Based on the framing configuration the pier can be classified as single or multiple column bent, hammerhead or pier wall type.

Abutments

Abutments are vertical structures used to retain the earth behind the structure. The dead and the live loads from the bridge superstructure is

supported by the bridge abutments.

The abutments are also subjected to lateral pressures mainly from the approach embankment. The design loads on the abutment is mainly

dependent on the:

• Type of abutment selected
• The sequence of construction

The figure below shows the primary functions carried out by an abutment.

As seen from the above figure, the abutments have the design requirements similar to retaining walls as well as in pier construction. The

abutments are primarily designed to resists the overturning and sliding. More focus is on the stability of the whole system. The special care has to

be provided for the foundations of abutments. The abutment foundation must overcome the problems of differential settlement and excessive

movements caused due to lateral forces or loads. The below figure shows the components of abutments.

Wing Walls and Returns

Structures constructed as an extension of the abutments to retain the earth present in the approach bank are called wing walls. This portion will

otherwise have a natural angle of repose. These are retaining walls constructed adjacent to the abutments. This wall can be constructed either

integrally or independent with the abutment wall. The rear of the wall must consider three design loads while designing. This includes:

• The earth pressure from the backfill
• The surcharge from the live loads or the compacting plant
• The hydraulic loads from the saturated soil conditions

The stability of the wing wall is mainly based on its resistance against the active earth pressures. The structural elements of the bridges are hereby

designed and constructed to resist the earth pressures at rest.

Parapets and Handrails/ Guard Rails or Curbs

These components of bridges are not of structural importance, but provided for the safety concerns. These are provided above the decks. This will

help in prevention of the vehicle from falling off the bridge into the water body below or as a means for the separation of traffic streams.

Foundation of Bridges

Foundation are structures constructed to transmit the load from the piers, abutments, wing walls and the returns evenly on the strata.

The foundation provided for bridge structures are deep in sufficient manner to avoid scouring due to the water movement or to reduce the chances

of undermining.

What are the effects of seismic zones?

It can be seen that period of vibration of building decreases as the severity of ground motion increases in different seismic zones;

because, in higher seismic zones, ground acceleration is more and therefore earthquake force coming on the structure is comparatively larger than

lower seismic zones.

Zone 5 covers the areas with the highest risk of suffering earthquakes of intensity MSK IX or greater. The IS code assigns a zone factor

of 0.36 for Zone 5. Structural designers use this factor for earthquake resistant design of structures in Zone 5.

3 span continuous bridge Position all the loads on the bridge having 12 m and 7.5 m carriageway transverse width with to the scale

drawings. Also mention all the clauses of IRC 6.

1. Dead Load

2. Earthpressure Load

3.Wind Load

4.Water Current Load

5.Wave Load

6.Snow Load

7.Temperature Load

8.Barge Impact Load.

1. Dead Load:

The dead load includes loads that are relatively constant over time, including the weight of the structure itself, and immovable fixtures

such as walls, plasterboard or carpet. The roof is also a dead load. Dead loads are also known as permanent or static loads.

2. Earthpressure Load:

Earth pressure loads on a shoring system are a function of the unit weight of the soil, location of the groundwater table, seepage forces,

surcharge loads, and the shoring structure system. Shoring systems that cannot tolerate any movement should be designed for at-rest lateral

earth pressure.

3.Wind Load:

Wind load is the load, in pounds per square foot, placed on the exterior of a structure by wind. This will depend on: The angle at which

the wind strikes the structure. The shape of the structure (height, width, etc.)

4.Water Current Load:

Whenever bridge piers are subjected to flowing water conditions or running water in the river they are subjected to a force called Water

Current Forces.

5.Wave Load:

Wave are caused by a disturbance of the water surface.

They develop due to disturbances like winds , boat or ship waves or other forces such as underwater landslides due to earthquakes.

When the wind blows on the sea waves occur according to the intensity of the wind and generate a force on the any bridge substructure

likes piers and abutments.

This is accounted as wave loads in the design of substructure for designing bridges in the sea.

6.Snow Load:

Snow load is the downward force on a building's roof by the weight of accumulated snow and ice. The roof or the entire structure can

fail if the snow load exceeds the weight the building was designed to shoulder. Or if the building was poorly designed or constructed. It doesn't

take a blizzard to cause problems.

7. Temperature Loads:

Temperature Loads. Temperature loads allow you to simulate temperature changes over your model. They provide valuable information

on how the structure of your model deforms due to a particular temperature change.

Various forces acting on the shallow foundations:

The five types of loads that can act on a structure are tension, compression, shear, bending and torsion.

Tension:

Tension forces pull and stretch material in opposite directions, allowing a rope bridge to support itself and the load it carries. Compression

forces squeeze and push material inward, causing the rocks of an arch bridge to press against each other to carry the load.

Compression:

Compression forces squeeze and push material inward, causing the rocks of an arch bridge to press against each other to

carry the load. Both types of bridges rely on abutments, the components of the bridge that take on pressure and dissipate it onto

the Earth.

Shear:

Shear stress occurs when two fastened structures (or two parts of a single structure) are forced in opposite directions. If left unchecked,

the shear force can literally rip bridge materials in half.

Bending:

The force of gravity, acts downwards on objects on the bridge. The reactions in the bridge supports make the beam bend in the middle.

This squashes (compresses), the top surface of the beam. At the same time the bottom surface is stretched (in tension).

Torsion:

When you pull on two ends of a rope in a game of tug-of-war, the rope experiences tension. Many parts of a bridge, including the cables of a

suspension bridge, are under high tension. When the tension in a beam or cable is too great, it will stretch or snap apart. Torsion is a twisting

stress.