Challenge 2

Ans of Question no-1

The structural component of a bridge are-

1. Foundation.
2. sub-structure.
3. Super-structure.

Detail Explanation-

1. Foundation:- Foundation are the lower part of a bridge, it transfer the load from sub-structure to subsoil , mostly pile foundation to be used.
2. Sub-Structure:- Substructure consist of pile cap, pier and pier cap, bearing . it transfer the load from superstructure to the foundation.
3. Super-structure:- Superstructure consist of girder, rcc slab and parapet or railing. This part directly takes the loads from moving train and self weight of the structure and transfer to the substructure.

Ans of Question no-2

Super imposed dead load means the weight of material present on the structure which are not a structural component, but permanent in nature. It can be two types- fixed or non variable, and variable type.

The loads that needs to be considered for SIDL is-

Weight of track from plinth / rails/fasteners/cables/parapet/hand-rail.

Ans of Question no-3

Different types of girder that can be used for a metro viaduct are-

1. I girder 2. U girder 3. Steel plate girder 4. Box girder

Ans of Question no-4

Bearing are the structural equipment install between girder and substructure to transfer the load including earthquake loads, wind loads, traffic load and self weight of the superstructure.

Types of bearings-

1. Elastomeric bearings.
2. Pot bearings.
3. Spherical bearings.

Elastomatic Bearing
Advantages	Disadvantage
1. Lowest initial cost. 2.Very low maintenance if install properly.	1.Not well suited for multi rotation. 2.It can walk out of place with time if not positively held in place.

Pot Bearing
Advantages	Disadvantage
1. Multi rotational 2. Relatively low stress on the bearing seats	1. Pot bearing require periodic maintenance. 2. Relatively low in height

Spherical Bearing
Advantages	Disadvantage
1. Multi rotational. 2. High vertical load capacity.	1. Require periodic maintenance. 2.Require special attention when installing.

Ans of Question no-5

Topographical check list that need to considered for designing the height of the viaducts are-

1. High flood level from past experience.
2. Depth of water passages.

Ans of Question no-6

Different types of girder that can be used for a metro viaduct are-

1. I girder
2. U girder
3. Steel plate girder
4. Box girder

A designer has to choose his girder type whilst designing on the basis of alignment, road geometry, local condition, span length and load.

Selection purpose of I girder is :- If the alignment of metro viaduct on curve ,so that in this case we use shorter length girder to maintain the curve. Span length of I girder varies from 2.2 to 2.3 meter.

Selection purpose of U girder is :- When we need quick installation and the required span length is 25 to 28 meter then we go through with U girder.

Selection purpose of Box girder is :- If required span length is more than 50 meter upto 270 meter and if required to resist torson then we use Box girder.

Selection purpose of Steel plate girder is :- If required span length is with in 50 to 70 meter we use the steel plate girder.

Ans of Question no-7

The designer choose the precast U girder because of-

1. Good effect of noise reduction.
2. No need for any parapet.
3. Chance of derailment is less due to short space available, if derail then it can automatically comes over rail.
4. Well drainage system attached with shear key.
5. easily erected.

Ans of Question no-8

Open web structure means the elevated metro viaduct which are open at the top portion.

Example- U girder, I girder, Box girder etc

Advantages of open web structure are basically it made with precast prestressed concrete so less time taken for erection and easily set over pier through launching gantry.

Ans of Question no-9

Load flow behaviour of open web structure-

Load flow behaviour are two types-

1.Longitudinal

2. Transverse

Longitudinal flow behaviour are of two types-

1. Design for flexture.
2. Design for shear.

Transverse flow behaviour are of one types-

1. Design for flexture.

In a U girder, Longitudinal direction prestress take the loads.

While in transverse direction Reinforcement take all loads.

Ans of Question no-10

Stress limitations for the serviceability limit state as per IRS(table-11)

When we design the metro viaduct at first we see that the types of materials I,e concrete or reinforcement or prestressing tendons as per material we check the types of stress on it. As per types of stress we find the compressive stress for concrete and yield stress for reinforcement for types of construction I,e RCC OR PSC.

For prestress concrete we found the allowable compressive strength and allowable tensile strength for construction stage and service stage from IRS-CBC. And also find out the allowable compressive stress for concrete and allowable yield stress for steel for limit state of serviceability stage as per IRS-CBC.

Applied moment increase 15% , so moment=1.15*applied moment.

The ratio between applied moment to ultimate moment should be less than 1.

Ans of Question no-11

Crack width:-

Cracking occurs in concrete when the restrained strain exceeds the tensile strain capacity of the concrete. Crack width is calculated by multiplying the crack including the strain and the crack spacing.

Design crack width are describe in bellow-

Exposure condition	Meaning	Design crack width(mm)
Moderate	Concrete surface seltered from several rain or freezing when wet	0.20
Severe	Alternate wetting and drying	0.10
Extreme	Surface of member in tidal zone,directly contact with aggressive chemicals	0.10

The value of above 0.20mm are not tolerable.