Railway Building Engineering Practice Exam paper
Question and Model Answers
Q.3. Attempt ANY THREE of the following.
a) Factors affecting site selection for construction of bridge.
Ans :-
Following factors affect the selection of site for a bridge:
(1) Width of river: The width of river indicates length of bridge.
It is desirable to have well defined and a narrow channel at bridge site as far as
possible which will help in providing least possible length of bridge.
The smaller the width of river, the cheaper will be the bridge in its initial cost as well
as maintenance cost.
(2) A straight reach :
The river should have straight reach over a reasonable long distance on upstream side
and downstream side of the bridge site so that the utility of bridge can be maintained
for the design period.
On the other hand the curved reach of river is not desirable as it creates problems
during construction and maintenance of bridge.
(3) Foundations :
The nature of soil at bridge site should be such that good sound foundations should
be available at reasonable depth.
Such type of bridge site will save expense, labour and time required.
(4) Connections with roads :
The bridge is constructed to connect the road on either side of a river.
The bridge site should therefore form a proper link between the roads on either side
of a river.
The approaches at the bridge site should be such that the do not involve heavy
expenditure.
(5) Firm embankments :
The embankment at bridge site should high, permanent, straight, solid and firm.
Such embankments will not get disturbed at the time of heavy floods and they do not
allow the course of stream toalter.
(6) Materials and labour :
The site of the proposed bridge should be such that labour, construction material
should easily available nearby site.
The transportation charges for material and labour at the bridge site should be
minimum.
This type of bridge site will provide economy in the overall cost of construction.
(7) Right angle crossing :
At bridge site, the direction of flow of water should benearly perpendicular to the centre-line of bridge. Such crossing is known as right angle crossing.
This type of site will help in providing square alignment of bridge which will result
in easy and economy in bridge construction.
(8) Velocity of flow :
The velocity of flow at bridge site should be between the range of non - silting and
non-scouring.
This type of site will result in minimum maintenance cost.
(9) Scouring and silting :
There should be no scouring and silting at bridge site, which will result in minimum
maintenance cost.
(10) Minimum obstruction to water way :
There should be minimum obstruction to natural waterway at the site of bridge.
(11) Sound, economical and straight approaches :
The bridge site should provide sound, economical and straight approaches.
In case of curved alignment, the bridge should be on the tangent and not on the curve,
since it is difficult to construct and maintain a curved bridge.
(12) Free board :
Sufficient free board should be available for the passage of boats, ships under the
bridge superstructure if the river is used for navigation.
b) Define the following
a)Economic Span b) Afflux c) Scour Depth d) Freeboard
a)Economic Span
The span for which the total cost of the bridge is minimum is knownas economical span of a bridge.
b) Afflux
It is the rise in water surface of water – course, caused due to the obstruction by the bridge in the flow of water. Or The heading up of the water above its normal level while passing under the bridge is called afflux.
c) Scour Depth:- The depth upto which a flowing stream erodes soil is known as scour
depth
d) Freeboard:-
Its is the difference between the HFL after allowing the afflux, if anuy,
and the lowest point on the under side of the bridge super structure is called free board.
c) Explain the functions of the following.
Ans :-
i) Pier ii) Abutment iii) Bearing iv) Wing wall
i) Functions of Pier:
i) To divide the length of bridge into suitable number of spans.
ii) To transfer the load from bridge superstructure to subsoil through foundations
ii) Functions of abutment :
1. To retain the earth pressure of embankment of the approaches.
2. To support the bridge superstructure and to transmit the load from itto the
subsoil lying underneath.
3. To finish up bridge so that it can be put for use./ To provide finalformation
level to the bridge superstructure
4. To transmit the reaction of superstructure to the foundation
iii)Functions of bearings:
a. To distribute the load received over large area.
b. To allow for longitudinal expansion or contraction due to changesin the
temperature.
c. To allow for angular movement at support due to deflection ofgirders.
d. To allow for vertical movement due to sinking of supports.
e. To transfer horizontal forces occurring due to application of brakesto the
vehicle etc.
f. To keep the compressive stress within safe limits.
iv)The functions of wing walls are as follows:
1. To retain the earth banks of the river.
2. To protect the earth banks from the action of water.
d) Write the the function of bridge bearing. Also write its types.
Function of bridge bearing:
1) To distribute the load received over large area.
2) To allow for longitudinal expansion or contraction due to changes in the
temperature.
3) To allow for angular movement at support due to deflection of girders.
4) To allow for vertical movement due to sinking of supports.
5) To transfer horizontal forces occurring due to application of brakes to the
vehicle etc.
6) To keep the compressive stress within safe limits.
Ans :-
Types of Bearing:
A. Fixed Bearing:
1. Fixed Plate Bearing
2. Deep Base Bearing
3. Rocker Bearing
4. Knuckle Bearing
B. Expansion Bearing:
1. Sliding Plate Bearing
2. Deep cast with curve plate
3. Rocker bearing with curved base
4. Rocker & roller bearing.
Q.4. Attempt ANY THREE of the following.
a) Write two advantages and two disadvantages of prestressed bridge.
Ans :-
ADVANTAGES OF PRESTRESSED BRIDGE
1) have higher load carrying capacity
2) fewer expansion joints
3) Reduced deflection of girders.
4) Lighter construction.
5) More aesthetic appearance.
6) More effective use of precast members.
7) Better resistance to fatigue due elimination of cracking of its members under
severe traffic loads.
8) Less cost of maintenance.
DISADVANTAGES OF PRESTRESSED BRIDGE
1) Use of high tensile steel results in high cost
2) Skill supervision required.
3) Special equipment are required.
b) Explain the sequential steps involved in bridge construction.
Ans :-
Following are the steps involved in bridge construction
Proposal:- Necessity of bridge hydraulic data collection
Site selection
Administrative approval
Technical sanction
Estimate
Sanctioned estimate
Design calculation
Details of estimate
Tendering process
Soil testing
Construction-substructure, super structure
Completion report
Open to traffic
C) Describe fore-poling method of tunneling in soft rock.
Ans :-
FORE-POLING METHOD
It is an ancient method of tunneling, but now it has been replace by compressed air
method. Thismethod needs large quantity of timber for supporting the ground. This
method used for theconstruction of small dimensions tunnels required for laying
sewers, gas, pipes etc. it is slowand tedious.In this method, a frame in the form of
letter ‘A’ is prepared and placed near the face ofthe tunnel covered with suitable
planks as shown in fig.The poles are then inserted at the top and continued to a depth
upto which they can beeasily taken up.These poles are supported by verticals
posts.Now excavation can be done under the forepoles.The excavations are also done
on sides and are supported by suitable timbering.In this way the full section of the
tunnel is excavated.
e) Give the points to be observed during pre-monsoon and post monsoon
inspection.
Ans :-
Pre-Monsoon Inspection
The inspection shall cover the following points
Foundation and substructure
Protective works
Superstructures
Detailed inspection of steel works of girder
Obstruction of water way
Inspection of drainage system
Development of cracks
Post Monsoon Inspection
The inspection shall cover the following points
Condition of slab girder, footpath, Drainage system
Condition of substructure, superstructure
Inspection of Development of cracks
Condition of Approaches of bridge
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