Two Mark Questions
Two Mark Questions
Two Mark Questions
1. How will you effective width of slab for a single concentrated load?
be = k a (1- (a / L)) + bw
Where,
k -Constant depending on B/L ratio
be- Effective Width of the slab
L- Effective span
bW- Dimension of the tire in the direction right angle to the span plus twice
the thickness of wearing coat.
a- Distance of centre of gravity of load for the near support.
2. What are the forces acting on bridges? (OR) Mention the various loads and forces to be
Considered in the design of bridge members.
Economic span is one for which total cost of the bridge is minimum.
For the most economical span is “cost of sub structures is equal to cost of super structures”
1. Explain the IRC Specifications for live load for IRC class AA loading?
T beam and slab continuous bridges are economical for the span range of 10 to 35 meters.
9. Explain the IRC Specifications for live load for IRC class B loading?
10. Explain the IRC Specifications for live load for IRC class 70R loading?
11. Explain the procedure for shear stress calculation in Solid slab bridges.
(Ref IRC - 21-2000 code book, Page no.35-37, Cls no. 304.7.1.2)
15. What are the types of bridges recommended if the span is (a) less than 10 m and
(b) between 500 to 2000 m?
a) Slab Culvert bridge is recommended for less than 10 m
b) Suspension bridges and cable stayed bridges is recommended for span between 500 m to
2000m.
16. What are the main differences between class ‘A’ loading and class ‘B’ loading as per
IRC?
Class A loading consists of a wheel load train composed of a driving vehicle and trailers of
specified axle spacings. This loading is normally adopted on all roads on which permanent
bridges are constructed. Class B loading is adopted for temporary structures and bridges in
specified areas.
(Ref IRC - 6-2010 code book, Page no.10-11, fig no. 2)
(Ref IRC - 6-2010 code book, Page no.12-13, fig no. 3)
17. How will you consider the impact effect for IRC class ‘A’ loading?
(Ref IRC - 6-2010 code book, Page no. 20, Cls no. 208.2)
18. What is the distribution coefficient suggested by Courbon’s theory? (or )what are the
parameters governing the distribution coefficient ?
Distribution coefficient = σ W / n [1+ nel1X1/ σ I X2]
W – Eccentric concentrated load
n = the number of longitudinal girders
e = the eccentricity of the wheel load from the center line of deck
X1 = the distance of the girder under consideration from the central axis of the deck
σ X2 = the sum of distances of longitudinal girders from the center line of deck.
I1 = the moment of inertia under consideration
I = the moment of inertia of n girders.
24.How will you consider the impact effect for IRC class A load?
Impact factor for reinforced concrete bridges = 4.5/(6+L)
Impact factor for reinforced concrete bridges = 9/(13.5+L)
25.What is the reason for the reduction in the length of the exterior spans in continuous bridges?
To determine the value of the quantity for a given system of loads on the span of the
structure.
To determine the position of live load for the quantity to have the maximum value and
hence to compute the maximum value of the quantity.
27. Write the advantages of prestressed concrete bridges.
High-strength concrete and high-tensile steel, besides being economical, make for
slender sections, which are aesthetically superior.
Prestressed concrete bridges can be designed as class I type structures without any
tensiles tresses under service loads, thus resulting in a crack-free structure.
Prestressed concrete is ideally suited for composite bridge construction in which
Precast prestressed girders support the cast in situ slab deck. This type of construction is
very popular since it involves minimum disruption of traffic.
Overall depth of plate girders, D: l/18 ≤ D ≤ l/12 (Highway bridges) and l/10 ≤ D ≤ l/7
(Railway
Pin bearing
Roller bearing
Rocker bearing
Metal sliding bearings
31.Give the typical forms of Box girder bridges.
Provide Lateral (horizontal) stability from wind and other horizontal (Racking) loads.
Provide additional vertical load capacity for the ends of the joists from point loads above.
40. What is the main function of vertical and bearing stiffeners in a plate girder?How they differ.
Vertical stiffeners prevent the web plate from buckling under shear stresses.
Bearing stiffeners are required in places where there are points of load concentration
and for locations where factored concentrated loads or reactions exceed the factored
compressive resistances of plate girder webs, bearing stiffeners are provided.
1. Shallow foundation
a) Footing and Raft Foundation
2. Deep foundation
a) Pile foundation
b) Well Foundation or Open Caissons
c) Pneumatic Caissons
45.How will you select span and profile of girder in continuous bridges?
The Exterior span made shorter than interior span. This result in reduction of moment in
span
The end spans are made about 16 to 20 % Smaller than intermediate span
The girder depth at support generally 1.5 to 2.5 times the minimum thickness at mid
span
A parabolic profile is generally adopted with maximum depth at intermediate support
and minimum depth at mid span as shown in figure
For span more than 15-20m t-beam bridges are not economical, since the depth of the
girder are large with large quantities of reinforcement. continuous span structures or ,RC arches
are not safe to construct on yielding soil since a slight settlement of a structure affects the nature
of the stress considerably . on such situations for spans in the range of 20-30m balance cantilever
bridges are the ideal solution for the following reasons
Advantage of continuity
reduction in moments
47.How will yo design end block of post tensioned PSC T- beam and slab bridges?
The bursting tension is computed using table 10.2 in IRC 18-2000.Area of the steel can be
calculate by dividing bursting force by 0.87 fy .
50. What are the circumstances under which balanced cantilever bridges are provided.
For span more than 15-20m t-beam bridges are not economical, since the depth of the
girder are large with large quantities of reinforcement. continuous span structures or ,RC arches
are not safe to construct on yielding soil since a slight settlement of a structure affects the nature
of the stress considerably . on such situations for spans in the range of 20-30m balance cantilever
bridges are the ideal solution for the following reasons
Advantage of continuity
reduction in moments
In recent years, single or multi-cell reinforced concrete box Girder Bridge have been
proposed and widely used as economic aesthetic solution for the over crossings, under
crossings, grade separation structures and viaducts found in modern highway system.
The very large Torsional rigidity of the box girder‘s closed cellular section provides structures
beneath is more aesthetically pleasing than open-web type system.
In case of long span bridges, large width of deck is available to accommodate prestressing
cables at bottom flange level.
For large spans, bottom flange could be used as another deck accommodates traffic also.
The maintenance of box girder is easier in interior space is directly accessible without use of
scaffolding.
52.List different types of bearings used in bridges.
A box girder is formed when two web plates are joined by a common flange at both the top and
the bottom. The closed cell which is formed has a much greater torsional stiffness and strength
than an open section and it is this feature which is the usual reason for choosing a box girder
configuration.
Advantages
Reduces the slab thickness and self-weight of bridge
Cost effective
Greater strength per unit area of concrete
Disadvantages
Structural steel girders are costly
Logistical inefficiencies and transportation cost
55. List the special features of PSC against RCC
1. The use of high strength concrete and high strength steel result in slender sections which
are aesthetically superior coupled with overall economy
2. Pre-stressed concrete bridges are designed as Class 1 structures without any tensile
stresses under service loads resulting in a crack free structure
4. In recent years, Partial pre-stressed concrete (Type 3 Structure) is preferred for bridge
construction with considerable savings in quantity of costly high tensile steel used in the
girder.
Concentrated load
Uniform distributed load
Weight offside walls
Water pressure inside culvert
Earth pressure on vertical side walls
59.Write critical loading stage in pre stressed concrete bridges.
Design shall be based on strength (Load Factor Design) and on behavior at service conditions
(Allowable Stress Design) at all load stages that may be critical during the life of the structure
from the time the pre-stressing is first applied.
60.Draw any two cross sections for the pre tensioned concrete bridges.
A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into
space, supported on only one end. For small footbridges, the cantilevers may be simple beams;
however, large cantilever bridges designed to handle road or rail traffic use trusses built
from structural steel, or box girders built from pre-stressed concrete.The suspended span may be
built off-site and lifted into place, or constructed in place using special travelling supports.
Steel truss cantilevers support loads by tension of the upper members and compression of the
lower ones. Many truss cantilever bridges use pinned joints and are therefore statically
determinate with no members carrying mixed loads.
62.What are the materials generally used for the construction of piers and abutments?
The Following Types of materials are commonly used for piers and abutments.
Live load, dead load, earth pressure being and no water pressure from inside.
Liveload, dead load, earth pressure acting from outside and water pressure from inside.
Liveload, dead load acting on the top of the slab and water pressure acting from inside
and no lateral pressure due to live load.
64. Draw any two cross sections for the post tensioned concrete bridges.
65. How will you find the eccentricity of cables in pre stressed concrete bridges?
The eccentricity of the cable at the center of span is obtained by the following relation.
ቀ𝑍𝑡.𝑍𝑏൫Finf −Fsup൯ቁ
𝑒= 𝐴൫Finf Zb−FsupZt൯
67.Under what situation shall engineers use jacking at one end only and from both ends in pre-
stressing work ?
During pre-stressing operation at one end, frictional losses will occur and the pre stressing force
decreases along the length of tendon until reaching the other end. These frictional losses include
the friction induced due to a change of curvature of tendon duct and also the wobble effect due to
deviation of duct alignment from the centerline.The stressing at one end only has the potential
advantage of lower cost when compared with stressing from both ends. For multiple spans ( e.g.
two spans) with unequal span length, jacking is usually carried out at the end of the longer span
so as to provide a higher pre-stress force at the location of maximum positive moment.
68. What is the consideration in selecting the orientation of wing walls in the design of bridge
Abutments.
Some of the most common arrangements of wing walls in cases of bridge arguments are as
follows:
Wing walls parallel to abutments:
This method is considered to take least amount of time to build and is simple as well. But on the
downside this method is not the most economical. The advantage of this type of design being
that they cause the least amount of disturbance to the slope embankment
Wing walls at an angle to abutments:
This design method is considered to be the most economical in terms of material cost
Wing walls perpendicular to abutments:
The characteristic of this design is it provides an alignment continuous with the bridge decks
lending a support to the parapets