RCC Flashcards
stirrups requirement of Column
special confinment zone =At least larger of D, h/6 and 450 mm
Spacing = not more wan D/4. but need
not be less than 75mm nor
mom than 100 mm
spacing in lapping = Spacing of ties in lap length
not more than smaller of
D/2 and 150 mm
beam ductility
maximum bottom r/f = 2.5%
spacing of link in lap joints < 150 mm
for hoop spacing = min(100mm, d/4, )
What is the effect of increasing carbon
content in the steel?
Effect of increasing the carbon content 1n
(a) Decreases the ductility of steel.
(b) Increases the tensile strength of steel.
(c) Increases the hardness of steel.
(d) Decreases the melting point of steel.
(e) Makes steel easier to harden with heat
treatments.
(f) Increases the difficulty of welding of steel.
Mild steel (low carbon steel) contains less than
0.3% carbon. Medium carbon steel contains 0.3
to 0.5% carbon. High carbon steel contains
more than 0.5% carbon. Cast iron contains
more than 2% carbon.
What is ductility? Why is it important?
Ductility can be described as the ability of a
material to undergo large deformations without
rupture before failure. If ductile members are
used to form the structure, the structure can
undergo large deformations before failure. This
is beneficial to the users of the structure as in
case of overloading, if the structure is to collapse, it will undergo large deformations
before failure. This gives a notice to the occupants and provides sufficient time for taking
preventive measures.
If steel is produced in the form of bars, how
will you make it corrosion resistant?
Corrosion prevention of reinforcing bars: The
following methods can be adopted for
prevention of corrosion in reinforcing bars viz.:
(a) Chloride ions in concrete should be limited
to its maximum permissible value which
is 0.15% by mass of cement as per IS:
456.
(b) Corrosion inhibitors like calcium carbonate ‘ aluminium oxide etc. can be added to
concrete which can either be anodic
cathodic or both. ‘
(c) Hot dip galvanizing the reinforcing bars does not affect the bond between concrete and steel but protects the bars from corrosion.
(d) Epoxy coated steel bars show significant resistance to corrosion
Why RCC is used in buildings?
[ESE2006]
RCC in buildings: RCC is predominantly used
in buildings than any other building construction
material. This is because of the fact that RCC
can with stand tensile stresses thereby reducing
the required cross-sectional area of beams,
columns, slabs etc. High rise buildings with
comparatively smaller sections and adequate
ductility is possible only with RCC than any other
construction material.
What is the title of IS 456: 2000?
(ESE2
The title of IS 456: 2000 is “Plain and Reinforced
Concrete- Code of Practice”
What are the different durability criteria givan
in IS 456: 2000?
Mix proportions
(b) Exposure conditions
(c) Shape and size of the aggregates
(d) Material constituents
(e) Freezing and thawing
What do you mean by concrete structure
durability?
The durabil ity of a concrete structure is its abil ity
to serve its intended purposes for a sufficiently
long period of time, or at least during its
expected service life.
However, although a d urable structure is
expected to serve without deterioration to the
extent that major repair is required before expiry
of its design life, it must not be presumed that
durabil ity is a substitution for good maintenance.
Even for a structure that has been designed and
constructed to a high durabil ity standard ,
regular inspection and routine maintenance to
restore the fitness for purpose of the structure
are needed .
What is the maximum strength of concrete?
ESE 2009
The maximum strength of concrete till date is
M80
better to search a good answer on google
What is water reducer? Give examples?
ESE 2009
Water reducer: Many of the admixture reduces
the water requirement of concrete thereby
making it possible to have lower w/c ratio.
These admixture are called as Water Reducers
(a)Lignosulphonic acids and associated salts
(b) Hydroxylated carboxylic acids and assoc1ated salts.
What are the advantages of concrete?
ESE 2009
Advantages of concrete: The following are
some of the advantages of concrete:
(a) Concrete has very high compressive
strength and does not get easily corroded.
(b) Fresh concrete can be handled very easily
and can be moulded into any shaped size.
(c) With steel, concrete can be put in use in
many different structures
(d) Concrete can be spraye on cracks for
repairs etc. by guniting process.
(e) Concrete can be pumped easily and t us
can be laid in difficult locations also.
(f) It is durable and fire resistant
What is the purpose of concrete testing?
ESE 2009
Purpose of concrete testing: Concrete is
tested to assess its quality on certain
parameters like its compressive strength ,
porosity, soundness, workability etc. Defects if
found in concrete testing, then suitable
measures can be adopted thereby ensuring the
safety of the structure.
How much cover is necessary for beams,
columns, slabs and foundation?
(ESE 2009, 2016, 2019)
Cover: The following minimum cover is required for: (a) Beams - 25 mm (b) Slabs -15 mm (c) Columns - 40 mm (d) Foundation-50mm
What are the different tests conducted for flexural design?
Tests for flexural design: As concrete is a
strong material in compression, it can take large
axial and flexural compressive stresses.
However determination of flexural tensile
strength of concrete is important to assess the
load at which cracks may occur. Thus flexural
tensile strength or modulus of rupture test is
conducted on concrete. The modulus of rupture
test is conducted on standard test specimen of
150 mm x 150 mm x 700 mm over a span of
600 mm or 100 mm x 1 00 mm x 500 mm over a
span of 400 mm under symmetrical two point
loading. Modulus of rupture is determined from
the moment at failure as f = M/Z
What do you mean by corrosion in steel in a
concrete columns and beams?
(ESE 2012, 2016)
The chemical or electrochemical reaction etween a material, usually a metal and its en iro ment tha produces a deterioration of the material and its properties is called as ta For steel embedded in concrete COrr�. results in the formation of rust Which �orr�· tour times the volume of the origi n al astwoto none of the good mechanical p Steel Qno oper Corrosion also produces pits and hoi . . f . f . es '" lh. surface 0 retn orctng steel, reduci n g s tr w� capacity as a result of the reduced � sectional area.
What are the various loads acting on floor
and roof?
The various loads acting on a floor are : Self
Weight of the slab itself floor finishes and other
dead loads, live load �tc.
At roofs: The loads acting are the self-weight
of the roof slab, weight of parapet walls, snow
load (if any}, live load etc
What are the differences between LSM and
WSM?
(ESE 2017)
Working Stress Method
• The Stresses in an element is obtained from
the working loads and compared with
permissible stresses.
•
•
•
•
•
The method follows linear stress-strain
behaviour of both the materials.
Modular ratio can be used to determine
allowable stresses.
Material capabilities are under estimat�d
to large extent. Factor of safety are used In
working stress method.
Ultimate load carrying capacity cannot be
predicted accurately.
The main drawback of this method is that
it results in an uneconomical section.
limit State Method
• The stresses are obtained from design
loads and compared with design strengt�.
• In this method, it follows linear strain
relationship but not linear stress
relationship (one of the major difference
between the t wo methods of design).
• The ultimate stresses of materials itself are
used as allowable stresses.
• The material capabilities are not under
estimated as much as they are in working
stress method. Partial safety factors are
used in limit state method.
What are the advantages of preccast
construction?
Since precast is manufact�r�d in a controlled environment 1t 1s eas1er to control the miX,
I d and monitored
quality can be easily controled
much more easily.
Weather is eliminated as a factor u can cast in any weather and get the same
cast m any to perfect mixes
results,
Less labor is required and
can be less skilled.
precast can be installed on site
immediately, there is no waiting or I o
strength and the modularity of
Repeatability-it’s easy to make many copies
of the s ame precast p roduc t; by
maximizing repetition, you can get plenty
of value from a mold and a set-up.
Accelerated curing, by heating the precast
parts, greatly increases strength gain,
reducing the time between casting the part
and putting it into service.
With the ability to so tightly control the
process, from materials to consolidation to
curing, you can get extremely durable
concrete.
What is split tensile strength and how it is
different from conventional tensile strength
of concrete?
(ESE 201 9)
The tensile strength of concrete is about 7 to
15 percent of compressive strength. It is very
d ifficult to perform direct tension test on
concrete specimen as it requires purely axial
force to be applied which is free of any
misalignment and secondary stresses in the
specimen . Thus, indirect tension test is
performed like flexural test or cylinder split test.
IS 581 6: 1 999 specifies the p rocedure of split
tensile strength of concrete. The s pl it tensile
strength of normal density con crete is about 2/
3
rd of modulus of rupture.
What are the different forces that act on a
building situated near the sea?
(ESE 201 9)
Apart from normal loads like dead and live load,
building s ituated near sea is exposed to
following additional forces:
• Wind force
• Tidal force
• Wave force due to sea waves
Why we won’t consider buckl ing c riterion in
cube strength?
( ESE 201 9)
In a cube, the slenderness ratio is near about
3.46 which is close to 3 and for columns with
slenderness ratio about 3 or l ess, crushing is
the failure criterion and thus in cube test,
buckling is not significant.
What is rol ler compacted concrete {RCC)
and how it is d ifferent from ordinary
concrete?
Roller compacted concrete (RCC) is just like
ordinary concrete having the same basic
ingredients viz. cement, water, sand
.
and coar�e
aggregates but it is somewhat dner and st1ff
nough to be compacted by vibratory rollers.
e .
Normally roller compacted concrete requ1res no
form work or finishing and also it does not
contain reinforcing bars. Roller �?m�acted
concrete can be used in the rehab1l 1tat1on of:
In case of slab, what is maximum spacing
of main reinforcement? Why we provide
lateral reinforcement?
In case of slab, m aximum spacing of main
rein orcement is 3d or 300 mm whichever is
less.
La eral reinforcement (in case of columns) is
Pro ided to confine the concrete within the core
and to avoid buckling of main longitudinal bars.
What is curtailment of reinforcement in
beam?
Curtai lment of reinforcement in a beam impl ies
cutting off the reinforcing bar at those sections
where it is no longer required. e.g. In a simply
supported beam subjected to a uniformly
distributed load throughout its span will have a
sagging BMD with most of the steel required
at the mid span and this steel requirement goes
on decreasing as one moves towards the
support. Thus reinforcement p rovided in the
tension zone of the beam is curtailed as per
the shape of the bending moment diagram
What is plinth level beam?
ESE 201 9
In general, plinth level is the level at which substructure and super-structure meet. A plinth beam is provided at the plinth level which acts as a tie beam and ties all the columns together at plinth level.
What is a torsion shear?
When a member is sub· subjected to torsion , it is subjected to the torsional shear, In RCC structure torsional shear is IS usually accompanied with flexural shear.
What is location of critical section for shear
in case of flat slabs?
Two way shear is more critical in case of flat
slabs and critical section for this two way shear
is at a distance of d/2 from face of column or
drop or column c apital , as the c ase m ay be,
where d id the effective depth of flat slab
If a beam fails in bond, how its bond strength
can be increased most economical ly?
Most economically, the bond strength c an be
increased by providing turn in the reinforcing
bar as each 45° turn increases the anchorage
length by 4d where d is the diameter of the bar.
What is single shear and double shear?
In single shear also called as one way shear or
beam shear, there is possibility of relative
translation • movement between the connecting
members in one direction.
Two way shear also called as punching shear
Predom1nates when a concentrated load acts
on a relat1vely small area like column load on
footing, flat sIabon column. Here there is a
POSS1 1 ‘b’l’ lty of one member to punch through the
other member
WhY the shear resistance of a RC beam
in creases with the Increase in shear
reinforcement ratio?
Because:
(a) Concrete gets confined between stirrup
spacing.
(b) The shear/web reinforcement itself provides
shear resistance
What are the braced columns and unbraced
columns?
Braced columns: The colu mns occurring in braced buildings or braced frame are called braced columns. In braced frames, the lateral loads like wind, earthquake, etc., are resisted by some special arrangements like shear walls bracing or other arrangement. In other words The Sideway or joint translation is not possibl� 1n such columns.
Unbraced columns: The columns occurring in Unbraced buildings or unbraced frames are called unbraced columns, In unbraced frames, no special bracing systems are adopted to resist horizontal force .
Which type of foundations are used In
bridges in India?
[ESE 2
Bridge foundations used in India: Depending
upon the location of bridge, bridge foundation
can be of any type like pile foundations, well
foundation etc. Where ever the bridges are
constructed across a river, there· mostly well
foundation is used.
For flyove rs, generally pile foundation Is
preferred.
What is the grade of concrete from which
sleepers are prepared?
Con c rete railway sle epers a re made of
Prestressed concrete and minimum grade of
concrete to be used in prestressed concrete
sleeper is M55
What is the minimum eccentric ity for a
column?
emln > 1/500 + 0/30 > 20 mm. Where ,
I= unsupported length of column in ‘mm’.
0 = lateral dimensions of column (All units are
in mm)
Why PSC sleepers are used instead of RCC sleepers now a days?
RCC sleepers are too brittle to withstand high levels of dynamic load. PSC sleepers are superior in reference to load carrying capacity.
PSC sleepers also offer smoother ride due to high dead weight and vertical & lateral stability
For most modern high speed railway PSC sleepers are used.
How you will design the earthquake resistant
building?
(ESE 2006, 201 4, 201 6, 201 7
Design of earthquake resistant building: A
earthquake resistant building is designed as per
fol lowing:
(a) As per IS: 1 893, in earthquake, full dead
load and part of live load is considered. If
live load is < 3kN/m2 then 25% and if live
load is greater than 3kN/m2 then 50% of
live load is assumed to take part during
earthquake. Also live load on roof is not
considered in earthquake.
(b) Earthquake induces g round acceleration
thereby inducing lateral force on the
building/structure.
(c) This induced lateral force is assumed to
be resisted by lateral load resisting
elements like shear walls, slabs, columns
etc.
(d) In static analysis of earthquake, shear force
at each floor le el is computed after
computing the total lateral load on the
building
F = A W
where, F = L tar I load on the structure
(f) In dynamic analysis, modal participation
of seismic loads in various modes fl
considered. As per IS: 1 893, the total m
participation of all the modes .;. 90% of total
seismic weight of the structure.
(g) The peak response value of each mode is
combined called as modal combination.
Various methods of modal combinations
are:
(i) Absolute modal combination (ABS)
(ii) Square root of sum of squares (SRSS)
(iii) Complete quadratic combination (CQC)
(iv) TAN etc
What is the recommendation of concrete
material for earthquake resistance buildings?
[ESE 2007]
(a) Properly g raded 20mm down coarse
aggregates to be used instead excess
amount of poor 1 Omm aggregates used in
most of the buildings.
(b) As per is IS 456: 2000, min. concrete grade
of M25 for beams, columns and shear walls
and M20 for floors and roof-slopes.
(c) Minimum cement content & water cement
ratio for the concrete mix should be clearly
specified and strictly adhered.
(d) Ensure adequate compaction of concrete
in the columns.
What Is soft storey?
ESE 201 6
Soft storey: As per IS 1 893 (Part - I) soft storey
is the one which has lateral stiffness less than
70% of that in the storey above or less than
80% of the average lateral stiffness of the three
stories above.
Causes of earthquake?
ESE 201 6, 201 7
There are several causes of Earthquake. Some i mportant causes are following: (i) Plate tectonic movements. (ii) Volcanic activity (iii) Underground explosions (iv) Land slides and rockfalls (v) reservoir induced sesmicity etc
How can you design earthquake resistance
buildings without providing ductil ity.
(ESE 201 6)
If we have to design the building earthquake
resistant without providing ducti lity then we
have to design the building more and more
stiffer to resist earthquake. Stiffness of building
is improved by general planning of the building.
Following aspects should be taken c are to improve the stiffness of building.
(i) symmetry of structure
(ii) regularity of structure
(iii) separation of blocks within then l arge 6
·
32
structure
(iv) simplicity of the structure
(v) enclosed area Ans.
(vi) separate buildings for different functions
Floor area ratio (FAR)
Floor area ratio (FAR) is the ratio of a building’s total floor area (gross floor area) to the size of the piece of land upon which it is built.
How is underwater concreting done?
ESE 201 2, 201 6
The most common method of handling concrete
under water is by tremie. A tremie consists
essentially of a vertical steel pipeline, topped
by a hopper and is long enough to reach from a
working platform above water to the lowest point
of the underwater formwork. By this technique
the steel pipeline, with a watertight seal at its
tip, is placed at the bottom of the formwork.
Depending upon depth, the pipe is filled or
partially filled with concrete. Then the pipe is
gently raised about 6 inches to release the
concrete letting it rise up around the tube. In
proper tremie placing, a closure value {plate) is
used to seal the pipe prior to plac·lng the
concrete. As the tremie is lowered to the bottom
of the form, water pressure holds the plate tightly
in position. Then the pipe and hopper are filled.
The plate retaining wire is released if it is single,
or withdrawn if it is double, and the tremie is
raised about 4 to 6 inches from the bottom of
the form, allowing the concrete to flow into place.
An effective plug can be provided by forcing
an inflatable rubber ball into the top of the pipe.
The ball is pushed downward by the weight of
the concrete. Using a ball for the plug offers the
advantage that it will pop to the surface on
leaving the pipe. Stoppages during tremie
placing can cause considerable difficulty and
every effort should be made to foresee and
avoid them. The main causes of stoppage are:
pipe diameter too small as the mix gradual�y
forms a bridge across the pipe walls; delay� In
delivery because the mix inside the pipe begi�
S
to stiffen; mix too harsh or too stiff makin� plastic
flow impossible; poor aggregate gradln
.
g and,
in particular, insufficient fines; the lubn�
at�on
coating on the pipe walls is broken and stiCking
follows.
