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DESIGN OF REINFORCED CONCRETEELEMENTS

2 Mark Question &Answers

Unit-1

1 !"at is #a$$e% Li it StateLimit State is a state of impending Failure Beyond which thestructure ceases its performance under service loads

2 De'ne #"ara#teristi#s stren(t"Characteristics strength of material is de ned as the value of itsstrength below which not more than 5% of the test results areexpected to fall

) De'ne #"ara#teristi#s $oa%Characteristics load clause !"#$ S&5"'$((() means the value of load which has a *5% probability of not being exceeded during thelife of the structure#

+he dead loads , live loads and wind loads given in S-./5 andseismic forces given in S-0.*! may be ta1en as characteristics load

* De'ne Desi(n Loa%s +he design load is determined by multiplying the characteristicsload by appropriate partial safety factors

+ !"at are t"e two t,-es o. $i it State o. Ser/i#ea0i$it, 2e3ection Crac1ing

Draw Stress Strain #ur/e .or #on#rete4efer page no "* of S &"5 '$(((

!"at is ean 0, Cra#ke% Se#tionn the concrete Section there is two sides one is compression sideand another one is tension side# f the concrete available on thetension side doesn t have crac1 means that section is called crac1edsection#

3 !"at %o ,ou ean 0, 4Mo ent o. Resistan#e 4o. t"ese#tion5

+he compression in steel C) 6 +ension in Concrete +) are e7ual inmagnitude but opposite in direction at any cross section # +his

0 6 8 4 9 8 : 4 9 2 B ; < r # S # = m a r 2 # # 2 , < # 9 , < S + 9 # ,


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couple develops a moment called 4esisting moment which is alwayse7ual to the applied bending moment at the cross section

7 Assu -tions a%e in workin( stress et"o% :t any Cross section +he plane before bending is remain plane

after bending +he tensile stress are ta1en by reinforcement alone only and

none by the concrete +he steel reinforcement is free from initial stresses when it is

embedded in concrete +he stress strain relationship of steel and concrete under

wor1ing load is a straight line

+he modular ratio >m has the value $.(?!@cbc @cbc'8ermissible compressive stress due to bendingin concrete in A?mm $

18 De'ne9:a$an#e% ;or< Criti#a$ se#tion +he stress in concrete and steel increases as bending moment atthe section increases# :t one stage , they one or both) reach theirmaximum permitted values # if the stresses in concrete and steelreach the maximum permitted values simultaneously as a section,that section is called a balanced section or Critical section

11 De'ne =n%er Rein.or#e% se#tionhen the area of tension steel provided at a section is less than thatis re7uired for a balanced section, it is said to be an =nderreinforced section# n this case the stress in steel will reach itsmaximum value rst# :t this stage the :ctual stress in concrete willbe less than its permissible stress#

12 De'ne o/er Rein.or#e% se#tionhen the area of tension steel provided at a section is more thanthat is re7uired for a balanced section# n this case, the stress inconcrete will reach its maximum permissible value rst#

1) De'ne Dou0$, rein.or#e% se#tionhen reinforcements are in the compression and tension ones in a4einforced concrete beam then it is called as 2oubly reinforcedsection

1* A%/anta(es o. %ou0$, rein.or#e% se#tion ;orerentiate 0etween t"e ter 4e>e#ti/e $en(t"? an%4unsu--orte% $en(t"? o. a #o$u n

+he vertical distance between the points of in3ection of thecompression member in the buc1led con guration in a plane istermed as eEective length le of that compression member in thatplane# +he eEective length is diEerent from the unsupported length lof the member, though it depends on the unsupported length andthe type of end restraints# +he relation between the eEective and

unsupported lengths of any compression member isle K 1 l

where 1 is the ratio of eEective to the unsupported lengths# Clause$5#$ of S &5" stipulates the eEective lengths of compressionmembers

* !"at are t"e a%/anta(es o. "e$i#a$ rein.or#e ent5:s compared to the others the helically reinforced column of

same cross sectional area the load bearing capacity is increased by 0#(5times

+ !"at is ean 0, 0ra#e% #o$u n5Columns provided with Lateral tie members to resist the

hori ontal forces are called as braced columns9 # columns of water tan1 or shear walls for the columns of tall

buildings

!"at is #a$$e% s"ort #o$u n & !"at is ean 0, $on( #o$u n5: compression member may be considered as short when

both the slenderness ratios lex?2 and ley?b are less than 0$ where lex KeEective length in respect of the maOor axis, 2 K depth in respect of themaOor axis, ley K eEective length in respect of the minor axis, and b Kwidth of the member# t shall otherwise be considered as a slendercompression member#

!"at is ean 0, -e%esta$8edestal is a vertical compression member whose eEective

length le does not exceed three times of its least hori ontaldimension b cl# $"#5#!#0h, Aote)# +he other hori ontal dimension2 shall not exceed four times of b

0$ 6 8 4 9 8 : 4 9 2 B ; < r # S # = m a r 2 # # 2 , < # 9 , < S + 9 # ,


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3 Ca$#u$ate ini u e##entri#it, .or a #o$u n o. si e 88B *+8 "a/in( unsu--orte% $en(t" )

7 !"at are t"e .un#tions o. trans/erse rein.or#e ent in#o$u n5 ;OR< !rite an, two .un#tions o. $atera$ ties in a RC#o$u n

a# +o 1eep the main bars in right positionb# +o distribute the loadc# +o resist the shear developedd# +o avoid the buc1ling of longitudinal bars

18 !"at is t"e aBi u #o -ressi/e strain in#on#rete in aBia$ #o -ression5

+he maximum design strength of concrete is (#&&" fc1 whenthe strain ranges from (#(($ to (#((!5# +he maximum design stress of steel is (#./ fy#

11 De'ne 4s$en%erness ratio? o. #o$u n +he slenderness ratio of steel column is the ratio of its eEectivelength le to its least radius of gyration r# n case of reinforced concretecolumn, however, S &5" stipulates the slenderness ratio as the ratio of itseEective length le to its least lateral dimension

12 !"at is t"e e uation to 'n% t"e $oa%#arr,in( #a-a#it, o. #o$u n5

8u K (#&fc1 :c Q (#"/fy :scwhere 8u K factored axial load on the member,fc1 K characteristic compressive strength of the concrete,:c K area of concrete,fy K characteristic strength of the compression reinforcement,and:sc K area of longitudinal reinforcement for columns#

1) !"at is t"e ini u %ia eter o. $on(itu%ina$ 0ars use% in a RC #o$u n5

+he minimum diameter of longitudinal bars used in a 4Ccolumn is 0$mm

1* In a RC #o$u n t"e %ia eter o. $on(itu%ina$0ar use% is 2+ t"e %ia eter o. #o$u n is +8 w"at is

t"e ini u #$ear #o/er to $on(itu%ina$ rein.or#e ent

0! 6 8 4 9 8 : 4 9 2 B ; < r # S # = m a r 2 # # 2 , < # 9 , < S + 9 # ,


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&( mm the cover to the longitudinalreinforcement shall not less than &(mm or dia of bar whichever is greater

1+ State t"e et"o%s re#o en%e% 0, t"e IS*+ to esti ate t"e e>e#ti/e $en(t" o. #o$u ns

Clause $5#$ of S &5" stipulates the eEective lengths of compression members vide :nnex 9 of S &5")#

1 !"at are t"e t,-es o. $oa%in( on #o$u ns5a# :xial Loadb# :xial Load with =niaxial moment

c# :xial Load with Biaxial moment

1 De'ne uniaBia$ 0en%in(f the column is subOected to bending moment in one direction

only then it is called as uniaxial bending

13 !"at is t"e ini u an% aBi u -er#enta(e o. stee$ a$$owe% in R C Co$u n5

(#.% and &%

17 !"at are t"e ini u nu 0ers o. $on(itu%ina$ 0ars inre#tan(u$ar an% #ir#u$ar #o$u ns5

+he minimum numbers of longitudinal bars in rectangularcolumns is & Aos

+he minimum numbers of longitudinal bars in circular columnsis " Aos

28 !"at is t"e a ount o. $on(itu%ina$ rein.or#e ent in a-e%esta$5(#05% of cross'sectional area of the pedestal

21 ow %o ,ou #$assi., a #o$u n as $on(5f the ratio of the eEective Length to the both lateral dimension of thecolumn is less than 0$ means the column is called as Short Column 6Ireater than 0$ means termed as Long column

22 Gi/e eBa -$e o. #o$u ns t"at are in -ra#ti#e su0@e#te%to unaBia$ an% 0iaBia$ 0en%in(

0& 6 8 4 9 8 : 4 9 2 B ; < r # S # = m a r 2 # # 2 , < # 9 , < S + 9 # ,


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all internal columns C0a to C0f) will be designed for axial force only# +he side columns C$a to C$O) will have axial forces with uniaxialbending moment, while the four corner columns C!a to C!d) shallhave axial forces with bi'axial bending moments

05 6 8 4 9 8 : 4 9 2 B ; < r # S # = m a r 2 # # 2 , < # 9 , < S + 9 # ,

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