Reinforced Concrete Design :Introduction

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REINFORCED CONCRETE

DESIGN

Engr. Randy G. Policarpio



Introduction

Concrete is a mixture o sand! gra"el! crus#ed roc$! or ot#er ag#eld toget#er in a roc$li$e mass %it# a paste o cement and %

• Sometimes one or more admixtures are added to c#ange cerc#aracteristics o t#e concrete suc# as its %or$a&ility! dura&iltime o #ardening.

• 's %it# most roc$li$e su&stances! concrete #as a #ig# comprstrengt# and a "ery lo% tensile strengt#.

Reinforced concrete is a com&ination o concrete and steel %#steel reinorcement pro"ides t#e tensile strengt# lac$ing in t#e

• Steel reinorcing is also capa&le o resisting compression orcused in columns.



Concrete Mixing andProportioning (or$a&ility

• (or$a&ility measured &y slump test

1. Layer 1: Fill 1/3 full. 25 stokes

2. Layer 2: Fill 2/3 full. 25 stokes

3. Layer 3: Fill full. 25 stokes

4. Lift cone and measure slump (typically 2-6 in.

) * + ,

)*-slump



Advantages of Reinforced Concrete as a Structural

1. It #as considera&le compressi"e strengt# per unit cost compared %it# most ot#er materials

2. Reinorced concrete #as great resistance to t#e actions o re and %ater and! in act! imaterial a"aila&le or situations %#ere %ater is present. During res o a"erage intensit

satisactory co"er o concrete o"er t#e reinorcing &ars su/er only surace damage %it#out a3. Reinorced concrete structures are "ery rigid.

4. It is a lo%1maintenance material.

5. 's compared %it# ot#er materials! it #as a "ery long ser"ice lie. 2nder proper conditions!structures can &e used indenitely %it#out reduction o t#eir load1 carrying a&ilities. T#is canact t#at t#e strengt# o concrete does not decrease %it# time &ut actually increases o"ermeasured in years! &ecause o t#e lengt#y process o t#e solidication o t#e cement paste.

6. It is usually t#e only economical material a"aila&le or ootings! 3oor sla&s! &asement %al

applications.7. ' special eature o concrete is its a&ility to &e cast into an extraordinary "ariety o s#ape&eams! and columns to great arc#es and s#ells.

8. In most areas! concrete ta$es ad"antage o inexpensi"e local materials 4sand! gra"el! andrelati"ely small amounts o cement and reinorcing steel! %#ic# may #a"e to &e s#ipped rocountry.

9. ' lo%er grade o s$illed la&or is re6uired or erection as compared %it# ot#er materialsteel.



isadvantages of Reinforced Concrete as a Structural M

1. Concrete #as a "ery lo% tensile strengt#! re6uiring t#e use o tensile reinorcing.

2. Forms are re6uired to #old t#e concrete in place until it #ardens suciently. In addior s#oring may &e necessary to $eep t#e orms in place or roos! %alls! 3oors! and sim

until t#e concrete mem&ers gain sucient strengt# to support t#emsel"es.• Form%or$ is "ery expensi"e.

• It should be obvious that when eorts are made to improve the economy of reinforcestructures, the major emphasis is on reducing formwork costs.

3. T#e lo% strengt# per unit o %eig#t o concrete leads to #ea"y mem&ers. T#is &ecoincreasingly important matter or long1span structures! %#ere concrete7s large dead %egreat e/ect on &ending moments. 8ig#t%eig#t aggregates can &e used to reduce conc

&ut t#e cost o t#e concrete is increased.4. Similarly! t#e lo% strengt# per unit o "olume o concrete means mem&ers %ill &e ran important consideration or tall &uildings and long1span structures.

5. T#e properties o concrete "ary %idely &ecause o "ariations in its proportioning anFurt#ermore! t#e placing and curing o concrete is not as careully controlled as is t#e pot#er materials! suc# as structural steel and laminated %ood.



esign Codes

• N'TION'8 STR2CT2R'8 CODE OF T9E P9I8IPPIN

4NSCP5:O82;E I < =uilding! To%ers and ot#er :ertical Struct

:O82;E II< Roads! 9ig#%ays and =ridges.

• ';ERIC'N CONCRETE INSTIT2TE 4'CI Code5

=uilding Code Re6uirements or Structural Concrete+)>5

T#is code is used primarily or t#e design o &uilding

Design re6uirements or "arious types o reinorced cmem&ers are presented in t#e codes along %it# a?commentary - on t#ose re6uirements.

. T#e commentary pro"ides explanations! suggestion





!ortland Ce"entPortland cement is a mixture o calcareous and argillaceous materials %#ic# are c$iln and t#en pul"eri@ed. (#en mixed %it# %ater! cement #ardens t#roug# a proce#ydration.

#$%es of !ortland Ce"entType IAT#e common! all1purpose cement used or general construction %or$.

Type IIA' modied cement t#at #as a lo%er #eat o #ydration t#an does Type I cement%it#stand some exposure to sulate attac$.

Type IIIA' #ig#1early1strengt# cement t#at %ill produce in t#e rst *, #ours a concrete

strengt# a&out t%ice t#at o Type I cement. T#is cement does #a"e a muc# #ig#er #eat

Type IV A' lo%1#eat cement t#at produces a concrete %#ic# generates #eat "ery slo%l"ery large concrete structures.

Type V A' cement used or concretes t#at are to &e exposed to #ig# concentrations o



Ad"i&tures;OST CO;;ON TBPES OF 'D;IT2RES

• Air-entraining admixtures! conorming to t#e re6uirements o 'ST; C* and C)>! are used primarily to resistance to ree@ing and t#a%ing and pro"ide &etter resistance to t#e deteriorating action o deicing salts. T#e acause t#e mixing %ater to oam! %it# t#e result t#at &illions o closely spaced air &u&&les are incorporated into tconcrete ree@es! %ater mo"es into t#e air &u&&les! relie"ing t#e pressure in t#e concrete. (#en t#e concrete t#

mo"e out o t#e &u&&les! %it# t#e result t#at t#ere is less crac$ing t#an i air entrainment #ad not &een used.• T#e addition o accelerating admixtures! suc# as calcium c#loride! to concrete %ill accelerate its early strengt

results o suc# additions 4particularly useul in cold climates5 are reduced times re6uired or curing and protection t#e earlier remo"al o orms. 4Section +..+ o t#e 'CI Code states t#at &ecause o corrosion pro&lems! calcium cadded to concretes %it# em&edded aluminum! concretes cast against stay1in1place gal"ani@ed steel orms! or preOt#er accelerating admixtures t#at may &e used include "arious solu&le salts as %ell as some ot#er organic compou

• Retarding admixtures are used to slo% t#e setting o t#e concrete and to retard temperature increases. T#ey conor sugars or sugar deri"ati"es. Some concrete truc$ dri"ers $eep sac$s o sugar on #and to t#ro% into t#e concrecaug#t in trac ams or are ot#er%ise delayed. Retarding admixtures are particularly useul or large pourtemperature increases may occur. T#ey also prolong t#e plasticity o t#e concrete! ena&ling &etter &lending or &opours. Retarders can also slo% t#e #ydration o cement on exposed concrete suraces or ormed suraces to producaggregate nis#es.

• Superplasticizers are admixtures made rom organic sulonates. T#eir use ena&les engineers to reduce t#econcretes su&stantially %#ile at t#e same time increasing t#eir slumps. 'lt#oug# superplastici@ers can also &e ucement ratios constant %#ile using less cement! t#ey are more commonly used to produce %or$a&le concretes %it#strengt#s %#ile using t#e same amount o cement. 4See Section ).)+.5 ' relati"ely ne% product! sel1consolidasuperplastici@ers and modications in mix designs to produce an extremely %or$a&le mix t#at re6uires no "i&rationcongested placement situations.

• Waterproofing materials usually are applied to #ardened concrete suraces! &ut t#ey may &e added to conadmixtures generally consist o some type o soap or petroleum products! as per#aps asp#alt emulsions. T#ey mpenetration o %ater into porous concretes &ut pro&a&ly don7t #elp dense! %ell1cured concretes "ery muc#.



Failure ;ec#anism o Concrete

hrinkage !icrocracks are t#e initial s#rin$agecrac$s due tocar&onation s#rin$age!

#ydration s#rin$age!and drying s#rin$age.




"ond !icrocracks areextensions o s#rin$agemicrocrac$s! as t#ecompression stresseld increases! t#es#rin$age microcrac$s%iden &ut do notpropagates into t#ematrix. Occur at )H1* ultimate strengt# oconcrete.




!atri# !icrocracks 1are microcrac$s t#atoccur in t#e matrix. T#e propagate rom* c. Occur up to

+1,H ultimatestrengt# o concrete.;atrix microcrac$sstart &ridge oneanot#er at JH.'ggregate microcrac$soccur ust &eoreailure 4K5.



Concrete Properties

T#e standard strengt# test generally uses a cylindrical sample. It is tater *> days to test or strengt#! c. T#e concrete %ill continue to

#arden %it# time and or a normal Portland cement %ill increase %ittime as ollo%s<



Concrete Properties

• Compressi"e Strengt#! 7c

• Normally use *>1day strengt# ordesign strengt#

• Poisson7s Ratio! ν

• ν L .)H to .*

•

2sually use ν = .)J

Ec

o u

.,H7c

c

7c



Concrete Properties• ;odulus o Elasticity! Ec

• Corresponds to secant modulus at .,H 7c

• 'CI +)>1KK 4Sec. >.H.)5<

%#ere % M unit %eig#t 4pc5

K pc %c )HH pc

For normal %eig#t concrete

4%c ≅ ),H pc5

(!33(5.1

psi f w psi E cc =

(!"""#5$( psi f psi E cc =



Concrete Properties

• Concrete strain at max. compressi"e stress!o

• See Fig. +.)J or typical cur"esin compression

• o "aries &et%een .)H1.+

• For normal strengt# concrete! o L

.* Ec

o u

.,H7c

c

7c



Concrete Properties

• ;aximum usea&le strain! u

•

'CI Code<u M .+

• 2sed or 3exural and axialcompression

Ec

o u

.,H7c

c

7c



Concrete Properties Typical Concrete Stress1Strain Cur"es in Compression



Concrete Properties

Types o compression ailure

T#ere are t#ree modes oailure.

) 2nder axialcompression concreteails in s#ear.

* t#e separation o t#e

specimen into columnarpieces &y %#at is $no%nas splitting or columnarracture.

+ Com&ination o s#earand splitting ailure.



Concrete Properties

*. Tensile Strengt#

• Tensile strengt# L > to )H o 7c

• ;odulus o Rupture! r• For de3ection calculations! use<

• Test<

'CI E6. K1K

P

r;max M PQ*a

unreinorced

concrete&eam

I

Mc f r ==

(!5.$ psi f f cr =



Concrete Properties

*. Tensile Strengt# 4cont.5

•

Splitting Tensile Strengt#! ct

• Split Cylinder Test

P

Concrete Cylinder

Poisson7s

E/ect



Concrete Properties

*. Tensile Strengt# 4cont.5

4Not gi"en in 'CI Code5

(!$5(

2

psi f to f

ld

P f

cct

ct

=

=

π



Reinforcing Steel• T#e reinorcing used or concrete structures m

t#e orm o &ars or %elded %ire a&ric.

• Reinorcing &ars are reerred to as plain or defor

• T#e deormed &ars! %#ic# #a"e ri&&ed proectioonto t#eir suraces 4patterns di/ering %it# manuacturers5 to pro"ide &etter &onding &et%

concrete and t#e steel! are used or almapplications.

• Instead o rolled1on deormations! deormed %indentations pressed into it.

• Plain &ars are not used "ery oten except or %

around longitudinal &ars! primarily in columns.



Reinforcing Steel). General

• ;ost common types or non1prestressed

mem&ers<• #ot1rolled deormed &ars

• %elded %ire a&ric



Reinforcing Steel



Reinforcing Steel



'rades of Reinforcing Steel

• Reinorcing &ars may &e rolled rom &illet steel! axle steel! or rail steel.

• T#ere are se"eral types o reinorcing &ars! designated &y t#e 'ST;.

• T#ese steels are a"aila&le in di/erent grades as Grade H! Grade ! and so on! %means t#e steel #as a specied yield point o H! psi! Grade means ! p• 'ST; ')H< Deormed and plain &illet steel &ars. T#ese &ars! %#ic# must &e mar$ed %it# t#e

o steel5! are t#e most %idely used reinorcing &ars. =ars are o our minimum yield strengt# le4*> ;Pa5 ! psi 4,* ;Pa5 JH! psi 4H* ;Pa5 and >! psi 4HH ;Pa5.

• 'ST; 'J< 8o%1alloy deormed and plain &ars. T#ese &ars! %#ic# must &e mar$ed %it# t#e lo steel5! are to &e used %#ere controlled tensile properties andQor specially controlled c#emicre6uired or %elding purposes. T#ey are a"aila&le in t%o grades< ! psi 4,* ;Pa5 and

;Pa5! designated as Grade 4,*5 and Grade > 4HH5! respecti"ely.

• 'ST; 'KK< Deormed rail steel or axle steel &ars. T#ey must &e mar$ed %it# t#e letter R 4or

• (#en deormed &ars are produced to meet &ot# t#e ')H and 'J specicationsmar$ed %it# &ot# t#e letters S and (.

(dentif$ing Mar)s on



(dentif$ing Mar)s onReinforcing *ars;ar$ings are descri&ed in t#e ollo%ing list<

1. T#e producing company is identied %it# a letter.

2. T#e &ar si@e num&er 4+ to )>5 is gi"en next.3. 'not#er letter is s#o%n to identiy t#e type o steel 4&illet! R in addition to a rail sign or rail steel! ' or axle! or lo% alloy5.

4. Finally! t#e grade o t#e &ars is s#o%n eit#er %it# nu

%it# continuous lines. ' Grade &ar #as eit#er t#e numon it or a continuous longitudinal line in addition to its m' Grade JH &ar %ill #a"e t#e num&er JH on it or t%o conlines in addition to t#e main ri&s.

(d tif i M ) R i f i



(dentif$ing Mar)s on Reinforcing*ars

). General• Standard

Reinorcing =ar;ar$ings




(dentif$ing Mar)s onReinforcing *ars









R i f i St l



Reinforcing Steel

+. Stress "ersusStrain

• Stress1Strain cur"eor "arious types osteel reinorcement&ar.



Reinforcing Steel

• Es M Initial tangent

modulus M *K!$si 4all grades5

• Note:

GR, #as a longer yield plateau

Stress

St

.*

GR ,

GR 4less du

E

s)



+oads

•

Per#aps t#e most important and most dicult taaced &y t#e structural designer is t#e accurateestimation o t#e loads t#at may &e applied to astructure during its lie.

• No loads t#at may reasona&ly &e expected to oc&e o"erloo$ed.

• 'ter loads are estimated! t#e next pro&lem is tot#e %orst possi&le com&inations o t#ese loads tmig#t occur at one time.



+oads

• ead +oads

• Dead loads are loads o constant magnitude t#at remain in one p T#ey include t#e %eig#t o t#e structure under consideration as %xtures t#at are permanently attac#ed to it.

• For a reinorced concrete &uilding! some dead loads are t#e rame3oors! ceilings! stair%ays! roos! and plum&ing.

• To design a structure! it is necessary or t#e %eig#ts or dead load"arious parts to &e estimated or use in t#e analysis.

• T#e exact si@es and %eig#ts o t#e parts are not $no%n until t#e sanalysis is made and t#e mem&ers o t#e structure are selected.

• T#e %eig#ts! as determined rom t#e actual design! must &e comt#e estimated %eig#ts. I large discrepancies are present! it %ill &necessary to repeat t#e analysis and design using &etter estimate



+oads

+ive +oads



+ive +oads

• 8i"e loads are loads t#at can c#ange in magnitude and position. T#ey include occupanc%are#ouse materials! construction loads! o"er#ead ser"ice cranes! e6uipment operatinmany ot#ers. In general! t#ey are induced &y gra"ity.

'mong t#e many ot#er types o li"e loads are<

• Traf$c loads for bridgesA=ridges are su&ected to series o concentrated loads o "aryi

caused &y groups o truc$ or train %#eels.• Impact loadsAImpact loads are caused &y t#e "i&ration o mo"ing or mo"a&le loads. It

crate dropped on t#e 3oor o a %are#ouse or a truc$ &ouncing on une"en pa"ement o agreater orces t#an %ould occur i t#e loads %ere applied gently and gradually. Impact lto t#e di/erence &et%een t#e magnitude o t#e loads actually caused and t#e magnitud#ad t#ey &een dead loads.

• %ongitudinal loadsA8ongitudinal loads also need to &e considered in designing some stStopping a train on a railroad &ridge or a truc$ on a #ig#%ay &ridge causes longitudinal applied. It is not dicult to imagine t#e tremendous longitudinal orce de"eloped %#en

,1ton trailer truc$ tra"eling at mp# suddenly #as to apply t#e &ra$es %#ile crossing&ridge. T#ere are ot#er longitudinal load situations! suc# as s#ips running into doc$s ano tra"eling cranes t#at are supported &y &uilding rames.

• !iscellaneous loadsA'mong t#e ot#er types o li"e loads %it# %#ic# t#e structural desto contend are soil pressures 4suc# as t#e exertion o lateral eart# pressures on %alls opressures on oundations5! hydrostatic pressures 4suc# as %ater pressure on dams! inerlarge &odies o %ater during eart#6ua$es! and uplit pressures on tan$s and &asement sloads 4caused &y explosions! sonic &ooms! and military %eapons5! and centrifugal forcecaused on cur"ed &ridges &y truc$s and trains or similar e/ects on roller coasters5.

+i + d



+ive +oads

+ive +oads



+ive +oads

, i t l + d



,nviron"ental +oads

• En"ironmental loads are loads caused &y t#e en"ironment in %#ic# t#e struct

located.• For &uildings! t#ey are caused &y rain! sno%! %ind! temperature c#ange! and

• Strictly spea$ing! t#ese are also li"e loads! &ut t#ey are t#e result o t#e en"%#ic# t#e structure is located. 'lt#oug# t#ey do "ary %it# time! t#ey are not gra"ity or operating conditions! as is typical %it# ot#er li"e loads.

:arious $inds o en"ironmental loads.

1. now and ice&

2. Rain& 3. 'ind

4. oil pressure

5. eismic loads&

& Temperature (ierentials



'N'8BSIS "s DESIGN

• 'N'8BSISGi"en t#e cross section! concrete strengt#! reinorcement si@e a

location! and yield strengt#! compute t#e resistance or strengt#compare to t#e strengt# re6uired.

In analysis t#ere s#ould &e one uni6ue ans%er.

•

DESIGNGi"en a actored design moment! normally designated as ! selec

suita&le cross section! including dimensions! concrete strengt#!or re6uired reinorcement.

In design t#ere are many possi&le solutions.

•

8I;IT ST'TE



8I;IT ST'TE

• (#en a structure or structural element is no longer acceunt or its intended use! it is said to #a"e reac#ed t#e li

;aor groups or Reinorced Concrete Structural 8imit S

). 2ltimate

*. Ser"icea&ility

+. Special



28TI;'TE 8I;IT ST'TE T#ese in"ol"e a structural collapse o part or all o t#e structure 4 "ery lo% prooccurrence5 and loss o lie can occur.

T#e maor 2ltimate 8imit States are as ollo%s<a. 8oss o e6uili&rium o a part or all o t#e structure as a rigid &ody 4tipping!

structure5.

&. Rupture o critical components causing partial or complete collapse 43exus#ear ailure5.

c. Progressi"e collapse

;inor local ailure o"erloads causing adacent mem&ers to ailure until ent

collapsed.d. Formation o plastic mec#anism1 yielding o reinorcement to orm plastic #

enoug# sections to ma$e structure unsta&le.

e. Insta&ility cased &y deormations o structure causing &uc$ling o mem&er

. Fatigue1 mem&ers can racture under repeated stress cycles o ser"ice loacause collapse5.



SER:ICE'=I8ITB 8I;IT ST'TESFunctional use o structure is disrupted! &ut collapse is not expected. ;ore oten toleratedultimate limit state since less danger o loss o lie.

T#e maor Ser"icea&ility 8imit States include t#e ollo%ing<

a. Excessi"e de3ections or normal ser"ice caused &y possi&le e/ects<

). ;alunction o mac#inery.

*. :isually unaccepta&le.

+. Damage to nonstructural mem&ers.

,. C#anges in t#e distri&ution o orces.

H. Ponding o roo 4collapse o roo5.

&. Excessi"e crac$ %idt# may &e unsig#tly and may allo%.

). 8ea$age

*. Corrosion o t#e reinorcement

+. Gradual deterioration o t#e concrete

c. 2ndesira&le :i&ration2ndesira&le "i&rations may distur& t#e users includes!

). :ertical "i&rations o 3oors and &ridges.

*. 8ateral and torsional "i&rations o tall &uildings.

+. :i&rations due to c#ange in loading.



SPECI'8 8I;IT ST'TES

Damage or ailures caused &y a&normal conditions or a&nloadings and includes<

a. Damage or collapse in extreme eart#6ua$es! 3oods.

&. Structural e/ects o re! explosions! or "e#icular collisions.

c. Structural e/ects o corrosions or deterioration.

d. 8ong term p#ysical or c#emical insta&ility 4normally not a pro&lemconcrete structure5.

DESIGN P9I8OSOP9B



). (ORING STRESS ;ET9OD

'lso called t#e 'llo%a&le Stress Design! it is a met#od o deon elastic stage o an structural mem&er. 9ence! t#e mem&er ion %or$ing loads! also reerred to as ser"ice loads or unactore

*. STRENGT9 DESIGN ;ET9OD

'lso called t#e 2ltimate Strengt# Design! it is a met#od &asultimate limit state design.

In t#e Strengt# ;et#od! t#e ser"ice loads are increase suUcactors to o&tain t#e load st %#ic# ailure is considered to &e ?i

T#is load is called t#e actored load or actored ser"ice load.

T#e Strengt# Design ;et#od re6uires<

•

STRENGT9 DESIGN ;ET9OD



S G S G O

accounts or<

a. Pro&a&ility o understrengt# o mem&er due to material strengt#

dimension.

&. Inaccuracies in design e6uation.c. Degree o ductility.

d. Importance o t#e mem&er in t#e structure.

•

Factored 8oad com&inations or re6uired strengt# 4u5



Factored 8oad com&inations or re6uired strengt# 4u5'CI +)>1KK

Dead and 8i"e 8oad

2 M )., D8

2 M )., D8 V ).J 88 4'CI K.*.)5

Dead! 8i"e! and (ind 8oads

2 M .K D8 W ).+ (8

2 M .JH 4)., D8 V ).J 88 W ).J (85 4'CI K.*.*5

Dead! 8i"e! and Eart#6ua$e 8oads

2 M .K D8 W ).+ ).) E8

2 M .JH 4)., D8 V ).J 88 W ).J ).) E85 4'CI K.*.+5




Factored 8oad com&inations or re6uired strengt# 4u5'CI +)>1*




Factored 8oad com&inations or re6uired strengt# 4u5'CI +)>1>




Factored 8oad com&inations or re6uired strengt# 4u5'CI +)>1))

Documents

Reinforced Concrete Design :Introduction