reinforced concrete design bs 8110

8/16/2019 Reinforced Concrete Design BS 8110

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Reinforced concrete design BS 8110

Rule of Thumb for RC Design

Fire

resistance

(hrs)

Minimum

beam idth

(mm)

Minimum

thic!ness of

floors (mm)

Minimum all

thic!ness

("#0$%&)

Min all

thic!ness

(0$%&

Min all

thic!ness

("'1&)

0.5 200 75 150 100 751 200 95 150 120 75

1.5 200 110 175 140 1002 200 125 - 160 1003 240 150 - 200 150

4 280 170 - 240 180

Source: Concrete Centre

Reinforcement for beams

• S"acing

The minimum spacing o stee! reinorcement "ars is1. #a$imum si%e o coarse aggregate p!us 5mm

&r

2. 'ar si%e()hiche*er is greater+

• umber of bars

#a$ "ars per !a,er or "eams ("eam )ith / 2 $ co*er / 2 $ !in iameter+(2 $ "ar iameter+

• Sie of bars

Beam idth (mm)Bar diameter (assuming *+mm

co,er)

25 32 40


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300 3 3 2350 4 3 3400 5 4 3450 6 5 4500 7 5 4550 8 6 5600 9 7 6650 10 8 6700 11 9 7750 12 10 8800 13 10 8900 15 12 91000 17 13 11

• -reas of reinforcement

#a$ o tension or compression reinorcement is 6 o cross sectiona! area o concrete#in percentages are sho)n in the ta"!e "e!o) )hich is Ta"!e 3.25 o 'S 8110

• Shear .in!s

Shear !ins shou! "e space no more than 0.75. o !ongituina! "ars shou! "e space morethan 150mm or rom a *ertica! !eg. Shear !ins shou! o!!o) the o!!o)ing reuirements:

Bar diameter (mm) 1/ 0 + * %0


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#a$ spacing (mm+ 192 240 300 384 480#in !in iameter (mm+ 6 6 8 8 10

Reinforced Concrete Design

!astic response is ue to app!ie !oas "ut p!astic "eha*ior can "e "e!o) an a"o*e ,ie! stress.Creep rate epens on the composition o the concrete an en*ironmenta! conitions.Simi!ar to stee! concrete mu!ti-store, "ui!ings can either consist o porta! rames or "racerames that epen on "racing or iaphragms )ith concrete core )a!!s or !atera! sta"i!it,.o)e*er or mu!ti-store, "ui!ings !atera! sta"i!it, has se*era! reuirements:

1. Sti hori%onta! iaphragms must nee to "e use )ith core )a!!s such as constructing!oors )ith insitu reinorce concrete. Concrete core )a!!s ()ith a minimum thicness o200mm or stee! reinorcement p!acement an concreting+ can "e in the orm o !it shatsor the surrouning )a!!s o staircases.

2. 'racing shou! "e use throughout the height o the "ui!ing un!ess transer structuresare use.

The shear center shou! "e coinciing )ith the point o )here the resu!tant o o*erturning orcesis.

Reinforced Concrete Column Design

Scheme Design

e )i!! a!)a,s esign co!umns an other compression mem"ers )here their *ertica! !oas actconcentrica!!, to the neutra! a$is o the structura! mem"ers. n these situations these structura!mem"ers are a$ia!!, !oae ", irect compressi*e stresses.

Concrete co!umns are structura! mem"ers that he!p structura! ura"i!it, an resist an supports*ertica! !oas. To istinguish concrete co!umns rom concrete piers an )a!!s the "igger cross-section imension shou! not "e !arger than our times its sma!!er imension.

n practica! app!ications *ertica! !oas act eccentrica!!, to the neutra! a$is o the structura!mem"er. Thereore in actua! practice "oth the compressi*e stresses that act concentrica!!, to theneutra! a$is o the structura! mem"er ; the "ening stresses inuce ", the compressi*e

stresses that act eccentrica!!, to the neutra! a$is o the structura! mem"er nee to "e accounteor in the structura! esign.

2e ill onl3 focus on com"ressi,e stresses that act concentricall3 to the neutral a4is in

scheme designs$

Concrete co!umns are consiere to "e "race )hen the o*era!! structure is esigne to resist!atera! !oas. 'race co!umns are co!umns in a sta"i!it, s,stem )ith shear or core )a!!s.


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;=+ $


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hich ould gi,e -c;"ro, < b 4 h ' -c;re5

=7 Determine a""lied moment on the columns

To estimate the app!ie moment on the co!umns it is suggeste to mu!tip!, the a$ia! !oa rom

the !oor a"o*e the co!umn ",:• 25 / interior co!umns• 5 / ege co!umns

• 2 / corner co!umns

Detail Design

1$ Find the effecti,e height7 le7 of the column

!e $ !)here ! u!! !ength Da!ues rom ta"!e "e!o)n conition 1 co!umn en is u!!, restraine ", moment connectionn conition 2 co!umn en is partia!!, restraine ", mono!ithic connectionn conition 3 co!umn en is simp!, supporte

Source: (C!ause 3.8.1.6 'S 8110+

$ Determine hether the column is a short column$

!e, " E 15 an !e$ h E 15 it is a short co!umn. "oth ratios are !arger than 15 it is a s!ener co!umn.

)here !e$ eecti*e height in respect o the maFor a$is!e, eecti*e height in respect o the minor a$is orma!!, reinorce co!umns shou! "e esigne as short not s!ener.

*$ Find re5uired area of steel reinforcement7 -sc;re5

Suicient stee! reinorcement content an reinorcement p!acement he!p to resist cracing in theconcrete co!umn. itiona! reinorcement shou! "e use such as "iners *ertica! !ins or ties.


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These aitiona! reinorcement resist !atera! "uc!ing inuce ", compressi*e stresses o mainreinorcement. tie shou! "e p!ace or e*er, corner "ar. The istance rom one reinorcement "ar to another shou! "e no !ess than 150mm.

Geinorcement near the concrete surace are more eecti*e at resisting "ening moment orces

than reinorcement p!ace at the centre o the co!umn.uation or a short an "race co!umn )hich supports rough!, s,mmetrica! arrangement o "eams an )here these "eam properties an si%es o not ier ", more than 15 is sho)n "e!o).

< 0$*+ 4 fcu 4 -c > 0$/: 4 -sc;re5 4 f3

here cu characteristic strength o concrete (mmH2+c area o concrete (mmH2+?, ,ie! strength o reinorcement (mmH2+sc area o reinorcement

ote: scAre is negati*e use the euation "e!o).scAre 0.4 $ cAnomina!

ote: The esign moment or s!ener co!umns inc!ues an aitiona! moment inuce ",eccentricit, o the geometr, section.

%$ Find a suitable number of reinforcement bars and the sie of the reinforcement bars7

;;;;;; T ;;;;;;

+$ Find the area "ro,ided b3 the reinforcement bars designed7 -s;"ro,c

Reinforced Concrete Beam Design

Scheme Design

The app!ie !oas inc!ue irect compression orces as )e!! as compressi*e an tensi!e stressesthat are cause ", sagging "ening moments to the "eam. The inuce compressi*e stresses are!ocate in the materia! i"res a"o*e the neutra! a$is o the mem"er an the inuce tensi!estresses are !ocate "e!o) the neutra! a$is.

1$ Determine f3 and fcu according to re5uired material "ro"erties

$ Determine "reliminar3 dimensions of the beam7 b and h


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*$ Find effecti,e de"th7 d

h - co*er - "ar iameter Concrete co*ers are to "e esigne or reuirements o ire resistance an ura"i!it,.

%$ Find s"ande"th ratio7 .d and ma!e sure that .d is less than 0

;e!ection shou! "e chece using the spanepth ratio.Cracing shou! "e esigne or S=S an shou! meet the reuirements o minimumreinorcement neee an spacing.

Detail Design

1$ Find

) 1.4;= > 1.6==$ Find the design moment and shear7 M and ?

Simp!, supporte )ith


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Canti!e*er 'eam )ith


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tThe eecti*e span o "eams ! shou! "e assume to "e the eecti*e span o the mem"er in itssimp!, supporte conition or conser*ati*e purposes. This span eua!s the e$act istance "et)een supports.

$ @stablish concrete grade7 fcu7 in mmA

*$ Find the de"th to neutral a4is7 47 in mm

;epth to neutra! a$is $ rom compression ace is !imite to:$ I 0.5 or cu I 45 mmH2$ I 0.4 or 45 E cu I 70 mmH2$ I 0.33 or 70 E cu I 100 mmH2

*$ Design rectangular beams for fle4ure

The esign u!timate moment # shou! "e esigne greater than the u!timate "ening moment.J!so app!ica"!e to !ange "eams )hen the neutra! a$is o the "eam !ies )ithin the !ange

KL 0.156 or cu I 45 mmH2KL 0.120 or 45 E cu I 70 mmH2KL 0.094 or 70 E cu I 100 mmH2


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K I KL compression reinorcement not reuire

$ (-%+0.45 or cu I 45 mmH2$ (-%+0.40 or 45 E cu I 70 mmH2$ (-%+0.36 or 70 E cu I 100 mmH2

K M KL compression reinorcement reuire

$ (-%+0.45 or cu I 45 mmH2$ (-%+0.40 or 45 E cu I 70 mmH2$ (-%+0.36 or 70 E cu I 100 mmH2


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an )here cu not reater than 80.

c. *c >*r E * E 0.8Ncu or * 7 mmO !ins or !ins )ith "ent-up "ars shou! "e pro*ie.=ins shou! not "e more than 50 o shear resistance.

Concrete shear stress *c

+$ Determine hether ma4imum deflection is belo deflection ca"acit3

!!o)a"!e =imit =250


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Reinforced Concrete Slab Design

T,pes o suspene s!a"s that are consiere (s!a"s )hich are supporte ", "eams co!umns or)a!!s+

• So!i s!a"so These s!a"s are mae out o so!i concrete )ith reinorcement that resist tension.

S!a"s can "e in-situ or proi!e meta! ecing. The top reinorcement can "e astee! mesh or the use o ire resistance. The "ottom reinorcement can "e a meta!ecing or tension reinorcement purposes.

• Gi""e s!a"s

o These s!a"s can achie*e the same structura! strength than so!i s!a"s )ith !essconcrete reuire. Gi""e s!a"s can "e series o in-situ concrete ri"s that are castmono!ithica!!, )ith *ois cause ", remo*a"!e ormers. Gi""e s!a"s can a!so "ea ho!!o) s!a"s )ith permanent *oi ormers.

• ?!at s!a"s

o These s!a"s )ith !at soits o not reuire the support o "eams. ;rops are otenuse to orm a thic stiening part "et)een the co!umns an the s!a".

• a!e s!a"s

o These s!a"s are so!i an !at )ith *oi ormers in the soits. There are series o1m )ie concrete "eams that can "e esigne or moment "ening.

o s!a"s shou! "e !ess than 125 mm thic ue to ire resistance reuirements.T)o )a, spanning s!a"s can "e 90 o thicness o one )a, spanning s!a"s

1$ Find

) 1.4;= > 1.6==

$ Find the design moment and shear7 M and ?

?in # an D euations a"o*e (Geer to "eam ca!cu!ations+.

*$ Design slab for fle4ure using ne 2a3 Slab method

?in K an %


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?in percentage o reinorcement in concrete area (st" +

Geinorcement "ars shou! "e esigne to u!i!! the minimum area capacit, an shou! "econstructe in "oth irections in the s!a". Stee! reinorcements he!p to resist cracing an toistri"ute concentrate !oas throughout the s!a".

The ma$imum amount o reinorcement in concrete mem"ers ("eams co!umns or s!a"s+ shou!not e$cee 4.

%$ Find the number of reinforcement bars and the sie of the reinforcement bars7 ;;;; T

;;;;;;$

+$ Find -s"ro,$

/$ Design slab for shear$

Geer to here or ru!es or each constant in the concrete shear stress euation "e!o).

https://sturdystructural.wordpress.com/2015/06/21/rc-beams/https://sturdystructural.wordpress.com/2015/06/21/rc-beams/


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#inimum stee! reuire 0.13

:$ Chec! "unching shear

Punching shear orces (shear orces aroun the perimeter o co!umns+ are usua!!, the critica!esign case or !at s!a" ounations. ecti*e shear is the shear orce that taes moment orcescause "et)een the s!a" an the co!umn an the shear orce o*er the area supporte ", theco!umn.

• ecti*e shearso nterna! co!umns -M De 1.15D

o Corner co!umns -M De 1.25D

o ge co!umns -M De 1.4D

Punching shear checs in !at s!a"s• Shear stress *o De

reinforced concrete design bs 8110

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