Draft

11.3ContinuousBeams 193

6. Check equilibriumof forces:

a=

Asfy

: 85 f

0

c

b

=

(2:42)in

2

(40)ksi

(:85)(3)ksi(11:5)in

= 3: 3 in

p

7. we have convergedona.


8. Actualisact=

2 : 42

(11:5)(20)

=: 011

9. bis equalto

b=: (^85 1)
f
0
c
fy
87
87 +fy
= (:85)(:85)
3
40
87
87 + 40
=: 037
10.max=: 75 = (0:75)(0:037)=: 0278 > 0 : 011
p
thusfs=fyandwe use As= 2: 42 in
2

11.3 CrackedSection,LimitState

28 Whereascoverageof continuousreinforcedconcretebeamsis beyondthescope of thiscourse,

Fig.??illustratesa typicalreinforcement in such a beam.

11.4 ACI Code

Attachedis anunauthorizedcopy of someof themostrelevant ACI-318-89designcodeprovi-

sions.

8.1.1- In designof reinforcedconcretestructures,membersshallbe proportionedforad-

equatestrength in accordancewithprovisionsof thiscode,usingloadfactorsandstrength

reductionfactors speci edin Chapter9.

8.3.1- Allmembersof framesor continuousconstructionshallbe designedforthemaximum

eectsof factoredloadsasdeterminedby thetheoryof elasticanalysis, exceptasmodi ed

accordingto Section8.4.Simplifyingassumptionsof Section8.6through8.9may be used.

8.5.1- Modulusof elasticityEcforconcretemay be takenasW

1 : 5

c

33

p

f

0

c

( psi)forvalues

ofWcbetween 90 and 155 lb per cuft. Fornormalweight concrete,Ecmay be takenas

57 ; 000

p

f

0

c

.

8.5.2- Modulusof elasticityEsfornon-prestressedreinforcement may be takenas 29,000

psi.

9.1.1- Structuresandstructuralmembersshallbe designedto have designstrengthsat all

sectionsat leastequalto therequiredstrengthscalculatedforthefactoredloadsandforcesin

such combinationsas arestipulatedin thiscode.

9.2- RequiredStrength

9.2.1- RequiredstrengthU to resistdeadloadD andlive loadL shallbe at leastequalto

U= 1: 4 D+ 1: 7 L

9.2.2- If resistanceto structuraleectsof a speci edwindloadWareincludedin design,

thefollowing combinationsof D, L,andW shallbe investigatedtodetermine thegreatest

requiredstrengthU

U= 0:75(1: 4 D+ 1: 7 L+ 1: 7 W)