Draft

Chapter 11

REINFORCED CONCRETE

BEAMS

11.1 FailureModesforR/CBeams.

1 Recallingthatconcretehasa tensilestrength(f

0

t) aboutonetenth itscompressive strength

(f

0

c

), concreteby itselfis a verypoor materialfor
exuralmembers.

2 To providetensile resistancetoconcrete beams,a reinforcement mustbe added. Steelis

almostuniversallyused asreinforcement (longitudinalor asbers),butin poorercountries

otherindigenousmaterialshave beenused(such as bamboos).

3 Thefollowinglectureswillfocusexclusivelyonthe
exuraldesignandanalysisof reinforced

concreterectangularsections.Otherconcerns,such as shear,torsion,cracking,andde
ections

areleftforsubsequent ones.

4 Design of reinforcedconcrete structures is governedin mostcasesby the BuildingCode

RequirementsforReinforced Concrete, of theAmericanConcreteInstitute(ACI-318).Someof

themostrelevant provisionsof thiscodeareenclosedin thissetof notes.

5 We will focuson determiningtheamount of
exural(that is longitudinal)reinforcement

requiredat agivensection. For thatsection,themoment which shouldbe consideredfor

designis theoneobtainedfromthemoment envelopeat thatparticularpoint.

11.1.1 Notation

6 In R/Cdesign,it is customaryto usethefollowingnotation