Reinforced Concrete Exam #2

Short beam ratio L=20-25 ft

d/b=1*(1/2)-2

Long span beam ratio L>25 ft

d/b=3-4

Wider shallower beams are used to ____

reduce floor heights

Beam widths are selected in multiples of __

2in or 3in

self-weight must be included in the member

resisting capacity

Member weight is ___until the member is dimensioned and designed

unknown

Self weight

actual weight of the beam

typical bars of size

#11 and smaller

Compression bars and stirrups are usually

different sizes

stirrups are used for

• Shear and torsion reinforcing

• Position of top bar

Minimum stirrup diameter for longitudinal bars #10 or smaller

3/8 in (#bars)

Minimum stirrup diameter for longitudinal bars #11 or larger

½ in (#4bars)

Minimum inside radius of the 90 degree stirrup bent around the outside longitudinal bar is___

2ds

Cover

minimum distance of reinforcement bar from the surface of concrete to provide protection

Cover improves ____between concrete and steel

bonding 

minimum spacing of bars

will be the greatest of

1in

db

(4/3)dagg

minimum spacing of bars will be the greatest of

1in

db

(4/3)dagg

If bars are placed in layers, upper layers bars should be _____

placed directly over the ones in lower layers

clear distance between layers >

1in

Maximum permissible aggregate size shall not exceed the least of:

1/5  of narrowest dimension between sides of forms

1/3 the depth of slabs

¾ of the minimum clear space between reinforcement

reinforcing bar develops ___by ____ concrete along its ____

stresses, bonding, length

Development length

minimum length in which a bar’s stresses can increase from 0 to fy

Development length vary with _____ and ___

cover, bar spacing

what reduce development length

larger cover values and larger bar spacing

minimum beam width

bmin=nD+(n-1)s+2(ds)+2(clear cover)

n=number of bars

D= diameter of largest bar

ds= diameter of stirrup

s=clear spacing between bars

Beam sizes considerations

economy and appearance

saves money

large bending moment should be sized to be as small as possible

outside dimensions to proportion as many as possible of the other beams in the same floor system

less steel is used for beams that support smaller bending moment

Considering economy and appearance, only a few different ____ should be used in a _________

beam sizes, particular floor system

This practice will ____ appreciable amounts of money by _____ the formwork

save, simplifying

Beam subject to the ___bending moment should be sized to be as ____as practically possible (fairly high 𝜌)

largest, small

Beam subject to the largest bending moment should be sized to be as small as practically possible

fairly high 𝜌

Use the above____ dimensions to ____ as many as possible of the other beams in the same ____

outside, proportions, floor system

Less steel is used for beams that support _____

smaller bending moment

flexural-resistance factor

Rn

For a given section (b and d known)  and Mu, f’c and fy can calculate

p

For a given section (b and d known)  and p, f’c and fy can calculate

Mu

For a given section (b and d unknown)  and given mu, fic, and fy, assume__and then calculate ___. 

p, bd²

if a section is designed (b and d unknown) then assume reasonable values for ___ and compute the required __for each width that the required bd²mis satisfied

b, d

Select a section size such that the ratio of b/d=

½ to 3/2

___ should be wider than the ____to improve constructability

Beams, column

Concrete beams with ____ proportions are unlikely to ___ , even if they are ______ and ___

normal, buckle laterally, deep, narrow

If significant ___ is present then the likelihood for___

torsion, lateral buckling increases

Lateral bracing of a beam is not required at intervals____

less than 50𝑏

If significant torsion is present, it must be considered in determining the ____for lateral support

maximum spacing

Beams with web depths that _____ tend to develop excessive ____ in upper parts of the ____zone

exceed 3 𝑓𝑡, wide cracks, tension

Adding additional ______ in the zone of _____ near the vertical side faces of their __ reduces these cracks

longitudinal reinforcement, flexural tension, webs

ACI318-19 Section 9.7.2.3 states that skin reinforcement must be provided for members with_____

depth ℎ > 36 𝑖𝑛

ACI318-19 Section 9.7.2.3 states that skin reinforcement must be provided for members with depth ℎ > 36 𝑖𝑛

• Uniformly distributed along both side faces of member

• Provided for a distance equal to ℎ/2 nearest the flexural reinforcing steel

Skin reinforcement may be considered in computing the ____ of members

bending strength

The use of skin reinforcement is appropriate only for__ for their positions relative to ___are used to determine bar____

strains, neutral axis,  stresses

Typically, total area of skin reinforcement in both side faces
of member____

2As<As/2