vertical forces review reinforced concrete design

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3/3/2017 1 SE EXAM REVIEW COURSE — March 2017 NCSEA Structural Engineering Exam Review Course Vertical Forces Review Reinforced Concrete Design Spring 2017 Presented by Lawrence Novak, SE, F.ACI, F.SEI, CERT, LEED®AP Senior Director of Structural Engineering & Codes SE EXAM REVIEW COURSE — March 2017 Learning Objectives Structural Concrete Design by ACI 318‐11 Behavior of Materials for Reinforced Concrete Strength Design Methodology Analysis and Design of elements Beams and one‐way slabs Columns Two‐way slabs Pre‐ and post‐tensioned structures Structural Detailing

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Page 1: Vertical Forces Review Reinforced Concrete Design

3/3/2017

1

SE EXAM REVIEW COURSE —March 2017

NCSEA Structural Engineering Exam Review Course

Vertical Forces ReviewReinforced Concrete Design

Spring 2017

Presented by Lawrence Novak, SE, F.ACI, F.SEI, CERT, LEED®AP

Senior Director of Structural Engineering & Codes

SE EXAM REVIEW COURSE —March 2017

Learning Objectives

• Structural Concrete Design by ACI 318‐11– Behavior of Materials for Reinforced Concrete

– Strength Design Methodology

– Analysis and Design of elements• Beams and one‐way slabs

• Columns

• Two‐way slabs

• Pre‐ and post‐tensioned structures

– Structural Detailing

Page 2: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Definitions

2

Load(lbs)Stress psi

Area(in. )

Strength MaximumStress

Deformation(in.)Strain

OriginalLength(in.)

AreaLoad

Leng

th

D

SE EXAM REVIEW COURSE —March 2017

Characteristics of Concrete

• Basic concept

– Strong in compression

– Weak in tensionFactor of 10!

Page 3: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Load-Deformation Characteristics for Concrete

SE EXAM REVIEW COURSE —March 2017

Rate of Loading

Faster loading rate 

Slower loading rate

ASTM loading rate

6

Page 4: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Styrofoam Beam – Loaded

Tension

Compression

SE EXAM REVIEW COURSE —March 2017

Plain Concrete Beam (no rebar)

Page 5: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Plain Concrete BeamLoad

Sudden Fracture

SE EXAM REVIEW COURSE —March 2017

Reinforced Concrete Beam

Page 6: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Deformed Reinforcement

fy

Strain, 1

Es fs = Ess

fs = fy

Neglect in Design

Idealized stress-strain

Stress, fs

SE EXAM REVIEW COURSE —March 2017

Deformed Reinforcement (ASTM)

0.002 Strain, 

fy

Stress, fs

y = fy/Es+ 0.002 

Page 7: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Reinforced Concrete Beam

Tension

Steel Reinforcement

Tension

Load

Load

Concrete

Concrete

Steel Reinforcement

SE EXAM REVIEW COURSE —March 2017

Load-Deformation for Plain and Reinforced Beams

Page 8: Vertical Forces Review Reinforced Concrete Design

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8

SE EXAM REVIEW COURSE —March 2017

Modulus of Elasticity

• For wc = 90 to 160 lb/ft3 

• For normal‐weight concrete (at 145 lb/ft3)

Ec = 57,000

Ec = wc1.533 cf '

cf '

SE EXAM REVIEW COURSE —March 2017

Strength Design Methodof ACI 318

Page 9: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Strength Requirements

• Design strength ≥ required strength

– Design strength = strength reduction factor () ×nominal strength

– Required strength = load factor × service load effects

SE EXAM REVIEW COURSE —March 2017

Strength Reduction Factor ()

• Understrength of a member

• Inaccuracies in the design equations

• Degree of ductility

• Importance of the member in the structure

Page 10: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Material Strength Reduction Factors ()

Tension-controlled 0.90

Compression-controlledTied 0.65Spiral 0.75

Shear and torsion 0.75

Bearing on concrete 0.65

SE EXAM REVIEW COURSE —March 2017

Design Strength

• Mn = design flexural strength

• Pn = design axial strength at given ecc.

• Vn = design shear strength = (Vc + Vs)

• Tn = design torsional moment strength

Page 11: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Load Types

• Dead (D)

• Live (L)

• Roof live (Lr)

• Snow (S)

• Rain (R)

• Wind (W)

• Seismic (E)

• Soil (H)

• Fluid (F)

• Temperature, creep, shrinkage (T)

SE EXAM REVIEW COURSE —March 2017

Primary Load Combinations

1. U = 1.4 D

2. U = 1.2 D + 1.6 L + 0.5(Lr or S or R)

3. U = 1.2 D + 1.6(Lr or S or R) +(1.0 L or 0.5 W)

4. U = 1.2 D + 1.0 W + 1.0 L + 0.5(Lr or S or R)

5. U = 1.2 D + 1.0 E + 1.0 L + 0.2 S

6. U = 0.9 D + 1.0 W

7. U = 0.9 D + 1.0 E

(see ACI 318‐11 Section 9.2 for additional information)

Page 12: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Strength Requirements

Mn ≥ Mu

Pn ≥ Pu

Vn = (Vc + Vs) ≥ Vu

Tn ≥ Tu

Design Strength ≥ Required Strength

SE EXAM REVIEW COURSE —March 2017

Question

If the service uniform dead load is 100 psf and the uniform live load is 50 psf, what is the maximum ultimate uniform load?

a. 140 psf

b. 150 psf

c. 200 psf

d. 225 psf

Page 13: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Question

If the service uniform dead load is 100 psf and the uniform live load is 50 psf, what is the maximum ultimate uniform load?

a. 140 psf

b. 150 psf

c. 200 psf  1.2 DL + 1.6 LL

d. 225 psf

SE EXAM REVIEW COURSE —March 2017

Design of Beams and One‐Way Slabs

Note: bw = 12 in. for one-way slabs

Page 14: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Flexural Requirements

SE EXAM REVIEW COURSE —March 2017

Nominal Flexural Strength

• Required

– Cross section

– Reinforcement h

bw

As

Page 15: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Design Assumptions

• Static equilibrium

– External loads and moments and internal stresses

• Compatibility of strains

– Plane section before bending remains plane after bending

SE EXAM REVIEW COURSE —March 2017

Strain Compatibility

h

bw

As

0.003

Strain

Neutral axisc

Page 16: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Design Assumptions• Tensile strength of concrete in flexural calculations = 0

SE EXAM REVIEW COURSE —March 2017

Stress Block Factor, 1

0.85

0.65

4000 8000

fc’

1

05.01000

4000f85.0

'c

1

Page 17: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Nominal Flexural Strength

Mn = (C or T) (d – ) = As fy (d – )2a a

2

Mn = As fy (d – )0.5As fy0.85fc b

(Applies when tension steel yields)

SE EXAM REVIEW COURSE —March 2017

Flexural Behavior

• Strength reduction factor, Φ depends on member behavior

Curvature

Bending moment

Tension controlled

Balanced condition

Compression controlled

Page 18: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Strength Reduction Factor, Strength reduction factor, ϕ, depends on

maximum net tensile strain, εt, 

at nominal strength, Mn

dt

t

0.003

SE EXAM REVIEW COURSE —March 2017

Strength Reduction Factor, 

0.65

t = 0.002 t = 0.005

Transition

0.90

= 0.65 + (t – 0.002)(250/3)

Compression-controlled

Tension-controlled

Net Tensile Strain

Spiral

Other

0.75

Page 19: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Design For Flexure

• Nominal flexural strength

Mn = As fy (d – )

Mn = bd fy (d – )0.5d fy0.85fc

0.5As fy0.85fc b

SE EXAM REVIEW COURSE —March 2017

Design For Flexure

• Nominal strength coefficient, Rn

Rn = fy (1 – ), Mn = Mu /=

0.85fc

fy1 – 1 –

2Rn

0.85fc

0.5fy0.85fc

Mn

bd2

One Layer of Tension Reinforcement

Page 20: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Design For Flexure

• For f’c = 4,000 psi, fy = 60 ksi, and  = 1.25%

Then the previous equation reduces to

Where 

– Mu is in kip‐ft

– As is in in2

– D is in inches

– Usable where  is less than 1.5%

As = Mu4d

Simplified Approach

SE EXAM REVIEW COURSE —March 2017

0

400

800

1200

0.00 0.01 0.02 0.03

bd/A s

2n

n bdM

R

t = 0.004

t = 0.005

fc’ = 5000 psi

fc’ = 6000 psi

fc’ = 4000 psi

fc’ = 3000 psi

Design Strength

t max

Page 21: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Minimum Reinforcement for Flexural Members

As,min = 3( fc/fy)bwd 

≥ 200bwd/fy(Governs when fc < 4444 psi )

= 0.33% for f’c = 4 ksi and fy = 60 ksi

SE EXAM REVIEW COURSE —March 2017

Question

The MOST important variable affecting the flexural strength is:

a. concrete strength

b. beam depth

c. beam width

d. area of rebar

Page 22: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Question

The MOST important variable affecting the flexural strength is:

a. concrete strength

b. beam depth 

c. beam width

d. area of rebar

SE EXAM REVIEW COURSE —March 2017

Development and Splices of Reinforcement

Page 23: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Rebar Development

Why the ribs?

SE EXAM REVIEW COURSE —March 2017

Figure R12.10.2

12.11.3

12.2.1 or 12.11.2

Positive M

Negative M

Rebar Development

Page 24: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Splices of Deformed Bars and Wires in Tension

• Lap length 12 in. for Classes A and BClass A   1.0dClass B   1.3d

• d  computed from ACI 318 section 12.2, but without– 12 in. min. of 12.2, and– modification factor for excess reinforcement.

SE EXAM REVIEW COURSE —March 2017

Reinforcing Bar Details

1 inch

db

1.33(max. agg. size)

No. 3 stirrup with No. 6 bars and smallerNo. 4 stirrup with No. 7 thru No. 11 bars

1½ inchclear (7.7.1)

cc

db

Min. clear space =

ds

r = ¾ inch for No. 3 stirrups

1 inch for No. 4 stirrups

cs

bw

Page 25: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Shear Requirements

SE EXAM REVIEW COURSE —March 2017

Shear and Stirrups

Crack (saw cut)

Stirrup (bungee cord through drilled hole in beam)

Page 26: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Shear and Stirrups

After concrete cracks, shear load supported by stirrups (stretching bungee cord)

Held together by stirrup

SE EXAM REVIEW COURSE —March 2017

Shear and StirrupsUnderstanding Strut and Tie

Actually a Strut and Tie System52

Tension in Stirrup (tie)Compression in member (strut)

Page 27: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Diagonal Tension Due to Shear

Stirrups

Section

SE EXAM REVIEW COURSE —March 2017

Shear Strength

h

bw

Av at s

Page 28: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Critical Section for Shear Design

Distributed loads

d Critical section

SE EXAM REVIEW COURSE —March 2017

Critical Section for Shear Design

d

Critical section

Point load within dist. d

Page 29: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Shear Design Strength

• Design strength =  nominal strength

= 0.75

Vn = Vc + Vs

SE EXAM REVIEW COURSE —March 2017

Shear Design Strength• Vn = (Vc + Vs) ≥ Vu

• Vs = Vu –VcVn = nominal shear strength

Vc = nominal shear strength provided by concrete

Vs = nominal shear strength provided by shear reinforcement

Vu = factored shear force at section

Page 30: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Shear Strength Provided by Concrete

• Members subject to shear and flexure

(lower bound without axial tension)

Vc = 2 bwdcf'

SE EXAM REVIEW COURSE —March 2017

Shear Strength Provided by Shear Reinforcement

• Members with shear reinforcement perpendicular to axis of member

Vs =Avfytd

s d

Avfyt

45o

ds

V

Avfyt

Page 31: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Ab

sAv = 2 × Ab for two legs

Shear Reinforcement

SE EXAM REVIEW COURSE —March 2017

Shear Reinforcement

• If Vu ≤ (Vc/2), no shear reinforcement is required

• If Vu > (Vc/2), at least minimum shear reinforcement must be provided (with exceptions)

Page 32: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Minimum Shear Reinforcement 

Av, min = 0.75 bws

fyt

50bws fyt

cf'

SE EXAM REVIEW COURSE —March 2017

Maximum Stirrup Spacing

– For Vu – Vc = Vs < 4   (i.e., low shear)

s < d/2 or 24 in.

– For Vu – Vc = Vs > 4  (i.e., high shear)

s < d/4 or 12 in.

C wf ' b d

C wf ' b d

Page 33: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Shear Design – Summary

SE EXAM REVIEW COURSE —March 2017

Question

For uniform loading, the critical section for beam shear is located at:

a. face of support

b. a distance d/2 from the face of the support

c. a distance d from the face of the support

d. all sections are critical and need be checked

Page 34: Vertical Forces Review Reinforced Concrete Design

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34

SE EXAM REVIEW COURSE —March 2017

Question

For uniform loading, the critical section for beam shear is located at:

a. face of support

b. a distance d/2 from the face of the support

c. a distance d from the face of the support 

d. all sections are critical and need be checked

SE EXAM REVIEW COURSE —March 2017

R/C Beam Design Example

6 in

. S

lab

Design 18 in.× 18 in. beam

d =18 in. – .5 in. – 0.5 in. –0.5 in.= 15.5 in.

f’c = 4ksi, fy = 60ksi

30 ft 0 in. typical (centerline)

Live load = 50 psf

SDL = 10 psf 15 f

t-

0 in

.15

ft-

0 in

.

Page 35: Vertical Forces Review Reinforced Concrete Design

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35

SE EXAM REVIEW COURSE —March 2017

R/C Beam Design Example

• Step 1: Geometry

d = 15.5 in. =

18‐1.5‐0.5‐0.5

h = 18”

b = 18 inches

SE EXAM REVIEW COURSE —March 2017

R/C Beam Design Example• Step 2: Determine dead load

– Dead load slab = 6”/(12’’/ft)*150pcf  =  75 psf– Dead load beam = 1.5ft*(1.5ft‐0.5ft)*150pcf/15’ =       15 psf– Superimposed dead load (given)  = 10 psf

Total dead load  = 100 psf

• Step 3: Determine ultimate uniform load

– wult = 1.2 DL+1.6 LL = 1.2(100 psf) + 1.6(50 psf)  =  200 psf

Page 36: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

R/C Beam Design Example• Step 4: Determine ultimate moments and longitudinal steel (top and 

bottom) by simplified approach (use ACI coefficients for moments)

– End moment at face of support = wult Ln2/10 

= 200psf × 15ft × (30ft – 1.5ft)2 / 10 = 244 kip‐ft = Mu‐

As = Mu / (4d) = 244 / (4 × 15.5) = 4.0 in2 use 5#8 top 

( = 1.4% < 1.5%  OK for simplified approach)

– Midspan positive moment = wult Ln2/16

= 200psf × 15ft × (30ft – 1.5ft)2 / 16 = 152 kip‐ft = Mu+

As = Mu / (4d) = 152 / (4 × 15.5) = 2.5 in2 use 4#8 bot

SE EXAM REVIEW COURSE —March 2017

R/C Beam Design Example

• Step 5: Shear design

– Ultimate shear at distance d from support

• Vu = 200 psf × 15ft × {30ft/2 – [1.5ft+15.5in./(12in./ft)]}  = 39 kips

– Determine Vc (concrete component)

• Vc = 2         = 2 ( ) × 18in. × 15.5in.   = 35 kips

– Determine required Vs (steel component)

• Vs req = Vu/ – Vc = 39 kips / 0.75 – 35 kips          = 17 kips

– Determine required Av/s for stirrups

• Av/s = Vs/(fy d) = 17 kips / (60 ksi × 15.5in.)           = 0.018 in2/in

– Select stirrups

• Use #3 at 6 inches (Av/s provided = 2 × 0.11/6 = 0.037 in2/in OK)

4 , 0 0 0 C wf ' b d

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SE EXAM REVIEW COURSE —March 2017

R/C Beam Design Example

• Summary

d = 15.5in. =

18‐1.5‐0.5‐0.5

h = 18in.

b = 18”

4#8

5#8

#3 at 6 in.

SE EXAM REVIEW COURSE —March 2017

Progressive Collapse  vs. Structural Integrity

• Design against progressive collapse requires extensive analysis and design assuming loss of one member at a time

• ACI 318 Structural Integrity Requirements Call for Minor Changes in Detailing of Reinforcement—no analysis or design needed

Page 38: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Ronan Point(1968)

Explosion on 18th

floorof  22 floors

Example

SE EXAM REVIEW COURSE —March 2017

Explosion in lower story

Local damage

Example

Page 39: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

R7.13 – What is Structural Integrity?

• It is the intent of the structural integrity provisions to improve the redundancy and ductility of structures, and thereby reduce the risk of failure or collapse of parts or all of a building due to damage occurring to a relatively small area of a building.

• The overall integrity of the structure can be substantially enhanced by minor changes in the detailing of reinforcement.

• The intent is to avoid “house of cards” type collapses.

SE EXAM REVIEW COURSE —March 2017

Conven onal Flexural Reinforcement―3‐Span Beam

Flexural Reinforcement

Bending Moment DiagramGreater of:

‐ d‐ 12 db‐ Span/16

6 in.(12.11.1)

(12.12.3)

Page 40: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Perimeter Beams and Other Beams

Largest of A+s1/4 or A+

s2/4 (Min. 2 Bars)

• Continuous

• Class B tension splice

• Mechanical or welded splice

A+s1

A+s2

A+s1/4

SE EXAM REVIEW COURSE —March 2017

Perimeter Beams

Largest of A–s1/6 or A–

s2/6 (Min. 2 Bars)

• Continuous

• Class B tension splice

• Mechanical or welded splice

A-s1 A-

s2

Page 41: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Perimeter Beams

or

Min. 135o Hook

Note: Size and spacing of stirrups is based on shear and/or torsion demand.

SE EXAM REVIEW COURSE —March 2017

Perimeter Beams

OR

Unacceptable OK

Crosstie

Page 42: Vertical Forces Review Reinforced Concrete Design

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SE EXAM REVIEW COURSE —March 2017

Columns

SE EXAM REVIEW COURSE —March 2017

Design Axial Strength

Pn,max ≥ Pn ≥ Pu

Spiral

Pn,max = 0.85[0.85fc(Ag – Ast) + fyAst ]

Tied

Pn,max = 0.80[0.85fc(Ag – Ast) + fyAst ]

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Pc

Axial Strength – Concrete Contribution

Concrete

Max. Pc = 0.85fcAc = 0.85fc(Ag – Ast)

L

P

SE EXAM REVIEW COURSE —March 2017

L

P

Steel

Ps

Axial Strength – Steel Contribution

Max. Ps = fyAst

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SE EXAM REVIEW COURSE —March 2017

L

P = Po

Po = Pc + Ps = 0.85fc(Ag – Ast) + fy Ast

Axial Strength

SE EXAM REVIEW COURSE —March 2017

Pn,max = Constant × Po

Constant = 0.85 (Spiral)

= 0.80 (Tied)

Nominal Axial Strength – (Pn,max )

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SE EXAM REVIEW COURSE —March 2017

Strength Reduction Factor

• Compression‐controlled section

– Tied = 0.65

– Spiral = 0.75

Design axial strength = Pn,max

SE EXAM REVIEW COURSE —March 2017

Preliminary Column Sizing• Reinforcement ratios in the range of 1–2% are usually the most economical.

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SE EXAM REVIEW COURSE —March 2017

Nonslender Square Tied Columns

Pn(max) = 0.80Ag[0.85fc’ + ρg(fy – 0.85fc’)]

ρg = Ast/Ag, %

Pn(max) = Pu

(kips)

= 0.65fc

’ = 4000 psify = 60,000 psi

SE EXAM REVIEW COURSE —March 2017

Nonslender Tied Columns

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SE EXAM REVIEW COURSE —March 2017

Short Tied Column Axial Design

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.5% 0.6% 0.7% 0.8% 0.9% 1.0% 1.1% 1.2% 1.3% 1.4% 1.5%

Pu / Ag    (ksi)

= As / Ag

Simplified Column Capacity (short tied column, fy = 60 ksi)

f’c = 6,000 psi

f’c = 5,000 psi

f’c = 4,000 psi concrete

Per ACI 10.8.4 

(not allowed for special moment frames for seismic)

SE EXAM REVIEW COURSE —March 2017

Short Tied Column Axial Design

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.5% 0.6% 0.7% 0.8% 0.9% 1.0% 1.1% 1.2% 1.3% 1.4% 1.5%

Pu / Ag    (ksi)

= As / Ag

Simplified Column Capacity (short tied column, fy = 60 ksi)

f’c = 6 ksi

f’c = 5 ksi

f’c = 4 ksi concrete

1% steel is generally optimum At 1% steel, Column Capacity (Pu / Ag) is approx. = f’c / 2

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SE EXAM REVIEW COURSE —March 2017

Circular Ties for Circular Columns7.10.5.4 —Where longitudinal bars are located around the perimeter of a circle, a complete circular tie shall be permitted. 

The ends of the circular tie shall overlap by not less than 6” and terminate with standard hooks that engage a longitudinal column bar. 

Overlaps at ends of adjacent circular ties shall be staggered around the perimeter enclosing the longitudinal bars.

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SE EXAM REVIEW COURSE —March 2017

Combined Flexural and Axial LoadThis image cannot currently be displayed.

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SE EXAM REVIEW COURSE —March 2017

Interaction Diagram

h

b

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SE EXAM REVIEW COURSE —March 2017

Interaction Diagram

Moment, Mn

Axi

al L

oad,

Pn

– Pure Compression

Po = 0.85fc(Ag – Ast) + fy AstThis image cannot currently be displayed.

cu = 0.0031

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SE EXAM REVIEW COURSE —March 2017

Interaction Diagram

Moment, Mn

Axi

al L

oad,

Pn 2

This image cannot currently be displayed.

cu = 0.003

SE EXAM REVIEW COURSE —March 2017

Interaction Diagram

Moment, Mn

Axi

al L

oad,

Pn

3

This image cannot currently be displayed.

cu = 0.003

t = 0

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SE EXAM REVIEW COURSE —March 2017

Interaction Diagram

Moment, Mn

Axi

al L

oad,

Pn

4

This image cannot currently be displayed.

cu = 0.003

t = y

SE EXAM REVIEW COURSE —March 2017

Moment, Mn

Axi

al L

oad,

Pn

5

This image cannot currently be displayed.

cu = 0.003

t > y

Interaction Diagram

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SE EXAM REVIEW COURSE —March 2017

Moment, Mn

Axi

al L

oad,

Pn

6

This image cannot currently be displayed.

cu = 0.003

t >> y

Interaction Diagram

SE EXAM REVIEW COURSE —March 2017

Simplified Interaction DiagramThis image cannot currently be displayed.

Zone 1Zone 2

Zone 3

Axial load

Bending moment

1

2

3

4

5s = y

s = 0

0.003

0.003

s = y /2

0.003

Strain

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SE EXAM REVIEW COURSE —March 2017

Strength Reduction Factor, 

0.65

t = 0.002 t = 0.005

Transition

0.90

= 0.65 + (t – 0.002)(250/3)

Compression-controlled

Tension-controlled

Net tensile strain

Spiral

Other

0.75

SE EXAM REVIEW COURSE —March 2017

This image cannot currently be displayed.

Nominal strengthPn, Mn

Design strengthPn, Mn

Po

Pn, max = 0.80Po

Compression-controlled

Balanced condition

Po

Pn, max

Interaction Diagram

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SE EXAM REVIEW COURSE —March 2017

This image cannot currently be displayed.

Pn, Mn

Pn, Mn

Compression-controlled

Tension-controlled = 0.90

Transition

Interaction Diagram

SE EXAM REVIEW COURSE —March 2017

This image cannot currently be displayed.

Nominal strength Pn, Mn

Design strength Pn, Mn

+ (Pu, Mu)OK

Interaction Diagram

+ (Pu, Mu)NG

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SE EXAM REVIEW COURSE —March 2017

Splices 

Moment

Axi

al lo

ad

fs = 0

Zone 1

Zone 1: Compression

Zone 2

Zone 2: Class A or B

fs = 0.5fy

Zone 3: Class B

Zone 3fs = fy

fs 0.5fy

SE EXAM REVIEW COURSE —March 2017

Slender ColumnsThis image cannot currently be displayed.

This image cannot currently be displayed.

Slender Columns

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SE EXAM REVIEW COURSE —March 2017

Question

What is the strength reduction factor, , for a tied column?

a. 0.65

b. 0.75

c. 0.90

d. Varies from 0.65 to 0.90 based on steel strain

SE EXAM REVIEW COURSE —March 2017

QuestionWhat is the strength reduction factor, , for a tied column?

a. 0.65

b. 0.75

c. 0.90

d. Varies from 0.65 to 0.90 based on steel strain  

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SE EXAM REVIEW COURSE —March 2017

Two‐Way Slabs

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SE EXAM REVIEW COURSE —March 2017

Two‐way Concrete Floor Systems

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Flat plate Flat slab

Waffle slab

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Two-way beam supported

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SE EXAM REVIEW COURSE —March 2017

Drop PanelThis image cannot currently be displayed.

d d1

/6 /6 h/4

h

SE EXAM REVIEW COURSE —March 2017

Shear Requirements for Slabs and Footings

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SE EXAM REVIEW COURSE —March 2017

Shear Strength for Slabs and Footings

• Critical shear sections

• Nominal shear strength of concrete

• Shear reinforcement

SE EXAM REVIEW COURSE —March 2017

Shear Strength

• Critical shear sections

– One‐way shear

– Two‐way shear

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SE EXAM REVIEW COURSE —March 2017

One‐Way Shear1

2

Tributary area

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Critical section

d

Slab plan viewd = effective flexural depth of slab

SE EXAM REVIEW COURSE —March 2017

Vu = 2

Vu = qu × Tributary area

One‐Way Shear

This image cannot currently be displayed.

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SE EXAM REVIEW COURSE —March 2017

Two‐Way Shear – Tributary AreasThis image cannot currently be displayed.

SE EXAM REVIEW COURSE —March 2017

Two‐Way Shear1

2

Tributary area

This image cannot currently be displayed. This image cannot currently be displayed.

This image cannot currently be displayed.

This image cannot currently be displayed.

Critical perimeter, bo

d/2

Slab plan viewd = effective flexural depth of slab

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SE EXAM REVIEW COURSE —March 2017

Shear Strength

• Select the maximum of three conditions

1. Maximum nominal shear strength, Vc

Vc = 4This image cannot currently be displayed.

SE EXAM REVIEW COURSE —March 2017

• Nominal shear strength, Vc

2. Reduction for rectangular columns

Vc = 2 + 4

= ratio of long to short column dimensions

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Shear Strength

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SE EXAM REVIEW COURSE —March 2017

• Nominal shear strength, Vc

3. Check for column location

Vc =sdbo

+ 2

s = 40 for interior columns

= 30 for edge columns

= 20 for corner columns

(Think 10 x the # of supported sides)

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Shear Strength

SE EXAM REVIEW COURSE —March 2017

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Critical Perimeter

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SE EXAM REVIEW COURSE —March 2017

Headed Shear Stud Reinforcement for SlabsThis image cannot currently be displayed.

1st Stud d/2 Stud Spacing

d/2 0.75d for prestressed slabs 

and footings

Section A‐A

Studs with base rail

Av = cross‐sectional area of studs on any peripheral line 

SE EXAM REVIEW COURSE —March 2017

This image cannot currently be displayed.

Headed Shear Stud Reinforcement for Slabs

Interior Column

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SE EXAM REVIEW COURSE —March 2017

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Two‐Way Slabs: Shear Stress at Critical Section (Shear Studs Compared to Stirrups)

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Stirrups (11.11.3) Shear Studs (11.11.5)This image cannot currently be displayed.

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This image cannot currently be displayed.

SE EXAM REVIEW COURSE —March 2017

Question

For the two‐way punching shear check for a slab, the equation (4) represents:a. the upper bound on Vcb. the lower bound on Vcc. Vcd. none of the above

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SE EXAM REVIEW COURSE —March 2017

Question

For the two‐way punching shear check for a slab, the equation (4 ) represents:a. the upper bound on Vcb. the lower bound on Vcc. Vcd. none of the above

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SE EXAM REVIEW COURSE —March 2017

Prestressed Concrete

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This image cannot currently be displayed.

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SE EXAM REVIEW COURSE —March 2017

Prestressed Concrete: General Principles

This image cannot currently be displayed.

Tension

Compression

No tension

Area A

Prestressing tendon

Ff

FA

Prestress Stress due to loading

Combined stresses

SE EXAM REVIEW COURSE —March 2017

Methods of Prestressing Concrete Members

• PretensioningThis image cannot currently be displayed.

This image cannot currently be displayed.• Post-tensioning

Anchorage

BeamBonded tendon

Jack

Stressing bed Abutment

Jacking end anchor

Jack

Unbonded tendon in ductBeam

Dead end anchor

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SE EXAM REVIEW COURSE —March 2017

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Prestressed Concrete Beams

SE EXAM REVIEW COURSE —March 2017

Advantages of Post‐tensioned Structures

• Reduced structural depth for lower story heights and reduced dead load– Additional savings in labor and material for M/E/P, elevator, and cladding

• Long economical spans

• Wide flexibility and variation in design

• Reduced cracking

• However, additional inspections are required.

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SE EXAM REVIEW COURSE —March 2017

Unbonded Tendons

• The prestressing strand is prevented from bonding and is free to move, relative to the surrounding concrete.

– 7‐wire strands (0.5 inch diameter)

– Sheathing

– Anchor

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SE EXAM REVIEW COURSE —March 2017

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Unbonded Tendons

• Prestressing force can only be transferred to the concrete through the anchorage

– Casting: 5 in. by 2¼ in. typical

– WedgesThis image cannot currently be displayed.

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Typical Tendon ProfileThis image cannot currently be displayed.

Continuous post‐tensioned beam

Drape Post‐tensioningtendon 

Neutral axis

DL3CBA L1 L2

SE EXAM REVIEW COURSE —March 2017

Post‐Tensioned Slabs (Option 1)This image cannot currently be displayed.

This image cannot currently be displayed.

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SE EXAM REVIEW COURSE —March 2017

This image cannot currently be displayed.

Post‐Tensioned Slabs (Option 2)

Not less than 300bwd/fy in each direction. Must be located inside column vertical bars.

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, Butd

SE EXAM REVIEW COURSE —March 2017

Structural Design Standards Relevant for Reinforced Concrete Design

In order of precedence of controlling requirements for forces and concrete design:• International Building Code: 

IBC 2012 Edition

• Minimum Design Loads for Buildings and Other Structures: 

ASCE 7‐10

• Building Code Requirements for Structural Concrete: 

ACI 318‐11

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Recommended References and Additional Study Materials

• PCA Notes on ACI 318‐11 Building Code Requirements for Structural Concrete  FREE PDF

• CRSI Design Handbook

• Design of Concrete Structures (McGraw Hill)

• Reinforced Concrete Mechanics and Design (Prentice Hall)

• PCA’s Simplified Design Manual  FREE PDF

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SE EXAM REVIEW COURSE —March 2017

“Engineering does not tell men what they should want or why they want it.  

Rather it recognizes a need and tries to meet it.”

‐ Hardy Cross, 1952This image cannot currently be displayed. This image cannot currently be displayed.

This image cannot currently be displayed.

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SE EXAM REVIEW COURSE —March 2017

NCSEA Structural Engineering Exam Review Course

Vertical Forces ReviewReinforced Concrete Design

Spring 2017

Presented by Lawrence Novak, SE, F.ACI, F.SEI, CERT, LEED®AP

Senior Director of Structural Engineering & Codes