Night School Session 1 - Fundamental Concepts, Part i (2)

Lecturer: Tom Murray, P.E., PhD Emeritus Professor, Virginia Virginia Tech

AISC NIGHT SCHOOL: FUNDAMENTALS OF CONNECTION DESIGN

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Copyright © 2013 American Institute of Steel Construction

Session 1 Fundamental Concepts, Part I January 14, 2013 1



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Fundamentals of Connection Design Session 1: Fundamental Concepts Part I January 14, 2013 Presented by Thomas M. Murray, Ph.D., P.E. Emeritus Professor Virginia Tech, Blacksburg, Virginia

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SCHEDULE • January 14, 2013 Fundamental Concepts Part I • January 28, 2013

Fundamental Fundament al Concepts Part II

• February 4, 2013

Shear Connections Part I

• February 11, 2013 Shear Connections Part II • February 25, 2013 Moment Connections Part I • March 4, 2013

Moment Connections Part II

• March 11, 2013

Moment Connections Part III

• March 18, 2013

Bracing Connections

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REFERENCE DOCUMENTS and NOMENCLATURE

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SPECIFICATION AND MANUAL PROVISIONS AISC/ANSI 360-10 Specification 360-10 Specification for for Structural Steel Buildings Buildings Chapter D Design D Design of Members Members for Tension Chapter J Connection, Joints and Fasteners 14th Edition AISC Manual of Steel Construction for Structural Joints Using RCSC Specification RCSC Specification for ASTM A325 or A490 Bolts

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SPECIFICATION AND MANUAL PROVISIONS

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Lecturer: Tom Murray, P.E., PhD Emeritus Professor, Virginia Tech


Nomenclature LRFD: Load and Resistance Factor Design Factored Loads and Resistance Factors, Required Strength < Design Strength R u < R n where R u = Required Strength using LRFD Load Combinations (Factored Loads) = Resistance Factor R n = Nominal Strength R n = Design Strength

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Nomenclature ASD: Allowable Strength Design Service Loads and Factors of Safety, Ω Factored Loads < Allowable Strength R a < R n/ Ω where R u = Required Strength using ASD Load Combinations (Service Loads) R n = Nominal Strength Ω = Factor of Safety R n /Ω = Allowable Strength

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Nomenclature Note: Available Strength is generic for Design Strength and Allowable Strength in the Specification. AISC 360-10 Specification for Structural Steel Buildings ► AISCS 14th Ed. Steel Construction Manual ►AISCM RCSC Specification ► Bolt Spec. 11

Nomenclature For the course: AISC 360-10 Specification for Structural Steel Buildings ► AISCS 14th Ed. Steel Construction Manual ►AISCM RCSC Specification ► Bolt Spec.

12





Nomenclature Resistance Factors: Ductile Limit States:

= 0.9

Example: Tension Yielding Non-Ductile Limit States: = 0.75 Example: Tension Rupture

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Steel Properties A36 Steel: Primarily Plates and Angles Fy = 36 ksi (Tension Yield Stress) Fu = 58 ksi (Tension Rupture Strength) A992 Steel: Beams and Columns Fy = 50 ksi

Fu = 65 ksi

Note: Shear Yield = 0.6 F y Shear Rupture = 0.6 F u 14





FUNDAMENTAL CONCEPTS PART I

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TOPICS • Types of Connections • Classification of Beam-to-Column Connections • Limit States in the Load Path • Basic Bolt related Limit states and Detailing • Basic Weld Related Limit States and Detailing

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CONNECTION TYPES • TENSION CONNECTIONS Direct Loaded Hanger Light and Heavy Bracing

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Hanger Connection









CONNECTION TYPES • COMPRESSION CONNECTIONS Column Splice Beam Bearing Plate Column Base Plate

21

Please do not design a beam bearing connection like one.

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CONNECTION TYPES • FRAMING (SHEAR) CONNECTIONS Double Angles Single Angle Shear Tab Shear End-Plate Tee Connections Seated 24





Double Angles

Single Angle





Shear Tab

Shear End-Plate





Tee Connection

CONNECTION TYPES • MOMENT CONNECTIONS Flange Welded Flange Plate Welded Flange Plate Bolted Tee-Stub Flange Angle Moment End-Plate 30





Flange Welded

Flange Plate Bolted





Tee-Stub

33

Flange Angle

34





Moment End-Plate

CLASSIFICATION OF CONNECTIONS

36





Classification of Connections Classification: All techniques depend on member length and moment diagram/magnitude of moment. Example: Beam Line/Connection Curve

37

Classification of Connections FR Moment Connection M = 0.9M F

M , t n e m o M

Typical Beam Line

PR Moment Connection

M = 0.2MF PR Pinned

Rotation,

S

38





Classification of Connections • Fully Restrained – FR Flange Welded Flange Plate Welded or Bolted Tee-Stub Moment End-Plate

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Classification of Connections • Partially Restrained – PR Flush End-Plate Flange Angle Double Angles

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Classification of Connections • Partially Restrained/Pinned – PR Double Angles Single Angle Shear Tab Shear End-Plate Seated Connections

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LIMIT STATES IN THE LOAD PATH

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Load Paths/Limit States Example: Tension Connection 5/16 5/8" PL

2L 4 x 3 1/2 x 1/4 LLBB

A

Tu

3/4" Dia. A325 Bolts, Typ

A

Section A-A

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Load Paths/Limit States 2

1

A

Tu

3,4 4 2

1

A

1. Angle Yielding 2. Angle Rupture including Shear Lag 3. Angle Bolt Bearing/Tear Out 4. Angle Block Shear 44





Load Paths/Limit States 5.

Bolt Shear

6.

Plate Bearing / Tear Out

7.

Plate Block Shear (N/A)

8.

Plate Rupture

9.

Plate Yield

5

9 8

10 6,7

10. Weld Rupture 98

7

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BASIC BOLT RELATED LIMIT STATES AND DETAILING

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Bolt Types A307 – machine bolts Ft = 45 ksi Group A – high strength bolts Ft = 90 ksi Group B – high strength bolts Ft = 113 ksi Ft = tensile strength from AISCS Table J3.6 47

Bolt Types Group A – high strength bolts – Ft = 90 ksi ASTM A325, A325M, F1852, A354 Grade BC, A449 Group B – high strength bolts – Ft = 113 ksi ASTM A490, A490M, F2280, and A354 Grade BD Note: F1852 and F2280 are “Twist-Off” Bolts 48





A325 and A490 Bolts 3/4 in. Dia. 7/8 in. Dia.

1 1/4 in. Dia.

Note: Thread length is a function of bolt diameter 49

ASTM F1852 Twist-Off Bolt

Note: Requires a special tightening tool.

50





Bolts: Connection Types Types of Connections: (a) Bearing Type N - threads included in shear plane X - threads excluded from shear plane (b) Slip Critical SC - slip critical (friction) Example Designations: ¾ in. A325 – N 1 in. A490 – SC 51

Bolts: Tightening -N or -X Bearing Type Bolts

• Snug Tight (Tightened so that a wrench is needed to remove the nut.) • Pretensioned with no faying surface preparation)

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Bolts: Tightening -SC Slip Critical Type Bolts Requires faying surface preparation and field inspection Pretensioning - Turn of Nut Method - Calibrated Wrench - Direct Tension Indicator - Twist-Off Bolt

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Bolts: Pretensioned Installation Turn of Nut Tightening

Θ from Bolt Spec. Table 8.2 Example: Bolt Length < 4db, Θ = 1/3 Turn 54





Bolts: Pretensioned Installation Calibrate Wrench Tightening

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Bolts: Pretensioned Installation Direct Tension Indicator

56





Bolts: Pretensioned Installation Twist Off Bolt

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Bolt Holes Hole Types and Dimensions (Table J3.3)

• Standard (STD) db + 1/16 in. • Oversized (OVS) db + (3/16 in. to 5/16 in.) • Short Slots (SS) STD by OVS + 1/16 in. • Long Slots (LS) STD by up to 2.5 bolt diameters (Standard Hole, STD, is Default for Course.) 58





Use of Slotted Holes

59

Bolt Tensile Strength Design Tensile Strength of one Bolt, rt (AISCS – J3.6) = 0.75 rt = Ft Ab Ab = nominal bolt area Ft = nominal strength from Table J3.2 rt = 0.75 Fv Ab = Design Tensile Strength Note: Tensile area is accounted for in F t.0 60





Bolt Shear Strength Design Shear Strength of one Bolt, rv (AISCS – J3.6) = 0.75 rv = Fv Ab Ab = nominal bolt area Fv = nominal strength from Table J3.2 rv = 0.75 Fv Ab = Design Shear Strength Note: Area at threads is accounted for in Fv. 61

Bolt Nominal Strengths

62





Bolt Nominal Strengths Table J3.2 Continued

63

Bolts: Connection Length Effect Table J3.2 Footnote [b]

64





Bolt Shear Strength Design Strength of the Connection R v = 0.75 rv x Number of Bolts x Number of Shear Planes φTn / 2 φTn φTn / 2

Ex. For three bolts per row, there are twelve (3x2x2) shear planes in this connection. 65

Bolt Slip (-SC Connections) Section J3.8. High-Strength Bolts in SlipCritical Connections rsc =

Du hf Tb ns

(J-3.4)

φ = 1.00 for STD and SS Perpendicular = 0.85 for OVS and SS Parallel = 0.70 for long slots Design Strength: rsc =

Du hf Tb ns

Note: Section J3.8 of ASICS indicates that Eq. J-3.-4 is “available” strength. It is actually “nominal strength.

66





Bolt Slip (-SC Connections) Section J3.8. High-Strength Bolts in SlipCritical Connections Continued rsc =

Du hf Tb ns

(J-3.4)

μ = mean slip coefficient depending on faying surface preparation: Class A – 0.3 Class B – 0.5 Du=1.13, a multiplier that reflects the ratio of the mean installed pretension to the specified minimum bolt tension 67

Bolt Slip (-SC Connections) Section J3.8. High-Strength Bolts in SlipCritical Connections Continued rsc =

Du hf Tb ns

(J-3.4)

hf = factor for fillers = 1.0 for no fillers or one filler = 0.85 for two or more fillers Tb= minimum fastener pretension, Table J3.1 Ns= number of shear planes 68





Bolt Slip (-SC Connections) IMPORTANT: • Slip Critical Connections are expensive because of faying surface preparation, tightening and inspection requirements. • SC-Connections are not needed for typical framing connections and most moment connections. • SC-Connections may be needed when dynamic or vibration loads are present or may be used to control drift in frames and are required in some moment connections. 69

Bolt Slip (-SC Connections)

70





Bearing Bolts: Combined Shear and Tension Strength f t

f v

Bearing Bolt Interaction Diagram 71

Bolts: Combined Tension and Shear Strength in Bearing AISCS J3.7 Combined Tension and Shear Bearing R n F'nt

F'nt A b 1.30Fnt

and f v

0.75 Fnt Fnv

f v

f t

Fnt

Fnv

f v

nominal tensile stress from Table J3.2 Fnv = nominal shear stress from Table J3.2

Fnt

f v =

the required shear stress = Vu/ Ab 72





Bolt Holes in Calculations • For all hole related limit states except tear out, the effective hole diameter used in calculations is d h = dh + 1/16 in. The additional 1/16 in. accounts for damage from punching and drilling.

• For tear out, the actual hole diameter is used. Note: For bearing, the bolt diameter is used. 73

Bolts: Bearing and Tear Out T

Bearing

u

T

Tear-Out

Lc

u

Lc 74





Bolts: Bearing and Tear-Out

Tear-Out

Bearing

75

Bolts: Bearing and Tear-Out Section J3.10 Bearing Strength at Bolt Holes = 0.75 For standard, oversized, and short-slotted holes R n = 1.2 L ct Fu < 2.4 db t Fu 1.2 L ct Fu is the tear out strength 2.4 db t Fu is the bearing strength Lc = clear distance between between holes or to edge Lc

T

Lc 76


76




Example: Determine the Bearing/Tear-Out Design Strength PL 1/2" x 7" A36, Fu = 58 ksi 11 2"

φTn

4" 11 2" 11 2" 3"

3/4" A325-N Bolts Std. Holes = 13/16 in.

Bearing Strength at Holes: 2.4dbtFu = 2.4 x 0.75 x 0.5 x 58 = 52.2 k 77

Example: Determine the Bearing/Tear-Out Design Strength Tear-Out Strength: Edge Bolts: L c = 1.5 – 13/32 = 1.09 in. 1.2LctFu = 1.2 x 1.09 x 0.5 x 58 = 37.9 k < 52.2 kips Other Bolts: L c= 3.0 – 13/16 = 2.19 in. 1.2 L ct Fu = 1.2 x 2.19 x 0.5 x 58 = 76.2 k > 52.2 k 78





Example: Determine the Bearing/Tear Out Design Strength Design Strength: Tn = 0.75 [2 x edge + 2 x other] = 0.75 [2 x 37.9 + 2 x 52.2] PL 1/2" x 7" A36, uF= 58 ksi

=135.2 k 11 2" 4" 11 2"

φTn

11 2" 3"

3/4" A325-N Bolts Std. Holes 79

Bolts: Minimum Spacing and Edge Distance e

s

e s

Tu

e

Section J3.3 Minimum Spacing The distance between centers of standard, oversized, or slotted holes, shall not be less than 2 2/3 times the nominal diameter of the fastener; a distance 3d is preferred . Typical spacing when db < 1 in. is 3 in. 80





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BASIC WELD RELATED LIMIT STATES AND DETAILING

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Weld Rupture J2. Welds J2.4. Design Strength Design Strength = Fw Aw.

θ

For Fillet Welds Weld φ = 0.75 Fw = 0.60 FEXX (1.0 + 0.50 sin 1.5 ) FEXX = electrode strength, ksi = angle of loading measured from the weld longitudinal axis, degrees = (angle of attack)

Tu

83

Weld Rupture Fw = 0.60 FEXX (1.0 + 0.50 sin 1.5 )

0o Fw

0.6FEXX

90o Fw

o

45 Fw

1.5x0.6FEXX

1.3x0.6FEXX 84





Weld Rupture – Special Case

Tu

R wt

°

R wl °

R n = max R wl + R wt 0.85R wl + 1.5R wt R wl and R wt are the weld strengths with θ = 0o. 85

Weld Rupture: Effective Areas t

t

t

teff = 0.707 t

t

for t < 3/8” teff = t for t > 3/8” teff = t + 0.11”

FCAW, GMAW, SMAW (Manual Welding)

SAW (Machine Welding) 86





Weld Rupture: SMAW Weld Example:

= 00

1/16

1"

E70xx

R n = 0.75 (0.6x70)(0.707x 1/16) = 1.392 k/in/1/16 Example:

1/4

5"

E70xx

Let D = no. of 1/16’s R n = 1.392 D Lweld= 1.392 x 4 x 5 = 27.84 k 87

Minimum Fillet Weld Sizes

88





Maximum Fillet Weld Size Maximum Fillet Weld Size: (AISCS – J2.2b) tp < ¼ in. tw = tp 1/16"

tp > ¼ in. tw = tp – 1/16 in.

89

Base Metal Strength at Weld Section J4.1 Shear Rupture Strength The design rupture strength for the limit state of rupture along a shear failure path in the affected elements of connected members shall be taken as R n = 0.75 (0.6 Fu Anw) Where Anw = area of the element at the weld Fu = tensile strength of base metal 90





Example: Determine Tn for Welds PL 3/8" x 8"

A36 Steel Fu = 58 ksi

E70XX

1/4

φTn PL 5/16" x 5"

5" Weld Rupture: Tn.= (1.392x4) (5x2) = 55.7 k Base Metal: Tn.= 0.75 (0.6 Fu Anw) = 0.75 (0.6x58) (5/16) (5x2) = 81.6 k Tn = 55.7 k 91

End of Session 1 Thank You for Attending Next Up 92



Night School Session 1 - Fundamental Concepts, Part i (2)

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