1. Tension Members Last Time
Structural Elements Subjected to Axial Tensile Forces
Trusses
Bracing for Buildings and Bridges
Cables in Suspension and Cable-Stayed Bridges

2. Gross Area – Specs D3.1 p 16.1.27 Last Time
Gross Area Ag:
Total Area of Main Body of Member

3. Net Area – Specs D3.2 p 16.1.27 Last Time
Net Area An :
Welded Connections An = Ag
Bolded Connections
An = Ag - Area of Holes

4. Net Area Last Time
Size of hole is larger than size of the bolt dh=db +1/16”
Additional 1/16” of material is damaged during drilling or punchning of holes (Commentary D3.2 p )

5. Staggered Fasteners Last Time
Geometry Constraints
Space Limitations

6. Net Area - Effect of Staggered Holes AISC Specs D3.1 Last Time
Reduced diameter T g s
g = gage
s = spacing
Failure paths on net section

7. Net Area - Gage Distance for an Angle Last Time
For holes on different legs

8. Effective Net Area – Specs D3.3 p 16.1.28 Last Time
Ae=AU
A = Area that depends on type of connection
A=Ag for welded
A=An for bolted
U = shear lag coefficient (accounts for eccentricities)

9. Shear Lag Factor Last Time
General category for any type of tension member except plates and round HSS with
Plates
Round HSS with
Alternative values for single angles
Alternative values for W,M,S and HP shapes

10. l Length of the connection
1. General category for any type of tension member except plates and round HSS with Last Time
Distance from centroid of connected area to the plane of the connection
l Length of the connection

11. 1. General category for any type of tension member except plates and round HSS with Last Time

12. 1. General category for any type of tension member except plates and round HSS with Last Time

13. a. Longitudinal welds on sides only
2. Plates Last Time
U=1.0
since cross section has one element and it is connected
Special Cases
a. Longitudinal welds on sides only

14. b. Transverse welds only (uncommon)
2. Plates Last Time
U=1.0
since cross section has one element and it is connected
Special Cases
b. Transverse welds only (uncommon)
An net area of directly connected members

15. 3. Round HSS with Last Time

16. 4. Alternative values for single angles Last Time
2 or 3 fasteners in direction of loading
4 fasteners in direction of loading

17. 5. Alternative values for W,M,S and HP shapes Last Time
Connected through flange with 3 or more fasteners in direction of loading

18. 5. Alternative values for W,M,S and HP shapes Last Time
Connected through flange with 3 or more fasteners in direction of loading

19. 5. Alternative values for W,M,S and HP shapes Last Time
Connected through web with 4 or more fasteners in direction of loading

20. Block Shear Last Time

21. Block Shear Chapter D User Note -> J4.3 (p. 16.1-112) Last Time
Anv: net shear area
Ant : net tension area
For angles and gusset plates

22. Block Shear Chapter D User Note -> J4.3 (p. 16.1-112) Last Time
Anv: net shear area
Ant : net tension area
AISC
Ubs=1 for angles, gusset plates and most coped beams
See AISC Commentary J4.3 for other less common cases

23. Design of Tension Members Tables for the Design
TODAY
Design of Tension Members
Tables for the Design
Threaded Rods and Cables

24. Design of Tension Members
Objective
Find a member with adequate gross and net areas
Find a member that satisfies L/r<300
Does not apply to cables and rods
Available Strength
(Nominal Resistance)
Required Strength
LRFD
max
LRFD
min
ASD
etc
max
ASD
min

25. Design of Tension Members
Determine required Area
LRFD
To prevent yielding
To avoid fracture
Yielding controls if

26. Design of Tension Members
Determine required Area
ASD
To prevent yielding
To avoid fracture
Yielding controls if

27. Step 1: Required Strength
LRFD - Example
Tension member with a length 5’-9” resists D=18 kips and L=52 kips
Select a member with rectangular cross section, A36 steel and one line 7/8” bolts
Step 1: Required Strength
Step 2: Required Areas

28. Step 3: Plate Selection based on Ag
LRFD - Example
Tension member with a length 5’-9” resists D=18 kips and L=52 kips
Select a member with rectangular cross section, A36 steel and one line 7/8” bolts
Step 3: Plate Selection based on Ag
Try thickness t = 1 in
Choose PL 1 X 3-1/2
See Manual pp1-8 for availability of plate products

29. OK LRFD - Example Step 4: Check Effective Area
Tension member with a length 5’-9” resists D=18 kips and L=52 kips
Select a member with rectangular cross section, A36 steel and one line 7/8” bolts
Step 4: Check Effective Area OK

30. OK LRFD - Example Step 4: Check Slenderness
Tension member with a length 5’-9” resists D=18 kips and L=52 kips
Select a member with rectangular cross section, A36 steel and one line 7/8” bolts
Step 4: Check Slenderness OK

31. Step 1: Required Strength
ASD - Example
Tension member with a length 5’-9” resists D=18 kips and L=52 kips
Select a member with rectangular cross section, A36 steel and one line 7/8” bolts
Step 1: Required Strength
Step 2: Required Areas

32. Step 3: Plate Selection based on Ag - Same as LRFD
ASD - Example
Tension member with a length 5’-9” resists D=18 kips and L=52 kips
Select a member with rectangular cross section, A36 steel and one line 7/8” bolts
Step 3: Plate Selection based on Ag - Same as LRFD
Try thickness t = 1 in
Choose PL 1 X 3-1/2
See Manual pp1-8 for availability of plate products

33. OK ASD - Example Step 4: Check Effective Area
Tension member with a length 5’-9” resists D=18 kips and L=52 kips
Select a member with rectangular cross section, A36 steel and one line 7/8” bolts
Step 4: Check Effective Area OK

34. OK LRFD - Example Step 4: Check Slenderness
Tension member with a length 5’-9” resists D=18 kips and L=52 kips
Select a member with rectangular cross section, A36 steel and one line 7/8” bolts
Step 4: Check Slenderness OK

35. Angles as Tension Members
Must have enough room for bolts
(if bolted connection)
Space is a problem if 2 lines of bolts in a leg
Usual fabrication practice – standard hole location
Manual pp 1-46
Leg 8 7 6 5 4
31/2 3
2-1/2 2
1-3/4
1-1/2
1-3/8
1-1/4 1 g
4-1/2
3-1/2
1-1/8
7/8
3/4
5/8 g1
2-1/4 g2

36. Example
Select and unequal-leg angle tension member 15 feet long to resist a service dead load of 35 kips and a service live load of 70 kips. Use A36

37. Step 1: Required Strength
Angle - Example
Step 1: Required Strength
Step 2: Required Areas

38. Step 3: Angle Selection based on Ag
Angle - Example
Step 3: Angle Selection based on Ag
Two lines of bolts, therefore min. length of one leg = 5 in
see table
Choose L6x4x1/2 A=4.75, rmin=0.864
See Manual pp1-42

39. NG Angle - Example Step 4: Check Effective Area
Length of connection not known
4 – bolts in direction of load U=0.8 NG

40. Step 3: Angle Selection based on Ag – TRY NEXT LARGER
Angle - Example
Step 3: Angle Selection based on Ag – TRY NEXT LARGER
Two lines of bolts, therefore min. length of one leg = 5 in
see table
Choose L5 x 3-1/2 x 5/8 A=4.92, rmin=0.746
See Manual pp1-42

41. NG Angle - Example Step 4: Check Effective Area
Length of connection not known
4 – bolts in direction of load U=0.8 NG

42. Step 3: Angle Selection based on Ag – TRY NEXT LARGER
Angle - Example
Step 3: Angle Selection based on Ag – TRY NEXT LARGER
Two lines of bolts, therefore min. length of one leg = 5 in
see table
Choose L8 x 4 x 1/2 A=5.75, rmin=0.863
See Manual pp1-42

43. OK Angle - Example Step 4: Check Effective Area
Length of connection not known
4 – bolts in direction of load U=0.8 OK

44. TABLES FOR DESIGN OF TENSION MEMBERS

45. Example
Select and unequal-leg angle tension member 15 feet long to resist a service dead load of 35 kips and a service live load of 70 kips. Use A36

46. Step 1: Required Strength Step 2: Choose L based on Pu
Example – Using Tables
Step 1: Required Strength
Step 2: Choose L based on Pu
Choose L6x4x1/2
A=4.75, rmin=0.980
See Manual pp 5-15

47. NG Angle - Example Step 3: Check Effective Area
Length of connection not known
4 – bolts in direction of load U=0.8 NG

48. Angle - Example
Shape did not work because table values are for Ae/Ag=0.75
In this problem Ae/Ag=3.1/4.75 =
Enter table with adjusted Pu as

49. Example – Using Tables
Step 4: Choose L based on ADJUSTED Pu
Choose L8x4x1/2
A=5.75, rmin=0.863
See Manual pp 5-14

50. OK Angle - Example Step 5: Check Effective Area
Length of connection not known
4 – bolts in direction of load U=0.8 OK

51. HOMEWORK
3.6-3
3.6-6
3.8-1