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## Tension Members Last Time

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**Tension MembersLast Time**Structural Elements Subjected to Axial Tensile Forces Trusses Bracing for Buildings and Bridges Cables in Suspension and Cable-Stayed Bridges**Gross Area – Specs D3.1 p 16.1.27 Last Time**Gross Area Ag: Total Area of Main Body of Member**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**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 16.1-250)**Staggered Fasteners Last Time**Geometry Constraints Space Limitations**Net Area - Effect of Staggered Holes AISC Specs D3.1 Last**Time T T T p Reduced diameter T g g = gage s = spacing s Failure paths on net section**Net Area - Gage Distance for an Angle Last Time**For holes on different legs**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)**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**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**1. General category for any type of tension member except**plates and round HSS with Last Time**1. General category for any type of tension member except**plates and round HSS with Last Time**2. PlatesLast Time**U=1.0 since cross section has one element and it is connected Special Cases 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 b. Transverse welds only (uncommon) An net area of directly connected members**4. Alternative values for single angles Last Time**2 or 3 fasteners in direction of loading 4 fasteners in direction of loading**5. Alternative values for W,M,S and HP shapes Last Time**Connected through flange with 3 or more fasteners in direction of loading**5. Alternative values for W,M,S and HP shapes Last Time**Connected through flange with 3 or more fasteners in direction of loading**5. Alternative values for W,M,S and HP shapes Last Time**Connected through web with 4 or more fasteners in direction of loading**Block ShearChapter D User Note -> J4.3 (p. 16.1-112) Last**Time Anv: net shear area Ant : net tension area For angles and gusset plates**Block ShearChapter 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**TODAY**• Design of Tension Members • Tables for the Design • Threaded Rods and Cables**LRFD**max LRFD ASD min min max ASD etc 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**Design of Tension Members**Determine required Area LRFD To prevent yielding To avoid fracture Yielding controls if**Design of Tension Members**• Determine required Area ASD To prevent yielding To avoid fracture Yielding controls if**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**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**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 4: Check Effective Area OK**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 4: Check Slenderness OK**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**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**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 4: Check Effective Area OK**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 4: Check Slenderness OK**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**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**Angle - Example**Step 1: Required Strength Step 2: Required Areas**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**Angle - Example**Step 4: Check Effective Area Length of connection not known 4 – bolts in direction of load U=0.8 NG**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**Angle - Example**Step 4: Check Effective Area Length of connection not known 4 – bolts in direction of load U=0.8 NG**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**Angle - Example**Step 4: Check Effective Area Length of connection not known 4 – bolts in direction of load U=0.8 OK**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**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**Angle - Example**Step 3: Check Effective Area Length of connection not known 4 – bolts in direction of load U=0.8 NG**Angle - Example**Shape did not work because table values are for Ae/Ag=0.75 In this problem Ae/Ag=3.1/4.75 = 0.6526 Enter table with adjusted Pu as**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**Angle - Example**Step 5: Check Effective Area Length of connection not known 4 – bolts in direction of load U=0.8 OK