Tension Rod Capacity
Tension Rod Capacity
(OP)
For Design of Carbon Steel Tensin (non-upstand) rods to AISC I understand the following limits to be applicable:
1. Gross Yielding (Chapter D)
a) ASD
Ab - gross area of rod i.e. (pi*d^2)/4 where d is the nominal diameter of the rod
Nominal Strength Fn = Fy*Ab
FS - ASD Factor of safety = 1.67
ASD Allowable Strength = Fn/FS = 0.6*Fy*Ab
b) LRFD
As above but reduction factor phi = 0.9
LRFD Design Strength = phi*Fn = 0.9 *Fy*Ab
2. Threaded Part Chapter J3
a) ASD
Nominal Strength Fn = 0.75*Fu*Ab
FS - ASD Factor of safety = 2
ASD Allowable Strength = Fn/FS = 0.38*Fu*Ab
b) LRFD
As above but reduction factor phi = 0.75
LRFD Design Strength = phi*Fn = 0.563*Fu*Ab
My quesitons is, is can the Chapter D equaiton for fracture in the net section based on the actual thread area Ae be used in lieu of the eqution for the thread capacity from J3?
3. Fracture in the Net Section
a) ASD
Ae - threaded area
Nominal Strength Fn = Fu*Ae
FS - ASD Factor of safety = 2
ASD Allowable Strength = Fn/FS = 0.5*Fu*Ae
b) LRFD
As above but reduction factor phi = 0.75
LRFD Design Strength = phi*Fn = 0.75*Fu*Ae
I ask this as we get more capacity if we use the fracture equation above for a rod of known threaded area Ae vs that of the equation for a threaded part based on the gross area. Is it correct to assume that the fracture equaiton and the threaded part equationa are actually the same, except that the threaded part equation usses an assumption of teh treaded area Ae being equivelent to 0.75*Ab?
Thanks
1. Gross Yielding (Chapter D)
a) ASD
Ab - gross area of rod i.e. (pi*d^2)/4 where d is the nominal diameter of the rod
Nominal Strength Fn = Fy*Ab
FS - ASD Factor of safety = 1.67
ASD Allowable Strength = Fn/FS = 0.6*Fy*Ab
b) LRFD
As above but reduction factor phi = 0.9
LRFD Design Strength = phi*Fn = 0.9 *Fy*Ab
2. Threaded Part Chapter J3
a) ASD
Nominal Strength Fn = 0.75*Fu*Ab
FS - ASD Factor of safety = 2
ASD Allowable Strength = Fn/FS = 0.38*Fu*Ab
b) LRFD
As above but reduction factor phi = 0.75
LRFD Design Strength = phi*Fn = 0.563*Fu*Ab
My quesitons is, is can the Chapter D equaiton for fracture in the net section based on the actual thread area Ae be used in lieu of the eqution for the thread capacity from J3?
3. Fracture in the Net Section
a) ASD
Ae - threaded area
Nominal Strength Fn = Fu*Ae
FS - ASD Factor of safety = 2
ASD Allowable Strength = Fn/FS = 0.5*Fu*Ae
b) LRFD
As above but reduction factor phi = 0.75
LRFD Design Strength = phi*Fn = 0.75*Fu*Ae
I ask this as we get more capacity if we use the fracture equation above for a rod of known threaded area Ae vs that of the equation for a threaded part based on the gross area. Is it correct to assume that the fracture equaiton and the threaded part equationa are actually the same, except that the threaded part equation usses an assumption of teh treaded area Ae being equivelent to 0.75*Ab?
Thanks






RE: Tension Rod Capacity
RE: Tension Rod Capacity
However, there seem to be two possible equations to desicrbie the net fracture failure under tension. The first comes from Chapter D and is based on the actual net area - i.e. the thread area, and the second comes form Chapter J for a threaded part, which appears to be a variation on the net fracture limit of Chapter D but here the nominal strength appears to be based on an approximation of the net area i.e. Ae = 0.75 Ab.
The latest 2005 specifications for Steel building design appears to confirm this in the commentary for Chapter J
RE: Tension Rod Capacity
RE: Tension Rod Capacity
Tensile stress area= 0.7854(D-.9743/n)^2 n=th'ds per inch
RE: Tension Rod Capacity
Chapter J, Table J3.2 and Equation J3-1 for tensile rupture
Nominal strength of threaded part 0.75*Fu*Ab
ASD Factor of safety 2
LRFD Reduciton factor 0.75
ASD Allowable strength 0.375*Fu*Ab
Chapter D, Equation D2-2, Tensile rupture
Nominal strength Fu*Ae
ASD Factor of safety 2
LRFD Reduciton factor 0.75
ASD Allowable strength = 0.5*Fu*Ae
2. AISC ASD Manual 9th Edition
Chapter J, Table J3.2
ASD Allowable Strength = 0.33 Fu*Ab
Chapter D, D1,
ASD Allowable strength on net area = 0.5Fu*Ae
RE: Tension Rod Capacity
The quesiton is
i) Can I ignore the Chapter J equaiton if I use the Actual thread area in the Chpater D equaiton for Net tensile fracture?
Chpater J appears to be an approximation to that of Equaiton D for net tensile fracture. The Chapter J equaiton appers to be very conservative and is used if one is unsure of the actural thread area.
RE: Tension Rod Capacity
RE: Tension Rod Capacity