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tRod: a small & mobile calculator for threaded hanger rod |
Need to check whether the proposed hanger rod can take the load? Need to calculate the tensile stress of the selected hanger rod? It's as easy as 1, 2, 3 with tRod Sizer - a small, mobile and handy tool for sizing of threaded hanger rod.
Aim: creating a mobile design environment (ShowMe!) for the practising engineers & designers in today's mobile world.
Results: Instant solutions at your fingertips.
Highlights:
- calculate threaded rod diameter, tensile stress or maximum load capacity.
- built-in thread dimensions as per ISO Metric series (SI units) & Unified UNC series (IP units).
- fully mobile & independent program for Pocket PC/Windows Mobile & Windows PC.
- in SI & IP units.
- save results function.
Calculation Explained: Tensile Stress Area vs Root Area |
The effective cross-sectional area of the threaded rod that resists rod fracture is the tensile stress area. It has been observed during the testing of threaded rod that an unthreaded rod, having a diameter equal to the mean of the pitch diameter and the minor diameter has the same tensile strength as the threaded rod. This cross-sectional area called the tensile stress area is used for the purposes of calculating the tensile strength of the rod.
For metric series, the tensile stress area (for steel) = (PI/4)*(D-0.938194P)^{2}
For inch series, the tensile stress area (for steel) = (PI/4)*[D-(0.9743/n)]^{2}
where
D = nominal diameter, P = thread pitch, n = threads per inch, PI = 3.1416
Don't be confused with Root area - a more conservative stress area that is still widely used such as in ASME B31.1 code. Root area is based on the root diameter of the threads, and therefore its stress area is smaller than the tensile stress area. Root area is not based on experimental data. It is designed to introduce a factor of safety in thread strength calculations. The designer pruposely assumes a "root" stress area smaller than the "real" tensile stress area to be sure that the rod isn't overstressed in service.
For metric series, the root area = (PI/4)*(D-1.3P)^{2}
For inch series, the root area = (PI/4)*[D-(1.3/n)]^{2}
Note: The built-in threaded rod data in tRod program uses tensile stress area. For greater flexibility, the user is allowed to input stress area when "u.input" is selected.
Did you know? tensile stress area . . . |
In the absence of thread dimensions/data, a common estimation practice is to use 70% of the rod cross-sectional area (based on rod diameter) for the tensile stress area. Be sure what you are doing - overestimating or underestimating!. tRod has built-in threaded rod data.
Did you know? allowable stress . . . |
Use yield stress (NOT ultimate tensile strength) for allowable (or working) stress with factor of safety for ductile materials. Design the hanger rod for a maximum allowable stress of 20-40% of the yield stress. In the absence of codes and standards, a good factor of safety is 4, i.e. 25% of the yield stress.
ASTM A36 mild (low carbon) steel is the most commonly available of the hot-rolled steels. It has yield strength of 36,300 psi (250 MPa). Taking 25% of the yield strength, the maximum allowable stress = 25% x 36,300 psi = 9,000 psi (62 MPa).
Example 1: Stress calculation for fire-rated ductwork hanger rod (in SI units) |
Determine the diameter of the threaded rod required to support 2-hr fire-rated ductwork, given that the permitted tensile stress level shall not exceed 10 MPa (N/mm^{2}). The total weight acting on one rod is 34.31 kg. Compare Case (a) without safety factor, and Case (b) with a safety factor of 1.5 on working load.
Case (a): No safety factor | Case (b): safety factor = 1.5 |
Load =34.31 kg x 1 SF =34.3 kg Allowable Tensile Stress =10 MPa (N/mm^{2}) Tensile area required =33.7 mm^{2} Selected Threaded Rod Size: Nominal diameter = 8 mm (M8) Tensile area = 36.6 mm^{2} | Load =34.31 kg x 1.5 SF =51.5 kg Allowable Tensile Stress =10 MPa (N/mm^{2}) Tensile area required =50.5 mm^{2} Selected Threaded Rod Size: Nominal diameter = 10 mm (M10) Tensile area = 58 mm^{2} |
<check actual tensile stress> Selected rod diameter =8 mm Tensile area =36.6 mm^{2} Load =34.3 kg Actual Stress =9.2 MPa | <check actual tensile stress> Selected rod diameter =10 mm Tensile area =58 mm^{2} Load =51.5 kg Actual Stress =8.7 MPa |
Example 2: Threaded rod capacity (in IP units) |
A 3/8" diameter threaded hanger rod is used to support general building services. Find its maximum load capacity.
Selected rod diameter =3/8 in Tensile area =0.0775 in^{2} Allowable Stress =9000 psi Max. Load =697.5 lb |
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OS requirements: Windows Mobile, Windows.
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