For a bearing bolt, work out the design shear capacity Vdsb and the design tension capacity Tdb from the bolt grade and size, then check (V / Vdsb)² + (T / Tdb)² ≤ 1.0. An M16 grade 10.9 bolt has Vdsb = 72.4 kN and Tdb = 112.8 kN, so under 60 kN of shear and 25 kN of tension the interaction ratio is 0.74 and it passes.
Reading a bolt name: M16 10.9
M16 is a metric thread with a 16 mm nominal diameter. The two numbers in 10.9 are the property class. Multiply the first number by 100 to get the ultimate tensile strength of the bolt material in MPa, so 10 gives fub = 1000 MPa. The second number is the ratio of yield to ultimate strength, so 0.9 gives a yield strength fyb of 900 MPa.
| Class | fub (MPa) | fyb (MPa) |
|---|---|---|
| 4.6 | 400 | 240 |
| 8.8 | 800 | 640 |
| 9.8 | 900 | 720 |
| 10.9 | 1000 | 900 |
Which standard covers which fastener
Bolt Mode in Steel Table India follows the Indian fastener standards. Hexagon bolts, screws and nuts are in IS 1363 and IS 1364. High strength friction grip (HSFG) bolts and their washers are in IS 3757 and IS 6649. Plain and spring washers are in IS 2016 and IS 3063. IS 1367, IS 4218 and IS 3935 are carried as reference, for property classes, metric threads and shear connectors. The guide to Indian standards for structural steel shows how these sit alongside IS 800 and IS 808.
The two areas that matter
A bolt has two areas that matter. The shank area Asb is the full circle, πd² / 4. The net tensile area Anb is smaller because the thread cuts into the section. IS 800 takes it as about 0.78 times the shank area for the common case.
For M16:
- Asb = π × 16² / 4 = 201.1 mm²
- Anb = 0.78 × 201.1 = 156.8 mm²
When the threads lie in the shear plane, shear is worked on Anb. When the unthreaded shank lies in the shear plane, it can be worked on Asb, which gives a higher capacity. The conservative and common assumption is threads in the shear plane.
Shear and tension capacity
With a single shear plane and threads in the shear plane, the nominal shear capacity is:
Vnsb = fub / √3 × Anband the design value divides by the bolt safety factor γmb = 1.25. For M16 grade 10.9:
Vnsb = 1000 / 1.732 × 156.8 = 90.5 kN, so Vdsb = 90.5 / 1.25 = 72.4 kNThe nominal tension capacity is 0.9 × fub × Anb, and the design value again divides by 1.25:
Tnb = 0.9 × 1000 × 156.8 = 141.1 kN, so Tdb = 141.1 / 1.25 = 112.9 kNSteel Table India shows 112.8 kN for this bolt. The 0.1 kN gap is rounding in the area constant, and it does not change the result.
There is a third check for bolts in bearing joints, the bearing capacity on the connected plate, which depends on plate thickness, edge distance and pitch. The optimizer has an option to include it.
The interaction check, worked
When a bolt carries shear and tension together, IS 800 requires:
(V / Vdsb)² + (T / Tdb)² ≤ 1.0Take a bolt group with a factored shear of 60 kN and a factored tension of 25 kN on a single bolt. For the M16 grade 10.9 bolt:
(60 / 72.4)² + (25 / 112.8)² = 0.687 + 0.049 = 0.740.74 is below 1.0, so the bolt passes with 74 percent utilisation. Now try the lower grade, M16 class 9.8. Its capacities are 65.1 kN in shear and 101.5 kN in tension:
(60 / 65.1)² + (25 / 101.5)² = 0.849 + 0.061 = 0.91It also passes, at 91 percent. That is a thin margin, so you would look closely at it. Both results match the percentages the app shows for the same inputs.
Capacities for common sizes
Here are design capacities worked from the same formulas for grade 8.8 bolts, single shear, threads in the shear plane. Use them for a quick sense of scale, and take final values from the standard or the app.
| Bolt | Asb (mm²) | Anb (mm²) | Vdsb (kN) | Tdb (kN) |
|---|---|---|---|---|
| M16 | 201.1 | 156.8 | 57.9 | 90.3 |
| M20 | 314.2 | 245.0 | 90.5 | 141.1 |
| M24 | 452.4 | 352.9 | 130.4 | 203.2 |
Slips to avoid
- Working loads in a factored check. The optimizer and the formulas expect factored loads.
- Forgetting the second shear plane. A bolt in double shear has a larger shear capacity, and a lap joint is single shear. Count the planes.
- Assuming the shank is in the shear plane. Unless the detail guarantees it, assume the threads are.
- Skipping bearing and slip. The bolt can pass while the plate bearing or, in a slip-critical joint, the friction capacity governs.
- Mixing units. Areas in mm² and strengths in MPa give newtons. Divide by 1000 for kN.
Let the optimizer pick the bolt
Bolt Mode in Steel Table India has an explorer, a side-by-side compare and an optimizer. Enter the factored shear Vsb and tension Tb in kN, choose the number of shear planes and whether threads are in the shear plane, pick a bolt family or leave it on all families, and optionally restrict it to preferred sizes. The optimizer lists every option that carries the load, smallest first, with its interaction percentage. Switch on the bearing check to include the plate. The compare screen sets two bolts, for instance M16 and M24, next to each other.
Questions people ask
What does 10.9 mean on a bolt?
It is the property class. The first number times 100 is the ultimate tensile strength in MPa, so 10.9 is 1000 MPa. The second number is the yield to ultimate ratio, so 0.9 gives a yield strength of 900 MPa.
What is the shear capacity of an M16 bolt?
For grade 10.9, single shear and threads in the shear plane, the design shear capacity is about 72.4 kN. For grade 8.8 it is about 57.9 kN.
What is the combined shear and tension check for bolts?
For a bearing bolt, (V / Vdsb)² + (T / Tdb)² must not exceed 1.0, where V and T are the factored shear and tension on the bolt and Vdsb and Tdb are its design capacities.
Why is the net tensile area smaller than the bolt area?
The thread removes material. IS 800 takes the net tensile area as about 0.78 times the shank area, so M16 goes from 201.1 mm² to 156.8 mm².
Which IS standards cover structural bolts?
IS 1363 and IS 1364 cover hexagon bolts, screws and nuts. IS 3757 and IS 6649 cover HSFG bolts and washers. IS 2016 and IS 3063 cover plain and spring washers.
Does passing the interaction check mean the joint is safe?
No. The joint also needs the bearing check, the plate and member checks, edge and pitch distances, and for friction grip joints the slip resistance. Have it checked by a qualified engineer.
Keep reading
Pick the right bolt in seconds
Bolt Mode in Steel Table India explores, compares and optimizes bolts to IS standards. Free on Google Play.
For reference, not for sign-off. Section and bolt values quoted here are as shown in Steel Table India, transcribed from the published IS 808:2021 tables and worked to IS 800:2007 methods. Transcription can contain errors, and these worked examples make simplifying assumptions stated in the text. Check critical values against the official Bureau of Indian Standards publications and have designs checked by a qualified engineer. IS 808 and IS 800 are published by the Bureau of Indian Standards.