Calculating Root Area for Bolt

What kind of threads?

You should post your work including the diagram your basing the trigonometry for the calculation. This will show the thread type and fit.

Hi,

Well, for an ISO metric screw you calculate it:

bolt root area =0.785*(d-0.9382*P)^2

Regards

Roman

Calculating bolt loads is complicated if done correctly. The notes below are very limited and are reasonable for none critical applications. There is much specialist information in this field as identified in the links on this page and on the screw index page. These notes do not include for fatigue loading, determination of stiffness of joint, joint settlement, load application factors.etc etc.

It should also be noted that the bolt torque required, to achieve the same bolt stress levels, increases greatly as the bolt size increases (torque = c. d ³). Therefore for larger bolts very high torques are required and used of specialist bolt tensioning systems such as the "Superbolt multi-jackbolt" option should be considered.

Nomenclature

• A _z = Area of plate - taking load ( m²)
• A _b = Bolt Cross Section = Bolt thread root Area (m ²)
• D _b = Bolt thread root diameter (m)
• d = Bolt nominal diameter (m)
• F _e = External Load (N)
• F _t = Thermal Load (N)
• F _p = Preload Load (N)
• F = Total Load On Bolt (N)
• E _z = Youngs Modulus of item z ( N / m²)
• L = Length of Bolt joint (m)
• L _b = Length of Bolt (m)
• L _j = Length of joint (m)
• k _z = Stiffness of component z (N/m)
• k _b = Stiffness of bolt (N/m)
• k _j = Stiffness of joint (N/m)
• t _z = Thickness of plate z (m)
• T = Bolt Tightening Torque (N.m)
• x _z = deflection of item z /unit load (m/N)
• x _b = deflection of bolt /unit load (m/N)
• α _z= Coefficient of thermal expansion of component z (m/m/Deg.C)
• δ = deflection (m)

Bolt Loading Notes

Enjoy, WP

Credits: Information taken from http://www.roymech.co.uk/Useful_Tables/Screws/Preloading.html

CR4 Admin: Removed copyrighted information, See CR4 FAQs

In the formula A_r = (pi/4) (d-kP)², the (d-kP) term is the root diameter, with the parameter k depending on the thread form.

You are not the only one to ask such a question here are ALL interesting dimensions for the Metric Thread