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(OP)
I have a problem where I need to determine if 4 grade 8.8 M36x4.0 bolts can be THREADED into (not nut & bolted) a block of steel which weighs 10,000# and hole the load when suspended from these bolts.  I am not sure how to determine load values when the load is hanging from the threads.  I would like a formula if possible not just the answer so I can use it in the future for other problems.  I would also like to know how to determine the minimum thread engagement needed to get full load potential.  Thanks a lot.

A typical rule of thumb for thread engagement is 1 times the diameter for hardened steel parts.  Thus, if you have about 36 mm thread engagement, you will develop full strength for the joint.  This may sound funny, but 10,000 pounds is not a lot of force (especially for M36 x 4) - you could use only one of these fasteners and still not come within 10% of the yield strength.  Below is information that you can use for the future.

Try the following threads at this site:

Try these websites:

http://euler9.tripod.com/fasteners/

Warning - Big File Here
http://astimage.daps.dla.mil/docimages/0001/34/77/H28-2B.PD9

Lastly, the most informative source for information regarding bolted joints is VDI 2230, Systematic Calculation of High Duty Bolted Joints.  Read more at

http://www.vdi.de/vdi/vrp/richtlinien/02842/index.php

1. Minimum Cross-Section of Bolt. The bolt must
satisfy the following two criteria:

Criterion 1: MS = PA t /(SF x P) - 1 ≥0
Criterion 2: MS = PA t /P b - 1 ≥0
2. Shear Pull-Out of Threads. If an internal thread
(nut, nut plate, tapped hole, etc.) is used that is not guaranteed to develop the full ultimate load capability of the bolt, or if the internal thread is not fully threaded onto the bolt, the following two criteria must be met:

Criterion 1: MS = PA s /(SF x P) - 1 ≥ 0
Criterion 2: MS = PA s /P b - 1 ≥ 0

NOTE: These two criteria need only be checked at ultimate load.

MS = VA/(SF x V) - 1 ≥ 0

MS = MA/(SF x M) - 1 ≥ 0

d. Combined Axial, Shear and/or Bending Load:
If the bolt is subject to a combination of loads, the following relationship must hold true for both maximum and minimum preload.
(R a + R b /K)2 + R s 3 ≤1
1 ≤K ≤K y

Where

K y = 1.0 for minimum preload
K y = A plastic bending factor based on actual material stress-strain curves and calculated such that permanent strains do not exceed 0.2% for maximum preload
R a = Ratio of axial load to axial load allowable
and is chosen as the maximum of
(SF x P)/PA t ; P b /PA t ; PLD max /PA t
R b = Ratio of bending load to bending load
allowable,
= (SF x M)/MA
R s = Ratio of shear load to shear load
allowable,
= (SF x V)/VA

NOTE: The axial and shear load allowable (PA t and VA) in this interaction equation are based on the cross-section at which the combined loads occur.

bwilcox:  (1)  What bolt installation torque value will you apply (above running torque) when installing these bolts?  (2)  Will they be installed dry or greased?  (3)  Do your bolt connections have any moment applied to them?  (4)  Will the bolt applied moment, if any, get to the bolt head?  Or instead will a thick, stiff plate having a sizable footprint (i.e., relatively large edge distances) convert any applied moment to bolt applied tension via stiff plate heel-toe prying?  (5)  What is the factor of safety against yield and/or factor of safety against material rupture for your project (or rather, for this lifting connection)?  (6)  Is your steel block A36?

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