Question

For
a bolted assembly with six bolts, the stiffness of each bolt is
kb=3 Mlbf/in and the stiffness of the members is km=12 Mlbf/in per
bolt. An external load of 85 kips is applies to the entire joint.
Assume the load is equally distributed to all the bolts. It has
been determined to use 1/2 in-13 UNC grade 8 bolts with rolled
threads. Assume the bolts are preloaded to 75 percent of the proof
load.

a) determine the yielding factor of safety.

np=

b) determine the overload factor of safety.

nL=

Answer #1

External Load applied (P) = 80 kips

Bolt stiffness (k_{b}) = 3(10^{6}) lbf / in

Member stiffness (k_{m}) = 12(10^{6}) lbf /
in

Diameter of bolts (d) = 1/2 in - 13 UNC grade 8

Number of bolts = 6

For Unified Screw Threads UNC and UNF

Tensile stress area (A_{t}) = 0.1419 in^{2}

SAE specifications for steel bolts for grade 8,

we have

Minimum proff strength (S_{p}) = 120 kpsi

Minimum tensile strength (S_{ut}) = 150 kpsi

Load bolt (P) = kips = 13.33 kips

given by,

Preload Stress

Stiffness Constant

a) Yielding Factor of Safety is given by,

b) Overload Factor of Safety is given by,

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