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### Wood Butt Joint Glue Strength Formulae and Calculator

Civil Engineering and Design

Wood Butt (End to End) Joint Glue Adhesive Strength Equations and Calculator

Wood adhesive joints play an important role in modern timber engineering. In order to add value to the raw material several highly engineered wood based products have been developed. Often these involve the use of adhesive joints. Typical adhesive are distributed over contact area, assembled and then pressure is applied while adhesive cures.

Allowed Joint stress in tension loading equation:

σA = SU / kT

Tensile stress in joint loading equation:

σ = F / ( b · s )

Minimum thickness of connected parts (adhesive glue line):

smin = F / ( b · σA )

Strength of adhesive glue line check:

σ ≤ σA

where:

SU = joint strength in tension of glue or adhesive [psi, MPa],
kT = tension safety coefficient (typically 2 or greater),
F = transferred force [lb, N],
b = width (minimum) of connected lumber [in, mm],
s = thickness (minimum) of connected lumber (in, mm].

Reference:

Kent's Machine Engineers Handbook, 12th Edition Design and Production, 1950 Colin Carmichael

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