1.1 This test method shall be used to determine the effective moment of inertia of aluminum composite sections.
1.2 This test method may also be used to determine the effective moment of inertia of complex aluminum sections in lieu of
calculations.
1.3 In general, the theoretical moment of inertia of a composite (assuming the aluminum sections are fixed in relation to each
other) will be greater than the effective moment of inertia calculated by this procedure.
1.4This test procedure is subject to several limitations:
1.4.1 The effective moment of inertia is only applicable within the elastic range of the composite section. Under certain
circumstances the thermal break material may reach its yield or even ultimate strength before the aluminum. This is
dependent upon the location of the thermal cavity and type of thermal material used. If such a condition exists, the section
will behave in the field with a smaller moment of inertia than the effective value calculated. If in doubt, consult qualified
engineering personnel.
1.4.1 Many thermal break materials (i.e. cast-in-place polyurethanes) are very temperature dependent. Specifically, the
modulus of elasticity decreases with increasing temperatures (the material becomes softer). For this reason, the effective
moment of inertia calculated at room temperature may be greater than actual field performance where metal temperatures can
reach 180~F. A possible solution is to test certain sections at elevated temperatures and reduce all room temperature results
by the calculated percentage.
1.4.2 The location of the thermal break may give different results for positive and negative loadings on the same section.