Rationale

Currently, there is some ambiguity and possible confusion on how to calculate equivalent thickness of solid CMU. A quick read of the section for calculating Equivalent Thickness in A1.6.5 can lead users to assume that calculation of equivalent thickness of solid units (which is determined using the average net volume, height and length of the unit) yields a different value that what is called out in the ACI/TMS 216 code for determining fire resistance of solid unit. ACI/TMS 216 dictates that the equivalent thickness of solid units is equal to the actual width (thickness) of the units. In actuality, C140 is in agreement with ACI/TMS 216 because the equation for Equivalent Thickness (A1.4) in A1.6.5 references 9.4 when determining the average net volume of full-size units and 9.4.1 stipulates that for regularly shaped solid units the net volume is simply equal to L x W x H. When this value is used in equation A1.4 it results in the equivalent thickness being equal to the width of the solid unit. This ballot item is proposing to add a note to A1.6.5 to clarify this issue.