Section 18.3.3 Service Tensile Stress Limit

A cross-section is defined as Class U, Class T, or Class C using the design strip segment or design section property "Environment". The limiting tensile stress values are outlined in the following table.

	Class U	Class T	Class C
Assumed behavior	Uncracked	Transition between uncracked and cracked	Cracked
Section properties for stress calculation	Gross section	Gross section	Cracked section
Tensile stress limit	$f_{t} \leq 7.5 \sqrt{{f^{'}}_{c}}$	$7.5 \sqrt{{f^{'}}_{c}} < f_{t} \leq 12 \sqrt{{f^{'}}_{c}}$	No limit
Deflection calculation	Gross section	Consider effects of cracking	Consider effects of cracking
Crack control	No requirement	No requirement	10.6.4 / 18.4.4
Computation of f_s for crack control	Not applicable	Not applicable	Cracked section analysis

Note: All post-tensioned two-way slabs are considered as Class U with ft ≤ 6 root fc'

If a design strip or section is defined as Class C, but the gross tensile stresses are within the Class T limits, the provisions of 10.6.4/18.4.4 will not be applied.

For sections with multiple concrete strengths, the minimum concrete strength is used to determine the limiting stress.

For sections with multiple concrete strengths, approximate extreme fiber stresses and centroid stresses are reported.

No check is made to ensure that the structure is post-tensioned.