Section 4.3.4.3 Flexural tension stresses in concrete

The interaction of the BS 8110 requirements, the TR 43 requirements, the different classes and the use of bonded and unbonded tendons makes describing the service tensile stress limits and requirements in text form very confusing. In some circumstances, BS 8110 and TR 43 conflict, while in other circumstances neither one explicitly considers a particular configuration.

Our implementation of these requirements is detailed in the table below. For each combination of tendon type, structure type and class, two limit stresses and a reinforcement calculation are listed. The first limit stress is the maximum stress allowed if no supplemental un-tensioned reinforcement is used. The second limit stress is the absolute maximum stress allowed. The reinforcement calculation details how to calculate the required supplemental reinforcement when stresses exceed the first stress limit.

Table 1. Flexural tension limit rule mapping
Tendons	Member Type	Class	Tension limit without supplementary reinforcement	Absolute tension limit	Reinforcement calculation
Bonded	Beam	1	0	0	4.3.4.3 (c)
Bonded	Beam	2	$0.36 \sqrt{f_{cu}}$	$0.36 \sqrt{f_{cu}}$	4.3.4.3 (c)
Bonded	Beam	3 / 0.1 mm	Tables 4.2 / 4.3	0.25f_cu	4.3.4.3 (c)
Bonded	Beam	3 / 0.2 mm	Tables 4.2 / 4.3	0.25f_cu	4.3.4.3 (c)
Bonded	One-way	1	0	0	4.3.4.3 (c)
Bonded	One-way	2	$0.36 \sqrt{f_{cu}}$	$0.36 \sqrt{f_{cu}}$	4.3.4.3 (c)
Bonded	One-way	3 / 0.1 mm	Tables 4.2 / 4.3	0.25f_cu	4.3.4.3 (c)
Bonded	One-way	3 / 0.2 mm	Tables 4.2 / 4.3	0.25f_cu	4.3.4.3 (c)
Bonded	Two-way	All	TR 43 Table 2	TR 43 Table 2	TR 43, 6.10.5
Unbonded	Beam	1	0	0	TR 43, 6.10.5
Unbonded	Beam	2	0	$0.36 \sqrt{f_{cu}}$	TR 43, 6.10.5
Unbonded	Beam	3 / 0.1 mm	0	Tables 4.2 / 4.3*	TR 43, 6.10.5
Unbonded	Beam	3 / 0.2 mm	0	Tables 4.2 / 4.3*	TR 43, 6.10.5
Unbonded	One-way	1	0	0	TR 43, 6.10.5
Unbonded	One-way	2	0	$0.36 \sqrt{f_{cu}}$	TR 43, 6.10.5
Unbonded	One-way	3 / 0.1 mm	0	Tables 4.2 / 4.3*	TR 43, 6.10.5
Unbonded	One-way	3 / 0.2 mm	0	Tables 4.2 / 4.3*	TR 43, 6.10.5
Unbonded	Two-way	All	TR 43 Table 2	TR 43 Table 2	TR 43, 6.10.5

Note: * - When Tables 4.2/4.3 are used with unbonded tendons, the values for "grouted post-tensioned tendons" and a 0.1mm crack width are used.