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4.1.8.11.(10)
OS2OP2OS2OP2
ObjectiveOS2 Structural Safety
Attribution
(a) [F20-OS2.1]
Application
Application 1: 
Determination of seismic torsional effects by applying torsional moments about a vertical axis at each level of the building, for the structural design of structures that are not torsionally flexible.
Exceptions: 
except as stated in Sentence 4.1.8.1.(1), which applies to areas where the spectral response acceleration amplified for site conditions equals the floor levels found in low seismicity regions with Site Class C (i.e. very dense soil and soft rock).
This applies to buildings described in Sentence 1.3.3.2.(1) of Division A and to buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9] that are required to be designed in accordance with the requirements of Part 4.
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Intent
Intent 1: 
To limit the probability that the calculation of loads due to earthquake will not take into account the forces due to expected seismic torsional moment at any level of the building, taking into account eccentricities between the centre of mass and centre of rigidity, including accidental eccentricities such as those due to stiffening provided by non-structural building elements, which could lead to structural failure, which could lead to harm to persons.
Intent 2: 
To direct Code users to Sentence 4.1.8.11.(6) for the calculation of the lateral force at each level of the building.
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