Section 6 Methods of Structural Analysis

This section (previously Section 7) has been completely revised. Notably, Section 6 now includes simplified methods of flexural analysis, using both Ductility Class N and Ductility Class L reinforcement, in areas of negative and positive design moment. Clause 6.10.2 indicates simplified moment calculations for beams and one-way slabs which can be used with the provisos outlined in 6.2.1. These relate to span geometry, load distribution, ratio of imposed and permanent actions, member geometry, arrangement of reinforcement. In addition, moments at supports can only be caused as a result of actions applied on the beam or slab.

Any predicted relative settlement of supports precludes the use of Ductility Class L reinforcement. Ductility of the bar is an issue after the bar has yielded and permanent plastic deformation of the bar has occurred.

6.10.2.2 Negative design moment

The negative design moment at the critical section, taken for the purpose of this Clause at the face of the support, shall be as follows (where Fd is the uniformly distributed design load per unit length, factored for strength):

(a) At the first interior support:

(i) Two spans only for Ductility Class N................................F_d L_n² / 9 ; or
     for Ductility Class L.............................................................F_d L_n² / 8
(ii) More than two spans..........................................................F_d L_n² / 10

(b) At other interior supports............................................................F_d L_n² / 11

(c) At interior faces of exterior supports for members built integrally with their supports:

(i) For beams where the support is a column.....................F_d L_n² / 16
(ii) For slabs and beams where the support is a beam....F_d L_n² / 24

6.10.2.3 Positive Design Moment

The positive design moment shall be taken as follows (where Fd is the uniformly distributed design load per unit length, factored for strength):

(a) In an end span..............................................................................F_d L_n² / 11

(b) In interior spans for Ductility Class N.......................................F_d L_n² / 16 ; or
     for Ductility Class L.......................................................................F_d L_n² / 14

Similar simplifed methods permitting the use of Ductility Class L reinforcement have been applied to the design of slabs supported on four sides, refer to Clause 6.10.3. Ductility Class L reinforcement is not permitted in the simplified design methods for multiple span two-way slabs as outlined in Clause 6.10.4.1. Differential shortening of columns or differential deflections of beams are considered too detrimental for the use of low ductility reinforcement.