Electronic Blueprint - Masonry subject to to earthquake
Electronic Blueprint and ENVIROSPEC provide building specifications,
details and training on safe and sustainable buildings to architects, engineers and
builders. Questions have arisen concerning the interpretation of AS 3700 Appendix
AA for masonry subject to earthquake loading.
Table AA2 provides reference to appropriate details for various masonry options. See
below for an example, the use of 140 mm loadbearing hollow masonry with wide-spaced
reinforcement.
Under such conditions, the masonry must be reinforced, but it is impractical to
reinforce 140 mm hollow masonry both horizontally and vertically. This means that,
in practice, it can only be reinforced vertically. Care must be taken to ensure
that the concrete grout is particularly fluid, ensuring that it completely surrounds
the reinforcing bars. AS 3700 Clause 8.3.6 requires that the reinforcement, of
wide-spaced reinforced walls, be designed to Clause 8.4 to 8.7. These are the main
design clauses, dealing with compression, bending, shear and tension. Depending on
the magnitude of the loads, reinforcement might be N16 or N20 vertical bars, at centres
in the range or 800 mm to 2,000 mm. Such walls with vertical main bars, do not
incorporate any horizontal reinforcement. The strength design process is the same
as published in the Concrete Masonry Association of Australia, Design and Construction
Manual, MA55;
- Compression - Design as unreinforced masonry, with the capacity discounted by 15% to
account for combined loads.
- Bending - Design as "mixed construction" i.e. wide spaced reinforced elements supporting
unreinforced masonry between, but allowing to compression flange up to four times the wall
thickness.
- Shear - Design on the basis that there is no horizontal reinforcement, using Clauses 8.6.2
or 8.6.3 as appropriate. Consider whether the wall is fixed to the floor by starter bars.
For further information contact:
Electronic Blueprint
phone: +61 2 4360 2255
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