Abstract
Background material to seismic design aspects of the draft masonry design code DZ4210 is presented. The design approach is based on specified lateral force levels appropriate to the available but limited ductility, and on the principles of reinforced concrete section analyses adapted for low material strengths. Ultimate masonry strengths for compression, shear and flexure are based on the construction techniques and extent of supervision rather than on the strengths of the masonry constituents. Design lateral force coefficients for flexural strength depend on the characteristics of the structural system adopted and Structural Type factors (S) are proposed that are more appropriate to masonry structures than current values incorporated in the Loadings Code NZS4203. Shear failure is proscribed by the implementation of capacity design principles, though simplified procedures are allowed for structures with high flexural S factors. Brief discussion is made of so-called non-structural masonry, including veneers, partition, infill and secondary walls.
Highlights
Masonry construction has in NewZealand as in many countries, a poor reputation for seismic performance
It is widely used in housing construction in the form of unreinforced veneer walls, and for commercial buildings in the forms of reinforced hollow masonry and the concern felt about seismic performance of masonry structures, until recently structural masonry has enjoyed little seismic related research activity
This has been reflected in New Zealand and elsewhere in design methods and codes of practice which have generally been based on traditional rather than modern approaches, specifying elastic design, and treating structural masonry as a low grade concrete, without recognition of the special limitations imposed by material behaviour and the structural forms utilised in masonry construction
Summary
STRUCTURAL MASONRY: many material codes still specify elastic design procedures for structural masonry under seismic loads, the levels of lateral loads specified are generally inadequate to ensure that behaviour remains elastic under the design level earthquake. 7 v the draft masonry code requires pierced shear walls with potential pier ductility to be designed for a structural type factor S = 4, implying near-elastic response, unless a rational analysis is carried out limiting the ductility of the pier units to that implied by equation 2b. To satisfy the high ductility demand generated in the spandrel beams diagonal reinforcement is generally required Such a system is unsuitable for structural masonry and rapid strength and stiffness degradation is likely, resulting in an increase in wall moments towards those appropriate to simple linked cantilevers (see Fig..6b).
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