(1) Macro Block. The macro block approach has been achieved by separately modelling each block or group of blocks in the structure and applying permanent static loads and seismic excitation to the base. Individual blocks of elements have
defined elastic and plastic materials and are arranged to the required bond. All joints and therefore potential discontinuities are predefined and have friction parameters assigned. It is assumed that failure at joints always develops before
blocks fail. However, the introduction of a von-Mises non-linear material model without hardening has been used to approximately represent block crushing thus giving a compressive stress cap. Material properties have been based on characteristic
values determined for the masonry as a whole.
(2) Brittle Material. Where masonry includes high strength mortar or where the strength of blocks is low, a brittle non-linear material model has previously been used. Here the continuum becomes discretised due to evolving fractures in
the blocks and possibly through joints. This is achieved in the analysis automatically using adaptive mesh algorithms. Using a Rankine material model, including fracture energy, newly generated cracks become contact surfaces requiring friction
parameters to be assigned as for the macro block approach. However, for ancient ashlar walls with little or no mortar the macro block approach is preferred.
4. Reinforcement Representation
The finite element technique is used to model the reinforcement independently of the masonry using a partially constrained spar formulation (Roberts, 1999). Connection between the reinforcement and masonry models is achieved through
non-linear bond elements. Modelling of reinforcement arrangements is completely automated without the need for topologically consistent element meshes thus accelerating the modelling process and permitting rapid comparison of designs. Currently,
the capacity for reinforcement elements crossing masonry joints to generate transverse shearing strength or dowel effects is ignored. This is believed to be conservative.
5. Shear Wall Investigation
a. As part of the continuing development of retrofitted reinforced masonry support system applications and the expansion of joint venture historic structure remedial projects, Gifford and Partners with Cintec International are undertaking
studies to investigate how the seismic resistivity of low-rise masonry buildings might be improved
(Cintec International Ltd, 2000).
b. Retrofitted reinforced masonry support system anchors are comprised of stainless steel bar(s), a grouting sock and an engineered grout. Installation is by precisely drilled holes using wet or dry diamond coring technology. The sock consists
of a specially woven polyester fabric shaped into a tubular sleeve to fit the required hole diameter. The use of the sock controls the volume of grout and ensures good contact is achieved with the surrounding masonry. The engineered grout has
similar characteristics to Portland Cement based products, contains graded aggregates and other constituents which, when mixed with water, produce a pumpable mixture that exhibits good strength with no shrinkage. The size of the steel anchor,
strength of grout and diameter of hole can be varied to provide the required design parameters and good stiffness compatibility with the masonry. Design parameters such as the bond strength between the grout and the masonry, which is often
critical, are normally derived from static pullout tests. Figure 1 shows a diagrammatic retrofitted reinforced masonry support system anchor manufactured by Cintec.
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