Download the thesis (PDF) - Ferguson Structural Engineering ...

As the load is reversed, the previously buckled longitudinal reinforcement
may fracture, effectively reducing the wall’s flexural capacity to zero. Examples
of the undesirable consequences of loss of the compression toe are shown by
Shear Wall Specimen 15b and Shear Wall Specimen 16.
Resistance to cracks along longitudinal reinforcement could be increased.
Longitudinal splitting cracks could be prevented by increasing the size of grouted
core or decreasing the bar diameter. This is equivalent to limiting the ratio of area
of the longitudinal reinforcement to area of core (area ratio).
The area ratio of a #5 (17 mm) bar in a 3-in. (76 mm) diameter grouted
core (4.4%) was observed to produce splitting along longitudinal bars in plastic
hinge zones. This is inherently undesirable for AAC shear walls. Such cracking
not been observed with #4 bars in 3-in. grouted cores, even at splices. A #4 (12
mm) bar in a 3 in. (76 mm) core corresponds to an area ratio of 2.8%. For that
reason, the proposed design provisions for AAC masonry and reinforced AAC
panels limit the maximum ratio of the area of reinforcement to the area of the
grouted core containing that reinforcement, to 3% in plastic hinge zones.
A.2.7 Analysis of Maximum Permissible Area Ratio if Longitudinal
Reinforcement Remains Elastic
Area ratios of reinforcement up to 4.5% are permitted, provided that radial
(splitting) stresses can be limited by limiting the bond stress, which in turn means
limiting the shear. The formation of radial stresses is explained in Section 8.8 of
this dissertation, and briefly reviewed here.
141