Civil Engineering Reference
In-Depth Information
cracks to form were diagonal cracks, initiated near the supports and above
the nib, spreading rapidly upwards and towards the middle of the wall. At
higher loads, these cracks lengthened and new cracks were formed near the
supports, propagating parallel with or at wider angles than previous cracks.
The failure of the specimens was brought about by local crushing of the
concrete at the support joints.
The development of cracks in walls W1, W2, W3, W4 and W5 under soffit
loading, was influenced largely by the amount of vertical reinforcement.
Different percentages of reinforcement were provided by varying the spacing
of the 6 mm vertical bars in the members. In general, the first crack was
observed at a depth of about 200 mm and extended horizontally along at least
the middle third of the span. With increased load, new cracks were formed
above the first, creating an arch-shaped pattern of cracks (
Figure 6.6
b
and c).
The average spacing between cracks on the central vertical section of the walls
varied with the spacing of vertical reinforcement. This is illustrated in Figure
6.5, which shows that for larger percentages of vertical reinforcement the
average spacing between horizontal cracks reduced.
Figure 6.5
Effect upon average spacing of cracks of vertical reinforcement under bottom
loading (L2).
Under combined top and bottom loads, the crack pattern was influenced
by both the ratio of top loads to bottom loads and the percentage of vertical
reinforcement. A selection of the final crack patterns exhibited in the tests is
given in Figure 6.6. Fuller details are available in Besser's thesis (1983).
