Behaviour of reinforced concrete frames with lightweight blockwork infill panels.

The current investigation concerns the behaviour of lightweight
blockork infill panels bounded by reinforced concrete frames. A
detailed and comprehensive review of the literature on different
frame-inf ill combinations is presented. Details are given of tests
on sixteen third-scale infilled frames and four open frames. These
were tested under two types of loading: horizontal racking loading
only and combined vertical loads on columns and racking loading.
The complete load-deflection response is considered in detail including.
initial elastic behaviour, influence of cracking and the formation of
collapse mechanisms after the attainment of peak load. The variables
investigated include the overall effects of the infill, the infill
thickness, the vertical loads, the amount of reinforcement, the change
in stiffness and strength of beams and of columns and the effect of
reinforcement detailing. Those found to have a major influence are
the vertical loads, the infill thickness, the reinforcement detailing
particularly in the opening corners of the frame, and the workmanship.
The principal parameters obtained from the tests are the initial
racking stiffness, the infill cracking strength, the ultimate load and
the plastic collapse load. Their values are compared to the available
empirical and theoretical methods. None of these methods is found to
safely predict the initial racking stiffness and the ultimate carrying
capacity of this type of structure. A plastic analysis is presented
to predict the two plastic collapse mechanisms identified in the tests.
The penalty factor to allow for idealization of plasticity of the
infill is found as part of the solution. A second penalty factor is
introduced to allow for the limited ductility of the frame. The
proposed method is found to yield satisfactory and safe predictions for the plastic resistance of these infilled frames. In conclusion
some design recommendations are proposed for the initial racking
stiffness and the cracking infill strength.