The use of lipped channel members as the reinforcing for composite beams in rib
and block type slab systems is advantageous due to its lightweight nature which
facilitates efficiently in construction. The main consideration in the design if such
composite members is the integrity of the shear bond at the concrete/ steel interface.
Premature de-bonding of the concrete from the steel results in an overall loss of
structural strength of the composite member. Certain guidelines are to be
established to facilitate in the design of such systems.
In this research project the shear bond strength of composite members using lipped
channel members is investigated by interrogating the results from three independent
research experiments. Design formulas from first principles are developed to more
easily benchmark the behaviour of such members. Complex and simple equations
are developed and the results obtained are compared to similar shear bond stresses
obtained from literature. A reasonably acceptable correlation is achieved.
A comparative study was also carried out between the various experimental beams
regarding vertical shear, flexural strength and short-term deflections. The purpose
was to ascertain what effect early shear bond failure has on these structural
properties. The formulas used to benchmark the results were the well known
formulas used for the design and evaluation of reinforced concrete members. The
results were tabulated showing the difference between the calculated and
experimental results.
As a result of the investigation the following conclusions seem justified :
The simple equations as developed for horizontal shear failure give
acceptable results which are within the range as given by more complex
equations.
The composite beam has a certain amount of reserve shear strength even
after the initial onset of horizontal shear failure.
iv
The reinforcing ratio, the concrete strength and the slenderness ratio of the
composite beam all have an influence on the level of horizontal stress failure.
The composite beams tend to fail at levels higher than that predicted by the
homogeneous shear equations but lower than the predicted flexural
equations. The parameters which influence this are again the reinforcing ratio,
the concrete strength and the slenderness ratio.
Once a composite beam has experienced shear bond failure the deflection
integrity of the beam is completely compromised.
The above conclusions show the designer that caution must be exercised when
using lipped channel members in rib and block slab systems.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/4784 |
| Date | 06 May 2008 |
| Creators | Pretorius, Jock Milne |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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