Exam Written Questions Flashcards
Sketch the failure mechanism of a rectangular RC beam that fails under TENSION shear. Clearly label each part to show how the failure progresses:
Shear compression failure:
Crushing of compressive concrete :
Failure of tension zone:
Briefly explain what the main considerations of the variable strut
inclination method are.
The variable strut inclination method is adopted by Eurocode 2 to derive the design
equations of a reinforced concrete beam in shear. The concrete acts as the top
compression member and as the diagonal compression members inclined at an angle θ
to the horizontal. The bottom chord is the horizontal tension steel and the vertical links
are the transverse tension members. The main assumption made by this model is that
all shear is resisted by the provision of shear reinforcement with no direct contribution
from the shear capacity of the concrete itself.
Briefly explain how the aggregate interlock and dowel action shear
transfer mechanisms contribute to the shear resistance of a beam.
Both mechanisms contribute to “the shear transferred by concrete”.
In case of aggregate interlock pieces of the aggregate protrude from the bases of the crack and provide a bearing surface to transfer shear. In case of dowel action, the shear is transferred by double curvature of the short length
of the rebar at the crack.
Briefly explain when, in a given reinforced concrete beam under a
vertical point load, the load corresponding to shear failure mechanism, Vshear, becomes higher than the load corresponding to the flexural failure mechanism, Vflexural, and why.
When the shear span to effective depth is smaller than 1.0. This is because failure of the
compressive struts governs the response under shear loads and hence the shear capacity
becomes much larger than the flexural capacity
Describe the punching shear failure mechanism
Punching shear can occur when a large point force is applied to a slab or
where a slab is supported on a column. The slab surrounding the column is
unable to resist the shear force and the column punches through.
ii) Describe the flexural failure mechanism for this structure. [2]
Flexural failure will occur through a combination of “hogging” cracks on the
surface between supports and “sagging” cracks growing diagonally from the
supports.
iii) Briefly compare and contrast the two failure mechanisms, flexural and punching shear
Punching shear is likely a sudden brittle failure mechanism that has been
associated with progression collapse. It is highly undesirable.
