Civil Engineering Reference
In-Depth Information
Loads are also shown acting through bearing plates. Again, this is
convenient shorthand which emphasises the need for reasonable force
transfer into the beam. In practice loads will be transfered to and from the
beam through concrete columns.
Typical truss models for continuous beams are presented in
Figures 4.5
and 4.6. Their detailed use will be illustrated in the design examples.
Conceptually, they are statically indeterminate trusses. Assuming yield of the
reinforcement, the truss is rendered determinate and the compression
member forces can be solved by the method of joints provided it is done in
an appropriate order.
Figure 4.6
Continuous truss models with web reinforcement
The solution procedure is as follows:
i)
For simplicity use a final effective concrete strength of 45% of the
specified strength. (For the models shown, no more than one tie will
be anchored at a joint.)
ii)
Draw the truss to scale (including strut widths).
iii)
Measure the strut slopes from the diagram.
iv)
Calculate the vertical and horizontal components for each strut
reacting against a stirrup assuming that, if it can, the stirrup will
yield, thus defining the vertical strut force. (Stirrups connected to
struts with inclinations steeper than 65° are not likely to yield.
These occur close to supports and point loads.)
