Page 39 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

the designer is confronted with the problem to BACKGROUND
design the beams economically in which case it Ragan and Warwaruk (1967) tested four model
1
is necessary to cut appropriate sized openings in beams each of span 6.09 m and full size beams
their webs to accommodate the required utility of span 36.58 m—all post-tensioned prestressed
installation. In all cases the design must take into concrete beams—with large rectangular
account the situation both between openings and openings in the web under a system of uniformly
at the openings. The proper design depends to distributed loadings. These experiments have led
some extent also upon the relative magnitudes of to the conclusion that the web openings do not
the bending moment and shear capacities of the significantly affect the strength as well as stiffness
member without openings. of beams. Similar results were obtained by Gene

2
Corley and Barney (1977) in their tests on pre-
The exact mathematical solution of structural tensioned beams, thereby showing the method
systems incorporating such openings is neither of prestressing does not appreciably change
simple nor straightforward and requires time the behaviour of beams with openings. Tests
and effort which may not be justified in normal conducted on rectangular prestressed concrete
design office procedure. Research work should beams with circular openings (1979) corroborated
3
then provide a reasonably simple procedure for the results cited above. Similar results have been
the analysis and design of such members. In the 4 5
analysis, due consideration must be given to the obtained by Nasser and Daniel , as well as Barker ,
deflection in limit state as well as at collapse since in tests carried out on reinforced concrete beams
the beam with large web openings is less stiff with large web openings.
than a corresponding prismatic beam. Hence, the
deflection should always be calculated in all cases
and is considered as one of the main criteria of the
design.

It is only recently that research work on prestressed
concrete beams with large web openings was
carried out. Of late, the problem has received a
great deal of attention abroad.

The published literature on the behaviour of
prestressed concrete beams with openings has
been totally inadequate. This experimental study
was initiated to find the effect of web openings
in post-tensioned prestressed concrete T-beams
subjected to flexure and to add some new
information to the existing literature.

Fig 1 Formwork for casting beams

40 The Indian Concrete Journal | November 2018