Page 38 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

Behaviour of post-tensioned prestressed concrete

T-beams with large web openings

V. Dinakaran and M. K. L. N. Sastry

The results of analytical and experimental investigation on the behaviour of simply
supported prestressed concrete T-beams with web openings are presented in this
paper. The study consisted of testing 9 T-beams of size 36 cm x 5 cm flange and 30 cm x 8 cm
web and of span 4.2m gradually loaded to failure. Each beam had web openings of size
36 cm x 12 cm. The variables considered were the size of openings, location of
openings and type of reinforcement around openings. The openings were
positioned both in the shear span as well as in flexure span. Measured ultimate
loads and moments are compared with those calculated from the theoretical
values computed from the codes of practice as well as those based on Vierendeel
truss analogy. The ratio of the observed to calculated ultimate load indicated
that there exists shear concentration at the openings. The deflections were well
within those allowed by the code provisions. The results show that large web
openings can be accommodated in post-tensioned prestressed concrete T-beams
without sacrificing the strength. Serviceability requirements are also found to be
satisfactory. The beams which were reloaded after failure carried 60 to 70 percent
of their ultimate load thus exhibiting the resilient characteristics of prestressed
concrete in spite of the discontinuities.
I

n construction practice, air conditioning ducts, electrical conduits, sanitary pipes and
similar utility components are carried below the beams and covered by a suspended ceiling.
This means that valuable space between the soffit of the beam and the suspended ceiling is
virtually wasted. The available headroom is also reduced. If the minimum headroom is to be
maintained the storey heights are increased and in turn the cost of the construction goes up. A
more satisfactory solution is to provide passage for the services within the depth of the beam.
Nowadays architects and engineers are more frequently specifying that the openings be provided
in the webs of both main and secondary girders and beams of buildings to accommodate these
utility components. Unless the structural engineer makes proper design of the beam with
web openings there is a risk that each of the subtrades will knock out openings to suit their
installations and possibly weaken the structural frame of the building to a critical degree. So,

The Indian Concrete Journal | November 2018 39