Abstract:
This study deals with the non linear finite element analysis of reinforced concrete beams
with opening basea on rate independent material non' linearity. Rate-independent
plasticity is characterized by the irreversible straining that occurs in a material once a
certain level of stress is reached. The plastic strains are assumed to develop
instantaneously, that is, independent of time. An eight-nodded iso-parametric threedimensional
solid element is used to model the inelastic response of brittle materials
based on a constitutive model for the tri-axial behaviour of concrete after Willam KJ. and
Wamke E.D. (1975). The intemal reinforcements were modelled using three dimensional
spar elements with plasticity. The non linear effects due to the cracking and crushing of
concrete and the yielding of steel reinforcement are included. An incremental finite
element technique is used which simulates the non linear load-deflection behaviour of
reinforced concrete stmcture.
This work is an attempt to correlate the numerical observation regarding the behaviour of
some reinforced concrete beam having rectangular web opening with those from the
previously experimented results. The entire numerical analysis has been perfonned using
general-purpose finite element code ANSYS. Results of the numerical study are
compared to that of the available experimental values. Several parameters such as
opening length and depth, horizontal and vertical location of the opening have been
varied. The effect of opening on the behaviour of beams under one point loading has been
presented in this study. Deflection due to opening at high moment end, stress distribution
over the entire section of the beam, strain distribution in the vicinity of the opening, crack
propagation pattern and failure mechanisms have been observed.
From a comparison of the numerical and the experimental results, it is concluded that the
developed finite element model used in the present study is suitable for analysing and
capturing the behaviour of reinforce concrete beam with opening. The good agreement
between the numerical and the experimental results establishes the validity and rationality
of the computational models. This model is general and may be used for any arbitrary
shaped structure. It is also useful in predicting cracking pattern, yield and ultimate load
carrying capacity. In addition it should be particularly attractive to designers when it is
required to predict deflection of a reinforced concrete system, for a given load, in addition
to its ultimate strength. From the finite element analysis of reinforced concrete beams
with web opening, it is observed that stiffness as well as yield capacity of the beams
decreases with the increase in opening length, depth and moment-shear ratio but stiffness
increases with the increase of opening eccentricity. In all cases of beam, change in stress
pattern occurred both in top and bottom chord. Long-term deflection has been calculated
using ACI Code (2002) formula from service load deflection. It was found that immediate
deflection due to service load is within the ACI Code (2002) limit.
