Fire Resistance Simulation for High Strength Reinforced Concrete

High strength reinforced concrete (HSRC) has been used more frequently in the construction of
high rise buildings and other concrete structures in recent decades due to its advantages and
excellent performance over normal strength and conventional reinforced concrete. Some of these
advantages include: higher strength, better durability and allowance for provision of using less
concrete and smaller section sizes. Although HSRC performs better than normal strength
reinforced concrete (NSRC) at ambient temperatures, NSRC has been found to perform better
than HSRC at elevated temperatures and fire conditions.
Provision of adequate fire resistance for reinforced concrete (RC) structures is essential as fire
represents an extreme loading and hazardous condition to which a structure might be exposed
during its life span. The fire resistance of RC members is evaluated using a prescriptive approach
which is irrational and conservative. Current codes of practice and construction in industry are
moving towards performance based fire design method with computing software, which is a
rationally based method with each structure designed to meets its own need. This method
requires comprehensive knowledge and modelling of concrete and reinforcement material
behaviour and their response at elevated temperatures.
The fire resistance of HSRC members (columns and beams) in this study was evaluated using a
three-dimensional Finite Element (FE) model created in ANSYS. The stress – strain behaviour of
concrete proposed in this research was used in modelling the behaviour of concrete in ANSYS,
while other concrete and steel material properties were accounted for by using models proposed
by other researchers. The fire resistance of the HSRC members is evaluated using coupled field
analysis (thermal – structural analysis) with performance based failure criteria provided in the
code of practice.
The accuracy of the FE model was verified by comparing the thermal response, structural
response and predicted fire resistance with fire test results obtained. Using the validated FE
model, parametric studies were conducted to investigate the influence of various parameters
affecting the fire performance of HSRC members exposed to fire. From the parametric studies
conducted, simplified calculation models were developed for evaluating the resistance of HSRC
members (columns and beams) exposed to fire. These models were validated with results from
ANSYS and a fire resistance test. The simple model accounts for major factors such as member size, load ratio and fire scenario, and therefore can be easily incorporated into structural design.
The FE model and simple calculation model provide a rational approach for evaluating the fire
resistance of HSRC (members) and predict a more accurate fire resistance than the prescriptive
approach.