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TECHNICAL PAPER

FRACTURE MECHANICS AS

THE BASIS FOR STRUCTURAL

DESIGN OF FIBRE AND TEXTILE

REINFORCED CONCRETE RAVINDRA GETTU*

Abstract explanation of strain-softening in concrete. Though considerable
work was dedicated to the study of the fracture process, size
Fibre and textile reinforced concretes are composites with effect of failure, modelling through finite element analysis and
cementitious matrices and reinforcement in the form of discrete criteria for crack propagation in concrete , little impact was
[1]
fibres or yarns. Since the matrices are brittle and defect sensitive, made on actual application, other than understanding the
which may also be the case for some reinforcements such as mechanisms or principles that governed these phenomena. The
glass and basalt, the behaviour is evidently governed by fracture main reasons for not being able to apply fracture mechanics
mechanics. The review presented here discusses relevant directly in the design of concrete structures are that the
developments, specifically at Indian Institute of Technology tensile response of concrete is largely ignored and that the
(IIT) Madras, related to these two materials with the objective presence of the ubiquitous reinforcement negates most of
of characterising them in a rational manner, so as to improve the fracture related response of concrete. However, important
the performance and structural design. The main highlight of developments based on fracture mechanics followed in the
the work has been the development of testing methods and areas of fiber reinforced concrete, in which case cracking occurs
models to represent the post-crack response of the composite, in a controlled manner and the tensile response can be used
such that this could be the input in the engineering of better advantageously in structural design.
materials and for structural design. Key research contributions
arising from the work have been reviewed, including the use of Substantial work has been carried at IIT Madras for more than
interface finite elements to represent the cracking; development two decades on fibre reinforced cementitious composites where
of a toughness test method that led to the IS: 17161, slab and fracture mechanics principles have been the bases for modelling
pavement design methods, the inverse analysis procedure for the response and formulating rational structural design.
determining the tensile constitutive relationship, fatigue and Additionally, an important objective of the trajectory has been to
creep responses of fiber reinforced concrete; and the uniaxial promote analysis and design for field applications. Some of the
tensile test method, including appropriate specimen fabrication relevant research outcomes are reviewed here with the intention
and end conditions, the transition in the stress-strain response of showing the evolution and the breadth of the work done,
from softening to trilinear to bilinear, efficiency factors, size and the references covered should be taken as illustrations of
effects in the tensile response, durability criteria for design, and the application of fracture mechanics. The paper is meant to be
degradation mechanisms of textile reinforced concrete. For the author’s perspective on institutional research on the topics
both types of composites, pilot projects, mostly novel in the covered, with an emphasis on scientific developments, and not a
Indian context, have been undertaken based on the research comprehensive or critical review.
outcomes, with many of these currently being in service on the
IIT Madras campus. 2. FRACTURE MECHANICS BASED ANALYSIS
OF NON-PLANAR CRACKING
1. INTRODUCTION
Cracking in concrete structures and many other cases is mostly
Fracture mechanics is the science of appropriately representing non-planar, which poses questions in fracture mechanics based
and modelling the growth of cracks in a solid. Significant analysis as to (1) whether the crack propagation is in mixed-
effort focused on the fracture mechanics of concrete from the mode (i.e., opening and sliding) or in pure Mode 1 (opening
early 1980s onwards and was a very popular research topic or tensile mode) and how to represent the crack as it develops
for a couple of decades, along with the characterization and and propagates. Such situations arise in the diagonal shear

42 THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026
* Corresponding author: Ravindra Gettu, Email: gettu@iitm.ac.in