In this research, the fracture mode of the specimen was determined by the ductility index
"[mu]" proposed by Jeong  shown in Figure 8.
(the ratio of deflection at ultimate load ([[DELTA].sub.u]) to deflection at yield load ([[DELTA].sub.y])) is calculated to show the effect of strengthening on the ability to carry inelastic deformation.
Although these specimens failed at similar maximum loads, SFRC-D10-S100, which was reinforced with steel fibers, exhibited the highest ductility index
calculated as follows:
. Ductility under the static load refers to the measure of performance of a concrete structure that can maintain inelastic deformation before failure without any significant reduction in the ultimate strength.
Under bending test, load-deflection curve of the bolt specimens indicated large ductility index
and clear strain hardening after reaching the proportional limit load.
is used as the basis to evaluate the material behavior that represents the ability of a concrete beam to undergo a large deformation while maintaining its load-resisting capacity or a significant portion of it.
The ductility index
, Eqn (12), is also used to study the effect of steel wall thickness on the ductility of the columns.
Beaumont and others define an adimensional parameter called ductility index
used to establish the impact performances of different materials with similar geometries.
The ductility index
was calculated according to Eq.
It is also clear that, strengthening with externally bonded GFRP strip in different layers to tension face of precracked and uncracked beams result in reduce the beam ductility index
(ratio between deflection at failure and its deflection at yield) than that of the control beam.
On the other hand, the ductility index
decreased as the number of CFRP layers increased.
The shear and flexural definition of ductility index
y consist of the ratio of the area of the load-deflection response.