PSI - Issue 70

Blessy Grant C J et al. / Procedia Structural Integrity 70 (2025) 247–254

253

The decay in strength i.e., reduction in ultimate load bearing capacity and its decreasing energy absorbtion capacity of LRC 45 is not as significant as LRC 60 and RC 90 on comparing the first load cycle. By comparing the cycle, the hysteresis loop of LRC 45 were fatter than LRC 60 and RC 90 showing larger area enclosed by the curves. 4.2 Ductility The ductility factor quantifies this ability and is defined as the ratio of maximum deflection at any load level to the deflection at first yield. The yield deflection is determined from the cyclic load-deflection curve, assuming bi-linear behavior.

Table 2. Comparison of average ductility (last cycle) of the specimens.

Specimen

Deflection at yield ( Dy )

Deflection at ultimate load ( Du )

Ductility factor

Average Ductility

+ve

-ve

+ve 25.8 12.0

-ve

+ve 2.15

-ve 2.0

LRC 45 LRC 60

12

11.0

22

2.08 1.50

7.50 6.0 11.7 8.0

8.40 1.60 10.40 1.35

1.40 1.30

RC 90 1.33 When a structure undergoes cyclic loading, the cumulative ductility refers to the sum of ductility attained in each load cycle at the maximum load level (Thirugnanam 2002).Thisparameteris crucialto be considered for a seismic resistant structure, asit provides insightregarding overall ductility of the structure. Higher the cumulative ductility factor, higher will be the load carrying capacity. This highlights that the beam’s ability to undergo higher deformation improved with the adoption of inclined shear reinforcement. 4.3 Energy absorption capacity The energy absorbed is represented by the area enclosed by the hysteresis loop and indicates the structural element's ability to mitigate seismic impact through inelastic behavior of reinforcing steel. This process may result in excessive cracking and permanent deformation, but it can effectively reduce the impact of the seismic event. The cumulative energy absorption was determined by summation of the energy absorption capacity from each load cycle. 14.85

Table 3. Stiffness degradation of the specimens. Cycle number LRC 45

LRC 60

RC 90

Forward cycle ( N/m )

Negative cycle ( N/m )

Forward cycle ( N/m )

Negative cycle ( N/m )

Forward cycle ( N/m )

Negative cycle ( N/m )

1 2 3 4

7 5

5.3 4.3 3.2 1.8

6

4.5 3.4

5.5

4

4.4 2.8 1.9

4

3.1 1.7

3.2

.8

2.5 1.8

2

1.6

1

4.4 Stiffness characteristics Stiffness is defined as the amount of load needed to produce a unit deflection in a specimen. In this experimental investigation, stiffness was measured by the slope of a tangent drawn at 75% of the maximum load in each cycle (Thirugnanam 2002). It was observed that all specimens exhibited a general degradation in the stiffness. Stiffness degrades as the load increased. The stiffness of LRC 45 was found to differ from 5.3 kN/mm in the first load cycle to 1.8 kN/mm in the last load cycle. The stiffness degradation of LRC 45 is less compared to LRC 60 and RC 90 as in Table 2. As the lace bars contribute to a larger value of moment of Inertia, the stiffness of the beam gets enhanced. In LRC beams, these laced bars are integrated into the web of the beam, forming a truss-like internal configuration,