Issue 78

S. A. Mustafa et alii, Fracture and Structural Integrity, 78 (2026) 298-314; DOI: 10.3221/IGF-ESIS.78.18

Stiffness degradation The lateral stiffness degradation characteristics of RC shear walls under increasing amplitude of cyclic loads were observed. Peak lateral strengths, initial stiffness values, and degradation characteristics of all specimens are summarized in Tab. 3, while extracted backbone curves are shown in Fig. 12. All walls reached their maximum base shear at relatively low drift levels, after which progressive degradation occurred. The secant stiffness, Ki is evaluated from Eq. (1) as the slope between the lateral load–displacement values at the maximum and minimum target displacements of each loading cycle, as illustrated in Fig. 13;

Fi   

Fi



(1)

Ki

  

i

i

where: ±Fi and ± Δ i are the positive and negative peak loads and corresponding displacement of peak point for each loading cycle i, respectively. Fig. 14 shows the development of the lateral degradation of secant stiffness for specimens at each loading cycle. As illustrated in this figure, the secant stiffness for all specimens decreased with the increase of cycle number. Also, the lateral secant stiffness of the control shear wall was the highest one. Drift capacity and ductility measures Ductility is an important parameter to measure the plastic deformation capacity of components and structures. To evaluate the ductility of specimens C.S.W, S.W.I 1, S.W.I 2 and S.W.I 3, two main parameters, displacement ductility factor μ and ultimate rotation angle δ , were used in this study. The displacement ductility factor μ is usually defined as the ratio of the ultimate displacement to yield displacement Eq. 2, while the ultimate rotation angle δ is usually defined as the ratio of the ultimate displacement to the specimen height Eq. 3. The expressions are as follows:

Δ Δ

u

(2)

  

y

Δ

H u

u  

(3)

However, there is no unified definition of yield displacement for shear walls as a result of the inconspicuous yield point. In this experiment, a conventional method proposed by Park et al., was adopted, and the yield displacement Δ y was defined as follows: a secant was drawn to intersect the lateral load–displacement curve at 60% F peak from 0, and this line was extended to the intersection with a horizontal line corresponding to F peak ; then the horizontal ordinate of the intersection was regarded as the yield displacement. For all specimens, the ultimate displacement Δ u was taken as the displacement when the remaining capacity dropped to 80% of the peak applied load. The experiment results are given in Tab. 4. C.S.W exhibited the most ductile behaviour among the specimens tested. The best behavior compared to C.S.W was the S.W.I 3.

Figure 13: Definition of stiffness degradation .

Figure 12: Envelope curves tested walls.

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