PSI - Issue 64

Austin Martins-Robalino et al. / Procedia Structural Integrity 64 (2024) 418–425 Martins-Robalino and Palermo / Structural Integrity Procedia 00 (2019) 000 – 000

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3.3. Increased Reinforcement Ratio Along Wall Base

A further modification included increasing the smeared reinforcement along the first row of elements in the model. This change reflected the fact that during fabrication of the reinforcement cages the horizontal reinforcement along the base of the wall provides additional confinement not captured in the preliminary models. Smeared reinforcement ratios are typically calculated as “strips” with a tributary distance of half the c/c spacing of reinforcement on each side of the reinforcing bar they represent. In the case of the first set of horizontal reinforcing bars and buckling ties which predominantly contribute to confinement of concrete above the foundation, the reinforcement ratio has a greater impact on the first row of elements. This modification controls the premature failure due to sliding along the base of the wall in the numerical models while not impacting the lateral load capacity. 3.4. Updated Models The load-displacement results of the updated set of models (V2) which incorporated the Modified Bentz 2005 with Local Fracture tension stiffening model, a reduction in bar area of 2.75% along the base, and an increased reinforcement ratio along the wall base are superimposed against the experimental results in Fig. 6. All changes were consistent between the models of Walls SWS and SWN. The V2 model for Wall SWS maintained similar peak load predictions to model V1 (131 kN and -122 kN), but provided a more reasonable ultimate displacement and failure mode by exterior steel bar rupturing along the base during the negative cycle to 84 mm. The V2 model for Wall SWN provided peak load predictions of 125 kN and -123 kN similar to the experimental results and model V1. Although the model does not provide significantly improved predictions for displacement, with failure during the 156 mm displacement cycle compared to the 168 mm cycle prediction provided by model V1, the failure mechanism is more representative of the experimental results. The V2 model failed due to buckling of a steel reinforcing bar in the web along the wall base, similar to the damage observed after completion of testing shown in Fig. 5.

a) b) Fig. 6. Lateral load-displacement response of (a) Wall SWS V2; (b) Wall SWN V2.

4. Discussion and Conclusions The focus of this study was to highlight local phenomena that should be considered in modelling SMA-steel hybrid and steel RC shear walls. Based on preliminary models not capturing proper failure modes and reasonable displacement capacities the inclusion of local fracture, reduction of bar area, and increasing the smeared reinforcement ratio along the wall base were applied based on the observed phenomena of the wall during testing. Note that for the reduction in bar area a 2.75% reduction was assumed. The intent was not to state a precise percentage that the bar area should be reduced, but to illustrate that in cases where strain gauges are installed on deformed reinforcement, numerical models should consider this phenomenon of reducing the bar area for more accurate results. When the three