PSI - Issue 64

Shamsoon Fareed et al. / Procedia Structural Integrity 64 (2024) 1057–1064 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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however, they are vulnerable to punching shear failure, which may prove to be catastrophic. Due to the increased population, the construction industry has expanded significantly over the years, and as a result, construction and demolition waste in millions of tonnes are generated annually all over the world. For sustainable construction, it is important to efficiently utilise all available natural and recycled resources; therefore, this waste may be utilised to produce recycled aggregate concrete (RAC). The usage of RAC in the construction of structural elements has shown beneficial outcomes in terms of strength, serviceability, and sustainability of building construction (Arezoumandi, 2015; Etxeberria, 2007; Seara-Paz, 2018; Khan, 2020; Ajdukiewicz, 2007; Choi, 2012; Hastemoglu, 2015). Slabs supported directly on the columns may exhibit sudden and abrupt failure due to the punching of columns in slabs. To avoid such failures, different strengthening and/or retrofitting techniques may be adapted to provide additional support to the members. The external strengthening provided by carbon fibre-reinforced polymer strips improved the strength of the structural elements but also exhibited ductile failure under severe loading conditions. Several researchers have conducted studies to examine the response of slab-column connections under punching shear. Based on these studies, decrease in the punching capacity of the RC slab was observed as the thickness of the slab increases due to the size effect (Guandalini et al., 2009). An increase in the slenderness ratio of the slab reduced both the flexural stiffness and shear capacity (Einpaul et al., 2016). The depth of the RC slab significantly influences the punching shear capacity (Rankin and Long, 2019). It was also found that flexural reinforcement increases the capacity of slab in punching irrespective of the spacing used for providing reinforcement used (Jang et al., 2019). Based on the investigation of the effect of compressive strength and replacement ratio of recycled aggregates in column-slab specimens, the punching capacity was found to increase with the increase in the concrete compressive strength. However, the 0%, 50%, and 100% replacement of the natural aggregates witht the recycled aggregate do not significantly influence the behavior of the specimen in punching (Sahoo and Singh, 2021). Furthermore, the punching capacity and ductility of the RAC slabs decrease with the increase in replacement percentage of RAC with NAC, whereas, the inclusion of steel fibres improves the overall integrity of the slab (Xiao et al., 2019). It is evident from above that the behaviour of the RAC reinforced concrete two-way slabs cast with has not been studied extensively. Furthermore, the punching response is also influenced by several parameters which have not been studied extensively. Therefore, the work presented herein numerically investigates the punching shear response of the RC two-way slabs strengthened and/or retrofitted with CFRP strips. 2. Numerical Investigation A comprehensive finite element (FE) study was conducted using ABAQUS (Abaqus, 2014) to study the response of the RC two way slabs, which may be influenced by several parameters. The parameters considered in this study include; (i) placement of the CFRP strips; (ii) thickness of slab; and (iii) concrete compressive strength. Figure 1 shows the matrix of variations for different parameters used in the numerical investigation. Initially, a finite element (FE) model was developed (Figure 2) with the same cross-section dimensions and thicknesses as used in the experimental investigation by Fareed and Khan (2022) to validate the model. In the experimental investigation, 75 mm thick two-way square slabs of 670 mm × 670 mm were used. A square column of 100 mm × 100 cross-section and an overall height of 275 mm was placed and cast at the centre of the slabs. Details of the two-way slabs used in the experimental investigation are shown in Figure 2. In total, eight slabs were prepared with four each of NAC and RAC were prepared. For the case of specimens prepared with recycled aggregates, 30% natural coarse aggregates were replaced. Two slabs each, from NAC and RAC, served as control slabs, and the other four specimens were strengthened with 80 mm wide CFRP strips as shown in Figure 3. It is pertinent to mention here that the slabs are constructed upside down. However, due to experimental restrictions, they are modeled the other way, as shown in Figure. To simulate punching effect on the slab, the two-way slab was vertically restrained along all edges for all FE models used in numerical investigation. To model the elastic properties of concrete, steel and CFRP, Young’s Modulus and Poisson’s ratios were defined. Overall behavior of steel, concrete and CFRP strips were modeled using already available metal plasticity, concrete damage plasticity, and Hashin models in ABAQUS, respectively. The material models used for FE investigation are enlisted in Table 1. It is essential to note that the concrete damage plasticity (CDPM) model is based on the concrete compressive strength and elastic modulus; thereby, NAC & RAC specimens were modeled using these values obtained from experimental program conducted by Fareed and Khan (2022).