PSI - Issue 6

Vimal Kumar et al. / Procedia Structural Integrity 6 (2017) 95–100 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

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(2017), Xiao et al. (2016), Travaš et al. (2009), Anil et al. (2016), Foti and Paparella (2014), Yousuf et al. (2013), Remennikov et al. (2011), Wu et al. (2015), to identify the resistance and behavior of plain, reinforced, fiber reinforced and steel-concrete composite structural members such as beams, slabs and columns subjected to falling weight impact loading. In fiber reinforced concrete studies, an increase in the volume of fiber content and their length in the concrete mix has been found to reduce the workability and viscosity of the concrete by Mastali et al. (2017). On the other hand, it found to improve the mechanical properties, strength and energy absorption capacity of the concrete by Mastali et al. (2017), Ulzurrun and Zanuy (2017). Increase in the strength of the concrete was also found to be sensitive with the variation in the fiber types (smooth, hooked, prismatic) by Ulzurrun and Zanuy (2017). The polyethylene terephthalate (PET) fiber has better corrosion resistant properties than the reinforcement therefore suggested an effective way for replacement of steel fiber to produce light weight concrete for adverse environmental conditions in Foti and Paparella (2014). Though, some compromise was made with the strength and other mechanical properties of concrete. In reinforced concrete studies, the failure mode of the target beam specimen has found to change from bending to shear when the rate of loading increased from static to impact conditions by Travaš et al. (2009). In addition, displacement in the reinforced concrete specimens has increased with increase in the number of repetitions in the fall of the impactor by Anil et al. (2016). This increase in the displacement was due to accumulated permanent damage in the concrete. The impact studies on the stainless steel-concrete and carbon steel-concrete structural members, Yousuf et al. (2013), Remennikov et al. (2011), showed that the former had relatively higher ductility and strength improvement against impulsive loading. Further, the replacement of infill concrete (in concrete filled tubes) with the foam material has reduced the energy absorption capacity of the composite members by Remennikov et al. (2011). The available studies pertaining to prestressed concrete (PC) specimens subjected to falling weight impact are very limited, Iqbal et al. (2017), Kumar et al. (2017 & 2017). An increase in the impact force and deflection of the slabs have reported with increase in the kinetic energy of the impactor. For a given drop height, the prestressed concrete has reported higher impact resistant and found to be higher energy absorbing material compared with reinforced concrete (RC). However, the behavior and damage resistance characteristics of prestressed slabs of high strength concrete is rarely reported in the literature. 2. Material and test specimens The high-strength reinforced and prestressed concrete slabs were square in the shape (800 mm) having a constant thickness 100 mm. The compressive strength of the concrete was obtained by casting of cubes (150 mm) from the same concrete batch used for casting of slabs and their testing under a Compression Testing Machine (CTM) at the loading rate approximately 140 kg/sq.cm/min. The unconfined compressive strength of the concrete obtained after a curing period of 28 days was 72 N/mm 2 . Both the prestressed and reinforced concrete target slabs were casted using the same concrete batch mix and also cured in water in identical ambient conditions for 28 days. The prestressed concrete slab had similar reinforcement pattern as provided in reinforced concrete slab with additional prestressing force. Thus, the only difference between PC and RC slabs was the applied pre-tensioning force, was studied in the present study. The initial stress induced in concrete was approximately 20% of its unconfined compressive strength. 3. Experimental approach The prestressed and reinforced concrete slabs were tested in a drop weight impact setup. The setup has the capacity to lift a steel weight of 300 kg up to a drop height of 1.75 m. In present study prestressed and reinforce concrete slabs were impacted by freely dropping a steel mass (243 kg) at the center of the slab span from 500 and 1000 mm. All the edges of the slabs were fixed in a steel frame to provide symmetric support conditions. The impactor was then lifted up to the predefined drop height and allowed to fall under gravitational force from rest, see Table 1. The generated impact force, support reaction, displacement and acceleration response was recorded in a data acquisitions system at a time interval of 1 × 10 -4 second and compared with that of the reinforced concrete slab.

Table 1. Details of target prestressed and reinforced concrete slabs.