International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 05 | May -2017
p-ISSN: 2395-0072
www.irjet.net
Impact Analysis on Slabs – A Review Kiran T.1, Arjun Murali2, Dr. Sadath Ali Khan Zai3 1,3Associate
Professor, Faculty of Engineering – Civil, UVCE, Bangalore University, Karnataka, India E. Student, Faculty of Engineering – Civil, UVCE, Bangalore University, Karnataka, India ---------------------------------------------------------------------***--------------------------------------------------------------------2M.
Abstract - Impact loads have gained attention in the past
impact. A steel sphere of size 127 mm diameter and weight 155 N was dropped from a height of 4.35 m at the centre of the slab. The slabs were supported using a stiff steel frame. A load cell was attached to the drop weight to measure the contact force. Displacement transducers and accelerometers were used for displacement and acceleration response measurement respectively. The slabs were impacted till failure and contact force, displacements, accelerations and strains in reinforcements at some specified points were recorded. It was observed that the contact force-time history plot for the impact is an isosceles triangle with duration of less than 2 milliseconds. The strain rate in steel was less than 4/second.
few years. It is important to analyse strategic important buildings like nuclear reactors, military establishments, etc. A lot of research is being conducted in the field of impact loads. This paper gives an introduction to impact loading, its types and responses. A few of the experimental investigations carried out in the impact analysis on slabs have been reviewed and summarized. Key Words: Impact analysis, Slabs, Drop weight
1. INTRODUCTION A civil engineering structure is subjected to many type of loads in its lifetime, of which impact load is a significant but not frequent loading case. Impact loads may be caused due to accidents like rock fall, vehicle or ship or aircraft collision, and terrorist or military conditions like missile impact and blast waves due to explosions, etc. Impact loads are extreme loading case with very little probability to occur during the lifetime of a structure. But, due to increased occurrences of terrorist activities, impact analysis has gained importance in the past few decades to ensure safety of the structures.
Ong et al.[3] (1999) studied the impact resistance of fibre concrete slabs under low velocity projectile impact with different types of fibres and volume fraction. Straight polyolefin, polyvinyl alcohol and hooked-ended steel fibres were used with volume fractions of 0, 0.5, 1 and 2%. The slabs were 1 m square and 50 mm thick. The slabs were simply supported on all four sides over a span of 900 mm in both directions. The impact was achieved by a hemispherical nose shaped projectile of mass 43 kg dropped from a height of 4 m. The impactor had accelerometer to measure the impact loads. All slabs were subjected to single impact only. Steel fibre concrete slabs showed better cracking characteristics, resistance to shear plug formation, energy absorption and integrity as compared to polyolefin and PVA fibre reinforced slabs. PVA fibre concrete slabs showed better energy absorption capacities than polyolefin fibre concrete slabs. It was observed that polyolefin fibres failed both by pull-out and rupture while PVA and steel fibres failed by pull-out only.
The impact loads on a structure can be classified into two limiting cases – hard impact and soft impact. A soft impact is where the resisting structure remains undeformed and the kinetic energy of the striking body is completely converted into deformation. Hard impact can be defined as where the striking body is rigid and kinetic energy of the striking body is completely or partially converted to the deformation of the resisting structure. The response of a structure to an impact load is significantly different than to static and seismic loads. The duration of loading is very short leading to a comparatively higher strain rate. The modes of structural deformation and failure is also different leading to a much complex dynamic response making it difficult to analyse using traditional computational methods. Hence, many researchers have worked on the behaviour of concrete and concrete composites under impact in the past few decades.
Chen and May[4] (2009) experimented on the high-mass lowvelocity impact behaviour of reinforced concrete slabs. Four slabs of 760 mm square and 76 mm thickness and two slabs of 2320 mm square and 150 mm thickness were tested under drop weight impact loading. Three 760 mm square slabs had a steel ratio of 0.6% and one had 1.1% with all concrete cube compressive strength of 60 MPa. The 2320 mm square slabs had a steel ratio of 0.5%. The slabs were clamped at all four corners with both horizontal and vertical movements restrained. Two types of impactors were used, one was stainless steel impactor with 90 mm diameter and a hemispherical profile of 125 mm radius, and the second of mild steel with a 100 mm diameter and flat contact face. The impact forces were measured using a load cell placed between the mass and the impactor. Acceleration at various points on the slab was recorded using
2. EXPERIMENTAL IMPACT ANALYSIS Aravindan and Kurian[2] (1993) studied the impact characteristics of reinforced concrete slabs under low velocity (less than 10 m/s) hard impact loading. 28 slabs of size 1100×1100 mm and thickness 100 and 70 mm and reinforced only at back face were tested under drop weight
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