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Authors: Srivastava, Major A. K.
Issue Date: 1990
Abstract: Composite materials have a high resistance to short duration - high intensity loads such as caused by impact of projectiles and accidental or deliberate blasts. The energy absorbing capacity of ferrocement is quite high, compared to conventional reinforced concrete. The two coupled together would be expected to give a very high penetration resistance and shatterproof properties against the above mentioned. loads. ' The reported study was based oh experimental investigations carried-out in three parts. One was on impact resistance and two on blast resistance. The impact resistance of ferrocemeht panels against heavy high veloCitY—h011ow. charge based projectiles, formed the first part panels were of the size 1.5 by 1.5m and had sectional thicknesses of 40 and, 50 mm. 8 layers of square woven wire mesh were used for both 40 mm and 50 mm thick panels. 4 panels of each type,were tested. The phenomena noted were the diameter of the.hole formed by the projectile and the crack pattern around the entry and exit points. The theoretical value of the sectional thickness required foripreventing perforation was also calculated, to- give idea of the lethality of the projectile, and to form the basis', for further investigation. The, second part consisted of -the study of resistance of hollow ferrocement cylinders to blast impulse loads. The cylinders were 20, 30 and 40 mm thick and contained 1, 2 and 3 layers of square woven wire mesh, respectively. 'The cylinders were subjected to external high pressure short duration blast loads, and the degree of damage was assessed qualitatively by studying the crack pattern and spalling, and quantitatively by measuring the leakage rate of water' at a constant head, through the cracks and the spalled area. (v) The third part of the investigations involved the testing of one fourth scale models of two separate wall structures of' laced concrete, which represented the headwall and sidewall respectively, of a blast resistant ammunition storage magazine (igloo). The walls were tested for failure against the blast loading which would be caused by the accidental detonation of the contents of an adjacent igloo. Each of the prototype igloos would contain 100 tonnes of TNT (NEC), and the investigation was carried out to determine whether the blast pressures generated by an accidental detonation, would cause failure of the walls, leading to the sympathetic detonation_of the contents of the receiver igloo. The cause for detonation would be residual blast wave pressures and impact of high velocity concrete projectiles from the donor igloo and those which may spall off the inner faces of the roof and wall's. The two walls had a sandwich type of construction, with laced concrete forming the core and.ferrocement the outer layers. The wall thickness, was scaled to 100 mm. One of the walls was earth-mounded, while the other was bare. The expected blast pressures were simulated by detonating different weights of TNT .cum plastic explosive charge at appropriately scaled stand off distances. Three blasts were applied to each wall-seParately, starting from a value below the design pressure and going beyond it, im_pre-designated steps. The phenomena observed were the dynamic strains at eight locations-, the deflections at the centre, and the blast pressures at the centre and top centre of both walls. All phenomena were recorded against time on sophisticated instruments brought specially from the Terminal Ballistics Research Laboratory, Chandigarh. (vi) It was observed that the sectional thicknesses of the ferrocement panels used for the. missile impact test were inadequate to nestr_tc.t penetration/perforation by the missile used. It was concluded by the means of existing empirical perforation equations that a sectional thickness 7 to 9 larger than that used, would be required to prevent perforation by the particular missile. The second part of the investigations 'revealed that cylinders having a wall, thickness..' of20 mm were unable to withstand the applied blast impulse load. However, cylinders with a wall thickness of 30 and 40 mm, respectively, were able to withstand the blast impulse load and retained their integrity.. The third part of the investigations on model igloo walls revealed that the uncovered wall was able to withstand reflected overpressures upto 10 bars, but showed signs of failure at reflected overpressures of 10 bars and above. The covered wall was able to withstand reflected overpressures upto 100 bars without failure. In fact this wall did not manifest any signs of failure except a whole, which may be attributed to lack of sufficient rigidity at the edges. The model earth covered wall was considered suitable for practical application in prototype form.
Other Identifiers: M.Tech
Appears in Collections:MASTERS' DISSERTATIONS (Civil Engg)

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