Experimental Studies Of Dynamically Loaded Footings On Sand
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Experimental Studies of Dynamically Loaded Footings on Sand
DENTIFIERS: Footings. An investigation of the strength and behavior of spread footings subjected to dynamic forces is reported. To this end a single-degree-of freedom model representing the spread footing and its supporting medium was developed. The supporting medium was restricted to either a cohesive or cohesionless soil. Tests were conducted to aid in the correlation of the model components with the anticipated response behavior of spread footings. A correlation between the analytical model and the experimental results could not justifiably be carried out as the container affected the test medium. Results showed a finite increase in the dynamic bearing capacity of spread footings over their static capacity. Within the limited instrumentation, the dynamic settlement of the test plates is due to the establishment of failure surfaces. For se tlements equal to the maximum dynamic settlement, the applied dynamic load varied from 1.20 to 2.28 times the equivalent static load. (Author).
A Model Study of Dynamically Loaded Square Footings on Dry Sand
The investigation reported herein was undertaken to develop an approach to modeling displacements of surface and shallow-buried footings on dry sand subject to high-intensity, single-pulse loads. A hypothetical shallow-bured structure with an isolated footing loaded by airblast overpressure produced by detonation of a nuclear weapon was assumed for design of load pulses on nine model footings used: footing widths of 4.5, 6.0, and 7.5 in. and depth-of-burial to footing width ratios of 0, 0.5, and 1.0. The principles of similitude were used to scale length, force, and time in the models. The models were placed in mobile test bins of uniform, fine, dry sand (90 percent relative density) and subjected to dynamic and static loading. Nondimensional load-displacement relations dependent only on depth-of-burial ratio were developed relating maximum displacement to peak dynamic load, footing width, and soil shear strength gradient. When the dynamic response of the footings in the form of reaction-displacement curves was compared with static response, an increase in initial stiffness and ultimate strength was observed for dynamic loading. However, these dynamic increases were greatest when the static shear strength was lowest, i.e. footings on the surface, and were least for footings buried at a depth equal to its width where the static overburden produced a substantial increase in shear strength. (Author).
Static and Dynamic Plate-bearing Tests on Dry Sand with Overburden
Six static and 53 dynamic soil-bearing tests were made under simulated overburden pressures of zero to 15 psi to determine the load-displacement characteristics of buried footings. The static bearing modulus increased as overburden pressure increased up to an overburden pressure of approximately 6 psi. The dynamic bearing modulus increased exponentially with overburden pressure to an overburden pressure of 15 psi. Up to 3 psi overburden pressure, dynamic modulus was larger than static; but the difference was less at 3 psi overburden than at zero. The relationship between static and dynamic moduli was not firmly established for overburden pressures greater than 3 psi. These tests were made on a 15-inch-diameter bearing plate in dry sand using the NCEL atomic blast simulator. (Author).