THE DYNAMIC RESPONSE OF SHALLOW-BURIED ARCHES SUBJECTED TO BLAST LOADING
A study was made of the effectiveness of the surrounding soil in restraining the lateral movement of shallow-buried arches subjected to blast overpressures from a nuclear explosion. The arches were considered to be buried near the surface of a semi-infinite soil mass. The term shallow-buried'' is used to refer to a configuration and amount of earth cover such that reflected and dynamic pressures are not effective in loading the arch and yet not so great as to provide significant free-field attenuation of air-blast-induced overpressures in the soil. Depths of cover over the crown exceeding one-half of the arch span were not considered. This restricted the location of the arch to a region adjacent to the earth's surface in which there appeared to be no measurable attenuation of freefield overpressures in the soil and in which the restraint offered to soil movement by the blast overpressure acting on the ground surface was significant. The approach used led to conservative results for deeper burial. A theory was developed for the expression of the combined resistance of the arch and the soil to dynamic loads. In writing the equations of motion the deformation resistance of the arch was expressed in terms of the capacity of the arch rib cross section while the deformation resistance of the soil was expressed using classical earth pressure theory to define the states of stress developed in the soil surrounding the arch as the arch-soil structure'' responds. The inertial resistance of the arch was related to the mass of the arch while the inertial resistance of the soil was related to that portion of the surrounding soil mass which may logically be assumed to move with the arch during response to a blast load. The theory was developed for parabolic arches with circular arches included as a special case. The arch may have any distribution of mass and thickness. The dynamic analysis was simplified by replacing the actual soil and arch system which is continuous and has an infinite number of degrees of freedom by a discrete framework consisting of a series of rigid bars, flexible joints and point masses. Both elastic and inelastic deformations were permitted. The equations of motion were solved using a step-by- step metirod of numerical integration. The problem was programmed for solution on the ILLIAC, the high-speed digital computer at the University of Illinois. A series of numerical solutions is presented for varying combinations of arch geometry and material, depth of earth cover, overpressure loading, seismic velocity in the soil, and ratio of horizontal to vertical overpressure induced in the soil by the shock wave in air. The effects of the various parameters are noted and discussed. It was concluded that well compacted soil surrounding a shallow-buried, underground arch contributes the major portion of the resistance of the archsoil structure'' to lateral deformation under the blast loading resulting from a nuclear explosion.
- Research Organization:
- Univ. of Illinois, Urbana
- NSA Number:
- NSA-16-022289
- OSTI ID:
- 4827415
- Journal Information:
- Dissertation Abstr., Vol. Vol: 22; Other Information: Orig. Receipt Date: 31-DEC-62
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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