Behavior Of Flexible Cylinders Buried In Sand Under Static And Dynamic Loading

Behavior of Flexible Cylinders Buried in Sand Under Static and Dynamic Loading

The general objective of the investigation was to study experimentally the behavior to failure of flexible, horizontally oriented cylinders buried at various depths in dense, dry sand and subjected to either static or dynamic surface overpressures. Static and dynamic tests were conducted on 33 different cylinders, fabricated of high-yield-strength aluminum. Results indicated that collapse of the cylinders occurred while the strains in the cylinder walls were still in the elastic range. The cylinders buried at the shallow depths (zero to one-half cylinder diameter above the crown) collapsed by a catastrophic snap-through or caving of the crown. For the cylinders buried at depths of three-quarters to two cylinder diameters above the crown, the mode of collapse was an instantaneous elastic buckle that occurred at the spring line or invert of the cylinder. The collapse mode of the cylinders under dynamic overpressure was similar to that of the cylinders collapsing under static overpressure. The results of the investigation verified the applicability of an equation for predicting the static collapse overpressure for smooth-walled, horizontally oriented, buried cylindrical structures and entranceways. The hoop-compression theory was found to be applicable for analyzing the structural design to determine if the cylinder would collapse in the elastic range. (Author).

Behavior of Stiff Cylinders Buried in Sand Under Static Loading

Behavior of Circular Tubes Buried in Sand Under Dynamic Loading

The general objective of this investigation was to study experimentally the behavior to failure of flexible, horizontally oriented circular tubes buried at various depths in dense, dry sand and subjected to dynamic surface overpressures. Dynamic tests were conducted on ten brass tubes in the Small Blast Load Generator. The tubes had a wall thickness of 0.005 inch, an outside diameter of 4 inches, and a specially isolated 5.75-inch-long test section. The tubes were flexible and had a stiffness EI/R3 of 0.018 psi. To examine the effect of depth of burial, tests were conducted in dense, dry sand at depths ranging from 1 to 16 inches, or four tube diameters above the crown. The dynamic tests were conducted at overpressures ranging from 6.2 to 34.9 psi. Measurements were made of the applied overpressure, and the tube deflection was recorded by means of a high-speed camera linked to the pressure-time base. Results indicate that collapse of the tubes was initiated by a buckle that occurred along a longitudinal seam where the tubes were spliced. The dynamic collapse overpressure increased greatly with increased depth of burial down to a depth of one tube diameter; subsequently, the increase in collapse overpressure with increase of burial depth to four tube diameters was insignificant. The dynamic collapse overpressure was approximately the same as the static collapse overpressure as determined from correlation with previously reported results. The results of this investigation have verified the applicability of an equation for predicting the dynamic collapse overpressure of very flexible tubes. (Author).