Theoretical and Experimental Investigation of Buried Concrete Structures. Volume III. Feasibility Study of Tensile Strain-Rate Sensitivity of Concrete.

摘要

For previous research conducted by the project team on the subject of dynamics of buried structures, it was determined that internal blasts excite an arch predominately in a breathing or tensile mode. The critical stresses and strains resulting from such loadings occur in the first few milliseconds after detonation. These critical values, and their relationship to the failure mechanism of plain concrete was the purpose of this research effort. Since a thorough investigation in this area is expensive and time consuming, a short feasibility study was undertaken and a number of reasonably uncomplicated experiments were conducted as a pilot study. Static and dynamic tensile splitting strength tests were performed with varying stress rates. Two loading techniques, an electro-servo-controlled hydraulic and a drop hammer, were tried. While the shape of the loading function was more easily controlled with the hydraulic system, only the drop hammer method was capable of producing the fast (1 to 40 ms.) rise time to failure that was desired. Conclusions were reached that the tensile failure strength of plain concrete can be accurately determined using a drop hammer equipped with a large capacity dynamic load cell (200,000 pound capacity) for rise times in the above mentioned range. (Author)