Chopter 4 BLAST EFFECTS The blast-effect program consisted of five projects under the categories of structures, crater survey, tree-stand studies, and minefield clearance. Within these categovies, the principal planned objectives of Program 3 were to: 1. Obtain further Jata on structural loading underair--blast conditions, for the puroose of developing prediction techniques applicable to the calculation of structural response and consequent damage from high-yield nuclear devices (Project 3.1; 2. Determine the dimensions cf the apparent craters furmed by Shots 1, 3, and 4, in order to assist in tae prediction of the crater produced by a high-vield nuclear weapcn. The two situations of particular interest on Castle were a surface burst on land and a surface burst in relatively shallow water (Project 3.2). 3. Obtain data on the blast effects on three natural tree stands in support of siuiies on blast-damage prediction to forested areas. These were to provide a method of aamage assessment to material and personnel, knowledge of the amount cf cover 2 forest a ords, and the impediment to trcop movements through or cut of a forested arza after a forest~ damaging detonation (Project 3.3). 4. Determine the effects of a surface-detorated nuclear device un a plarted sex rinefield (Project 3.4). An additional objective was added during Castle to provide for tie documentation af damage inflicted upon miscellaneous structures from the unexpectedly high vield of Shot 1 (Project 3.5). 4.1 STRUCTURES PROGRAM The structures program consisted of a planned Project 3.1, in which a 6-by-6-by-12foot rigid concrete cubicle was instrumented for blast loading, and an unplanned Project 3.5, which consisted of dccumentaticn of unexpected damage to structures from Shot 1. Until late in the pianning stage, it had been intended to reinstrument a test structure remaining from Operation Greenhouse —-a multistory building 26 feet in height, 196 feet in width, and 52 feet in length, sectionalized into various types of construction (Ariny Tests Structure 3.1.1). It was planned to perform limited rehabilitation of the structure, to augment the existing gage mounts with mounts to obtain more corner and edge joading detail, and to make limited use of displacement gages. A change in cetonationsites made it necessary to abandon this plan, and adopt instead a different approach (see Appendix). Both the original and final plans for Project 3.1 were modest in scope, since construction costs in the EPG were very high, all construcdon was difficult, aad iand area suitable for a structures program was very limited. In addition, no extensive structures program could be justified until the extensive data obtained at Upshot-Knothole had been analyzed, a task which was just being initiated when decisions on the Castle program had to be made. Accordingly, Castle Project 3.1 was designed to provide blast-loading data only on the rigid concrete cubicle (Figure 4.1). The cubicle size and gage locations were determined 58