9g o f a” BACKGROUND e Previsg:: ~nalytical and exverimental worzee2/ on isolated coniferous trees established that aerodynamic drag of tree crowns due to the action of particle velocity is a factor causing stem and branch breakage. The impulse given the tree crowns by the peak static overpressure is small since static pressure equalizes around individual components of the crown with the shock velocity. Structures having natural periods substantially longer than the time required for pressure gqualization respond to the drag impulse of the dynamic pressure 1/2pu° where eo is the air density following the shock and u the particle velocity. The dynamic pressure pulse is characterized by/its peak value, the positive phase duration, and bhe wave form factor.— Crown characteristics and drag measurements 240 combined with breakage deflection and breakage force measurements,’ resulted in an analytical prediction system for breakage of isolated trees. Breakage force-deflection measurements for static loading of ponderosa pines chow that force and deflection at breakage vary approximately 300 per sent between the extremes. On UPSHOT-KNOTHOLE an artificial stand of coniferous trees 320 ft long by 160 ft wide, composed of 145 ponderosa pine trees everaging 51 ft in height, was exposed at 4.5 psi seak static overpressure. The stand was instrumented along and across the stan’ with ground level static pressure gages and plitot-type dynamic pressure gages at three elevations 250 ft from front of stand. Ground-level pressure measurements showed no significant attenuation in peak static pressure or increase in rise times. UPSHOT-KNOTHOLE results indicate that the prediction system for isolated trees was conservative when applied to small coniferous stands. However, in view of the unknown degree of attenuation for stands of large extent and the tenuous nature of the specification of military damage with respect to tree damage, isolated tree damage predictions were assumed representative of damage tu tree stands. On the basis of ana.ysis of all available data, a general breakage prediction system was developed which represents various levels of probability of breakage 2/ Operations Research Office, Preliminary Study of the Consequences of an Atomic Explosion Over a Forest, ORO-T-105, 1950, CONFIDENTIAL. 3/ AFSWP, SNAPPER, Project 3.3, Blast Demage to Trees--Isolated Conifers, WI-509, January, 1953, CONFIDENTIAL--Restricted Data. 4/ AFSWP, UPSHOT-KNOTHCLE, Project 3.19. 5/ U. S. Dept. of Agriculture, Forest Service, Div. of Fire Research, Experimental Investication of Aerodynamic Drag in Tree Crowns Exposed to Steady Wind--Conifere, Phase Report for Operations Research Office, December, 1951, CONFIDENTIAL. 6/ U. S. Dept. of Agriculture, Forest Service, Div. of Fire Research, Crown Characteristics of Several Coniferous Tree Species, AFSWP interim Tech. Report 416, Ferruary, 1975. 7/ U. S. Dept. of Agriculture, Forest Service, Div. of Fire Research, Tree Breakage Characteristics Under Static Loading, AFSWP Interim Tech. Report 400, January, 1953, CONFIDENTIAL. 14 SECE T- RESTRICTED DATA vO rit > Fo. Se ie 4 1.2