STATIC AND DYNAMIC PROPERTIES OF FIRE - RESISTANT WOODEN STRUCTURAL ELEMENTS October 1966

A series of treated and untreated laminated Douglas fir beams and plywood panels were subjected to static and dynamic loads to study the effects of pressureimpregnation with fire-retardant chemicals on the mechanical properties of wood and to extend the existing knowledge cf the dynamic properties of wood. Results from the beam tests indicate that designs should be based on use under wet conditions when large timbers are to be pressure-impregnated with fire-retardant chemicals; this is because of the hygroscopic nature of treated lumler. It was also found that the allowable static design load can be applied dynamicjlly without damage to the beam. Ultimate resistance of dry untreated beams to dynamic loads was about 1.6 times the allowable design load for dry wood; for treated beams, the ultimate resistance to dynamic loads was about 1.4 times the allowable design load for wet lumber. Results from the plywood shear tests indicate that fire-retardant treatments reduce the mechanical properties of plywood in shear and that the reduction is proportional to the amount of salt retained in the wood. :e nmtErni Mfftann c .UTM. mJdJfc^