IN-SITU STRENGTH EVALUATION OF THERMALLY DEGRADED FIRE- RETARDANT-TREATED PLYWOOD

FIRE-RETARDANT TREATED PLYWOOD, FRTP, HAS BEEN USED AS ROOF SHEATHING IN APPROXIMATELY ONE MILLION DWELLING UNITS THROUGHOUT THE EASTERN UNITED STATES. IN THE MID AND LATE 1980'S A SIGNIFICANT NUMBER OF STRUCTURES BEGAN TO EXHIBIT SEVERE THERMAL DEGRADATION OF FRTP AS A RESULT OF ABSORBED SOLAR ENERGY. DUE TO A VARIETY OF FACTORS, IT IS NOT POSSIBLE TO PREDICT HOW FRTP WILL PERFORM IN ANY PARTICULAR STRUCTURE. CURRENTLY, THERE IS NO RELIABLE, EASILY USED METHOD OF IN-SITU NONDESTRUCTIVE EVALUATION OF FRTP. VISUAL INSPECTION OF SUSPECT MATERIAL IS PRESENTLY THE MOST COMMON METHOD OF ASSESSING THE CONDITION OF FRTP, YET SIGNIFICANT STRENGTH LOSS CAN OCCUR BEFORE THERE IS ANY VISUAL EVIDENCE. A METHOD IS PROPOSED TO EVALUATE FRTP IN-SITU WHICH INVOLVESTHE RELATIONSHIP BETWEEN MECHANICAL IMPULSE AND THE PHYSICALPROPERTIES OF MATERIALS. SPECIFICALLY A NUMBER OF LOW ENERGY MECHANICAL IMPACTS WILL BE DELIVERED TO THE FRTP AND THE IMPULSE RECORD (FORCE OVER TIME) WILL BE MEASURED AND ANALYZED AS AN INDICATOR OF RESIDUAL PANEL STRENGTH. A SMALL PILOT STUDY CONDUCTED UNDER LABORATORY CONDITIONS BY ENGINEERING DATA MANAGEMENT, INC. INDICATES THAT THE APPROACH HAS GOOD POTENTIAL FOR SUCCESS.