Predicting bending strength of fire-retardant-treated plywood from screw-withdrawal tests
This report describes the development of a test method and predictive model to estimate the residual bending strength of fire-retardant-treated plywood roof sheathing from measurement of screw-withdrawal force. The preferred test methodology is described in detail. Models were developed to predict loss in mean and lower prediction bounds for plywood bending strength as a function of a screw-withdrawal force. Our analysis of fire-retardant-treated plywood from three different studies, each with various fire-retardant-treatment, processing, plywood thickness, and exposure temperature groupings, clearly indicated that different fire-retardant-treatments and plywood thicknesses could not be grouped into a single “universal” model. Nevertheless, some grouping was possible; parameter estimates for several grouped fire-retardant formulations and plywood thicknesses are reported for mean trends and lower prediction boundaries. Although the models were shown to acceptably predict plywood bending strength, additional work is needed to expand these models to address the effects of plywood quality, wood temperature, and moisture content at time of test.
Effects of fire retardant retention, borate buffers, and redrying temperature after treatment on thermal-induced degradation
All wood products are prone to strength loss from extended exposure to temperatures above 65°C (150°F). The higher the temperature, the less time required to produce a given reduction in strength. In the United States, problems with fire-retardant-treated plywood roof sheathing and roof-truss lumber have occurred in the field; thermal degradation has occurred in as few as 2 to 5 years after installation. Before the thermal-induced degradation of treated wood can be fully modeled, we must more completely determine the relationships of treatment processing factors, mixtures of chemical components, post-treatment (redrying) temperature, and in-service moisture to performance, and relate the results to in-service temperature-induced strength degradation. In the study reported here, variation in redrying temperature from 49°C (120°F) to 88°C (190°F) had little effect on the magnitude or rate of subsequent thermal degradation when the treated plywood was exposed at 65°C (150°F) for up to 290 days. The addition of borate-based buffers to fire-retardant-treatment chemicals was found to significantly mitigate thermal degradation. Finally, the results imply that the combined effects of phosphate retention and accumulated thermal exposure (from both redrying and in-service high temperatures) are additive and cumulative.
Woodrow Wilson: The Essential Political Writings
Chapter 1 Preface Chapter 2 Introduction to Wilson's Political Thought Part 3 Progress and the Organic State Chapter 4 The State (chapters 1, 2, 13, 16) Chapter 5 "Christ's Army" Chapter 6 "Christian Progress" Part 7 Political Liberty and the Scope and Ends of Government Chapter 8 "Socialism and Democracy" Chapter 9 "A Calendar of Great Americans" Chapter 10 "Address on Thomas Jefferson" Chapter 11 "The Authors and Signers of the Declaration of Independence" Chapter 12 The New Freedom (chapters 1, 2) Part 13 Institutional Reform Chapter 14 "Cabinet Government in the United States" Chapter 15 Congressional Government (chapter 2 & conclusion) Chapter 16 Constitutional Government in the United States (chapters 3, 8) Chapter 17 "Wanted - A Party" Part 18 Political and Administrative Leadership Chapter 19 "Leaders of Men" Chapter 20 "The Study of Administration" Part 21 Foreign Policy Chapter 22 "War Message to Congress" Chapter 23 "Fourteen Points" Part 24 Appendix A. Chronology of Wilson's Academic Work and Other Selected Events Part 25 Appendix B. Selected Bibliography