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.
Ring characteristics and screw withdrawal resistance of naturally regenerated Chamaecyparis obtusa var. formosana trees
The ring characteristics and screw withdrawal resistance (SWR) of naturally regenerated Taiwan yellow cypress (Chamaecyparis obtusa var. formosana) trees were explored. Significant differences in average ring width (RW), earlywood width, latewood width, ring density (RD), earlywood density (ED), latewood density (LD), highest density (Dmax), lowest density (Dmin), latewood percentage (LWP), and SWR were observed between trees, rings (SWR excluded), and tree height positions. The RW components in the radial direction increased from the pith outward to about the 3rd to 5th ring and then decreased to about the 25th ring; it was almost constantly sustained toward the bark side. The RD in the radial direction slowly decreased from the pith outward to the bark side. Average ring width and ring density were significantly affected by the various tree growth rates, radial ring numbers, and tree height positions. ED, LD, Dmax, Dmin, and LWP were the most important factors determining the overall RD. RW did not correlate with tree RD. SWR is correlated with ED, RD, Dmin, LWP, and intra-ring density variation (IDV). Thus, the SWR can be used to predict wood density and in nondestructive evaluation of a living tree.
Human Rights Obligations and Transnational Corporations: The Limits of Direct Corporate Responsibility
To date, multinational corporations have had no direct human rights obligations under international law. Nonetheless, international lawyers can no longer ignore the increasing role of non-state actors in international society. This article suggests analysing existing mechanisms and new proposals for enhancing the accountability of transnational corporations, grouped into those focusing on the responsibility of the home and host states and those centred on the imposition of direct obligations on corporations. This article will specifically draw attention to the limits of some of the suggested normative changes, from a legal-theoretical perspective and in terms of their capacity to address effectively the challenges of the lack of respect for human rights laws.