On preventing the adhesion of an earthy crust to the inner surface of steam boilers

Abstract

There is a consistent reduction in member strength associated with long-term use of structural wood members. It is hypothesized that this reduction in strength is due to “use and aging” effects such as cracks, splits and checks developed from drying stresses, moisture cycling, and fastener holes originating from initial construction techniques. The focus of this research effort was to develop an accurate model of the behavior and performance of the recycled timbers containing fastener holes. The flexural capacity of structural wood joists and planks containing fastener holes was modeled utilizing finite element analysis (FEA) coupled with the tensor polynomial (Tsai–Wu) strength theory. Each model presented herein represents a connection detail that is commonly used in construction. To validate the analytical approach, virgin timbers with drilled holes were conditioned to simulate in situ conditions and tested to failure. Comparing the results of the analytical model to experimental behavior, the FEA results were slightly conservative with predicted strength values falling within one standard deviation from the mean value of the experimental data and thus, producing accurate results. A critical hole location exists where the hole produces the largest reduction in strength. Based on the results, it is recommended that the edge of the hole not be located within 6 mm from the extreme fiber in both the compression and tension regions. If this does occur, then possibly some post processing needs to be performed such as planing the member down such that the hole is located on the edge, or the hole is completely eliminated from the section.