A system which integrates architectural and structural design issues for timber connections will be developed for a limited number of connections and loading conditions which are dealt with in various national and international codes and standards. The scope of engineering issues relevant to connections will be expanded to include a wide range of timber connections and engineering solutions which are not covered by code procedures. This will include cases such as 3-dimensional loading configurations, dynamic analysis of connections and more rigorous analysis procedures. Progress on these objectives is described.
Higher bearing strength values for Hem-Fir, where justified, will allow designers to realise the full strength potential of the lumber. Machine stress rated (MSR) lumber would benefit the most from an increase in the Hem-Fir bearing strength. Although there are few Hem-Fir MSR lumber producers, it is anticipated that given the recent or planned increase in installed kiln capacity on the west coast, more mills will be considering producing MSR lumber. Acceptance of Hem-Fir MSR lumber in the marketplace will depend on the design values assigned to Hem-Fir MSR lumber. The objective of this project is to establish characteristic bearing strength values for the Hem-Fir species group in CSA O86.1 and progress to date is described.
This publication characterizes nine commercial tree species of Alberta. Included are descriptions of the range and volume of each species, their wood properties, and present and potential manufacturing uses.
Changes to the Canadian timber engineering codes over the last 10 years have made it necessary for the wood truss industry to update the wood truss design procedures. The Truss Research Project was established to assist the truss industry to resolve some of the issues arising from the code changes. While most of the issues deal with the analysis of metal plate connected trusses and are therefore specific to the truss industry, some issues that deal with the fundamental strength properties of lumber apply to other engineered timber construction. One area that requires research is the strength of lumber under combined bending and axial loading conditions. A program to model the within-member strength variations of lumber is underway at the University of British Columbia. The purpose of this Forintek project is to develop equipment that can test lumber under combined bending and axial loads. This equipment will be used to validate the lumber strength model. The equipment to test lumber under bending and axial loading has been developed. This report presents a discussion of the equipment specifications and some of the limitations of the equipment identified to-date. The combined loading tester for lumber is currently undergoing verification and trial testing. It will be ready for use in the 1995/96 fiscal year.
Compression perpendicular-to-grain (C-Perp) is one of many structural design checks that must be made by the design engineer. Up until now, much of the effort in updating the Canadian timber design code, CSA-O86, has focused on the more prominent strength properties such as bending, tension and compression parallel-to-grain strength. With the increased use of machine stress rated (MSR) lumber in engineered wood products such as trusses, designers have encountered instances where design details must be revised in order to meet the compression perpendicular-to-grain requirements specified in the timber design code. Where design details cannot be revised, certain species of lumber cannot be used although these species are able to provide more than enough strength in bending, tension or compression parallel to the grain. Inconsistencies in C-Perp design resulting from code changes for the 1989 edition as well as developments in engineered wood products have made it necessary to review the design procedures for compression perpendicular-to-grain design. The aim of this project is to rationalise the design procedures and assist the CSA task group on C-Perp in updating design values for MSR S-P-F lumber. This task has been completed. The work has resulted in new design procedures and design values for compression perpendicular-to-grain in the 1994 edition of CSA-O86.1. A background paper on these changes was presented at the July 1994 meeting of CIB Working Commission (W18A) - Timber Structures in Sydney, Australia.
In a previously completed study, lumber obtained from a 95-year old lodgepole pine sample representing a final stand density of 700 live stems/hectare (s/ha) was found to have relatively low modulus- of-rupture (MOR) and modulus of elasticity (MOE). It was determined that this resulted from lower than average basic wood density, and larger than average knot size particularly in large diameter trees. It was also determined that average MOR and MOE could be predicted to some extent (R2 > .60) on the basis of tree diameter-at-breast height (d.b.h.) and breast-height average basic wood density. Before accepting the above results as typical of lodgepole pine of similar age and final stand density, it was considered important to compare the relationships between d.b.h. and breast-height wood density observed in this 700 s/ha sample with that of trees in open-stand-densities in other regions. Average branch size added only marginally to explained variation in the predictive equation, but knot size is known to effect lumber strength. Thus a measure of branch size was included in the current study plan. Biogeoclimatic zones were chosen as the basis for regional comparisons. A minimum of 30 trees were selected from open-stand sites in each of the following five biogeoclimatic zones: Montane Spruce (MS), Engelmann Spruce-Subalpine Fir (ESSF), Interior Douglas-Fir (IDF), Interior Cedar-Hemlock (ICH) and Sub-Boreal Spruce (SBS). Sampling was systematic by d.b.h. to ensure representation of small, medium and large diameter trees. Stem counts were made in 1/200 ha plots around each sample tree to ensure that samples were indicative of a relatively open stand density. Average basic wood density at breast height was determined from two pith-to-bark increment cores obtained from each sample tree. The size and height of the largest branch in the first 5 m of tree height was measured and recorded. Average basic wood density values and estimates of branch size obtained for the five samples in this study were compared to the values and estimates obtained from the original 700 s/ha sample site. Basic wood density obtained from three of the sites was not significantly different from that of the 700 s/ha sample. It was significantly higher in one site (ICH) and significantly lower in another (ESSF). The higher wood density was possibly the result of a slower growth rate to 30 years combined with older average tree age. The significantly lower wood density was attributed to a younger average stand age (80 years). Basic wood density showed a consistent relationship with d.b.h. in all of the tree samples, tending down as d.b.h. increased. There was a less consistent relationship between knot size and d.b.h. but what relationship there was would serve to reinforce the effect of differences in wood density on lumber strength and stiffness. Average size of the largest knots was smallest in the tree sample where wood density was highest, and largest in the sample where wood density was lowest. Important lumber strength determining tree characteristics (wood density and knot size) that resulted in the low MOE and MOR at the original 700 s/ha sample site were found to be unexceptional when compared to trees of similar age and final stand densities in other biogeoclimatic zones. Although a slower than average growth rate to 30 years offers a plausible explanation for the higher than expected wood density in the ICH sample, further investigation is recommended.