Robert J. Leichti

Effect of Adhesive Stiffness and Thickness on Stress Distributions in Structural Finger Joints

Abstract Environmental, political, and socioeconomic actions over the past several years have resulted in a decreased wood supply at a time when there is an increased demand for forest products. This combination of increased demand and decreased supply has forced more emphasis on engineered wood products, a varied category usually connected with adhesively-bonded end joints, of which the most common type is the finger joint. This paper presents the results of a finite-element analysis of structural finger joints, and focuses primarily on the effect of adhesive stiffness and thickness on stress distribution patterns in finger joints. Results indicate that a flexible adhesive layer concentrates adherend longitudinal and radial stresses at the finger base, whereas a stiff adhesive layer minimizes adherend stresses but increases adhesive stress levels. Results also show that a thin adhesive layer concentrates longitudinal adherend stresses at the juncture of the finger tip and flexible finger base and concent...

Wood Materials, Nails, and Sheathing Connections from Early 20th Century Residential Buildings

Assessment of light-frame wood structures for wind and seismic loadings requires engineering information about the wood materials and connections in the subject building. The knowledge base can be developed by inspection and further enriched by knowledge of age effects on materials and connection properties. Nineteen wood-frame structures built between 1905 and 1970 and scheduled for demolition were located through local municipal building departments and sampled for wood materials and nail connections prior to demolition. The project plan was to evaluate the materials from the buildings while watching for trends in materials over time, calculate the expected connection capacity using the materials’ test results, and then compare the calculated allowable connection capacity to tests of single-fastener connections extracted from the same buildings. Insect damage and fungal deterioration were present in many of the structures and were avoided when sampling for test specimens. Inferences are not made regardi...

Boundary Condition Role in Tests of Wood Compression Webs

The important role of boundary conditions in tests of compression members was evaluated when determining the instability loads of asymmetric and nonprismatic compression webs for wood trusses. The compression webs were created by nailing a side member to the truss web so that the cross section was L-shaped. In the analytical investigation, the side members were assumed to be as long as the truss web, and the boundary conditions were for pinned and elastically restrained connections. In the experiments, L-reinforced webs were tested with pinned and metal-plate-connected boundary conditions and with side members of various lengths. The boundary conditions had a significant effect on stability load and the failure mode. Capacity of the L-reinforced truss web may be governed by the metal connector plate rather than wood strength or instability.

Flexural Creep Apparatus and Testing for Structural Composite Lumber

A specification to test and evaluate the flexural creep and duration of load effects for structural wood-based products was finalized as ASTM D 6815-02. The test method requires relatively large forces be sustained for at least 90 days. Further, the test is conducted in an environment that is moisture and temperature controlled. The typical apparatus for this test uses weights and ratio pulleys, but the heavy loads make loading and unloading difficult and potentially dangerous and the footprint must be large enough to provide space for lifting. This paper describes an apparatus that requires a minimum of floor space and uses hydraulic loading so that it is safer to load and unload. Operation and typical data for the test are used to demonstrate the specification and the apparatus.