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

Abstract

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 regarding the effect of biological deterioration and climatic conditions on the wood material properties. The Douglas-fir studs and plank-shiplap sheathing extracted from the source structures had an average dowel bearing strength (Fe=29 MPa) that was statistically similar to the National Design Specification for Wood Construction table value for a specific gravity (SG) of 0.47 for dowels with diameters of less than 6.35 mm. The nails had average bending-yield strength of 671 MPa as compared to the contemporary reference value of 690 MPa for nails in this diameter class. No time trend was observed in the SG of the wood or the bending-yield strength of the nails. In general, the connection tests yielded good agreement between the European yield model equations and calculated connection capacity. Validation of the material conditions in older structures requires cautious inspection. The inference from this investigation as related to rehabilitation is that nailed connections without deterioration due to decay, insects, temperature, and/or moisture perform in a manner consistent with the current design standard.