Effects of Wood Decay on the Shear Performance of Nailed Timber Joint

Abstract

Degradation of shear resistance of nailed joints by wood decay was estimated experimentally. We conducted decay treatments of Todomatsu Abies Sachalinensis specimen for compressive and single-shear tests of nailed joints with Todomatsu main members, steel side plates and CN50 nails by brown-rot fungus Fomitopsis palustris , which is commonly observed in Japan. After the decay treatment, we measured the compressive strength parallel to the grain and the single shear resistance of nailed joints, and the depth of steel pin penetration burst into the wood. Test results showed that degradation of the maximum shear resistance of the nailed joints at an early stage of decay was not as rapid as the degradation analogized by compressive strength, which is often fitted with an exponential curve. Tearing of nail heads, which caused brittle joint failures, was typically observed in the tests of sound nailed joints in this study. The nails of decayed joints, however, were pulled from the wood members before being torn off at their heads. This difference in failure mode resulted in a gradual decrease of lateral loads beyond the maximum resistance without sudden drops of loads. The degradation of the maximum shear resistance of decayed nailed joints was compared with the estimated resistance by the European Yield Theory EYT based on the bearing strengths of the wood members derived empirically from the depth of steel pin penetrations, which showed the ultimate shear resistance of decayed nailed joints could be estimated from onsite measurement of the depth of steel pin penetration.

Withdrawal strength of nailed joints with decay degradation of wood and nail corrosion

“…We measured the depth of pin penetration for all specimens using Pilodyn, which is a widely used apparatus to measure degree of decay [4,6,8,10,17,18]. Pilodyn that we used has 2.5 mm pin diameter, 40 mm maximum penetration depth, and 6 J penetration energy.…”

“…A number of studies have investigated the strength of wood when exposed to wood-decaying fungi [1][2][3][4]. Recent studies have examined the effects of decay on the strength of timber joints with respect to the shear performance of nailed joints, dowel-type joints, and screwed joints exposed to decay fungi [5][6][7][8][9][10]. However, there has been little investigation into the relationship between the withdrawal strength of nails and decay.…”

Lateral strength of nailed timber connections with decay

“…There have been several researches on the strengths of nailed connections exposed to a wood-decaying fungus. Studies on nailed connections have been conducted with side members composed of oriented strand board [9,10], steel plate [11,12], plywood, and medium density fiberboard [13]. These studies have indicated the decrease in strength of nailed connections caused by the decay.…”

Fractography of shear failure surface of softwood decayed by brown-rot fungus

“…Numerous studies that are based on the biological, biochemical and mechanical viewpoints [3][4][5][6][7][8][9][10][11] have been performed on the wood deterioration by brown-rot fungus.…”

“…Especially, because the strength deterioration of decayed wood may largely affect safety of timber structures, estimation of degree of deterioration have been performed on partially decayed wood. Methods applied in such studies to date are the pin-penetration depth [5,6], acoustic emission [7,8], infrared spectra [9,10], X-ray microdensitometry [11]. However, the values obtained by those were influenced by moisture content and distribution of decay.…”