Lateral resistance of anchor-bolt joints between timber sills and foundations II. Effective lateral resistance of multiple anchor-bolt joints

Monte Carlo simulations were conducted to estimate the effective lateral resistance of multiple anchor-bolt joints with ordinary specifications of Japanese post and beam constructions. Basic lateral load-slip curves of single anchor-bolt joints required in the simulations were determined from the test results of our earlier report. The effective lateral resistance of multiple anchor-bolt joints was estimated for some combinations of loading direction, length/diameter ratio of anchor bolts, lead-hole clearance, and number of anchor bolts. The principal results of the simulations are: (1) anchor-bolt joints loaded perpendicular to lateral forces are not recommended to be counted as supplementary resisting elements because their supplementary shares are far less than those expected from their allowable lateral resistance; (2) multiple anchor-bolt joints with small length/diameter ratios have comparatively lower effective resistance ratios than multiple anchor-bolt joints with large length/diameter ratios; (3) the effective resistance of multiple anchor-bolt joints is affected not only by lead-hole clearance or number of bolts but also variance of load-slip characteristics of single anchor-bolt joints. Part of this work was presented at WCTE2004, Lahti, June 2004     

Required sample size for estimating soil respiration rates in large areas of two tropical forests and of two types of plantation in Malaysia

We estimated the required sample sizes for estimating large-scale soil respiration (for areas from 1 to 2 ha) in four ecosystems (primary and secondary forests, and oil palm and rubber plantations) in Malaysia. The soil respiration rates were 769 ± 329 mg CO₂ m⁻² h⁻¹ in the primary forest (2 ha, 50 sample points), 708 ± 300 mg CO₂ m⁻² h⁻¹ in the secondary forest (2 ha, 50 points), 815 ± 363 mg CO₂ m⁻² h⁻¹ in the oil palm plantation (1 ha, 25 points), and 450 ± 178 mg CO₂ m⁻² h⁻¹ in the rubber plantation (1 ha, 25 points). According to our sample size analysis, the number of measurement points required to determine the mean soil respiration rate at each site with an error in the mean of no more than 10% ranged from 67 to 85 at the 95% probability level. These results suggest that evaluating the spatial heterogeneity of soil respiration rates in the tropics may require more measurement points than in temperate forests.     

Growth and wood quality of sugi (Cryptomeria japonica) planted in Akita prefecture (II). Juvenile/mature wood determination of aged trees

Variations of certain anatomical and mechanical indices within tree stems of aged sugi (Cryptomeria japonica) trees planted in Akita prefecture were studied. The determination of the juvenile/mature wood boundary was also discussed, and the effects of wood structure on mechanical properties were investigated. On the basis of radial and vertical variation of the anatomical and mechanical indices, modulus of elasticity (MOE)/ shear modulus (G) was chosen as the index for determining the juvenile/mature wood boundary. The increase rates of MOE/G at the points of 1%, 2%, and 3% were discussed. It was found that for aged trees, all three points were thought to be effective for dividing juvenile and mature wood. However, for younger trees, the point of 2% was recommended, which was mostly consistent with the result obtained by the increase rate of 1% for tracheid length (TL). Among mechanical properties, the MOE showed more significant juvenile/mature wood differences than did modulus of rupture (MOR) and . By correlation analysis, it was suggested that microfibril angle largely contributed to the indices of MOE and G, and specific gravity largely contributed to the indices of MOR and .Part of this report was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003     

Virtual forest: design and evaluation of a walk-through system for forest education

Forest education is generally conducted in a real forest to provide learners a direct experience with reality. However, often it is not easy to participate in forest education programs carried out in remote places due to distance, limited time, or economic or physical restrictions. Therefore, we developed a walk-through system for forest education in a virtual forest and evaluated its educational efficacy as well as usability through indoor experiments. The virtual forest was constructed with omnidirectional images taken in a forest using a digital camera with an omnidirectional vision sensor. The results of the postquestionnaire showed that the developed system was highly evaluated by the participants in the experiments in terms of educational efficacy and enjoyment. Also, comparison of results of prequestionnaire and postquestionnaire showed that it had educational value. On the other hand, some technical problems in the developed system were revealed. For example, 45.0% of the participants answered that the walk-through in the virtual forest did not proceed with sufficient smoothness, and encountered unexpected slowdowns and stops. In addition, image quality was not high enough to identify small objects in the virtual forest. Regardless of these problems, we believe that the computer-based forest education was successful because 88.3% of the participants answered that they would like to join a similar program again and 90.0% answered that they would like to visit the real forest that the virtual forest imitated.     

Spontaneous vacuolar degeneration of the thyroid follicular epithelium in cynomolgus monkeys

Vacuolar degeneration of the thyroid follicular epithelium was observed in two untreated female cynomolgus monkeys assigned to control groups. In light microscopy, large vacuoles containing a homogenous substance occupied the basal region of the epithelium, and the nuclei had shifted toward the apical region. The vacuoles showed negative reactions to PAS and thyroglobulin. Electron microscopic observation revealed dilatation of the rough endoplasmic reticulum corresponding to the vacuoles. The plasma TSH, T3 and T4 levels determined for the samples kept frozen were within the normal ranges, suggesting that the thyroid function was kept intact.     

Shear resistance and failure modes of nailed joints loaded perpendicular to the grain

Shear tests were conducted on nailed joints in wood that were loaded perpendicular to the grain; these joints had 21 specifications depending on different combinations of wood species, nail dimensions, number of nails, and edge distances of the main members, and their effects on the shear resistance of the nailed joints were also investigated. The nailed joints with CN75 nails had higher initial stiffness than the joints with CN50 nails, provided the initial stiffness of nailed joints connected with 3 or 5 nails was not always a simple product of the number of nails and the initial stiffness of nailed joints connected with a nail, and instead depended on the combination of wood species of the main member and nail dimensions. When the edge distance decreased, the maximum load and energy capacity decreased, thereby affecting the energy capacity. The maximum load of the nailed joints with CN75 nails may be smaller than those with CN50 nails depending on the combination of wood species and nail dimensions. When the edge distance of the nailed joints was less than 26 mm, the energy capacity of the nailed joints with CN75 nails was less than or similar to those with CN50 nails.     

Effective lateral resistance of combined timber joints with nails and bolts

An experimental study on combined steel-to-timber joints with nails and bolts is conducted in this study. Principal results are as follows: The initial stiffness and effective allowable resistance of combined joints depend obviously on clearances in predrilled bolt-holes. The combined joints with nails and bolts have high potential of energy capacity to resist strong earthquake forces. There are upper limits of clearances in predrilled bolt-holes that allow advantages of considering the synthetic resistance of combined joints in practical structural design. Combining the joint components with appropriate design will give higher performance against strong earthquakes increasing the safety margin and energy capacity until the failure. The combined joints should be designed under the restrictions of particular specifications in closed design systems because the advantages of combining the joint components are influenced obviously by various actual conditions, which are too difficult to consider in detail in open design systems.     

Windthrow resistance of apple trees grafted in an orchard

Pull-down tests were conducted for apple trees grafted in an orchard and for support posts in order to discuss the failure mode in windthrow damage, the effect of rootstock types on the uprooting strength, and the reinforcing effect of support posts on young trees. The test samples were ten mature trees (20–23 years old) of three varieties grafted on two types of rootstocks, three young trees (7 years old) grafted on dwarf rootstocks, and nine support posts of larch logs and steel pipes. The failure modes were found to be uprooting for mature trees and rootstock breakage for young trees. The uprooting strength of apple trees was considerably smaller than the uprooting strength of forest trees reported in previous studies. However, the windthrow resistance of the apple trees with respect to the critical wind velocity was estimated to be sufficient despite their low uprooting strength because of their small height. Young trees should be supported with wooden posts for a few years after grafting so that they acquire sufficient windthrow resistance. Part of this study was published in the report for the Grant-in-Aid for Collaborative Research by NOASTEC (No. H17-kyo-048)     

Evaluation of quality indexes of bending performance and hardness for hardwoods

The mechanical properties of 613 small clear specimens of 35 species (11 ring-porous hardwoods, 19 diffuse-porous hardwoods, and 5 softwoods) were evaluated. The aim of the study was to examine indexes of wood quality that are easy to measure and that exhibit a high correlation with bending performance and hardness that are essential properties of hardwood products. The modulus of rigidity, dynamic modulus of elasticity, bending properties (modulus of elasticity, modulus of rupture, stress at the proportional limit, absorbed energy, Tetmajer’s modulus), dynamic energy absorption by an impact bending test, compressive strength parallel to the grain, shear strength, partial bearing strength, and Brinell’s hardness were measured. A high correlation was found between dynamic modulus of elasticity and static modulus of elasticity. Bending stress at the proportional limit was found to be approximately equivalent to the compressive strength parallel to the grain. Static energy absorption correlated with dynamic energy absorption. Tetmajer’s modulus was found to be closely related to the ratio of the initial stiffness within the elastic range to the secant modulus at the maximum load. A high correlation was observed between Brinell’s hardness and partial bearing strength. The difference in the regression coefficients obtained for these correlations between the species groups was small. Part of this study was presented at the All Division 5 Conference of IUFRO, Taipei, October 2007