Collapsing process simulations of timber structures under dynamic loading I: simulations of two-story frame models

In this study we tried to develop an analysis program that can simulate the collapsing process of timber-frame structures under dynamic loading by adopting the extended distinct element method (EDEM). Using the EDEM, it is possible to trace the movement of any parts that were separated from unity after the failure of connecting elements, a property that fits our purpose well. As a preliminary study, simple two-story frame structures were modeled and examined by our program. Each model is an assembly of frame members composed of the EDEM elements. The spring elements of the joints have less rigidity than those of the frame members. Several models were analyzed under dynamic loading. The models varied in the configuration of bracing shear walls. Experiments with a one-ninth model were carried out under similar conditions, and the results were compared with the results from numerical simulations. Simulated results showed various collapsing processes corresponding to the arrangement of the bracing shear wall, and the simulated aspects gave good agreement with the results of the experiments under similar conditions.Part of this paper was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000     

Collapsing process simulations of timber structures under dynamic loading III: numerical simulations of real-size wooden houses

In this study, we developed a new analysis method that enables numerical simulations of the collapse process of real-size wooden houses and evaluated the accuracy thereof by carrying out numerical simulations by shaking table tests. The distinct element method was adopted as the basic theory of our numerical analysis. This research is the first approach in which the extended distinct element method was used for Japanese timber post-and-beam construction. The size of the analysis model is a 5.5 m × 5.5 m, two-story real-size wooden house. The three analytical models were developed in terms of the strength of exterior mortar walls. The simulation results were compared with the shaking table test results. One of the collapsing processes of the numerical simulation corresponds well to the experiment results. Assessment of the possibility of collapse for real-size wooden houses was determined to be possible using our newly developed numerical analysis method.     

Pseudodynamic tests and earthquake response analysis of timber structures II: two-level conventional wooden structures with plywood sheathed shear walls

Pseudodynamic (PSD) tests were conducted on two-level timber structures with plywood-sheathed shear walls, which each had an opening of different configuration, to study the effects of the mechanical properties of the first and second levels on the earthquake response of the structure. The specimens had two-level conventional post and beam frames that were 3 m wide, 3 m deep, and 6 m high with plywood sheathings nailed on one face of the structure. The first and second levels had different opening configurations of window, door, or slit. Lateral forces were applied at the top of the first and second levels, calculating step by step the next displacement based on the North-South (NS) components of the 1940 El Centro earthquake. The test results were compared with those of the time-history earthquake response analysis using the lumped mass model and hysteresis model presented in the companion article (part I). The experimental and simulated results showed that the simulation by means of the lumped mass time-history earthquake response analysis predicted quite well the response of the first level, but tended to underestimate the response of the second level, and that the PSD tests of an individual wall system with the mass supported by that particular wall generally show a conservative estimate of the response.     

Kinetics of the hydroxymethylation of phenol I: Rate equation and method of analysis

Seven reactions take place consecutively and competitively during the hydroxymethylation of phenol in aqueous alkaline media. This hydroxymethylation is the first step in the formation of phenolic resins and has long been studied. However, the rate equation, which can describe the seven reactions in those reaction systems where the alkali/phenol molar ratios are <1.0, has not yet been obtained. The authors present a rate equation (in a differential form) for a computer simulation. This equation involves the concentration of hydroxide ion, [OH^–], which changes with the change in the composition of the reaction system and cannot be expressed as a function of reaction time. However, the value of [OH^–] can be obtained by numerical calculation. In the computer simulation the reactions occur for an infinitesimal unit of time, and the changes in the concentrations of formaldehyde, phenols, and hydroxide ion are calculated. The next step of the reaction takes place according to the reaction conditions that result from the previous step. In this manner the reactions progress step by step in a computer. Using this method we can describe the reaction time course, (i.e., the changes in the concentrations of phenol, formaldehyde, and five species of hydroxymethylphenols with the reaction time).Part of this paper was presented at the 47th Annual Meeting of the Japan Wood Research Society, Kochi, April 1997     

Development of LVL frame structures using glued metal plate joints II: strength properties and failure behavior under lateral loading

In past years high priority was given to developing a seismic design for wood structures, including research on the response of wood structures to earthquakes. In this study a new type of portal frame with relatively large span was developed for the traditional Japanese wooden houses with large openings at the front to strengthen the structure. Stainless steel plates coated with zinc and glued with epoxy adhesives on laminated veneer lumber (LVL) members, composed of Douglas fir veneer and bonded with phenolformaldehyde resin, were used. The connection between the frame's beam and columns and between the columns and groundsills was mechanical, with bolts. The subject of this research was to analyze strength properties and failure behavior of glued LVL metal joints used as structural components and to evaluate the response of LVL portal frames under cyclic lateral loading. The results show that portal frames using glued LVL metal plates have a good multiplier for the shear walls and may be applied to traditional Japanese structures. The equivalent viscous damping provided good energy dissipation in the frames. The joints displayed good mechanical behavior during tests; moreover, the structures demonstrated high strength, stiffness, and ductility, which are necessary for a seismic design.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kouchi, April 1997; and at the 5th world conference on timber engineering. Montreux, Switzerland, August 1998     

Creep of the beam in Japanese conventional structures composed of green and kiln-dried timber II: predictive model for relative deflections

We conducted creep tests to evaluate creep behaviors of conventional Japanese framing (jikugumi) structures as reported in a previous article. We measured beam deflections of two structures: one of them was composed of only green timbers (G) and the other with only kiln-dried timbers (D). Besides the two structures, we prepared green and kiln-dried beams to measure moisture content (MC), weight, and dynamic Young’s modulus (E _f) by the longitudinal vibration method. We attempted to predict deflections of beams in the structures by using experimental data for single beam specimens. The proposed simple predictive model was derived from two equations: a relation between MC and equilibrium moisture content calculated with temperature and relative humidity, and a relation between MC change and relative deflection change. Beam deflections were traced for 2.5 years, while the predictions were based on experimental data from loading to the 11th day of the test. It was assumed that sensitivity of deflection change to MC should differ during desorption or adsorption. Although annual cyclic changes were observed in E _f, there was no obvious relationship between E _f and beam deflection. Part of this article was presented at the Annual Meeting of the Architectural Institute of Japan, Kyushu, September 1998     

Kinetics of the hydroxymethylation of phenol II: values of rate parameters and results of simulation experiments

The reaction course of the sodium hydroxidecatalyzed hydroxymethylation of phenol was analyzed by use of high-performance liquid chromatography (HPLC), and the rate constants for the seven reactions taking place consecutively and competitively were evaluated by means of a computer simulation technique. Calibration was done at the quantification of the six phenolic monomers from the peak areas in the HPLC chromatogram, taking the differences in molar ultraviolet absorption intensities of the six compounds into account. The values of the energies of activation for the seven reactions obtained differed greatly from those reported by Eapen and Yeddanapalli. Simulation experiments carried out by use of the newly obtained rate parameters showed that the amounts of phenol left unreacted and 2,4,6-trihydroxymethylphenol in the final reaction product increased as the reaction temperature was increased and the alkali/phenol molar ratio decreased. These phenomena can be attributed to the differences in the energies of activation for the seven reactions and differences in the acid strengths of the six phenolic monomers.Part of this paper was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998 and at the 1998 annual meeting of the Forest Products Society, Merida, Mexico, June 1998     

Mechanism for deformation of wood as a honeycomb structure II: First buckling mechanism of cell walls under radial compression using the generalized cell model

Coniferous woods were modeled as honeycomb cellular solids consisting of hexagonal-prism tracheids to examine the mechanism for radial compression. Because of the abrupt breaks of radial cell walls, it was assumed that the flrst break followed Euler's equation of buckling. The nominal stress at the buckling of the radial cell wall was theoretically obtained based on this assumption, and the actual nominal stress was obtained experimentally. The theoretical stress was found to correspond almost to the experimental value. This finding suggests that the abrupt first break that occurs in wood under radial compression can be mainly attributed to the buckling of radial cell walls.Part of this work was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997 and at the 1997 meeting of the Research Society of Rheology in the Japan Wood Research Society, Tsukuba, December 1997     

Lateral resistance of anchor-bolt joints between timber sills and foundations III: numerical simulations of the effect of sill thickness on the effective lateral resistance of multiple anchor-bolt joints

Effective lateral resistance of multiple anchorbolt joints was estimated by considering sill thickness or length/diameter ratios of anchor bolts. Load-slip relationships of single anchor bolt joints were analyzed by the stepwise linear approximation based on the generalized theory of a beam on an elastic foundation and the criterion of “fracture bearing displacement” for several sill thicknesses or length/diameter ratios of anchor bolts. Monte Carlo simulations of the effective lateral resistance of multiple anchor-bolt joints were conducted using the analyzed load-slip curves of single anchor-bolt joints. Effective resistance ratios of multiple anchor-bolt joints were simulated for some combinations of length/diameter ratios of anchor bolts, lead-hole clearances, and number of anchor bolts. The simulated results are: (1) the influence of lead-hole clearance becomes more apparent as length/diameter ratios of single anchor-bolt joints decrease; (2) there is no obvious effect of number of anchor-bolts over the range of 5 to 15; (3) average effective resistance ratios can be adopted for allowable stress design; and (4) reduction of effective resistance ratios should be considered particularly for small length/diameter ratios of anchor-bolt joints.     

Fatigue of structural plywood under cyclic shear through thickness I: fatigue process and failure criterion based on strain energy

The fatigue behavior of plywood specimens under shear through thickness was examined on the basis of strain energy to obtain common empirical equations for the fatigue process and failure criterion under various loading conditions. Specimens were cut from commercial plywood panels of 9-mm thickness. Loading conditions were set as follows: a square waveform at a loading frequency of 0.5 Hz, a triangular waveform at 0.5 Hz, and a triangular waveform at 5.0 Hz. Peak stress applied was determined to be 0.5, 0.7, and 0.9 of static strength, that is, stress levels of 0.5, 0.7, and 0.9. The stress-strain relationships were measured throughout the fatigue test, and the strain energy was obtained at each loading cycle. Loading conditions apparently affected the relationship between stress level and fatigue life. On the other hand, the relationship between mean strain energy per cycle and fatigue life was found to be independent of loading conditions. Mean strain energy per cycle obtained as the fatigue limit was 5.85 kJ/m³ per cycle. Assuming that the accumulation of strain energy is a fatigue indicator, the fatigue process and failure criterion for the plywood specimens under the three loading conditions were commonly expressed by the relationship between cumulative strain energy and loading cycles.     

ANALYSIS OF THE THERMOPHYSICAL PARAMETERS OF MOIST WOOD PARTICLE MATERIAL IN A COUPLED HEAT AND MASS TRANSFER PROCESS OF FREEZING BY USING FINITE ELEMENT METHOD

he coupled heat and moisture transfer in a freezing process of wood particle mate-rial was mathematically modeled in the paper.The models were Interactively solved by using thenumerical method(the finite element method and the finite difference method).By matching thetheoretical calculation to an experiment,he nonlinear problem was analyzed and the variablethermophysical parameters concerned was evaluated.The analysis procedure and the evaluation ofthe parameters were presented in detail.The result of the study showed that by using the method asdescribed in the paper,it was possible to determine the variable(with respect to temperature,mois-ture content and freezing state)thermophysical parameters which were unknown or difficult tomeasure as long as the governing equations for a considered process were available.The methodcan signifieantly reduces the experiment efforts for determining thermophysical parameters whichare very complicated to measure.The determined variable of the effective heat conductivi     

Veneer strand flanged I-beam with MDF or particleboard as web material III: effect of strand density and preparation method on the basic properties

Optimizing the manufacturing conditions of veneer strand-flanged I-beams was continued in this study and focused on the strand density and preparation method. Three levels of strand density were used, while the strands were prepared by either saw or roll-press splitter. The main results indicated that: within the compaction ratios (1.4–2.3) investigated in this study, the strand with lower density showed slight improvement in the dimensional stability and the bond strength between web and flange, but not in bending properties of the I-beams. The strand preparation method was concluded to be dependent on species for akamatsu, sugi, and bamboo strands; roll-press splitter-prepared strands tended to negatively affect dimensional stability and mechanical properties of the I-beams. When using akamatsu or sugi strands, low density allowed the possibility of using lower resin application rates between strands. Part of this paper was presented at the 54th Annual Meeting of the Japan Wood Research Society in Sapporo, August 2004     

Piezoelectric behavior of wood under combined compression and vibration stresses II: Effect of the deformation of cross-sectional wall of tracheids on changes in piezoelectric voltage in linear-elastic region

This study investigated and clarified the relation between the piezoelectric voltage and microscopic fracture of hinoki (Chamaecyparis obtura Endl.), in particular the deformation of the cross-sectional wall of the tracheid in linear-elastic regions under combined compression and vibration stresses. The piezoelectric voltage-deformation (P-D) curve consisted of a linear region starting from the origin followed by a convex curved region. The linear region of theP-D curve was only about 60% of that of the load-displacement (L-D) curve. By applying combined stresses to a specimen, the cross-sectional walls of the tracheid were deformed mainly at the radial walls. When a tracheid was regarded approximately as a hexagonal prism, the elastic buckling stress of the radial wall was estimated from scanning electron microscope images and our method based on a modification of the Gibson and Ashby method. As a result, it was estimated that the elastic buckling stress was only about 80% of the stress at the proportional limit of theP-D curve. It is found that there are two consecutive regions before the proportional limit of theP-D curve: One is the region up to the spot where the radial cell wall generates the elastic buckling, and the other is the region starting from the end of the aforementioned region up to the proportional limit of theP-D curve.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 3–5, 1997