A new laser-based system was successfully developed in the pilot plant for veneer thickness and roughness measurements. This system was tested for both green and dry spruce veneer. The comparisons were made between the green veneer measurement and dry veneer measurement, and between the laser-based system measurement and actual digital measurement. A linear mixed effect model was used to estimate the within-sheet and between-sheet variations of veneer thickness and roughness and their causes.
A good correlation was found between the laser-measured thickness and caliper-measured thickness. The laser-measured average roughness could also capture the trend of veneer surface roughness determined by the visual classification. Thus, the new laser-based system can be a useful tool for measuring both veneer thickness and roughness.
For veneer thickness, the within-sheet variation seemed to be larger than the between-sheet variation, and the laser-based measure had a larger variation than the digital-based measure for both green and dry veneer sheets. With the green veneer, higher veneer moisture content and density would lead to a larger difference between the two measurements. The laser-based method tended to classify more "thick" sheets than the digital-based method, but this tendency was not obvious with the dry veneer. Such tendency also became negligible by factoring in either veneer moisture content or density. Thus, in the real applications, the accuracy of the new laser system can be improved for measuring green veneer thickness with a calibration of moisture content and/or density.
For veneer roughness, the within-sheet variation was again larger than the between-sheet variation, and the dry veneer had a larger variation than the green veneer. Further, the tight side variation was generally larger than the loose side variation. The above information is deemed useful for establishing an overall veneer quality criterion for industrial applications. Further work is scheduled to adopt the new laser-based system for real-time measurement of green veneer thickness and roughness.
The objectives of the site visit were to document the damage to wood-frame and other wood buildings from the May 12, 2008 Wenchuan (Sichuan) earthquake and to compare the performance of wood-frame buildings with non-wood buildings of similar size.
Because of the limited number of wood-frame buildings in the affected region, all the available wood construction close to the seismically affected area was investigated as follows:
2 wood-frame houses in Dujiangyan
3 solid timber cabins in Dujiangyan
2 houses of wood-frame construction in Chengdu
6 houses of post-and-beam construction with wood-panel infill in Songpan.
The houses in Chengdu and in Dujiangyan are located, respectively, in low intensity and moderate-to-high intensity regions of shaking during that earthquake. From the inspection of the four houses and other concrete buildings nearby, it can be stated that even under light and moderate-to-high levels of seismic shaking the wood-frame houses examined suffered significantly less damage than nearby reinforced concrete houses of comparable size.
Based on a design-oriented analysis of seismic capacity it is shown that the wood-frame Houses A and B can withstand a pseudo-spectral acceleration of at least 0.89 and 1.01 g, respectively. This is judged to be a conservative estimate since the positive contribution of the exterior stucco and the second interior gypsum wall board (GWB) has not been included in the analysis.
The three timber cabins examined in Dujiangyan also performed very well, showing no signs of seismic-induced distress. The six post-and-beam wood buildings with wood-frame infill in Songpan also showed no signs of seismic damage, although for the latter the intensity of shaking was quite low.
From some examples of damaged concrete buildings, it was observed that numerous infill walls were damaged or had collapsed and thus subjected the inhabitants to mortal danger. Lightweight wood-frame infill walls for concrete frames could provide a safer alternative to the heavy and relatively brittle brick infill walls. Furthermore, the resulting reduction in building weight would further enhance seismic safety of the entire building.
It is recommended that for the Chinese code the GWB contribution be considered for normal seismic loading. However, the GWB should not be included in the design check for rare earthquakes because of the limited ductility of shear walls sheathed with GWB at the high levels of shaking associated with the rare seismic events.