|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1996 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1995 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Stress-laminated deck consist of lumber lamination that are placed edgewise between supports and are compressed transversely with high-strength prestressing elements. The load transfer between laminations of this type is developed by compression and friction between the laminations. The concept of stress-laminated lumber was originally developed in Ontario, Canada, in the mid-1970's. Further research and development hasoccurred in the United States. Although the first application of stress laminating in Ontario involved the rehabilitation of an existing bridge, the method offered a variety of possibilities for construction of new bridges.
One of the most important characteristics of stress-laminated deck is its influence of moisture content change. The moisture content of wood below the fiber saturation point (the moisture content at which cell walls are completely saturated but no water exists in cell cavities) condition is a function of the both relative humidity and temperature of th
e surrounding air. Wood changes dimension as it gains or loses moisture below fiber saturation point. Since wood's dimension is affected by moisture content, the value of prestressing can vary considerably under humidity conditions.
The purpose of this research is to obtain a measure of the prestressing changes of the effect of moisture content. During the research, two small-size stress-laminated deck are constructed and tested in the environmental laboratory. The tests are conducted at constant temperature of 20ﾟC, and lelative humidity of the surrounding air are changed. The five layrs glued laminated timber with 2*2.5cm dimension lumber of 80cm length is used in this investigation. Four cyclic condition cases of relative humidity are used in this study.
Case (1) : 30%-60%-90%, 10days at each condition.
Case (2) : 90%-60%-30%, 10days at each condition.
Case (3) : 60%-90%-60%, 10days at each condition.
Case (4) : 60%-30%-60%, 10days at each condition.
The rate of change in the prestressing of steel rod increased about 40% during the case (1), and that rate decreased about 90% during the case (2). Less