The Effect of Moisture Content Changes on the Mechanical Properties of Stress-Laminated Deck

应力叠层桥面由沿边缘放置在支座之间的木材叠层组成，并用高强度的预应力元件横向压缩。这种类型的层板之间的载荷传递是通过层板之间的压缩和摩擦来实现的。应力叠层木材的概念最早是在20世纪70年代中期S在加拿大安大略省提出的，后来在美国进行了进一步的研究和开发。虽然应力叠层在安大略省的首次应用包括修复一座既有桥梁，但该方法为建造新桥提供了多种可能性。应力叠层桥面最重要的特点之一是其对含水率变化的影响。低于纤维饱和点(细胞壁完全饱和但细胞腔中没有水分的水分)条件下的木材含水率是相对湿度和Th…温度的函数。更多的是周围空气。木材在纤维饱和点以下获得或失去水分时会改变尺寸。由于木材的尺寸受含水率的影响，在湿度条件下，预应力值可能会有很大的变化。本研究的目的是获得预应力变化对含水率的影响的量度。在研究过程中，建造了两个小型应力叠层桥面板，并在环境实验室进行了试验。试验在20ﾟC的恒温下进行，改变周围空气的相对湿度。本研究采用5层胶合层合板，尺寸为2×2.5 cm，木材长度为80 cm。本研究采用四种相对湿度循环工况，方案(1)：30%-60%-90%，每种方案10天；方案(2)：90%-60%-30%，每种方案10天；方案(3)：60%-90%-60%，每种方案10天；方案(4)：60%-30%-60%，每种方案10天。方案(1)钢筋预应力变化率增加约40%，方案(2)减少约90%。较少

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 … More 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