Stress relaxation of grouted entirely large diameter B-GFRP soil nail

One of the potential solutions to steel-corrosion-related problems is the usage of fiber reinforced polymer (FRP) as a replacement of steel bars. In the past few decades, researchers have conducted a large number of experimental and theoretical studies on the behavior of small size glass fiber reinforce polymer (GFRP) bars (diameter smaller than 20 mm). However, the behavior of large size GFRP bar is still not well understood. Particularly, few studies were conducted on the stress relaxation of grouted entirely large diameter GFRP soil nail. This paper investigates the effect of stress levels on the relaxation behavior of GFRP soil nail under sustained deformation ranging from 30% to 60% of its ultimate strain. In order to study the behavior of stress relaxation, two B-GFRP soil nail element specimens were developed and instrumented with fiber Bragg grating (FBG) strain sensors which were used to measure strains along the B-GFRP bars. The test results reveal that the behavior of stress relaxation of B-GFRP soil nail element subjected to pre-stress is significantly related to the elapsed time and the initial stress of relaxation procedure. The newly proposed model for evaluating stress relaxation ratio can substantially reflect the influences of the nature of B-GFRP bar and the property of grip body. The strain on the nail body can be redistributed automatically. Modulus reduction is not the single reason for the stress degradation.     

三层轻木-混凝土混合结构足尺模型模拟地震振动台试验研究

轻型木结构在地震作用下的性能已有了一定的研究基础,但轻木混合结构的抗震性能研究尚未得到充分认识。本文重点介绍了首次进行的3层轻木-混凝土混合结构振动台试验,试验房屋下部一层为钢筋混凝土框架结构,上部二层为对称轻型木结构,模型平面尺寸为6.1m×3.7m。对5个上下抗侧刚度比不同的足尺模型,采用3种地震动沿房屋纵向激振,峰值加速度依次为0.1g~0.5g。每次激振后测定房屋自振频率及对应的阻尼,各层加速度和水平位移,木结构底部与混凝土结构顶部之间竖向相对位移以及螺栓锚固力等。试验结果表明:(1)轻木-混凝土混合结构具有良好的抗震性能;(2)上部木结构与底层混凝土结构间连接可靠;(3)5个模型的振动均以第1振型为主,但对于刚度比大的模型,下部混凝土结构的2阶振动较明显;(4)刚度比大的模型其地震反应小于刚度比小的模型。