论文标题:FRP螺旋锚的拉拔试验与应用设计
Design and Experimental Investigation on FRP Helical Anchor
论文作者
论文导师 王钊,论文学位 硕士,论文专业 岩土工程
论文单位 武汉大学,点击次数 103,论文页数 64页File Size6236k
2005-03-01论文网 http://www.lw23.com/lunwen_439903472/
FRP; Helical plate anchor; Pullout test; Partial material safety factors method; Geotechnical anchorage
纤维增强塑料(Fiber Reinforced Plastics,FRP),由于具有抗拉强度高,耐腐蚀、抗疲劳性能好,质量轻,抗磁性等优点,被视为代替铁材和铝材的一种新型岩土锚固材料。 本文首先回顾了岩土锚杆的历史和现状,并着重阐述了在岩土锚固领域所面临的挑战和主要任务。 接着对新型FRP螺旋锚杆的背景、概念、结构、施工工艺、FRP筋物理力学性能、设计方法、拉拔试验、验收试验、长期性能观测等内容展开论述。 ① FRP筋具有优良的物理力学性能,且FRP筋的耐腐蚀性能、抗拉强度、抗剪强度及长期力学性能对锚杆性能影响较大。 ② 根据FRP筋的近乎线性的应力-应变关系、高抗腐蚀性、较小的弹性模量、极低的抗剪强度、较大的强度离散性以及FRP筋材的蠕变特性,提出FRP锚杆与金属锚杆不同的设计理念。FRP螺旋锚杆若采用分项安全系数法进行设计,能充分地考虑FRP筋对锚杆安全性能的影响。 ③ 注浆锚杆的极限抗拔力为:R=π·η·D·L·q_(sk)。而无注浆锚杆由于破坏形式不同,具有不同极限抗拔力。1) 破坏类型为浅层破坏和过渡破坏时:R=破坏区土柱重量+破坏面处总摩阻力;2) 破坏类型为深层破坏时:R=π·β_c·(D~2-d~2)·C_u/4。 ④ 测得锚杆试验所在土层的物理力学性质为:密度,1.84g/cm~3;含水量,26.3%;液限,51.0%:塑限,20.6%;粘聚力c,43.7kPa;内摩擦角φ,6°。 ⑤ 对不同的入土深度、不同的静置时间的10组锚杆进行拉拔试验后,就锚杆的构造,施工工艺,极限拉拔力等归纳出以下结论: 1) 4组锚杆破坏是由于锚头锚具处的FRP筋断裂而提前破坏,锚杆锚具是FRP筋锚杆设计的难点。 2) 6组拉拔试验锚杆的破坏形式为锚固土体深层破坏,测得其极限抗拔力为8.33kN,实测值与理论值(10.37kN)还是较为接近的。 3) 另外,锚杆钻头下锚能力有限,灌浆施工困难,钻杆间连接方式有待改进,拉拔试验机具的性能有待提高。 ⑥ 根据下锚扭距与抗拔力的线性关系提出一种快速精确、经济可靠的螺旋锚杆的验收试验方法,根据CFRP筋的自感知性能,提出一种新型的锚杆长期监测仪器。 总之,提高FRP筋材的抗腐蚀性能、抗剪强度、长期力学性能,FRP筋螺旋锚杆的应用前景是广阔的。
With high corrosion and fatigue resistance, high tensile strength, light weight, electromagnetic neutrality, Fiber Reinforced Plastics (FRP) has received considerable attention as alternatives to steel and aluminum as new-type geotechnical materials in construction.The history review and current state of geotechnical anchorages, to begin with, are presented. The brief tasks and the future challenges in the field of ground anchors are described emphatically.And, so far as the new-type FRP helical anchor is concerned in this paper, it is as follows, the properties of FRP tendons, the back ground of anchor, the assembly of anchor, the workmanship of anchor, the design philosophy of anchor, the anchor pullout test, the acceptance test of ground anchor, and the long-term monitoring of anchor.(1) The FRP tendons have a lot of attractive properties, and the performance of ground anchor is briefly effected by FRP materials properties, such as corrosion-resistance, tensile strength, shear stresses, long-term behavior of FRP.(2)The design philosophy of FRP anchor is different from the one of steel anchor because of the mostly linear relationship of strain to stress, high corrosion-resistance, low value of elastic module, low shear stress, large variation coefficient of strength, and creep property of FRP. And, the design of grouted helix anchor can adopt the partial material safety factors method.(3)The ultimate pullout capacity of the grouted helix anchor can be evaluated as follows, R= π · η· D · L · q k. The non-grouted helix anchors have different ultimate pullout capacities, with different anchor installed depths. 1) In shallow or transition depths, R=Gravity of anchorage failure zone+ Total friction of rupture surface. 2)In deep depths, R= π· B_c· (D~2-d2) · C_u/4.(4)The properties of soil in the anchor pullout tests are as follows,the density is 1.84g/cm2, the water content is 26.3%, the liquid limit is 51.0%, the plastic limit is 20.6%, the cohesive force is 43.7 kPa, the internal friction angle is 6°.(5)The results from the anchor preliminary improve tests with different constructive factors can be concluded as follows:1) The key problem facing the application of FRP tendons in post-tensioning is how to anchor them. The performances of four anchorage systems are bad in the in-site test.2) The failure in soil is observed in six deep anchors, and the pullout capacity is 8.33kN meanly. This value is close to the theoretic one (10.37 kN).3) And, the installation ability of anchor is limited, the grouted workmanship is bad, the joints between drill bars should be changed, and the performance of instrument for anchor pullout tests should be improved.(6) According to the linear dependent relationship between the installation torque and the pullout forces, the acceptable test method of helical anchor is presented, which can prove the work anchor quickly, precisivly, economically, and reliably. And, owing to the sensing properties of CFRP, a new-type instrument for long-term monitoring FRP anchor is presented.Overall, the new-type FRP helical anchor has a great prospect, when the corrosion resistance, shear strength, and long-term behavior of FRP are improved.
|
