【作者】 蒋田勇；

【导师】 方志；

【作者基本信息】 湖南大学 ， 桥梁与隧道工程， 2008， 博士

【摘要】 由于高级复合材料-碳纤维增强塑料CFRP (Carbon Fiber Reinforced Polymer/Plastics)筋或拉索是一种横观各向同性材料,其抗剪强度与抗拉强度之比较低,导致传统的预应力筋或拉索锚具不再适用于CFRP预应力筋或拉索,否则将会由于抗剪强度过低而导致过早失效。因此,若在预应力混凝土或拉索结构中应用CFRP预应力筋或拉索,必须研制适合CFRP预应力筋或拉索的锚固系统。目前有关CFRP预应力筋或拉索锚固系统的系统研究成果及其应用仍较少,为了使其研究成果进一步完善,应用范围进一步扩大,对CFRP预应力筋及拉索的锚固系统进行系统研究具有重要的实用价值和理论意义。本文依托国家自然科学基金资助项目和教育部优秀青年教师资助基金对CFRP预应力筋及拉索的锚固系统进行了系列的试验研究和理论分析。主要的研究内容及其相应的研究成果如下:(1)开发了一种新的CFRP筋粘结式锚具,即采用活性粉末混凝土RPC(Reactive Powder Concrete)作为粘结介质的粘结式锚具。静载试验详细研究了CFRP筋在RPC中的锚固性能,试验参数包括CFRP筋的表面形状、预张拉力、锚固长度、根数、间距以及套筒内壁倾角等。试验结果表明,对于抗拉强度不大于3000MPa的表面压纹CFRP筋,RPC抗压强度不小于130MPa,普通粘结试件的临界锚固长度为20倍筋材直径;对于预张拉粘结试件,当预张比为56%时,锚固系统具有最短临界锚固长度,为13倍筋材直径。根据试验结果,建立了平均粘结强度、平均粘结强度对应的滑移量、临界锚固长度以及粘结滑移本构模型,并验证了其适用性。(2)通过试验研究得到了CFRP筋在RPC中粘结应力沿埋长分布的实测曲线,并建立了粘结应力沿埋长分布的位置函数的计算式。在试验研究的基础上,从粘结锚固性能的平衡方程、变形方程以及本构方程出发,推导了粘结应力、CFRP筋轴向应力、滑移量以及位置函数等锚固变量沿锚长分布的理论计算公式。试验结果验证了理论推导的可行性。对CFRP筋的粘结锚固变量沿埋长分布进行了预测分析及相关的参数分析。分析结果表明,对于光滑CFRP筋,当埋长在15倍筋材直径至45倍筋材直径之间时,不均性系数变化均很小,且接近1.0;对于压纹CFRP筋,当锚长小于或等于12.5倍筋材直径时,粘结应力沿埋长分布较为均匀,其不均系数在1.02～1.05之间;当埋长大于12.5倍且小于或等于临界锚固长度20倍筋材直径时,粘结应力沿埋长分布不均匀,其不均性系数在1.06～1.14之间。(3)研究了FRP筋粘结式锚具的粘结界面模型以及界面径向弹性模量,推导了受钢套筒约束的粘结介质及FRP筋在径向应力作用下的位移计算式,并验证了其可行性。然后再根据弹性应变能等效原则,得到了由径向位移表达的界面径向弹性模量的计算式。参数分析了各变量对界面径向弹性模量的影响。分析表明,当粘结介质外径大于1倍筋材直径,筋材肋间距大于1倍筋材直径,筋材肋宽大于0.5倍筋材直径,钢套筒厚度大于2.5mm时,其粘结介质RPC外径、筋材肋间距、筋材肋宽、钢套筒厚度等参数对粘结界面的径向弹性模量影响较小。在有限元数值分析时,考虑界面径向弹性模量的Bar-scale模型能够较好的预测粘结模型的径向反应。(4)传统的夹片式锚具应用于CFRP预应力筋时必须进行改进,改进后的夹片式锚具由夹片、锚杯、塑料薄膜以及薄壁铝套管等组成。试验研究锚杯长度、锚杯倾角、夹片预紧力、筋材预张拉、凹齿间距、深度和宽度以及铝套管厚度等参数对夹片式锚具极限承载力及CFRP筋和夹片的滑移量等锚固变量的影响。试验结果表明,当锚杯倾角为3°、夹片预紧力为100kN、铝片厚度为1mm、凹齿间距和深度分别为12.85mm和0.3mm时,夹片式锚具的实测极限荷载最大为185kN,相应的锚固效率系数为96.4%。锚杯环向应力和轴向应力的实测值与预测值吻合良好,验证了锚杯应力分析的可靠性。基于试验结果建立了夹片式锚具极限荷载的计算式。(5)采用ANSYS软件建立了CFRP筋夹片式锚具数值模型,该模型为轴对称模型,涉及材料非线性和接触非线性。计算终止判断依据为Tsai-Wu准则。计算结果与实测结果对比验证了数值模型的有效性。参数分析表明,各参数的最佳取值:锚杯倾角为2.5°、夹片与锚杯之间的角度差为0.1°、锚杯长度为90mm、锚具自由端处夹片端部至锚杯端部之间的距离为10mm、薄壁铝套管的厚度为1mm、夹片与锚杯之间的摩擦系数为0.03、铝套管和CFRP筋之间的摩擦系数为0.50。数值结果是试验结果有益的补充。(6)根据普通拉索锚固体系的特点,提出了锚固CFRP筋的复合式锚具。静载试验研究了锚杯长度、粘结锚固长度、夹片预紧力、筋材预张拉力等试验参数对复合式锚具的极限承载力及CFRP筋和夹片的滑移量等锚固变量的影响。试验结果表明,当锚杯长度为60mm、粘结锚固长度为100mm、夹片预紧力为60kN时,复合式锚具的极限荷载最大,其值为208kN,对应的锚固效率系数为108.2%,大于95%,满足规范要求。提出的复合式锚具极限荷载计算公式具有较好的适用性。更多还原

【Abstract】 Due to it that the ratio of the shear strength to the tensile strength of the Carbon Fiber Reinforced Polymer/Plastics (CFRP) tendons is lower, so the shear strength is the major concern. The wedge anchor for prestressing steel tendons can’t be applied to anchor CFRP tendons, otherwise the shear stress causes premature failure of the tendon. Thus, the anchorage system for CFRP tendons must be investigated when used in pretressing concrete or cable structure. The researches on anchorage system for CFRP tendons have arrived considerable accomplishments, but they are still insufficient for CFRP tendons/cables application. So it is of important practical and theoretical significance for the investigation on the anchorage system.An experimental study and corresponding theory analysis are conducted to investigate the anchorage performance of CFRP tendons under the financial support of Natural Science Foundation of China and Excellent Young Teachers Program of Ministry of Education of China. This dissertation involves mainly the following investigations and corresponding results:1. A new bond-type anchor for CFRP tendons is developed, whose bond medium is Reactive Powder Concrete (RPC). Due to the Reactive Powder Concrete with excellent performance, it has been put forward as the bond medium and a series of tests have been carried out to develop a new bond-type of anchorage system for CFRP tendon and cable. Those parameters of surface shape, pretensioning load, bond length, number and space of CFRP tendons, the slope of inner wall of outer steel tube used in the anchorage system, have been studied. The tests results show that the grouted length of 20 diameters of CFRP tendon is enough for the indented surface CFRP tendon of tensile strength less than 3000 MPa. When the pretensioning load arrives 56% of ultimate load of general CFRP bar, the indented surface CFRP tendon with tensile strength is less than 3000 MPa, critical bond length of the pretensioning tendon in RPC of compressive strength 130 MPa is 13 diameters of CFRP bar. The equations developed to determine bond capacity, and the corresponding slip, and critical bond length are applicable. An analytical model of bond stress–slip relationships for CFRP tendon has been proposed.2. The bond stress distribution of CFRP (Carbon Fiber Reinforced Polymer/Plastics) tendon in RPC (Reactive Powder Concrete) along bond length has been studied. Based on the experimental investigation, CFRP tendon stress and slip and displacement funtion along bond length can be presented from the equilibrium equations and the linear elastic relationship between stress and strain and constitutive model. Comparison of experimental and analytical results with CFRP tendon stress and bond stress shows good agreement, so its effectiveness to represent the theory equations has been demonstrated. Bond stresses of CFRP tendon without groove along bond length are obtained and parameter analysis results show that when the grouted length of the smooth surface for CFRP tendon is ranged between 15 bar diameters and 45 bar diameters, the ratios of maximum to minimum bond stress and maximum to average bond stress are about 1.0. When the grouted length of the indented surface CFRP tendon is less than 12.5 diameters of CFRP tendon,bond stress distribution along bond length is comparatively uniform, and the ratios of maximum to minimum bond stress and maximum to average bond stress are about 1.02～1.05. When the grouted length of the indented surface CFRP tendon is more than 12.5 diameters and less than or equal to 20 diameters of CFRP tendon,bond stress distribution along bond length is not uniform, and the ratios of maximum to minimum bond stress and maximum to average bond stress are about 1.06～1.14.3. Base on the investigation on radial elastic modulus of an interface between FRP reinforcement and concrete, bond model and radial elastic modulus of an interface of bond-type anchorage for FRP tendon is defined. Based on this equivalence measure of the strain energies stored in the elastic bodies, closed-form elastic solutions are obtained for axisymmetric hollow or solid cylinders subjected to a radial traction. The overall agreement between the analytical and numerical solutions suggests that the analytical solution is correct. Then radial elastic modulus of an interface for bond-type anchorage is available from the analytical expressions. Those parameters such as constituent properties, outside radius of bond medium, thickness of steel sleeve, radial traction, material constants and so on have been studied. The results show that when bond medium radius is more than 1.0 bar diameters, the periodic length of the bar’s surface structure is more than 1.0 bar diameters, the rib’s width is more than 0.5 bar diameters, steel sleeve thickness is more than 2.5mm, it is lesser influence to radial elastic modulus of an interface for bond medium radius and the periodic length of the bar’s surface structure and the rib’s width and steel sleeve thickness. The radial response can be evaluated preferably in Bar-scale model, in which radial elastic modulus is considered.4. Conventional wedge-type anchorage systems for steel tendon must be improved for CFRP tendons due to their material particularity. Wedge-type anchors for CFRP tendons have been developed. The new anchors are assembled from smooth indented wedges, conical barrel, a plastic film, and an aluminum soft metal sleeve. The static tests show, when the anchor involves 3°of slope of conical barrel, 100kN of presetting load level, 1.0 mm of thickness of an aluminum soft metal sleeve, 12.85 mm of space and 0.3 mm of depth of indented wedges, the anchorage system can perform well and undertake 185kN load of the ultimate capability, the related anchorage efficiency is 96.4%. Many factors were demonstrated to affect the anchorage performance and the slip of CFRP tendon, which include length and slope of conical barrel, presetting load level, space and depth and width of indented wedges, and thickness of an aluminum sleeve. Based on the agreement with the analytical and experimental stresses of conical barrel, the present approach is proved. The equations developed for evaluating ultimate load of the anchors are feasible.5. Finite element model of wedge-type anchor for CFRP tendons is established using ANSYS soft with array parameters. The model is axisymmetric with plasticity and contact analysis. Tsai-Wu failure criterion is as terminative condition. Based on the good agreement with the analytical and experimental results, the validity of the present approach is proved. The optimum values of various parameters are obtained. The results show that slope of barrel is 2.5°, angle difference between the wedge and barrel is 0.1°, length of conical barrel is 90 mm, seating distance of the wedge is 10 mm, thickness of an aluminum sleeve is 1 mm, friction coefficient between the wedges and barrel is 0.03, friction coefficient between the tendon and aluminum sleeve is 0.50. So the numerical results are benefit to improve the test results.6. Based on the character of anchorage systems for steel tendon, mechanical gripping-bond type anchorage system is developed for CFRP tendons usage in the stay-cable bridge. Those parameters of barrel length, bond length presetting load level, pretensioning load used in the anchorage system are studied. The static tests show, when the anchor involves 60 mm of barrel length, 100 mm of bond length, 60 kN of presetting load level, the anchorage system can perform well and undertake 208kN load of the ultimate capability, the related anchorage efficiency is 108.2%, which is more than 95%. The equation developed for evaluating ultimate load of the mechanical gripping-bond type anchorage systems is applicable.更多还原