Research On Mechanical Behaviors Of CFRP Cables And Its Connected Joint For Tension Cable Roof

The cable structure is the type of structure with the largest span in the world.It is widely applied in building and bridge structures.The cable structures also represent the level of science and technology of construction for a country.Although the cable structures have a rapid development and mature application,some problems are hard to solve during the application of the cable structures,such as limit span,corrosion of steel cables and prestressing loss of steel cables.A main reason of these problems is related to the material properties of steel,so replacing the steel by high performance composite to make the cable become a focused research field.With the advantages of high tensile strength,low weight,good resistance to corrosion,creep and fatigue,and low linear expansion coefficient,Carbon Fiber Reinforced Polymer(CFRP)can be used as the material of prestressed cables.CFRP cables have been applied in cable bridges firstly,and several bridges with CFRP cables were built in some countries.The research of application of CFRP cables on other cable structures,cable roofs,especially the tension cable roofs,is just at the beginning.Many basic researches should be accomplished.Based on the research status of tension cable roofs with CFRP cables,the effective connection between the CFRP cables and other structural elements of cable roof is the problem to be solved firstly.The effective connection is the premise and foundation of the study of structural behaviors for the tension cable roofs.It has a great significance to the development of tension cable roofs with CFRP cables.In this paper,the research focuses on the problem of connection between CFRP cables and other structural elements.The mechanical behaviors of CFRP cables and its connected joint in the tension cable roofs are researched.For the transverse enhanced CFRP cables,its transverse mechanical tests are designed and conducted,including compression,shear and bending.Based on the analysis of transverse failure mechanism,the relationship between the transverse strength and diameter of CFRP tendons is illuminated.In the study of longitudinal mechanical behaviors,the tensile and compressive tests of CFRP tendons and plates are designed and conducted.The effect of geometrical dimension,geometrical shape and boundary conditions on the longitudinal mechanical behaviors of CFRP cables are analyzed and discussed.For two kinds of load that often load on the CFRP cables,longitudinal tension and transverse compression,the types of damages of CFRP cables caused by different load and evaluations of fracture behaviors are determined by fracture tests.The suitability of fracture toughness and fracture energy is compared for evaluating the fracture behaviors of CFRP cables.Based on the results of digital image correlation(DIC),the fracture failure mode and damage extension mechanism of damaged CFRP cables is analyzed.For the anchor of CFRP cables in tension cable roofs,a new type of large angle wedge anchorage is designed and developed.Different types of anchor failure modes are determined by anchor tests.The application value of large angle wedge and the effect of anchorage’s elements on the anchor performances are analyzed.Combined with the results of numerical simulation about the contacting behaviors between different of anchorage’s element,the improved measures of anchorage are suggested.For the connection between CFRP cables and struts in the tension cable roofs,the effect of chamfering of cable clamping plate on the shear behaviors of CFRP tendons is researched through the double shear test.An effective transverse safeguard of CFRP cables in the cable-strut joint is suggested.The following conclusions can be drawn.(1)The experimental results of transverse mechanical behaviors show the transverse enhanced CFRP tendons have a better transverse strength than commercial products,achieving the transverse enhanced purpose.The CFRP tendons have a higher compressive strength than plates,but all transverse mechanical strength of CFRP tendons decrease with its diameter increasing.Based on the analysis of failure mechanism,the main reason is that the decreasing of the ratio of initial bearing area to the cross section area.The decreasing of transverse mechanical strength of CFRP tendons need to pay attention when the CFRP cables are applied in engineering.(2)The experimental results of longitudinal mechanical behaviors show the CFRP tendons have a better tensile strength than plate with a bigger thickness,so CFRP tendons,fabrics and pultrusion plate with small thickness are the best choice as the CFRP cables.The wedge is not suitable to anchor the CFRP plates due to its poor transverse compressive strength.For the CFRP tendons and plates,no one has the absolute advantage to obtain a perfect anchor performance.Compared with plates,the CFRP tendons have a better transverse compressive strength.In the case of equal cross section area,CFRP plates with the width-to-thickness ratio greater than 3.14 have a longer anchorage length of cross section than tendons.Based on the tests results and failure mechanism analysis,the geometrical shape has no effect on the longitudinal compressive properties of CFRP pultruded profiles,but the end restraint has a significant effect.Therefore,the end protection,the auxiliary force transferring at the end of element,and avoiding more constraint at the end of element are several methods to improve the longitudinal compressive strength of CFRP pultruded profiles.(3)The fracture failure mode and critical energy release rate of damaged CFRP cables are determined by fracture tests.Based on the fracture characteristics,the concept of fracture energy is suitable to evaluate the fracture behaviors of CFRP cables.The computing method of critical fracture energy is suggested by DIC technique.The fracture mechanism show the failure of fiber/matrix is the root of the damage extension for unidirectional CFRP composites.Regardless of the types of damages for unidirectional CFRP composites,these damages will develop into longitudinal cracks and lead to the splitting failure of CFRP cables under longitudinal tension.Based on the results of tests,the prestress applied for CFRP cables in the tension cable roofs is sufficient to cause damage extension and splitting failure.(4)In the research and development of large angle wedge anchorage,the results of anchor tests show that this type of anchorage has an effective anchor to 5mm-diameter-CFRP tendons,but not to 7-mm and 9mm-diameter CFRP tendons.The test results demonstrate the large angle wedges have an actual application value.It can provide a research direction to miniaturization of anchorage.Based on the test results,the reasons of different anchor failure modes and anchor failure mechanism are analyzed and illuminated.The optimized geometric parameters of elements of the anchorage are suggested.The results of numerical simulation illuminate the effect of the friction coefficient between the wedge and shell and the wedge angle on the anchorage performances.According to the results of test and simulation,some improved measures are summarized to the further research in the future.(5)The results of double shear tests show that the chamfering can change the shear failure mode of CFRP tendons completely,avoiding the complete fracture of CFRP tendons.It is beneficial to improve the application safety of CFRP cables.Therefore,the chamfering of cable clamp plate in the cable-strut joint is an effective safeguard to protect the transverse loading of CFRP tendons.