Kuangyi Zhang’s research while affiliated with Hunan University and other places

Research works related to the fiber-reinforced polymer (FRP) tendons have focused on the anchor system, but the anchor is not the only contribution to performance. Since civil structures require tendons consisting of multiple rods (e.g., cables, suspenders in bridges, or rock bolts in ground anchors), the characteristics of multirod tendons require targeted research. This paper presents a study on the behavior of tendons with multiple carbon FRP (CFRP) rods. Four specimens including two cable-type assemblies (TA12-9 and TA12-20) and two ground anchors (GA12-9 and GA12-20) with large-tonnage capacities were built and tested. Using strain gauges set along individual rods, the nonuniform force distribution among individual rods was observed and is discussed. The test results showed that nonuniformity is a recurring feature of a multirod tendon, with the variation in the initial length of the rods caused by installation error as its main reason. Based on the premise that tension in multiple rods obeys a normal distribution, the relationship between the nonuniformity coefficient, η, and a corresponding capacity reduction coefficient, λ, was established. The tendon consisting of nine CFRP rods in TA12-9 (GA12-9) shows a capacity reduction factor of 0.83 (0.89), while the capacity reduction factor of the tendon consisting of 20 rods in TA12-20 (GA12-20) decreases to values of 0.79 (0.87).

The poor performance and durability of traditional steel tendon and cement grout have become serious constraints to the development of ground anchor systems, especially when these systems are permanent features in large-scale projects such as ground anchors with capacities of more than 4,000 kN in Aizhai Bridge, China. This paper presents a large-scale ground anchor system with carbon fiber-reinforced polymer (CFRP) tendon and reactive powder concrete (RPC) grout as the bonding media in both above-ground and below-ground parts. Two full-scale ground anchor specimens named GA12-20 and GA12-9 were designed and installed at the construction site, and their behavior was systematically studied through monotonic and cyclic load testing. The two systems displayed acceptable displacements under both monotonic load testing with maximum tension twice the design lock-off load and in cyclic load testing under about 90% of its bearing capacity, with residual displacements all less than 5 mm. Furthermore, the bond stress distributions in the grouted portions of the rods in tendon showed both systems have reliable bonding capacities under tension. This innovative ground anchor system with CFRP tendon and RPC grout showed a good behavior and successfully served as the ground anchor of the Aizhai Bridge.

This paper presents a bond-type anchorage system for multi-rod CFRP (Carbon Fiber-Reinforced Polymer) tendons with a bonding medium of ultra-high performance RPC (Reactive Powder Concrete). A full-scale specimen of the CFRP tendon-anchorage assembly GA12-9 for nine 12.6-mm-diameter CFRP rods was made, and its behavior was studied extensively through tensile tests. During the tests, the load distribution among the rods in tendon was monitored until the bonds of the multi-rod system failed. The test results showed that the capacity reduction resulting from inherent non-uniformities in multi-rod anchoring systems should be considered, and the corresponding capacity reduction factor has been provided. Furthermore, the equations for evaluating the bond strength and critical bond length of either single or multiple CFRP rods embedded in RPC grout were established and shown to be in good accordance with the test results. For a CFRP rod with a wrapped surface and tensile strength of 2300 MPa, a bond length of 25 times the rod diameter ensures that a tendon of 9 rods with clear spaces among rods of not less than a rod diameter can be anchored in a RPC medium of 130 MPa.