Experimental research on hybrid anchorages of prestressed composite strips for structural strengthening

The prestressed unidirectional carbon fibre reinforced polymer (CFRP) strips are currently often used for flexural strengthening of concrete structures. To ensure reliable strengthening, strips have to be anchored at their ends to the surface. However, anchoring of unidirectional CFRP strips is difficult because of their weak transversal mechanical properties. Although several CFRP strip anchorage approaches have been developed to date, only very few were applied on-site. The paper presents the development of hybrid bonded/bolted anchorages of CFRP strips used in a novel prestressing system. The anchorages are made of thin steel plates, clamped with the high-strength friction grip (HSFG) bolts and epoxy adhesive, to fix the CFRP strips. The paper describes the results of full-scale tests carried out on a series of axial tensile specimens. The developed anchorage has an ultimate tensile strength of about 200 kN, i.e. 70% of the ultra-high CFRP strips’ strength, which is sufficient for strengthening purposes. After a series of tests in the laboratory, the anchorages have been implemented on-site and an example is presented in the paper.

The development of nature-inspired gripping system of a flat CFRP strip for stress-ribbon structural layout

The elegant stress-ribbon systems are efficient in pedestrian bridges and long-span roofs. Numerous studies defined corrosion of the steel ribbons as the main drawback of these structures. Unidirectional carbon fiber-reinforced polymer (CFRP) is a promising alternative to steel because of lightweight, high strength, and excellent corrosion and fatigue resistance. However, the application of CFRP materials faced severe problems due to the construction of the anchorage joints, which must resist tremendous axial forces acting in the stress-ribbons. Conventional techniques, suitable for the typical design of the strips made from anisotropic material such as steel, are not useful for СFRP strips. The anisotropy of СFRP makes it vulnerable to loading in a direction perpendicular to the fibers, shear failure of the matrix, and local stress concentrations. This manuscript proposes a new design methodology of the gripping system suitable for the anchorage of flat strips made from fiber-reinforced polymers. The natural shape of a logarithmic spiral Nautilus shell describes the geometry of the contact surface. The continuous smoothly increasing bond stresses due to friction between the anchorage block and the CFRP strip surface enable the gripping system to avoid stress concentrations. The 3D-printed polymeric prototype mechanical tests proved the proposed frictional anchorage system efficiency and validated the developed analytical model.

Numerical study on rehabilitation of the U-rib butt weld fatigue crack in orthotropic steel deck using carbon fiber reinforced polymer strip

<p>The U-rib butt weld fatigue crack is a typical crack form in orthotropic steel bridge decks. However, there is no completely mature rehabilitation method so far. In this paper, the carbon fiber reinforced polymer (CFRP) strip is used to reduce the stress concentration at the crack tip. Finite element model of U-rib segment was established and parameter analysis was conducted to investigate the influence of the CFRP strip design parameters on the rehabilitation effect. The results indicate that the influence of the three parameters on the reduction of stress concentration is: CFRP layer number &gt; paste width &gt; paste area. Specifically, it is recommended that number of CFRP layers does not exceed 3. For paste width and area, it is only required that the CFRP strip can cover the cracked area.</p>

Stress Loss of Pre-Tensed CFRP Strips Strengthening Square RС Column

Pre-tensing the CFRP strip strengthening RC column can improve the strain lag of the confined concrete and avoid unloading of column in advance. The pre-stress of strip has an important influence of strengthen. Stress loss of the strip pre-tensed by using the device proposed were investigated by using an experimental test. Firstly, the reasons for the stress loss of strip were analyzed according to the working principle of the device and the strengthening procedure. Then the primary causes of the stress loss, such as friction, relaxation and removing device, were experimentally tested. The influence of the pretension, detail and sectional geometric dimension on the stress loss of the strip were studied. The results show that all three types of pre-stress losses increase significantly with the initial stress. Increasing the cross-sectional size would reduce the relaxation and unwinding losses, but it has little effect on friction losses. The influence of fillet radius on the pre-stress loss was negligible, but in order to avoid premature tearing of local CFRP caused by stress concentration, the chamfer should be made as large as possible within the thickness of concrete protective cover. The test also found that friction was the main cause of stress loss, and friction loss accounts for more than 90% of the total loss.