Jacob Wittrup Schmidt

Strain Measurement Using Embedded Fiber Bragg Grating Sensors Inside an Anchored Carbon Fiber Polymer Reinforcement Prestressing Rod for Structural Monitoring

Results are reported from a study carried out using a series of Bragg grating-based optical fiber sensors written into a very short length (60 mm) optical fiber network and integrated into carbon fiber polymer reinforcement (CFPR) rod. Such rods are used as reinforcements in concrete structures and in tests were subjected to strain through a series of cycles of pulling tests, with applied forces of up to 30 kN. The results show that effective strain measurements can be obtained from the different sensors mounted along the rod. Additionally, the tests show that close agreement with the results obtained from the calibrated force applied by the pulling machine and from a conventional resistive strain gauge mounted on the rod itself is obtained. Calculations from strain to shear stress show a relatively uniform stress distribution along the bar anchor used. The results give confidence to results from various methods of in situ monitoring of strains on such CFRP rods when used in different engineering structures.

Development of Mechanical Anchor for CFRP Tendons Using Integrated Sleeve

A durable and very efficient external strengthening system is achieved if steel tendons for posttensioning applications can be replaced with carbon fiber-reinforced polymer (CFRP) tendons, and if reliable anchorage systems are developed. This paper presents a newly developed and simple-to-use, two-piece wedge anchorage for CFRP tendons with an integrated sleeve and a differential angle between barrel and wedge sections. Three longitudinal slits are cut into the one-piece wedge, with one slit open and the other two stopping 1 mm from the inner wedge hole. The integrated sleeve holds the wedge’s sections together during presetting and loading, resulting in a circumferential confined gripping of the CFRP tendon and optimized surface friction area. Therefore, the one-piece wedge differs from conventional wedge systems, where the wedges act separately with adjacent spaces, wedging the separate tendon sleeve in the longitudinal direction. Evaluation of the failure modes during testing was one of the main keys i...

Reinforced Concrete T-Beams Externally Prestressed with Unbonded Carbon Fiber-Reinforced Polymer Tendons

Unbonded carbon fiber-reinforced polymer (CFRP) offers promise for use in prestressing applications due to its minimal creep and relaxation, low weight and high resistance to degradation. This study highlights the potential of CFRP rods in external and unbonded prestressing applications. A series of experiments were conducted on seven beams prestressed with unbonded external CFRP tendons anchored using a newly developed anchorage and post-tensioning system. The experiments investigated the effects of varying the initial tendon depth, prestressing force, and the presence of a deviator. The experimental results were compared to those observed with analogous beams prestressed with steel tendons, predictions made using an analytical model adapted from the literature and common beam theory. Results showed that steel and CFRP tendons had very similar effects on the structural behavior of the strengthened beams. Minor differences were observed that could be attributed to the difference between the modulus of elasticity of the CFRP and the steel used in the tests. Reinforced concrete beams prestressed with external bonded CFRP tendons exhibited the expected increase in strength, stiffness, and failure load, as well as decreased ductility, relative to unstrengthened beams. Under the loads examined in this study, the bending of CFRP tendons due to beam deflection did not significantly affect the tendon’s performance. Although the models predicted the beams’ load-bearing behavior accurately, they were less effective at predicting the stress experienced by the tendons. The findings from this study contribute to a better understanding of structural behavior of reinforced concrete beams post tensioned with external unbonded CFRP tendons throughout the load scheme.

Numerical Simulation and Experimental Validation of an Integrated Sleeve-Wedge Anchorage for CFRP Rods

The tensioning of carbon-fiber-reinforced polymer (CFRP) rods for prestressed concrete applications or posttensioning repair and strengthening has been met with mixed success. This is primarily because of limitations inherent in the use of traditional wedge anchors typically used for steel tendons. Recently, an integrated sleeve-wedge anchorage has been successfully developed specifically for CFRP rods. This paper presents a numerical simulation of the newly developed anchorage by using ABAQUS. The three-dimensional (3D) finite-element (FE) model, which considers material nonlinearity, uses hexagonal elements for the barrel, CFRP rod, and tetrahedral elements for the integrated sleeve wedge. The simulated barrel surface strains are shown to compare well with optically measured strains; however, the numerical results are shown to be sensitive to the mechanical properties of the anchorage and CFRP rod and especially the transverse elastic modulus of the CFRP rod. Finally, the simulated strain distributions ...