Behavior of RC Slabs Flexurally Strengthened with Prestressed NSM CFRP Laminates

摘要

This work is related to the study of the flexural strengthening of RC slabs using prestressed Carbon Fiber Reinforced Polymer (CFRP) laminates applied according to the Near Surface Mounted (NSM) technique. The NSM technique involves the installation of narrow strips of CFRP laminates, of rectangular cross section, into thin slits opened on the concrete cover of the tensile zone of RC elements. The experimental assessment of the effectiveness of NSM technique with prestressed CFRP laminates, the numerical simulation of the tested RC slabs, a parametric study for the evaluation of the influence of different parameters on the performance of NSM technique with prestressed CFRP laminates and the development of an analytical approach are research tasks covered in this document. This work starts with the literature review of the use of CFRP materials for the flexural strengthening of RC structures, having been given special attention on the use of NSM technique with prestressed CFRP materials. The experimental research is presented in two sections. The first part consists of the description of the preliminary tests carried out to assess the potentialities of the application of NSM technique with prestressed CFRP laminates for the flexural strengthening of RC slabs. In the second part, for investigating the effect of the prestressed NSM CFRP laminates on the behavior of strengthened RC slabs, an extensive experimental research was executed and the influence of the following parameters was determined: level of prestress; percentage of existing steel reinforcement; concrete quality and level of damage in the RC slabs prior to the strengthening (pre-crack). For obtaining an accurate estimation of prestressed load in the RC slabs, the variation of strain in CFRP laminates was surveyed to investigate the strain loss. The strain loss was studied for all prestressed strengthened slabs over time and along the length of the slabs. The flexural behavior of the tested RC slabs was simulated numerically and compared with the experimental results. A parametric study was executed in order to evaluate the influence of different parameters on the behavior of the RC slabs flexurally strengthened with prestressed NSM CFRP laminates. An analytical approach was developed to predict the cracking, yielding and maximum loads of RC slabs flexurally strengthened with prestressed NSM CFRP laminates. Additionally, an upper limit for the prestress level was proposed. Finally, the most relevant conclusions extracted from the present study are presented, and work to be developed in the future is also suggested.