Flat prestressed unbonded retrofit system for strengthening of existing metallic I-Girders

Abstract

In this study, a novel retrofitting system is developed to strengthen existing metallic I-girders using prestressed unbonded carbon fiber reinforced polymer (CFRP) plates. The system relies on a pair of mechanical clamps. Each clamp holds two CFRP plates (each having cross-sectional dimensions of 50 × 1.4 mm) and anchors their prestressing forces to a metallic I-girder via friction. A finite element (FE) model was established to optimize the design of the required mechanical components, and a set of pull-off tests was performed to evaluate the capacity of the optimized system. The proposed flat prestressed unbonded retrofit (FPUR) system was then applied on a 6.4-m-long steel I-beam, and the excellent performance of the system, in terms of stress reduction in the beam bottom flange, was confirmed based on the results of a set of static four-point bending tests. Moreover, a fatigue fourpoint bending test was conducted on the steel I-beam, strengthened using the proposed FPUR system with a prestressing level of 53% (i.e., approximately 1120 MPa prestress in the CFRPs). Experimental results of the high-cycle fatigue test confirmed the excellent fatigue performance of the proposed FPUR system, as no prestress loss was observed after 20 million fatigue cycles. An analytical model is proposed to accurately predict the stress state in an I-girder strengthened with the proposed FPUR system, while design recommendations are provided concerning the practical use of the system.Relying on the laboratory experimental test results, the proposed FPUR system was used to strengthen the metallic cross-girders of a 121-year-old bridge in Australia.

Mixed mode I/II fatigue crack arrest in steel members using prestressed CFRP reinforcement

“…As is schematically depicted in Figure 8 with a data collection frequency of 2400 Hz (see [43] for further details).…”

“…To avoid any creep-rupture of CFRP composites, it is recommended to limit the prestress level in such reinforcements to 65% of their nominal tensile strength (σ f,n ) or 65% of the anchorage capacity, whichever is lower [43]. It should also be mentioned here that, even though the fatigue strengthening of structural steel members is the focus of this study, the ultimate state of any prestressed CFRP-strengthened member should always be considered during the strengthening design procedure.…”

“…It should also be mentioned here that, even though the fatigue strengthening of structural steel members is the focus of this study, the ultimate state of any prestressed CFRP-strengthened member should always be considered during the strengthening design procedure. In other words, the tensile stress level in the prestressed reinforcements should be calculated to ensure that CFRP tensile rupture is prevented at the ultimate state through a proper design of the strengthening solution (see [43] for further details).…”

“…The reason is attributed to the relatively low bond capacity of prestressed bonded reinforcements (PBRs) prior to their debonding failure, as well as certain concerns that are associated with the durability and fatigue performance of adhesively bonded CFRP-to-steel joints [40,41]. Consequently, various prestressed unbonded retrofit (PUR) solutions were introduced [42,43], and their excellent performance has been demonstrated for the fatigue strengthening of metallic bridge girders in Switzerland [44] and Australia [45,46].…”

Practical Application of CFRP Strengthening to Steel Floor Beams with Web Openings: A numerical Investigation

“…Given the relative weakness of the bond interface, a number of researchers have investigated use of unbonded pre-stressed CFRP plate as means of retrofitting steel structures e.g. Kianmofrad et al [10] and the technique has recently been used in the field to strengthen full scale bridge girders of historic steel construction, Ghafoori et al [11], Hosseini et al [12].…”