Flexural behavior of precast concrete box beams posttensioned with unbonded, carbon-fibercomposite cables

Behaviour of precast concrete beams prestressed with CFRP strandsCorrosion presents a serious problem in severe marine environments, especially for bridges. This paper explores the use of carbon fibre reinforced polymer (CFRP) strands for prestressing precast concrete girders. The research includes a practical prestressing process using the prestressing jacks normally applied in the precast industry. Bending tests are made on prestressed concrete T-beams (scaled models of typical T-section). The design and casting processes, and the test set-up used to load the beams up to failure, are discussed, and failure mechanisms are reviewed. Test results are compared with the ACI 318 guidelines. Ponašanje predgotovljenih betonskih greda prednapetih pomoću CFRP užadi Korozija predstavlja ozbiljan problem u otežanim uvjetima morskog okoliša, i to naročito kod mostova. Rad istražuje primjenu užadi izrađenih od polimera armiranog ugljičnim vlaknima (eng. carbon fiber reinforced polymer ili CFRP) za prednapinjanje predgotovljenih betonskih nosača. Istraživanje uključuje proces prednapinjanja pomoću uobičajenih preša koje se koriste u industriji predgotovljenih proizvoda. Provedena su ispitivanja na savijanje na prednapetim betonskim T-nosačima. Analiziran je postupak proračuna, izvedba nosača, postupak ispitivanja do sloma uz razmatranje mehanizma sloma. Rezultati ispitivanja uspoređeni su sa smjernicama ACI 318.

Section: State Of the Fieldmentioning

confidence: 99%

Ponašanje predgotovljenih betonskih greda prednapetih pomoću CFRP užadi

2016

JCE

“…Linearly varying strength reduction factors were suggested from 0.65 for compression-controlled sections to 0.85 for tension-controlled sections with CFRP (aramid fiber-reinforced polymer) tendons. Determining q U pfb becomes more challenging for prestressed beams with unbonded FRP tendons, as the tensile stress of the unbonded tendons depends on the averaged elongation of concrete at the level of unbonded tendons along the beam span (Naaman and Alkhairi 1991a, b;Kato and Hayashida 1993;Maissen and De Semet 1995;Grace et al 2006Grace et al , 2008Du et al 2008;Heo et al 2013). Consequently, it is expected that q U pfb is always smaller than q B pfb , and prestressing the beam with a reinforcement ratio of unbodned CFRP tendon (q U pf ) greater than q B pfb would preserve the compression-controlled section with a higher degree of plasticity, avoiding an abrupt brittle failure.…”

Section: Introductionmentioning

confidence: 99%

Balanced Ratio of Concrete Beams Internally Prestressed with Unbonded CFRP Tendons

Shin

Int J Concr Struct Mater

2016

The compression or tension-controlled failure mode of concrete beams prestressed with unbonded FRP tendons is governed by the relative amount of prestressing tendon to the balanced one. Explicit assessment to determine the balanced reinforcement ratio of a beam with unbonded tendons (q U pfb) is difficult because it requires a priori knowledge of the deformed beam geometry in order to evaluate the unbonded tendon strain. In this study, a theoretical evaluation of q U pfb is presented based on a concept of three equivalent rectangular curvature blocks for simply supported concrete beams internally prestressed with unbonded carbon-fiber-reinforced polymer (CFRP) tendons. The equivalent curvature blocks were iteratively refined to closely simulate beam rotations at the supports, mid-span beam deflection, and member-dependent strain of the unbonded tendon at the ultimate state. The model was verified by comparing its predictions with the test results. Parametric studies were performed to examine the effects of various parameters on q U pfb .

“…Although much experimental and theoretical research has been conducted for characterising the flexural behaviour of concrete beams prestressed with bonded FRPs (Burke and Dolan, 2001;Dolan and Swanson, 2002;Ehsani et al, 2001;Naaman et al, 1993;Yonekura et al, 1993), fewer studies have been conducted on concrete beams prestressed with unbonded FRPs (Grace et al, 2006(Grace et al, , 2008Heo et al, 2013;Kato and Hayashida, 1993;Maissen and de Smet, 1995). To gain a better understanding of the flexural behaviour and practical application of such beams, it seems necessary to develop a theoretical model that can incorporate the properties of both concrete and reinforcing materials and member-dependent tendon strains in the simulation of the non-linear flexural behaviour of these beams.…”

Section: Introductionmentioning

confidence: 99%

Modelling of load–deflection of concrete beams internally prestressed with unbonded CFRP tendons

Shin

Magazine of Concrete Research

2015

A theoretical model was developed for predicting the flexural load-deflection of simply supported concrete beams internally prestressed with unbonded carbon fibre reinforced polymer (CFRP) tendons under four-point loading. At each state in the load-deflection curve (initial cracking state, initial yielding state (if any) and ultimate load state), three equivalent rectangular curvature blocks, which can closely simulate the beam rotations at the supports and the midspan beam deflection, were determined by iteratively correcting the strain value of the unbonded tendon. The validity of the model was demonstrated by comparing its predictions with the test results of four rectangular beams and two T-beams with different prestressing reinforcement ratios, initial prestressing and type of auxiliary bar. The developed model was used to examine the effects of different parameters on the first cracking and ultimate strengths of the beam and the additional strain of the unbonded tendon to the effective strain.