Delaying the Occurrence of Bar Buckling in RC Columns Confined with SRG Jacketing

This paper investigates experimentally the structural performance of substandard reinforced concrete (RC) short columns confined with steel-reinforced grout (SRG) jackets under monotonically increasing uniaxial compression. The study comprised 24 square cross section short RC columns having alternative arrangements of shear reinforcement (ratio of stirrup spacing to longitudinal bar diameter ranging from 4.2 to 12.5). The short columns were retrofitted with externally applied SRG jacketing differing by the density of the fabric (4 cords/in and 12 cords/in) and the number of fabric layers (1 and 2). The test results showed that retrofitting significantly changed the behaviour of the specimens compared to the unconfined counterparts. For columns at risk of premature failure due to insufficient support of compression bars provided by the sparse stirrups, the SRG jackets delayed bar buckling, enabling the members to achieve greater strength and deformation capacity. The well-detailed specimens helped establish the maximum effectiveness of SRG confinement

Bond of reinforcing bars to steel fiber reinforced concrete

Steel fiber reinforced concrete (SFRC) has been increasingly used during recent years. Regarding bond of rebars to concrete, fibers provide passive confinement and improve bond capacity in terms of bond strength and, more importantly, toughness. An extensive experimental programme has been carried out, and SFRC specimens with embedded rebars have been subjected to the Pull Out Test to obtain the bond stress slip curves, retaining the bond strength and the area under the curve as measures of the bond capacity of concrete. The following parameters were considered: concrete compressive strength (30-50 MPa), rebar diameter (8-20 mm), concrete cover (between 30 mm and 5 times rebar diameter), fiber content (up to 70 kg/m(3)), and the slenderness and length of the steel fibers used. Predictive equations have been obtained to relate the experimental results to the factors considered, and the trends observed have been analyzed and discussed. (C) 2015 Elsevier Ltd. All rights reserved.The authors of this work wish to thank both the Research Bureau of the Spanish Ministry of Science and Innovation for the funding of the projects 'BIA 2009-12722' and 'BIA 2012-35776-AR', this research being a part thereof.García Taengua, EJ.; Martí Vargas, JR.; Serna Ros, P. (2016). Bond of reinforcing bars to steel fiber reinforced concrete. Construction and Building Materials. 105:275-284. https://doi.org/10.1016/j.conbuildmat.2015.12.044S27528410

Bond between glass fibre reinforced polymer bars and high - strength concrete

YesIn this study, bond properties of glass fibre reinforced polymer (GFRP) bars embedded in high-strength concrete (HSC) were experimentally investigated using a pull-out test. The experimental program consisted of testing 84 pull-out specimens prepared according to ACI 440.3R-12 standard. The testing of the specimens was carried out considering bar diameter (9.5, 12.7 and 15.9 mm), embedment length (2.5, 5, 7.5 and 10 times bar diameter) and surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) as the main parameters. Twelve pull-out specimens reinforced with 16 mm steel bar were also tested for comparison purposes. Most of the specimens failed by a pull-out mode. Visual inspection of the tested specimens reinforced with GFRP (HW-SC) bars showed that the pull-out failure was due to the damage of outer bar surface, whilst the detachment of the sand coating was responsible for the bond failure of GFRP (SC) reinforced specimens. The bond stress – slip behaviour of GFRP (HW-SC) bars is different from that of GFRP (SC) bars and it was also found that GFRP (SC) bars gave a better bond performance than GFRP (HW-SC) bars. It was observed that the reduction rate of bond strength of both GFRP types with increasing the bar diameter and the embedment length was reduced in the case of high-strength concrete. Bond strength predictions obtained from ACI-440.1R, CSAeS806, CSA-S6 and JSCE design codes were compared with the experimental results. Overall, all design guidelines were conservative in predicting bond strength of both GFRP bars in HSC and ACI predictions were closer to the tested results than other codes

Background to the European seismic design provisions for retrofitting RC elements using FRP materials

This paper is a comprehensive background document on the state of the art in European seismic design provisions which was assembled by fib committee 5.1 to support the development of design guidelines regarding the use of externally applied fibre reinforced polymer (FRP) materials in the seismic retrofitting of reinforced concrete structures. In the context of developing design guidelines, the underlying mechanistic models that support the derivation of provisions were assembled following critical evaluation of the existing proposals and with careful reference to the experimental evidence available, the comparative assessment of past models in the literature and requirements established from first principles

An Example-Guide for Rapid Seismic Assessment and FRP Strengthening of Substandard RC Buildings

This paper presents a rapid seismic assessment and Fibre Reinforced Polymer (FRP) retrofit design methodology which relies on the European design guidelines recently published in Chapter 8 of fib Bulletin 90 on the use of externally applied FRP reinforcement in the seismic retrofitting of reinforced concrete (r.c.) structures. For this purpose, an example-guide is developed with step-by-step hand calculations aiming to facilitate engineers of practice and researchers working in the field to easily understand the proposed methodology. A three-storey, pilotis-type residential r.c. building is selected typical of the Mediterranean construction practice in the 1970s. The methodology followed only aims to provide preliminary results on seismic assessment and retrofitting before the implementation of more sophisticated analysis if need be (e.g., in case of irregular buildings). The assessment procedure identified that the columns of the ground storey, being the most critical structural elements for the stability of the structure, are vulnerable to brittle failure modes. To remove all the brittle failure modes attributed to inherent deficiencies and enhance the overall deformation capacity of the building, the strengthening schemes applied in the ground storey (pilotis) is a combination of local strengthening measures, such as FRP wrapping, and global interventions. The latter may refer to the addition of r.c. jacketing to the central column to remove slenderness and of metal X-braces to modify the lateral deflection shape of the building and thus moderate the interstorey displacement demand