Experimental investigation of substandard RC columns confined with SRG jackets under compression

This paper aims to explore the behaviour of substandard reinforced concrete (RC) columns confined with Steel-Reinforced Grout (SRG) jackets under monotonically increasing uniaxial compression. A total of 24 specimens of short RC columns of square cross section were designed to fail due to longitudinal reinforcement buckling. Single-layered SRG jackets were applied to 18 of these specimens, whereas the rest served for control without SRG jackets. Parameters of this investigation were the type and density of the steel fabric as well as the corner radius of the cross section. The employed SRG jacketing managed to increase the strength and strain capacity and postpone the buckling of the longitudinal steel bars to occur at higher compressive strain level. Confinement effectiveness with respect to the lateral confining pressure exerted by the used SRG jacketing is discussed along with the observed mode of failure

A review on the shear performance of reinforced concrete (RC) beams strengthened with externally bonded mortar-based composites

This paper reviews the performance of shear strengthened reinforced concrete (RC) beams with the use of externally bonded mortar-based composite jackets (e.g. FRCM, ECC, UHPFRC). An experimental database was compiled gathering all the known studies in strengthening shear deficient RC beams using innovative mortar-based systems. The role of the RC beams’ inherent deficiencies as well as the impact of the design parameters of the alternative jacketing configurations were identified. Existing design models proposed to predict the contribution of the mortar-based composites to the shear strength of RC beams were assessed using the database and conclusions were drawn regarding their accuracy

Metallic fabric jackets: an innovative method for seismic retrofitting of substandard RC prismatic members

This paper presents the results of a recent experimental research study where metallic (high-strength steel cord) fabric jackets (MF jackets) were utilised for the seismic upgrading of substandard reinforced concrete members. The proposed intervention method and its practical application are described in detail. Specimens were cantilevers with a square cross-section, representing a typical building column at half scale. The length of the test region corresponded to half the span of a typical storey building column under lateral sway. Due to lack of adequate seismic detailing the specimens were susceptible to various modes of failure such as web shear failure, buckling of compression reinforcement or failure in the lap splice region. The as-built specimens were first damaged up to failure after being subjected to combined axial loading and cyclic lateral displacement reversals simulating seismic loading. In the next phase, specimens were retrofitted with both composite and metallic fabric jackets and then tested again under the same load history. The results of this preliminary experimental research programme show that the metallic fabric jackets performed in an excellent way compared to glass- and carbon-fibre reinforced polymer jackets, increasing substantially both the strength and the deformation capacity of the repaired members. The excellent mechanical performance of the metallic fabrics combined with many of the advantages of the synthetic wraps (easy handling, no change in member dimensions) and the intrinsic favourable properties of steel (fire resistance), underline the potential of this novel material in repair/strengthening of reinforced concrete as an alternative option for jacketing applications

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

Concrete confinement with steel-reinforced grout jackets

The potential of steel fiber reinforced jackets combined with inorganic matrix (cementitious grout matrix) as an alternative strengthening system to fiber-reinforced polymer (FRP) jackets was investigated experimentally in the current study. For this purpose, the novel jacketing device was applied on cylindrical specimens subjected to monotonic concentric uniaxial compression load. Parameters of investigation were the type of the steel fiber reinforced fabric, its density, the overlap length, and the concrete compressive strength. The 3X2 and 12X types of steel fabric were used with three alternative densities, characterized as high, medium and low density. Experimental evidence has shown that a single layer of SRG jacket has increased substantially both axial strength and deformation capacity. From the response of the SRG confined cylinders the degree of penetration of the grout matrix through the fabric as well as the overlap length are considered rather critical parameters for the effectiveness of the method. The experimental data were used for the derivation of a simple empirical confinement model which correlated well with other well-established FRP confinement models. The knowledge gained from this experimental study renders SRG jacketing a remarkably promising retrofit solution for reinforced concrete confinement

A FEM-based model to study the behavior of SRG-strengthened R/C beams

In this paper, a new time‐effective modeling approach is proposed for predicting the response of shear‐deficientreinforced concrete (R/C) beams strengthened with steel‐reinforced grout (SRG) jackets. Solid finite elementsare utilized for concrete using a fracture‐plasticity constitutive law, while both high‐strength steel cords andconventional reinforcement are modeled using embedded truss elements with multilinear stress–strain laws.The efficiency of the proposed method is assessed by comparing numerical against experimental data of nineshear‐deficient beams strengthened with various SRG jacketing configurations. The comparison demonstratedclose correlation both in terms of failure mode and force–displacement curves. The numerical analysis predicted the observed crack pattern and failure modes accurately, whereas deviation in terms of load and deflection was, on average, less than 1% and 10%, respectivel

Design and assessment spectra for retrofitting of RC buildings

This article presents a novel approach for deriving Retrofit Design Spectra (RDS) that are intended for use in preliminary development and assessment of seismic upgrading scenarios of existing structures. The new spectral representation relates the characteristics of the intervention method chosen as the core of the upgrading strategy, with the ductility and strength demand of the retrofitted structure. The methodology utilized for the derivation of the RDS is based on the Capacity Spectrum Method where the capacity curve is described by relationships for global and local intervention methods that are parameterized in terms of fundamental response quantities. The proposed spectra provide direct insight into the complex interrelation between the characteristics of the intervention method and the implications of the upgrading scenario on demand. Alternative retrofit solutions are thus assessed in an efficient way. A case study is used to illustrate practical application of the new approach

Flexural behaviour of reinforced concrete jacketed columns under reversed cyclic loading

The objective of the present study is the development of an analytical model for predicting the response under reversed cyclic loading of structural members with ‘old-type’ detailing, strengthened with reinforced concrete (RC) jacketing. The analytical model introduces one additional degree of freedom between the existing member (core of the retrofitted member) and its outer RC shell, thus allowing slip to take place at the interface between the existing member and the jacket. Shear resistance mechanisms, such as aggregate interlock, friction, and dowel action, are mobilized to resist slip. Existing constitutive models are further improved to describe the mechanisms that resist sliding under cyclic shear reversals and implemented for the first time in an analytical model for deriving the response of RC jacketed members. A calculation algorithm is developed to estimate the flexural response under cyclic loading taking into account slip at the interfaces. The sensitivity of the proposed analytical model to the shear transfer mechanisms degradation rules, as well as to the crack spacing estimation, was evaluated. The validity of the proposed analytical model is assessed against experimental results

Background to the Monolithicity Factors for the Assessment of Jacketed Reinforced Concrete Columns

The paper presents the background to the expressions adopted in the new Eurocode 8—3 for jacketed reinforced concrete columns. These are based on the commonly adopted concept of monolithicity factors (ratios of resistance of the jacketed section to that of an identical monolithic one). These factors are derived here in two ways: (i) by fitting experimental results for jacketed columns and (ii) by an extended parametric study of substandard reinforced concrete (R/C) members that were retrofitted by adding R/C jackets, analysed using a model developed by the authors that takes into account slip at the interface. Apart from the cross-section geometry and the thickness of the jacket, parameters of the investigation were the material properties of the core cross-section and the jacket, as well as the percentage of longitudinal reinforcement of the jacket and the percentage of dowels placed to connect the existing member to the jacket. It was found that the parameter that had the most visible effect on these factors was the normalised axial load (ν). The finally adopted factors are either simple functions of ν or constant values