Steel Reinforced Grout Research Articles

Axial compressive behavior of predamaged RC columns retrofitted with precast steel-reinforced grout jackets

Steel jacketing and concrete jacketing are popular retrofitting techniques to strengthen the axial compressive behavior of reinforced concrete (RC) columns. However, these retrofitting methods lack efficiency in practical application due to intensive labor and time-consuming installation. In order to improve the retrofit efficiency of damaged RC columns, this study proposed a novel precast steel-reinforced grout jacket (PSRGJ) consisting of early-strength cementitious grout and a steel frame. Ten columns were tested to investigate the axial compressive behavior of predamaged RC columns retrofitted with PSRGJ. The tested parameters were the stirrup reinforcement ratio, the transverse reinforcement ratio of PSRGJ, and the predamage level. The results indicated that the columns’ peak load and ductility index I10 were significantly improved by PSRGJ retrofitting and increased with the increase of transverse reinforcement ratio of PSRGJ. Besides, the peak load and the initial stiffness of PSRGJ-retrofitted RC columns decreased with the predamage level, while the ductility index I10 increased. In addition to the confinement effect, PSRGJ carried 11%−17% of the peak load through the interfacial bonding effect. Based on the test results, the actual confinement pressure model and interfacial bonding strength model were proposed. Further, peak load models considering the size effect were developed for PSRGJ-retrofitted intact and predamaged RC columns. The predictions of the proposed models agreed well with the test results from this study and the literature.

Prediction of compressive strength of brick columns confined with FRP, FRCM, and SRG system using GEP and ANN methods

This study assesses the strength capacity of brick columns under various confinement materials, including fiber-reinforced polymer (FRP), fiber-reinforced cementitious matrix (FRCM), and steel-reinforced grout (SRG) using gene expression programming (GEP) and artificial neural networks (ANN) models. To achieve this, a comprehensive database of masonry column test results from existing scientific literature is compiled. The models' performance is evaluated using statistical errors like the coefficient of linear correlation (R2), mean absolute error (MAE), mean square error (MSE), and root mean square error (RMSE). Additionally, sensitivity analysis is carried out to assess the significance of individual parameters in the models. The findings reveal that ANN predictions closely match empirical data, demonstrating a strong correlation coefficient of 0.95. The accuracy of the ANN approach is reasonably high, with only 26% of the predicted values deviating by more than 20% from the actual data. Based on the statistical analyses, the correlation coefficient between the actual and estimated data was 0.88, for GEP method. Also, the GEP model yields outcomes, with roughly 43% of the predicted values differing by 20–50% from the actual data. In a comparison of the two models, the ANN model outperforms the GEP model, displaying a 40% reduction in error when estimating the compressive strength of masonry columns. The data estimated by the GEP were sparser than those estimated by the ANN. Nevertheless, the GEP model still maintains an acceptable correlation coefficient and error rate, making it a viable choice for precise predictions. It offers a user-friendly formula and meets the needs of both customers and builders.

Review of Out-of-Plane Strengthening Techniques of Unreinforced Masonry Walls

When a seismic load is applied horizontally or laterally on unreinforced masonry walls (URM), the walls behave in two different ways, viz., in-plane (IP) and out-of-plane (OoP). This review beneficially provides a literature overview of the most cited research papers on Scopus, and the database is evaluated with VOSviewer software for scientometric analysis. This review paper delves into the practical applications of various types of reinforcement for masonry walls, specifically focusing on four commonly used systems: externally bonded strengthening techniques using fiber-reinforced polymers (FRP), steel-reinforced grout (SRG), fabric-reinforced cementitious mortar (FRCM), and textile-reinforced mortars (TRM). The main objective of the paper is to explore the efficacy of these reinforcement techniques in strengthening masonry walls, and to provide a comprehensive overview of their respective advantages and limitations. A further detailed study of the extent of the literature is performed about the effect of the different strengthening systems on the mechanical properties of different categories of masonry walls like a cement block, stone, and clay brick are described and categorized. The efficiency of OoP strengthening can depend on various factors, such as the types of masonry units, the rendering mortar, the type of strengthening system, the bond between the different materials interfaces, the geometry of the wall, and the loading conditions. By utilizing the practical method of Dematel (Decision-making trial and evaluation laboratory) analysis, this review can delve deeply into the impact of various factors and precisely identify the crucial components of the cause-and-effect connection. The results indicate that the bond between material interfaces is the critical factor. This meticulous and structured review offers valuable perspectives for researchers and engineers, showcasing current research trends and presenting potential avenues for future exploration.

Simple non-linear numerical modelling of masonry arches reinforced with SRG using elasto-fragile and elasto-ductile truss finite elements

A general and simple numerical strategy that can be used in common practice even by unexperienced users is proposed to analyze masonry arches reinforced with Steel Reinforced Grout (SRG). The reinforcement pack is modeled with elastic steel elements interacting with the substrate by means of non-linear interfaces. Bricks are meshed with elastic quadrilateral elements, whereas mortar joints and interface between substrate and reinforcement steel are modeled with trusses assumed either elastic perfectly brittle or elastic perfectly ductile (cutoff bars). The aim is to reproduce the non-linear behavior of mortar under both a mode 1 and mode 2 deformation and the possible debonding of SRG. The dependance of the ultimate tangential resistance of the joints upon the acting compressive stress is accounted for simply updating the strength value of the shear cutoff bars at the end of each iteration step, considering the normal stresses calculated in post processing at the previous iteration and using a Mohr Coulomb cohesive frictional relationship. For the interface between steel and substrate, three different non-linear models are considered, the first relying in a fragile cutoff bar interposed between reinforcement and substrate, the second constituted by two in parallel fragile cutoff bars and the third characterized by the presence of three in parallel cutoff bars (two fragile and one ductile). The procedure is benchmarked on a masonry arch reinforced with SRG and tested in place, for which experimental data and a variety of previously presented results obtained through numerical models characterized by different levels of complexity are available. From the thorough analysis carried out on the global force displacement curves so obtained and a detailed observation of the non-linearity developing in the structural model, the reliability and simplicity of the approach proposed are assessed.

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.

Behavior Under Repeated Loading of RC Beams Externally Strengthened in Flexure with SRG Systems

Steel-reinforced grout (SRG) systems are effective methods for the flexural strengthening of reinforced concrete (RC) beams. In this study, the effect of a limited number of repeated loads on the structural response and debonding evolution of strengthened beams was experimentally investigated. The number of available research concerning the cyclic behavior of SRG-strengthened members is quite limited and this research attempts to cover this knowledge. A total of ten full-scale RC beam specimens were tested under a four-point bending scheme. The effectiveness of the traditional externally bonded (EB) strengthening technique was compared with a promising innovative technique referred to as inhibiting/repairing/strengthening (IRS). The test variables included the use of two SRG configurations using high and low steel strip density. The experimental results revealed that the performance of the beams was largely dependent on the spacing of the steel strands within the reinforcing strip. Under repeated loading, the debonding of the external system takes place when steel fiber with high mass per unit of area was used. By increasing the matrix impregnation of the steel strip, the composite system was not affected by debonding. Further, the efficiency in terms of flexure enhancement, local and global ductility performance and energy dissipation of the beams are also discussed.

Prediction of compressive strength and evaluation of different theoretical standards and proposed models of brick columns confined with FRP, FRCM, or SRG system

The strength capacity of confined masonry column is one of the topics that need to be studied. In this study, the efficiency of using different types of advanced composite (non-corrosive materials) such as fiber reinforced polymer (FRP), fiber reinforced cementitious matrix (FRCM), or steel reinforced grout (SRG) in confining masonry columns is investigated. A wide range of experimental database of masonry column specimens has been collected from the results that available in scientific literatures. Different theoretical standards and proposed models that used to predict the capacity of masonry columns confined with FRP and FRCM are evaluated based on collected experimental database. Since there is no standard code or specific proposed model for SRG system, the confined capacity of this system is predicted and evaluated using the FRCM proposed models. The justification of using these models is that both FRCM and SRG systems have the same concept of using inorganic material as a paste material. An index named “equivalent fiber reinforcement index (EFRI)” is proposed to capture the key factors that control the behavior of the confined masonry columns with different advanced composite. This index is used as reference parameter for the purpose of the comparison between different strengthening systems. As a result, all types of advanced composite presented a significant increase in ultimate capacity. Also, the behavior of the masonry columns was significantly dependent on the type of fabric used. Different modes of failure were reported, including crushing of masonry block, as well as a deboning of FRP from the masonry substrate and deboning or slippage of fabric within inorganic paste matrix. Compared with other models and standards, the American Concrete Institute Committee 440 (ACI 440) and American Concrete Institute Committee 549 (ACI 549) shows very good predictions for the confined capacity of masonry columns strengthened by FRP and FRCM or SRG respectively.

Confinement of masonry columns through SRG: experimental results and analytical prediction

Steel Reinforced Grout (SRG) composites represent, nowadays, a very compatible, reversible, and profitable strengthening solution for existing masonry buildings in earthquake prone regions. They can be employed to enhance the in-plane and out-of-plane behavior of masonry panels or to confine masonry columns. When these materials are applied to columns, different layouts can be adopted, mainly differing in the number of reinforcing layers.The objective of the present research is to evaluate the effectiveness of the use of SRG for the confinement of masonry columns. In more detail, clay brick masonry columns are realized and strengthened with 1 to 3 SRG layers. Uniaxial compression tests are then performed to evaluate the benefit provided by the composite material. Comparisons between the unreinforced and the strengthened samples are carried out in terms of load bearing capacity, deformability, and failure mode. In general, an increase in terms of strength and deformability was obtained by increasing the number of SRG layers applied.An analytical approach, derived by adapting the Spoelstra-Monti approach – formulated for FRP-strengthened concrete columns – to the case of SRG-strengthened masonry columns, is also adopted to predict the compressive behavior of the confined samples. The comparison between analytical and experimental results shows a good agreement, confirming the accuracy of the analytical prediction.

Numerical Strategy for Column Strengthened with FRCM/SRG System

The use of fabric-reinforced cementitious mortar (FRCM) or steel-reinforced grout (SRG) is now recognized to be effective in enhancing the axial capacity of masonry columns when confinement is achieved. Numerous experimental tests demonstrated the symbiotic role of the fabric and the inorganic matrix. An open issue is still related to the numerical simulation. In fact, if the compressive behavior by the numerical simulation of the unreinforced and reinforced masonry columns confined by a FRCM/SRG jacket may follow different approaches. The inorganic matrix transfers the stresses from the substrate to the fabric differently, depending on the presence or absence of cracks. The fabric consists of an open grid whose yard could be differently stressed after the matrix damage because of the occurrence of a possible slippage at the fabric–matrix interface. Definitely, these aspects are difficult to numerically predict. The paper herein is devoted to the assessment of different numerical approaches for the FRCM/SRG confinement of masonry columns by considering data from the literature and varying the parameters related to the matrix, the fabric, and the masonry itself. The goal is to best fit the experimental outcomes (from different available sources) with different strategies based on a finite element (FE) modeling. The results show good matching between the experimental and theoretical curves for the different FRCM/SRG systems. The results evidenced that the accuracy of the experimental versus the numerical curves match is met for the different FRCM/SRG systems.

Experimental and numerical investigation of the uniaxial compression behavior of SRG-Jacketed R/C columns

This paper presents an experimental and numerical investigation of Reinforced Concrete (R/C) short columns strengthened with Steel Reinforced Grout (SRG) jackets. Nine specimens were constructed and tested under concentric monotonic uniaxial compression, measuring compressive force, axial and lateral displacements. Parameters of investigation were the influence of internal steel reinforcement (i.e. no reinforcement, sparse or dense stirrups) and the number of the externally applied SRG jackets (i.e. one or two layers). Subsequently, a three-dimensional finite element methodology was developed, aiming to predict the response of those specimens. Experimental results show that the strength and deformation capacity of the specimens was significantly enhanced with the addition of the SRG jackets, since the strengthening schemes provided sufficient passive confinement. The comparison between experimental and numerical results, in terms of failure mode, axial and lateral stress–strain curves, demonstrated satisfying correlation, proving the efficiency of the proposed numerical model.

Repair and Retrofit of RC Bridge Piers with Steel-Reinforced Grout Jackets: An Experimental Investigation

Many concrete bridges around the world have passed their service life and are at high risk of collapse, especially in active seismic regions. This is particularly true in many developing and underdeveloped countries, where deficient construction and underpreparedness would result in a major catastrophe should a major seismic event occur. Thus, there lies a need to introduce an efficient, cost-effective, and readily available method of bridge rehabilitation. In this study, steel-reinforced grout (SRG) jacketing is used as a seismic strengthening technique for reinforced concrete bridge piers. Two bridge piers, one seismically damaged and one seismically deficient, were jacketed with SRG and then tested to observe their seismic response. The findings from the experimental program revealed that SRG jacketing can rehabilitate/repair a damaged bridge pier, and restore its flexural capacity, energy dissipation capacity, and ductility. While strengthening a seismically deficient pier, results showed that the flexural capacity and energy dissipation capacity could be improved, and ductility could be enhanced.

Influence of the Strengthening Configuration on the Shear Capacity of Reinforced Concrete Beams Strengthened with SRG (Steel-Reinforced Grout) Composites

In this paper, the influence of the strengthening configuration on the structural response of U-wrapped SRG (Steel-Reinforced Grout) shear-strengthened reinforced concrete beams was analyzed both experimentally and theoretically. The parameters varied were the ratio sf/wf, sf being the distance between two consecutive U-shaped strips and wf the width of the strips, and the number of steel fabric layers (one and two). Two series of real-scale beams, eleven beams in total with one un-strengthened and ten strengthened, were tested up to failure (the results obtained in the first series of tests were reported in a previously published paper). The obtained results highlighted that the debonding phenomena, which occurred for all the examined strengthening configurations, strongly affected the shear capacity of strengthened beams. An analytical model found based on the “effective strain” of the SRG strips was developed to predict the shear capacity of SRG shear-strengthened reinforced concrete beams. Two analytical relationships were proposed to evaluate the “effective strain” of the SRG strips: The first one was based on a statistical analysis of results obtained by tests on FRCM (Fabric-Reinforced Cementitious Mortar) and SRG shear-strengthened reinforced concrete beams, while the second was developed through the results of single lap direct shear tests performed on SRG-to-concrete joints. The effectiveness of the proposed analytical methods was evaluated through the comparison of their predictions and available experimental results.

Bond Behavior of Steel Cords for SRG Systems to Cementitious and Lime Based Mortar

Over the past two decades, different innovative systems have been developed for the rehabilitation and retrofitting of existing structures. In particular, SRG (Steel Reinforced Grout) strengthening systems have proven to be very effective in increasing the load carrying capacity and global ductility of reinforced concrete and masonry structures, and their use as an alternative seismic retrofitting solution is increasing rapidly. Although several studies have focused on the characterisation of the mechanical performance of SRG composites subjected to direct tension or bonded to concrete/masonry substrates, the local bond behaviour of steel cords to mortar, which is critical for the overall structural performance of these composites systems, needs to be examined in more depth. To this end, a series of pull-out tests was carried out to study the bond stress transfer of high strength galvanized steel cords embedded in two types of inorganic matrices, including a cementitious and a lime based mortar. In addition, the steel cord to mortar bond was examined through the implementation of a surface-based cohesive contact model in a non-linear finite element framework and the distribution of stresses within the mortar surrounding the steel cord was analysed.

Prediction of Bonding Strength of Externally Bonded SRP Composites Using Artificial Neural Networks.

External bonding of fiber reinforced composites is currently the most popular method of strengthening building structures. Debonding performance is critical to the effectiveness of such strengthening. Many models of bond prediction can be found in the literature. Most of them were developed based on laboratory research, therefore, their accuracy with less popular strengthening systems is limited. This manuscript presents the possibility of using a model based on neural networks to analyze and predict the debonding strength of steel-reinforced polymer (SRP) and steel-reinforced grout (SRG) composites to concrete. The model is built on the basis of laboratory testing of 328 samples obtained from the literature. The results are compared with a dozen of the most popular analytical methods for predicting the load capacity. The prediction accuracy in the neural network model is by far the best. The total correlation coefficient reaches a value of 0.913 while, for the best analytical method (Swiss standard SIA 166 model), it is 0.756. The sensitivity analysis confirmed the importance of the modulus of elasticity and the concrete strength for debonding. It is also interesting that the width of the element proved to be very important, which is probably related to the low variability of this parameter in the laboratory tests.

Strength, bond and durability of stainless steel reinforced grout

Steel Reinforced Grout (SRG) is an effective, cost-efficient and versatile technology for strengthening existing structures. However, the high strength properties exhibited by steel textiles can rarely be fully exploited in design, due to the premature occurrence of bond failure and deterioration. Because of the small diameter of steel cords or wire ropes, and the alkalinity and vapour permeability of the inorganic matrices, the long-term effectiveness can be affected by the combined action of the salt and alkali attack. Although largely overlooked, the use of stainless steel can be a breakthrough for this technology. This work presents the first comprehensive characterization of a Stainless SRG system (SSRG) with a lime-based matrix. Its tensile strength, bond capacity, pull-out behaviour and durability against various ageing conditions were investigated, and design parameters were determined. According to test results, stainless steel combined with lime mortar has excellent mechanical properties and durability, making it the most appropriate solution for the long-lasting strengthening of masonry structures.

Experimental cyclic behaviour of shear masonry walls reinforced with single and double layered Steel Reinforced Grout

Recent research on the mechanical characterisation of Steel Reinforced Grout (SRG) has highlighted its excellent performance as strengthening solutions for masonry structures. Using SRG with limited fabric density ensures a good textile-matrix interlocking, preventing at the same time the failure due to slippage or debonding from the substrate. This paper presents an experimental investigation on the use of SRG as in-plane strengthening solution for shear masonry walls composed of handmade solid clay brick and hydraulic lime mortar. Cyclic shear compression tests were carried out on walls strengthened with SRG comprising low density steel sheets (LDS). The SRG was applied on both faces of the walls with a strip configuration, using one and two layers of LDS. The experimental programme aimed to study the influence of the number of textile layers on the in-plane response of strengthened masonry walls in terms of failure mechanism, load-bearing capacity, energy dissipation, and ductility.

Effect of Wet-Dry Cycles on the Bond Behavior of Fiber-Reinforced Inorganic-Matrix Systems Bonded to Masonry Substrates.

In recent years, inorganic-matrix reinforcement systems, such as fiber-reinforced cementitious matrix (FRCM), composite-reinforced mortars (CRM), and steel-reinforced grout (SRG), have been increasingly used to retrofit and strengthen existing masonry and concrete structures. Despite their good short-term properties, limited information is available on their long-term behavior. In this paper, the long-term bond behavior of some FRCM, CRM, and SRG systems bonded to masonry substrates is investigated. Namely, the results of single-lap direct shear tests of FRCM-, CRM-, and SRG-masonry joints subjected to wet-dry cycles are provided and discussed. First, FRCM composites comprising carbon, polyparaphenylene benzobisoxazole (PBO), and alkali-resistant (AR) glass textiles embedded within cement-based matrices, are considered. Then, CRM and SRG systems made of an AR glass composite grid embedded with natural hydraulic lime (NHL) and of unidirectional steel cords embedded within the same lime matrix, respectively, are studied. For each type of composite, six specimens are exposed to 50 wet–dry cycles prior to testing. The results are compared with those of nominally equal unconditioned specimens previously tested by the authors. This comparison shows a shifting of the failure mode for some composites from debonding at the matrix–fiber interface to debonding at the matrix-substrate interface. Furthermore, the average peak stress of all systems decreases except for the carbon FRCM and the CRM, for which it remains unaltered or increases.

Bond behaviour of multi-ply steel reinforced grout composites

This paper presents an experimental investigation on Steel Reinforced Grout (SRG) systems comprising multiple layers of galvanized UHTSS textiles, with either 4 or 8 cords/in density, embedded within a geopolymer mortar. Lap-splice tests and single-lap bond tests were performed to develop an improved understanding of the textile-to-textile load transfer capacity and of the SRG-to-concrete substrate bond behaviour. The effects of number of textile plies, cord density and compressive strength of concrete on the bond behaviour are analysed.

A Theoretical Model for Debonding Prediction in the RC Beams Externally Strengthened with Steel Strip and Inorganic Matrix.

This paper shows a theoretical model for predicting the moment–curvature/load–deflection relationships and debonding failure of reinforced concrete (RC) beams externally strengthened with steel reinforced geopolymeric matrix (SRGM) or steel reinforced grout (SRG) systems. Force equilibrium and strain compatibility equations for a beam section divided into several segments are numerically solved using non-linear behaviour of concrete and internal steel bars. The deflection is then obtained from the flexural stiffness at a mid-span section. Considering the appropriate SRGM-concrete bond–slip law, calibrated on single-lap shear bond tests, both end and intermediate debonding failures are analysed. To predict the end debonding, an anchorage strength model is adopted. To predict intermediate debonding, at each pair of flexural cracks a shear stress limitation is placed at concrete–matrix interface and the differential problem is solved at steel strip–matrix interface. Based on the theoretical predictions, the comparisons with experimental data show that the proposed model can accurately predict the structural response of SRGM/SRG strengthened RC beams. It can be a useful tool for evaluating the behaviour of externally strengthened RC beams, avoiding experimental tests.

Shear strengthening of reinforced concrete beams with SRG (Steel Reinforced Grout) composites: Experimental investigation and modelling

In the paper, the shear performances of reinforced concrete beams strengthened with externally bonded SRG (Steel Reinforced Grout) composites were analyzed experimentally, analytically and numerically. The aims of this study were: i) to assess the experimental behavior of the SRG shear strengthened reinforced concrete beams by the evaluation of the influence of the main mechanical and geometrical parameters such as the strengthening configuration (continuous and discontinuous U-shaped SRG strips), the distance between the U-shaped SRG strips, the number of SRG layers and, the presence/absence of anchors; ii) to evaluate the effectiveness in predicting the shear capacity of strengthened beams of an analytical model found on a new formulation of the “effective strain” determined through the results of direct shear tests and, iii) to define a numerical model found on a finite element procedure developed through commercial software to predict the whole behavior of SRG strengthened beams. Nine reinforced concrete beams, one un-strengthened and eight strengthened in shear with U-shaped SRG (Steel Reinforced Grout) strips were tested. The experimental results evidenced that in comparison with the un-strengthened beams, the shear capacity: a) increased up to 80% and 53% in beams strengthened with continuous and discontinuous U-wraps, respectively; b) increased with the number of SRG layers (19% and 80% in beams strengthened by continuous U-shaped strips with one and two layers of SRG layers, respectively; 25% and 53% in beams strengthened with discontinuous U-shaped strips with one and two SRG layers, respectively); c) decreased with the distance between the U-shaped strips and, d) increased in average of the 90% in presence of the anchors.Experimental results, those described in this paper and others available in the literature, were used to evaluate the effectiveness of both the proposed analytical and numerical models. The obtained results allow evidencing that the analytical model furnishes predictions of the shear capacity of SRG strengthened beams in good agreement with the experimental results (the average value of the predicted/experimental ratio was 0.98). A very good estimation of both the ultimate loads and corresponding deflections of strengthened beams with negligible errors (less than 5%) whit respect to experimental results was, also, obtained by the numerical model.