Reinforced Concrete Layers Research Articles

Effect of Bonding Type on the Failure of Reinforced Concrete Beam Strengthened with In-Situ High Performance Fibre Reinforced Concrete Layer

High performance fibre reinforced concrete (HPFRC) materials with tensile hardening behaviour can effectively be used for strengthening reinforced concrete beams. A perfect bond between the original and the reinforcing layer cannot be formed, the load-bearing capacity and ductility of the strengthened beam can significantly be affected by the interfacial bond strength between the contacting surfaces. In this paper, beam retrofitting with cast in-situ strengthening type is examined. The purpose of this experimental study is to investigate the impact of the different bond types on the load-bearing capacity, ductility, and failure mode of the strengthened beams in the case of cast in-situ strengthening. Twenty-four beam tests were performed with untreated and rough surfaced beams, with or without connecting elements. The effect of the bond type proved to be significant regarding the failure mode in the case of compression side strengthening, stronger bond resulted in higher load bearing capacity and ductility, too. When tensile side reinforcement was investigated no average increment was experienced in the maximal force and ductility due to the stronger bond. Based on the results, it can be concluded that the generally applied analytical models that assume perfect connection may lead to exaggerated results in the case of a compressed side HPC-strengthened beam. Therefore, it is necessary to develop a model that considers the effect of the imperfect bond.

Performance of engineered cementitious composite (ECC) monolithic and composite slabs subjected to near-field blast

To improve the performance of reinforced concrete (RC) structural members subjected to blast, especially the spalling due to the brittleness of concrete, engineered cementitious composite (ECC) was applied in monolithic and composite slabs and their responses subjected to near-field blast were experimentally investigated in the present study. First, two different ECC materials were prepared and tested with quasi-static direct tension and flexural tests, whose results showed significantly improved tensile ductility and strength compared to normal concrete. Then a field test was conducted to investigate the response of ECC monolithic and composite slabs under near field blast, with an RC slab as reference. The responses of these slabs were compared in terms of response mode, residual deformation, crack initiation and development, spalling, strain time history, etc. The test observations suggested that in addition to the ductile response and failure of ECC subjected to quasi-static direct tension and flexural tests, ECC still exhibited ductile response at high strain rate when applied in monolithic and composite slabs under near field blast. Compared to the perforation and spalling of RC slab, the ECC monolithic or composite slabs underwent large deformation, until collapse failure with a major crack in the mid-span occurred. Importantly, throughout the whole response process, even the ECC monolithic and composite slabs collapse with a major crack at mid-span, no spalling was observed. Furthermore, no delamination occurred in the interface between the RC and ECC layer of the RC/ECC slabs. Both the ECC monolithic slab and RC/ECC composite slab exhibited favorable performance subjected to near-field blast. These observations implied that the ECC is promising in the potential application of structural protection against blast, not only for replacing certain key components in the newly built structures but also for retrofitting existing RC structures.

Concrete with a High Content of End-of-Life Tire Materials for Flexural Strengthening of Reinforced Concrete Structures.

This research investigates the performance of Steel Fiber Reinforced Rubberized Concrete (SFRRC) that incorporates high volumes of End-of-life tire materials, (i.e., both rubber particles and recycled tire steel fibers) in strengthening existing reinforced concrete (RC) beams. The mechanical and durability properties were determined for an environmentally friendly SFRRC mixture that incorporates a large volume (60% by volume aggregate replacement) of rubber particles and is solely reinforced by recycled tire steel fibers. The material was assessed experimentally under flexural, compressive and impact loading, and thus results led to the development of a numerical model using the Finite Element Method. Furthermore, a numerical study on full-scale structural members was conducted, focusing on conventional RC beams strengthened with SFRRC layers. This research presents the first study where SFRRC is examined for structural strengthening of existing RC beams, aiming to enable the use of such novel materials in structural applications. The results were compared to respective results of beams strengthened with conventional RC layers. The study reveals that incorporation of End-of-life tire materials in concrete not only serves the purpose of recycling End-of-life tire products, but can also contribute to unique properties such as energy dissipation not attained by conventional concrete and therefore leading to superior performance as flexural strengthening material. It was found that by incorporating 60% by volume rubber particles in combination with recycled steel fibers, it increased the damping ratio of concrete by 75.4%. Furthermore, SFRRC was proven effective in enhancing the energy dissipation of existing structural members.

Study on the impact performance of RC fences strengthened with high strength strain-hardening cementitious composites

This paper presents a numerical study on the impact performance of reinforced concrete (RC) fences strengthened with high-strength strain-hardening cementitious composite (HS-SHCC) through finite element (FE) modeling. To accurately simulate the peculiar material characteristics of HS-SHCC, the MAT_72R3 material model was calibrated and verified against experimental data. A comparison study for RC and HS-SHCC panels subjected to drop hammer impact was conducted to observe the impact performance of HS-SHCC. Results showed that the impact resistance and energy dissipation capacity of HS-SHCC are significantly higher due to its high strength and high ductility. A full-scale study of pick-up truck collisions was then conducted to investigate the response, failure, and best strengthening configuration of conventional RC fences strengthened with HS-SHCC layers. Results showed that both strengthened configurations under moderate impact energy could significantly improve the impact resistance and reduce the residual deflection. While in the case of large impact energy, the back-strengthened RC fence gave notably better performance and higher impact resistance due to the composite effects between RC and HS-SHCC layers. Based on the analysis of the failure modes and energy dissipation, the mechanism of such composite effects was summarized.

Numerical Investigation of a Reinforced Concrete Structure Rehabilitated by New Reinforced Concrete Layers

Numerical Investigation of a Reinforced Concrete Structure Rehabilitated by New Reinforced Concrete Layers

Buckling behavior of composite double-layer space-grid structures

In order to better understanding the structural response of double-layer flat grids, the effects of using of a reinforced concrete (RC) topping in composite action with double-layer space-grid structures on the buckling behavior of such grids are studied. Both non-composite and composite flat grids (with and without any integral RC topping) with different span lengths are considered. The base models with span lengths of 15, 30 and 60 meters are initially selected and designed employing the well-known weight–density procedure. The finite element models are then developed in the ABAQUS environment with special consideration in the modeling procedure for beam type elements of pin connections at two ends in order to employ the capabilities of the software for buckling and post-buckling analyses. Elastic buckling analyses as-well-as non-linear analyses incorporating both the geometric and material non-linearities emphasizing the structural stability and post-buckling behavior are performed. It was found that the presence of a RC cover in composite action with double-layer flat grids can lead a decrease in the weight of steel around 29 % as-well-as maximum vertical deflection around 61 %. The presence of a RC layer can also improve the elastic buckling capacity up to 94 %. The results showed that the ultimate strength of such structures in composite state increases significantly. Finally, the RC layer can improve the post-buckling behavior which can lead an increase in the structural reliability from progressive failure or sudden loss of the structural strength.

Cyclic behavior of beams rehabilitated by reinforced concrete layers

AbstractOne of the well‐known methods for rehabilitation of insufficient or damaged reinforced concrete (RC) beams is to add a new RC layer. Although RC beams strengthened or repaired in this way have proved themselves under monotonic and repeated loads, the behavior under cyclic loads has not been adequately investigated yet. In this experimental research, beams were strengthened, repaired, or revived (repaired after heavy damage) using familiar RC layer adding methods and tested under reversal cyclic loading. Ten half‐scaled specimens, composed of columns and a beam, were prepared and 18 tests were conducted on these specimens. The obtained results showed that the strengthened and repaired beams mostly could achieve the monolithic behavior. However, sufficient ductility could not be maintained for the revived ones.

Finite element model to predict structural response of predamaged RC beams reinforced by toughness-improved UHPC under unloading status

This paper simulates the structural response of strengthened predamaged reinforced concrete (RC) beams with reinforced ultrahigh performance concrete (UHPC) layer using finite element (FE) analysis. The FE models simulate the whole strengthening procedures for the predamaged RC beams by using UHPC to replicate the actual test conditions. A ‘tracking and positioning elements and nodes’ technology is applied for UHPC elements when the strengthening UHPC layer is activated. Concrete damaged plasticity (CDP) model is used for normal strength concrete and UHPC. The nonlinear behavior of reinforcing bars is taken into account. A newly developed interfacial model for the UHPC-RC interface is included in the FE model. The FE models are calibrated and validated by comparison with the experimental results. Load-deflection curves, characteristic loads, and damage patterns extracted from the FE simulation agree well with the experimental results. Finally, a parametric study is conducted to investigate the effect of height of the UHPC layer, height of the RC layer (size effect), and reinforcement ratio inside the UHPC layer on the flexural response of the strengthened beam with pre-damage in the RC beam. This study might provide a reference for future design and construction of predamaged RC beams reinforced by UHPC layer, to extend their service life and reduce maintenance costs.

Flexural strengthening of large-scale damaged reinforced concrete bridge slab using UHPC layer with different interface techniques

This paper investigated the flexural behavior of large-scale damaged reinforced concrete (RC) bridge slab strengthened with the ultra-high performance concrete (UHPC) layer at the tensile side. The RC slabs were preloaded under flexure to introduce cracks. The pre-damage degree was evaluated using the crack width at the highest load. Then, two types of interface technique of the RC substrate were conducted before strengthening of the UHPC layer. The first technique was a combination of embedded studs and rough surface (S-R) on the RC substrate. The second technique was rough surface (R) only. Experimental results indicated that the UHPC layer enhanced the flexural capacity and stiffness of the damaged RC slab. The UHPC layer also restrained and delayed the crack development in the RC and UHPC layers. It should be highlighted that the strengthened slab with the S-R interface technique exhibited significant mechanical performance compared with the interface treated using the R technique only. Therefore, the enhanced flexural performance of the UHPC-RC slab using the S-R technique may have an impact on the analysis and design of strengthening large-scale damaged RC bridge slab.

Buckling behaviour of composite double-layer braced barrel vaults

Investigation of different potential instability phenomena is an essential part of a study of the structural behaviour of double-layer braced barrel vaults. In this context, the effects of the use of a reinforced concrete (RC) topping in composite action with double-layer grid-works on the instability behaviour of such structures were studied. Two types of double-layer flat grids and barrel vaults were considered: without any integral RC topping (non-composite grid-works) and with a RC topping in composite action with the spatial grid (composite grid-works). The primary models were selected and designed adopting a consistent procedure utilising the weight–density method. Initially, elastic buckling analyses were performed. Complementary studies included a series of non-linear finite-element analyses accounting for geometric and material non-linearities emphasising structural stability and the post-buckling behaviour. It was found that the presence of a rather thin layer of RC covering, in composite action with double-layer grids, increased both the initial buckling and the ultimate strengths of such structures substantially, and also significantly improved their post-buckling behaviour, resulting in much improved reliability against progressive failure and sudden loss of strength.

Bending model for composite UHPFRC-RC elements including tension stiffening and crack width

The application of a thin ultra-high performance fiber-reinforced concrete (UHPFRC) layer at the tensile side of reinforced concrete (RC) elements has lead to an efficient structural concept with promising capacities. Composite UHPFRC-RC elements have an increased bending capacity with respect to the RC member. In addition, the serviceability and durability are also improved as the composite element has higher stiffness and smaller crack widths. In order to widen the application of composite UHPFRC-RC elements, practitioners and designers need analytical and numerical tools with a sound mechanical background, if possible conceptually analogous to well-established models for conventional concrete structures. The paper starts with a discussion of the main drawbacks of existing models for UHPFRC-RC elements in bending. Secondly, new experimental basis is provided with own tests where the digital image correlation (DIC) technique is exploited to understand the crack pattern development and interfacial behaviour of UHPFRC-RC. Finally, the main goal of the paper is the proposal of a new model for UHPFRC-RC elements in bending which includes tension stiffening and the interaction at the steel-concrete and concrete-UHPFRC interfaces by means of a new composite tension chord model. The tension chord model is based on the stress transfer mechanisms between adjacent cracks, which include the explicit consideration of bond stresses between the constituent materials (i.e. steel and concrete, and UHPFRC and concrete). The compatibility condition between the UHPFRC and the RC layers is established in terms of the extension of each layer between adjacent cracks, as the classic compatibility of strains based on perfect bond assumption cannot be used upon macrocrack formation. Rather, the extension of the UHPFRC layer includes the contribution of cross-sections within the elastic, hardening or softening stages of the UHPFRC. The proposed model allows estimating the whole bending response, including calculation of crack widths and average curvatures between cracks.

Testing of insulated sandwich panels with GFRP shear connectors

This paper focused on the panel which sandwiches an Expanded Polystyrene (EPS) layer between two Steel Reinforced Concrete Layers (SRCLs). The EPS layer provides thermal insulation in the panel while the two exterior SRCLs are connected by Glass Fiber Reinforced Plastic (GFRP) shear connectors to form the composite action and hence achieve a higher flexural resistance in the panel. Four types GFRP shear connectors which consist of diagonal web members, webs with circular perforations, webs with slotted perforations and solid webs, respectively, were considered in this research. To experimentally address the flexural responses of the panels with the four types of GFRP shear connectors, four full-scale experimental specimens were constructed and tested. The test results show that generally any of the four GFRP shear connectors can enable the panel to exhibit satisfactory flexural performance although the GFRP shear connectors with the solid webs tend to increase the ultimate flexural resistance of the panel. Beyond the experimental work, an analysis model based on the transformed cross-section approach and elastic beam theory was developed for capturing the flexural response of the panel up to the cracking limit state. Moreover, an analysis model based on the assumed strain and stress diagrams was established to compute the ultimate flexural resistance of the panel.

Flexural performance of reinforced concrete beams strengthened with fibre reinforced geopolymer concrete under accelerated corrosion

The use of additional Reinforced Concrete (RC) layers or jackets is one of the most commonly used techniques for the strengthening of existing structural elements. A crucial parameter for these applications is the durability and the corrosion resistance of the RC layers. However, to date there are not any published studies on the use of novel cementitious materials for the improvement of the durability of the strengthened elements. In this study, a novel strengthening technique is proposed using additional high performance Fibre Reinforced Geopolymer Concrete (FRGC) layers and jackets reinforced with steel bars. The main goal of this technique is the improvement of the structural performance of the existing elements and at the same time the improvement of the durability and corrosion resistance of the strengthening layers. RC beams strengthened with reinforced FRGC layers were examined under standard and accelerated corrosion conditions. Accelerated corrosion tests were performed using the induced current technique followed by flexural tests. The results indicate superior performance for beams strengthened with FRGC and improved performance of the interface between the additional layer and the initial RC beam.

Seismic Behaviour Factor for Unreinforced Concrete Block Masonry Walls Retrofitted by RC Layers

This paper reports on experimental and numerical investigations of the seismic behaviour of unreinforced concrete block masonry (URCBM) structural walls, externally retrofitted on one, or both sides, by reinforced concrete (RC) layers. The behaviour factor (R) components are extracted from nonlinear static pushover analyses of full-scale masonry walls having different aspect ratios. It is found that R-value of masonry shear wall increases with an increase in the aspect ratio of the wall. Also, application of RC layers to the wall has a profound effect on the behaviour factor, as it directly affects both ductility and ultimate capacity of the wall. Finally, based on findings presented, R-values of 2.0, 2.5 and 3.0 are proposed for URCBM, one-sided and two-sided retrofitted concrete block masonry shear wall construction, respectively.

Strengthening of reinforced concrete beams using ultra high performance fibre reinforced concrete (UHPFRC)

In this study the efficiency of the use of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) for the strengthening of existing Reinforced Concrete (RC) beams has been investigated. Experimental work has been conducted to determine UHPFRC material properties. Dog-bone shaped specimens have been tested under direct tensile loading, and standard cubes have been tested in compression. These results have been used for the development of a numerical model using Finite Element Method. The reliability of the numerical model has been validated using further experimental results of UHPFRC layers tested under flexural loading. Further numerical study has been conducted on full-scale beams strengthened with UHPFRC layers and jackets, and these results were compared to respective results of beams strengthened with conventional RC layers and with combination of UHPFRC and steel reinforcing bars. Superior performance was observed for strengthened beams with UHPFRC three side jackets, and the efficiency of this technique was highlighted by comparisons with other strengthening techniques.

BI-LAYER DIAPHRAGM WALLS: STRUCTURAL AND SECTIONAL ANALYSIS

The bi-layer diaphragm wall, a new slurry wall type designed to cope with the problem of watertightness is studied in this paper. These walls consist of two bonded concrete layers, the first, a conventional Reinforced Concrete (RC) diaphragm wall, and the second, a Sprayed Steel Fibre Reinforced Concrete (SFRC). The main objective of this paper is to analyze the structural and sectional behaviour of these walls. A study in the form of an uncoupled structural-section analysis based on various hypothetical cases of bi-layer diaphragm walls was performed to fulfil the objective. It is concluded that there exists a potential of reduction in the reinforcement of the RC layer through the structural use of the SFRC layer. However, when the reduction is quantified, even though a reduction of between 3.2% and 1.7% in the RC reinforcement is confirmed, it appears insufficient to offer a cost-effective solution. Nonetheless, the system becomes a promising solution when particular conditions are taken into account, such as basement space limitations.

Bending behaviour of Textile Reinforced Concrete sandwich beams

A prefabricated concrete sandwich panel, with insulating material acting as a structural layer able to transfer the shear stresses, is discussed. The use of an in-pressure casting technique allows to avoid the use of glue and to prevent the debonding between the layers thanks to the good bond obtained during the production. Sandwich beams characterized by a thick internal expanded polystyrene foam core and by two thin external Alkali-Resistant glass Textile Reinforced Concrete layers are experimentally investigated according to four point bending scheme. The significant role played by the tangential non linear behaviour of the EPS foam is shown.

Bi-layer diaphragm walls: Parametric study of construction processes

The bi-layer diaphragm wall is a new type of slurry wall, designed to improve watertightness and to counter leakage problems. These walls consist of two bonded concrete layers: the first, a conventional Reinforced Concrete (RC) diaphragm wall and the second, a sprayed Steel Fibre Reinforced Concrete (SFRC) layer with a waterproof additive. Here, we analyse and quantify the influence of different construction process parameters on the effectiveness of the bi-layer diaphragm wall technique. Thirty numeric simulations were conducted with an uncoupled structure-section analysis, placing special emphasis on the SFRC layer contribution. The results show that, in all cases, the main flexural strength is provided by the RC layer, with a secondary flexural contribution (between 8% and 15%) by the sprayed SFRC layer. Using satisfactory spraying sequences (detailed herein), a reduction in the steel reinforcement of the RC layer can be obtained in every structural configuration and construction sequence, reaching a maximum percentage reduction of 7.0% of the total bending reinforcement. The displacements are almost completely governed by the thickness of the first layer, and a minor reduction (less than 7.3%) is obtained, when the second layer is included.

Seismic Evaluation of Masonry Structures Strengthened with Reinforced Concrete Layers

AbstractCoating the walls with reinforced concrete layers is a conventional method of strengthening masonry structures in Iran. However, because of the lack of analytical and experimental information about the behavior of strengthened masonry walls with this method, the design of these walls is generally conducted based on empirical relations and decisions that may result in uneconomical or underdesigned strengthening details. This paper aims to develop a rational method for design and seismic evaluation of unreinforced masonry walls strengthened with reinforced concrete layers. In the proposed method, four failure modes are considered for these walls, and the strength relations and acceptance criteria for each of them are provided in accordance with FEMA 356 and ASCE 41 relations for reinforced concrete and masonry walls. The accuracy of the proposed method in predicting the nonlinear behavior and governing failure modes of the strengthened walls is validated by comparing the results with available exper...