Transverse Steel Reinforcement Research Articles

Long‐term seismic performance of reinforced concrete bridges under steel reinforcement corrosion due to chloride attack

SUMMARYThis work presents a new seismic evaluation methodology for corroded reinforced concrete bridges on the basis of nonlinear static pushover analysis. Corrosion of steel reinforcement by chloride attack is considered. At the material level, the effects of corrosion are considered by modeling the degradation of the mechanical properties of steel reinforcement, softening of cover concrete under compression, degradation of core concrete due to confinement steel corrosion, and reduction of bond strength between concrete and steel reinforcement. At the structural level, the effects of corrosion on both flexural behavior and shear behavior, and their interaction are considered. Eleven bridges of various structural types in Taiwan that are located within 6.5 km of their nearest coastline are analyzed to identify their long‐term seismic performance. Relationships between the yield and collapse peak ground accelerations (PGAs), and service time and corrosion level are established for each bridge. Analysis results show that chloride corrosion starts in 2–32 years. The transverse steel reinforcement typically starts corroding before the longitudinal steel reinforcement, as the former has a thicker cover. Research results show that collapse PGA reduces by 0.94% or 1.23% per 10 years when the mean value plus 1 or 2 standard deviation of the collapse PGA values are considered, respectively. Therefore, we suggest increasing the design PGA from 4.70% to 6.15% for a bridge adjacent to a coastline to ensure adequate long‐term seismic performance for 50 years, the typical design life span of a regular bridge. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of transverse steel on the performance of RC T-beams strengthened in shear zone with GFRP sheet

The focus of the present paper is on the study of the effect of transverse steel on the performance against shear and modes of failure of simply supported reinforced concrete (RC) T-beams strengthened in shear zone with glass fiber reinforced polymer (GFRP) sheet. Eighteen RC T-beams of 2.5m span with and without transverse steel reinforcement are cast at the structural laboratory of IIT Kharagpur. Nine beams are used as control beam specimens in three different stirrups spacing such as without stirrups and with stirrups at 200mm and 300mm spacing and rest nine beams are strengthened in shear zone with GFRP sheet in U-jacket, side bonded and U-jacket with anchorage in each type of stirrups spacing. All the beams are tested in 300 Ton Universal Testing Machine (UTM). The test result clearly demonstrates the GFRP sheet in U-jacket with anchorage is much more effective than the U-jacket scheme.

Hybrid shear strengthening system for reinforced concrete beams: An experimental study

This research mainly investigates the efficacy of the mechanically fastened fiber reinforced polymer (MF-FRP) and the hybrid externally bonded/mechanically fastened FRP (EB/MF-FRP) strengthening systems for beam shear strengthening as compared to the well-established EB-FRP counterpart. The results of twenty-one (21) beam specimens categorized into four types, namely, reference specimens, EB-FRP, MF-FRP-FRP and hybrid EB/MF-FRP strengthened specimens are reported. The work presented is part of a research campaign on the use of the newly developed MF-FRP and EB/MF-FRP strengthening systems. A comprehensive study is presented on the effect of using the MF-FRP and the hybrid EB/MF FRP strengthening systems on the modes of failure of the strengthened beams. Utilizing the MF- and hybrid EB/MF-FRP strengthening systems aims mainly to avoid the debonding type of failure that is often experienced when using externally side bonded FRP strips. The effect of the interaction between the external strengthening strips and the internal transverse steel reinforcement on the shear capacity of the beams is qualitatively assessed for the EB-, MF-, and hybrid EB/MF-FRP strengthening systems. This has been achieved by testing specimens with and without transverse steel reinforcement within the critical shear span. Moreover, different parameters have been assessed through utilizing wide versus narrow and vertical versus inclined FRP strips in addition to utilizing two different patterns of fasteners for the MF- and the hybrid EB/MF-FRP strengthening systems.

Numerical crack modelling of tied concrete columns under compression

In the present paper the problem of monotonically compressed concrete columns is studied numerically, accounting for transverse steel reinforcement and concrete cracking. The positive confinement effect of the ties on the core concrete is modeled explicitly and studied in the case of distributed or concentrated vertical load. The main aim is to investigate the influence of transverse reinforcement steel characteristics on the column load carrying capacity and ductility, in order to provide an evaluation about some standards requirements about the class and ductility of steel to be used for ties. The obtained results show that the influence of transverse reinforcement steel class of ductility is negligible both on the column load carrying capacity and on its ductility. Also the dissipated energy is basically unchanged. In view of these evidences, some standards requirements about the steel class of ductility to be used for ties appear to be rather questionable.

Software for adaptable eccentric analysis of confined concrete circular columns

This paper describes the varying material model, the analysis method and the software development for reinforced concrete circular columns confined by spiral or hoop transverse steel reinforcement and subjected to eccentric loading. The widely used Mander model of concentric loading is adapted here to eccentric loading by developing an auto-adjustable stress-strain curve based on the eccentricity of the axial load or the size of the compression zone to generate more accurate interaction diagrams. The prediction of the ultimate unconfined capacity is straight forward. On the other hand, the prediction of the actual ultimate capacity of confined concrete columns requires specialized nonlinear analysis. This nonlinear procedure is programmed using C-Sharp to build efficient software that can be used for design, analysis, extreme event evaluation and forensic engineering. The software is equipped with an elegant graphics interface that assimilates input data, detail drawings, capacity diagrams and demand point mapping in a single sheet. Options for preliminary design, section and reinforcement selection are seamlessly integrated as well. Improvements to KDOT Bridge Design Manual using this software with reference to AASHTO LRFD are made.

Strength and ductility of R.C. columns strengthened with steel angles and battens

In this paper the behaviour of R.C. members externally strengthened with steel angles and battens subjected to axial force and bending moment is analysed. A fibre model was utilised to predict the moment–curvature diagrams of the strengthened members on the basis of stress–strain curves of the constituent materials (confined concrete, steel bars and angles) recently derived by the author. The stress–strain curves utilised for compressed concrete were able to take into account the confinement effects induced by longitudinal (bars and steel angles) and transverse (stirrups and battens) steel reinforcements. Constitutive laws in compression for confined concrete and steel bars and angles were utilised for a preliminary calibration of the compressive response of axially loaded columns strengthened with steel cages. Therefore axial force and bending moment diagrams and moment curvature diagrams were derived and verified against experimental data available in the literature. Finally, a parametric analysis showing the influence of the main parameters governing the problems (angle and strip geometry and mechanical properties of constituent material) was carried out, mainly referring to moment axial force domains, moment curvature diagrams. The analysis showed the effectiveness of this reinforcing technique in improving both the strength and the ductility of R.C. columns.

Shear strength model for RC beam–column joints under seismic loading

This paper presents a new shear strength model for reinforced concrete (RC) beam–column joints subjected to cyclic lateral loading. In the proposed model, the reinforced concrete in the joint panel is idealized as a homogenous material in a plane stress state. The contribution of the joint shear reinforcement (including both the transverse steel reinforcement and the intermediate longitudinal steel reinforcement of the column) is taken into account through the nominal tensile strength of the idealized material. The effect of tensile straining in the transverse direction on the compressive strength of the idealized material is accounted for using the Kupfer–Gerstle biaxial tension–compression failure envelope. Comparisons with the results of 106 existing tests of both exterior and interior beam–column joints, with and without transverse steel reinforcement, demonstrate the accuracy of the proposed model. These comparisons also illustrate the superior accuracy of the proposed model over existing models. A subsequent trend analysis using the test database confirms that all key parameters influencing the shear strength of beam–column joints have been appropriately considered in the proposed model. The proposed model is believed to be suitable for design use due to its simple form, wide applicability and accuracy.

Experimental Tests and Design Model for RC Beams Strengthened in Shear Using the Embedded Through-Section FRP Method

AbstractThis paper presents results of an analytical and experimental investigation on RC T-beams retrofitted in shear with embedded through-section (ETS) fiber-reinforced polymer (FRP). The ETS FRP rod method is a promising method to increase the shear strength of RC beams. As this method develops, the structural behavior of RC beams strengthened with the ETS method needs to be thoroughly characterized and the influencing parameters addressed. In this research study, nine tests were performed on 4,520-mm-long RC T-beams. The parameters of this study are (1) the effect of the surface coating on the FRP bars, (2) the effect of internal transverse steel reinforcement on the FRP shear contribution, (3) the effect of FRP bar spacing, (4) the effect of FRP rod diameter, and (5) the efficiency of the embedded through-section FRP rod method. The main objective of the study is to analyze the behavior of RC T-beams strengthened in shear with ETS FRP rods by varying the parameters just mentioned. New design equatio...

Adequately FRP confined reinforced concrete columns under axial compressive monotonic or cyclic loading

The study presents the experimental behavior of reinforced concrete square section specimens, externally confined by carbon or glass Fiber Reinforced Polymer (FRP) sheets. The columns are subjected to axial compressive monotonic or repeated load-unload cycles gradually increasing up to failure. The research focuses on columns with longitudinal bars which are critical to premature buckling while examining their effect on lower limit cases of strengthening through FRP confinement. Experiments include also plain concrete FRP confined columns and columns with bars adequately supported by transverse steel reinforcement for comparison. External FRP strengthening covers a wide range of volumetric mechanical FRP confinement ratios allowing comparative investigations. A significant variation in the behavior of FRP confined concrete comes up when bars are unstable, for a light external strengthening scheme as well as for monotonic or cyclic loading. The lower limits proposed by existing recommendations for adequate FRP confinement strengthening of columns are examined.

Constitutive Model for Fiber-Reinforced Polymer- and Tie-Confined Concrete

Although the existing steel stirrups in a column’s section contribute, along with a fiber-reinforced polymer (FRP) jacket, to section confinement, this existing steel reinforcement is often neglected in compressive strength models of confined concrete. This study expands a previously proposed FRP confined concrete model to take into account the confining effect of the already-existing steel reinforcement when retrofitting a reinforced concrete column with FRP jacketing. Confining pressures contributed at each step of deformation by the case of existing transverse and longitudinal steel reinforcement were evaluated, considering the stress-strain law of the reinforcing steel. The compatibility of strain in the lateral direction between the jacketing system and the encased concrete also was enforced. The bilinear stress-strain response of FRP-confined concrete was terminated by jacket rupture, owing to hoop strains exceeding the strain capacity of the material or to interaction of the jacket with the buckled longitudinal bars. The proposed iterative procedure correlates satisfactorily with experimental results.

External CFRP repairing of pretested beams reinforced using prestress rebars

This paper presents experimental and theoretical investigations on flexural CFRP strengthening/repairing of pretested (i.e., damaged) beams reinforced using prestress rebars. Six beams were fabricated and tested under a four-point bending system to failure. The internal longitudinal tensile and transverse steel reinforcements of these beams were reinforced using prestress and mild steel rebars, respectively. After the application of load, these pretested (i.e. damaged) beams were repaired and tested using externally bonded Carbon Fibre Reinforced Polymer (CFRP) reinforcement. This study investigated the effects of number of CFRP plies, three different grades of concrete, and wrapping layouts. The results confirm that the CFRP repaired beams reinforced with prestress rebars efficiently increased the flexural capacity, however the trend of ductility was inadequate as in damaged-unstrengthened beams. Experimental results show that the flexural capacity of the repaired beams increased to a maximum enhancement of 172.4% over the damaged-unstrengthened beam. It was experimentally observed that CFRP repaired beams with low grade of concrete could provide better performanceas compared to higher grades of concrete. The comparison of experimental and theoretical results had good agreement for higher grades of concrete, whereas, in case of low grade concrete, the experimental results were relatively greater than the theoretical results.

HIGH-STRENGTH CONCRETE HOLLOW BEAMS STRENGTHENED WITH EXTERNAL TRANSVERSAL STEEL REINFORCEMENT UNDER TORSION / SUKTINĖS STIPRIOJO BETONO DĖŽINIO SKERSPJŪVIO SIJOS, SUSTIPRINTOS IŠORINE PLIENINE SKERSINE ARMATŪRA

Some bridges have to withstand high levels of torsion forces. As a consequence, box type beams are often the obvious solution. It could be possible that the balance of transversal to longitudinal torsion reinforcement is not fully reached. If the transversal reinforcement is somehow underestimated, the box beam needs to be transversally strengthened. From the various solutions, external transversal reinforcement is certainly one possibility. The investigation presented here aimed to study such solution. The authors tested four hollow beams under pure torsion. The level of the non balanced ratio between internal longitudinal and transversal torsion reinforcement was one of the parameters that were considered in this investigation. Other parameter was the existence or the no existence of external transversal strengthening reinforcement. The experimental results of the tests have shown the effectiveness of the use of the external transversal strengthening steel reinforcement to compensate the lack of balance of internal transversal to longitudinal torsion reinforcement with respect to various behaviour aspects, such as: increasing of torque strength, increasing of ductility, increasing of cracking torsion moment, and better distribution of cracking. Santrauka Kai kurie tiltai turi atlaikyti dideles sukimo jėgas. Tam tikslui dažnai naudojamos dėžinio skerspjūvio sijos. Gali būti, kad tarp sukimui atlaikyti naudojamos skersinės ir išilginės armatūros ne visada pasiekiamas tinkamas balansas. Jei skersinė sija armuota nepakankamai, dėžinio skerspjūvio sijas gali tekti papildomai stiprinti. Vienas iš įvairių galimų stiprinimo variantų – armavimas išorine skersine armatūra. Šiame straipsnyje pateikiama tokio stiprinimo analizė. Autoriai išbandė keturias grynojo sukimo veikiamas dėžinio skerspjūvio sijas. Vienas iš tyrimo parametrų – skersinės ir išilginės sukimo armatūrų santykio nesubalansuotumo lygis. Kitas parametras – išorinės skersinės stiprinimo armatūros buvimas arba nebuvimas. Eksperimentinių tyrimų rezultatai parodė stiprinti naudojamos išorinės plieninės skersinės armatūros veiksmingumą, kompensuojant vidinės skersinės ir išilginės suktinės armatūrų tarpusavio nesubalansuotumą. Efektyvumas buvo įrodytas tokias aspektais: padidėjusi sukamoji galia ir elastingumas, padidėjęs plyšių atsiradimo sukimo momentas bei geresnis plyšių pasiskirstymas.

Seismic retrofit of shear-critical reinforced concrete beams using CFRP

Ageing infrastructure and improvements to design code shear provisions has led to a situation in which many older structures are now considered structurally deficient and are in need of rehabilitation or retrofit. Many of these structures may be at risk of catastrophic failure if their shear-critical components fail in a brittle manner, which could be induced during an earthquake or due to overloading. An effective method for upgrading these shear-critical components is by applying externally bonded fibre reinforced polymers (FRP), which have been shown to significantly enhance shear strength. However, current design codes (ACI 440.2R-08, CSA S6-06) fail to accurately predict strength improvements and have yet to be verified with large-scale beams or those subjected to cyclic loading. As such, large-scale (400×650×3600mm) shear-critical reinforced concrete beams were tested under reversed cyclic loading to simulate a seismic event. The beams contained less than design code recommended transverse steel reinforcement for shear and were retrofitted with various FRP wrap configurations. It was found that the FRP retrofits greatly improved shear strength under reversed cyclic loading, attributed to the relatively elastic-like behaviour of the retrofitted specimens. In addition, retrofits with sufficient FRP strengthening to promote flexural yielding were found to improve ductility by reducing post-yield shear strength deterioration.

Behavior of full-scale RC T-beams strengthened in shear with externally bonded FRP sheets

Recently many research studies have investigated the shear behavior of reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) composites. However, most were conducted on small-scale specimens. Thus, analytical models and design equations developed from those studies may not predict the actual behavior of large-scale RC beams strengthened with FRPs. In this study, an experimental study was performed on this topic using full-scale RC T-beams in order to understand the behavior of full-scale bridge beams strengthened in shear with FRP. The main parameters investigated in this study were the transverse steel reinforcement ratio and the effect of mechanical anchorage systems.

Numerical simulation of tested reinforced concrete beams strengthened by thin fibre-reinforced cementitious matrix jackets

The paper presents a study on the numerical simulation of the behaviour of conventional reinforced concrete (RC) beams strengthened by thin fibre-reinforced cementitious matrix (FRCM) jackets. The study covers the cases of retrofitting RC beams with or without stirrups with jackets reinforced with longitudinal and transverse steel reinforcement or with light wire mesh. The strengthened RC beams to be modelled were tested under static monotonic and fully reversing cyclic loading. The numerical results show that the numerical model used predicted quite well the experimental results.

Embedded Through-Section FRP Rod Method for Shear Strengthening of RC Beams: Performance and Comparison with Existing Techniques

Embedded through-section (ETS) technique is a recently developed method to increase the shear capacity of reinforced concrete (RC) using fiber-reinforced polymer (FRP) rods. The ETS method presents many advantages over existing methods, such as externally bonded FRP sheets (EB FRP) and near-surface mounted FRP rods (NSM FRP). Unlike EB and NSM methods where the FRP relies on the concrete cover of RC beams, in the ETS method, the FRP relies on the concrete core of the RC beam, which offers a greater confinement and hence improves bonding performance. Additionally, the ETS method requires less concrete preparation compared with EB and NSM methods. The objective of this paper is to present results of an experimental investigation that studies the effectiveness of the ETS method and compares the performance of the ETS method with both EB and NSM methods. In total, 12 tests are performed on 4,520-mm-long T-beams. The parameters investigated are as follows: (1) the effectiveness of the ETS method, compared with EB FRP sheet and NSM FRP rod methods; (2) the presence of the internal steel; and (3) the internal transverse steel reinforcement ratio (i.e., spacing). The test results confirm the feasibility of the ETS method and reveal that the performance of the beams strengthened in shear using this method is significantly superior compared with that of the beams strengthened with EB and NSM methods.

Effect of Transverse Steel on the Response of RC Beams Strengthened in Shear by FRP: Experimental Study

The present paper shows and discusses some of the results obtained within an experimental investigation carried out on 15 reinforced concrete (RC) beams strengthened in shear by externally bonded fiber-reinforced plastics (FRP) sheets. The aim of the study is to analyze the influence that the geometrical percentage of transverse steel reinforcement could have on the FRP resisting action. In particular, the objectives of the experimental campaign are to explore the possible interaction between FRP and steel transverse reinforcement resisting actions, analyzing the deformation behavior of the shear resisting system (FRP, transverse steel, and concrete) and the modes of failure of the strengthened and not strengthened beams. The results of the tests in terms of shear capacity are compared to the design formulations provided by the American Concrete Institute and the National Research Council of Italy code-format recommendations.

Investigation on Effects of Variables on Shear Capacity of Precracked RC T-Beams with Externally Bonded Bi-directional CFRP Discrete Strips

This study aims to investigate the shear performance of partially precracked Reinforced Concrete (RC) T-beams bonded externally with bi-directional Carbon Fiber Reinforced Polymer (CFRP) discrete strips. A series of twelve RC T-beams are fabricated with internal transverse steel reinforcement and subjected to four-point and three-point bending systems. The external CFRP reinforcement strips are applied on the web and soffit of the beam with two-component epoxy system. The parameters investigated in the experimental program included (i) longitudinal tensile reinforcement ratio, (ii) shear span to effective depth ratio, (iii) spacing, and (iv) orientation of discrete CFRP strips. The experimental results show that the bi-directional CFRP discrete strip reinforcement significantly increases the shear capacity between 18 and 54% over the control beams. It is found that the test variables have significantly influenced the shear capacity of the CFRP strengthened beams. This study also validates the obtained experimental results with different existing theoretical models.

Normal- and High-Strength Concrete Circular Elements Wrapped with FRP Composites

Reinforced concrete columns usually have a minimum amount of transverse steel reinforcement this transverse reinforcement can have non negligible effects on the response of columns retrofitted with fiber-reinforced polymers (FRP). This paper presents a test program that was designed to study the behavior of small- and large-scale normal- and high-strength concrete circular columns confined with transverse steel reinforcement, FRP, and both transverse steel reinforcement and FRP under concentric loading. The effect of the main variables—such as the unconfined concrete strength, the volumetric ratio, the type and the yield strength of the transverse steel reinforcement, the concrete cover, and the number of FRP layers—are studied in this research program. The test results show that the enhancement of the confined concrete strength and strain is more pronounced in specimens with normal-strength concrete. It is also shown that the rupture of the FRP in the specimens with higher volumetric transverse steel rei...

Some recent findings on concrete members under localised compression

Concrete members under localised compression often exhibit splitting failure in a region close to the loaded surface. In this investigation, a numerical analysis is first performed to show that splitting failure should initiate from the lateral surface of the member. Experiments are then carried out to demonstrate that transverse reinforcements closer to the lateral surface are more effective in increasing the failure load. The current practice of placing transverse reinforcements uniformly across the section should therefore be revisited. Two series of tests are also performed to compare fibre reinforced cementitious composites members and concrete members with and without steel stirrups. According to the test results, fibre reinforced cementitious composites performs much better than plain concrete under localised compression, and can be employed to replace all or part of the transverse steel reinforcements. The potential use of fibre reinforced cementitious composites to resist splitting failure under localised compression is demonstrated.