Longitudinal Reinforcement Bars Research Articles

Seismic performance analysis of coastal reinforced concrete frames considering the pitting corrosion in the longitudinal reinforcement bars

Reinforcement corrosion is a major factor that influences the durability of reinforced concrete (RC) structures. In this study, the detrimental effects of pitting corrosion of longitudinal reinforcement and the dominant wind direction on the seismic performance of RC frame structures were investigated on the basis of a reliable numerical simulation method, which considers the degraded mechanical properties of the longitudinal reinforcement, confined concrete and bond-slip under a chloride ion attack. Two typical collapse failure modes, namely, column and beam failure modes, are observed in the corroded frames with increasing service time. The column failure mode is caused by the failure of compressive reinforcement for the bottom column. Meanwhile, the beam failure mode is caused by the failure of tensile reinforcement for the frame beam. The collapse failure mode of the structure changes from the column failure mode to the beam failure mode with increasing service time. Moreover, this transition is more likely to occur, and the ultimate deformation capacity of the structure is further reduced when the effects of pitting corrosion and wind direction are simultaneously considered.

Refinement in the understanding of confinement of concrete

The compressive axial load-deformation curve of a reinforced concrete (RC) member reflects the contributions of the concrete in compression and tension, the longitudinal and transverse reinforcement bars in compression and bending, and the aggregate interlocking in concrete in its dilated state. Together these factors enhance the axial response of RC compared to its plain counterpart. Even though expressions proposed in the past capture the composite response of this confining effect in an empirical sense, none of them separate the said individual contributions. This study provides a mechanics-based method to obtain the axial-load deformation response of a RC member, and thereby the stress-strain curve of confined concrete, by assembling the combined effect from each contributing parameter. The governing contributions are fundamental and physically intuitive; they include contributions of unconfined concrete, transverse reinforcement, longitudinal reinforcement (including buckling), and aggregate interlocking. The stress-strain curves from the proposed method compare well with those obtained from many tests on confined concrete available in the literature, and seem to better estimate the response than two popularly used confinement expressions. Similar comparisons are made with the axial load-deformation curves. A parametric study is undertaken to capture the effects of section geometry, high-strength materials, and area ratio on the confinement of concrete. Finally, a refined understanding is presented of the estimation of strength of confined of concrete.

Pre-tensioned steel straps for seismic retrofit of reinforced concrete columns under combined loading of flexure, shear and torsion

Confinement is a sustainable and cheap approach to strengthen the older deficient or inadequate design columns in seismic zones. There are many confinements proven to be effective for retrofitting the columns. However, the studies of strengthening the reinforced concrete columns using active confinement are scarce. This paper presents an extensive experimental work on examining the use of steel straps tensioning techniques (SSTT) in retrofitting the reinforced concrete (RC) columns. Nine reinforced concrete columns specimens were prepared and tested. Seven out of nine of the columns were retrofitted with SSTT under different confinement ratio (layers and clear spacing). The columns were loaded under quasi-static cyclic lateral load with constant axial load. The loading point of cyclic lateral load were slightly altered to create different torque-to-moment ratio (T/M). The seismic performances of columns before and after retrofitting were evaluated through load deformation curve, torque twist curve, energy dissipation, equivalent viscous damping coefficient, column cross-section curvature, strain value of longitudinal reinforcement bars and steel straps. From the laboratory results, SSTT managed to alter the failure mode and avoid sudden failure. Seismic behaviours of SSTT-confined columns, such as load carrying capacity, ductility, and energy dissipation improved. Load carrying capacity was increased up to 75.35% while ductility was increased up to 268.25%. High ductility of SSTT-confined columns resulted in with less crushing damage as it will be more deformable. It is believed that the proposed SSTT active confinement can aid structural engineers in the retrofitting the older deficient or inadequate design columns into a strong and ductile structures especially in the seismic region.

Shear capacities of reinforced concrete interior beam-column joints subjected to cyclic loading

The primary focus of this research is the experimental investigation of internal RC beam-column joints with cyclic loads. There were two interior RC beam-column joints test specimens made without shear reinforcement. The longitudinal reinforcement ratio of the beams served as the study’s test variable. The specimen test results were compared to the theoretical capacity given in SNI 2847-2019 after that. The test revealed the following: (a) shear and flexural beam capacities; (b) shear and flexural column capacities; and (c) shear capacities of joints. The results showed that there was a significant impact on the shear capacity of the beam-column joint as a result of the variation in the reinforcement bars of the beam. After the longitudinal reinforcement bars of the beam yielded in both instances, the degradation of the beam-column joint occurred. A sharp decline in the load value that the specimen can support serves as evidence.

Investigation of the effect of using geogrid, short glass, and steel fiber on the flexural failure of concrete beams

This research studies the flexural behavior of concrete beams reinforced with biaxial geogrids, distributed short glass and steel fibers. No longitudinal steel reinforcement bars were used. Therefore, an amount of short glass and steel fibers was used to improve the concrete beam behavior against flexural failure. Eleven specimens of single reinforced (flexural reinforcement) concrete beams and double reinforced (compression and flexural reinforced) concrete beams using two biaxial geogrids sheet layers, with randomly distributed short glass and steel fibers were cast. The samples were tested using two points of load along the beam specimen span with an increment of loading by 5 KN to evaluate several parameters. The studied parameters are using geogrids as a main flexural reinforcement, using geogrid sheet layers as a flexural and compression reinforcement, using short glass and steel fibers as an additional reinforcement of concrete with various ratios 0.25 %, and 0.75 %. The test results indicated that the use of geogrid layers as the main flexural reinforcement improved the behavior of the concrete beam specimens at failure. As well as; more enhancement of beam specimens at failure was observed when using short glass and steel fibers with geogrid reinforcement in concrete beams. The tested beam specimens which were reinforced by geogrids in the flexural and compression zone using 0.75 % of steel fibers gave better results due to modes of failure, toughness, failure load capacity, crack width, and post cracking stiffness.

Nonlinear finite element analysis of high and ultra-high strength concrete beams reinforced with FRP bars

ABSTRACT A finite element (FE) model is carried out to study the bending behavior of concrete beams constructed of high and ultra-high strength concrete (HSC/UHSC) under three-point bending. The simulated beams are reinforced with longitudinal reinforcement bars from fiber reinforced polymer (FRP) material. The ABAQUS FE software is used in the modeling. The FE model was calibrated using the experimental data of the specimens carried out by M.W. Goldston et al. (2017). Twenty-eight validated FE models were performed to study the effects of concrete compressive strength (high and ultra-high), type of FRP longitudinal bars (AFRP, BFRP, CFRP and GFRP), main FRP reinforcement ratio (0.74%, 1.16% and 1.67%), compression FRP reinforcement ratio (As’ %; 25%, 40%, 100%), and both of beam width and depth (b and d). From the results; it is found that the concrete strength has a small effect on the ultimate capacity. However, the deflection is higher for beams with lesser strength. For all the cases, CFRP reinforced beams showed higher capacity and lesser ductility, while GFRP reinforced beams showed lesser capacity and higher ductility. As’ ratio has insignificant effect on load capacity, but it can improve deflection; it is recommended that As’ did not exceed 40% from AFRP. The beam width has insignificant effect on carrying capacity, but it decreases the corresponding deflection, while increasing the beam depth led to increase the maximum load and decrease the corresponding deflection. Comparable error is generally obtained when using the both equations of Issa and Issa (2017) and ACI440.1 (2015).

FE analysis of pulled-out eccentrically spliced longitudinal headed bars for precast beam-footing connections

ABSTRACT Load transfer in structural elements of RC constructions and the behavior of such constructions are basically dependent on the detailing of both the structural elements and their connections. Assessing analytically the characteristics and behavior of such structural elements and their connections under likely occurring loads is an important issue. For common detailing of footings in steel and precast structures, longitudinal reinforcement of foundation beams is bent horizontally and spliced with reinforcement of cast-in-place footings to insure an adequate juncture for load transfer. In this study, as concerned with reducing construction time and cost, instead of bending longitudinal reinforcement bars of both, beams and footings, headed reinforcement bars are adopted. By doing so, a discontinuity region is created where longitudinal bars of footings become eccentric to those of beams that are embedded in the footings. To allow the flow of tensile forces from longitudinal bars of beams to longitudinal bars of footings, a set of reinforcing ties is provided between them. As such setting of headed reinforcement bars is not common, thorough investigations have been carried out to confirm the relevance of the proposed tie reinforcement. In this paper, results of a finite element numerical investigation of pulled-out eccentrically spliced longitudinal headed bars with different detailing of transverse reinforcement, proposed for precast beam-cast-in-place footing connection, are presented and compared to test results. The elaborated modeling could fairly reproduce the global behavior of the six specimens, where the numerical results acceptably approached the experimental results in terms of initial stiffness, ultimate strength, crack pattern and strain of reinforcement.

A new Distinct Element meso‐model for simulating the rocking‐dominated seismic response of RC columns

AbstractThe rocking‐dominated seismic response of reinforced concrete (RC) columns is a complex mechanism that entails P‐Δ effects, concrete crushing and spalling, rupture and dislocation of steel bars and stirrups, as well as combined localized failures causing splitting and shear‐flexure cracking. In this paper, we present a new meso‐scale numerical modeling strategy for the detailed simulation of the rocking response of slender RC columns under seismic actions. This work advances the current state‐of‐the‐art by exploring the unprecedented use of the Distinct Element Method (DEM), originally conceived for geotechnical studies and whose applicability in earthquake engineering has been primarily limited to the assessment of unreinforced masonry sub‐structures. To decrease analysis time and enable the use of DEM for RC problems, concrete is herein idealized as an assembly of solid macro‐block layers of size directly proportional to their distance from expected plastic hinges. These layers are connected by nonlinear interface springs to simulate tensile and shear cracking via a simplified Mohr‐Coulomb criterion. Crushing of concrete in deformable blocks is modeled using the Feenstra and De Borst strain‐softening linearized compression law, while confinement and combined failures are accounted for numerically through the explicit representation of longitudinal and transversal reinforcement bars, idealized as link elements. Previous experimental static and dynamic tests on full‐scale RC column specimens and results from fiber‐based Finite Element and sectional analysis models are used to evaluate DEM results and quantify the influence of key modeling parameters, including block number and deformability, as well as the amount of damping. The agreement between simulated failure modes and force and displacement capacities and their experimental counterparts demonstrate the applicability of the proposed approach, while demonstrating the pros and cons of simplified numerical methods.

Parametric investigation and economic design of slender steel fibre reinforced concrete beams using shear resisting mechanisms approach

The shear resisting mechanisms (SRM) in slender steel fibre reinforced concrete (SFRC) beam (without stirrups) comprised of four shear resisting mechanisms (uncracked concrete in the compression zone, the dowel action of the longitudinal reinforcement bars, the aggregate interlocking through the aggregates protruding at the critical diagonal shear crack, and the steel fibres bridging the diagonal crack). These shear resisting mechanisms are interrelated to each other and very complex to quantify. However, parametric analysis is one of the methods which can easily be applied and quantify their interconnection. As a result, the parametric analysis has been carried out in this research with the main focus on the effect of influential parameters on shear strength, shear resisting mechanisms, and the interrelationship between them. Thus, the SRM model has been again verified and validated through the results of parametric investigation. Furthermore, the SRM based model has been further modified, and a cost analysis for economic beam design was performed. Finally, design recommendations from the standpoint of practical application have been proposed.

Experimental investigation on progressive collapse resistance of precast concrete frame structures with different beam-column connections

In this paper, twelve 1/4-scale precast concrete (PC) substructural specimens with different beam-column connections under progressive collapse scenario were tested and the results were compared with that of the corresponding conventional reinforced concrete (RC) subassemblies. For assembled monolithic concrete (AMC) specimens, the top longitudinal reinforcement bars of beam passed though the beam-column joint continuously. However, the bottom longitudinal reinforcement bars of beam were either anchored as a 90° bend or lap spliced in the cast-in-place joints. Moreover, the flange effects as well as the effects of transverse beam and slab were also investigated according to spatial subassemblies with or without precast composite slabs. For fully assembled concrete (FAC) specimens, dowel bars and corbel connections, as well as steel plates and hidden corbel connections were used in the beam-column joints. Test results showed that the AMC specimens with or without precast composite flanges (slabs) exhibited almost the same progressive collapse resistance as RC specimens in the literatures, except for the peak value of the vertical load at the compressive arch action (CAA) stage for the AMC specimen with lap-splice of bottom rebars in the joints. Significant CAA at small deformation stage and subsequent tensile catenary action (TCA) at large deformation stage developed in the laminated beams under column removal scenarios. Furthermore, the transverse beam and composite slab effects could obviously increase the capacity of an AMC two-span beam. However, unlike RC specimens, CAA and TCA were not completely developed in the FAC specimens due to pull-out failure of the rebars in the beam-column joints or premature failure of the welding points between steel plates and rebars.

Experimental testing on the structural capacity of coupling beams with non-anchored longitudinal rebars

Coupling beams are structural elements which connect shear walls to improve the lateral stiffness and allow to transfer shear forces, while possessing sufficient ductility to dissipate the energy produced due to the lateral displacement. An error in the construction of a 16-story buildings resulted in that only the bottom layer of the longitudinal reinforcement bars in all coupled beams are anchored into the lateral walls, the upper longitudinal bars are cut before anchored to the lateral walls. The reconstruction of all coupled beams in the building is technical and economically non-feasible therefore, to propose a more efficient and less costly retrofit procedure, an experimental study is undertaken to analyze the real structural capacity of these coupling beams. Carbon fiber reinforced polymer (CFRP) is chosen as the reinforcement material for the upper part of the beams. A total of three specimens are tested, two of them under cyclic quasi-static load to determine the flexural capacity of the cross section in the interface wall-coupling beam, and one of them under monotonic loading to determine the shear capacity of the cracked cross section. The results of the cyclic test showed a very limited contribution of the CFRP in the flexural capacity when the fiber is in tension. However, the flexural behavior of the section with the lower reinforcement in tension is not affected by the upper non-anchored bars and showed a flexural capacity and energy dissipation according to the existing rate of the steel reinforcement. The experimental results are used to develop a finite element model which reproduce the structural behavior of the beams with the construction error.

Theoretical Analysis of Factors Affecting Ultimate Nominal Load of Reinforced Concrete Axially Loaded Short Squire Columns (Pu) Comparing use Prokon Program

One of this theoretical study, parameters that affecting the ultimate load capacity of the axially loaded column are studied. The parameters such as compressive strength of concrete and steel reinforcement ratio. Throughout study a different value of each factor will be assumed. Then the nominal load-carrying capacity of axially loaded column was calculated for these different factors parameters according using the simplified methods provided in (ACI-318- 14) building code requirement for structural concrete and Prokon Program. It is observed that increasing the compressive strength of concrete result in improving the ultimate load capacity. Using compressive strength of concrete more than 40MPa which results in increasing of (Pu) from (2362kN) to(5918KN) . On other hand The total area of longitudinal reinforcement bars (AST), and the gross area of concrete section (Ag) have a significant effects also on increasing of (Pu) value but not as (Fcʹ).
 
 

Testing the applicability of design code provisions - case of unconventional shear reinforcement

ABSTRACT Common transverse reinforcement of reinforced concrete members with circular cross-section consists of round ties or spirals. Its purpose in members that are not subjected to significant shear loading is to provide proper confinement for concrete, and eliminate buckling of the longitudinal reinforcement bars. If spirals are to be used as both shear enabler and confiner for reinforced concrete beams, then under combined action of moment and shear, spirals will be required to provide or contribute to proper shear resistance. Hence a proper assessment for spiral shear contribution is required. The validity of concepts which underlines current methods for shear design used in design codes will be investigated in this paper especially for beams with the shear configuration used, which violates basic code rules in truss formation. A simplified model based on sectional crack analysis for assessing spiral shear contribution is proposed for practical design consideration.

Behavior of GFRP bar reinforced geopolymer concrete filled GFRP tube columns under different loading conditions

This paper proposes a new type of column. The glass fiber reinforced polymer (GFRP) bar reinforced geopolymer concrete (GPC) filled GFRP tube column is presented as a potential substitute of steel reinforced ordinary Portland cement concrete (OPC) column. Type of concrete (OPC and GPC), type of longitudinal reinforcement bars (steel and GFRP) and type of transverse reinforcement (steel helix and GFRP tube) were the test parameters investigated in this study. The specimens of 200 mm diameter and 800 mm height were tested under different loading conditions. Experimental load-axial deformation, load-lateral deformation and flexural load-midspan deflection of the tested specimens are presented and discussed. An equation was also proposed for the prediction of the concentric load capacity of the column. It was found that GFRP reinforcement and GFRP tube confinement resulted in a higher ductility enhancement for GPC based specimens as compared to the OPC based specimens. Also, the ductility of GFRP bar reinforced GPC or OPC filled GFRP tube columns increased with the load eccentricity. Whereas, the ductility of the steel reinforced specimens decreased with the increase of load eccentricity.

Flexural capacity of RC beams strengthened with near-surface mounted steel bars

An experimental study carried out to observe the flexural capacity of reinforced concrete beams strengthened with Near Surface Mounted (NSM) steel bars is presented. The test was carried out on nine concrete beams. All tested beams were subjected to two-point monotonic loads. The ratio of longitudinal reinforcement (1%, 1.4%, and 2.4%) and NSM bars (1D16 and 2D16) were used as test variables. It was found from the test result that NSM steel bars significantly increase the flexural capacity of reinforced concrete beams. However, the strengthened beams failed in brittle mode, as indicated by a sudden drop of beams capacity. An analytical study was also conducted to obtain the flexural response of the specimens through all ranges of elastic and post-peak load. The prediction of the flexural capacity of the beams compares well with the test result.

Lateral shear strength of rectangular RC columns subjected to combined P-V-M monotonic loading

An analytical method is presented to estimate lateral shear strength (and identify likely mode and location of failure) in reinforced concrete (RC) cantilever columns of rectangular cross-section under combined axial force, shear force and bending moment. Change in shear capacity of concrete with flexural demand at a section is captured explicitly and the shear resistance offered by concrete estimated; this is combined with shear resistance offered by transverse and longitudinal reinforcement bars to estimate the overall shear capacity of RC columns. Shear–moment (V-M) interaction capacity diagram of an RC column, viewed alongside the demand diagram, identifies the lateral shear strength and failure mode. These analytical estimates compare well with test data of 107 RC columns published in literature; the test data corresponds to different axial loads, transverse reinforcement ratios, longitudinal reinforcement ratios, shear span to depth ratios, and loading conditions. Also, the analytical estimates are compared with those obtained using other analytical methods reported in literature; in all cases, the proposed method gives reasonable accuracy when estimating shear capacity of RC columns. In addition, the method provides insights into the shear resistance mechanism in RC columns under the combined action of P-V-M, and it is simple to use.

Stress assessment in reinforcement for columns with concrete creep and shrinkage through Brazilian technical normative

In this paper, the induced stress in longitudinal reinforcement bars with cross sections subjected to concrete creep and shrinkage was evaluated. The study was performed for a reinforced concrete column, with loading varying from zero—in which the structure is exclusively subjected to self-weight—to forces close to the loss of stability by bifurcation of equilibrium. A real precast concrete pole, extremely slender, with geometry varying lengthwise, was the structure chosen for the analysis. The aspects related to the material nonlinearity, as well as creep, shrinkage and the development of characteristic concrete strength, were taken into account following Brazilian normative recommendations in NBR 6118:2014 (Design of structural concrete—Procedure) by the Brazilian Association of Technical Standards (ABNT). The critical buckling load was defined according to the structural frequency by using particularly nonlinear formulations. The results were obtained for different instants without exceeding the expected time for convergence of results. The maximum relative value found for the reinforcement stress was 1.24% of the steel yield strength, eliminating the possibility of yielding material.

Cyclic performance of RC beam-column joints with mechanical or forging (GPW) splices; an experimental study

Beam-column joints affect the performance of structures remarkably, therefore, finding an appropriate method for their construction has always been one of the major concerns of researchers. In the present study, the influence of incorporating mechanical and forging (gas pressure welding) splices in longitudinal reinforcement bars of beams on the cyclic performance of RC beam-column joints is evaluated experimentally. Totally five RC joints with non-spliced, mechanically (threaded couplers) spliced and forging spliced bars were examined under axial and cyclic loads applied to columns and beams, respectively. Crack propagation of specimens are analyzed and load-drift hysteresis curves are provided as test outputs. Moreover, the influence of the splice method and number of spliced bars on joints’ behavior is assessed in terms of seismic parameters including displacement ductility, stiffness and cumulative absorbed energy. Results showed that forging splices can be considered as an efficient and reliable method for bar splicing and mechanical splices might affect joints’ behavior significantly.

Performance of fixed beam without interacting bars

Increasing the bending capacity of reinforced concrete (RC) elements is one of important topics in structure engineering. The goal of this study is to develop a transferred stress system (TSS) on longitudinal reinforcement bars for increasing the bending capacity of RC frames. The study is divided into two parts, i.e., experimental tests and nonlinear FE analysis. The experiments were carried out to determine the load-deflection curves and crack patterns of the ordinary and TSS fixed frame. The FE models were developed for simulating the fixed frames. The obtained load-deflection results and the observed cracks from the FE analysis and experimental tests are compared to evaluate the validation of the FE nonlinear models. Based on the validated FE models, the stress distribution on the ordinary and TSS bars were evaluated. We found the load carrying capacity and ductility of TSS fixed beam are 29.39% and 23.69% higher compared to those of the ordinary fixed beams. The crack expansion occurs on the ordinary fixed beam, although there are several crack openings at mid-span of the TSS fixed beam. The crack distribution was changed in the TSS fixed frame. The TSS fixed beam is proposed to employ in RC frame instead of ordinary RC beam for improving the performance of RC frame.

Ductility and Strength Behavior of Reinforced Concrete Columns Confined by Glass and Carbon FRP Sheets

Background: Fiber reinforced composite materials are becoming popular in civil engineering construction practices. One of the most practical applications of these materials is concerned with the strengthening and retrofitting of reinforced concrete compression members by means of external confinement with the GFRP sheets. The role of FRP for strengthening of existing or new reinforced concrete structures is growing at an extremely rapid pace owing mainly to the ease and speed of construction, and the possibility of the application without disturbing the existing functionality of the structure. Objective: The ductility and strength behavior of reinforced concrete columns (Square & Circle) confined by glass and carbon Fiber Reinforced Polymer (FRP) sheets were experimentally investigated Methods: In the library, we tested and cast a total of fourteen column specimens. The tested specimens in this study were square and circle columns, the square specimens tested in this experimental study had dimensions of 135x135 mm cross-section while the circle specimens had 150 mm diameter. The columns were loaded at their supports and made prepared to avoid local failure at supports due to steel plates. Two types of fiber reinforcements sheets were used for strengthening the columns (Carbon and Glass fiber polymer sheets). To prevent the highly stressed slender longitudinal bars from buckling outward, adequate amounts of steel ties were utilized in the height of the columns. During the test of the columns, the central deflection and central fiber strains were measured using dia1 gauges and strain gauges Discussion: The CFRP strains progressed very slowly before the yielding of longitudinal reinforcement bars but quickly, eventually, due to the concrete expansion in the plastic hinge. The wrapped CFRP sheets contribute to both the shear strength and the confinement of concrete in column specimens. The results signify that the percentages of increase in the carrying load capacity due to strengthen, using carbon and glass FRP sheets, were greater in the circular columns compared with the square columns for all the types of confinements used in this study. The ductility factor increased by the strengthen column ranged between 1.35-2.78, while the greatest ductility factor obtained when the circular columns strengthen with glass FRP sheets fully wrapped. Conclusion: -The maximum ratio of increase in the carrying load capacity obtained when the column strengthens fully wrapped. - The columns (circular and square) strengthen with carbon FRP sheets, the greater carrying load capacity obtained when compared the columns strengthen with glass FRP sheets. -The percentages of increase in the carrying load capacity due to strengthen, using carbon and glass FRP sheets were greater in the circular columns compared with the square columns for all the types of confinements. - The stains developed in the confined circular columns are greater than stains in the confined square columns. -The ductility factor increased by the strengthen column, while the greatest ductility factor obtained when the circular columns strengthen with glass FRP sheets fully wrapped.