Continuous Reinforced Concrete Beams Research Articles

Modal‐based identification method of fire damage in reinforced concrete T‐beams using support vector machine and firefly algorithm

To determine the degree of fire damage in reinforced concrete (RC) T-beams, a damage identification method based on an improved support vector machine and firefly algorithm (FA-SVM) is proposed herein. First, based on the fire test of 10 simply supported beams, a refined finite element model of simply supported T-beams was established. A modal analysis of the simply supported beams was performed to obtain a sample library of the input and output parameters for the FA-SVM identification network. Subsequently, the trained FA-SVM identification network was used to predict the fire exposure duration of the samples. The sectional temperature during the fire exposure duration could be calculated by using the finite element model, and the bending stiffness and bending capacity of the simply supported beams after exposure to the fire were calculated. The test sample results were similar to the experimental results of the simply supported beams exposed to fire for 60, 90, and 120 min, which demonstrated the feasibility and effectiveness of the proposed method. Finally, a three-step method for fire damage identification suitable for RC continuous beams was developed based on the FA-SVM identification network. An example calculation analysis of three-span continuous beams was performed, and the results demonstrated accuracy of the identification results. The identification sample magnitude was significantly reduced using this method, which can be conveniently used in practical engineering applications.

Fatigue behavior of corroded reinforced concrete continuous beams with multi-intervention system

The corrosion of steel rebars in reinforced concrete (RC) structures will lead to the deterioration of fatigue performance and fatigue life. For the sake of resolving the corrosion problems of RC structures, the Impressed Current Cathodic Protection (ICCP) and Structural Strengthening (SS) techniques are often applied to repair the corroded RC structures. In this study, the ICCP-SS techniques are combined to retrofit the deteriorated RC continuous beams by using the carbon-fabric reinforced cementitious matrix (C-FRCM), and the C-FRCM composites comprised of carbon fabric mesh and inorganic cementitious matrix will served as anodic material for ICCP and the structural strengthening material in the ICCP-SS multi-intervention system. By analyzing the test results of fatigue life, failure mode, cracks in concrete, mid-span deflection, tensile strain of steel rebars and internal force redistributions of the test beams under fatigue load, the influence of reinforcement corrosion and the ICCP-SS retrofitting method on the fatigue performance of RC continuous beams were discussed. The test results showed that the strengthening effect of C-FRCM composites can reduce the generation of cracks in concrete and improve the flexural rigidity as well as fatigue life of the continuous beams effectively, however, the improving effect will decrease for the specimens with higher circulated charge density along with a higher polarization effect of C-FRCM composites.

Effect of Long-Term Soil Deformations on RC Structures Including Soil-Structure Interaction

Lifetime service of Reinforced Concrete (RC) structures is of major interest. It depends on the action of the superstructure and the response of soil contact at the same time. Therefore, it is necessary to consider the soil-structure interaction in the safety analysis of the RC structures to ensure reliable and economical design. In this paper, a finite element model of soil-structure interaction is developed. This model addresses the effect of long-term soil deformations on the structural safety of RC structures. It is also applied to real RC structures where soil-structure interaction is considered in the function of time. The modeling of the mechanical analysis of the soil-structure system is implemented as a one-dimensional model of a spring element to simulate a real case of RC continuous beams. The finite element method is used in this model to address the nonlinear time behavior of the soil and to calculate the consolidation settlement at the support-sections and the bending moment of RC structures girders. Numerical simulation tests with different loading services were performed on three types of soft soils with several compressibility parameters. This is done for homogeneous and heterogeneous soils. The finite element model of soil-structure interaction provides a practical approach to show and to quantify; (1) the importance of the variability of the compressibility parameters, and (2) the heterogeneity soil behavior in the safety RC structures assessment. It also shows a significant impact of soil-structure interaction, especially with nonlinear soil behavior versus the time on the design rules of redundant RC structures. Doi: 10.28991/cej-2020-03091618 Full Text: PDF

Numerical analysis of the shear behavior of FRP-strengthened continuous RC beams having web openings

Web openings are usually constructed in continuous reinforced concrete (RC) beams to accommodate the utility pipes and cables. This paper investigates numerically shear strengthening of continuous RC beams having web openings with FRP layers. The finite element analysis software ABAQUS/standard was used to construct non-linear finite element model (FEM) to analyze continuous RC beams having web openings strengthened with different schemes of fiber reinforced polymers (FRP) layers. The FEM was verified using the available experimental studies of both FRP-strengthened simply supported and continuous RC beams with/without openings found in literature before conducting the numerical investigation. The numerical investigation was carried out using the validated numerical FEM to investigate the impacts of crucial parameters such as opening location, opening area and strengthening configuration on the shear behavior of continuous RC beams strengthened with FRP layers. Three different locations were suggested along the length of the RC beam to construct the web openings. On the other hand, the effects of five different opening area on the load capacity and failure patterns were investigated. Moreover, two different FRP strengthening configurations were considered either strengthening above and below the opening or strengthening the whole RC beam height. Results showed that continuous RC beams containing openings at zone II group was the most affected among analyzed locations. The reduction in load capacities of this group ranged from 7.3 to 66.1% compared to the solid beam. The ultimate loads of specimens strengthened over the whole RC beam height exhibited the highest values among analyzed specimens.

Flexural capacity of continuous reinforced concrete beams strengthened or repaired by CFRP/GFRP sheets

The flexural strengthening of reinforced concrete (RC) beams by bonding external composite materials has proved to be an effective and convenient technique. Several works, focus on mechanical behaviour of continuous reinforced concrete beam with two spans strengthened by composite materials, were reported in literature. This paper presents the flexural capacity of continuous RC beams with three spans strengthened or repaired by bonding carbon or glass fibre reinforced polymer (CFRP or GFRP) sheets. Experimental program consists of eight continuous RC beams strengthened by CFRP or GFRP sheets and one beam of reference. The dimension is the same for all beams with a length 9 m and a section 15x25 (cm). Experimental tests with monotonic loading were carried out by varying damaged level of the beams, composite material type and strengthening thickness. Five failure modes of strengthening beams were observed. The results show that the ultimate bending moment of the beam can be improved between 14.8 and 26.6% in case of the beams by bonding CFRP sheets and between 7.2 and 11.8% by bonding GFRP sheets. The beam, which was pre-damaged under pre-loading level 100% of the failure load, can be repaired as strengthened continuous RC beam. The optimal strengthening thickness in the positive and negative bending moment region was obtained. The variation of the strain in the positive and negative bending moment was analysed.

Moment redistribution and flexural performance of RC continuous T-beams strengthened with NSM FRP or steel bars

This paper discusses the flexural strengthening of continuously reinforced concrete (RC) beam constructions in hogging or sagging regions using near-surface mounted (NSM) technique. The main difficulties in strengthening RC continuous beams in hogging are the vertical middle column which prevents continuity of the NSM reinforcement bars and end anchorage of the NSM reinforcement. A test program consisted of seven two-span T-beams was used; one control beam, which was used for comparison, four beams were strengthened at the hogging region, and two beams were strengthened at the sagging regions. Two types of strengthening material were adopted in this study, carbon fiber reinforced polymers (CFRP) rebars, and high tensile steel bars. An RC column loaded with a constant load (120 kN) was used as the middle support. The main test parameters were the type of the reinforcement bars, continuous NSM bars beside the middle column, or NSM bars anchored inside the middle column, as well as the strengthened region. Besides, the impact of using embedded through-section (ETS) end anchorage of NSM CFRP bars was investigated as well. The experimental results were evaluated for the effects of strengthening technique and materials on the load-carrying capacity of beams, deformation, ductility index, and moment redistribution. The experimental results showed that strengthening with NSM steel bars could improve the service load carrying capacity by 23–40%, whereas the NSM CFRP rebars improved the service loads by 33–36%. The ETS end anchorage at the hogging region and the NSM steel bars at the sagging region helped to achieve the flexural rigidity by a very significant amount relative to the other strengthened beams and control beam by 270%. The moment redistribution achieved after the beam cracking load until the failure load varies in accordance with the strengthening region and the strengthening material type.

Moment Redistribution in Continuous RC Beams Top Strengthened with Steel and CFRP Plates

It is common practice to retrofit continuous reinforced concrete (RC) beams by fiber reinforced polymer (FRP) or steel plates. This can cause a significant amount of moment redistribution (MR) which results in an efficient and economic design when taken into consideration. There is lack in research regarding MR in continuous RC beams when strengthening plates are applied only at the top side at the hogging regions. The main purpose of this paper is to assess MR in continuous RC beams top strengthened with steel and/or carbon fiber reinforced polymer (CFRP) plates. In this respect, a nonlinear finite element model was developed using ABAQUS 6.14 and validated using experimental research program. The model was found capable of stimulating the behavior of such beams and hence assessing the percentage of MR which can be achieved using steel and CFRP strengthening. A parametric study is conducted to investigate the effect of various parameters, different from those investigated in the experimental program, on the MR in continuous RC beams. Parameters related to the concrete compressive strength, reinforcement ratio, beam thickness and thickness of strengthening plates were considered in this study. The results showed that significant amounts of MR can be achieved using either steel or CFRP plates and that MR is enhanced with the change in concrete compressive strength. Moreover, it was found out that the change in steel bars reinforcement ratio or in thickness of the strengthening plates has different effect on the beams strengthened with steel plates than those strengthened with CFRP plates.

Flexural behaviour of C-FRCM strengthened corroded RC continuous beams

This paper presents an experimental investigation on the flexural behaviour of corroded reinforced concrete (RC) continuous beams strengthened by carbon fabric-reinforced cementitious matrix (C-FRCM). A total of ten specimens with different degrees of corrosion were tested under in-plane bending. The strengthening C-FRCM plates were prefabricated with different layers of carbon fabric meshes for reinforcement, while some specimens were further strengthened by U-shaped wrapping for C-FRCM plates as the end anchorage. The flexural behaviour including failure modes, load-carrying capacities, deflections and redistribution of bending moment were carefully studied. The test results show that the load-carrying capacities of RC continuous beams were enhanced by the prefabricated C-FRCM plates and the enhancement further increased with the increase of the layer of carbon fabric meshes, in particular the specimens strengthened by U-shaped wrapping that effectively inhibited the debonding of C-FRCM plates. However, the redistribution capacities of the bending moment of RC continuous beams were weakened by the prefabricated C-FRCM plates. The design flexural strengths calculated using the design formulae given in ACI 440.2R-08, ACI 549.4R-13, AC434-0616-R1, FIB Bulletin 14 and CECS 146-2003 (2007) are also compared with the test flexural strengths, in which ACI 549.4R-13 and AC434-0616-R1 are the identical design guidelines for FRCM system, while the other three design guidelines are specific to FRP system. It is shown that the current design guidelines are all conservative for C-FRCM strengthened RC continuous beams, especially the specimens further strengthened by U-shaped wrapping, in which FIB Bulletin 14 provides the best predictions with the smallest value of COV.

Assessment of the flexural behavior of continuous RC beams strengthened with NSM-FRP bars, experimental and analytical study

This paper deals with strengthening statically indeterminate reinforced concrete (RC) beams with carbon and glass Fiber Reinforced Polymers (FRP) rods by using the Near Surface Mounted (NSM) technique. The test program consisted of six two-span beams; one control beam, which had exploited for comparison purposes, and five others initially strengthened in flexure with NSM-FRP rods in both hogging and sagging regions. The main test parameters were type, ratio and length of the FRP bars as well as characteristics of the filling material. The study presents and discusses their impacts on the global flexural behavior of continuous RC beam that mainly includes investigating the overall capacity, failure mode, moment redistribution and ductility state.All NSM-FRP strengthened beams displayed higher overall capacity than the control beam; the test results showed that implementing the NSM technique in an appropriate way could significantly improve the yielding capacity and load-carrying capacity of RC beams without large decrease in the ductility index or the moment redistribution degree despite the non-conventional failure mode. The beam failure was primary affected by the strengthening length; terminating the FRP bars before the zero moment point caused to change the failure mode from pull out of the FRP bars to premature peeling off of the concrete cover. On the other hand, moment redistribution and ductility of the NSM-FRP beams were negatively affected by: (I) Increasing the FRP reinforcement, (II) Decreasing the FRP length or (III) Using mortar as a filling material instead of epoxy-resin. Adopting a nonlinear analysis of the cross-sections could accurately quantify the moment–curvature and the ultimate load of the NSM-FRP continuous beams.

Experimental and analytical investigation of continuous RC beams strengthened by SMA strands under cyclic loading

Shape Memory Alloys (SMAs) are a new type of alloy that are capable of strengthening reinforced concrete structures. This study aims to investigate the behavior of continuous reinforced concrete (RC) beams strengthened by SMA strands. The superelastic behavior of Nitinol to recover the deformation of concrete beams under cyclic loading is discussed. We present the experimental results of research to determine the effects of reinforcement ratio and two types of normal and high strength concrete (NSC, HSC) in eight strengthened or non-strengthened continuous beams. The results indicate that SMA strands demonstrate acceptable superelasticity. High strength concrete beams strengthened by Nitinol strands show more ability to recover flexural cracks. However, the recovering capacity of midspan deflection and flexural crack width in SMA-NSC beams is more than their corresponding HSC beams. A better distribution of cracks is observed on both normal and high strength concrete beams strengthened by Nitinol strands. In addition, comparison between experimental deflection and predicted values based on the moment-area method exhibits a good agreement up to yielding of the steel reinforcements. Because of the superelasticity of SMAs, energy absorption capacity and residual stiffness of SMA RC beams increased significantly. Besides, the moment–curvature response leads to more ductile behavior of RC beams strengthened by SMA strands.

Strengthening of Reinforced Concrete Continuous Beams using GFRP

This research paper gives the behaviour of reinforced concrete continuous beams under static loading by externally bonding with GFRP sheets. A standard two span continuous beams of size (300×300×2500)mm were casted. Reference beam with no external bonding is prepared to compare the values. Identical reinforcement arrangement is done for all beams. RC beams are tested for failure, load capacity and deflection analysis. Test results are compared for reference and GFRP bonded beams.

Flexural performance of corroded continuous RC beams rehabilitated by ICCP-SS

Continuous reinforced concrete (RC) beams are popular structural components. However, RC structures in corrosive environments can be degraded due to steel reinforcement corrosion. In this study, a dual-functional intervention method, i.e., impressed current cathodic protection and structural strengthening (ICCP-SS), is adopted to repair degraded beams. The carbon fabric-reinforced cementitious matrix (C-FRCM) composite serves dual functions in the intervention method. The effects of reinforcement corrosion, cathodic protection and the C-FRCM strengthening system on the behaviors of continuous beams should be investigated. This study provides experimental data on continuous RC beams rehabilitated by ICCP-SS in corrosive environments and investigates the structural responses, moment redistributions and design rules of these beams. The electrochemical monitoring results showed that steel reinforcements in continuous beams under corrosive environments are successfully protected. Five-point bending test results showed that beams strengthened with C-FRCM composites have higher yielding loads and ultimate loads than corroded beams without protection. Comparison of the predicted and measured moment capacities at the central support and midspan showed that the design methods generally underestimate the moment capacities of unstrengthened sections and overestimate those of strengthened sections.

Continuous Reinforced Concrete Beams with Various Carbon Fiber-Reinforced Polymer Systems under Soil Settlement

Continuous Reinforced Concrete Beams with Various Carbon Fiber-Reinforced Polymer Systems under Soil Settlement

Serviceability Assessment of Continuous Beams Strengthened by SMA Strands under Cyclic Loading

Since the wide cracks or large deflections can have a significant effect on the appearance of concrete elements and may cause some uncommon behavior, therefore, serviceability of concrete structures requires investigation. The main objective of this paper is to study experimentally the serviceability of continuous reinforced concrete (RC) beams strengthened by Ni-Ti strands. In addition, some building code provisions were used to calculate crack width and deflection. The current study presents the experimental results to verify the accuracy of building codes’ provisions for continuous RC beams strengthened by SMA strands. Although a pattern of smaller width cracks was monitored for strengthened beams, more than 50% of the crack widths were recovered because of super elastic SMA strands. The performance of crack width provisions illustrates an overestimated crack width for SMA RC beams. Moreover, the predicted values for immediate deflections based on building codes provided a good agreement, although the effective reinforcement ratio (steel reinforcement and SMA strands) had a significant effect on immediate deflections of reinforced concrete beams strengthened by SMA strands under service loads.

Flexural Strengthening of Continuous Reinforced Concrete Beams with Near-Surface-Mounted Reinforcement

Flexural Strengthening of Continuous Reinforced Concrete Beams with Near-Surface-Mounted Reinforcement

装配式钢筋混凝土连续梁桥抗震性能分析

装配式钢筋混凝土连续梁桥抗震性能分析

Prediction of Moment Redistribution in Statically Indeterminate Reinforced Concrete Structures Using Artificial Neural Network and Support Vector Regression

In this paper, a new prediction model is proposed that fully considers the various parameters influencing the moment redistribution in statically indeterminate reinforced concrete (RC) structures by using the artificial neural network (ANN) and support vector regression (SVR). Twenty-four continuous RC beams and 12 continuous RC frames with various design parameters were tested to investigate the process of moment redistribution. Based on the experimental results obtained from this study and the published literature, a reliable database with 111 datasets was developed for the training and testing of the models. The predicted values of the proposed models, together with the estimations of the widely used code methods, were compared with the experimental results in the database. The analysis results showed that both the proposed ANN and SVR models exhibit high accuracy and reliability for the prediction of the moment redistribution.

Experimental Investigations of the Stress and Strain State of Continuous Reinforced Concrete Beams Under the Action of Low-Cyclic Repetitive and Alternating Loads

The article is devoted to the experimental studies of the stress and strain state of the two-pass reinforced concrete beams under the influence of low-cyclic repeated and alternating loads. Based on the results of experimental studies, the effect of low-cyclic repeated and alternating loads on the change of the stress and strain state of continuous reinforced concrete beams has been established. In the course of testing the sample, it was found that the stress and strain state of the beams under the action of the above mentioned loads is significantly different from the stress and strain state of the beams under the action of nonalternating static loads, namely, the decrease of the bearing capacity, the increase of the deflections and the width of the cracking. All this is due to the change in the physical and mechanical properties of concrete in response to the above-mentioned loads on experimental.

Assessment of the flexural behavior of reinforced concrete beams strengthened with concrete jackets

Analysis of continuous jacketed Reinforced Concrete (RC) beams requires accounting for the nonlinear behavior of the interface and the materials as well as redistribution of moments. This kind of analysis is complex and require an advanced level of knowledge and experience to perform. Engineers need simplified yet robust tools to practically predict the actual behavior of jacketed RC beams. In the current practice, slip is neglected in the analysis and monolithic behavior is assumed for the jacketed section, which result in higher estimates of stiffness and/or capacity. This paper provides a simplified method to analyze continuous jacketed RC beams taking into account the interfacial slip distribution and the actual nonlinear behavior of both concrete and steel. An iterative calculation algorithm is developed to determine the moment–curvature curves of a jacketed beam at different sections. The developed method allows the evaluation of interfacial slip and shear stress distributions in ductile reinforced concrete beams. The developed method is utilized to conduct an extensive parametric study, which resulted into modification factors that can be used to calculate the capacity and deformations of a strengthened beam considering the interfacial slip.

Finite element modeling of debonding mechanisms in carbon fiber reinforced polymer‐strengthened reinforced concrete continuous beams

This paper presents three‐dimensional (3D) and two‐dimensional (2D) finite element models to analyze strengthened reinforced concrete (RC) continuous beams with carbon fiber reinforced polymer (CFRP) which has become familiar technique in the last decade. Experimental results in the literature showed that two different debonding failure modes, either by interfacial debonding of fiber reinforced polymer (FRP) or by concrete cover separation may occur. This study takes the two possible debonding failure modes into account by considering two cohesive surfaces; the first is inserted in the adhesive layer, whereas the second is inserted between the reinforcing steel and the concrete cover. The proposed cohesive surfaces take the slippage into account considering the cohesive surface fracture energy. The numerical models are verified utilizing five symmetrical RC continuous beams available in the literature. The numerical results of 3D and 2D models for the plated beams (beams strengthened with FRP plates) agreed well with the experimental results. Additionally, the effect of the CFRP plate length, and the parameters of the cohesive surfaces on the behavior and debonding failure modes (in the adhesive layer and between the reinforcing steel and the concrete cover) of CFRP‐strengthened RC continuous beams are investigated.