Continuous RC Beams Research Articles

Prediction of Nonlinear Flexural Behavior of Continuous RC Beams Pre-Damaged by Corrosion

Numerical simulation models capable of predicting the nonlinear flexural behavior of continuous reinforced concrete (RC) beams with corroded reinforcement were developed. Laboratory tests were conducted to validate predictions of the numerical models. A parametric study was carried out to examine the effect of varying the location and severity of corrosion on the nonlinear flexural behavior of continuous RC beams. The load capacity of continuous RC beams decreased linearly with an increase in the severity of corrosion, regardless of its location. The corrosion of reinforcement in the sagging region was, however, more detrimental to the load capacity than hogging corrosion. The rate of the strength reduction for the beam models with sagging corrosion was approximately 70% higher than that of the models with hogging corrosion. The beam models with sagging and hogging corrosion concurrently exhibited the poorest performance. The rate of the strength reduction of the beam models with corrosion in both sagging and hogging regions was approximately 2.7 times that of the models with hogging corrosion only. The moment redistribution ratio at the ultimate load for the beam models with sagging corrosion only ranged from 2–22%. The beam models with corrosion in the hogging region only exhibited the highest moment redistribution ratio of 22–50% at the ultimate load. The beam models with sagging and hogging corrosion simultaneously exhibited a constant moment redistribution ratio of 18% at the ultimate load.

Effect of the strengthening patterns on the flexural performance of RC continuous beams using FRP reinforcements

Statically indeterminate RC elements such as continuous beams are the most widely used structural form. Their flexural behavior and failure modes are considerably different from those of simply supported ones. The use of FRPs for flexural strengthening and retrofitting continuous RC beams has hardly been studied. Therefore, this paper compares the impacts of NSM-FRP and EB-FRP systems in two-span beams. The overall experimental program of this study consisted of fourteen large-scale bending tests. The performance of each strengthening system is presented and discussed in terms of failure mode, yielding and load-carrying capacities, ductility, and energy absorption capacities, FRP debonding strain, and serviceability state. The experimental results showed that the failure mode is mainly dependent on the type, length, and position of the FRPs, however, a general improvement in the flexural performance of strengthened beams was observed. The NSM technique allows the FRP tensile strength to be better exploited than the EB technique.

Experimental and numerical investigation on the effectiveness of NSM and side-NSM CFRP bars for strengthening continuous two-span RC beams

This paper aims to present and analyze the results of an ongoing research project on the use of NSM and side-NSM-FRP composites for the purpose of increasing the load-carrying capacity of two-pan continuous RC beams. This research study comprises two parts; an experimental part and a finite element (FE) part. First, three large-scale two-span beams were statically investigated; one control beam and two other beams initially strengthened in bending with two 6 mm diameter CFRP bars. Second, a three dimensional (3D) FE model was developed, using the computer software ABAQUS, in order to predict the flexural performance of the tested beams and to investigate the influence of the models applied to the CFRP-resin-concrete interfaces. The results obtained indicated that the side-NSM-CFRP bars system is a convenient alternative to the conventional one for strengthening continuous beams. For some strengthening configurations, the side-NSM technique proved to be more efficient than the NSM technique, particularly when the CFRP bars were applied solely in the hogging region or the sagging regions. The moment redistribution of strengthened beams was negatively affected when the steel reinforcement ratio in the hogging region was increased. Nevertheless, the moment redistribution degree was significantly affected by the position and arrangement of the CFRP bars. The 3D-FE analysis developed with the cohesive zone model can capture the main aspects observed from the experiments.

Required ties in continuous RC beams to resist progressive collapse by catenary action

Ties are mandated by many design guidelines and codes to prevent the progressive collapse of buildings initiated by local failures. This study develops a model to estimate catenary/cable action capacity and the required ties in continuous reinforced concrete beams to bridge above the potential failed interior columns. The developed model is derived based on virtual work method and verified using test results presented in the literature. Also, parametric investigations are conducted to estimate the required ties in continuous reinforced concrete beams supporting one-way slab systems. A comparison is conducted between the estimated tie reinforcement using the developed model and that provided by satisfying the integrity provisions of the ACI 318-14 (2014) code. It is shown that the required tie reinforcements to prevent progressive collapse using the developed model are obviously larger than that provided by the integrity requirements of the ACI 318-14 (2014) code. It has been demonstrated that the increases in the demanded tie reinforcements over that provided by satisfying ACI 318-14 (2014) integrity provisions are varied between 1.01 and 1.46.

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

An experimental study was conducted on eight T-section continuous reinforced concrete beams top strengthened with CFRP and steel plates. The beams had a constant cross section and flexural steel reinforcement which was designed to prevent brittle failure due to crushing of concrete before steel yielding. The plates were installed on both sides of the slab above the beam web as near surface mounted or externally bonded to investigate the effect of different plating techniques on the moment redistribution in reinforced concrete beams. The number of plates in each specimen was changed. Steel stirrups were used and designed so that no premature shear failure occurs. The experimental results show that the steel plating can cause up to 40 % redistribution of moments from the sagging to the hogging regions compared to the control specimen as well as a significant increase in the loading capacity of the beams. The results also revealed that the application of CFRP plates can lead to substantial amounts of moment redistribution when they are installed as near surface mounted plates, but without enhancing the load carrying capacity.

A fast and robust procedure for optimal detail design of continuous RC beams

The purpose of the present study is to present a new approach to designing and selecting the details of multidimensional continuous RC beam by applying all strength, serviceability, ductility and other constraints based on ACI318-14 using Teaching Learning Based Optimization (TLBO) algorithm. The optimum reinforcement detailing of longitudinal bars is done in two steps. in the first stage, only the dimensions of the beam in each span are considered as the variables of the optimization algorithm. in the second stage, the optimal design of the longitudinal bars of the beam is made according to the first step inputs. In the optimum shear reinforcement, using gradient-based methods, the most optimal possible mode is selected based on the existing assumptions. The objective function in this study is a cost function that includes the cost of concrete, formwork and reinforcing steel bars. The steel used in the objective function is the sum of longitudinal and shear bars. The use of a catalog list consisting of all existing patterns of longitudinal bars based on the minimum rules of the regulation in the second stage, leads to a sharp reduction in the volume of calculations and the achievement of the best solution. Three example with varying degrees of complexity, have been selected in order to investigate the optimal design of the longitudinal and shear reinforcement of continuous beam.

Flexural behavior of continuous RC beams strengthened with externally bonded CFRP sheets

The survey of the previous literature showed the need for research studies on the behavior of strengthened continues reinforced concrete (R.C.) beams. To meet this need, this paper aims to study the effect of strengthening schemes on the flexural behavior of continuous R.C. beams under a wide range of parameters. Seven beams were constructed experimentally and studied to discuss two parameters which are the length and number of layers of carbon fiber reinforced polymers (CFRP) sheets. Also, finite element Models (FEM) was developed by using ANSYS. The experimental results were used as verification for the FEMs’ results. A parametric study was conducted by using 540 specimens to discuss more parameters. Test results showed that the common mode of failure in hogging zone is a rupture, while de-bonding occurs at the sagging zone. When the number of layers has increased the mode of failure is likely de-bonding. The parametric study concluded; the reinforcement ratio affects the failure mode by 22%. The fcu has an effect upon many variables up to 40%. A relation was deduced between the variables. The failure strain at mid-span and above the middle support is deduced by using an equation based on the gene expression programming (GEP). By using this relation, the designer will be able to predict the mode of failure and the CFRP sheets’ failure strain of any strengthened equal spans continuous R.C. beam.

CFRP shear strengthening of reinforced concrete beams in zones of combined shear and normal stresses

Strengthening RC beams using FRP laminate becomes one of the main strengthening techniques. Failure of these beams is usually controlled by the bond strength between the laminate and the concrete surface. As such, ACI 440.2-08 limits the bond strength via a bond reduction factor, which is adopted to reduce the effective strain in the FRP laminate. Equations characterizing the shear strength of such beams, which explicitly include the said bond reduction factor, has been verified for region of high shear stress and negligible normal stress. Such conditions simulate the high shear stress zone in a simply supported beam in the vicinity of the support; however, they fail to mimic the high shear and normal stresses zones in continuous beams existing in the vicinity of any intermediate support. Allegedly, the ACI 440.2-08 adopts the bond reduction factor for zones of combined high shear and normal stresses because “it is sufficiently conservative”. Consequently, this paper presents an experimental investigation performed on continuous RC beams strengthened with CFRP sheets: sheets were U-wrapped around the intermediate support of eight two-span beams. The investigation serves to confirm whether or not the currently adopted bond reduction factor is conservative for regions of combined normal and shear stresses.

Shear Strengthening and Shear Repair of 2-Span Continuous RC Beams with CFRP Strips

AbstractAn experimental investigation on initially strengthened and repaired 2-span continuous RC beams with carbon fiber–reinforced polymer (CFRP) strips was conducted. Fourteen full-scale beam sp...

Modelling of creep in continuous RC beams under high levels of sustained loading

A nonlinear theoretical model is developed in this paper for the long-term analysis of continuous reinforced concrete beams. The model accounts for creep, cracking, nonlinear behaviour in compression, shrinkage, aging, yielding of the reinforcement. The constitutive relations follow the modified principle of superposition, which are presented in the form of nonlinear rheological generalized Maxwell models with strain and time dependent springs and dashpots that account for material nonlinearity and aging of the concrete. The governing equations are presented in an incremental form, and are solved through a step-by-step algorithm in time along with the numerical shooting method for the solution along the beam. An iterative procedure is implemented at each time step for the determination of the rigidities and the creep strains. The capabilities of the model are demonstrated through numerical examples. The results show that creep and shrinkage have various influences on the structural response, and they may decrease the load carrying capacity and the factor of safety of continuous reinforced concrete beams with time.

A structural engineering approach to adhesive bonding longitudinal plates to RC beams and slabs

Retrofitting by plating structures has been found to be very efficient. However, tests have shown that externally bonded longitudinal plates are prone to premature debonding. Furthermore, a comprehensive study of published research has also shown that there can be large discrepancies between debonding mathematical models and tests. To overcome this problem and to allow structural engineers to adhesively bond plates with safety and efficiently, a structural engineering approach is suggested whereby many of the debonding mechanisms can be prevented by judicious detailing; this approach can be applied to tension face plates, compression face plates, side plates, U-sectioned plates, and angle-sectioned plates. Four continuous reinforced concrete beams have been retrofitted with adhesively bonded longitudinal plates and tested in order to illustrate this design approach, to directly compare the performance of longitudinal side plates with longitudinal tension face plates, to compare FRP plating with steel plating, and in particular to illustrate the effect of debonding on the sectional ductility of longitudinally plated continuous RC beams.

Deflection and ductility of continuous RC beams

Recent research work by the Author in the fields of deflection and ductility of reinforced concrete beams has shown that in design-oriented procedures both these aspects can be controlled through effective depth-linked requirements. The present study compares the required effective depth to meet a specified deflection limit with the effective depth satisfying a given ductility capacity. Domains are identified that are governed by deflection or by ductility limitations. It has been concluded that many practical continuous beams that meet the usual deflection limits are also satisfactory in regard to ductility. Thus the need to examine ductility falls away in many instances. A numerical example is used to illustrate the findings of this study.