Shear-critical Reinforced Concrete Research Articles

A Simplified Approach to Investigate the Seismic Ductility Demand of Shear-Critical Reinforced Concrete Columns Based on Experimental Calibration

ABSTRACT A simplified approach is proposed to investigate the seismic ductility demand of shear-critical reinforced concrete (RC) columns based on experimental calibration. Incorporating with the Bouc–Wen–Baber–Noori (BWBN) model, the governing equation of the equivalent single-degree-of-freedom (SDOF) system is first presented to describe the typical hysteresis characteristics, where the relationship between the inelastic restoring force and translational displacement is calibrated by comparing with the experimental data of shear-critical RC columns under quasi-static cyclic testing. Based on the developed governing equation, the strength reduction approach is further implemented to estimate the seismic ductility demand of shear-critical RC columns by establishing the constant strength-ductility demand spectral (CSDDS) method. Finally, an empirical expression is regressed to predict the mean and standard deviation of seismic ductility demand of shear-critical RC columns. This study verifies the feasibility of the proposed approach to assess the seismic ductility demand of shear-critical RC columns. The presented idealized SDOF system can simplify the establishment of CSDDS method. The lognormal assumption cannot well describe the probabilistic characteristics of seismic ductility demand if all the uncertainties in model parameters and earthquakes are considered. The developed empirical expression is applicable to investigate the probabilistic seismic risk of shear-critical RC columns under different earthquake excitations.

Structural Health Monitoring and Interface Damage Detection for Infill Reinforced Concrete Walls in Seismic Retrofit of Reinforced Concrete Frames Using Piezoceramic-Based Transducers Under the Cyclic Loading

In this work, the piezoceramic-based transducers are used to perform the structural health monitoring (SHM) and interface damage detecting of non-ductile reinforced concrete (RC) frames retrofitted by post-installed RC walls. In order to develop the post-embedded piezoceramic-based transducers that can be used to identify interface failure or cracks between two structural members in retrofit construction, this work adopts the cyclic loading to test two specimens with post-embedded piezoceramic-based transducers (PPT). Since the failure of an interface between the post-installed wall and beam occurs, one of the specimens has damage in the foundation and existing boundary column and the other has damage in the top ends of column and wall. During the cyclic loading test, one transducer was used as an actuator to generate the stress waves and the other transducers were used as the sensors to detect the waves. In damaged specimens, the existence and locations of cracks and the interface damage can be detected by analyzing the wave response. Moreover, the severity of damage to the specimens can also be estimated. The experimental results indicate the effectiveness of the piezoceramic-based approach in the SHM and locating damage in shear-critical RC structural members under the seismic loading.

Low-Elevation Impact Tests of Axially Loaded Reinforced Concrete Columns

Conventionally, structures are designed to resist dead and live loads. However, there is a rising risk of structural members being subjected to impact loads as a result of unexpected events, accidents, or intentional attacks. In the case of frontal street-level columns of buildings and columns in parking spaces, they can potentially be exposed to high-intensity dynamic loads caused by vehicular impacts. Furthermore, most of these columns are not designed to resist these effects. This research demonstrates the vulnerability of conventionally designed reinforced concrete (RC) columns against vehicle impacts. A special drop-weight test setup was designed and established to simulate the vehicle collision impact in the performed tests. In the scope of this study, four fullscale axially loaded RC members were tested under drop-weight test setups to represent low-elevation transverse impact loads on the specimens. The performance of RC columns under static and impact loading conditions (applied by increased magnitude of impact energy) was examined and the changes in their structural performances were evaluated. The mode of failure was observed to be transformed from pure flexure in static tests into a more brittle character dominated by shear under impact loading conditions. Consequently, conventionally designed RC columns were found highly shear-deficient against vehicular impacts; therefore, they should be designed with a certain safety margin to have reserve shear and deformation capacities to eliminate their vulnerability. Based on the test results, dynamic response ratio recommended for shear-critical RC members can be used in the design of street-level columns against vehicular impact.

A modelling approach for existing shear-critical RC bridge piers with hollow rectangular cross section under lateral loads

Most of the existing Reinforced Concrete (RC) bridges were designed before the recent advancements in earthquake engineering and seismic codes. The performance assessment of these bridges is, therefore, a crucial issue for seismic safety of bridge infrastructures and estimation of losses due to seismic events. Despite the seismic assessment of columns with solid cross-section in ordinary buildings may be considered as quite comprehensive, a similar conclusion cannot be drawn for shear-critical hollow core piers, widespread in existing bridge structures. The present work aims at contributing to the investigation about the response of RC piers with hollow rectangular cross-section under cyclic loading. The main goal of the study is the definition of a comprehensive and practice-oriented modelling approach for the assessment of seismic response of RC hollow rectangular piers, able to account for all the deformability contributions, and, particularly, able to reliably predict drift-capacity at shear failure and subsequent degrading stiffness. A three-component model, accounting for flexural flexibility, shear flexibility and slippage of rebars is adopted. The shear capacity assessment is dealt with more in details. A proper experimental database is collected, made up of cyclic tests on hollow rectangular piers failing in shear, with or without yielding of longitudinal reinforcing bars. A new empirical formulation for the assessment of the displacement capacity at shear failure, specifically for the investigated structural elements, is calibrated. The degrading stiffness also is empirically calibrated to completely define the degrading shear response. Finally, the proposed numerical model is validated through the comparison with the experimental results carried out by the Authors (also in terms of local deformability contributions) and with test results collected from literature, proving that it can be a simple and reliable tool for the seismic assessment of existing shear-critical bridge piers.

Different FRCM systems for shear-strengthening of reinforced concrete beams

This paper presents the results of an extensive experimental study on the efficacy of different fabric-reinforced cementitous matrix (FRCM) systems for the strengthening of reinforced concrete (RC) beams, which are critical in shear. Three types of FRCM systems were assessed; namely, Carbon–FRCM, polyparaphenylene benzobisoxazole (PBO)-FRCM, and Glass–FRCM. Tensile characterization tests were carried out on fifteen (15) FRCM coupons with the purpose of identifying the tensile properties of the FRCM systems. In the core part of this study, sixteen (16) shear-critical RC beam specimens were tested under three-point loading for assessing the effect of FRCM stiffness/type, FRCM configuration, and FRCM anchorage on the load and deformational capacities of the strengthened beams.As for the study results, the average enhancement of the load carrying capacity achieved by FRCM strengthening with respect to the reference specimen is 51%. Continuous strengthening significantly improved all aspects of structural performance of the strengthened beams compared to those of the intermittent counterpart. The effect of FRCM configuration appeared to be significantly related to the amount and the orientation of the effectual fabric within the FRCM system. Moreover, the effect of the FRCM anchorage used in this study was observed to be insignificant on the load carrying capacity of the strengthened beams. Theoretically-predicted values for load carrying capacity were obtained, and showed a reasonable agreement with the experimental results.

Nonlinear finite element study on the improvement of shear capacity in reinforced concrete T-Section beams by an alternative diagonal shear reinforcement

In the study a new shear reinforcement configuration named as diagonal shear reinforcement (DSR) is proposed as an easily applicable, economical and alternative technique to improve the shear capacity and ductility of shear critical reinforced concrete (RC) beams under monotonic and cyclic loadings. For this objective a numerical nonlinear finite element (FE) study is performed by considering two tested beams with flexural and shear failure modes. These two tests results are first verified numerically then DSR is included to existing FE model to start a parametric study for highlighting the efficiency of proposed DSR shear reinforcement configuration.The numerical results demonstrate that there is a significant increase in shear and ductility capacity of RC beams when proposed DSR is included. Moreover, with an increase in diameter and yield strength of DSR, the shear capacity further improves and failure mechanism shifts from shear to flexure. Thus, more ductile behavior for shear critical RC beams is achieved by the proposed DSR reinforcement configuration.

Hysteretic Model for Shear-Critical Reinforced Concrete Columns

AbstractA continuous and smooth hysteretic model for shear-critical reinforced concrete (RC) columns was identified and calibrated based on an efficient stochastic search technique and an experimental database consisting of 30 shear-critical RC columns. The inelastic restoring force of shear-critical columns was described by the Bouc-Wen-Baber-Noori (BWBN) model to produce the requisite strength and stiffness degradation as well as pinching effect. Meanwhile, the backward Euler and Newton-Raphson schemes were adopted to determine the inelastic restoring force by solving the ordinary differential equations. Then a differential evolution (DE) algorithm was utilized to identify the control parameters of the BWBN hysteretic model based on an experimental database consisting of 30 shear-critical rectangular columns under cyclic loading. Finally, prediction equations for the BWBN model parameters were developed in terms of four structural physical parameters. The capability and accuracy of the calibrated hyster...

Multi-scale based Simulation of Shear Critical Reinforced Concrete Beams Subjected to Drying

The impact of drying at both material and structural levels is discussed based on the multi-scale thermo-mechanistic modeling. The effects of hygral states at nano to micro scales on the macro scale mechanics are focused on. It is quanti- tatively confirmed that the moisture state-dependent tensile strength and crack-dependent moisture diffusivity models play a key role in tackling with the responses of reinforced concrete (RC) members subjected to combined hygro- mechanical actions. Full 3D thermo-mechanics simulation of shear critical RC beams with effective depths, which ranges from 250mm to 1000mm, is carried out from the onset of casting. It is found that the impact of drying increases with the increasing effective depth at the constant beam width. Overall, it is emphasized that linkage of material science and structural mechanics is indispensable for holistic understanding of RC members under coupled mechanical loading and drying. The multi-scale analytical scheme is proved to be applicable for the performance assessment of RC mem- bers at ultimate states as well.

Strengthening of shear critical RC beams with various FRP systems

The use of fiber reinforced polymer (FRP) sheets to shear strengthen reinforced concrete (RC) beams has been studied and proven repeatedly. However, numerous strengthening configurations and materials can be combined to maximize the increase in strength and repair. This study investigates the effectiveness of using commercially manufactured carbon FRP (CFRP), glass FRP (GFRP) and fiber reinforced cementitious matrix (FRCM) sheets to increase the shear capacity of RC shear critical beams. Nine RC shear deficient slender beams were tested. The test variables included the use of three different FRPs (CFRP, GFRP, and FRCM), and the presence and type of FRP anchors (CFRP or GFRP). The experimental results revealed that applying FRP sheets increased the overall shear capacity, full depth u-wrapped FRP sheets perform better over companion partial depth u-wrapped FRP sheets, the use of FRP anchors further improved the shear capacity and ductility of failure, FRP strengthening could change the mode of failure from a shear to flexural failure and FRP debonding was delayed with the presence of FRP anchors. A comparison of the experimental load capacities with predicted values indicates that they correlate well with predictions using the current Canadian design codes.

FRCM Strengthening of Shear-Critical RC Beams

AbstractThis paper presents the results of an experimental study conducted to investigate the effectiveness of different types of fabric-reinforced cementitious matrix (FRCM) composite systems to strengthen shear critical reinforced concrete (RC) beams. Seven shear-critical RC beams were tested. The test variables included the strengthening material (glass FRCM or carbon FRCM) and the strengthening scheme (side bonded or u-wrapped). The test results revealed that FRCM strengthening is effective in enhancing the load-carrying capacity of shear-critical RC beams. The increase in load-carrying capacity of the FRCM-strengthened beams ranged between 19 and 105%. Both strengthening schemes (side bonded and u-wrapped) exhibited similar behavior, suggesting that the excellent bond of the FRCM to concrete may not require u-wrapped applications for anchorage. The experimental results were also compared with theoretical predictions according to fiber-reinforced polymer (FRP) design guidelines in North America with s...

Multi-objective seismic retrofit method for using FRP jackets in shear-critical reinforced concrete frames

Many research studies have been conducted on seismic retrofits of existing reinforced concrete (RC) frames with fiber–reinforced polymer (FRP) jackets. Although existing RC columns are vulnerable to shear failure because of insufficient transverse reinforcement and deficient seismic details, little research exists on the reinforcement locations and FRP reinforcement level required to prevent column shear failure. In this paper, the optimal seismic retrofit method that uses FRP jackets for shear-critical RC frames is presented. This optimal method uses non-dominated sorting genetic algorithm-II (NSGA-II) to optimize the two conflicting objective functions of the retrofit cost as well as the seismic performance, simultaneously. To minimize the retrofit cost and maximize the seismic performance of a structure, this optimal method minimizes the amount of FRP required and the coefficient of variation of inter-story drift ratios while satisfying the constraint conditions on the shear failure prevention, maximum inter-story drift ratio, and maximum compressive strain of concrete. Both the flexural reinforcement method and shear reinforcement method of FRP jackets are adopted to strengthen the flexural capacity and shear strength of columns, respectively. The two reinforcement methods are applied sequentially to minimize the total amount of FRP material required. The proposed method is applied to 3-story RC frame and the optimal retrofit schemes that suggest the reinforcement locations and the number of FRP reinforcement plies are obtained.

Structural performance of shear-critical RC deep beams with corroded longitudinal steel reinforcement

Abstract The effect of corrosion of longitudinal reinforcement on the structural performance of shear-critical reinforced concrete (RC) deep beams was experimentally investigated. A total of eight medium-scale reinforced concrete beams were constructed. The beams measured 150 mm wide, 350 mm deep and 1400 mm in length. The test variables included: corrosion levels (0%, 5%, and 7.5%), existence of stirrups and FRP repair. Six beams were subjected to artificial corrosion whereas two beams acted as control un-corroded. Following the corrosion phase, all beams were tested to failure in three point bending. The test results revealed that corrosion of properly anchored longitudinal steel reinforcement does not have any adverse effect on the behaviour of shear critical RC deep beams. Corrosion changed the load transfer mechanism to a pure arch action and as a result the load carrying capacity was improved. A strut and tie model was proposed to predict the failure loads of shear-critical RC deep beams with corroded longitudinal steel reinforcement. The predicted results correlated well with the experimental results.

Nonlinear Analysis of Shear-Critical Reinforced Concrete Beams Using Fixed Angle Theory

This paper proposes a solution methodology for the application of the fixed-angle theory to predict the shear response of reinforced concrete (RC) beams subjected to the combined actions of shear and flexure. The proposed solution, based on the fixed-angle theory, takes into account the effect of flexural moment on the shear strength of RC beams and calculates the concrete constitutive relationships by transforming the concrete stresses and strains from the principal direction of concrete stresses to that of the applied stresses. To verify the effectiveness of the proposed solution method, seven shear-critical RC beams were tested and their corresponding experimental shear stress-strain relationships were compared with the predicted ones by using the proposed methodology. Furthermore, the shear strengths of 150 RC test beams, reported in the literature with various shear span-to-depth ratios, steel reinforcing ratios, and support conditions, were compared with the predicted shear strengths obtained by the proposed method and other existing truss models. The results presented in this paper show that the proposed formulation can predict the shear response of RC beams with reasonable accuracy.

Component damage functions for reinforced concrete frame structures

Displacement-based damage functions for the components of reinforced concrete (RC) moment resisting frames have been developed. RC columns, beams and brick infills were considered in this study as the structural elements that contribute to the seismic behavior of RC moment resisting frames. Finite element analyses were carried out on RC columns and beams to investigate effects of their material and geometrical properties on the behavior of these elements, and also to develop the damage functions. The independent parameter used in the damage functions developed for RC columns was the interstorey drift ratio, while rotation was used as the main parameter to evaluate damage in RC beams. The equivalent strut models available in the literature were used to determine the parameters affecting the damageability of brick infills and to develop drift-based damage functions. Additional damage functions for shear critical RC columns and beams were also developed. The damage functions proposed were validated via comparison to the test results available in the literature. These damage functions are proposed to be used for the seismic performance evaluation of RC moment resisting frames.