Circular Reinforced Concrete Bridge Research Articles

Probabilistic curvature limit states of corroded circular RC bridge columns: Data-driven models and application to lifetime seismic fragility analyses

Reinforcement corrosion has been recognized as an influential factor in the seismic fragility, both demand and capacity models, of aging reinforced concrete (RC) bridges. For capacity models, accurate and applied prediction tools accounting for aging effects are yet to be well established. Current practices usually perform numerical analyses to obtain time-variant capacity models, which are time-consuming particularly when multi-source structural and environmental uncertainties are considered and sometimes even suffer computational non-convergence. To address these issues, this study leverages a rigorously optimized artificial neural network architecture to develop data-driven models for rapid estimates of probabilistic curvature capacity of corroded circular RC bridge columns with flexural failure modes. An extensive database of multi-level curvature limit states (i.e. slight, moderate, severe, and complete) is created through experimentally validated moment–curvature analyses. A new threshold for the moderate limit state is defined based on the strain of core concrete, rather than cover concrete, to account for the potential full erosion of the cover with drastic corrosion. The data-driven probabilistic capacity models are applied to aid the lifetime seismic fragility assessment of a typical highway bridge, where the spectral acceleration at 1.0 s (Sa-10), peak ground velocity (PGV), and Housner intensity (HI) are found consistently, for the first time, as optimal intensity measures for probabilistic demand modeling of RC columns with different extents of aging effects. For the ease of application, the database and code for the data-driven probabilistic capacity models are accessible at https://bit.ly/3uAa8EY .

Design Aids for Calculating Idealized Moment-Curvature Relationships of Circular Reinforced Concrete Bridge Columns

Design Aids for Calculating Idealized Moment-Curvature Relationships of Circular Reinforced Concrete Bridge Columns

Improvement of energy damage index bounds for circular reinforced concrete bridge piers under dynamic analysis

AbstractAn improvement of energy damage index bounds for circular reinforced concrete (RC) bridge piers under dynamic time history analysis is presented in this study. The energy‐based damage model has been defined as a ratio of hysteresis dissipation energy to input energy for performance evaluation of circular RC bridge pier systems. Based on the energy balance equation, the mentioned damage model can consider all energy aspects, including kinematic energy, strain energy, hysteresis energy, damping energy, and input energy. Additionally, the effect of ground motion duration, amplitude, and frequency content is appropriately considered in this damage model. For this purpose, the damage limit state bounds for two empirical RC bridge piers are statistically evaluated under the 22 far‐field ground motion sets of FEMA‐P695 for simulation of strong‐earthquake motion and consideration of record‐to‐record variability. First of all, appropriate validation between empirical and numerical fiber element models is implemented to estimate accurate results. Then, damage data at each performance level through strain limit states are collected by developing energy incremental dynamic analysis curves. Statistical results on collected damage data are presented in all performance levels to determine damage index bounds by the convolution of fragility curve distribution. Hence, five damage index bounds at five performance‐level are suggested, including very slight, slight, moderate, extensive, and complete damage. Finally, the effect of the other damping ratios on the modified energy damage model is carried out by using the beta coefficient in the formula. In the end, the modified energy damage model is compared with other damage indices to investigate the efficiency of the proposed damage model.

Effectiveness of CFRP seismic-retrofit of circular RC bridge piers under vehicular lateral impact loading

The effectiveness of Carbon Fiber Reinforced Polymer (CFRP) seismic-retrofit of circular Reinforced Concrete (RC) bridge piers under vehicular lateral impact loading is addressed in the present work performing experimental tests. Sixteen 1/3 scale RC bridge piers with circular cross-sections characterized by three different configurations of longitudinal and transverse reinforcements were tested with and without CFRP seismic-retrofit. In the first case, tested columns represent common shear-deficient RC bridge piers designed with obsolete design practice or for non-seismic areas. In the second case, CFRP wrapping is applied according to common seismic-retrofit practices to increase the shear capacity and ductility of columns.Experimental tests were carried out under static and lateral impact loading with propped cantilever conditions reproducing a typical short-span viaduct bridge pier configuration. In the static tests, the lateral load was applied monotonically through a hydraulic jacket under equivalent impact conditions. In impact tests, the lateral impact load was applied through a colliding truck equipped with a rigid hammer at the typical vehicular impact location adopting two different impact velocities (3 and 4.5m/s). A critical investigation of the transient dynamic characteristics, damage evolution, and post-impact damage is conducted by comparing the results obtained with and without CFRP seismic-retrofit, and under static and dynamic loading conditions. It is shown that CFRP seismic-retrofitting of circular RC bridge pier can also be effective in reducing the vulnerability under lateral impact loading. The CFRP-retrofit approach adopted in this study meets the requirement of multi-hazard prevention improving the robustness of the bridge. Finally, a semi-empirical equation for predicting the maximum displacement under impact loading is derived based on experimental results. The proposed equation adopts the results of a static test as a proxy for assessing the dynamic behavior allowing for the design of the required shear and flexural load-carrying capacity.

Seismic Repair of Circular Reinforced Concrete Bridge Columns by Plastic Hinge Relocation with Grouted Annular Ring

ABSTRACT Modern seismic design practice for bridge structures involves the implementation of capacity design principles which localize plastic hinges in columns, while protecting against other modes of failure. The resulting structures are capable of reliably sustaining far greater deformations than their predecessors; however, despite their initial resilience, the formation of plastic hinges can result in buckling and rupture of longitudinal steel, typically leading to the structure’s demolition and reconstruction. Replacement is deemed necessary since the inelastic strain capacity of reinforcing bars severely diminishes once buckling occurs, rendering the structure vulnerable to collapse in future earthquakes. Recent research demonstrates the feasibility of a repair technique in which the previously damaged region is strengthened such that future inelastic action occurs at a new location, although there are presently a limited number of tests on which to base reliable design recommendations. Results of an experimental program are presented in this paper, in which six extensively damaged columns are repaired using the plastic hinge relocation technique and retested. The proposed repair strategy consists of a grouted annular ring composed of conventional materials (i.e. steel rebar, a steel sleeve, and concrete or grout). The results substantiate plastic hinge relocation as a viable repair option for columns with buckled and fractured longitudinal bars and serve to expand the existing data set considerably. A novel analytical model which accurately predicts the behavior of the repaired column is also presented.

Machine Learning–Based Failure Mode Recognition of Circular Reinforced Concrete Bridge Columns: Comparative Study

AbstractThe prediction of failure mode of columns is critical in deciding the operational and recovery strategies of a bridge after a seismic event. This paper contributes to the critical need of f...

Seismic Assessment of Existing Hollow Circular Reinforced Concrete Bridge Piers

ABSTRACT Experimental works in literature have paid proper attention to the seismic response of hollow circular piers only quite recently, despite their widespread use in existing bridges. Herein, experimental cyclic tests on two scaled reinforced concrete piers with hollow circular cross-section, representative of typical existing Italian bridges, are carried out. Design criteria, adopted setup, experimental response, and damage evolution are discussed. A focus on shear–critical piers is performed, collecting an experimental database of tests from literature. The more specific existing shear strength models are compared with the collected data. Model by Ranzo and Priestley [2001] has finally shown promising results.

Fiber-based damage analysis of reinforced concrete bridge piers

A fiber beam-column element is adopted to simulate the damage development process of reinforced concrete (RC) bridge piers under quasi-static and earthquake loadings considering global buckling and low-cycle fatigue of longitudinal bars. The tensile strain and low-cycle fatigue are used to represent the damage to longitudinal bars while the compression strain is adopted to calculate the damage to the cover concrete. A section damage index is proposed based on the material damage definition and bridge performance assessment. A set of circular RC bridge piers tested under different uniaxial quasi-static loading regimes are adopted to verify the reliability of the fiber beam-column element and the proposed damage model. Square RC columns subjected to different uniaxial and biaxial quasi-static loadings are used to verify the applicable scope of the fiber element and the damage index in biaxial quasi-static loading. In addition, a series of shaking table model tests on square, rectangular and circular piers subjected to bilateral earthquake ground motions are simulated to further verify the versatility of this model. The results show that, the fiber beam-column element can simulate RC columns/piers with different sections and loading regimes with good accuracy. The damage index proposed in this paper is compared against experimental results and other damage indices and it is found that the proposed index can reflect the damage state at any stage and the gradual accumulation of damage in RC columns/piers more convincingly than most other indices available in literature.

Seismic collapse assessment of non-seismically designed circular RC bridge piers retrofitted with FRP composites

The seismic vulnerability of a bridge pier is generally expressed in terms of fragility curves, which reveal the conditional probability of exceeding a predefined performance damage state at different levels of earthquake intensities. This research presents the results of fragility curves of typical single circular reinforced concrete (RC) bridge piers. The different parameters considered in the analysis include: the strength of concrete, yield strength and amount of longitudinal steel rebar, level of axial load, shear span-depth ratio, and carbon fiber reinforced polymer confinement layer. Nonlinear static pushover analysis (NSPA) is conducted along with incremental dynamic analysis using suits of earthquake ground motions with scaled peak ground acceleration (PGA) to investigate the nonlinear dynamic behavior of the retrofitted piers. The impact of various parameters is evaluated under probability point of view in terms of its influence on the bridge pier fragility curve. Considering collapse drift as demand parameters, fragility curves were generated with different parameters of non-seismically designed RC circular bridge piers. It was observed that the amount of reinforcement, shear span-depth ratio, and level of the axial load could significantly affect the collapse fragility curve of the retrofitted bridge piers.

Seismic performance of circular RC bridge columns with flexure–torsion interaction

Reinforced concrete (RC) bridge columns for skewed, curved bridges and other kinds of irregular bridges can be subjected to combined loadings with axial load, shear force, flexure and torsion under multi-dimensional earthquake excitations. Combined loadings including torsion probably affect the seismic performance of these bridge columns. The experimental investigation on the seismic performance of circular RC bridge columns under combined cyclic bending and torsional loading is conducted in this paper. Twelve circular RC bridge column specimens are tested under various loading conditions: cyclic bending, cyclic torsion, and combined cyclic torsion and cyclic bending. Several combinations of cyclic bending and cyclic torsion are applied to evaluate the interaction between torsion and flexural capacity of bridge columns. The experimental results showed that the flexural capacity decreases and the damage tends to occur upward outside the flexural plastic hinge region as the level of applied cyclic torsion increases, and the torsional capacity decreases as the level of applied cyclic bending increases. The failure mode and deformation characteristics of RC bridge columns will be changed due to the effect of combined flexural and torsional loadings. The locking and unlocking effect of the spiral reinforcement on torsional and flexural envelopes of columns under pure torsion and combined cyclic bending and torsion is found. The influence of aspect ratio, longitudinal reinforcement ratio and type of spiral reinforcement on the seismic performance of columns under combined action with the same rotation-drift ratio is also discussed. An empirical flexural and torsional hysteretic model for circular RC columns with single spiral stirrup under combined cyclic bending and torsion is proposed based on the experimental results.

Fiber-Based Modeling of Circular Reinforced Concrete Bridge Columns

This article presents the application of fiber-based analysis to predict the nonlinear response of reinforced concrete bridge columns. Specifically considered are predictions of overall force-deformation hysteretic response and strain gradients in plastic hinge regions. This article discusses the relative merits of force-based and displacement-based fiber elements, and proposes a technique for prediction of nonlinear strain distribution based on the modified compression field theory. The models are compared with static and dynamic test data and recommendations are made for fiber-based modeling of RC bridge columns.

변위연성도 기반 철근콘크리트 교각의 한정연성 내진 설계법과 성능평가 방법

Until recently Korea is considered to be immune from the earthquake hazard because it is located for away from the active fault. However, we have noticed that recent strong earthquakes inflicted enormous losses on human lives and nation`s economy all over the world. Hence, there has been raised the importance of the earthquake resistant design for various infrastructures. In this research, new methodologies for the seismic design and performance assessment of reinforced concrete(RC) bridge pier were proposed from experimental results of 82 circular RC bridge piers and 54 rectangular RC bridge piers tested in domestic and aboard. New seismic design method was based on the concept of the limited ductile design, which could be practically used for low or moderate seismic regions like Korea. Further study for the seismic safety of RC bridge piers was carried out to enhance the seismic performance of aged RC bridge piers, which were designed and constructed before implementing the 1992 seismic design provision in Korea. New formula for the seismic performance assessment of RC bridge piers was proposed and practically used for the decision on the need of repair and retrofit of many aged RC bridge piers.

Deformation Limit States for Circular Reinforced Concrete Bridge Columns

Through the use of moment-curvature analysis of circular bridge columns, dimensionless serviceability and damage control curvature relationships are developed that depend only on the column axial load ratio and section diameter. These relationships are used to establish curvature, displacement ductility, drift ratio, and equivalent viscous damping capacities for the design limit states considered. It is shown that current code-based design approaches, which imply a constant ductility factor, will generally result in damage levels that are highly variable. The paper also discusses implications of the study on limit-states design approaches such as displacement-based design.

Response Modification Factors for Seismic Design of Circular Reinforced Concrete Bridge Columns

The response modification factors for circular reinforced concrete single column bridge bents were calculated for a wide range of periods based on three target values: the capacity to demand displacement, displacement ductility ratio, and longitudinal reinforcement ratio. The validity of using the ratio of capacity to demand displacements as a check in the column design process and the effect of confinement steel ratio on the response modification factors were also investigated.

Optimal Trends in Seismic Design of Single Column Circular Reinforced Concrete Bridge Piers

An algorithm is developed to incorporate seismic capacity design philosophy in a computer program for the optimal design of single column circular reinforced concrete bridge piers for seismic loading. The program designs the circular column as a single degree of freedom system under the combined effect of axial and lateral seismic loads over a broad range of axial load ratio, column height and design displacement ductility capacity. Flexural, confinement and shear reinforcement requirements are then assessed for the entire range of parameters and cost calculations performed. For a given column height, design displacement ductility and axial load level, results indicate the existence of an optimal column diameter and ductility level. As the column diameter is reduced, cost savings are effected by reduced volume of concrete, but tend to be offset by P-Δ effects, increased longitudinal reinforcement for flexure, and increased transverse reinforcement for confinement and shear. Based on common trends, solutions are provided for the most economical range of the axial load ratio and design displacement ductility capacity for a given column height.