Concrete Bridge Columns Research Articles

Accuracy and uncertainty of predicted maximum and residual displacements of RC bridge columns under earthquake excitations

Fundamental to the performance-based seismic design is the accuracy of predicted responses under earthquake excitations. This study evaluates the accuracy and uncertainty of predicted maximum and residual displacements of concrete bridge columns subjected to different types of ground motions. A series of nonlinear time-history analyses considering a wide range of element formulations and model parameter combinations was performed to reproduce measured responses from previous shake table tests. Variations in element formulation had little influence on the accuracy and uncertainty of predicted maximum displacements. The gradient inelastic force-based element, however, predicted bar tensile strain profiles across the plastic hinge with higher resolution, but at a higher computational cost than displacement-based and beam with hinges elements. Models with tangent stiffness-based Rayleigh damping produced the most accurate predictions of the maximum drift ratios with an RMSE of 0.011, indicating that the maximum displacement (or drift ratio) can be predicted with reasonable accuracy. Residual displacements, on the other hand, were predicted with unreasonable levels of error and uncertainty. A data-driven model was thus proposed to correct predicted residual displacement. Following correction, the RMSE of the predicted residual drift ratios was reduced by 43 % to 0.006.

Advanced analysis of intact, fire-damaged, and CFRP retrofitted bridge pier columns under vehicle collisions: Empirical equivalent static force equation and framework

A series of numerical simulations were completed to investigate the behavior of intact, fire-damaged, and Carbon Fiber-Reinforced Polymers (CFRP) retrofitted reinforced concrete (RC) bridge columns of varying sizes subjected to vehicle collisions. Three-dimensional finite element models of isolated RC columns and their foundation systems surrounded by soil volumes were developed using LS-DYNA. A comprehensive parametric study was carried out to investigate the effects of nine demand and design parameters on the performance of bridge columns. Studied parameters included: column diameter, column height, unconfined compressive strength, steel reinforcement ratio, fire duration, CFRP wrap thickness, wrapping configuration, vehicle’s mass, and vehicle’s speed. For each studied scenario, Peak Twenty-five Milli-second Moving Average (PTMSA) was employed to estimate the Equivalent Static Force (ESF) corresponding to each vehicle collision scenario. Resulting ESFs were then utilized to assess effectiveness of the current ESF approach available in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO-LRFD) Bridge Design Specification for analyzing and helping design bridge columns under vehicle collision. Multivariate nonlinear regression analyses were used to derive an empirically based, simplified equation to predict the ESF that corresponds to a vehicle collision. Rather than constant design force, this equation established a correlation between ESF and kinetic energy, column axial capacity, and column height. Results indicated that the proposed equation is reliable and can accurately predict ESFs over a diverse range of collision scenarios that included intact, fire damaged, and CFRP retrofitted columns. To facilitate realistic implementation of the derived equation, an ESF assessment framework was also devised.

Performance-based seismic design of Ultra-High-Performance Concrete (UHPC) bridge columns with design example – Powered by explainable machine learning model

Ultra-high-performance concrete (UHPC) has rapidly become a material of choice in modern construction owing to its favorable properties, such as superior strength, toughness, and durability. Yet, accurate quantification of damage states using appropriate engineering demand parameters (EDPs) remains a significant challenge in the performance-based seismic design (PBSD) of UHPC columns. This gap is especially evident in the scarcity of research focused on the PBSD of UHPC columns. Therefore, this study aims to develop an explainable machine learning (ML) powered predictive model for the drift ratio limit states of UHPC bridge columns across four damage states. To achieve this, a fiber-based numerical model was developed and then validated against large-scale experimental results of UHPC columns tested under reverse cyclic loading. The Latin hypercube sampling method is employed to generate a comprehensive database of UHPC bridge columns (10,000 UHPC columns), considering uncertainties across a spectrum of design factors, including column geometry, material characteristics, reinforcement ratio, and axial load ratio. The drift ratios at the initiation of four damage states are determined using the numerical model. Subsequently, the power of the ML algorithm is leveraged to introduce drift ratio limit states for UHPC columns that capture the onset of four different damage states. The efficacy of the developed model is assessed using a range of statistical metrics, including the composite fitness score, DX% metrics, coefficient of determination, root mean squared error (RMSE), normalized RMSE, and mean absolute error, which demonstrated high predictive accuracy of the drift ratio limit states on both the training and unseen or test datasets. Furthermore, a model-agnostic Shapley Additive exPlanation (SHAP) is used to explain the output of the model and examine the influence of various design factors on drift ratio across the damage states. Notably, the axial load ratio and aspect ratio are found to be major factors in determining the drift ratios across the damage states. The developed model is deployed into a software tool in order to enable its practical application. Additionally, the implementation of the developed model in the context of PBSD is illustrated through a design example. Furthermore, the study proposed capacity uncertainty parameters to aid the fragility assessment of UHPC columns. Finally, the proposed model, along with capacity uncertainty parameters, is used for the fragility assessment of UHPC columns reinforced with varying steel bar grades. The results demonstrate the less vulnerability of UHPC columns reinforced with higher bar grade, yet the effect of bar grade lessens at severe damage levels.

Effects of enhanced confinement on cyclic behavior of concrete bridge columns with partially unbonded seven-wire steel strands

The effects of enhanced confinement on the proposed bridge columns under lateral cyclic loading were investigated in this research by testing large-scale column specimens. The proposed column used nonprestressed partially unbonded seven-wire strands as elastic elements to increase the post-yield stiffness of the column to reduce the residual displacement under seismic loads. The enhanced confinement included rectilinear transverse reinforcement with an increased amount (specimen CSCR) and reduced spacing or innovative five-spiral reinforcement (specimen CSCS). Test results showed that all the specimens exhibited a positive post-yield stiffness ratio of 3.5–6.4 %. However, the enhanced confinement reduced the post-yield stiffness by 42–45 % but increased the lateral strength of the column, which is beneficial for controlling the residual displacement. The enhanced confinement did not affect the drift ratio when the positive post-yield stiffness ended (6 %) but significantly increased the deformation capacity by 15–31 % and the energy dissipation capacity by 37–63 % of the column. Even with a smaller amount of transverse reinforcement, the specimen with the innovative five-spiral reinforcement showed deformation and energy dissipation capacities better than the other specimens with conventional rectilinear transverse reinforcement. A pushover analysis model was developed and modified to better account for the effect of the enhanced confinement and the strand slip, and to consider the end point of positive post-yield stiffness. The comparison with the test result showed that the proposed pushover model well captured the envelope responses of the specimens. Finally, a simplified method was proposed for estimating the moment strength of the proposed column.

Capacity of Reinforced/Prestressed Concrete Compression Members Strengthened/Repaired Using Ultra-High-Performance Concrete Encasement

Currently, 36% of bridges in the United States need major repair work or replacement and 7% of them are classified as structurally deficient. Most of these bridges can be repaired or strengthened to meet the current load demands and withstand the environmental impacts for the remaining service life. Ultra-high-performance concrete (UHPC) has shown immense potential as a repair and strengthening material thanks to its exceptional characteristics such as high workability, excellent strength and durability, and remarkable energy absorption capacity. This paper presents an analytical approach to predict the capacity of reinforced or prestressed concrete compression members with UHPC encasement (jacket) under combined axial and bending effects. The approach is based on strain compatibility and uses idealized UHPC material models in tension and compression according to the new AASHTO Guide Specifications. The approach uses integration to develop accurate interaction diagrams for any section with complex geometry, which overcomes the approximations of the lamina approach. The paper also provides a comprehensive literature review on UHPC usage in repairing and strengthening concrete bridge columns and piers. A design example of a circular reinforced concrete column is presented to illustrate the proposed approach and to calculate the nominal and design capacities of the composite section. This example has shown that increasing the thickness of the UHPC jacket has a prominent effect on enhancing the axial capacity but only a slight effect on the flexural capacity of compression members.

The strain demand of reinforced concrete bridge columns under seismic loading

The steel in reinforced concrete (RC) members that form plastic hinges must possess sufficient strain capacity to dissipate seismic deformation demands. Unfortunately, there is limited information on the seismic strain demands of bridge column plastic hinges. Instead, designers rely on a perception of cyclic strain capacity that is an approximate rule of thumb. A standard methodology needs to be established for quantifying the strain demand on these structural members as a function of the expected seismic hazard. To develop this methodology, 1944 columns were analyzed with nonlinear time-history analyses (NLTHAs) using ground motions from a range of earthquakes. This study evaluates the strain demand on RC bridge columns by defining the relationship between the strain demand and earthquake intensity. The results of the model are defined in terms of the peak tensile strain of the reinforcing bar, [Formula: see text]. The earthquake intensity with the highest correlation to the [Formula: see text] was determined to be the elastic spectral displacement at the optimal period ([Formula: see text]), which is defined as 75% of the effective period. The relationship between [Formula: see text] and [Formula: see text] can be used to predict the strain demand for an RC bridge column at a given geographic location. Results are presented as a probability density function (PDF), representing strain demand, compared to a PDF of the column capacity. The intersection of the capacity curve and demand curve represents the maximum acceptable strain given as a function of [Formula: see text]. This methodology can help understand the demand placed on a structural system given a region’s seismicity.

Machine Learning–Aided Rapid Estimation of Multilevel Capacity of Flexure-Identified Circular Concrete Bridge Columns with Corroded Reinforcement

Machine Learning–Aided Rapid Estimation of Multilevel Capacity of Flexure-Identified Circular Concrete Bridge Columns with Corroded Reinforcement

Reinforced Concrete Bridge Column Multihazard Performance: A Computational Tool to Assess Response to Vehicle Impact, Air Blast, and Fire

Reinforced Concrete Bridge Column Multihazard Performance: A Computational Tool to Assess Response to Vehicle Impact, Air Blast, and Fire

Repairable Precast Concrete Bridge Columns for Seismic Events

In multispan bridges excited by ground shaking, columns are usually the target ductile members. Although current practice is successful in attaining the no-collapse objective for bridges, columns are usually damaged at displacements associated with this performance level. Minor damage can be repaired, but excessive damage is usually beyond repair. A new design paradigm with minimal damage and repair need is gaining interest. The benefits of such a design can be increased if low-damage technologies are combined with accelerated bridge construction techniques. The main goal of the present study was to develop rein¬forced concrete bridge columns that are fully precast concrete, low damage, and repairable through compo¬nent replacement. To achieve the project objectives, 20 repairable precast concrete alternatives were developed and ranked. Subsequently, the top three candidates were designed at 50% scale, constructed at a precast concrete plant, and tested in a laboratory. The precast concrete columns incorporated different exposed fuses, such as stainless steel bars and steel tendons, advanced materials such as ultra-high-performance concrete, a self-centering mechanism, or an accelerated bridge construction socket connection. A reference cast-in-place concrete column was included for comparison. Each precast concrete column was tested twice. It was found that the repair of the precast ultra-high-perfor¬mance concrete columns with exposed tendons was easy,

Loading protocols for quasi-static cyclic testing of flexure dominated reinforced concrete circular bridge columns under crustal, subcrustal, and subduction earthquakes

Experimental procedures involving quasi-static cyclic tests have been the most prevalent for seismic performance assessments of structural and non-structural components and systems. However, there is a lack of consensus among experimentalists and researchers on a standard loading protocol. This study aims to propose a set of standard loading protocols representative of the seismic demands imposed on typical flexure dominated reinforced concrete bridge columns under uniaxial bending. Variable parameters: axial-load ratio, aspect ratio, longitudinal and spiral reinforcement ratios, concrete compressive strength, and steel yield strength were initially screened for significance in terms of their influence on the number of inelastic cycles and cumulative displacement ductility - two key reference parameters for the development of loading protocols. The number of inelastic cycles cumulative displacement ductility were then determined for reinforced concrete bridge columns having unique combinations of upper and lower levels of the significant parameters under different earthquake types (crustal, subcrustal, subduction) and displacement ductility demand levels (2, 4, 8). These target ductility demands intend to capture a wide range of structural responses including minimal and collapse damage states. Statistical analyses revealed that for the considered bridge columns, it is feasible to develop one representative loading protocol for each earthquake type and target displacement ductility demand level. Hence, nine loading protocols were proposed and then compared against equivalent loading protocols found in standards and literature. Standard protocols were found to impose unrealistic damage on bridge columns subjected to crustal and subcrustal earthquake hazards leading to inaccurate assessments. The proposed loading protocols for subduction earthquakes had a comparable number of inelastic cycles to those found in the literature for the same earthquake hazard and are representative of the seismic demands imposed on bridge columns.

Behaviour of circular concrete bridge columns internally reinforced with GFRP under reversed-cyclic loading including torsion

This study investigates experimentally the behaviour of circular reinforced concrete (RC) bridge columns internally reinforced with glass-fiber-reinforced polymer (GFRP) bars and spirals under cyclic combined loading conditions of bending, shear, and torsion. The study involved testing four large-scale column-footing connections, including one steel and three GFRP-RC columns. The effects of the reinforcement type (GFRP and steel) and torsion-to-bending ratios (tm) (0, 0.2 and 0.4) on seismic indexes, such as mode of failure, deformation and twist capacity, hysteretic responses, energy dissipation, ultimate strength and stiffness were evaluated. The results showed that the mode of failure varied according to the tm. Under combined loading with a tm of 0.2, both GFRP-RC and its steel-RC counterpart specimen were able to sustain similar lateral load and torsional moment capacities. Moreover, under the effect of combined loadings, the GFRP-RC columns showed a stable seismic response with adequate deformability. The GFRP-RC columns exhibited a decrease in ultimate lateral load and displacement capacity with increasing tm, however, their torsional moment carrying capacity increased. All GFRP-RC columns met the ductility requirements of North American codes, while their torsional stiffness degraded faster than their bending stiffness under combined torsion and bending loadings.

Experimental and Theoretical Development of Load–Moment Interaction Diagrams of Circular Hollow GFRP-Reinforced Concrete Bridge Columns

Experimental and Theoretical Development of Load–Moment Interaction Diagrams of Circular Hollow GFRP-Reinforced Concrete Bridge Columns

Numerical modeling and design sensitivity of seismic behavior of UHPC-NSC bridge piers with the longitudinal grooved contact surface

Normal strength concrete (NSC) has low structural and durability resistance to meet the comprehensive performance requirements of modern construction. The reinforced concrete bridge column quickly degrades, particularly when exposed to environmental compartments, causing the concrete to deteriorate and the reinforcement to corrode. The phenomenon significantly reduced the durability and load-bearing capacity of the column, which impacted the functionality of the bridge and threatened its recovery operation. The superior behavior of advanced cementitious ultra-high-performance concrete (UHPC) has drawn increasing benefits among the construction industries. However, the high cost of UHPC has developed a concern that resulted in its small-scale application. Therefore, incorporating UHPC with NSC has the potential to balance the low performance of NSC and the economic cost of UHPC. Therefore. This study incorporates UHPC and NSC in a large-scale two-column bridge pier and investigates its seismic performance. The study aims to understand the general behavior, failure modes, and effect of design parameters of developed UHPC-NSC bridge columns with longitudinally grooved contact surfaces through finite element analysis. The pushover response of the UHPC-NSC two-column with a typical geometry and gravity load of a representative bridge was investigated. A comprehensive parametric study was carried out to evaluate the effect of interface groove geometry, longitudinal reinforcement ratios, core NSC compressive strength, and reinforcement grade on the characteristic behavior of the columns. The study shows that the capacity of the composite UHPC-NSC bridge column under gravity load is 11 % higher than the conventional NSC concrete. The UHPC-NSC column with 300 × 300 mm interface groove, reinforced with 4 % HRB500 longitudinal rebars, can sustain over 80 % of the peak capacity up to 5 % drift. A higher axial load ratio of up to 14 % can increase the capacity of the UHPC-NSC two-column by 75 %, which has a more significant impact than what is often observed on NSC piers.

The role of overstrength in welded joints for rebar substitution in damaged RC columns

Rehabilitating corroded or seismically damaged reinforced concrete (RC) bridge columns often involves replacing the longitudinal steel rebar. Welded joints offer a practical and efficient in-situ solution for connecting new rebar segments to existing undamaged rebar, even with irregularities in the steel reinforcement. However, traditional approaches to rebar joint welding have paid little attention to the overstrength of the welding seam, which can result in a brittle response. Properly designing such joints should aim for a ductile rebar failure. However, in-situ rehabilitation solutions often require reducing the seam length to save time and material costs and, not secondarily, avoiding the plastic hinge formation in the rehabilitated column. Therefore, providing the seam with adequate overstrength is crucial to achieving a ductile failure of the welded joint. This study presents an experimental investigation into the most effective methods for connecting existing and new rebar segments through welding, addressing on-site welding challenges such as limited operational space and weld orientation. Over 100 tensile tests have been conducted at Fuzhou University’s laboratory in China to understand the response of nine welded joints. Among indirect butt joints, the study identifies two performance groups based on the ductile failure rate as the welding seams reduce. The symmetry of the joint and the presence of additional direct butt welding also in asymmetric joints can significantly improve the joint performance, determining a ductile failure with minimal welding lengths. In a second step, following a probabilistic approach, the study assesses the overstrength of indirect butt joints as a function of seam length for the two identified performance groups. Empirical failure probabilities of the rebar and the seam are estimated to fit probability density functions representative of the tensile strength of the rebar and the seam. Based on a target reliability class, the overstrength factors are estimated.

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

Refined deformation limit states for circular reinforced concrete bridge columns

AbstractOne hurdle against the widespread implementation of the performance‐based design (PBD) for bridges is the lack of consensus among practitioners, researchers, and code committees on engineering demand parameter (EDP) limits defining the onset of various types of damage and their variability. This study seeks to bring consistency to the PBD methodology by establishing refined EDP limits at concrete cover spalling and bar buckling for circular reinforced concrete bridge columns. To this end, a database consisting of 118 previously tested flexure‐dominant bridge columns was formulated and analyzed. The EDP limit considered at the member level was drift ratio, whereas, at the sectional level, the EDP limits considered were material strain and curvature ductility. State‐of‐the‐art symbolic regression was adopted to fit the resulting data to mathematical expressions. At the member level, predicted drift ratio limits at the two damage states obtained with the proposed expressions were associated with lower root‐mean‐square error (RMSE) than those obtained from other similar expressions in the literature. At the sectional level, drift ratios at concrete cover spalling were adequately predicted with compressive strain limits in concrete ranging from 0.004 to 0.007 and a curvature ductility limit of 6.3. More accurate predictions of drift ratios at bar buckling were attained with variable sectional EDP limits, particularly for columns subjected to relatively high axial load. Two expressions predicting the tensile strain limit in the rebar and curvature ductility limit at bar buckling were proposed. The ratios of the measured drift ratio at bar buckling to the drift ratio predicted based on the proposed variable tensile strain limit had a mean of 0.99 and a coefficient of variation (COV) of 33%. Corresponding ratios based on the proposed variable curvature ductility limit had a mean of 1.02 and a COV of 31%. Fragility functions relating the likelihood of concrete cover spalling and bar buckling to the considered EDP limits were also developed.

Effective Stiffness and Seismic Response Modification Models Recommended for Cantilever Circular Columns of RC Bridges, First Part: Serviceability Limit State

This paper’s main aim was to explain the process of characterising the structural over-strength factor (R), seismic behaviour factor (Q), and the effective elastic stiffness, Keff, of cantilever-reinforced concrete (RC) urban bridge columns with solid circular cross-sections for use in seismic design under the Serviceability Limit State (SLS). Similarly, mathematical models have been proposed to determine the average values of effective stiffness and seismic response modification factors suggested for cantilever-reinforced concrete bridge columns at SLS. This is because multiple design codes stipulate that cantilever RC bridge columns must meet the SLS requirements. Therefore, to comply, the lateral displacement ductility demand must not exceed unity after a moderate or small earthquake. While the behaviour of the materials remains in the elastic range, this performance criterion can be conservative. If the materials undergo small deformations, the slight damage can be quickly repaired to meet the SLS.

Variability of mechanical properties of steel rebars in North America and its effects on the seismic fragility of reinforced concrete columns

This study examines the variation in mechanical properties of reinforcing steel bars and its impact on the seismic design of reinforced concrete (RC) bridge columns. The variation of mechanical properties of rebar as per American Society for Testing and Materials (ASTM) A615 and ASTM A706 is studied using 685,351 and 950,000 tensile testing results obtained between the years of 2009 and 2019 from various mills across North America. An analysis is performed using classification and regression trees (CART) to identify parameters with the highest relative influence considering source mill, bar size, and weight per meter. Probability distribution functions are developed for yield and ultimate tensile strength data. The beta distribution shows better agreement with the distributions of yield strength and ultimate tensile strength. Results show that 0.12% of the tensile test data fall below the minimum ASTM standard requirements. In addition, the study also examines the effect of the variability of yield strength of longitudinal rebars on the seismic response of circular bridge columns using fragility analysis.

Self-centering technique for existing concrete bridge columns using prestressed iron-based shape memory alloy reinforcement

Reinforced concrete (RC) bridge columns are expected to undergo large inelastic displacements during major earthquake events, which in turn can result in residual displacements that can potentially affect the functionality of the bridge. While post-tensioning has been used to develop self-centering column systems for new bridge construction, the self-centering of existing bridge columns remains a challenge, mainly due to the limitations associated with the application of conventional post-tensioning techniques to existing structures. This study aims to address this important research gap by developing a robust self-centering technique to mitigate the residual displacements of the existing bridge columns. The proposed self-centering technique exploits the unique self-prestressing characteristics of iron-based shape memory alloy (Fe-SMA) bars to prestress existing bridge columns. The effectiveness of the proposed technique was evaluated through the large-scale experimental investigation of four columns. The variables of the study included the ratio of steel to Fe-SMA reinforcement, the total longitudinal reinforcement, and the initial prestress. The experimental results showed that the proposed technique could significantly reduce the residual drifts of existing bridge columns. The residual drift of the columns was found to be less than 1% up to a target drift of 4% when the ratio of steel to Fe-SMA reinforcement was ≤ 0.3. The paper concludes with a discussion of the self-centering mechanism of columns reinforced with prestressed Fe-SMA bars, where it is shown that, unlike post-tensioning tendons which do not contribute much to the energy dissipation of columns, prestressed Fe-SMA bars begin to contribute to the energy dissipation after the initial prestressing is lost at high drifts, resulting in an enhanced seismic resilience of the columns.

Cyclic loading test of self-centering precast segmental concrete high-speed railway bridge columns with UHPC-filled duct connections

Precast concrete high-speed railway (HSR) bridge columns are attractive for standardized HSR bridges, but their applications are rare partly due to a research gap in their lateral behavior. Traditional under-reinforced HSR bridge columns have huge lateral stiffness and poor drift capacity, which means that their prefabrication is not a simple separation-assembly process and requires special research. This study aims to develop a novel self-centering precast segmental concrete (SPSC) HSR bridge column, which is designed to have five major improvements including adopting large-diameter deformed bars as energy dissipation (ED) bars, inter-locking multi-hoops, unbonded post-tensioning (PT) tendons, a cast-in-situ ultra-high performance concrete (UHPC) layer at the bottom joint, and UHPC-filled duct connections. A 1/6 scaled cyclic loading test was conducted on three specimens to validate prefabrication feasibility and assess seismic behavior. The research results show that inter-locking multi-hoops can enable the developed bridge columns to have ductile flexural failure and a drift capacity of up to 5 %. The bridge columns have increased lateral stiffness and strength as well as decreased ductility. UHPC-filled duct connections can cause the strain amplification of ED bars at the bottom joint. The bottom joint opening dominates lateral deformation while the influence of joint sliding can be neglected. The bridge columns have good ED capacity and the equivalent hysteretic damping ratio of about 20 % at the drift ratio of 5 %. The bridge columns have the excellent self-centering capacity to control residual drift ratio in an allowable range before flexural failure. The acceptable drift ratios are suggested to be 3.5 % and 4.0 %, respectively, for the SPSC HSR bridge columns without and with PT force.