Bridge Bents Research Articles

Experimental investigation and numerical simulation on seismic performance of self-centering bridge bents with energy-dissipation beams

This study explores the creation of self-centering bridge bents with energy-dissipation (ED) beams to enhance seismic resilience. This design combines the concepts of cast-in-place bridge bents with ED components and self-centering rocking piers. The self-centering bridge bent with ED beams integrates cooperative mechanisms, for bearing, stability, energy dissipation, and recoverable capacity. Two types of specimens were designed and constructed: self-centering bridge bents with and without ED beams, referred to as specimens SCB-EDB and SCB, respectively. Quasi-static tests were conducted to thoroughly assess the seismic performance, including lateral force, stiffness, energy dissipation, and self-centering capacity, of these specimens. The results show that both specimens exhibit a distinct flag-shaped hysteresis curve, demonstrating good self-centering capacity. However, the ED beams slightly reduce the self-centering capacity of the bridge bent. Specimen SCB-EDB shows significantly higher lateral force, stiffness, and energy dissipation capacity than specimen SCB. The ED beams also contribute to reducing damage and sliding of the column. Numerical models were established in OpenSees to reproduce the test results of specimens SCB-EDB and SCB. The numerical results closely match the corresponding test results, effectively capturing the hysteresis behavior, skeleton curves, stiffness variations, and energy dissipation capacity. Consequently, both numerical models could accurately replicate the quasi-static test results.

Seismic performance of precast bridge bents with prestressed piles and new pocket connection design: Experimental and numerical study

Pile-slab bridges with prestressed high-strength concrete (PHC) piles or prestressed and reinforced high-strength concrete (PRC) piles are widely used in low-seismic zones. To further understand the seismic performance of pile-slab bridges and to promote their applications in high-seismic regions, specimens of PHC bent (PHCB) or PRC bent (PRCB) from pile-slab bridges with a new bent-cap-pile pocket connection are studied through quasi-static cyclic tests. Seismic performance of the PHCB and PRCB is evaluated and compared in terms of damage development, failure mode, lateral stiffness, residual displacement, peak strength, displacement and energy-dissipation capacity. The experimental results show that both PHCB and PRCB fail due to non-ductile fracture of prestressing rebars in the piles, and the proposed bent-cap-pile pocket connection remains functional throughout the tests. Additional mild rebars of PRCB significantly increase displacement capacity of PRCB against PHCB. Finite element (FE) models are then developed and validated by the experimental results, after which the influence of initial prestressing force level and longitudinal prestressing reinforcement ratio of piles is investigated through parametric study based on the validated models. The proposed FE models can accurately predict the overall hysteretic behavior. Based on the parametric study, the seismic performance of both PHCB and PRCB can be improved by decreasing initial prestressing force level or increasing longitudinal prestressing reinforcement ratio.

Performance-Based Seismic Design for Retrofitting Deficient Bridge Bents: Developing Performance-Based Damage States

Performance-Based Seismic Design for Retrofitting Deficient Bridge Bents: Developing Performance-Based Damage States

Performance-Based Seismic Design for Bridge Bents Retrofitted with BRBs Using the Ductility Demand Spectra of SDOF Oscillators with Bilinear Fuses

ABSTRACT Reinforced concrete bridge bents with double columns in bridge substructures are commonly used, but it has suffered severe damage during strong earthquakes. The seismic retrofit with structural fuses is used to effectively mitigate seismic damage of bridge bents. To obtain the displacement ductility demand for dual systems including the primary structure (PS) and structural fuses (SF), the corresponding ductility demand factor spectra were developed. The interaction between the PS and SF is described by defining two parameters of dual systems: the yield displacement ratio (α) and the initial stiffness ratio (β), and the influence of α, β, and strength reduction factor on the ductility demand factor spectra are also analyzed. For seismic retrofitting in bridge bents, buckling-restrained braces (BRBs) are used as energy dissipation fuses, and the steel core lengath of BRBs with three configurations forms, including diagonal, inverted-V, and toggle systems, are also explored. Then, based on the structural fuses concept and ductility demand factor spectra of dual systems, a performance-based seismic design procedure is proposed for bridge bents retrofitted with BRBs to ensure that the bridge bents maintain the target ductility under design-level earthquakes. Finally, the procedure was utilized to design the bridge bents with BRBs, and the procedure’s feasibility was verified by nonlinear time-history analysis.

Hybrid bridge bent using stretch length anchors with post-tensioning and shear key alternatives

Precast concrete bridge bents are good candidates for accelerating bridge construction. In seismic regions, in addition to construction speed, there is a need to improve seismic performance of bridges. One promising solution is self-centering bridge bents that use post-tensioning and external energy-dissipation devices as a hybrid system. This paper presents cyclic load experiments of hybrid two-column bridge bents to assess their performance regarding self-centering and hysteretic energy dissipation. The cyclic experiments were conducted on 42% scaled bridge bents that used unbonded post-tensioning (PT) bars for self-centering and stretch length anchors (SLAs) as external energy dissipators. A total of six experiments are investigated: three with PT bars and SLAs and three with PT bars only. The variables included the number of PT bars in each column (two or four), the initial post-tensioning force in the columns, and the shear key details in the footings and cap beam. The PT bars remained elastic until 4.0% drift ratio but some variation was observed in the post-tensioning forces especially for columns with two PT bars. For post-tensioned bridge bents with or without SLAs, increasing the number of PT bars in each column from two to four enabled efficient self-centering by limiting the residual drift ratio to 0.5%. There was no damage to the concrete for bents with four PT bars and there was repairable concrete damage for bents with two PT bars. The hysteretic energy dissipated by bridge bents with SLAs in addition to PT bars was 1.8 to 3.2 times the hysteretic energy of bridge bents with only PT bars.

A generalized, model-free framework for assessing scour-induced bridge pier instability

Flood-induced scour is one of the leading causes of bridge failures in the United States, accounting for 53 % of recorded failures between 1989 and 2000. With many existing bridges considered “scour critical”, it is essential to closely monitor its development for effective mitigation. However, despite advances in scour hole measurement techniques, continuous monitoring of scour remains underused and little guidance is available to maintenance engineers to assess structural stability from scour depth measurements. This research presents a proof-of-concept, model-free bridge pier structural assessment framework. This framework is built on a library of bridge pier failure surfaces – curves that define failure limits for combinations of scour, wind, and flood loading for a range of structural configurations and site conditions. User input is limited to basic structural and site information, from which a corresponding failure surface is automatically selected, either directly or through interpolation between surfaces in the library. In this study, the creation of a failure surface library and framework is focused on pile bent pier designs, due to their widespread use. A broad scope of parameters was modeled such that common configurations of pier bent bridge designs and site conditions in Florida were considered. Sensitivity studies were performed to identify parameters for which modeling simplifications could be made to build the failure surface library with reduced computational burden. Results from three case study bridges are presented to verify that the resulting assessment framework maintained reasonable representation of structural response.

Performance of steel tube reinforced concrete-filled weathering steel tubular members under lateral impact loading

Weathering steel tube is superior to mild steel tube in corrosion resistance, but it is less used in engineering projects due to its high price. To balance the performance and cost, mild inner steel tube reinforced concrete-filled weathering steel tube (STRCFWST) members are proposed in this study, and the lateral impact loading test is carried out. The impact responses of concrete-filled weathering steel tube (CFWST) members and STRCFWST members are studied and compared experimentally. It is indicated that the presence of the inner steel tube can remarkably enhance the impact resistance of STRCFWST members. The outer steel tube has a stronger influence over the impact resistance as compared to the inner steel tube. A constitutive model for the weathering steel is developed based on the material test results. The impact performances of STRCFWST, CFWST and conventional CFST members are compared and discussed using numerical simulation. Finally, parameter analysis of the impact performance of STRCFWST members is carried out by taking into account the actual stress state of bridge bents. The results show the proposed model can predict the mechanical behaviors of weathering steel, making it suitable for numerical modeling. The CFWST member suffers fracture failure a little earlier than the CFST member. A large diameter-thickness ratio is recommended for inner steel tubes on the premise of guaranteeing construction conditions. The optical area ratio of internal and external steel depends on the prices of weathering steel and mild steel, and the diameter ratio of inner and outer steel tube.

A novel self-centering friction damper with elastic post-buckling plates to retrofit bridge bents

The self-centering energy dissipation dampers (SCEDs) have been demonstrated in mitigating the residual deformation of structures under strong ground motions. However, existing researches show that the damping force demand of SCEDs is higher than conventional dampers such as viscous dampers, BRBs or friction dampers for same design displacement of self-centering retrofitted structures, which could lead to higher base shear and acceleration responses of structures. In order to alleviate the problem, a novel self-centering damper composed of elastic post-buckling plates and adjustable friction devices (PBSCFD) was proposed. Compared with conventional SCEDs, the proposed PBSCFD has low secondary stiffness and adjustable energy dissipation capacity, which is beneficial to control the additional internal force of members adjacent to the damper in self-centering retrofitted structures. Based on the configuration and working principle of the PBSCFD, the theoretical force-displacement relationship of the damper was derived. Subsequently, a scaled PBSCFD was manufactured and tested under quasi-static loading to investigate its mechanical properties and to verify the theoretical constitutive model. In order to demonstrate the seismic performance of PBSCFDs, the double-column bridge bent retrofitted with PBSCFDs was designed by direct displacement-based seismic design method (DDBD), and its seismic performance was examined by elastic-plastic time-history analysis. Finally, effects of secondary stiffness ratio of self-centering dampers on seismic mitigation of self-centering retrofitted bridge bent were investigated. The results show that PBSCFDs have certain advantages in controlling the base shear and acceleration of the retrofitted bridge bent compared to conventional SCEDs with significant secondary stiffness.

Cyclic Behavior of Precast Double-Column Bridge Bents with Lap Splice Connections by UHPC

Cyclic Behavior of Precast Double-Column Bridge Bents with Lap Splice Connections by UHPC

Test and simulation on tall reinforced concrete bridge bents with shear links as structural fuses components

Shear links (SLs) are effective energy dissipation devices for seismic damage mitigation and resilience improvement of bridges or bridge bents. This study is to assess the influences of the SLs on controlling seismic damage or response of tall reinforced concrete (RC) bridge bents. Therefore, two tall RC bridge bent models with and without SLs are designed and tested using the shaking table. The dynamic characteristics and seismic responses are separately presented for both test models under the white noise and three input motions. Both finite element models are conceived to replicate the test results. These results demonstrate that the SLs decrease the maximum curvature and reinforced strain at the column bottom due to the SLs dissipating the seismic energy. The tall RC bridge bent model without SLs suffers seismic damage under the input motions of 0.30 g, whereas the tall RC bridge bent model with SLs undergoes seismic damage until the input motions of 0.50 g. Compared to the tall RC bridge bent model without SLs, the maximum displacements of the tall RC bridge bent model with SLs reduce because the SLs enhance the stiffness of bridge bents, leading to the displacement spectra values reduction for the S-Wave and E-Wave. Both finite element models successfully reproduce the typical test results of the tall RC bridge bent models with and without SLs and track the response variations caused by the SLs. Therefore, the effects of the SLs on controlling seismic damage and improving the seismic resilience of tall RC bridge bents are verified using shaking table tests and numerical simulations.

Risk-based seismic design of diagonal self-centering shape-memory alloy wire-based bracing system in multi-column bent bridges

In this paper, a risk-based seismic design method for diagonal self-centering braces (SCB) with shape memory alloy (SMA) wires implemented in multi-column bents is proposed to enhance the performance of older concrete bridge classes. An existing SMA-SCB system that improves the performance of older reinforced concrete building frames was adopted to numerically examine further applications to nonductile bridges. To this end, risk-based seismic design of the SMA-SCB to minimize the probability of collapse and demolition of bridge classes was developed by adopting a sophisticated finite element model that reflects the recentering behavior of an actual SMA-SCB; probabilistic bridge models considering uncertainties associated with the material and geometrical properties of bridges; refined failure condition; and the total probability theorem. A comparison of the results of the traditional seismic fragility-based and proposed designs indicated that the amount of SMA-SCB required by the former is nearly half of that required by the proposed approach because the traditional approach overemphasizes the demand at larger ground motion intensities.

Seismic performance of double-column tall pier bents using fusing connections

The dynamic responses of tall pier bridges with single column have been extensively investigated, while the research on double- or muti-column tall pier bent bridges is limited to date. This paper investigates the seismic performance of this type of tall pier bents and proposes a fusing connection between pier columns and link beams, to alleviate damage and improve seismic resilience. By setting strength hierarchies among various components, the proposed fusing connection is designed to yield prior to both column and link beam. Therefore, the nonlinear damage and energy dissipation during earthquakes are shifted to these connections, and the pier column and link beam are protected. To validate the efficiency of the proposed fusing connections, a typical double-column tall pier bent constructed at Southwest China is employed as a prototype. Through the nonlinear time history and fragility analysis procedures, the performance of the tall pier bent using fusing connection is evaluated and compared with the prototype in deterministic and probabilistic ways, respectively. The results show that the utilization of fusing connections effectively suppresses both the section curvature and shear force demands of pier columns. Thus, the seismic vulnerability of the prototype is reduced, and the seismic performance is improved, in both linear and nonlinear stage. Furthermore, the link beams are also protected by the connections and remain elastic during excitations, indicating lower probability of secondary damage, as well as reduced post-earthquake repair work and cost.

Seismic design and performance analysis of bridge bents retrofitted with multistage buckling-restrained braces

Buckling-restrained braces (BRBs) are often used to retrofit RC bridge bents to increase their strength and stiffness, and dissipate the seismic energy through hysteretic behavior. However, the post-yielding stiffness of BRBs is very low, and the total stiffness of the retrofitted bent drops sharply when the brace yields, which can lead to more serious damage to the primary structure contrary to the design purpose. Accordingly, multistage buckling-restrained braces (MSBRBs), consisting of steel cores with different yield strains, were used for the seismic retrofitting of bridge bents in this study. By controlling the low yield point (LYP) core yield before the bridge bents and high yield point (HYP) core yield after the bents, the expressions for the steel core length related to the geometric parameters of the bridge bents were derived. Furthermore, a preliminary seismic design method based on the structural fuse concept was proposed, which realized that the MSBRB dissipates energy while providing stable stiffness to improve the safety of the entire system. The advantages of the MSBRB in controlling the peak and residual displacement of the RC bent were proved via nonlinear time history analyses. Finally, the effects of the stiffness ratios, yield displacement ratios, and different configurations on the seismic performance of retrofitting bridge bents with MSBRBs were examined. The results showed that seismic performance of reinforced bents can be improved by increasing the stiffness ratio appropriately. The LYP core is primarily related to the energy dissipation capacity of the MSBRBs, and the value of βL should be less than 0.5. The HYP core is largely responsible for controlling the deformation of bridge bent, and βH must be greater than 1.0. Compared to other configurations, the diagonal MSBRB system has a greater energy dissipation capacity and higher seismic reduction rate.

Seismic Analysis of Posttensioned and Hybrid Bridge Bents with Buckling Restrained Braces

A numerical model is presented for a rocking bridge bent specimen consisting of two precast concrete columns with posttensioning (PT) bars, two footings, and a cap beam, with or without a buckling restrained brace (BRB). First, a numerical model of the posttensioned bridge bent specimen without a BRB is developed; emphasis is placed on modeling the rocking mechanism at the joint between precast concrete members joined only through PT bars. The numerical model is extended to a hybrid specimen consisting of a two-column posttensioned bridge bent with a BRB as an external energy dissipation device. Experimental results obtained from quasi-static cyclic tests of the posttensioned and hybrid specimens are compared with the numerical models. Satisfactory agreement of the numerical models with the experimental results is observed in terms of structural response, hysteretic energy, and PT-bar forces. The numerical models are subsequently extended to a previously tested three-column bridge bent for two configurations: (1) a posttensioned bridge bent with PT bars, and (2) a hybrid bridge bent with PT bars and two BRBs. A fiber-based bridge bent model is built, which includes soil–structure interaction (SSI) using simplified springs. A comparison of the posttensioned and hybrid bridge bents using far-field and near-field ground motions shows that the hybrid bridge bent displays superior performance compared with the posttensioned-only bridge bent.

Design and analysis of bridge microstructure under the condition of large-scale geographical environment

The design and analysis of bridge microstructure are two indispensable parts of bridge construction and maintenance and the two always complement each other throughout bridge's life cycle. Furthermore, bridge microstructure design and analysis under large-scale geographic environment are more complicated. In order to ensure bridges' safe construction and normal traffic under this environmental condition, it is necessary to find a suitable microstructure and use a scientific classification method to analyze it. Under large-scale geographic condition, the design and analysis of bridge microstructure should be planned from multiple steps after construction party puts forward bridge planning and construction goals. The stability of bridge engineering geology should give more consideration to the feedback mechanism of internal structural system characteristics for microstructure design and analysis, and must have a geographical viewpoint. Therefore, on the basis of summarizing and analyzing previous research works, this paper expounds the current research status and significance of large-scale geographic environment, elaborates the development background, current status and future challenges of bridge microstructure design and analysis, introduces the methods and principles of single-degree-of-freedom energy structure reaction and the dynamic microstructure characteristics, constructs bridge microstructure model, conducts bridge microstructure data analysis, performs bridge microstructure design under large-scale geographical environment condition, proposes the combined analysis of load effect, discusses the optimization analysis of structural topology, puts forward the bridge microstructure analysis under large-scale geographic environment condition, and finally carries out a simulation experiment and its result analysis. The study results show that when the large-scale geographic environment is divided into regular rectangular plots, the bridge microstructure can maintain its design cohesion, and the stretch and continuity of those plots and bridge convey a strong sense of structure. Microstructure parameters represent the stiffness caused by the average properties of cross-sectional materials of bridge microstructure. For a uniform classical continuous microstructure, the design can accurately describe bridge's bending resistance. The study results of this paper provide a reference for further researches on the design and analysis of bridge microstructures under the condition of large-scale geographic environment.

Quasi-Static Cyclic Testing of Hybrid Posttensioned Bridge Column Supported on a Monopile Foundation

In this research, a low-damage posttensioned rocking solution referred to as dissipative controlled rocking (DCR) connection is proposed for bridge columns supported on monopile foundations. The DCR connection is a low-damage system that replaces the plastic hinge mechanism in a column and aims to minimize and potentially eliminate the repair time and costs after an earthquake. A DCR bridge system combines unbonded posttensioning and replaceable dissipaters to provide self-centering and energy absorption capabilities, respectively. Current research on DCR column systems has focused on the performance of bridge bents founded on a fixed foundation, neglecting soil damping effects. In this research, a one-third scaled bent supported on a monopile with passive soil resistance was tested under quasi-static cyclic loading to validate the lateral seismic response of a DCR bridge bent with the contribution of the soil–foundation–structure interaction. When developing the details for the DCR connection, particular emphasis was made on utilizing conventional construction materials and forms for a low-damage bent that yields a similar construction cost to a monolithic joint. Nevertheless, the proposed DCR connection can be easily and quickly repaired or replaced after a significant seismic event. The performance of the bent was compared against a benchmark structure with an emulative connection type that resembles a monolithic cast-in-place joint. Results from testing suggest a greater performance of the low-damage DCR column. The dynamic response of the DCR column built on a flexible foundation differed from that of a fixed-base structure, which is primarily due to the energy dissipation capability of the flexibly supported structure. Flexibility in the soil foundation increased the structural period of the structure and reduced the seismic response of the DCR column. Damage to the DCR bent was limited to concrete crushing at the rocking interface, which proved to be easily repairable. In contrast, the bent with an emulative connection developed plastic hinging at the bottom of the column, which was nonrepairable.

Synthesis and Mesophase Properties of Triphenylene Dimers Linked through Linear and Bent Alkyne‐Aryl‐Alkyne Bridges

AbstractNematic mesophase formation in disc‐like systems remains relatively rare compared to higher‐order columnar organisation, but it is observed in some rigid dimeric systems. Mesophase formation in rigid discotic dimers has been sequentially probed and is shown to be predictably controlled through structural choice of the bridge. Moderately bent bridges shorten the discogen separation and reduce conformational freedom. Severely bent dimers (1,2‐phenylene bridge) show no mesophases but, as the angle is widened, columnar and nematic organisation becomes possible and progressively more favoured. The linear arrangement gives the most stable columnar mesophase and a narrow‐range nematic mesophase.

Rectification of a Slanted Box-Girder Bridge Caused by Unbalanced Soil Load

Aims: Rectification of a slanted continuous concrete box-girder bridge is presented in this paper. Background: Several bridge piers slanted due to uneven ground settlement, inducing excessive width of some expansion joints and oversize sliding displacement of some bridge bearings. The uneven ground settlement occured due to the unbalanced soil load on the ground. Methods: In this project, reverse ground loading was first applied to produce opposite-direction deformation of the bending bridge piles, thereby rectifying the slanted bridge piers rigidly connected to the piles. The procedure was accelerated by constructing several stress release holes on the opposite side of the reverse ground loading. Results: To stabilize foundation and prevent landsides of riverbank, combimationn of jet grouting piles and deep mixed piles was apliied to reinforce foundation soil, providing lateral restraint on the bridge piles as well. Finally, a hydraulic power system was used to reset the bridge piers, girders, and expansion joints. A similar system and additional equipment were used to replace the damaged bridge bearings. Conclusion: The recommended rectification techniques are suitable for rectifying bridges with similar geotechnical conditions and structure types and for replacing damaged bridge bearings.

Fragility-informed seismic design of multi-column bridge bents with post-tensioned concrete columns for accelerated bridge construction

Accelerated Bridge Construction (ABC) is playing an increasingly large role in bridge construction within urban centers due to faster installation, improved quality and lower cost. Concrete columns are prefabricated and connected together with footings and cap beams using either grouted splice sleeves, socket connections, or through post-tensioning. Precast unbonded post-tensioned (PT) concrete columns are protected from damage due to their ability to mitigate seismic demand through rocking. A numerical model is developed for rocking columns which is validated using published data. Seismic assessment of a two-column bridge bent constructed with precast PT concrete columns is carried out; column height-to-width ratio and ratio of initial posttensioning force to axial column capacity are selected as the assessment parameters. Performance limits are defined for the bridge model using non-linear pushover analysis. Probabilistic seismic hazard analysis is carried out using nonlinear time-history analysis for a set of eighty ground motions. The results show that PT concrete columns provide sufficient re-centering to the bridge bent so that it remains serviceable after a large earthquake. An ABC bridge bent with unbonded PT concrete columns is designed using the outcome of seismic fragility analysis. The seismic performance of the fragility-designed PT bridge bent is compared to that of a bent with conventional cast-in-place (CIP) concrete columns using nonlinear time-history analysis. The seismic performance of the ABC PT bridge bent using fragility analysis satisfied performance objectives similar to a monolithic CIP bent designed according to the latest seismic design codes; in addition, the residual drift of the PT bent was practically zero. The fragility-informed approach for designing ABC bridge bents constructed with unbonded PT concrete columns presented is expected to promote post-earthquake serviceability and functional recovery after a large earthquake.

Damage Assessment of Simply Supported Double-Pier Bent Bridge under Heavy Truck Collision

Studying the failure or collapse mechanism of an entire bridge under vehicle–pier collision has engineering demand and practical meaning, while the existing damage assessment work mainly focuses on the impacted pier. This study aims to numerically clarify the collapse mechanism and evaluate the damage level of the entire bridge. First, the previously validated finite-element (FE) model of a simply supported RC bridge with double-pier bent when impacted head-on by a heavy truck. The model improved by incorporating the nonlinear behaviors and damage of the bridge superstructure. According to the truck mass and impact velocity involved in the actual collision accidents, 20 truck–pier collision scenarios are designed and numerically simulated by adopting the nonlinear FE program LS-DYNA. The damage/failure or collapse mechanism of the entire bridge, as well as the vehicular impact force and bridge structural dynamic behaviors, are examined. It shows that (i) the overall collapse of the bridge structure is an impact-successive and damage-accumulative process, which is not completely coincident with the failure of impacted pier; and (ii) the cargo-induced internal forces of the impacted pier have two peaks attributed to the initial contact and the following pushing–drag effect of cargo, respectively. Then, based on the damaged area of concrete and effective plastic strain of reinforcement, the damage levels of the main bridge components, including the pier, bent cap, tie beam, pile, girder, and deck, are qualitatively assessed and classified, followed by the clarifications of their corresponding inner correlations. Furthermore, by proposing two quantitative damage indexes, a feasible on-site approach for assessing the post-collision damage of the bridge structure is established and validated by eight additional collision scenarios, and the dependency of bridge damage level on both the vehicular impact velocity and mass is graphically presented. The proposed approach can be practically generalized to on-site damage evaluation of a bridge structure after actual accidents and can provide useful reference in design and restoration of RC bridges.