Bent Cap Research Articles

Experimental research and numerical analysis on mechanical behavior of lightweight-design precast bent caps with large cantilevers

Two innovative lightweight-design schemes for large cantilevered precast bent caps (PBCs) commonly used in China are proposed in this study. In Scheme 1, a monolithic bent cap is divided into two symmetrical precast pieces that are parallel to the bent cap center line (hereafter referred to as PPBCs) and connected together by a cast-in-place wet joint. In Scheme 2, U-shaped and inverted U-shaped cross-section bent caps are designed to facilitate monolithic precast. Four scaled bent cap specimens are loaded monotonically to study the crack development, failure mode, deformation of the cantilevers, and ultimate load-carrying capacity. The test results show that all the specimens failed in the desired bending. However, the connectivity of the two precast pieces in the PPBCs was damaged after cracking occurred in the wet joint, leading to a slightly decreased ultimate load-carrying capacity, compared to the corresponding monolithic bent cap. The tensile stresses of the stirrups in the cavities of the U-shaped and inverted U-shaped cross-section bent caps were larger than those at other positions. Therefore, the arrangement of the stirrups should be strengthened in the cavities. The numerical modeling strategy validated by the test results was used to predict the mechanical behavior of full-scale lightweight-design bent caps from construction to final failure. The analysis results indicated that, all lightweight-design PBCs remained uncracked in both the construction and service stages. Finally, the PPBC and hollow cross-section PBCs failed under load combinations that were 1.9- and 1.7-time the Strength I load combination.

Analysis of the Seismic Behavior of a Wall Pier of a Covered Bridge Based on the Multi-Layer Shell Element

To investigate the seismic behavior of the wall pier of a covered bridge, the multi-layer shell element in OpenSEES was used to carry out the numerical analysis under a horizontal low cyclic loading in the weak axis direction. The effects of the mesh divisions of the wall pier models were evaluated and the hysteretic curves, skeleton curves, bearing and energy dissipation capacity, stiffness degradation and displacement ductility of the wall pier with different lateral loading modes were mainly researched. The results demonstrate that the discretization of layers along the thickness direction of the multi-layer shell element model has a very limited effect on the hysteretic and skeleton curves. The mesh division of the horizontal direction depends on that of the vertical, and the vertical mesh spacing shall be longer than the plastic hinge with a length of 0.5744 m. The arrangement of the loading points is critical for the seismic behavior of the wall pier. The pier suffering the force from the five points presents a relatively strong energy dissipation and larger ductility, but this layout may cause a more concentrated force at the local position. When the loading points are evenly distributed, the capacity and displacement changes sharply and the ductility diminishes. Successively, the seismic performance indexes at the local position of the wall pier tend to be more consistent with the increasing loading points. The deformation and energy dissipation capacity of the nearby position with the denser side loading points becomes larger, but this has a minor impact on the seismic performance of the position far from the points. The wall pier without the bent cap and with three bearings set is supposed to be more reasonable for the covered bridge through the overall analysis of seismic performance.

Optimization of Columns and Bent Caps of RC Bridges for Cost and CO2 Emission

This paper describes a methodology for optimal seismic design of reinforced concrete 3D columns and bent caps (beams) of bridges. Design variables include compressive strength of concrete, geometry, as well as longitudinal and shear reinforcement of columns and beams. The optimization is performed to minimize the cost and CO2 emissions using the enhanced colliding bodies optimization (ECBO) algorithm. The trade-off between cost and CO2 emissions shows that in the design for minimizing CO2 emissions compared to the design based on the cost minimization, increasing 1.4 % in cost can decrease CO2 emissions by 6.1%.

Load balancing external post-tensioning for strengthening existing inverted-T bent caps

Inverted-T bent caps have been widely used to provide increased clearance beneath bridges. Bridges with inverted-T bent caps often experience a prevalence of cracking at the web-to-ledge interface. To prevent these cracks, ledges require sufficient capacity to enable the transfer of applied loads from the girder seats to the pier column. This experimental investigation develops a retrofit solution which uses externally installed post-tensioned strands to balance dead loads thereby improving the capacity of the in-service inverted-T bent caps. Based on experimental results, the solution successfully improved the load carrying capacity of the bents and restrained existing cracks. The cracking load estimation is investigated to evaluate serviceability of the inverted-T bent caps without and with the PT retrofit. Ultimate strength predictions calculated using code-specified sectional methods and limit analysis are compared and contrasted with the experimental observations to evaluate their accuracy in estimating the observed ultimate strength. Based on the experimental observations and analytical comparisons; design, repair, and retrofit recommendations are provided, including their limitations.

Connections in GFRP reinforced precast concrete frames

Glass fiber reinforced polymer (GFRP) is an effective alternative reinforcing solution to tackle problems associated with steel corrosion in reinforced concrete structures located in harsh environments. However, there are multiple construction challenges when cast-in-place GFRP reinforced concrete is used. Cast-in-place concrete is both labor and time intensive on account of timely assembly of falsework and formwork as well as pouring and curing of concrete. To avoid such challenges and accelerate the construction process, GFRP reinforced precast concrete elements can be used to avoid corrosion problems, improve the quality of the construction and reduce the associated risk and total cost. While GFRP reinforced precast concrete elements exhibit behavior comparable to those reinforced with steel, research on connections between precast elements is limited. This study aims to investigate the performance of bent cap connections for GFRP precast concrete elements for applications in bridge and jetty structures. An experimental investigation was designed and conducted on a large-scale concrete frame constructed out of GFRP reinforced precast concrete elements with four different types of pocketless connections. The effectiveness of using epoxy resin rather than conventional cement grout to accelerate the construction process was investigated. Also investigated were the effect of pre-stressing, the number of connecting reinforcement elements, and the type of reinforcement (i.e. bars and bolts). The frame was subjected to cyclic lateral loading and was tested in two stages. Results and discussion on the general behavior, failure modes, energy dissipation, damping ratio and ductility were presented. The results of the pocketless test frame were also compared with a similar frame tested previously by the same research group where pocket connections were used to transfer moment between the beam and column members. The results showed that using connecting bars/bolts in pocketless connections outperform the behavior of pocket connections. This study concluded that avoiding pockets and providing the integrity of the beam-column joint through bolt/bar connection can improve the general performance of the beam-column connection compared to connections with pockets. This method also increases the speed of construction and simplifies the manufacturing procedure.

Collapse analysis and damage evaluation of typical simply supported double-pier RC bridge under truck collision

Vehicular collision with bridge pier can cause significant structural damage, and even partial or full collapse of the bridge, while the existing work mainly focuses on the vehicular-impact resistance of bridge pier. This study aims to study the collapse process and damage levels of the bridge collided by medium and heavy trucks. Firstly, the refined finite element (FE) model of the typical simply supported two-span double-pier RC bridge is established via the commercial software LS-DYNA, and the adopted material constitutive models and numerical algorithms are validated by comparing with the prototype truck-pier collision test and full-scale drop-weight test on RC beam. Then, the validated FE model is employed to numerically reproduce the actual heavy truck collision accident involving the collapse of bridge, and the dynamic behaviors and collapse process of the collided bridge are analyzed. It shows that, for the present bridge type: (i) truck-bridge collision is not a single impact but a successive impact with bumper, engine and cargo, in which the shear failure on the reinforced concrete bridge pier (RCBP) induced by the engine impact is the dominant factor resulting in the bridge collapse; (ii) during the collision process, the impacted RCBP firstly suffers shear failure at the bottom, and followed by the inclination of the bent cap and superstructure, and then the neighboring RCBP sustains flexible-shear failure at the top, which eventually results in the instability of substructure and collapse of superstructure. Furthermore, a total of 35 truck-bridge collision cases are numerically simulated and assessed, and a new quantitative damage evaluation approach, including the modified damage index, damage level and evaluation criterion, is proposed for the bridge under vehicular collision. In addition, the relationship between the damage level of the collided bridge and superstructure inclination is clarified, which is beneficial for bridge engineers to feasibly assess the vehicular-impact resistance of bridge.

Dynamic responses of highway bridge subjected to heavy truck impact

This study aims to numerically analyze the dynamic responses and damage/failure of bridge substructure during the vehicle-pier collisions, by employing the refined finite element (FE) models of a heavy truck and a simply-supported prototype highway bridge. Firstly, the adopted numerical algorithm and material model parameters to capture both the flexural and shear failures are validated through the simulations of two lateral flexible impactor crash tests. Then, the full-scale FE model of a typical four-span reinforced concrete (RC) bridge with two-pier bents is established, and a high-fidelity heavy truck FE model established previously is improved and further certified by comparisons with the eccentric and aligned full-scale crash test data. Furthermore, a series of numerical simulations are conducted to examine the heavy truck collision process and analyze the failure modes of bridge structure, as well as the parametric influences, including truck mass, impact velocity, and impact angle. Finally, the linear relationships of initial engine momentum, maximal vehicular impact force, 25-ms moving average, sectional force, and lateral displacement are proposed. It indicates that, (i) compared with the *MAT_CONCRETE_DAMAGE_REL3 and *MAT_WINFRITH_CONCRETE, *MAT_ CSCM_CONCRETE can well depict the flexural and shear failure modes of the pier subjected to heavy truck impact in actual accidents; (ii) the ultimate failure of the impacted pier is mainly caused by the impact of the cargo rather than the engine in the heavy truck; (iii) the impact angle significantly amplifies the possibilities of the T-girder falling off and the failure of bent cap, increasing the potential risk of overall collapse of the bridge superstructure.

Experimental study on skew inverted-T bent caps with minimum traditional and skew transverse reinforcing

In this paper, the shear behavior of six full-scale Inverted-T Bent Caps (ITBC) specimens with skew angles of 30°, 45°, and 60° are reported to study the effect of skew angle and rebar arrangement on structural performance. The transverse reinforcement in skewed ITBCs is designed as per the traditional methods the TxDOT Bridge Design Manual LRFD, which conform to the AASHTO LRFD Bridge Design Specifications. The traditional design of flaring the transverse rebar in skew ITBCs brings notable difficulty in manufacturing. An alternative way is to apply uniform skewed reinforcing, which is compared to traditional design in this research. The minimum ratio of transverse reinforcement required by AASHTO LRFD specifications was adopted in this research to investigate the most unfavorable design. The load–displacement curves, the internal force diagrams, the strength and displacement capacity, and the strain measuring results are reported in detail. The specimens with a skew angle of 30° or 45° fail in shear-critical mode, while the specimens with a skew angle of 60° fail in torsion-critical mode. The experimental results show that replacing the traditional reinforcement with the skew reinforcement does not reduce the capacity of ITBCs. The cracking behavior of ITBCs with skew rebar are better than the ITBCs with traditional rebar. Based on the extensive experimental study on ITBCs, general design guidelines for the design and construction of the skewed reinforcing in ITBCs are provided.

Research on Construction Crack Diagnosis and Treatment Technology of Double-Column Large Cantilever Pre-Stressed Bent Cap

This paper took a pre-stressed bent cap of a high pier of a bridge as the research object, expounded the crack type and construction process of the bent cap, combined with the numerical calculation and analysis of the construction process to study the crack generation mechanism and its influence during the construction period of the bent cap. Besides, it gave the repair and treatment technology of jacking and unloading combined with pressure glue, so as to provide reference for the disease diagnosis and treatment of similar bridge structures.

Seismic hazard assessment of existing reinforced concrete bridge structure using pushover analysis

The present paper focuses on the nonlinear static pushover analysis of a 3-span existing RC bridge located in Indian seismic Zone IV as per IS1893-2016 using the Finite Element Method (FEM). The 3D model of the RC bridge is simulated using the FEM technique and pushover analysis is performed to analyze the structure for modal mass participating ratio, performance level, spectral demand, and capacity of the structure. The bridge pier and longitudinal girder are modeled using the two noded beam element and bent cap and abutment of the bridge structure is modeled using the 8 noded brick element. The base of the column is assumed fixed condition. The pushover analysis is performed using Displacement Modification (FEMA 440) and Capacity Spectrum Method (ATC 40). The outcomes of results appear that the considered bridge has inadequate capacity to cope up with any of the desired performance levels because spectral demand is greater than the spectral capacity. The modal analysis of the 3D bridge exposes that it has many closely-spaced modes. The mass participating ratio for the higher modes is not very high. After performing pushover analysis of the exiting RC bridge structure it has been concluded that the existing bridge structure does not meet seismic criteria of spectral demand as per the ATC 40 and FEMA 440, therefore retrofitting is required for bridge component i.e. piers, abutment, and bent cap.

Parametric Study on the Structural Behavior and Failure Mechanism of Skewed Inverted-T Bent Caps

Abstract In the past several decades, the inverted-T bent caps (ITBCs) have been frequently used as an innovative type of bridge superstructure worldwide. In some specimens, the bent caps have to b...

Structural performance assessment of a 60‐year‐old reinforced concrete bent cap

AbstractAs the world's reinforced concrete (RC) civil infrastructure continues to age and exhibit visual signs of distress (e.g., cracking), the challenge of how to process this visual information is becoming increasingly important. While research is ongoing in this field, limited work has been done involving structures that are truly representative of real‐world, aged civil infrastructure requiring assessment. Thus, this paper presents the results of an experimental program and subsequent numerical investigation into the performance of a diagonally cracked, RC bent cap that was removed from a 60‐year‐old bridge in Texas. Extensive work was done to document the cracking behavior and characterize the mechanical properties of the bent cap prior to ultimate load testing. The numerical investigation included both “conventional” methods and nonlinear finite element analysis (with and without consideration of existing damage). Ultimately, the results of the experimental and numerical investigations suggest that, while the bent cap was exhibiting large‐width shear cracks in service, the damage was not indicative of an impending shear failure.

Flexural Behavior of a Fully Prefabricated Lightweight UHPC Bent Cap

Abstract A novel lightweight prestressed ultrahigh-performance concrete (UHPC) bent cap is proposed, consisting of a large cantilevered thin-walled box girder weighing approximately 40% less than n...

Assessment of deep beams with inadequate web reinforcement using strut-and-tie models

The objective of the study summarized in this paper was to evaluate the strut-and-tie design provisions of the 2017 AASHTO LRFD Bridge Design Specifications as a capacity assessment tool for structures with non-code-compliant crack control reinforcement detailing, that is, members which do not contain the minimum volume of reinforcement and/or violate the maximum allowable spacing. A database of 905 deep beam tests was filtered down to 253 tests to complete this evaluation. Six different methods for selecting concrete efficiency factors were investigated using the database. Furthermore, a case study of an approximately 60-year-old bent cap was completed. Ultimately, it was found that, with few adjustments, the current provisions could be used to estimate the capacity of structures with out-of-date reinforcement detailing practices safely and effectively.

Numerical modeling of deteriorated concrete bridge bent caps with externally bonded CFRP retrofit

Deterioration of old concrete bridge bent caps due to spalling and rebar corrosion is a common occurrence. Carbon fiber-reinforced polymer (CFRP) laminate external retrofit is a viable option for regaining such bent cap capacity and serviceability. In this study, a three-dimensional numerical modeling of significantly deteriorated bent caps from a 78-year old cast-in-place bridge in Forney, Texas, was performed. The purpose was to determine the effectiveness of the repair and strengthening process. Numerical models of the bent caps in the original undamaged, damaged, epoxy mortar repaired and CFRP strengthened states were created and calibrated using strain data obtained from full-scale live load testing. The calibrated model strains showed good agreement with those from the load testing. With short span lengths and deep sections, the model strains were small and the effect of the repair/strengthening at modest levels. The neutral axes of the bent cap sections, found from numerical modeling, moved slightly downward after the repair/strengthening process. The model with no section loss showed the highest tensile capacity, and subsequent levels of concrete spalling resulted in progressively smaller capacity. After the first crack initiation, inelastic behavior set in along with crack opening, which explains the increased rate of strains. Truck live loads were adequately represented in the developed numerical models.

Experimental Behavior of Reinforced Concrete and Pretensioned Concrete Bent Caps

AbstractAccelerated bridge construction using precast bridge substructures can enable reduction of traffic disruption, increased worker safety, and increased quality through controlled conditions a...

Experimental Behavior of Pretensioned Bent Caps with Internal Voids for Weight Reduction

AbstractPrecast bent caps offer the opportunity to reduce onsite labor and materials and to accelerate the speed of construction. For many bridges, the weight is manageable for shipping and placeme...

Research on the Influence of the Stiffening Plates on the Stress of Hold Hoop of Bent Cap

In order to improve the mechanical behaviour of bridge steel hoops, the plate shell finite element models of several steel hoops were established by using the general finite element software ABAQUS. Through changing the structural parameters of the stiffening plates, the influence of the stiffening plates on the mechanical properties of the steel hoops was explored. The calculation results show that the stress distribution at both ends of the steel hoop is uneven and there is a phenomenon of stress concentration. The spacing of stiffening plates has great influence on the mechanical properties of steel hoop. Some measures to improve the mechanical properties of steel hoop are given.

LBJ express project: an example of accelerated bridge construction techniques for large and complex projects

ABSTRACTThe I-635 Managed Lanes project, also known as the LBJ Express, was a USD$2.7 billion, 22 kilometres highway reconstruction that more than doubled the capacity of the existing corridor. It is the largest significant transportation improvement project in northern Texas (USA), with the goal to relieve severe congestion along the I-635 and IH-35 in a dense urban area of Dallas. The LBJ Express project has over half million square metres of deck, as large as 120 football fields, more than 5,700 precast beams, 100 km of piling, and over 300,000 square metres of retaining walls with 7 million cubic metres of earthworks, this article presents the innovative design approach and the accelerated bridge construction techniques implemented for the structures, which was an exceptionally complex project. Through the use of innovative structural solutions for the bent caps (headstocks) and straddle bents (extended headstocks), skilled design optimisation, and careful construction analysis, including the ad-hoc design of launching gantries, the team was able to accelerate the bridge construction ensuring traffic flows in excess of 270,000 vehicles per day.

Full‐Scale Testing of Precast Concrete Bridge Using Internal Connector in Negative Moment Region

Conventional concrete marine structures are difficult to construct on site and can cause pollution of the environment. Therefore, concrete marine structures require the development of methods that can minimize the amount of construction that needs to be performed in the field. This study aims at facilitating assembly through the use of precast girders and precast bent cap and at improving construction efficiency by minimizing cast‐in‐place structures. The proposed bridge can reduce the negative moment of the girder through continuous connection. In this study, a full‐scale connection specimen with a 10.0 m span was fabricated, and the behavior of the precast connection was evaluated by performing a negative moment performance test. In addition, a finite element model was developed to compare each loading step with the test results. The failure mode of the specimen was that the reinforcing bars yielded at the joint of the cast‐in‐place section and the precast girder. As a result of the study, this proposed bridge is easy to construct because it minimizes the process of connecting the coping and girders using the internal connector. Also, the proposed bridge has 155% higher structural performance than the designed load at the negative moment connection part.