Bridge Specimen Research Articles

Shaking Tables Test on Seismic Responses of a Long-Span Rigid-Framed Bridge Considering Traveling Wave Effect and Soil–Structure Interaction

The traveling wave effect and soil–structure interaction have significant influence on the seismic response of large-span bridges with complex site conditions. In this paper, a 1/10 scaled-down large-span rigid-framed bridge model was designed and fabricated, and a shaking tables test considering the traveling wave effect and soil–structure interaction was carried out on a large-scale continuous rigid bridge model by a real-time substructure hybrid test technique. Influences of the traveling wave effect and soil–structure interaction on the seismic responses of the rigid-framed bridge specimen were systematically analyzed with experimental data. The test results showed that when the apparent wave speed was small, the traveling wave effect increased the seismic responses of the rigid-framed bridge. With the increase in apparent wave speed, the structural response under traveling wave excitation and uniform excitation was basically the same. The SSI effect lead to a great change in the seismic input peaks and spectral characters at the bottom of the pier, and increased the seismic responses of the rigid-framed bridge. When both traveling wave and the SSI effect were considered, there was a phase difference in the seismic excitation. The dynamic responses of a continuous rigid-framed bridge could not be simply obtained by superposition of the separate traveling wave effect or SSI effect. Meanwhile, the real-time substructure test method in this paper solved the problems that the traditional soil box experiment cannot be applied to the test of a large-scale model, the soil and bridge structure find it difficult to meet the unified similarity ratio, and the boundary conditions are difficult to simulate accurately.

Predicting low-cycle fatigue-induced fracture in reinforcing bars: A CNN-based approach

In low-damage structures such as rocking columns in bridges where the column ends are protected from spalling through confinement, the longitudinal reinforcing bars undergo reversing strain cycles, leading to fracture due to low-cycle fatigue. Several challenges arise due to the unsuitability of strain gauges to measure high strain ranges, in addition to the inability to visually inspect reinforcing bars after seismic events due to the use of confining details at the ends. Building on previous research that identified the fracture of reinforcing bars using column ends’ rotation to estimate reinforcing bars’ strains in conjunction with low-cycle fatigue models, this paper presents substantial development to predict the low-cycle fatigue-induced fracture of reinforcing bars using convolutional neural networks (CNNs) solely from strain time series data. The fracture was identified through strain measurements measured from a shake table testing of a quarter-scale, two-span resilient bridge specimen subjected to seismic excitations at the Earthquake Laboratory at the University of Nevada, Reno. The developed CNN model utilizes the Markov Transition Field technique to encode the strain time series into images and then uses the encoded images as input for channels in the input layer. These images are stacked in sequence to create a 3D array with 11 channels, one for each of the 11 different earthquake excitations that caused the damage. A three-layered CNN architecture with Adam optimizer was employed in training the model, achieving an accuracy of 100 % during training and more than 96 % during testing. To evaluate the model's performance, three distinct training/testing scenarios are proposed. The results demonstrate the efficacy of using CNNs to detect and characterize damage in structural elements using strain data. This approach has the potential to revolutionize the estimation of material fracture due to low-cycle fatigue in scientific fields using only the recoded strains.

Pure Effect of Temperature on Rectangular and Trapezoidal Box-Girder Bridges – A Finite Element Investigation

Since the temperature distributions on concrete bridges are nonlinear, they lead to the self-equilibration of the stress distributions. To have a discussion about strains, deflection, and moment brought on by temperature changes. Three-dimensional finite element, Computers and Structures, Inc (CSI) Bridge finite element software is used to analyze 2 box girder bridge specimens; rectangle and trapezoidal cross section. The box girders were same in depth, span length, cross section details and material properties. These specimens were subjected to different temperatures values. They were tested under AASHTO thermal loading and temperature gradient specification. The finding showed that changing the temperatures at a constant rate during the days of the year, by increasing and decreasing, affects by a fixed amount all of the values of deflection, stresses, and moments, for each of the rectangular and trapezoidal sections by the same amount. Through the values of deflection, stresses and moments for both the trapezoidal section and the rectangular section, it can be seen that the trapezoidal section is affected by the temperature change in a lesser way than the rectangular section. That happened because the rectangular section is affected by the temperature gradient along the section in a greater proportion than the trapezoidal section by 16% in stresses and 56% in terms of deflection.

Fatigue performance of ECC link slab incorporated full RC girder joint-free bridges

The use of link slab (LS) made of Engineered Cementitious Composite (ECC) in the construction of joint-free bridge deck can meet structural performance requirements and enhance durability to minimize life cycle costs. Studies documented in the literature to date have been limited to composite steel-concrete I-deck girder bridges despite their commonly used reinforced concrete (RC) girder counterparts in construction. This paper deals with two span full RC deck girder joint-free bridges with ECC link slab (ECC-LS) constructed and tested under static and fatigue loading up to 1,000,000 cycles at 4 Hz subjected to mean stress level of 40% of girder ultimate load, followed by post-fatigue static loading to failure. Residual load, deflection, moment, rotation, stiffness, and energy absorbing capacity of fatigued bridge specimens are compared with its virgin (non-fatigued) counterparts to assess structural performance. Experimental moment capacities are compared with those obtained from existing analytical equations. The comparative performance of joint-fee bridge with RC deck girder is compared with its composite steel-concrete I-girder counterpart to assess its feasibility of construction.

Assessment of Residual Stresses in Laser Powder Bed Fusion Manufactured IN 625.

Residual stresses pose significant challenges in the powder bed fusion of metals using a laser (PBF-LB/M), impacting both the dimensional accuracy and mechanical properties. This study quantitatively analyzes deformation and residual stresses in additively manufactured Inconel 625. Investigating both as-built and stress-relieved states with varied scanning strategies (90°, 67°, strip, and 90° chessboard) in PBF-LB/M/IN625, distortion is evaluated using the bridge curvature method. Quantitative measurements are obtained through 3D laser surface scanning on pairs of bridge specimens-one measured before and after detachment from the build plate, and the other undergoing stress-relieving heat treatment at 870 °C for 1 h. The findings reveal that, among as-built specimens, the 90° and 90° strip strategies induce the least distortion, followed by the 67° and chessboard 90° strategies. Furthermore, stress-relief treatment significantly reduces residual stress levels. After post-treatment, the deformation in X-axis samples with 90° and 90° strip strategies decreases by 39% and 42%. In contrast, the samples with the 67° and 90° checkerboard strategies exhibit more pronounced reductions of 44% and 63%, respectively. These quantitative results contribute useful insights for optimizing PBF-LB/M/IN625 processes in additive manufacturing.

Impact of asymmetrical corrosion of piers on seismic fragility of ageing irregular concrete bridges

This article investigates the seismic fragility of ageing irregular multi-span reinforced concrete (RC) bridges. Different irregularity sources are considered, including: (i) substructure stiffness irregularity arising from the unequal-height piers, (ii) substructure stiffness irregularity arising from the spatially variable (asymmetrical) corrosion damage of piers and (iii) irregular distribution of effective tributary masses on piers of varying heights. To this end, a three-dimensional nonlinear finite element model is developed for multi-span RC bridges and verified against a large-scale shake table test results of a two-span concrete bridge specimen available in the literature. Nonlinear pushover, incremental dynamic and seismic fragility analyses are performed on three groups of two-span RC bridges with different configurations. Moreover, a time-dependent dimensionless local damage index is employed to evaluate the failure sequence and collapse probability of selected bridge layouts. The analysis results of the three studied irregularity sources show the considerable significance of spatially variable corrosion of bridge piers and substructure irregularity on the failure sequence of piers and seismic fragility of multi-span RC bridges. Furthermore, analysis outcomes show that uneven corrosion of piers triggers an unbalanced distribution of seismic ductility demands and irregular seismic response of equal-height multi-span RC bridges.

The origin of modern marlins (Teleostei: Istiophoridae): new fossil evidence from the Lower Miocene of Austria

ABSTRACT We report the oldest fossil record of Istiophoridae from the Northern Alpine Foreland Basin (Western Paratethys) in Pucking, Austria (Lower Miocene, lower Aquitanian, ∼22.4 Ma). The studied specimen consists of fragments of five articulated vertebrae and a partially preserved second dorsal fin. We found that the Pucking specimen is only surpassed in age by an isolated vertebra from the Chandler Bridge Formation (South Carolina, U.S.A.), with ∼24.7–23.5 Ma. Pucking and the Chandler Bridge Formation differ in age by ∼1.1–2.6 Ma. The fossil istiophorid from the Chandler Bridge Formation was considered controversial due to the large gap in the fossil record between the first appearance of Istiophoridae and the last appearance of any other extinct billfish clade. Here we report that Pucking (Lower Miocene) and South Carolina (Oligocene) share the occurrence of Istiophoridae, †Xiphiorhynchinae (Xiphiidae), and †Aglyptorhynchinae (†Palaeorhynchidae). Our finding demonstrates that the coexistence of different groups of billfishes is maintained over time and that the Chandler Bridge specimen is a reliable record. Our work closes a temporal gap of ∼4.4 Ma between the previously recognized oldest Istiophoridae (∼18 Ma) and the last appearance of †Xiphiorhynchinae and †Aglyptorhynchinae. This result supports a longer evolutionary history for Istiophoridae, establishes continuity in the billfish fossil record, and is significant for future time calibrated phylogenies.

Seismic vulnerability analysis of irregular multi-span concrete bridges with different corrosion damage scenarios

This paper investigates the seismic performance and vulnerability of multi-span Reinforced Concrete (RC) bridges with unequal height piers exposed to varied corrosion damage scenarios. An advanced three-dimensional nonlinear finite element modelling technique is developed and verified with available experimental results of a reference shake table test on a large-scale RC bridge. In addition to the pristine state of the reference bridge, various hypothetical corrosion scenarios, including the symmetrical and asymmetrical corrosion of piers, are considered. Several nonlinear analyses, including the pushover and Incremental Dynamic Analysis (IDA) approach, are performed to evaluate the seismic behaviour and vulnerability of hypothetical RC bridge specimens. The influence of symmetrical and asymmetrical corrosion of piers on nonlinear dynamic behaviour and failure mechanism (both in the global and local scales) of studied bridges are then discussed. Finally, the IDA results are used to develop time-dependent fragility curves. The analyses show that seismic vulnerability of a deteriorated irregular multi-span RC bridge crucially depends on the corrosion scenario of its piers, where the unbalanced distribution of seismic ductility demand might be regulated/intensified by different corrosion scenarios. Moreover, some corrosion scenarios resulted in near-synchronised failure of unequal height piers.

Experimental and simulation studies on the mechanical performance of concrete T-Girder bridge strengthened with K-Brace composite trusses

In this paper, a new transverse strengthening method was proposed for T-girder bridges with K-brace composite trusses. A series of experiments and simulations were conducted to study the strengthening effects under four different loading conditions, including non-eccentric loading, transverse eccentric loading, longitudinal eccentric loading, and bidirectional eccentric loading modes. Altogether four groups of specimens were fabricated and studied. Each group consisted of a control specimen and a strengthened one. Furthermore, the concrete plastic damage model was used to simulate the mechanical behaviors of the specimens. The results showed that such a strengthening method could significantly upgrade the mechanical behaviors of the T-girder bridge specimens, especially the local deformation and crack propagation manner of the T-girder. Compared with the control specimen, the deflection of concrete T-girder bridge specimen strengthened with the K-brace composite trusses was significantly decreased, with a maximum reduction of 38.6% under the prescribed load. Moreover, the K-brace composite trusses can markedly better the load distribution and improve the failure modes of the specimens, where the crack widths decreased even by 44.0%. They distributed along the beam more evenly. So, it provides a new method to strengthen and upgrade the mechanical properties of T-girder bridges.

Seismic Response of a Cable-Stayed Bridge considering Non-uniform Excitation Effect: Model Design and Shake Table Testing

In the absence of intensive tests on the cable-stayed bridges under non-uniform excitation, this study provides a practical and accurate approach to investigate the seismic response of cable-stayed bridges considering spatially varying earthquake inputs. The cable-stayed bridge model with a scale ratio of 1:120 was designed and tested on a newly-developed dual shake table system. Firstly, the modal test was conducted to evaluate the accuracy of the designed specimen. Secondly, both the same input cases and the different inputs cases were executed to study the wave passage effects on bridge specimen's dynamic response. Lastly, the effects of non-uniform excitation and site classification on the experimental bridge's seismic performance were studied with test results of various soil condition cases. The test results showed that the bending of the girder was magnified, while the swing of the tower was subdued when the effect of wave propagation was considered. Moreover, compared with the same input cases, the different inputs cases reported a larger response to the extent of 80%. Regarding the effects of site conditions, it was concluded that the site of soft soil had more influence on the dynamic responses of such bridge structures than that of the firm soil site.

Real-Time Hybrid Simulation of a Single-Span Girder Bridge Using a Shake Table Coupled with an Actuator

This paper recounts a real-time hybrid simulation (RTHS) that employed a shake table coupled with an actuator to evaluate the seismic performance of a single-span girder bridge. The test specimen for this RTHS was a scaled single-span girder bridge, which was subjected to Loma Prieta excitation in the test. In the RTHS, the bridge specimen, which lacked mass on top of the bridge deck, was physically tested by a shake table and an actuator, whilst the mass on the bridge, as well as the pile foundation and the soil were modeled numerically. OpenSEES was used for numerical modeling and OpenFresco was used for the communication between the test system and numerical model. An adaptive time series (ATS) technique was employed to compensate for time delay in the RTHS. In this way, a novel bridge engineering RTHS application case composed of shake table and actuator control was presented. To validate the results of the RTHS, a shake table test (STT) of the bridge structure with full mass on the bridge deck was conducted correspondingly. Comparing the RTHS and STT results, it can be concluded that acceleration histories, bearing deformation histories, and strain histories of the selected points matched well. The application of RTHS to assess the seismic behavior of the single-span girder bridge was reasonably verified in this paper.

Experimental Research and Finite Element Analysis on Blast Damage of Unreinforced Steel Fiber Concrete T-beam Structures

To reveal the dynamic behavior and damage mechanism of unreinforced concrete T-beam bridge under blast loads, three specimens were designed. Dynamic strain, acceleration and acoustic velocity pro- and post-blast of three specimens were measured respectively, and the generation, development process and distribution condition of cracks were investigated. The results indicated that ribbed slab fracture failure was a key to the unstable failure of the whole T-beam bridge specimen. Adding steel fiber evenly to the T-beam bridge deck can change the degree of blast damage from “severe damage” to “moderate damage”, which improves the explosion anti performance of the bridge structures. The damage evaluation results provide the basis for damage repair and reinforcement treatment after explosion.

Benchmarking Unmanned Aerial Systems-Assisted Inspection of Steel Bridges for Fatigue Cracks

Inspection agencies have been increasingly implementing unmanned aerial systems (UAS) for bridge inspections. Currently, UAS are typically used for long-range monitoring and surveillance tasks, but bridge managers are hopeful that they may be utilized for detailed inspection, such as condition assessments and the inspection of fracture critical members (FCMs) in the near future. As an assistive tool for visual inspections, the accuracy of UAS-assisted inspections is unknown. This study investigates the relationship between the characteristics of the individual inspectors and a set of performance metrics associated with UAS-assisted FCM inspections. Four bridge inspectors used a UAS to inspect a series of full-sized bridge specimens with known fatigue cracks. The inspection videos were later shared with 19 bridge inspectors for a desk review. The performance of each inspector was evaluated and compared with the results from 30 hands-on inspections of the same specimens. The results showed that an inspector’s past experience with UAS, licensure, and academic degree could have a significant influence on one or more of the three defined performance metrics. The comparison between the results of the UAS-assisted inspections and the hands-on inspections revealed that crack detection was comparable. However, the hands-on inspections were more accurate.

Robust characterization of anisotropic shear fracture strains with constant triaxiality using shape optimization of torsional twin bridge specimen

In-plane torsion test has been drawing attention as an effective strategy to obtain good shear properties. Herein, a framework of shape optimization for a twin bridge specimen is presented to improve the performance while ensuring better machinability. The framework includes the consideration of material anisotropy and the determination of design variables. In this study, TRIP1180 sheet was employed as a target material. The optimized design was verified by an actual in-plane torsion test. The experimental results demonstrate that the proposed framework can optimize the shape of the twin bridge for maintaining zero triaxiality up to fracture occurrence.

Research on Longitudinal Collapse Mode and Control of the Continuous Bridge under Strong Seismic Excitations

Bridge collapse events are common in major earthquakes around the world, among which continuous girder bridges are the most involved. In order to explore the collapse mechanism of a continuous girder bridge in an earthquake, the collapse mode of a two-span continuous girder bridge specimen which had been studied by the shaking table test was analyzed. Then, on the basis of the conventional plate rubber bearing system, the collapse control strategies which were high damping rubber bearing, fluid viscous damper, lock-up clutch control methods were discussed. It is found that high damping rubber bearing can delay the collapse time but the collapse mode remains the same; lock-up clutch has the best displacement control effect for the superstructure, but its energy consumption performance is not as good as that of a fluid viscous damper; high damping rubber bearing is quite suitable for protecting the substructure under short-period ground motion to avoid the bridge collapse caused by the failure of piers; fluid viscous damper and lock-up clutch are suitable for protecting the superstructure under long ground seismic motion to avoid the bridge non-use resulted from girder lowering; three collapse control methods can improve the anti-collapse ability of the bridge specimen, although no matter which control method is used, the bridge specimen may still collapse under strong earthquakes, but the target of postponing collapse time can be realized by means of various effective control methods.

Deep learning models for bridge deck evaluation using impact echo

Impact echo (IE) is a common nondestructive evaluation (NDE) method to detect subsurface defects in concrete bridge decks. The conventional approach for analyzing the IE data requires user expertise to define analysis parameters that could hinder broad field implementation. In this paper, the feasibility of using deep learning models (DLMs) for autonomous subsurface defect detection in bridge decks using IE has been investigated. A set of eight laboratory-made reinforced concrete bridge specimens with artificial defects were constructed at the Federal Highway Administration Advanced Sensing Technology NDE laboratory. A total number of 2016 of IE data was collected from these specimens. A one-dimensional (1D) convolutional neural network (CNN), and a 1D recurrent neural network using bidirectional long-short term memory units, were developed and applied on the IE data. In addition, two-dimensional (2D) world renowned CNNs were applied on the 2D representatives of the IE data, i.e., spectrograms. The proposed 1D CNN was the most accurate model achieving an overall accuracy of 0.88 by classifying 0.70 of the defects and 0.95 of the sound regions correctly. The proposed 1DCNN was superior to previous machine learning models that were previously used for IE classification. The results of this study showed the feasibility and the potentials of the DLMs for subsurface defect detection.

Experimental Study on Seismic Performance of Concrete Continuous Bridge with HDR Bearings

Several earthquakes have shown that concrete continuous bridges suffer from major damage and permanent deformations. This paper investigates the use of high damping rubber (HDR) bearings to improve seismic performance of concrete continuous bridge. The shaking table array test of a two-span isolated continuous bridge specimen with 1:3 scale was carried out to study the seismic response characteristics of the continuous bridge with HDR bearing isolation. The experimental results were compared with the seismic response of non-isolated continuous girder bridge specimen. The results indicated that the seismic response of continuous girder bridge varied with input ground motion, direction and PGA. In terms of HDR bearing isolation system, there was time lag between seismic responses of the upper and lower structures, and the acceleration of the side pier was larger than that of the middle pier while displacement response has better symmetry than non-isolated specimen. The effect of vibration isolation varied with shaking frequency, intensity and direction. The seismic damage was mainly concentrated in the bottom of the middle pier column and the middle bearing. The horizontal shear capability model of the HDR bearing is proposed as the bilinear restoring force model. The numerical analysis model of the bridge specimen established on the simplified bearing model can reflect the damping effect of the HDR bearing on the concrete continuous bridge.

Application of the Euler Motion Amplification Algorithm to Bridge Vibration Analysis

In this study,the Euler subtle motion amplification (MA) algorithm is applied to bridge vibration analysis. First,a series of digital images of bridge structures is continuously captured using an ordinary digital camera. Then,the micro-vibration of the bridge is amplified using the related algorithm of Euler MA. The time history image of the bridge specimen under conventional video sampling frequency is obtained by decomposing the amplified digital image. Lastly,the holographic dynamic displacement measurement results of the test bridge are obtained by analyzing the edge features of the marking points in the image sequences. The proposed analysis method is feasible compared with the displacement sensor and dial indicator. It can meet the application requirements of bridge dynamic displacement measurement. It can also perform preliminary quantitative analysis of several vibration characteristics of bridges and identify the micro-vibration displacements of a bridge structure.

Modelling of debonded reinforcement in ABC connections designed for seismic zones

There are multiple design and detailing approaches for accelerated bridge construction (ABC) in seismically active zones. One of the most common methods is the use of precast components. When using precast components, a technique that can improve seismic behavior is debonding of the longitudinal reinforcement and/or prestressing strands; this can achieve the following objectives: (1) reducing concrete stress concentration, (2) promote rocking behavior, and (3) controlling/delaying the fracture of longitudinal bars. One example of debonding column reinforcement for ABC systems was a pretensioned rocking system that was tested using the shake table facility at the University of Nevada, Reno in 2014. A new numerical modelling strategy was developed to model the debonded reinforcement using external elements explicitly modelled and connected to the column element using rigid links at their proper arms. A numerical model was developed using Opensees for the selected bridge specimen by implementing the suggested strategy to capture the measured response in global and local domains. By incorporating a fatigue material with the reinforcement steel model, this strategy showed excellent agreement with the measured response. Then, the calibrated numerical model was used to explore methods to improve the performance of the system by delaying reinforcing steel fracture. The parametric studies show that increasing the bar sizes and the locally debonded length of the reinforcement were both effective strategies to reduce and delay bar fracture.

Shaking table test of a high-speed railway bridge with a new isolation system

With the rapid development of high-speed railway bridge construction in seismic areas, it is necessary to investigate the seismic performance of these bridge structures. A new type of seismic isolation system with function separation is presented in this study. By considering an actual high-speed railway bridge as a representative example, the performance parameters of the new type of isolation system were numerically optimized. Based on the results of optimization design, a shaking table test was performed on a reduced scale high-speed railway bridge specimen employing the new isolation system. The comprehensive optimization design and the experimental results demonstrate that the new isolation system can minimize the bending moment of pier while ensuring that the pier’s seismic response in terms of acceleration and displacement is within the allowable range of normal operation of high-speed railway bridges. The proposed new isolation system is expected to offer a cost effective and safe solution in the design of high-speed railway bridges.