Bridge Collapse Research Articles

Frequency analysis of extreme scour depths at bridge piers and their contribution to bridge collapse risk

ABSTRACT Bridge failures due to scour occur more frequently than expected, although bridge design considers conservative scenarios, evidencing a stochastic scour behaviour and the need for improvements in current design procedures. In this paper, a new method for determination of design local scour depth at bridge piers is proposed. The results show that peaks-over-threshold series are better suited than annual-maximum series of maximum scour depths for frequency analysis. Extreme scour depths follow the heavy-tailed Cauchy distribution. Scour depths with a 100-year return period resulted in 22 to 202% of the equilibrium scour depth currently used in design, evidencing the need for a different criterion to select the design scour depth. The proposed method computes the design local scour depth based on its probability of occurrence, introducing a novel probabilistic approach in bridge design for enhanced infrastructure risk management compatible with multi-hazard analysis.

Research into stress-strain state of the mass under open pit with a change in the open-pit bottom width

Purpose. Studying the stress-strain state of the rock mass under the open pit, taking into account the change in the open-pit bottom width in order to reveal the geomechanical state and determine the safe parameters of the rock bridge. Methods. The peculiarities of the stress-strain state formation in the transition zone have been studied according to the methodology using numerical research methods and taking into account the geological strength index (GSI). Using this index, it is possible to take into account rock fracturing, water cut, lithology and other strength indicators, due to which there is a correct transition from the rock sample strength to the mass strength. Findings. Based on the numerical modeling results, it has been determined that an increase in the open-pit bottom width leads to a decrease in the zone of tensile stresses concentration in the arch pillar of the stope block. This, in turn, has a positive effect on the rock bridge stability, that is, the probability of the rock bridge collapse does not increase with an increase in the width of the open-pit bottom. Originality. For the first time, the dependence has been obtained of the horizontal stresses σ3 distribution at the stages of the open-pit bottom expansion at the Akzhal Zinc-Lead Mine. This makes it possible to realistically predict changes in the geomechanical state of the rock bridge depending on the width of the open-pit bottom. Practical implications. When predicting the change in the stress-strain state in the transition zone and determining the rock bridge safe parameters, it is possible to reduce the probability of their destruction and make timely management decisions on safe conditions for mining the reserves.

Probing inside a charged hairy black hole in massive gravity

In this paper, we investigate the internal structure of a charged hairy black hole solution in the non-linear massive gravity. We first consider the impact of various configurations of massive gravity on the condensate operator and then probe the black hole interior dynamics. Like a standard holographic superconductor system, just below the critical temperature, the interior evolves through several distinct epochs, including a collapse of the Einstein-Rosen bridge, Josephson oscillations of the scalar field, and finally a Kasner (or Kasner inversion) cosmology. However, for the large massive gravity parameter, we see distinguishing features for the interior dynamics. In this regime, at a given temperature, the Einstein-Rosen bridge collapse and subsequent Josephson oscillations epochs completely disappear from the interior dynamics and the final Kasner cosmology epoch starts exactly after the would-be inner horizon and the system does not experience the Kasner inversion epoch.

Field test and probabilistic vulnerability assessment of a reinforced concrete bridge pier subjected to blast loads

Bridge piers have a high risk of being attacked in wartime, which has the potential to trigger progressive bridge collapse. This study aims to predict the failure probability of reinforced concrete (RC) piers exposed to military attack scenarios. Field explosion test and axial compression test were conducted to investigate the damage and post-blast performance of the RC pier first. Then, the uncertainties sourcing from the weapon accuracy were investigated. A performance-based (PB) vulnerability probabilistic assessment framework is developed which combines the Monte Carlo simulation (MCS) with a full-scale finite element (FE) model which was verified with test results. A probabilistic vulnerability assessment of a typical RC pier subjected to stochastic blast loading is conducted, and the vulnerability curve corresponding to three performance levels is developed. In addition, the damage modes and post-blast performance of the RC pier under blast loading are analyzed. Results show that the blast-induced damage to an RC pier had a significant influence on the axial bearing capacity, and the pier presents different damage modes at different scaled distances, which has a critical value of 0.65 m/kg1/3 between local and global damage modes. The failure probability of the pier corresponding to different performance levels increased with an increase in the TNT charge. The pier’s probability of collapse is less than 20 % when the TNT charge weight does not exceed 500 kg.

Use of spur dikes with different permeability levels for protecting bridge abutment against local scour under unsteady flow conditions

Local scour around abutments is one of the most important reasons for a bridge collapse, making it a major concern for hydraulic and river engineers. Available studies on scour control around abutments have been limited to steady flow conditions. In this light, the present experimental study investigates using a single spur dike with different levels of permeability (0%, 35%, 50%, and 65%) to reduce scour around a short vertical-wall abutment (abutment length/flow depth ≤ 1) under unsteady flow conditions. The hydrographs with Gaussian distribution and different base flow times (i.e., duration of 15, 30, 60, and 90 min) were used to simulate the unsteady flow. Abutment scour depth variations with time showed that the final scour depth always appeared after the peak discharge of the hydrograph regardless of whether a spur dike was used. It was shown that the spur dike has successfully reduced local scour around the abutment. The maximum depth of scour hole around abutment was reduced by 47%, 32%, and 11%, when spur dikes with 35%, 50%, and 65% permeability were, respectively, used. Using an impermeable spur dike not only prevented the scour upstream nose of the abutment but also led to some deposition that raised the bed level by nearly 0.47 La (where La is the abutment's length) in that area. However, the maximum depth of scour hole around the impermeable spur dike was nearly identical to that occurred around the abutment for the experiments without a spur dike, making it necessary to arrange for scour protection around the spur dike.

Interior of helical black holes

We study the interior structure of five dimensional neutral helical black holes in Einstein gravity and charged helical black holes in Einstein-Maxwell gravity. Inside the neutral helical black holes, the systems evolve to a stable spacelike Kasner singularity. The metric field related to the helical deformation strength exhibits oscillation behavior close to the horizon at low temperature and small helical deformation strength. Inside the charged helical black holes, we show that the inner Cauchy horizon can not exist. The systems also evolve from the horizon to a stable Kasner singularity. We find that the oscillations can exist and there is a special feature that the oscillations occur near the horizon and before the collapse of the Einstein-Rosen bridge for the charged helical black holes.

Explaining the Flood Behavior for the Bridge Collapse Sites

Given the increasing intensity and frequency of flood events, and the casualties and cost associated with bridge collapse events, explaining the flood behavior for the collapse sites would be of great necessity. In this study, annual peak flows of two hundred and five watersheds, associated with two hundred and ninety-seven collapse sites, are analyzed. Generalized Extreme Value distribution together with other statistical analyses are used to derive and analyze the shape parameters of the distributions which represent the extremeness of flood events. Random forest mechanism is employed in order to identify the predictor variables (and the associated importance levels) for the shape parameters. Peak flows are also classified in order to find the extremes and the associated return periods. The results indicate that most of the bridge collapse sites across different physiographic regions, i.e., Appalachian Highland, Central Lowland, Coastal Plain, and Interior Highlands, exhibit common characteristics such as (a) variation of important predictor variables, (b) human interference, (c) extremeness of flood events similar to the regions with hydrologic heterogeneity, and (d) frequent occurrence of extreme flows. These results indicate a commonality in flood behavior, as stems from specific settings, for the collapse sites studied. The findings instigate the revisiting of the bridge design practices and guidelines and provide some basis to assess the risk of future collapse.

Evaluation Of Post Tensioned Bridges’ Tendon Ducts By NDT And Minor Invasive Measures

This presentation introduces the author’s accumulated long experience in applying state of the art NDT methods for post tensioned bridges’ grout injection evaluation together with minor invasive investigations for validating NDT results and for evaluation of prestressing system condition including duct’s grout injection and prestressing steel corrosion. The injection grout (cementitious based grout) has a crucial role in protecting the prestressing steel against corrosion caused by different environmental stresses. Corrosion of prestressing steel may cause dangerous fracture mechanisms such as hydrogen embrittlement and stress corrosion cracking. In addition, the injection grout has the important role of intermediating the prestressing forces from the prestressing steel to the concrete structure. Therefore, successful grout injection is critical for the correct structural functionality of a post tensioned bridge. The introduced NDT methods (ultrasound tomography and Impact-Echo), used together with invasive investigations, have already been successfully applied by the author in over 110 inspections of post tensioned bridges in the past 12 years, mostly in Finland. In situ evaluation of NDT testing results pinpoint the logical locations for invasive investigations. These include opening of tendon ducts and evaluation of the steel duct, injection grout and condition of the prestressing steel (ocular corrosion evaluation). There are thousands of aging post-tensioned bridges, frequently on critical transportation routes, built mostly in the 1960s-1970s. Occasionally the prestressing was applied in a faulty manner due to various reasons. In some cases, when stress from the environment is added to faulty construction, the consequences may be severe and possibly affect the safe usage of bridges. Faults and damages in prestressing systems are hidden from the eyes. Therefore the severity of the situation is unknown and it may result in extreme cases even in sudden collapse of bridges - as witnessed in the 2018 catastrophic collapse of the Morandi Bridge in Genoa Italy where apparently, according to publications, a post tensioned main structural part failed. Significant part of the aged post tensioned bridges have already reached renovation time. Therefore, their condition should be assessed. Bridge condition evaluation usually involves “traditional” inspection techniques which do not provide information on the internal prestressing system even though it has a crucial role in the bridge load carrying capacity. The abovementioned NDT methods combined with invasive investigations enable this critical evaluation task. In addition, those abovementioned NDT methods are suitable as quality assurance measures in newly constructed post tensioned bridges for ensuring long service life of bridges since day one.

Investigation of Bridge Collapse Phenomena due to Heavy Rain Floods: Structural, Hydraulic, and Hydrological Analysis

Investigation of Bridge Collapse Phenomena due to Heavy Rain Floods: Structural, Hydraulic, and Hydrological Analysis

Detection of Nut–Bolt Loss in Steel Bridges Using Deep Learning Techniques

The early detection of bolts and nuts’ loss on bridges has a huge tendency of averting bridge collapse. The aim of this research is to develop a novel framework for the detection of bolt–nut losses in steel bridges using deep learning techniques. The objectives include: to design a framework for the detection of nuts and bolts and nut holes using deep learning techniques, to implement the designed framework using Python programming, and to evaluate the performance of the designed framework. Convolutional neural network (CNN) and long- and short-term memory (LSTM) techniques were employed using 8 × 8 blocks of images of bridges as inputs. Based on the proposed models, which considered the CNN in its ordinary form, and combined with the LSTM and You Only Look Once (YOLOv4) algorithms, the CNN achieved average classification accuracy of 95.60% and the LSTM achieved an accuracy of 93.00% on the sampled images. The YOLOv4 algorithm, which is a modified version of the CNN with single forward propagation, was utilized, and the detection accuracy was 76.5%. The relatively high level of detection accuracy recorded by the CNN is attributed to its stepwise extraction by convolution and pooling processes. However, a statistical test of the hypothesis at the 5.0% level of significance revealed that there was no statistically significant difference between object detection and classifications among the models used in the built framework. Therefore, the use of the CNN model is recommended for the detection of nuts and bolts and nut holes on steel truss bridges for effective structural health monitoring (SHM) purposes based on its high level of detection accuracy and speed.

The Z, C or I High Scale Stright Girder Section to Light Up the Miami Pedestrian Bridge Collapse: Hard Price to a New Structural Typology

This document presents some Spaniards successful realizations for girders using the Z and the C section in big scale. It is tried to describe the way they work under torsion actions in a simple way. It is done a theoretical extrapolation to describe and quantify the Miami pedestrian bridge collapse causes under the available documentation the author had got in the moment it is done.

Fragility analysis of existing prestressed concrete bridges under traffic loads according to new Italian guidelines

AbstractAfter the 2018 collapse of Morandi highway bridge in Genova, new Italian guidelines (GL) were issued for prioritization of safety evaluations and retrofit interventions on existing bridges. Among several novelties, GL introduced new traffic load models (TLMs) which can be adopted for existing bridges in case of noncompliant safety checks according to the Italian building code (NTC) provisions. In this study, a class of simply supported, beam‐type, prestressed concrete bridge decks built between 1970 and 1980 in Italy is considered. Assuming geometric, material, and load random variables together with consideration of capacity model uncertainty, Monte Carlo sampling technique was implemented in MATLAB in order to randomly generate deck models and to evaluate their traffic‐load fragility. Fragility analysis was carried out to compare vulnerability levels of existing Italian bridges under different load patterns provided by GL and NTC. In addition to a prescribed TLM, the sensitivity of fragility to bridge usage limitations, such as reduced distance of external load lane from kerb or reduced number of lanes, was also quantified to support decision‐making by road management companies. In the final part of the study, the annual failure probability of selected bridges was estimated using a European weigh‐in‐motion database and convolution of fragility and hazard. Analysis results show that structural fragility significantly depends on the load pattern, indicating that more realistic vehicle models should be developed to achieve a target safety level conforming to modern codes for constructions.

On the time dependence of holographic complexity for charged AdS black holes with scalar hair

In the presence of a scalar hair perturbation, the Cauchy horizon of a Reissner-Nordström black hole disappears and is replaced by the rapid collapse of the Einstein-Rosen bridge, which leads to a Kasner singularity [1, 2]. We study the time-dependence of holographic complexity, both for the volume and for the action proposals, in a class of models with hairy black holes. Volume complexity can only probe a portion of the black hole interior that remains far away from the Kasner singularity. We provide numerical evidence that the Lloyd bound is satisfied by the volume complexity rate in all the parameter space that we explored. Action complexity can instead probe a portion of the spacetime closer to the singularity. In particular, the complexity rate diverges at the critical time tc for which the Wheeler-DeWitt patch touches the singularity. After the critical time the action complexity rate approaches a constant. We find that the Kasner exponent does not directly affect the details of the divergence of the complexity rate at t = tc and the late-time behaviour of the complexity. The Lloyd bound is violated by action complexity at finite time, because the complexity rate diverges at t = tc. We find that the Lloyd bound is satisfied by the asymptotic action complexity rate in all the parameter space that we investigated.

Interior structure and complexity growth rate of holographic superconductor from M-theory

We study the interior dynamics of a top-down holographic superconductor from M-theory. The condense of the charged scalar hair necessarily removes the inner Cauchy horizon and the spacetime ends at a spacelike singularity. Although there is a smooth superconducting phase transition at the critical temperature, the onset of superconductivity is accompanied by intricate interior dynamics, including the collapse of the Einstein-Rosen bridge, the Josephson oscillations of the condensate, and the final Kasner singularity. We obtain analytically the transformation rule for the alternation of different Kasner epochs. Thanks to the nonlinear couplings of the top-down theory, there is generically a never-ending chaotic alternation of Kasner epochs towards the singularity. We compute the holographic complexity using both the complexity-action and the complexity-volume dualities. In contrast to the latter, the complexity growth rate from the complexity-action duality has a discontinuity at the critical temperature, characterizing the sudden change of the internal structure before and after the superconducting phase transition.

Kinematic approach for scour analysis of masonry arch bridges

The scour-induced bridge collapse is a critical contributor to the failure of brick or stone masonry arch bridges, which forms a significant share of the existing rail and road infrastructure across the world. Holistic information on the possible failures and the associated collapse mechanisms is essential in formulating suitable mitigation strategies for arch bridges susceptible to scouring. In this context, a novel, quantitative procedure based on limit analysis is developed in this research to quantify the collapse behaviour of masonry arch bridges subjected to scouring at the bridge foundation. Critical foundation movements initiated by scouring are identified as a function of bridge typology and scour-location. Linear kinematic analysis procedures are formulated for the identified collapse mechanisms corresponding to each foundation movement. The proposed iterative procedure uses minimum geometric information to quantify the collapse behaviour of arch bridges with sufficient accuracy.

Collapse of the Chirajara Cable-Stayed Bridge in Colombia

The Chirajara Bridge is part of a highway project located about 40 mi to the southeast of Bogota, Colombia. The collapsed structure was a cable-stayed bridge consisting of two diamond-shaped towers, with a main span length of 940 ft and two side spans of 262 ft. On January 15, 2018, while under construction and with only 164 ft of the floor system remaining to be constructed between the towers, the western tower suddenly collapsed, destroying that part of the bridge. The other tower remained standing, approximately in the same construction stage as the collapsed tower. Modjeski and Masters was engaged one week after the collapse to conduct a forensic investigation that included: an in situ inspection of the collapsed structure, analytical studies, an evaluation of the design, a review of the construction documentation, and testing of materials from critical structural components. Global analyses were performed to determine the loading effects in the bridge before collapse, and refined nonlinear analyses were conducted to estimate the capacity of the tower and to identify the failure mode. The investigation was concluded 4 months after the collapse and, based on the resulting data, the cause of the collapse was determined to be a deficiency in the strength of the tower. The design erroneously assumed that the reinforcing along most of the height of the diaphragm between the lower legs of the tower was effective to resist the horizontal tensile force caused by the tower’s geometry, as opposed to typical practice which utilizes a tension tie at the change in direction of the tower legs.

Vehicular Impact Resistance of FRP-Strengthened RC Bridge Pier

As-built bridge piers are likely to be subjected to vehicular collisions, causing severe damage to the bridge substructure and even resulting in the collapse of the entire bridge. This study aimed to evaluate the effectiveness of fiber-reinforced polymer (FRP) strengthening in enhancing the vehicular impact resistance of as-built bridge piers. A typical local, refined finite-element (FE) model of a simply supported two-span, double-column, reinforced-concrete (RC) bridge was established. The adopted material constitutive models and the FE analytical approaches were then validated through reduced vehicle model lateral impact tests on bare and carbon fiber–reinforced polymer (CFRP)-strengthened RC columns. The effective schemes for FRP strengthening of bridge piers against vehicle impact are discussed from the aspects of fiber orientation, number of layers, and strengthened height as well as by FRP type. Based on the FRP strengthening scheme, 48 vehicle–bridge collision scenarios were designed to evaluate the collapse of bridges with/without FRP-strengthened piers. It was found that (1) external FRP wrapping can effectively enhance vehicular impact-resistance of as-built bridge piers (e.g., reducing the degree of damage and deformation of the impacted pier); (2) for typical bridge piers, the effective strengthening scheme comprised a fiber orientation of 0° in reference to the circumferential direction, a 3-m strengthened height, and four-layer CFRP wrapping; (3) compared with bare bridge piers, FRP-strengthened piers could improve the vehicular impact-resistant safety redundancy of as-built bridges and, to some extent, avoid bridge collapses under truck collisions at high speed. Furthermore, through introducing the dynamic increase factors of concrete strength, reinforcement rebars, and FRP, and considering the nonuniform distributions of the strain rate of FRP-strengthened bridge piers caused by vehicular collision, the dynamic shear capacity of strengthened bridge pier was formulated.

Blast-Loading Effects on Structural Redundancy of Long-Span Suspension Bridge Using a Simplified Approach

Long-span suspension bridges are typically designed against wind and earthquake loadings without considering blast loads because existing blast-resistant design guidelines for bridges are limited and in fact not detailed enough to fully explicate the consequences of a blast event. This study performed detailed dynamic analysis of a long-span suspension bridge to parametrically evaluate its structural redundancy under small to large blasts detonated at different locations. To accomplish this, the blast-structure interaction problem was solved by a simplified approach whereby the blast aspect was modeled as nodal loads by simulating the pressure contour area on the deck surface caused by the explosion; the structural aspect was modeled as a three-dimensional fishbone skeleton finite-element model. In particular, major attention was paid to the blast load effects on the main cable and hangers designed at safety factors of 2.2 and 2.5, respectively. This study concluded that the main cable and hangers show sufficient and insufficient structural redundancies, respectively under small to medium blasts, whereas a large blast was proven to be detrimental to both the main cable and hangers, which may further trigger progressive collapse of the entire suspension bridge.

Endurance time analysis of seismic performances of long-span continuous rigid-frame bridges with corrugated steel webs

The seismic performances of continuous rigid-frame bridges must be evaluated efficiently and accurately using simplified methods during their design and strengthening. As a simplified method to evaluate the seismic performances of bridges, the endurance time method can be used to simulate the complete process of the collapse of an intact bridge via nonlinear time history analysis. The endurance time method is a novel approach of generating seismic acceleration time steps, which allow engineers and researchers to obtain maximal information from the states of the structures with the lowest computational cost. The Fei-Long Bridge—a long-span continuous rigid-frame bridge with corrugated steel webs—has the largest span of this kind in the world and is situated in a medium-risk seismic zone. In this study, we investigated the applicability and accuracy of the endurance time method to estimate the seismic performance of the bridge. Three endurance time accelerograms were generated as seismic inputs based on the design response spectrum provided by the Chinese specifications for the seismic design of highway bridges. In addition, 16 natural far-field and 16 natural near-fault ground motions were selected for incremental dynamic analysis. The seismic response characteristics of the bridge obtained by the endurance time method and incremental dynamic analysis were compared. The results of the endurance time method are observed to be within the envelope of the incremental dynamic analysis results, with an average error lower than 5%, and the median value of the endurance time method agrees well with the mean curve of the incremental dynamic analysis results. Therefore, the endurance time method can be used as a novel simplified and efficient method to evaluate the seismic performances of continuous rigid-frame bridges with corrugated steel webs.

Displacement-based blast-resistant evaluation for simply-supported RC girder bridge under below-deck explosions

An increasing trend of the intentional and accidental explosions has been threatening the safety of bridges. At present, the blast-resistant evaluation for the simply-supported RC girder bridge under below-deck explosions was conducted by numerical simulations. Firstly, by comparisons with three series of field explosion tests on the reduced-scale RC piers/columns and bridge, the adopted finite element (FE) analysis approach was validated. Then, the refined FE model of a typical two-span prototype bridge was established, and 24 explosion scenarios with three typical explosion sources specified by Federal Emergency Management Agency (FEMA) were numerically simulated. The influence of pier designs on the local damage of pier and global response of bridge was further examined, and it derives that, (i) for compact sedan and sedan bombs, increasing the concrete grades is the most feasible way and decreasing stirrup spacings are also recommended, while increasing pier diameter does not definitely enhance the blast resistance; (ii) for the cargo van bomb, the abovementioned pier designs are not effective to prevent bridge collapse. Finally, the linear relationship between the mass loss of pier and vertical displacement of bridge deck was established, and thus the traffic capacity of the post-blast bridge can be practically evaluated by analyzing a single pier instead of the whole bridge.