Perspective Chapter: Bridge Deterioration and Failures

Abstract

The purpose of this chapter is to present research on bridges failures, the conditions that produce structural failures in bridges, and to better understand the processes that impact and degrade the performance and service life of bridges. While rare, bridge failures can have devastating consequences with loss of life. Bridge deterioration and the risk of failure is a continuing challenge for transportation infrastructure owners. Bridge deterioration is caused by many factors, to include increased service loads, deicing chemicals, and aggressive environmental conditions. By looking at basic bridge types and their components, the focus of research in this chapter examines seven bridges failures and the conditions that led up to their failures. The research in this chapter produced two significant findings. The causes of bridge failures can be traced back to human error in the life cycle of the bridge. The second result is insufficient systematic analysis of bridge failures, their causes, and how to prevent them. While analyzing the causes of bridge deterioration and the processes that contribute to bridge failures the goal of this chapter is to provide a better understanding how bridges deteriorate to minimize failures in the future and to build better bridges. Bridge failures are preventable.

1. Introduction

One of the challenges for infrastructure owners of large national networks of highway and railroad bridges is maintaining the performance of the bridges over their designed service life without the risk of failure. But bridges do fail for a number of reasons. A bridge failure is most often the result of some failure in the life cycle of a bridge from concept through design, construction and maintenance during its service life. The direct failure of bridges is the result a number of factors to include structural over loading, material failures, poor designs, faulty construction, inadequate oversite and control of bridge construction, inadequate inspections, delayed maintenance, earthquakes, and flooding.

In research work on the frequency and causes of bridge failures K. Wardhana, et al., studied over 500 failures of bridge structures in the United States between 1989 and 2000 with the age of the failed bridges ranging from 1 year (during construction) to 157 years, having an average age of 52 years. They state “The most frequent causes of bridge failures were attributed to floods and collisions. Flood and scour, with the major flood disaster in 1993, contributed to the frequency peak of bridge failures (almost 53% of all failures). Bridge overload and lateral impact forces from trucks, barges/ships, and trains constitute 20% of the total bridge failures. Other frequent principal causes are design, detailing, construction, material, and maintenance. Comparison made among three periods of similar studies (1977–1981, 1982–1988, and 1989–2000) revealed almost similar trends, with most failures occurring during the bridge’s service life. Also, human-induced external events occurred frequently in all three periods, but were most dominant in the first and third periods [1]. While Wardhana studied three periods of bridge failures in the United States the statistics are representative of bridge failures around the world in all years.

This chapter examines bridge failures and structural deterioration for the purpose of understanding the elements that cause deterioration in bridge structures and the factors that lead to the structural failures. There are a number of elements that cause the material in bridge structural components to degrade and deteriorate over time, in both steel and RC (reinforced concrete) bridges. The two dominate elements causing deterioration are deicing chemicals (chlorides) and vehicle over loading. These two elements affect all types of bridges and their components. In extreme cases extensive deterioration potentially leads to structural failure. Of the bridge failures presented in this chapter each failure has one or more of these factors which contributed to the bridge collapsing.

2. Background

The means and methods for bridge failure analysis used in this research paper involved a literature survey of papers that studied and analyzed the causes of bridge failures. Their papers address the types of bridge failures, their root causes, and events and processes that led up to their failures. In most all cases the cause of failure can be traced back to human error.

To provide a basis for the examining the six bridge failures presented in in this chapter a description of the seven bridge types is provided together with an outline of the basic components of a bridge structure, to include foundation, substructure, and superstructure. It is worthy to note that in the service life of a bridge deterioration can occur in any of these components to a degree that can increase the potential for a bridge structural failure. Deterioration is a process changing an object, in our case bridges, to a lower quality state in which a degraded condition can lead to structural failure. A steel bridge with structural beams in a rusted condition is an example of advanced deterioration.

For this chapter bridge failure analysis is the process to understand why structures, components, systems, methods, and processes fail. Failure analysis is a science to analyze how structural systems fail by determining the sources and causes of failure. The bridge failure analysis process includes structural analysis which incorporates the fields of mechanics, dynamics and failure theories. From a theoretical perspective, the primary goal of structural analysis is the computation of deformations resulting from internal and external forces and stresses. In practice, structural analysis reveals the structural performance of the engineering design and ensures the soundness of the structural integrity in design. Using an array of methods, to include nondestructive testing, the failure analysis process collects data on failed components for examination and analysis to determine the cause of failure. The objective of bridge failure analysis is to develop corrective actions and better structural designs with improved reliability to prevent bridge failure over its service life.

The description of a bridge failure is presented in a paper by G. Zhang, et al.

“Bridge failure, is generally associated with serious economic and life losses is dedefined as the incapacity of a constructed bridge or its components to perform as specified in the design and construction requirements. Principal causes can be divided into internal causes and external causes or natural factors and human factors. Design error, construction mistakes, hydraulic, collision, and overload are the top 5 leading causes of bridge failures, resulting in more than 70% of the bridge failures. Causes of bridge failures are closely related to regional economy, structural type, type of use, material type, and service age. The failure rate is high for steel bridges, which is inseparable from excessive emphasis on structural strength and the lack of consideration on structural stability and fatigue in early years.” [2].

The paper from Zhang makes an important point. The issue involves understanding the rate of fatigue in structural elements in both steel and reinforced concrete bridges and the impact on bridge performance relative to the weakest point(s) in the bridge structure. Not identifying through inspection and testing the weakest points in a bridge increases the risk of failure.

A description of four highway and two pedestrian bridge failures are presented in this paper. The failure analysis process used for each bridge looks at the bridge type and structure, its failure mode, the events leading up to the failure, and the factors contributing to its failure. Of all the factors contributing to a bridge failure the one common factor in all the failures is the role human errors played in the chain of events leading up to the bridge collapse. Stakeholders, designers, bridge engineers, inspectors, and maintainers are responsible for preventing bridge failures. Bridge failures are preventable.

3. Bridges

Seven basic types of bridges represent a majority of the highway, railroad, and pedestrian bridges in North America, and around the world. These include truss, tied-arch, suspension, arch beam, cable-stayed, and cantilever. Each type of bridge fulfills a specific requirement for a specific location. The distribution of stresses, both horizontal and vertical, determines the type of bridge structure required. It is interesting to note many bridge designs have been in practice for a number of centuries without major changes. For example the arch bridge was perfected by the Romans over 2000 years ago.

3.1 Arch bridge

Arch bridges are the oldest bridges in existence, with the Arkadiko bridge in existence today with many still in use. The basic design of the arch bridge allows the arch span to transmit lateral pressure to supporting abutments on a solid Greece, from the thirteenth century BC, still in service. Over 900 roman arch are in foundation. The simple design of the arch bridge with stone under compression allows for an extremely stable bridge, which explains why older arch bridges are still in existence and in use today, Figures 1 and 2.

Figure 1.

Roman Alcantura Arch Bridge in Spain Built 103–106 AD. CC BY-SA 3.0.

Figure 2.

Stari Most Arch Bridge Built 1557 Mostar, Bosnia Hersogevina. CC BY-SA 3.0.

An example of older arch bridges still in service is provided in a paper by D. Trajber et al. [3], in which they examine the condition of the bridges and assess the degree and rate of deterioration from anthropogenic and environmental factors, with the goal of providing accurate condition assessments and establishing necessary maintenance. In their paper they state “Historical masonry arch bridges still form an important part of Croatian transportation network. There are approximately 680 masonry arch bridges and culverts currently being used for railways and roadways. Many of these bridges are relatively old (more than hundred years in most cases) but still in usage. Increasing vehicle load and speeds as well as deterioration due to anthropogenic and environmental influence have highlighted the need for reliable assessment of their service condition and regular maintenance. The aim of this study is to provide a review of existing masonry arch bridges in Croatia. Firstly, a historical review of bridges is given showing the time period in which they were built, indicating the materials and design principles used for their construction. Next, bridge typologies are presented as well as their detailed analysis of geometric characteristics for brickwork bridges. Finally, a short review of damages and their impact on serviceability of bridges is given. This review presents masonry arch bridges in Croatia and the need for reliable method of assessing their service condition in order to provide proper maintenance, repairing and retrofitting.” [3].

3.2 Beam bridge

One of the simplest types of bridge, Figure 3, is the beam bridge with abutments supporting two or more beams over relative short spans. The two main beams can have cross beams to add strength and stability. The beam bridge does not transfer load stress as in an arch bridge. Many small and medium beam bridges on main and secondary roads are beam bridges.

Figure 3.

Example of a steel beam bridge. CC BY-SA 3.0.

3.3 Cable-stayed bridge

A cable stayed bridge, Figure 4, consisting of cables connected to load-bearing tower pylons and the deck below are used to span large distances. By connecting the cables to the pylons a fan like pattern is created. In effect the cable-stayed bridge is a statically indeterminate continuous girder bridge where the dead and live load internal forces are smaller than a girder bridge. With their structural members in tension the cable-stayed bridge makes more efficient use of materials.

Figure 4.

Cable-stayed bridge Rio Antirrio Bridge in Greece. Opened 2004 length 2.8 km. CC BY-SA 3.0.

In a paper by J. Radic et al. [4] the authors point out a great number of parameters are required for the shaping of cable-stay bridges, where principal requirements for the shaping of beams, stay cables and pylons are explained. Cable-stayed bridge design analysis must take into account strong interactions between principal load-bearing structural elements. As an example the principal properties of the Jarun bridge cable-stayed bridge in Croatia are explained in the light of guidelines for the shaping of cable stay bridges, and an accent is placed on specific features of this bridge [4].

3.4 Cantilever bridge

The cantilever bridge, Figure 5, made from structural steel or pre-stressed concrete, using simple trusses and beams, connects two cantilever arms in a suspended span center piece with no direct support underneath. Horizontal beams and diagonal bracing support the bridge load with no vertical bracing. The first cantilever bridge in 1866 was the Hassfurt Bridge over the Main River in Germany, with a span of 124 feet, and was considered a major engineering breakthrough in bridge construction at the time. The Canadian bridge Pont de Quebec, Quebec City, Figure 4, which opened in 1919, after 30 years and two collapses, is the longest cantilever bridge in the world.

Figure 5.

Pont de Quebec Opened 1919 987 m. CC BY-SA 3.0.

In a paper by Rajeshirke et al., India [5] the authors describe the use of balance cantilever bridges in India which are widely used in hilly regions where supporting from the bottom is difficult. The name Balance Cantilever Bridge is a construction methodology which balances out the cantilever portion and is one of the most effective methods of building bridges without the need of false work. Balanced cantilever bridges are used for special requirements like construction over traffic, short lead time compared to steel and use local labour and materials. Extradosed bridge is a unique type of bridge between Girder Bridge and cable-stayed bridge. As most of the literature covers either balance cantilever bridge or extradosed bridge, this paper introduces and attempts to summarize comparative study of balance cantilever and extra dose bridge with its span arrangement, span by depth ratio, and pre-stressing of steel [5].

3.5 Suspension bridge

Developed in the early 1800s suspension bridges were a marvel in bridge engineering and capable of spanning great lengths. The basic components of a suspension bridge are main cables, towers, and secure anchorages at both ends of the bridge. The deck carrying the dead load and vehicle traffic is hung from the suspension cables with vertical suspenders. The load carrying members are the main cables as tension members made of high-strength steel and are efficient in carrying loads. With this suspension cable configuration the dead weight of the bridge can be reduced making longer spans possible. Early suspension bridges had problems with vibrations and wind loading before the dynamics of wind loading on bridsges was understood. John Roebling was the first engineer to build suspension bridges designed for wind loading with the Roebling bridge in Cincinnati, Ohio, Figure 6, and the Brooklyn bridge in New York City.

Figure 6.

John R Roebling Suspension Bridge Cincinnati, OH Opened 1867. CC BY-SA 3.0.

In a paper by Arioglu [6] the author describes “suspension bridges as masterpieces of the engineering profession with conceptually clear cut 5-piece load-bearing systems which are highly hyperstatic and undergo large displacements under loads having nonlinear behavior and are sensitive to horizontal loads, such as wind loading. Suspension bridges are the most elegant, aesthetic and relatively economic structures of our civilization. Suspension bridge designs are based on mathematical models, using known patterns of physical behavior, but have many unknowns and uncertainties. This paper explores practical mathematical expressions obtained through regression analyses to predict key design parameters of long span suspension bridges such as main geometric dimensions, material quantities/qualities and dynamic properties for preliminary design calculations.

A large design parameter database matrix for 20 long span suspension bridges was collected to bring out heuristic approximations through regression analyses. These regression models are used to examine the design parameters of 1915 Çanakkale Bridge Project, which will break the longest span record with a main span length of 2023 m and the tallest tower record with 318 m (IP Point). It was observed that the dimensions, mass distributions and material qualities selected for the design of 1915 Çanakkale Bridge agree with the findings of this study.” [6].

The key design parameters for regression models used by Arigulo on existing suspension bridges correlated well with the design parameters for the new 1915 Canakkale Bridge over the Dardanelles in Turkey. The bridge opened in March 2022 with a span of 3.7 km and is the longest suspension bridge in the world.

3.6 Truss bridge

The truss bridge is a load-bearing structure efficiently incorporating trusses in an array of triangular sections and has been around for centuries. Dynamic loads are accommodated by triangular elements which absorb tension and compression. The combination of tension and compression ensures the structure of the bridge is maintained and the decking area remains uncompromised even in relatively strong winds.

3.7 Tied arch bridge

Incorporating an arch structure supported by vertical ties between the arch and the deck, the tied arch bridge creates downward pressure from the arch structure to the deck of the bridge which translates into tension by the vertical ties. The tips of the arch structure are connected by a bottom chord. The deck strengthening chord connects the tips of each end of the acting like a bowstring which absorbs pressure.

4. Bridge components

Consideration is given to the three primary components of a bridge structure and their subcomponents of which all are subject to elements of deterioration and potential failure.

4.1 Foundation

A bridge foundation, for all types of bridges, consists of the following components:

Piles: The initial foundation of a bridge are piles, wood, steel, or concrete, driven into the ground to support the entire weight of a bridge. By distributing p Piles distribute weight and stresses applied by the bridge evenly through the ground making it stable and strong.

Caps: To provide additional load transferring capacity pile caps are placed on top of the pile foundation provide additional load transferring capacity to the piles and give maximum strength to the upper part of the bridge.

Bents: Forming the foundation for the substructure bents connect piles and caps.

4.2 Substructure

A bridge substructure consists of the follow components which transfer the bridge load forces to the foundation:

Abutments: Capable of withstanding high levels of horizontal force abutments are the vertical support at the ends of the bridge.

Piers: Providing support points for the bridge piers are mounted at the end of each span to reduce the effects of forces and vibrations.

Pier Caps: Acting as a space for the girders pier caps function to transfer loads on bearings from the superstructure components on the top.

4.3 Superstructure

The bridge superstructure.

Girders: Girders (or beams) join pile caps together and give support to the deck and can be over a single span spans joining all the bents, dependent on the length of the bridge. Girders usually have a truss design to improve stress and load resistibility, passing pressure to the foundation.

Bearings: Bearings are structural members capable of transferring loads from the deck to the substructure. These displace stresses and load to the piers through the girders to allow movement between parts of a bridge. The movement can be linear as well as torsional.

Trusses: Trusses are made by joining triangular components to divide loads and bending moments through the bridge. Some types are simple trusses, suspension, and also cantilever trusses. The truss network provides a surface for transportation which can be built as a deck truss, pony truss, or through truss. Each truss differs in how the traffic will move on the bridge.

Decks: Decks made of concrete or metal direct traffic load and include drainage systems, curbs, expansion components, sidewalks and approach slabs.

Barriers: Bridges have barriers on the sides for safety and protection of the decks.

Arches: A bridge with arches has a high degree of strength. Arches control the safety and load bearing ability of the bridge. The quantity of arches and materials used for construction is very important.

Spandrel: A space connecting the bridge pillars and deck beam is called the spandrel. There can be open or closed spandrels depending on the arch design.

5. Concrete bridges

Known for their longevity and low maintenance costs reinforced concrete (RC) bridges are designed to maintain their service life over long periods of time. But they deteriorate from the same elements as steel bridges: poor construction, and outdated designs for today’s traffic loads. Subject to aggressive factors, such as over loading, vibration, extreme weather, freeze thaw cycles, chlorides in de-icing salts, plus air borne chlorides in marine environments the service life of the RC bridge is degraded. As the Federal Highway Administration has stated “Salt contamination is probably the most significant single contributor to bridge deterioration”. These five primary elements are the contributing factors to the deterioration of RC bridges.

5.1 Elements of deterioration on concrete bridges

For reinforced concrete bridges there are two primary elements, or factors, that contribute to the deterioration of concrete structural members: salts and loads exceeding the original design criteria.

5.1.1 Deterioration from water and salt

The effect of salt on the decks and substructure of an RC bridge can be significant. The chloride ion as a major component of sodium chloride and calcium chloride is the most destructive element to an RC bridge in the corrosion deterioration process on the reinforcing bars, which expands and induces high tensile stresses in the surrounding concrete. Hairline cracks enlarge from freeze/thaw and traffic causing delamination and spalling of concrete. Water seepage (with salt) through faulty deck joints cause deterioration in abutment back walls, beam seats, pier caps, concrete pads, and end diaphragms.

5.1.2 Deterioration from overloading

The effect of heavier truck loads on today’s bridges, which in many cases were designed over 50 years ago, produces an element of deterioration on the bridge deck and supporting components. Increased truck weights, volumes and speeds produce more cycles of larger stress ranges reducing the fatigue life of beams and girders. The longitudinal and vertical forces induced by heavy trucks tend to exacerbate the deterioration of the bearings, which are already weakened by salt-laden water and debris. An additional problem is many existing bridges lack sufficient grillage reinforcement which results in cracks and spalls on the abutments and piers near the bearings. If the bridge approach slabs are insufficient the impacts of heavier trucks hitting the bridge produce higher incidents of cracks and spalls of concrete header and back walls at the abutments [7].

6. Steel bridges

Widely used in different structural forms around the world steel bridges provide large span lengths for highway and railway bridges. With its strength, ductility, rapid construction, and compressive and tensile strengths of 370 N/sq. mm steel had advantages over other construction materials. It has higher strength in both tension and compression than concrete, and has strength to cost ratio and stiffness to weight ratio. Strength, ductility, toughness, weldability, weather resistance, chemical composition, shape, size, and surface characteristics are important properties of structural steel for designing and construction of steel bridges [7].

6.1 Elements of deterioration in steel bridges

Corrosion is the major element of deterioration in steel structures. Fatigue damage and brittle fracture are special problems for steel structures resulting from repetitive loadings over a long period of time. As Contreras-Nieto et al. [8] state in their paper as a significant number of steel bridges are approaching the end of their service life, understanding deterioration characteristics and rate of deterioration will help bridge stakeholders prioritize bridge maintenance, repairs, and rehabilitation. One prediction model uses data mining techniques to include logistic regression, decision trees, neural networks, gradient boosting, and support vector machine to the United States’ national bridge inventory to estimate the probability of steel bridge superstructures reaching deficiency. The model uses data based on the defined scope of the research: design material (steel), type of design (stringer/multi-beam or girder), and deck type (cast-in-place concrete). The predictors of the model include age, average daily traffic, design load, maximum span length, owner, location, and structure length. The magnitude that these factors contribute to the likelihood of a steel bridge superstructure’s deficiency was identified. Outcomes of the analysis afford bridge stakeholders the opportunity to better understand the factors that are correlated to steel bridge deterioration as well as provide a means to assess risks of superstructure deficiency for the sake of prioritizing bridge maintenance, repair, and rehabilitation [8]. The prediction model the author proposes considers a wide range of factors which correlate to a risk assessment on the rate of deterioration of the steel structure, with which the owners can determine maintenance and rehabilitation priorities.

6.2 Critical defects in steel bridges

The following are key factors causing deterioration of steel bridges:

1. Major cracks in girder flanges or in tension cords are critical.

2. Loss of section through corrosion in compression elements, or floor beam connection angles and rivets.

3. Fracture-critical member is one whose failure will result in a failure of the bridge structure, which have the material property of fracture toughness, and is dependent on material toughness.

4. Welds, holes, notches, loss of section, and pitting will affect a steel member’s fatigue strength, in which welded members are more sensitive to fatigue induced cracks. Cover plate terminations, flange and butt splices, lateral bracing connections, stiffener end welds, are areas of concern for welded girders.

5. Lack of ductility, material toughness, stress conditions, drop in temperature will cause brittle fracture.

6. Out-of-plane bending distortion is a typical cause of fatigue-related failures.

7. An expansion bearing failure may occur caused by corrosion or pier or abutment movement subjecting main members to large tension or compression stresses. Temperature changes can also cause increases in stress levels [1].

7. Bridge failures

The following bridge failures are just a few of the many bridges that have collapsed in North America over the past decades, which unfortunately have taken many lives. The failures are contributed to many factors, all of which lead back to human error in the phases of the bridge design, construction, inspection, and maintenance.

7.1 Pittsburgh bridge collapse

On Jan 28, 2022, at 6:45 am a 52-year old steel-framed bridge, Figure 7, which spans a deep ravine in Frick Park, collapsed, sending six cars and a metro bus down with it. Fortunately no one was killed. Six people had minor injuries. According to the mayor, an inspection of the bridge was performed in September. The bridge has been described as in “poor” condition in previous reports from 2011 to 2017. A structural evaluation described the bridge meeting “minimum tolerable limits to be left in place as is.”

Figure 7.

Collapsed Pittsburg bridge January 2022. CC BY-SA 3.0.

Failure analysis: The root cause of the bridge failure was a single point of failure in a corroded structural element. The bridge was non-redundant and fracture critical, meaning a single point of failure will cause the bridge to collapse. Contributing factors were a failure in the inspection process to assess and accurately determine the structural capacity of the corroded steel elements and the decision to keep the bridge open despite a poor condition.

7.2 Pedestrian bridge failure: Florida

A concrete pedestrian bridge under construction at the International University in Miami suddenly collapsed in March 2018. The bridge, which had not yet opened, killed five people. The 174 foot concrete structure, Figure 8, weighing 930 tons was non-redundant and fracture critical. Seven days before opening numerous wide and deep structural cracks developed, with cracks lengthening daily. Before the collapse the EOR stated there were no safety concerns.

Figure 8.

Collapsed pedestrian bridge Miami, FL. CC BY-SA 3.0.

Failure analysis: Root cause was a failure in a single structural element. Among the contributing factors was a failure by the Engineer of Record (EOR) and the Construction Engineer and Inspector (CEI) to recognize the severity of the developing cracks. In addition there was a lack of a clear line responsibility for enforcing safety and structural issues.

7.3 I-35 W Interstate Highway Bridge Collapse

In August 2007, in Minneapolis, MN, at 6 pm in rush hour traffic, the I-35 W bridge across the Mississippi river collapsed taking with it 111 vehicles, killing 13 people, and injuring 145.

The bridge, Figure 9, constructed in 1967, was non-redundant and fracture critical, meaning if one member failed the entire bridge could collapse. The cause of the bridge failure was a gusset plate which tore along a line of rivets. It was determined the gusset plate was too thin. The failure was triggered by the additional weight of construction equipment parked on the bridge and rush hour traffic. In the previous years the bridge was identified as having deficiencies, to include the gusset plates.

Figure 9.

I-35 W Mississippi River Bridge collapse. CC BY-SA 3.0.

In a paper by Salem et al. [9] the authors analyzed the cause of the I-35 collapse. The I-35 Bridge over the Mississippi River in Minneapolis, Minnesota catastrophically failed during the evening rush hour on August 1, 2007, collapsing into the river. In the years prior to the collapse, several reports cited problems with the bridge structure.

The author’s research analytically investigated the cause of the collapse using the Applied Element Method. The bridge was modeled using construction drawings, with relevant structural details and loadings. Structural details included the steel truss, gusset plates, concrete slabs, concrete piers, while structural loading included traffic and construction. AEM provided the cause of collapse of the I35-W Bridge. The cause of collapse was found to be the failure of the gusset plates at connections L11 and U10, which well agreed with the field investigations of the collapsed bridge. The under-designed thickness of the plates, their corrosion, and over loading due to traffic and construction loads at time of collapse were the reasons for the bridge collapse [9].

Failure analysis: The cause of the collapse was a single ½” gusset plate failing along a line of rivets. There were a number of contributing factors that came together leading to the bridge failure: design flaws, inadequate design review, inadequate inspection, MnDot policies not being followed, poor information flow, the organizational structure not addressing bridge conditions and safety. All these factors combined led to the bridge collapsing. It is noteworthy to note the AEM program used by the authors with the model of the bridge’s construction drawings and structural details and loadings predicted the failure of the bridge exactly at gusset plate L11 and U10.

7.4 Hyatt Regency Hotel skywalk failure

The Hyatt Regency Hotel in Kansas City, Missouri, suffered a structural collapse in July 1981, in which two overhead walkways, Figure 10, failed under the loading of a large number of people. 114 people were killed and 216 injured. The primary cause of the failure was the induced vibrations from a number of people on the skywalks (overloaded) dancing to the rhythm of the music on the ground floor. It was the worst civil engineering failure in US history. With about 40 people on the second-level walkway, and another 20 on the fourth floor walkway, the fourth floor walkway gave way from a failed bolt connection, dropped onto the second floor walkway, where both plunged to the atrium floor.

Figure 10.

Fourth and second floor skywalks falling to the atrium. CC BY-SA 3.0.

Failure analysis: The root cause was the failure of the fourth floor skywalk suspension rod in a welded channel iron causing the skywalk to drop onto the second floor skywalk with both then dropping on the ground floor. Among the contributing factors was inadequate design in the skywalks, a failure in engineer review of shop drawings and field changes, a lack of oversight responsibility, and clear lines of authority starting with the Engineer of Record.

7.5 Silver Suspension Bridge

The Silver Bridge, Figure 11, at Point Pleasant WVA, crossing over to Gallipolis, Ohio, over the Ohio River, opened in 1928, Figure 10, and was the first bridge un the US to use the eye bar-link suspensions system. At 5 p.m. 15 December 1967, a single eye bar failed causing the bridge to collapse in seconds, killing 46.

Figure 11.

The Silver Bridge in 1928, as failed in December 1967. CC BY-SA 3.0.

Failure analysis: A cleavage fracture in lower limb of the eye of eye bar 330 was the cause of the bridge failure. The single-point failure caused entire bridge to collapse. The contributing factors were the fact the bridge had no redundancy, the cracked eye in the eye bar was not found during routine inspections, and the combined action of stress corrosion and corrosion fatigue over 40 years. As result the US Congress passed a federal law requiring systematic inspection of all US bridges.

7.6 I-880 Cypress Freeway Collapse

The Loma Prieta earthquake in 1989 caused heavy damage in Santa Cruz County which collapsed the double-deck Cypress Street Viaduct, Figure 12, of Interstate 880 in West Oakland. The 6.9 magnitude earthquake caused 63 deaths and 375 injuries.

Figure 12.

Collapse of the I-880 freeway in the 1989 Loma Prieta earthquake. CC BY-SA 3.0.

Moehle [10] states the viaduct was built-in the late 1950s on reclaimed marsh land the Cypress Street Viaduct was a double-deck freeway section made of non-ductile reinforced concrete. The Viaduct was designed as a two-tier multi-lane highway constructed of reinforced concrete upper and lower levels were connected by two-column bents in a combination of cast concrete and four pin (shear key) connections. The upper deck in some sections was not securely fastened to the lower deck, making this concrete susceptible to vibrations [10].

Yashinsky [11] indicates two major factors led to the collapse. The first was the geotechnical aspect of the central San Francisco Bay area. The second was the design of the concrete columns and bent caps and pin connections. Strong ground shaking in the marshland caused soil liquefaction. As the bridge vibrated during the earthquake, the pins connecting the upper level to the lower level also began to vibrate, causing the concrete surrounding the pins to crumble and break away. Without the presence of concrete under the support columns, the columns slid sideways under the weight of the upper deck and allowed a large portion of the upper deck to collapse [11].

Failure analysis: The root cause of the collapse of the Cypress Express Freeway was failure of pins connecting the upper and lower levels due to the strong ground shaking. Contributing factors were inadequate transverse reinforcement in the columns and deficient bent cap and pin connection designs and lack of compensation for the weak soil conditions [11].

Tests were performed by Monteiro et al. [12] on pieces of concrete extracted from the wreckage to assess structural integrity; many components of the Viaduct were found to be structurally sound. It was concluded that the concrete used had more than satisfactory strength. In addition, micro structural analysis of concrete samples taken from undamaged columns within the region of collapse showed that the concrete was produced and cast according to the proper procedures at the time of construction [12].

7.7 Pont de Quebec Collapse 1907

In August 1907 the Pont De Quebec, Figure 13, under construction on both sides of the St. Lawerence River, suddenly collapsed killing 75 workers and injuring 11.

Figure 13.

Pont de Quebec collapse in August 1907. CC BY-SA 3.0.

Failure analysis: The root cause of the failure was an overweight structure for the bridge structural design. The primary contributing factor was an error in the design calculations causing the steel structure to collapse under its own weight. Other contributing factors were lack of review by an independent bridge engineer and clear lines of project responsibility and authority.

Construction resumed in 1910. In 1916 the center span during assembly collapsed, killing 16 works. The cause was failure of a casting used in the hoisting of the center section. The bridge finally opened in 1919 (Figure 14).

Figure 14.

Pont De Quebec in 2009 [13]. CC BY-SA 2.5.

8. Results and findings

This chapter presents the results and findings of seven research papers that focus on the causes of bridge failures and methods to analyze bridge structures. Presenting frequency of bridge failures Wardhana looks at causes from design, construction, material, and maintenance. Zhang considers structure type and material with an emphasis evaluating structural strength and stability in a bridge’s early life to monitor the rate of fatigue in structural elements. Evaluating arch bridges Trajber considers structure type and service age proposing repair and rehabilitation to reduce the rate of deterioration in arch bridges. For cable-stayed bridges Padic analyses the number of design parameters needed to account for the interaction of load-bearing structural elements. Pajeskirke evaluates balanced cantilever bridges in India used for hilly terrain with little bottom support which require special construction requirements. Arioglu uses regression models to examine design parameters for suspension bridges with application to the new 1915 Canakkale Bridge in Turkey. In looking at the I-880 freeway collapse in California in 1989 Mochle points out the failures was the result of not identifying the weakest point in the bridge, specifically the connection pins between the two decks. Analyzing the I-35 bridge collapse in Minnesota Salem uses the Applied Element Method (AEM) to accurately identify the exact gusset plate that failed. The I-35 bridge had long standing deficiencies.

The seven bridge failures presented this paper highlight a variety of causes that led to structural failures. In each of the seven failures there are valuable lessons to be learned. These lessons should be used by designers to build stronger and better bridges with longer service lives. Bridges should not fail.

By looking at bridge failures and their causes Heggade, VP of Board of Management of Gammon India Ltd., presents in his paper the fact there are valuable lessons to be learned in failures. He notes a majority of bridge failures occur in service without external action, during construction and in false works. He indicates there have been an alarming trend of bridge failures in Asian countries and discusses aspects of learning lessons in bridge failures from the Indian context. The point he makes is that accurate documentation of bridge failures is necessary for improved bridge designs. Study of failure improves design concepts for robustness, extrapolation, and durability. The study of bridge failures is an invaluable source of information on bridge design limitations. Bridge design is a process of anticipation of failure. Heggade states bridge designers must learn from past bridge failures to improve deigns to prevent bridge failure [14].

In recommending improved methods to reduce bridge failures Zhang points out:

“Researchers need to strengthen their research on the stability and fatigue of steel bridges, as well as inspection and maintenance. Extreme loads such as flood, collision, and overload contribute to a large number of bridge failures because of the lack of extreme loads data and design theory defects. It is critical for bridges to have sufficient redundancy and capacity protection measures to reduce the probability of bridge failure due to extreme loads. Previous statistical methods and classification methods for the characteristics and causes of bridge failures lack unified standards, and a more scientific method needs to be established [8].

The key point Zhang makes is that unified standards with better scientific methods are needed to classify the characteristics and causes of bridge failures. More research is needed to significantly improve risks reduction of bridge structural failure.

One of the key findings to come out of the research for this paper is the need to better understand how and why bridge failures occur and to apply the lessons learned in failures to design and build better bridges, of all types, that will not fail.

9. Preventing future bridge failures: inspection and maintenance

Bridge inspection and maintenance are the two most important activities for an existing bridge to preserve its function and service life and to provide public safety. The American Society of Civil Engineers reports that one out of every nine bridges in the US structurally deficient. Age and deteriorated bridge conditions are a contributing factor to many recent bridge failures.

9.1 Inspection

As Silano and Henderson [7] states in his book “Bridge inspection and Rehabilitation” the primary purpose of bridge inspections is to ensure public safety. The secondary purpose is to preserve the remaining life of bridge structures through the early detection and addressing of deficiencies. Federal law governs the requirements of the Bridge Inspection Program. The United States Code (23 U.S.C. 151) requires the Secretary of Transportation, in consultation with State transportation departments, to establish national bridge inspection standards for the proper safety inspection and evaluation of all highway bridges. These requirements are spelled out in the Code of Federal Regulations (Part 650, Subpart C) and govern the National Bridge Inspection Standards (NBIS) through purpose, applicability, definition of terms, qualification of personnel, inspection frequencies, inspection procedures, inventory procedures, and supporting references. Federal Highway Administration (FHWA) has developed 23 Metrics for the Oversight of the National Bridge Inspection Program. These metrics are a risk-based assessment of the performance of state bridge inspection programs and compliance with the NBIS. Each year, bridge Inspection programs are audited by the FHWA for compliance on these metrics. And yet bridge failures still occur [7].

9.2 Maintenance

With proper inspection and identification of maintenance requirements to preserve the integrity of bridge structural members deterioration of bridge components to the point of failure can be prevented. Corrosion, one of the leading causes of section loss in steel members and concrete reinforcement, leads to strength degradation and increases the risk of failure. Timely maintenance can prevent bridge deterioration and potential failure. Lack of bridge maintenance is the most preventable of all bridge failure causes.

9.3 Non-destructive testing

The use of non-destructive testing (NDT) on concrete and steel bridge components is useful in determining material condition. Of the many NDT methods available for the bridge inspector, visual inspection is one of the most effective. To test for voids and de-laminations in concrete the impact-echo method is effective in detecting substrate de-laminations. This method was applied with a small mobile impact machine to detect de-bonding of CFRP plates on the bridges in Macedonia [15]. NDT impact methods used in the periodic inspections of bridges provide significant data on the bridge condition [16].

10. Conclusion

Bridges deteriorate and bridges fail. The challenge for bridge owners is how to reduce the rate of bridge deterioration and to prevent bridge failures. Bridge failures are rare but they do occur. The goal of this chapter is to understand the nature of elements that cause deterioration in concrete and steel bridges and the effects these elements have on bridge structural components. The chapter presents an overview of the seven basic types of bridges used world-wide in varying configurations and lengths to meet requirements for specific locations. Components of a bridge, from foundation to superstructure are discussed, of which all bridge components are subject to deterioration in some form. The two primary elements of deterioration are water with deicing chemicals on concrete and steel, and heavy vehicle traffic. To preserve the structural integrity and service life of bridges comprehensive inspection, maintenance, and strong funding programs are required. Inspection emphasis must be placed bridges that are non-redundant and fracture-critical to prevent future failures.

Seven bridge failures and seven research papers are presented in this paper. As became evident in researching bridge failures, all bridge failures have a common characteristic: human error involving flawed designs, a lack of design review and construction oversight, lack of clear lines of authority, coupled with inadequate inspection and maintenance over the service life of the bridge. Bridge failures are preventable. By using the lessons learned in each bridge failure designers, engineers, and inspectors can prevent future bridge failures. Bridge failures are preventable.

Conflict of interest

The author declares no conflict of interest.