Bridge Failure Studies and Safety Engineering 2. 1 HISTORY OF DISASTERS AND SAFETY MANAGEMENT 2. 1. 1 Unexpected Material Deterioration and Failure Engineering is usually about avoiding failures and investigating why failures occur and ways to fix the problem. There is a need to understand the conditions giving rise to past failures and ways to avoid such failures so that loss of life can be minimized. Historical events and selected case stud-ies demonstrate the causes of each type of failure. Future design codes can make use of the deficiencies identified in order to develop guidelines for safe practice.
If failures are interpreted correctly, a great deal of information for correct analysis, anticipated behavior, detailed design, and construction can be obtained to help formulate accurate design guidelines. Failures occur in different forms in a material. Physical forms of failure can be seen as infinitely large deformation and metallurgical disintegration of elements. It can be localized cracking without collapse or discontinuity or total separation in a component. At failure, critical sections for plastic hinges are located at the midspan of beams or under the concentrated load where deflection or bending moment is highest.
It can also be at a support where shear force, reaction, or negative bending moment is the highest. Failures are encountered on construction sites and are not just confined to the collapse of structures. Deaths and injuries to construction workers by far exceed the number of fatalities of the bridge users in failure events. Structural design methods related to construction loads and equipment need to be refined. Physical causes are varied such as erosion, reversal of stress, impact, vibra-tions, wind, and extreme events. Usually, it is a combination of dead load stress 9 ombined with one or more external transient forces resulting in a compound critical stress. If dead load stress is already high and approaching the elastic limit of members, any applied force or stress will exceed the allowable limit and lead to failure. Scour evaluation reflects the scour sufficiency rating or coding. Scour rating and evaluation needs to be based on a more refined analysis. 3. 1. 2 Aftermath of a Bridge Failure 1. Shutdown of approaches to traffic. 2. Emergency relief work by police such as calling hospital ambulances and helicopters. 3. Provision of a detour or alternate route. . Emergency repairs and retrofits, if applicable. 5. Forensic engineering to resolve litigation issues. 6. Reconstruction. 7. Deficient bridges need to be replaced by efficient bridges designed by using the latest criteria. Issues include: • Solving design challenges • Availing of benefits provided by new materials • Deploying new techniques such as extending the span length by beam splicing and post-tensioning • Rapid reconstruction. 2. 1. 3 Studying the Reasons for Failure 1. Past failure studies have shown that failures occur due to a variety of reasons.
The primary causes of failure and the numerous secondary causes contributing to failure need to be investigated. Primary effects may not all be dangerous by themselves, but when combined with secondary effects, their cumulative action can trigger a collapse. Lessons need to be learned from each failure. It appears that much water has flowed over the bridge since the disaster at Schoharie Creek in New York State. If such failures can be prevented or even minimized, the engineer has done his duty for the community. Failure of a bridge due to flood is shown in Figure 3. . 2. There is an abundance of information available about failures that are attributed to design limitations and construction quality, in addition to those caused by extreme events. 3. Eliminating the root causes leading to failure: One of the duties of any engineer is to mini-mize the possibility of failure. Engineering maintenance is not just patching concrete. It means preventing failure by managing, disciplining, and applying structural mechanics to the structural domain of bridge components, made up of single or composite materials.
It is important to understand both the mechanics and mechanism behind a failure and the applicable theory of yielding and fracture so that structural integrity is maintained and future designs are made safer. 2. 1. 4 Steps to Failures No list can be complete since many failures or even near failures in the past have not be-come public knowledge. A structural review of hundreds of failed bridges provides important data for: 1. Those bridges which collapsed. 2. Those which get demolished due to their poor condition, since allowing them to continue would result in imminent failure. . The wide variety of failures can be classified as: • Old bridge failures––Such failures are expected due to eventual disintegration of ma-terials. 10 Figure 1. 1 School children visiting the site of a railway bridge failure in India in 2005. The bridge was washed by floods causing the deaths of 114 people. • Landmark or historic bridges have improved inspection and maintenance and last longer than other old bridges of the same era. • Failure of new bridges––These are relatively few but occur due to design or construction errors. 3.
Design deficiency leading to bridge collapse: In 2007, a newly built prestressed concrete curved girder bridge collapsed in Karachi, Pakistan during rush hour killing over a dozen people and injuring dozens more (Figure 1. 2). Figure 1. 2 Immediately after recent collapse of the bridge in Karachi, ambulances assemble to carry the injured to hospitals. 11 5. Failure during construction: A surprising number of failures have occurred during construc-tion due to a lack of skilled labor, failure of lifting equipment and cranes, fabrication errors, or instability during erection. . 1. 5 Detailed Objectives Failures are like open books. There is an old saying that “failures are the pillars of success. ” It is based on deductive reasoning that if you identify, eliminate, or minimize the reasons for failure step by step, you have reduced the risk and probability of failure, thereby leading to eventual success. Primary objectives of our study are to identify all causes of failure and to understand the technical issues and reasons behind failure. The knowledge and experience gained from failure analysis can be applied: 1. To save lives and property. 2.
To study failure mechanisms, formation of plastic hinges, and modes of failure. 3. To develop analytical methods and efficient design codes; perform post design checks. 4. To study actual load combinations leading to collapse. 5. To study the behavior of materials. 6. To refine ultimate load methods of design including load factors, distribution factors, and resistance factors. 7. To improve construction practices and to implement reconstruction methods correctly. 8. To resolve disputes for insurance claims during forensic engineering. 2. 2 THE ROLE OF FORENSIC ENGINEERING 2. . 1 Combining Science, Engineering, and Legal Requirements 1. Forensic engineers explain how and why failures occur. The forensic process gets to the roots of the problem. It gives a clear insight into structural behavior and lack of maintenance, providing an independent account of deficiencies that lead to loss of life and/or damage. Conducting forensic engineering involves: • Expert witnessing • Technical knowledge • Detective skills • Legal aspects of the damage caused. 2. The basic procedures of conducting a forensic engineering investigation are applied following a failure.
Ultimately, based on the knowledge gained from past experiences, the engineer is better prepared technically to successfully face the challenges that will arise in the future. 3. A forensic engineer knows that if design and reconstruction criteria were correctly imple-mented a failure could be prevented. As a routine, bridges get demolished from sabotage, fatigue and fracture, old age, inherent defects, or a lack of compliance to normal functions. In addition, they may fail unexpectedly or due to continued neglect. 4. Collapse due to earthquake could be delayed when standard details, such as ductile moment resistance connections are used.
The expected life of 75 years or more for modern bridges and their components may not be achieved without regular inspection, structural evaluation, preventive action, and timely rehabilitation. 2. 2. 2 Documentation for Various Phases of Investigation 1. The structural forensic engineer, who is called in following a collapse, plays a crucial role in determining what the first steps of an investigation should be. He is the most qualified 12 to recognize perishable evidence and its potential value. The decisions made will directly affect the evidence upon which investigations will depend. 2.
For examination by the judicial process, the design engineer will maintain important records for the bridge such as contract documents including feasibility studies, site selection, selec-tion of bridge type, and value engineering. In particular documents must refer to: • Design criteria used and compliance with AASHTO and state codes • Design assumptions, calculations, and computer output––Evidence of client approval for use of computer software • Contract drawings • Special provisions of technical specifications which are not covered by state standard specifications • Approved shop drawings prepared by contractors A record of requests for information (RFI) and design change notices (DCN) during construction • As-built drawings. 3. Methodology for Forensic Analysis Accidents at construction sites can often result in serious injuries or death from defective or collapsing scaffolds and falls through roofing structures. Other cases include electrocutions, ladder injuries, defective machinery (cranes, hoists, conveyors, tractors, forklifts, etc. ), malfunc-tioning tools, and injuries or death from collapse of walls or floors. If the failure involves a construction site accident, the investigation will include: • Workplace safety and liability Compliance with OSHA The first steps after failure: The first steps following a collapse are critical (Figure 1. 3). The structural forensic engineer who is called in following a collapse is responsible for documenting Figure 1. 3 Failure of the I-35W bridge in Minneapolis, Minnesota on August 1, 2007. 13 this vital information. Immediate issues that a structural forensic engineer may be faced with when arriving at a collapse site and in the ensuing days include issues such as: • Safety • Preserving perishable evidence • Reserving samples • Documentation • Interviews • Document gathering • Preliminary evaluation of causes of failure. . Formal in-Depth Inquiry into the Defects Contributing to Failure The condition of a failed bridge needs to be thoroughly examined. The following are some of the deficiencies a forensic engineer will typically encounter in his investigations: 1. Inability to define loads accurately, such as magnitude and unpredictable level of stress distribution from settlement. 2. Limited redundancy in the structural system. 3. Inability to fully include plastic behavior or composite action between the concrete deck slab and repeated beams, arching action, creep and shrinkage strain distribution in the deck slab. . Lack of information on fracture mechanics in general and lack of understanding of fracture of new materials, in particular. 5. Inelastic behavior of connections and joints, splices, gusset plates, bolts, and welds. 6. Complex behavior as a unified assembly of uncombined multiple components of mixed (old and new) materials and structural systems, resulting from rehabilitation or widening methods. 7. Delamination and reduction in strength of the concrete deck due to deicing salts (as observed from chain drag test). 8.
Malfunction and locking of old bearing assemblies due to lack of maintenance, freezing of expansion bearings, large thermal forces causing compression, and local buckling of truss members and flanges. 9. Inability to prevent scour at pile top. 10. Inability to fully incorporate different types of soil interaction at abutments. 11. Lack of drainage behind abutments and pressure build-up behind abutments. 12. Inadequacy of Rankine, Coulomb, or Mononobe-Okabe theories for non-homogenous soil conditions for wing walls and stub abutments resulting in unstable design. . Forensic Engineering as a Diagnostic Tool An area where forensic science is required is failure from blast loads. Accidental explosions have resulted from numerous sources, including high explosives. These impulsive events call for specialized forensic analysis methodology. The damaging loads exist for only short durations, making conventional static analysis inappropriate for backing out possible root causes. Examin-ing structural load path transfer during a blast is required in order to provide additional support to portions of the structure under attack.
An important part of an explosion forensic analysis is to use damage indicators from the surroundings to determine the strength of the blast wave. The damage indicators are: 1. Deformed structural members. 2. Deflections in metal panels. 3. Debris throw. 14 The final result from analyzing many indicators leads to an understanding of the manner of explosion and magnitude of the explosion source energy. Correlation methods used are: 1. Semi-empirical damage correlations to single-degree-of-freedom analysis. 2. Semi-empirical damage correlations to dynamic nonlinear finite element analysis. 3.
Use of multiple damage indicators to identify the manner of explosion. 6. Preparing Judicial Reports An investigation report will clearly identify the reasons behind the failure and will cover any administrative and technical lapses or force majeure. Knowledge of state and federal laws addressing the rights of victims affected by the disas-ter will be required. Training in global bridge engineering to include forensic engineering is desirable for designers to appreciate the consequences of failures resulting from their actions or inactions. Continuing education seminars to create interest in objective designing need to be made mandatory. . MANY ASPECTS OF FAILURES 1. Table 3. 1 lists additional causes in light of more recent events. They may be identified on the basis of old and new technology. Additional causes of failures may be listed as: • Joints and connection failures (I-35W bridge failure in Minnesota) • Tornados and hurricanes (Louisiana disaster from Hurricane Katrina) • Bomb blast and vandalism (a bridge collapse in Manchester, New Hampshire and the 1992 A406 flyover in England) • Ice damage (author’s structural solutions as structural engineer for timber fender col-lapse at the navigable Delaware and Raritan River bridges for the New Jersey Turnpike Authority) Earthquake damage to bridges in Pakistan (author was a member of the U. S. AID Team which compiled a reconstruction report after the 2005 earthquake) • Scour collapse of Peckman’s River Bridge from Hurricane Floyd (the six-lane collapsed bridge on Route 46 was replaced with an integral abutment bridge, using deep pile foun-dations and shielded with sheet piling). 2. Failures during construction and due to earthquakes have been much higher than those shown by the earlier studies and need to be taken seriously in designing for construction loads or for seismic events. 3.
Design and detailing errors need to be minimized with QA/QC procedures and checking. 4. In the past, less attention has been paid to extreme events and construction conditions. How-ever, AASHTO LRFD Bridge Design Specifications have included both extreme events and construction loads in design. Further research is needed in these relatively new disciplines. 3. A DIAGNOSTIC APPROACH 2. 4. 1 Comparative Study of Failures The identification and diagnosis of failures is the starting point for meeting rehabilitation objectives and drafting a comprehensive code of practice for design.
The author has carried out in-depth studies of such causes and their prevention from many independent sources. Only five major sources are listed here: 1. According to Jean Louis Briaud of Texas A&M, a great number of bridges continue to fail due to flood, collision, and overload. Bridges with narrow waterway openings and erodible soils are most susceptible to bridge collapse. Other frequent principal causes are design, detailing, construction, and material defects. 15 Table 1. 1 Influence of technology level on bridge failures. Bridge Component |Old Technology |New Technology |Remarks | | | | | | |Deck slab |Open steel grid or steel |HPC, Exodermic and FRPC |Concrete deck is replaced | | |floor beam supported or low | |every 15 or 20 years | | |strength concrete | | | |Overlays for protection |Bitumen or screed for |Latex modified concrete, |Wearing surfaces added (FWS) | | |concrete deck |corrosion inhibitor aggregate |as required | | | |concrete | | Girders or trussesMade of cast iron, wrought iron, or mild steel with low yield strength Made of Grade 50 steel,Hybrid girders being used HPS 70W and HPS 100W Structural system |Use of non-redundant |Use of redundant multiple | |Composite action due to shear | | |through trusses |girder system | |connectors | |Joints and connections |Riveted connections |High strength bolts and welds |Detailing procedures revised in | | | | | |subsequent codes | |Parapet and railing |Non-crash tested |Crash tested | |Through girders also used as | | | | | |parapets in old system | |Seismic resistance |Rigid connections in |Use of ductile moment resisting |Substructure detailing | | |substructure |frames for piers | |procedures changed | |Bearings |Rocker and roller |Elastomeric pads or multi- | |New bearings allow thermal | | | |rotational | |changes and seismic | | | | | |movements | |Corrosion protection |Lead-based paint |Weathering steel with selected |Paint costs have increased as | | | |paint system | |percentage of total cost | |Foundations |Shallow or on timber piles |Deep oundations, steel piles |In-depth soil information is | | | |or drilled shaft | |required | |Protection against scour |Use of riprap |Gabions, sheet piles and | |Additional cost of | | | |articulated concrete blocks | |countermeasures is incurred | | | | | | | |Design Aspects | | | | | | | | | | |Live load |H-15 and H-20 |HS-20, HS-25, HL-93, and |Majority of old bridges are posted | | | |permit trucks | | | |Strength design |Allowable stress or load factor |Load and resistance factor |New designs are economical or safe | | | |design (LRFD) | | | |Load combinations |Extreme conditions not |Collision, seismic analysis, |Use of computer software has | |for analysis |considered |and scour analysis considered |made possible over a dozen load | | | | |combinations | |Inspection methods |Visual |Visual and SHM |Frequency of inspections is | | | | |increased | |Rating methods |Load factor |Load and resistance factor |Scour vulnerability and seismic | | | |rating (LRFR) |vulnerability introduced | | | | | | | 16 2. Wardhana and Hadipriono studied over 500 bridge structure failures in the United States. The age of the failed bridges ranged from one year (or during construction) to 157 years. The most frequent causes of bridge failures were floods and collisions. Bridge overload and lateral impact forces from trucks, barges/ships, and trains constitute 20 percent of the total bridge failures. In the U. S. alone, over 36,000 bridges are either scour critical or scour susceptible. 3. Campbell R.
Middleton of the University of Cambridge Engineering Department has orga-nized comprehensive databases summarizing the failure records according to the chronology of events, country of occurrence, reasons of failure, and bridge type. 4. Bjorn Akesson in his 2008 book “Understanding Bridge Collapses,” estimates scour as responsible for about 50 percent of bridge failures. The book presents useful information on structural details and deficiencies of 20 well-known bridges that failed between 1847 (Dee Bridge on River Severn, England) and 2003 (Sgt. Aubrey Cosens VC Memorial Bridge in Canada) through analysis of failures. Other causes of failures listed in his book are lack of material strength and maintenance, accidents, fatigue, brittle fractures, buckling, wind loading, aerodynamic instability, fire, and poor anchorage capacity.
While failures of very old bridges built before 1940 appear to be of academic interest due to a different level of technology, (much lower intensity and frequency of truck live loads), the failures in the past 75 years (erstwhile generation of bridges) are of practical interest. A 70-year life span is the current minimum design life of each generation of bridges based on fatigue, as sug-gested by AASHTO LRFD Specifications. Many of the bridges listed by Akesson failed much earlier. 5. Jana Brenning in the Scientific American Journal was one of the earliest to address the causes of failures in 1993. Since then more information has been compiled. Technological advances in information systems have a great impact on data collection and analysis. Water, salt, stress, and corrosion can make a bridge structurally deficient. A decrease in the load rating will result in imposing weight limits. 2.
Understanding the Multiple Structural and Fracture Causes The most common causes of bridge failure include: 1. Overstress of girders from section loss (Figure 1. 4), design defects, and deficiencies: See Section 3. 6, Design Deficiency and Preventive Actions, for historical events and recom-mended preventive actions. Figure 1. 4 The deterioration of girders is a potential cause of bridge failures. 17 Pre-collapse deficiencies can include incorrect assumptions, data errors, incorrect analysis, noncompliance with code guidelines, incorrect connection details, and mistakes in drawings. Other frequent principal causes are design, detailing, and use of substandard materials. . Long-term fatigue and fracture (see Section 3. 7, Fatigue Failures and Suggested Preventive Actions): Failures can be due to fatigue of steel or concrete girders from repeated reversal of stress. Brittle fracture results in the unplanned loss of service, very costly repairs, concern regarding the future safety of the structure, and potential loss of life. 3. Failures during construction (see Section 3. 8, Construction Deficiency and Suggested Preven-tive Actions): Include constructability issues such as construction inspection, construction supervision, quality control, use of substandard materials, and deficient design of temporary works.
Heavy construction loads and construction defects such as poor workmanship, sub-standard materials, inadequate concrete curing, imperfections in steel, lack of fit, and lack of quality control are other possible causes. 4. Accidental impact from ships and vessels (see Section 3. 9, Vessel Collision or Floating Ice and Suggested Preventive Actions). 5. Accidental impact from trains and defects in geometry such as vertical under clearance (see Section 3. 10, Train Accidents Causing Bridge Damage and Preventive Action). 6. Accidental impact from vehicles (see Section 1. 11, Vehicle Impact and Preventive Action). 7. Failures due to blast loads (see Section 1. 12, Blast Load and Preventive Action). 8. Failures due to fire damage (see Section 1. 3, Fire Damage to Superstructures and Preventive Action): Fire may result from accidental spraying of gasoline, any stored material under the bridge catching fire, overturned vehicles, lightning, or vandalism. 9. Failures due to earthquakes (see Section 1. 14, Substructure Damage Due to Earthquake and Preventive Actions): Includes failure due to earthquake from limited bearing seat width or plastic hinge formation. 10. Failures due to heavy winds, tornados, and hurricanes (see Section 1. 15, Wind and Hurricane Engineering). 11. Failures due to lack of inspection (see Section 1. 16, Lack of Maintenance and Neglect). Lack of maintenance or inspection leads to: • Malfunction of bearings • Corrosion of steel: Lack of painting.
Failures due to corrosion of steel girders caused by evaporation and condensation of river water. 12. Failures due to unforeseen events in spite of maintenance (see Section 1. 17, Unforeseen Causes Leading to Failures). • Ice damage of piers and failure of timber fenders (unexpected loads and load combina-tions: Force majeure • Poor deck drainage: Negligence • Soil settlement: Force majeure • Freezing of bridge surface: Negligence • Failure due to gussets or connections: Design deficiency. 13. Failure due to experimentation: Some failures may occur due to experimentation with new types of materials or new systems such as undefined and unpredictable material properties in cast in place or precast construction.
Although this approach may be unavoidable in certain disciplines such as space exploration, caution is necessary. Any one of the above factors may contribute to bridge failure or may trigger a collapse, but failures actually occur due to a combination of loads, of which the principal or additional cause can be one of those listed above. Although load combinations have been defined by AASHTO LRFD Bridge Design Speci-fications, they do not include some of those listed above. |18 | | | | | |Table 1. Recent international bridge failures, and the nature of each collapse. | | | | | | | | | |Location |Year |Description |Nature of Collapse | | | | | | | | |Shershah Bridge Karachi, Pakistan |2007 |Ten people died. |Bridge less than two weeks old | | |(see Figure 3. ) | | | | | |Southern China |2007 |Many casualties |Bridge over river hit by a ship in fog | |Kashiwazaki City, |2007 |Many casualties |Due to earthquake | | |Nigata, Japan | | | | | |Laval, Quebec, Canada |2006 |Autoroute 19 overpass collapsed killing five |Not available | | | | |and injuring six. | | | |India |2005 |A rail disaster killed 114 people. |Flood washed a rail bridge away | | |Southern Spain |2005 |A section of a highway bridge collapsed killing |Under construction | | | | |six people. | | |Daman, India |2003 |Long span suspension bridge |Bridge collapse over a river | | |Central China |2002 |Two bridges killing a combined 19 people |Not available | | |Lisbon, Portugal |2001 |Collapse caused a tour bus to plunge into a |Bridge collapse over a river | | | | |river, killing more than 50 people. | | | |Seongsu Bridge, Seoul, South Korea 1994 |Collapse killed 32 and injured 17. Not available | | | | | | | | 4. A HISTORICAL PERSPECTIVE OF RECENT FAILURES 2. 5. 1 Bridges Not Located on Rivers Bridges have failed the world over and continue to do so. Most failures can be avoided with efficient monitoring and timely maintenance. Some examples of recent bridge failures in the U. S. are given below where full or partial failures have resulted from: 1. Fatigue and fracture (numerous railway and highway bridges). 2. Corrosion and web cracking of steel girders (I-95 curved bridge located near the Philadelphia Airport). 3.
Collision damage due to limited vertical under clearance (North Jersey Bridge). 4. Fire and excessive heat (I-95 bridge northeast of Philadelphia). 5. Earthquake movements (bridge failures in California). 6. Excessive wind (Tacoma Narrows Bridge). Examples of more recent failures outside the U. S. : A brief description of casualties is pro-vided in Table 3. 2. 2. Examples of Foundation Scour 1. Failure due to foundation scour and settlement from soil erosion is a threat to bridge struc-tures. The majority of scour-related failures can be avoided by providing modern countermea-sures at their foundations to prevent erosion. 2. Scour from Riverine Flow
Foundation scour is a major cause of bridge failures. Foundation settlement is caused from erosion and weak soil conditions. When a pier tilts (Figure 3. 6), there is potential for a bridge to collapse without warning. This is a definite safety issue for travelers. Scour likely reduces the capacity of existing foundations due to the removal of scoured ma-terial. Section 46 of the NJDOT LRFD Design Manual for Bridges and Structures, developed 19 Figure 1. 5 Sudden collapse of Shershah curved girder bridge in Karachi, Pakistan. by the author, requires precautionary scour protection at all times based on a scour analysis. Countermeasures are needed based on HEC-23.
Other examples of bridge failure include a bridge in Ellis County, Texas in 2004 and an-other major failure in New York (Schoharie Creek bridge located on the NY state thruway) in 1987. 3. Scour from tidal flow: Tidal scour analysis using procedures outlined in HEC-18 and HEC-25 is required. • Tidal scour is more common than the fluvial flood flows of shorter durations. The destruc-tive nature of scour evolves in cumulative smaller steps rather than occurring in a single flood event. Figure 1. 6 Abutment settlement, backwall collapse, and bearing failure. 20 Table 1. 3 Recent bridge failures in the U. S. , including the nature of each collapse. Location |Year |Description |Nature of Collapse | | | | | | |Interstate 35W Minneapolis, MN |2007 |Twelve people died. |Bridge collapse over a river | |Webbers Falls, OK over the |2002 |A 500-foot section of the I-40 bridge |A barge struck one pier of bridge, | |Arkansas River (see Figure 3. 10) | |collapsed, killing 14 people. |causing partial collapse. | |Walnut St.
Bridge, Harrisburg, PA |1996 |Some injuries |Bridge collapse over a river | |Tennessee River Bridge, Clifton, TN |1995 |Some casualties |Bridge collapse over a river | |Schoharie Creek Thruway Bridge, |1987 |A total collapse of the bridge killed |Bridge collapse over a river | |Amsterdam, NY | |10 people | | |Sunshine Skyway Bridge, Tampa, FL |1980 |A ship hit the bridge during a storm, |Bridge collapse over a river | | | |35 people were killed in the collapse. | | | | | | | • Scour is induced due to wave action. • Scour is induced due to tidal currents. • Effects of the interaction of simultaneous fluvial and tidal currents may be present. • The effects of littoral drift can increase lateral migration and affect long term erosion. Bridges located on tidal waterways are also subjected to contraction and local scour. 3. The physical factors affecting tidal scour include: • Peak tidal velocities Variations between flood velocity and ebb velocity • Range of tidal amplitude between neaps and spring tides • Locations and shapes of scour under different flow conditions • Cumulative effect of a series of tides. Bridges on rivers (subjected to floods or accidents) seem to be affected the most. Historic failures due to flood scour in the U. S. and abroad: Table 1. 4 lists some of the recorded scour failures in the U. S. , Canada, Germany, Britain, Austria, Portugal, India, China, South Korea, and Australia. 3. Diagnostic Case Studies by Author Temporary underpinning and replacement design of New Jersy’s Route 46 bridge on Peckman’s River.
Due to Hurricane Floyd in 1997, overtopping of bridge occurred. Much of Route 46 Peckman’s River area was fully flooded. A replacement bridge was designed by the author using integral abutments with a single row of piles. Abutment settlement occurred and heavy cracking of approaches took place (Figures 1. 6 and 1. 7). Temporary pile bents (with piles over 90 feet long) were driven in front of abutments to transfer the load from the abutments. In addition to replacing the damaged bridge, the approach slab had to be reconstructed. Planning recommendations for Peckman’s Bridge: 1. The direction of the abutment skew is now parallel to the meandered direction of river flow to minimize scour. 2.
Based on hydraulic analysis, the opening size has been increased to minimize overtopping flood. 3. Use of integral abutments and integral approaches make the bridge more resistant to longi-tudinal forces. 4. Steel girders have been replaced by prestressed spread box beams to prevent corrosion. |21 | | | | | |Table 1. 4 Historic failures due to flood scour. | | | | | | | | | |U. S.
Bridges | |Location |Year |Details of Failure | | | | | | |Interstate 29 West Bridge |Sioux City, IA |1962 |Natural hazard (flooding scour) | |Bridge near Charleston, SC |Cooper River, SC |1965 |Natural hazard (flooding scour), pier failure | |Interstate 17 Bridge |Black Canyon, AZ |1978 |Natural hazard (flooding scour) | |Schoharie Creek Bridge |Near Fort Hunter, NY |1987 |Flooding and storm led to collapse of two spans after | | | | | |scouring of a pier. |Twin I-5 Bridges |Coalinga, CA |1995 |Scour of bridge foundations | |(Arroyo Pasajero River) | | | | |Tennessee River Bridge |Clifton, TN |1995 |Scour | |Walnut Street Bridge |Harrisburg, PA |1996 |Scour and ice damage | |(Susquehanna River) | | | | |Hatchie River|Bridge |Near Covington, TN |1999 |Scouring and undermining of the foundations | |Interstate 20 bridge on |Near Pecos, TX |2004 |Scour from floodwaters after two days of heavy rain | |Salt Draw River | | | | |Lee Roy Selmon Expressway |Tampa Bay, FL |2004 |Scour hole developed under a concrete pier causing bridge | | | | | |to drop. |Rural Bridge (Beaver Dam Creek) |Near Shelby, NC |2004 |Natural hazard (flooding scour) causing bridge washout | |Canadian Bridges | | | | |Bridge over a river |British Columbia |1981 |Flood scour and tree debris in water destroy bridge. | |German Bridges | | | | |Bridges over Weser River |Bremen |1947 |Flooding, floating ice, and ships led to the collapse of | | | | | |the bridges. | |Bridge over Mosel River |Near Koblenz |1947 |Flooding and floating ice led to collapse of the bridge. |Esslingen Bridge |Esslingen |1969 |Water entering sheet pile wall caisson and flooding during | | | | | |construction | |Bridges in Germany |South and East |2002 |Extensive flooding in South and East Germany due to scour | | | |Germany | | | |British Bridges | | | | |Drimsallie Bridge |Inverness, Scotland |1973 |One span of bridge collapsed due to washout of abutment | | | | | |in flood—foundation scour | |Glanrhyd Railway Bridge over |Near Llandeilo, Wales |1987 |Flooding, bridge collapsed as a train drove over it— | |River Towy | | | |flood scour. |Multispan masonry arch |Inverness, Scotland |1989 |Heavy floods washed multispan masonry arch bridge away, | |Ness viaduct | | | |just after a freight train had passed over it—flood scour | |Five-span bridge at Forteviot, |10 km south of Perth, |1993 |Flooding, erosion of the gravel bed beneath the | |(May River) | |Scotland | |downstream face of the shallow founded pier, concrete bag | | | | | |scour protection washed away—flood scour. | 22 Table 1. 4 Historic failures due to flood scour (continued). Austrian Bridges |Location |Year |Details | | | | | | |Motorway Bridge |Near Salzburg |1959 |Scour due to flooding | |Two-span truss bridge over |Between Linz |1982 |Scour led to loss of pier and partial collapse of bridge | |Traun River |and Selzthal | |girder. | |Five-span box girder motorway |Near Kufstein |1990 |Scouring led to settlement and major damage of | |bridge over Inn River | | |distorted superstructure. | |Bridge in Braz |Braz, Vorarlberg |1995 |Express train plunged into ravine after mudslide | | | | destroying rail bridge—scour due to floods | |Bridges in Austria |Various locations |2002 |Flooding in Thurnberg, Engelstein, Salzburg and other cities | | | | |—scour | |Portuguese Bridges | | | | |Bridge over river |Lisbon |2001 |Bridge collapse caused a tour bus to plunge into a river | Indian Bridges |Bridge between Jabalpur |Madhya Pradesh |1984 | |and Gondia | | | |Bridge (Nalgonda district) |Near Veligonda |2005 | Railway bridge |India |2005 | |Long span suspension bridge |Daman |2003 | |over river | | | |Chinese Bridges | | | |Two bridges |Central China |2002 | South Korean Bridges Flooding scour Floodwaters from two breached reservoir tanks upstream washed away the embankment leaving only the rail tracks dangling in the air. Train derailed and plunged into a rivulet due to breaches on the track. Flood washed a rail bridge away—foundation scour. Flood velocity Floods Bridge over river |Seoul |2004 |Foundation scour | |Australian Bridges | | | | |River bridge 40 km west of |Queensland |2005 |A man was checking floodwaters when the bridge he was | |Charters Towers | | |standing on collapsed—flood scour. | | | | | | 5. Deep sheet piling sections were used to minimize scour of abutment and wingwalls. 6. Both superstructure and substructure designs are based on the LRFD method. Figure 3. 8 shows the completed bridge. 7. Replacement design of the Rancocas Creek Bridge by the author (see Figure 1. 9) shows the parapet type used by Burlington County, NJ.
Flooding of Rancocas Creek and occasional overtopping of the bridge showed that the bridge was functionally obsolete. It had become dangerous and its hydraulic opening needed to be increased. Unlike the spread box beams of Peckman’s River Bridge, adjacent box beams were used which helped to reduce life cycle costs by avoiding corrosion and repainting. 23 Figure 1. 7 Installing temporary pile bents on Peckman’s River Bridge. 2. 5. 4Preventive Action against Foundation Scour Performing scour analysis and use of effective countermeasures, such as deep foundations and river training, may be required in addition to conventional shielding. Design of countermea-sures will be based on HEC-23 procedures.
Scour countermeasure options include river training measures, dredging, driving sheet piles around the piers and abutments, and filling the gaps with riprap. Alternate measures such as grout bags, cable-tied blocks, and AJAX type blocks will be considered, based on tidal flow conditions. Figure 1. 8 Overhead sign structure and integral abutment designed by author. 24 Figure 1. 9 Author’s design of aesthetic, strong, and easy-to-repair concrete parapet. Wide cracks at piers need to be pressure grouted with epoxy grout, as recommended in the inspection report. Design of required repairs and retrofits to substructure will consider: • Modern countermeasures technology requires new construction techniques.
The contractor performing such tasks will need properly trained construction crews. • Providing cofferdams, sheet piling, and bed armoring will require temporary construction work. Alternatives for using quick construction should be considered. Figure 1. 10 Failure of Webbers Falls bridge in Oklahoma in 2002. 25 • The available flow width may be reduced due to construction of cofferdams. • Velocities through the remaining opening will increase, thereby increasing scour in the channel and around the structure. • Any river pollution from construction material needs to be monitored. Regular cleaning of the channel may be required. • Approvals for stream encroachment permits will be necessary. The effect of driving sheeting or bed armoring on existing utility needs evaluation. • Countermeasures may extend into adjacent property limits. Any construction easement needs to be carefully evaluated and permits obtained. • Tidal conditions will affect working methods and working hours for construction. • The health and safety of construction personnel will be a concern due to water depth. 5. DESIGN DEFICIENCY AND PREVENTIVE ACTIONS 2. 6. 1Incorrect Design Assumptions or Modeling Errors Table 3. 5 shows reasons for failures from assumptions which are usually made in analysis. Failures result when assumptions do not truly represent the behavior of the superstructure in the field. Figure 3. 1 shows a newspaper cartoon published in Karachi, Pakistan after the 2007 col-lapse of a bridge. 2. 6. 2General Preventive Measures 1. Provide space for bearing inspection chambers. 2. Apply load and resistance factors based on LRFD methods. 3. Ensure seismic retrofit against minor and recurring earthquakes. 4. Provide scour countermeasures. 5. Effectively monitor through remote sensors. 6. Study failure mechanisms of different types of structural systems. 7. Maintain quality control and personnel safety during construction. 8. Develop and make available codes for rehabilitation of mixed structural systems should be developed and made available. Figure 1. 1 The impact of engineering decision on bridge users: A cartoon shows a family in Karachi offering prayers before crossing a bridge. The public is cautiously aware of bridge safety conditions. |26 | | | | | | | |Table 1. 5 History of failures due to design deficiency. | | | | | | | | | | | | |U. S.
Bridges |Location |Year |Reasons for Failure | | | | | | | | | | |Tacoma Narrows suspension bridge |Washington State |1940 |Insufficient bending and torsion stiffness, | | | | | | |aerodynamic instability | | | |King’s River Slough Bridge |Near Fresno, California |1947 |Overloading from an agricultural train | | | |Elbow grade bridge, timber truss |Willamette |1950 |Parts of truss underdesigned | | | |National Forest | | | | | |Silver bridge, chain suspension bridge |Ohio River |1967 |Fatigue | | | |Bridge over Kaslaski River |Illinois |1970 |Not anchored against uplift—design error | | | |Syracuse bridge |New York |1982 |Torsional buckling due to lacking lateral support | | | |Oakland highway bridge |California |2007 |Design deficiency | | | |Canadian Bridges | | | | | | |Second Narrows Bridge |Vancouver, |1958 |Web buckling of transverse girder due to | | | | |British Columbia | |design error | | | |The Autoroute 19 Overpass bridge |Laval, Quebec |2006 |Design deficiency | | | |German Bridges | | | | | | |Continuous truss bridge over |Near Leer |1960 |Earth pressure horizontal load not considered | | | |Leda River | | |—design error | | | |A2 bridge |Near Lichtendorf, |1968 |Moving supports due to creep, shrinkage, and low | | | |Schwerte | |temperature-pier head destroyed, settlement of | | | | | | |bridge—design failure | | | |Rodach River bridge |Near Redwitz |1973 |Bridge collapses under overload from ready-mix | | | | | |concrete mixer—design failure | | | |Vorland Bridge |Hochheim |1973 |High temperature resulting in support plates | | | | | |moving – design failure | | | |Zeulenroda Bridge |East Germany |1973 |Buckling of steel box section flange plate due to | | | | | | |lack of stiffeners | | | |Austrian Bridges | | | | | | |Reichsbrucke |Vienna |1976 |Lack of reinforcement in pier footing | | | |Indian Bridges | | | | | | |Assam bridge |Assam |1977 |Heavy train—overloading | | | |Punjab Province bridge |Punjab |1977 |Packed coach on bridge—overloading | | | |Dombivli Railway Station |Dombivli |2004 |Faulty design, not enough resistance—failed | | | |foot overbridge | | |during construction | | | |South Korean Bridges | | | | | | |Seongsu Bridge |Seoul |1994 |Design deficiency | | | | | | | | | | 27 9. Cracks in substructure due to foundation settlement needs to be prevented by underpinning. (see Figure 3. 12). 10. Develop codes for new materials such as FRP decks should be developed. New techniques of repairs as discussed in this book need to be incorporated in the codes. 11. Implement greater vendor and construction engineer participation in revising and developing design codes. 6. FATIGUE FAILURES AND SUGGESTED PREVENTIVE ACTIONS 2. 7. 1Fatigue of Members and Connections/ Controlling Level of Truck Traffic 1. Load-induced fatigue damage assessment: In 2005 ASCE Proceedings, J.
Robert Connor and John W. Fisher of Lehigh University, Bethlehem, Pennsylvania, and William J. Wright of FHWA reported on brittle fractures in steel and preventive maintenance strategies. Cumulative fatigue damage of uncracked members and fasteners that are subjected to repeated variations or reversals of load-induced stress needs to be assessed. The lists of detail categories and illustrative examples to consider in a fatigue damage assessment are shown in AASHTO specifications and the AISC Handbook. If cracks have already been visually detected, a more complex fracture mechanics approach for load-induced fatigue is required instead of the procedure outlined here.
Generally, upon visual detection of cracking, the vast proportion (perhaps over 80 percent) of the fatigue life has been exhausted and retrofitting measures should be initiated. Infinite fatigue life or remaining finite fatigue life needs to be evaluated. 2. Calculated fatigue stress range: The factored live load stress range, produced by the method given in the LRFD code is considered an approximate method of analysis. 2. 7. 2Suggested Preventive Action Against Excessive Fatigue Adequate man hours need to be spent in analysis and design to conform to all aspects of AASHTO LRFD code. To avoid failures: 1. Durability requirements need to be addressed on a scientific basis. 2.
AASHTO code provisions and other relevant codes need to be followed. 3. Fatigue failures are most critical when there is no evidence of fatigue cracking leading up to Figure 1. 12 Foundation settlement cracks at the junction of the abutment and wingwall create a potential danger of collapse. 28 the fracture. Hence, they occur without warning and the details are essentially non-inspect-able. The following preemptive retrofit strategies appear to be highly desirable: • Avoid use of high carbon brittle steel • Avoid poorly executed welding leading to high residual stress level • Avoid bad detailing • Avoid dynamic loads that cause high strain rates and reversal of stress CAD drawings should have sufficient details. Emphasize increasing the strength of joints by adding bolts and the strength of the girder web and flanges by adding plates, etc. • QA/QC procedures should ensure adequate checking of criteria, method of analysis, design details, and technical specifications. 7. CONSTRUCTION DEFICIENCY AND SUGGESTED PREVENTIVE ACTIONS 1. Lack of Quality Control or Construction Supervision Failure or early demolition of a bridge needs to be avoided at all costs. The most vulnerable stage is during construction. During construction, critical items are inadvertently overlooked, thereby leading to failure. Critical items include: 1.
Inadequate design of formwork or its premature removal. 2. Inadequate bracing. 3. Improper sequence of concrete placement. 4. Improper sequence of erection. 5. Improper placement of reinforcing bars. 6. Incorrect profiles of post-tensioning tendons. 7. Welding deficiencies in steel connections. 8. Incorrect thickness of gusset plates. Table 3. 6 shows reasons for failures during construction or by negligence in the field. It is an area of weakness where expertise in construction techniques is desirable. Many failures seem to happen during construction. One of the difficulties is that construction practice varies from state to state and from job site to job site.
Site organization is based on selec-tion of one general contractor, who in turn selects several sub-contractors who have specialized in a particular trade such as concreting, formwork, steel fabrication, bearings, reinforcing steel, etc. Construction procedures need to be streamlined. 2. Method of Construction 1. Current specifications do not adequately cover construction related design and temporary loads. Future construction codes should address issues created by the use of the latest technology such as new construction loads. Technical specifications may also be made comprehensive to give minutest details of construction procedure. 2. Accelerated bridge construction: Modern construction technology seems to be pulling the train on design methods. Precast technology is a world apart from traditional wet construc-tion methods.
Self-propelled modular transportation (SPMT) has enabled the transportation of long span assembled girders without the need for splices, resulting in increased factory production. The connection design used for precast construction is different than that used in traditional construction. Joint strength must be be tested in a structures laboratory. 3. Suggested Preventive Action against Construction Failures 1. Design of temporary works such as scaffolding supports and formwork supporting a deck during concreting needs to be in accordance with AASHTO temporary works design manual 29 Table 1. 6 History of failures during construction (constructability issues). |U. S.
Bridges |Location |Year |Construction Deficiencies | | | | | | |Hinton truss bridge |West Virginia |1949 |Insufficient design capacity of cantilever arm during | | | | |construction | | | | |phase |Sullivan Square Viaduct |Boston, Massachusetts |1952 |Instability of scaffolding during construction | |motorway bridge | | | | |Buckman Bridge |Jacksonville, Florida |1970 |Voided pier filled with sea water during construction—expansion | | | | |of pier—partial collapse of bridge | |Motorway bridge |Near Pasadena, California |1972 |Scaffolding collapsed under weight of fresh concrete | |(Arroyo Seco River) | | | | |Concrete 5-span box girder |Near Rockford |1979 |Large cracks, failure of epoxy-filled joint | |bridge near | | |(not enough hardened to take design shear force) | |Multiple span box girder bridge |East Chicago, Indianapolis |1982 |Scaffolding collapsed under weight of fresh concrete | |Prestressed concrete precast |Saginaw, Michigan |1982 |Temporary support elements too weak during construction | |box girder bridge | | | | |Walnut Street Viaduct over I-20 |Denver, Colorado |1985 |Failure of pier head during construction sent eight bridge | | | | |girders onto road | |El Paso bridge |El Paso, Texas |1987 |Inadequate scaffolding during construction | |Motorway bridge |Near Seattle, Washington |1988 |Girders not tied together by diaphragms, domino effect | | | | |during construction | |Box girder bridge |Los Angeles, California |1989 |Collapsed when scaffolding was removed during construction | |Baltimore bridge |Baltimore, Maryland |1989 |Prestressing not in place, asymmetric loading | | | |during construction | |Truss bridge |Concord, New Hampshire |1993 |Stiffener mounted at wrong place during construction | |3-span 3-girder composite bridge |Near Clifton, Tennessee |1995 |Executed construction sequence different from the one planned | |Marcy bridge (Utica-Rome |Marcy, New York |2002 |Global torsional buckling during concreting, bridge not | |Expressway project) | | |braced properly | |Imola Avenue Bridge |Napa, California |2003 |3- 100-ton hydraulic jacks to raise falsework failed to support | | | | |poured-in-place concrete deck slab | |Bridge near Pawnee City |Near Pawnee City, Nebraska |2004 |Failure of falsework caused bridge collapsed during concrete | | | | |pouring | |I-70 Bridge |Denver, Colorado |2004 |Bracings, fastened to bridge with bolts, came loose as girder | | | | |collapsed—construction failure | |Canadian Bridges | | | | |Dawson Creek suspension bridge |British Columbia |1957 |Movement of anchorages on footings which were not fixed | |(Peace River) | | |properly—sub-standard construction | |Second Narrows Bridge |Vancouver |1958 |Bad construction details detected, but no action taken | |(Gerber hinge) | | |—construction failure | |Arch bridge over Rideau River |Ottawa |1966 |Scaffolding collapsed under weight of fresh concrete | | | | |—construction failure | |3-span rch bridge |Elwood |1982 |Lateral buckling of scaffolding due to insufficient lateral | | | | |supports—construction failure | |Composite bridge near Sept-Iles |Near Quebec |1984 |Failure during construction from faulty calculations | | | | |—design errors | 30 Table 1. 6 History of failures during construction (constructability issues) (continued). German Bridges |Location |Year |Details | | | | | | |Motorway bridge |Near Frankenthal |1940 |Failure of lifting equipment during construction | |Hindenburg bridge over |Cologne |1945 |Collapse during refurbishment | |Rhine River | | | | |Motorway composite bridge |Near Kaiserslautern |1954 |Insufficient stiffness of top members about weak axis | | | | |—construction failure | |Nordbrucke bridge over |Dusseldorf |1956 | |Rhine River | | | |Continuous motorway bridge |Near Limburg |1961 | |Heidingsfeld motorway |Heidingsfeld |1963 | |composite bridge | | | |Vorland Rees-Kalkar plate |Between Rees and Kalkar |1966 | girder bridge | | | |Bridge near Wennigsen, |Near Wennigsen, |1971 | |Niedersachsen |Niedersachsen | | |Steel box girder bridge over |Koblenz |1971 | |Rhine River | | | |Continuous Hangbrucke over |Near Koblenz |1972 | |Laubachtal | | | |Steel box girder bridge |Zeulenroda |1973 | |Bridge over Leubas River |Near Kempten |1974 | |Brohltal bridge, segmental |Brohltal |1974 | |construction | | | |Timber truss |Bad Cannstatt |1977 | |13-span Rottachtal bridge |Near Oy |1979 | |Bridge near Dedensen |Near Dedensen |1982 | |Simple span, steel truss bridge |Road bridge |1982 | |Bridge on DB Lohr-Wertheim |Near Kreuzwertheim |1984 | |railway line | | | |Composite Czerny Bridge |Heidelberg |1985 | |New (composite) Grosshesselohe Munich |1985 | |bridge | | | Insufficient crane capacity to carry double load— construction failure Settlement of temporary foundations, load redistribution, scaffolding collapse—construction failure Temporary concrete support plates underdesigned— construction failure Temporary supports underdesigned—construction failure
Scaffolding collapsed under weight of fresh concrete —construction failure Plate buckling of bottom chord in compression— cantilevered construction failure Scaffolding collapsed under weight of fresh concrete —construction failure Plate buckling of bottom chord—cantilevered construction failure Scaffolding collapses under weight of fresh concrete —construction failure Incremental launch construction led to concrete crushing when low prestressing cable positions are over support, settlements Construction sequence not thought out— construction failure Incremental launch, large cracks, inversed position of gliding plate (top/bottom)—construction failure
Lateral buckling of construction support girder during removing of lateral supports Temporary support elements too weak— construction failure Use of uncertified lifting bars and too weak bolt nuts —construction failure Use of wrong bolts—construction failure Ignorance of load case “displacement of mobile scaffolding”—construction failure (Table continues on next page) 31 Table 1. 6 History of failures during construction (constructability issues) (continued). |German Bridges |Location |Year |Details | | | | |A3 motorway bridge (Main River) Near Aschaffenburg |1988 |Critical load case during incremental launch not included, | | | | |shear failure during construction | |Approach bridge |Cologne-Wahn Airport |1995 |Scaffolding collapsed under weight of fresh concrete | |(beam-and-slab) | | |—construction failure | |British Bridges | | | | |Barton Bridge |Lancashire, England |1959 |Buckling of temporary props—construction failure | |Cleddau Bridge |Milford Haven, Wales |1970 |Incremental launch of long span, box girder plate buckling | | | | |over support—construction failure | |Loddon Bridge |Berkshire, England |1972 |24 m span collapsed during placing of concrete due to | | | | |failure of falsework—construction failure | Austrian Bridges Fourth Danube Bridge (plate |Vienna |1969 | |box girder bridge) | | | |Soboth prestressed concrete |Soboth |1970 | |bridge | | | |Prestressed concrete bridge over Gmund |1975 | |Tauern motorway | | | |Rheinbrucke bridge |Near Hochst, Vorarlberg |1982 | |over Rhine River | | | |Spanish Bridges | | | |Highway bridge |Southern Spain |2005 | |Indian Bridges | | | |Bihar district bridge |Bihar |1978 | Japanese Bridges | | | |Prestressed concrete bridge |Avato, Japan |1979 | |Tokyo West bridge over |Tokyo West |1984 | |Tama River | | | |Hiroshima bridge |Hiroshima |1991 | Australian Bridges Plate buckling of bottom chord in compression— construction failure Collapsed during cantilevered construction, prestressing bars badly put in place Concrete resistance not yet achieved, construction not in accordance with design Scaffolding collapses under weight of fresh concrete —construction failure Under construction Construction failure
Incremental launch, when cantilevers coming from two sides were to be joined, differences in length appear. Temporary construction to correct it led to collapse of both cantilevers—construction failure Scaffolding removal sequence was not well-thought-out —construction failure Stability problem, sliding—construction failure |Westgate Bridge over Yarra River |Melbourne |1970 |Plate buckling due to weak splicing of longitudinal stiffeners | | | | |—construction sequence was not well-thought-out | |Loddon River bridge |Near Victoria |1972 Scaffolding collapsed under weight of fresh concrete | | | | |—construction failure | | | | | | 32 and OSHA standards. Lack of quality control for materials testing and an unrealisticly quick construction schedule need to be avoided. 2. New foundation construction techniques: Many problems and substandard performance of foundations observed in structures on expansive soils occur from faulty construction practices. The construction equipment and procedures that are used depend on the founda-tion soil characteristics and soil profiles. Construction techniques that promote a constant moisture regime in the foundation soils should be used during and following construction. 3.
Self-consolidating concrete (SCC) for use in drilled shaft applications: When conventional concrete is used in congested drilled shafts, coarse aggregates may bridge between reinforc-ing bars, which may lead to segregation of the concrete between the inside and outside of the reinforcing cage. SCC is feasible for use in congested drilled shaft applications. 8. VESSEL COLLISION OR FLOATING ICE AND SUGGESTED PREVENTIVE ACTIONS 2. 9. 1 General Bridge piers located on navigable rivers are likely to be hit in fog or in darkness usually from barges or ocean going ships. Damage to timber fenders which shield the piers may also be caused by floating ice at high velocities. The EOR must assemble the following information: 1. Characteristics of the waterway including: • A nautical chart of the waterway • Type and geometry of the bridge Preliminary plan and elevation drawings depicting the number, size, and location of the proposed piers, navigation channel, width, depth, and geometry • Average current velocity across the waterway. 2. Characteristics of the vessels and traffic including: • Ship, tug, and barge sizes (length, width, and height) • Number of passages for ships, tugs, and barges per year (prediction for 25 years) • Vessel displacements • Cargo displacements (deadweight tonnage) • Draft (depth below the waterline) of ships, tugs, and barges • The overall length and speed of tow. 3. Accident reports. 4. Bridge importance classification. Table 3. 7 shows failure details for a large number of impacts from ships, which is also a cause of concern for the shipping industry. 2. Design Vessel
The design of all bridges over navigable waters must be checked for possible vessel colli-sion. Conduct a vessel risk analysis to determine the most economical method for protecting the bridge. The number of vessel passages and the vessel sizes are embedded as an integral part of the vessel collision risk analysis software. 1. The Florida DOT’s MathCAD software for conducting vessel collision risk analysis may be used. The software computes the risk of collision for several vessel groups with every pier. When calculating the loads and load factors probability, the overall length of each vessel group is used instead of the length overall (LOA) of a single design vessel. . Widening of bridge on navigable waterway: Major widening spanning navigable waterways must be designed for vessel collision. Minor widening spanning navigable waterways will be considered on an individual basis for vessel collision design requirements. |33 | | | | |Table 1. 7 |History of failures due to accidents or impact from ships (human error). | | | | | | |U. S.
Bridges |Location |Year |Failure Details | | | | | | |Swing bridge |Boston-Charlestown, |1945 |Ship impact hit half-open swing bridge | | | |Massachusetts | | | |John P. Grace Memorial Bridge |(Cooper River), South |1946 |Ship forced by wind into bridge deck | | | |Carolina | | |Bridge near Charleston |(Cooper River), South |1965 |Ship impact, error of ship captain | | | |Carolina | | | |Chesapeake Bay Bridge |Annapolis, Maryland |1970 |Military ship lost control and hit the bridge during stormy | | | | | |weather, five spans collapse, 11 other spans damaged | |Sidney-Lanier Bridge |Brunswick, Georgia |1972 |Ship impact, misunderstanding between captain and staff | |Chesapeake Bay Bridge |Annapolis, Maryland |1972 |Ship impact, two spans collapse, five other spans damaged | |Lake Pontchartrain bridge |Lake Pont |1974 |Ship impact, captain slept | |21-span, Pass Manchac Bridge |Louisiana |1976 |Ship impact, error of ship captain | |Benjamin Harrison Memorial |Near Hopewell, Virginia |1977 |Ship impact, failure of ship guidance electronics | |Bridge (James River) | | | | |Bridge over Passiac River |Union Avenue, New Jersey |1977 |Ship impact caused two spans collapse | |Southern Pacific Railroad Bridge |Berwick Bay, Louisiana |1978 |Ship impact caused steel truss of 70 m to falls into water | | | | | |and sink | |Sunshine Skyway Bridge |Near St.
Petersburg, |1980 |Ship impact, not enough care by captain in bad weather | | | |Florida | | | |Herbert C. Bonner Bridge |North Carolina |1990 |Ship impact, four piers damaged, five spans collapsed | |(Oregon Inlet) | | | | |Truss bridge |Near Mobile, Alabama |1993 |Ship impact | |Queen Isabella Causeway |South
Padre Island, Texas |2001 |Four barges and a tugboat struck the bridge | |Interstate 40 Bridge |Webber Falls, Oklahoma |2002 |Ship collides with one of the piers, bridge collapses on 150 m | |over the Arkansas River | | |of length | |Canadian Bridges | | | | |Fraser River Swing Bridge |New Westminster/ |1975 |Ship impact caused 120 m spanto collapses—accident | | | |Vancouver | | | |Australian Bridges | | | | |Tasman Bridge over |Hobart, Tasmania |1975 |Ship impact, inexperienced captain | |Derwent River | | | | |Recent Chinese Bridges | | | | |Bridge over river |Southern China |2007 |Bridge was hit by a ship in fog | |Swedish Bridges | | | | |Almo Bridge |Near Gothenburg, Sweden |1980 |Ship impact on steel arch due to lack of visibility in bad weather | | | | | | | 34 3. Span length: The length of the main span between centerlines of piers at the navigable channel must be based upon Coast Guard requirements, the vessel collision risk analysis (in conjunction with a least-cost analysis), and aesthetic considerations. 4. Soil conditions: Soil depth that is subject to local and contraction scour
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