Engineering Failure Analysis 45 (2014) 339–346

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Engineering Failure Analysis

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Failure of Chauras bridge

http://dx.doi.org/10.1016/j.engfailanal.2014.06.0151350-6307/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail addresses: h_birajdar@yahoo.co.in (H.S. Birajdar), prmaiti.civ@itbhu.ac.in (P.R. Maiti), prof_pks@yahoo.co.in (P.K. Singh).

Harshad Subhashrao Birajdar, Pabitra Ranjan Maiti, Pramod Kumar Singh ⇑Department of Civil Engineering, IIT (BHU), Varanasi, UP 221005, India

a r t i c l e i n f o

Article history:Received 1 March 2014Received in revised form 9 June 2014Accepted 25 June 2014Available online 12 July 2014

Keywords:Composite bridgesBucklingEnduranceLimit statesLoad factor

a b s t r a c t

Sudden collapse of 190 m long Chauras bridge in Uttarakhand, India, which was a threespan (40 m + 110 m + 40 m) continuous deck type truss bridge, took place during castingof the deck slab after successful launching of the truss. The incidence occurred when52.5 m length of the deck slab was cast starting from middle of the 110 m span towardsthe right pier. Whereas, collapse of I-35W bridge took place due to failure of one of its gus-set plates, analysis results show that Chauras bridge collapsed due to buckling of itsU13U14 top chord compression members when 173.8 N/mm2 stress in the memberoccurred against calculated permissible compressive stress of 149.8 N/mm2. Suddencollapse of the bridge claiming six lives with it, due to slight increase in stress beyondthe permissible compressive stress indicates that steel girder bridges must also be checkedfor reserve strength at the limit state of strength. As per Indian and European Standards, inaddition to 1.1 material safety factor and 1.5 load factor used for compression and tensionmembers in limit state of serviceability for fatigue design, additional load factor of 1.5, bothfor dead and live loads, for laterally unsupported compression members should be used forchecking the design at the limit state of strength. No such additional load factor for tensionmembers and joints is required.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In the past a number bridges have failed during various stages of construction or service. The failures have been partial, ortotal collapses have taken place. In case of truss bridges, failure of gusset plates connecting members of truss, and bucklingfailure of compression members are the most happening failures [1].

In 1892 the Semi-parabolic truss arch bridge near Ljubicevo over river Morava in Serbia, failed during load testing. Thecause of failure was buckling of compression chord due to defective connection of two part compression members [1].

Lessons from these failures may be treated as learning experiences, because when a bridge collapses it has certainly beenpushed to the limit in some way. Therefore, structural collapses in general, and particularly bridge collapses, which are oftenmost spectacular, have a significant effect on the development of the knowledge of structural action and material behaviorand have spurred research into particular fields [2].

Failures may happen in service, but probably more often during construction. Physical causes are various such as erosion,reversal of stress, impact, vibrations, wind, and extreme events [1]. Failure during construction is due to unexpectedincreased load on the bridge which many times might be beyond the scope of structural designer’s knowledge.

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Bridge collapse or collapse of any structure is either progressive or sudden. In progressive collapse one can judge probablefailure of structure by inspection of various critical parts of the structure and can take preventive measures to fix the prob-lems in the structure. But sudden collapse takes place without any warning and the collapse may occur within few secondstaking many lives and property loss with it.

1.1. Failure of I-35W bridge

One such notable example of sudden collapse is collapse of I-35W bridge [4] over the Mississippi River in Minneapolis,Minnesota on August 1, 2007 resulting in deaths of 13 people and injury to more than 100 others.

The superstructure of the bridge consisted of two main longitudinal trusses continuous over three spans of 81 m, 139 mand 81 m. The two longitudinal trusses were connected to each other with transverse trusses at each panel point. There wereeight lanes of traffic on the bridge [2].

All joints of the bridge were connected by 1 inch thick gusset plates, except top chord joint U10, where half inch thickgusset plates were used (Fig. 1) [4]. Investigation and Finite Element analysis by many researchers concluded that, theundersized gusset plate at joint U10 was the cause of catastrophic and sudden failure.

2. Failure of Chauras bridge

Failure of 190 m long Chauras Bridge in Uttarakhand, India, which was a three span (40 m + 110 m + 40 m) continuousdeck type truss bridge, took place during casting of the deck slab (Fig. 2). The bridge was proposed to connect two citiesnamely, Srinagar on left bank and Chauras on right bank of the river Alakhnanda. After launching of the steel truss ontwo piers and two abutments, casting of deck slab was initiated on 24.03.2012 at 11.00 AM from mid portion of the110 m span of the bridge towards right pier. During deck slab concreting, when concrete was placed in 52.5 m length frommiddle of the 110 m span towards right pier, bridge suddenly collapsed calming six lives with it (Fig. 2).

Fig. 1. Failure of gusset plate at U10.

Fig. 2. Failure of Chauras bridge during casting of deck slab.

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3. Analysis of Chauras bridge at failure

3.1. Details of Chauras bridge

The 190 m span bridge was designed for 2-lanes, 7.5 m wide carriageway and 1.5 m wide footpaths on either side. It was aLattice truss girder bridge with subdivided top chord members. Distance between top and bottom chord members was8.66 m and c/c distance between two trusses was 7.5 m. It was divided into 38 panels of 5.0 m length each. The bridge con-sisted of one central span of 110 m and two end spans of 40 m. Top and bottom chords of the bridge consisted of built up boxsections, 500 mm wide and 600 mm deep, comprising four angles at four corners, and 2 � 575 mm and 2 � 390 mm widefour vertical plates. Diagonal and vertical members of the bridge consisted of channel sections and plates. Fig. 3 showsarrangement of the bridge.

3.2. Failure analysis

A 3-D analysis of the Chauras bridge truss using STAAD Pro V8i software was carried out under the loadings existing at thetime of collapse. Under self weight of bridge no lifting reaction at abutment supports was there. But when casting of deckslab was started from mid span, lifting of 40 m end spans started gradually. Hence to analyze the bridge at ultimate stage ofcollapse, compression only spring supports are used at abutment locations.

At the time of collapse, the bridge was subjected to following loadings.

Weight of steel truss = 10,000 kN.Weight of deck slab (52.5 m) = 2166 kN.Weight of formwork and equipments = 2 kN/m2 (assumed).

Under the above load, member forces are given in Table 1, and axial stress as obtained from the STAAD analysis is shownin Fig. 4.

From analysis results of STAAD it is found that the compressive stress in member U13U14 at the time of collapse was173.8 N/mm2, and maximum force in the upper chord members was 6000.1 kN in member U18U19.

3.3. Permissible stress in U13U14

Cross sectional details of the failed top chord member U13U14 are given in Fig. 5.Permissible compressive stress due to buckling for the built up section, as per IS: 800-2007, is given by;

Table 1Membe

Mem

U13UU14UU15UU16UU17UU18U

rcr ¼ 0:6fcb � fy

ðfcbÞn þ ðfyÞn� �1

n

0@

1A ¼ 149:8 N=mm2 -working stress method

Fig. 3. Arrangement of Chauras bridge.

r forces as per STAAD analysis.

ber Cross sectional area (mm2) Axial force (kN) Member stress (N/mm2) Permissible stress (N/mm2)

14 21,596 3754.2 173.8 149.815 30,068 4619.7 153.6 149.716 36,740 5258.5 143.1 149.717 43,640 5707.9 139.7 149.718 46,508 5954.1 128.0 149.719 51,008 6000.1 117.6 149.7

Fig. 4. Stress diagram under loading at the time of collapse.

Fig. 5. Cross section of member U13U14.

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rcr ¼fy

cm0

/þ ½/2 � k2�0:5¼ 224:7 N=mm2 -with 1:5 load factor

where / ¼ 0:5 1þ aðk� 0:2Þk2þ� �

; k ¼ffiffiffiffifyfcc

q; f cc ¼ p2E

KLrð Þ2

Elastic critical buckling stress for individual 8 mm plates, as per equations 9–7 given by Timoshenko and Gere [8];

rcr ¼ kp2 E12ð1� l2Þ

� �t2

b2

� �¼ 140:0 N=mm2

Buckling stresses for the built up section (149.8 N/mm2) and individual plates (140.0 N/mm2) are quite close, and theseare less than the actual stress developed at failure (173.8 N/mm2). Therefore, it is not clear whether the local buckling at thedouble welded plates or buckling of the entire member U13U14 initiated the collapse (Fig. 6). Steel samples collected fromthe collapsed bridge were tested in laboratory and were found to be satisfactory.

3.4. Built up sections

Common hot rolled and built-up steel members used for carrying axial compression, usually fail by buckling. Bucklingstrength of these members is affected by residual stresses, initial bow and accidental eccentricities of load, for whichdepending on their shape, different buckling class of members are defined in the code [10]. Minimum width to thicknessratio for built up box sections is also limited to 30.

Fig. 6. Joints U13, U14 and buckled member U13U14.

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Welded box section (Fig. 5), when used as a compression member, has limitations from individual component buckling[10]. In the case of member U13U14 the width to thickness ratio of individual 575 mm wide, 8 mm thick plates was 72,which was in far excess of the 30 limit.

3.5. Casting sequence of deck slab

Design of the bridge was checked for 2-lanes of Class-A loading and it was found to be marginally safe. Casting of the deckslab in Chauras bridge started from middle of the 110 m span, which caused lifting of the 40 m end span. The ideal castingprocedure for the deck slab would be to start from the supports and proceed towards mid spans. Proper deck casting pro-cedure might have saved the bridge during deck casting, but the bridge would have remained vulnerable under live loadconditions.

4. Buckling of compression members

Mild steel or structural steel of grade E250 used in Chauras bridge had ultimate tensile strength (fu) of 410 N/mm2 andyield strength (fy) of 250 N/mm2. Permissible tensile stress for mild steel as per Indian standards is 0.6 fy (=150 N/mm2). Forslenderness ratio less than 10 maximum permissible compressive stress is also 0.6 fy (=150 N/mm2), which decreases withincrease in the slenderness ratio. Similarly, for E410 grade of steel yield strength is 410 N/mm2 and ultimate tensile strengthis 540 N/mm2. Permissible tensile stress and maximum permissible compressive stress for this steel is also 0.6 fy (Fig. 7).

Fig. 7. Stress–strain curves of compression or tension member for mild steel of grades E250 and E410.

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Tension and compression members of a steel truss have entirely different behavior before failure (Fig. 7). Compressionmembers suddenly buckle and fail without any reserve strength in them beyond maximum up to yield stress, while tensionmembers have reserve strength after yielding up to the ultimate tensile strength.

5. Behavior of gusset plates

Maximum compressive force in the member U18U19 of Chauras bridge at collapse stage was 6000.1 kN and correspond-ing stress in the 12 mm thick gusset plate was 416.75 N/mm2. But the gusset plate did not fail even at such a high compres-sive stress, as it was prevented against buckling by the rivets.

Compressive force in member U13U14 was 3754.2 kN and corresponding stress in the gusset plate was 260.7 N/mm2.Gusset plates at joints U13 and U14 remained intact at this high stress (Fig. 8), whereas, member U13U14 buckled and failedat a lower stress of 173.8 N/mm2.

Thus, gusset plates if connected properly to the members and prevented from buckling can take compressive or tensilestress up to ultimate strength of the plate.

6. Design for serviceability limit state

Generally steel bridges are designed for 100 years of service life and six million fatigue load cycles.Fracture endurance limits for E250 (fy = 250 N/mm2, fu = 410 N/mm2) and E410 (fy = 410 N/mm2, fu = 540 N/mm2) mild

steel are shown in Fig. 10. Endurance limit for yielding is proportionately scaled down from the fracture endurance limitcurve. Therefore, whereas fracture endurance limit for six million cycles is taken as 2

3 fu (=273 N/mm2), endurance limitfor yielding is 2

3 fy (=167 N/mm2). Thus, Adapting material safety factor as 1.1, permissible stress in compression or tensionfor the limit state of serviceability is adopted as 0.6 fy [9].

In a steel truss, in service condition, maximum permissible member stresses from deformation criterion for E250 andE410 grade steel shall be limited to their yield stresses (Fig. 9).

6.1. Design of truss members

As evidenced in Chauras bridge case, sudden collapse of the bridge took place due to buckling of top chord compressionmembers U13U14 without any warning claiming six lives with it, and therefore, design of tension and compression membersof a truss warrant separate design considerations.

6.1.1. Design of tension membersTension members designed as per ultimate tensile strength will have excessive deformation due to yielding. Therefore,

permissible fatigue stress in service condition of 167 N/mm2 (23 fy) for E250, and 271 N/mm2 for E410 may be adopted for

design.Thus, in the limit state of serviceability condition, adapting 1.1 material safety factor [9,10], tension members should be

designed for permissible stress of 0.6 fy (=0.66 fy/1.1) with a load factor of 1.5.

6.1.2. Design of compression membersReferring to Fig. 7 and adapting 1.1 material safety factor and 1.5 load factor, maximum permissible compressive stress in

the serviceability condition for compression members of grade E250 and E410 may also be adopted as 0.6 fy [9,10].

Fig. 8. Intact gusset plates at joints U13 and U14.

Fig. 9. Endurance limits for E250 and E410 grade steel.

Fig. 10. Arrangement of vehicles for fully loaded deck condition.

H.S. Birajdar et al. / Engineering Failure Analysis 45 (2014) 339–346 345

7. Design at limit state of strength

Unexpected circumstances may take place during construction and service stages of the bridge. Apart from uncertainty inthe material strength for which material safety factor of 1.1 is generally adopted, the following uncertainties affecting thesafety of the bridge may be there;

a. Uncertainty about loading.b. Uncertainty about structural dimensions and behavior.

7.1. Uncertainty about dead load

Dead load (DL) on the bridge may increase even after its construction due to time to time repair works. In the case of I-35W bridge [3,5,6,7,12,13], due to two major deck repairs the dead load of the bridge increased by 30%. Therefore, safeincreased dead load on a bridge during its lifetime may be taken up to 1.5 times its dead load.

7.2. Uncertainty about live load

Bridge loading standards provide for specified gap between two trains of vehicles. In adverse conditions these gaps mayalso be occupied by vehicles.

In order to calculate increase in live load (LL) due to full occupancy of the deck, 7.5 m wide carriageway with two lanes ofClass-A train of vehicles [11], having total plan area of 18.8m � 5.5 m and nose to tail spacing of 20.0 m is considered. Theremaining 2.0 m width of the deck is considered loaded with 5.0 kN/m2 other live loads (Fig. 10).

Thus, maximum possible live load (without impact) to normal live load (with impact) ratio;

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¼ 2� 554ð1þ 20:0=18:8Þ þ 5:0� 2:0� 38:8½ �= 2� 554� 1:088ð Þ � 2:2

Vehicle loads keep on increasing as the years pass and consequently the loading standards are revised. Corrosion andwear and tear of the bridge also require higher load factor.

A load factor of 1.5 and material safety factor of 1.1 are included in the design during service condition. Thus, anadditional load factor of 1.5 (P2.2/1.5) in live load may be reasonable for the limit state of strength condition resultingin total load factor of 2.25.

7.3. Design of compression members

Compression members buckle and suddenly fail without warning causing loss to life and property, and consequently anadditional load factor of 1.5 may be required at the limit state of strength.

In case lateral buckling of compression members is prevented, as in the case of top chord compression members in com-posite deck system, no additional load factor may be required.

8. Conclusions

From the presented case study of Chauras bridge, the following main conclusions can be drawn.

1. Analysis results show that the compressive stress in members U13U14 of Chauras bridge at the time of collapse was173.8 N/mm2 against permissible stress of 149.8 N/mm2. Therefore, failure took place due to buckling of membersU13U14. Buckling of the member was also facilitated because the compression members comprised pairs of 8 mm thickplates, in place of 16 mm thick plates.

Therefore, welded built up sections must be carefully dimensioned, so that buckling of individual members may not bepossible. In this connection width to thickness ratio of the constituent plates should be limited to 30.

2. As evidence in Chauraas bridge collapse, compression members buckle and suddenly fail without warning claiming lifeand property with it. Also, compression members do not have reserve strength like tension members, which have reservestrength beyond yield stress up to ultimate strength. Therefore, design of laterally unsupported compression membersshould be checked at the limit state of strength for 1.5 times higher load factor for DL + LL case.

No additional load factor at the limit state of strength is required for tension members and gusset plates.Steel girder bridges are generally designed for limit state of serviceability condition only. Due to fatigue in the members,

maximum permissible stress in service condition is limited to 0.6 fy in tension members, and depending on slenderness ratioto maximum 0.6 fy in compression members. However, the design must also be checked at the limit state of strength. Due tobuckling and sudden failure of compression members, load factor for checking design at limit state of strength for laterallyunsupported compression members should be taken 1.5 times more to 2.25(DL + LL). For tension members and gusset platesreserve strength beyond the yield stress exists up to the ultimate strength, and therefore, design load for these shall benormal 1.5 (DL + LL).

References

[1] Zlatko Šavor, Marta Šavor, Jing Gao, Marin Franetovic, Failures of arch bridges – causes, lessons learned and prevention, 3rd Chinese – croatian jointcolloquium on sustainable arch bridges (2011).

[2] Abolhassan Astaneh-Asl, Progressive collapse of steel truss bridges, the case of I-35W collapse, in: 7th International conference on steel bridges,Guimaraes, Portugal, 4–6 June, 2008.

[3] Roberto Ballarini, Taichiro Okazaki, The infamous gusset plates, the city, the river, the bridge, University of Minnesota Press.[4] Liao Minmao, Okazaki Taichiro, Ballarini Roberto, Schultz Arturo E, Galambos Theodore V. Nonlinear finite element analysis of critical gusset plates in

the I-35W bridge in Minnesota. J Struct Eng ASCE 2010.[5] NTSB-Dockets, Press releases, reports, photos and other information on I-35W, the National Transportation Safety Board Docket on the Internet, 2007–

2008.[6] Astaneh-Asl A. Behavior and design of steel and composite structures, including seismic effects. EPS; 2008.[7] IS: 800-1984, Indian Standard, Code of Practice for General Construction in Steel (based on working stress method), India, 1984.[8] Timoshenko Stephen P, Gere James M. Theory of elastic stability. Tata McGraw-Hill; 2010. Edition.[9] BS EN 1993-1-1:2005, Design of steel structures – Part 1-1: general rules and rules for buildings, Europe, 2005.

[10] IS: 800-2007, Indian Standard, Code of Practice for General Construction in Steel (based on limit state method), India, 2007.[11] IRC: 6-2010, Standard specifications and code of practice for road bridges, Section II, Loads and Stresses (Fifth revision), India, 2010.[12] Gerry Johnson, I-35W bridge failure analysis report, 25/11/2007.[13] Hao S. I-35W bridge collapse. J Bridge Eng ASCE 2010;15(5).