Bridge Engineering Institute Conference 2019 (BEI-2019)
Honolulu, Hawaii, USA, July 22-25, 2019

Analytical Estimation on Remaining Load Bearing Capacityof Aging Truss Bridge by Using Whole Bridge Modeling

Ryoko Koyama1, Tatsumasa Kaita2*, Tatsuro Yamane3, and Tsutomu Imai4
1

UBE machinery corporation, ltd., Ube, Japan; email: 36708u@ube-ind.co.jp
Tokuyama College of Technology, Department of Civil engineering and Architecture, Shunan,
Japan; email: kaita@tokuyama.ac.jp
3
Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan; email:yamane.tatsuro.17@cee.ehime-u.ac.jp
4Road division, Construction Department, Shunan city government office, Shunan, Japan; email:imai4bb@city.shunan.lg.jp
2*: corresponding author

Keywords: pony truss; non-linear FEM; shell element; load bearing capacity; collapse behavior
Abstract: Considering the life extension of aging steel bridge, it is important to estimate
accurately the remaining load bearing capacity. Even if the bridge with low-traffic state, it isdifficult to decide to remove or to stop the bridge because it is an important life infrastructure forusers. For the reason, it is considered that estimate the strength against traffic volume and traffic
needs will more reasonable and economic maintenance basing on the remaining load bearing
capacity. In this study, the finite element analyses focusing on the following two points wereconducted for actual pony truss bridge.

1) Confirmation of the safety of the 4-ton truck load which was the result of resident's
questionare of actual usage and traffic needs.
2) Grasp of corrosions and members to be emphasized in maintenance management.
In the analysis, the model of the whole bridge by the shell element was used, and the actualcorrosion was reflected on the whole bridge. The main conclusions in this study are asfollows:1) Assuming a 4-ton truck load, the stress concentration occurred in the groove-like corrosion
at the upper chord member. The safety factor to the yield state of this bridge was estimatedas 1.3.
2) It will be estimated that the ultimate load bearing capacity of this bridge has decreased by
24% due to extensive corrosion and severe corrosion accompanied like through holes.
1. Introduction
Recently, the maintenance of aging steel bridges becomes one of the important social problem inJapan. Especially, many local municipalities have strict conditions in terms of financial
difficulties and human resources, and it is difficult to keep all the bridges in the good condition.
However, even if low traffic volume and short span, regional bridge is the foundation of living
and disaster prevention, removal or replacement will not able to be done easily. For the reason, it714

Bridge Engineering Institute Conference 2019 (BEI-2019)
Honolulu, Hawaii, USA, July 22-25, 2019is considered that estimating the minimum required load bearing capacity against actual traffic
volume and traffic needs may realize more practical and economic maintenance.
Table 1. Analytical cases

Fig. 1. Analytical model

In this study, the finite element analyses using whole bridge model of an actual aging pony truss
bridge which has severe corrosion damages were conducted to estimate the ultimate load bearing
capacity and collapse behavior.
2. Whole bridge modeling for finite element analysis
2.1. Outlines of objective steel bridge
The main span of the bridge to be analyzed is simply-supported Warren truss with curved chords
and used for 99 years at mountain area in present location. All structural members areconstructed by rivet joints combined several simple-shaped steels and many racing bars. Themain span is 29.3m and the clear width is 4.5m, respectively. It can be noticed that the maximum
height of main truss is kept as low as 2.9m from the considering of pony truss without lateralmembers. For the traffic needs of this bridge, it is confirmed that up to 4-ton truckload is enoughfrom the viewpoint of daily life and disaster prevention based on the results of the residents
questionnaire (Koyama et al. 2017). 27 years have elapsed since the repainting repair last time,and various types of corrosion are distributed throughout the bridge. Especially, severe corrosion
damages tend to concentrate on the upper chord members at center span such as groove-likecorrosions at the boundary of splice plate and pitting corrosions on the upper flange.
2.2. Whole bridge modeling and analytical conditions
The non-linear finite element analyses in this study were performed by using ABAQUS/Standard
6.14-5. Fig. 1 shows the analytical model in this study. In this model, all main structuralmembers are constructed by the shell element with 4 nodes, and the all rivet joints were modeled
as the rigid connection. The size of each shell element was set to under 40mm square in order toconsider the corrosion damages which have a certain area. Based on the tensile tests, the materialproperties were assumed to be elastic modulus E=203.5 [GPa], yield stress y=312.3 [MPa], andPoisson's ratio =0.274 respectively. The stress-strain relation was assumed to the perfect elastoplasticity. For the boundary conditions, the rotations and displacements in all directions are fixedbased on the actual state, because all shoes are fixed directly to piers by using 4 anchor bolts in abase plate. The RC slab is not modeled, because it is not structural member for main loads. In thecorrosion modeling, the maximum corrosion depth was applied to the entire corrosion area.

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Bridge Engineering Institute Conference 2019 (BEI-2019)
Honolulu, Hawaii, USA, July 22-25, 2019

2.3. Analytical cases and loading conditions
In all analytical models, the dead load of steel members was acted to entire bridge as the bodyforce. However, the dead load of RC-slab and live load were distributed as external force on all
stringers based on the influence lines for reaction force of stringers. Also, 4 analytical cases wereprepared depending on loading and corrosion condition as shown in Table 1.

244.0MPa258.1MPa(a)(b)

273.0MPa

303.3MPa(c)(d)

Fig. 2. Mises stress distribution around the groove-like corrosion (Case-1): (a) T-4 truckload; (b)T-6 truckload; (c) T-9 truckload; (d) T-14 truckload

In Case-1, 4 kinds of truckload (T-4~14) assuming severest state were loaded on stringers. T-4(4-ton) truckload means the actual traffic needs which was based on the questionnaire results forlocal residents. The loading intensity of each truckload was calculated from the result of dividing
the assumed vehicle weight of each load by the occupied area. The truckload was given to theside of road width for increasing the load share in one-sided main truss. Case-2 and Case-3
assumed the L load defined in JSHB (Japan Specifications for Highway Bridges). Here, L load
p1 which means the large-size trailer was excepted from loading condition, because such large
vehicles cannot enter to this bridge from the problem on plan shape of connection road.
Therefore, only L live load p2(3.5 kN/m2) was loaded to analytical model in Case-2~3. Also, thelive load was multiplied by the magnification factor , and was gradually increased until thecollapse of the whole bridge. The ultimate load bearing capacity of the whole bridge is estimatedby the maximum magnification factor cr when the bridge collapsed.
3. Results and discussions
3.1 Truckload
Fig. 2 shows the Mises stress distribution diagram focusing on the groove-like corrosion
occurring in the upper chord member at center span when T-4~14 truckload was loaded. Thestress arround the groove-like corrosion increases as the truckload increases and concentrates
particularly around the through hole. When T-14 truckload was assumed, the stress level reached
to almost y. Assuming a T-4 truckload which was the minimum required load for this bridge,
the stress generated in this part was 244MPa, and the yield safety factor was 1.3. However, the716

Bridge Engineering Institute Conference 2019 (BEI-2019)
Honolulu, Hawaii, USA, July 22-25, 2019

corrosion damages in this analytical model were modeled larger than the actual state, and thetraffic frequency of 3-ton truckload or more was low. So, it is thought that current state of thisbridge will not be serious condition soon. If more life extending is considered, the load
restriction of 4-ton and repair to the groove-like corrosion of the upper chord member may comein sight view.
3.2 Ultimate load bearing capacity and collapse behavior
In this section, the ultimate load bearing capacity and the collapse behavior were estimated fromthe analytical results for Case-2 and Case-3 in which the L load was increased to the ultimatestate(a)

(b)

(c)
Fig. 3. Deformation ( 20) and stress distribution in ultimate state (Case-2): (a) cr=6.91 at peakload; (b) =6.62 after peak load; (c) Out-of-plane buckling of upper chord member

(a)

(b)

Fig. 4. Deformation ( 20) and stress distribution ( cr=5.28) (Case-3): (a) Plan view; (b) In-plane
buckling of upper chord member

by the magnification factor . From Fig. 3 and Fig. 4, Case-2 without corrosion was disintegrated
at cr=6.91, but Case-3 with corrosion damages collapsed at cr=5.28. These results will meanthat load bearing capacity of whole bridge decreased by 24% due to corrosion for 99 years. Also,
in both Case-2 and Case-3, though the buckling was occurred in the ultimate state on same upper
chord member at the center span of downstream side, the direction of buckling was different
each other. It could be confirmed that the buckling behavior will change from out-of-plane
buckling caused by full cross-section yielding to in-plane buckling due to pitting corrosions onupper flange.
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Bridge Engineering Institute Conference 2019 (BEI-2019)
Honolulu, Hawaii, USA, July 22-25, 2019

4. Conclusions
1) Assuming a 4-ton truck load, the stress concentration occurred in the groove-like corrosion
at the upper chord member. The safety factor to the yield state of this bridge was estimatedas 1.3. However, it is thought that current state of this bridge will not be serious conditionsoon.
2) It will be estimated that the ultimate load bearing capacity of this bridge has decreased by
24% due to extensive corrosion and severe corrosion accompanied like through holes.
3) The main collapse trigger of entire bridge was the local buckling toward in-plane direction
on an upper chord member at center span. This buckling was caused by a lot of large pitting
corrosions on upper flange.
5. References
Koyama, R., Kaita, T., Yamane, T., Kaneshige, K. and Imai, T. 2017. Analytical Estimation onLoad Bearing Capacity for Aging Pony Truss Bridge Considering Actual Traffic Conditions, The
15th East Asia-Pacific Conference on Structural Engineering and Construction, Proc. of EASEC15, pp.1914-1922.

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