a note on dynamic fracture of the bridge bearing due to the great hanshin–awaji earthquake

$: A note on dynamic fracture of the bridge bearing due to the great Hanshin–Awaji earthquake$
International Journal of Impact Engineering 27 (2002) 153–160

A note on dynamic fracture of the bridge bearing due to thegreat Hanshin–Awaji earthquake

Shinji Tanimuraa,*, Takashi Satob, Tsutomu Umedaa, Koji Mimuraa,Osamu Yoshikawac

aDivision of Mechanical Systems Engineering, Graduate School of Engineering, Osaka Prefecture University,1-1, Gakuen-cho, Sakai, Osaka 599-8531, Japan

bGraduate School of Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka 599-8531, JapancOsaka Institute of Technology, 5-16-1, Omiya, Asahi-ku, Osaka, Osaka 535-8585, Japan

Received 14 December 2000; received in revised form 15 June 2001; accepted 6 July 2001

Abstract

The great Hanshin–Awaji earthquake, which occurred in Japan in 1995, caused fracture and destructionof a large number of structures. One of the examples, whose mechanism is not clear, is the fracture of abridge bearing part of the Nielsen bridge type that does not occur under ordinary static or dynamic loading.The fracture probably resulted from a very high stress due to an unexpected dynamic mechanism or animpact. In this paper, the three dimensional dynamic behaviour of a bridge of the Nielsen bridge type wasanalysed, for a collision/impact between the upper and the lower bridge bearings, which might haveoccurred in the great Hanshin–Awaji earthquake. The numerical results show that an impact due to arelative velocity of 5–6m/s between the upper and the lower bridge bearings generates a stress sufficient tolead to the fracture in the upper bridge bearing. The location and the direction of the maximum principalstress determined numerically in the upper bridge bearing coincide fairly well with the observed features ofthe actual fracture plane. r 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Dynamic fracture of structure; Collision; Earthquake; Numerical simulation; Bridge bearing

1. Introduction

One of the examples of unusual fractures of structures which occurred due to the greatHanshin–Awaji earthquake [1–4], is the fracture of a bridge bearing part of the Nielsen bridgetype, as shown in Fig. 1, that might not occur under ordinary static or dynamic loadings. One

*Corresponding author. Tel.: +81-722-54-9209; fax: +81-722-54-9904.

E-mail address: [email protected] (S. Tanimura).

0734-743X/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved.

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Fig. 1. Fracture of bridge bearing of Nielsen bridge type: (a) Nielsen bridge. (b) Fracture of the upper bridge bearing.

(c) An expanded view of the fracture surface near the root of boss. (d) Detail of the fracture surface near the root ofboss.

S. Tanimura et al. / International Journal of Impact Engineering 27 (2002) 153–160154

explanation of the cause of that fracture was presented by assuming a high stress concentration atthe root of the boss as shown in Fig. 1(c). Through careful observation of the fracture surfacenear the root of the boss, however, one may find that the fracture surface does not start at the rootof the boss but somewhat inside of the root of boss as shown in Fig. 1(c) and (d). The assumptionis also not substantiated sufficiently to explain the cause of the high enough tensile force whichacts to the upper part of the bearing and leads to the tensile fracture. Multi-fracture like a multi-spallation, which is sometimes caused by a plate impact, can be observed on part of the fracturesurface, as shown in Fig. 1(c).We then hypothesized a new mechanism by which such an unusual fracture can be

explained reasonably. That is, we assumed that the upper part of bridge bearing was onceseparated from the lower part of that during a severe vibration of the Nielsen bridge (Fig. 1(a))due to the strong near-source earthquake and then collided with the lower part of the bearing.This might cause a sufficiently high tensile stress to lead to the unusual fracture of the upper partof the bearing.To substantiate this hypothesis, we analysed the three dimensional dynamic behaviour of the

entire Nielsen bridge together with the ground by using DYNA3D code [5]. It was found that,when the upper and lower parts collide with each other with the relative velocity of about 6m/s,the high tensile stress, which might cause the tensile fracture, occurs on the plane in the upperbearing which corresponds well to the actual fracture surface, and also the principal axis ofmaximum principal stress is almost perpendicular to the actual fracture plane in the upperbearing.

2. Numerical methods and results

2.1. Numerical methods

Fig. 1(b) is a view of the fractured upper part of the bridge bearing which was locatedat position as shown in Fig. 2. Cracks were observed also in the upper part of the bearingof . These bridge bearings consisted of an upper part with a concave surface of thespherical bearing and a lower part with a convex surface (Fig. 3). The finite element model of abridge of the Nielsen bridge type together with the ground was made on the basis of the designdrawing of them and the measured values of the elastic properties of the ground around thebridge, as partly shown in Fig. 2. The whole model shown in Fig. 2 was separated into two parts.That is, the upper part of the model consisted of the upper beam, the lower beam and the upperpart of bearing, and the lower part of the model consisted of the lower part of bearing, the pierand the ground.The material of the upper part of bearing, where fracture occurred, was SCMn1A of JIS

standard (yield strength is X 275MPa, tensile strength is X 540MPa, elongation is X17%). Thematerials of the upper beam, lower beam and pier were of steel. The material properties of theroad section, ground and others were chosen as the values given in the design drawing and themeasured values of ground properties around the bridge. In the modeling, all of the materials wereassumed to remain elastic to evaluate simply the values of the dynamic tensile stresses which occurduring the three dimensional dynamic behaviour of the models after the collision.

S. Tanimura et al. / International Journal of Impact Engineering 27 (2002) 153–160 155

The boundary conditions on the dynamic contact surface between the concave and convexsurfaces of the spherical bearing allowed separation from each other and rotation. Friction on thecontact surface was taken into account. The acceleration due to gravity �9:8 m=s2 was also takeninto account in the direction of the z-axis.

Fig. 2. View of whole FE model in y direction (m).

Fig. 3. Oblique view of FE model of bridge bearing (mm).


To sustantiate the hypothesis, the three dimensional dynamic behaviour of whole model wasanalysed for various relative impact velocities between the upper and lower models by changingthe initial velocity of the upper model in the vertical direction.The accuracy of the analysis was checked to confirm the acceptability of the obtained numerical

results by changing the total number of finite elements from 4000 to 5000 and choosing smallerelements for the parts of the bearing near to the dynamic concave and convex contact surfaces ofthe bearing.

2.2. Results

It was observed that the maximum value of the principal stress s1 occurred insideof the upper part of bearing at the elapsed time after collision tC0:3 s; and also theprincipal axis of the maximum stress was almost perpendicular to the actual fractureplane in the upper part of the bearing. Fig. 4 shows an example of distributions of principalstress on the plane which corresponds fairly well to the actual fracture surface of the upper part ofbearing.The maximum values of the principal stresses occurred on the plane corresponding to the actual

fracture surface of bearing shown in Fig. 4. The relative impact velocity between the upperand lower parts of the bearing was changed from 1 to 6m/s, as shown in Fig. 5, where h denotesthe depth of the ground. On the bottom of the lower model, that is on the bottom surface of theground, the displacement of the bottom surface in the vertical direction is restricted in theDYNA3D code. To evaluate the effect of this restriction, which might cause reflection of somepart of the stress waves, the depth of ground h was assumed as h ¼ 140m when the effect might berelatively small. We can observe in Fig. 5 that the maximum values when the depth was assumedas h ¼ 140m are about 80MPa smaller than the h ¼ 35m case.When the value of mechanical impedance rc only was changed to the values of 50% and

10% of that value based on the properties measured at the ground around the bridge, andthe other conditions were not changed, the values of the maximum principal stresses became91% and 84% of those values shown in Fig. 5, respectively. These results imply that the valuesof the maximum principal stresses in the upper part of bearing due to the collision betweenthe upper and lower parts of bearing, are also affected by the mechanical properties of theground.The dynamic yield strength of the material, SCMn1A, of the upper part of the bearing at strain

rates 102100 s�1 can be estimated as about 400MPa, and the strain hardening rate of the materialis almost zero. If high enough tensile stresses over about 4002500MPa occurred in the upper partof the bearing due to the collision, the initiation of the tensile failure might be caused at thosepoints in the bearing. A fracture like the actual bearing fracture shown in Fig. 1(b) might thereforebe caused when the upper and lower parts of bearing collide with each other with a relativevelocity of about 526 m=s: It might be noted that a relative velocity of about 526 m=s is not theground motion but is the relative velocity between the upper and lower parts of the bridge bearingwhich might be caused during a severe vibration of the Nielsen bridge due to a strong near-sourceearthquake.A number of unusual paterns of structural failure were observed in the near source area at the

Hanshin–Awaji earthquake. For example, an unusual plane symmetrical buckling of rectangular


Fig. 4. Distribution of principal stress s1 at position in the cross section of the upper bridge bearing at t ¼ 0:3 s:

Fig. 5. Variation of maximum principal stress with impact velocity for various ground depths.


steel piers of T-type steel bridge, an axisymmetrical buckling of a steel pier of a Gate-type steelbridge [4] and the fracture of a bridge bearing, etc., it may be easy to understand the cause of theseunusual failures by considering the new fracture mechanism induced by collision between theparts of a structure, as studied above, even for the structural failures during a severe vibration dueto the strong near-source earthquakes.Authors would like to point out here, the importance of taking into account the fracture

mechanism induced by the collision between constituent parts of the structure due to the strongnear-source earthquakes. It might be one of the important subjects for a future study on thefracture mechanism by collision for the structural failures due to earthquakes and the preventivemeasures required against the fracture mechanism.

3. Conclusions

The great Hanshin–Awaji earthquake caused a peculiar fracture of the bridge bearing of theNielsen bridge type, whose fracture may not be caused by the ordinary quasi-static or dynamicloading conditions. The possibility of the occurrence of the fracture was studied by analysing thedynamic behaviour of the bridge, based on the hypothesis that the upper and the lowerbridge bearings once separated under the violent earthquake motion and then collided with eachother.It was clarified through a numerical analysis that a high stress sufficient to lead to fracture of

the upper bridge bearing, where the actual fracture occurred, when a relative impact velocity of526 m=sec exists between the upper and the lower bridge bearings. The location of the maximumprincipal stress coincides fairly well with that of the actual fracture plane in the upper bridgebearing. The direction of the principal axis corresponding to the bridge bearing. The direction ofthe principal axis corresponding to the maximum principal stress is also almost along the directionnormal to the observed actual fracture plane.It can be recognized that there is a high possibility of fracture in such structures, as in the

bridge bearing studied in this paper, when the collision between constituent parts of thestructure is caused by a violent earthquake motion. The authors would, therefore, like to pointout that to prevent such a peculiar fracture, it might be important and effective that struc-tures should be designed to avoid any separation of components. This would preventcollision(s) between components under the violent motion like that in the great Hanshin–Awajiearthquake.

Acknowledgements

This work was supported by the Special Coordination Funds for Promoting Science andTechnology (SCF), the Science and Technology Agency (STA), Japan, as one of studies of thenew research project ‘‘Enhancement of Earthquake Performance of Infrastructures Based onInvestigation into Fracturing Process’’. This work was also supported by the Ministry ofEducation, Culture, Sports, Science and Technology, Japan through the Grant-in-Aid forScientific Research (B)(2)(10450050). Those financial supports are gratefully acknowledged.


References

[1] Tanimura S, Mimura K, Mizuuchi M, Saito T. A note on impulsive buckling failure of column supporting a bridge.

Proceedings of the 71st Annual Meeting of JSME Kansai–Branch, Vol. 964(1), 1996, p.176–7.[2] Tanimura S, Mimura K. Dynamic failure due to the great Hanshin–Awaji earthquake. In: Lok TS, editor.

Proceedings of the 2nd Asia-Pacific Conference on Shock & Impact Loads on Structures. Melbourne, Australia,1997, p. 547–52.

[3] Tanimura S, Mimura K, Liu K. Dynamic failure of structures due to the great Hanshin–Awaji earthquake. In: ShimVPW, Tanimura S, Lim CT, editors. Impact Response of materials & structures. Oxford: Oxford University Press,1999. p. 87–99.

[4] Tanimura S, Mimura K, Nonaka T, Zhu W. Dynamic failure of structures due to the great Hanshin–Awajiearthquake. Int. J. Impact Eng. 2000;24(6–7):583–96.

[5] Hallquist JO, DYNA3D User Manual, University of California, Lawrence Livemore National Laboratory, Report

UCRL-MA-107254, 1991.


a note on dynamic fracture of the bridge bearing due to the great hanshin–awaji earthquake

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