Collapse Analysis of Utatsu Ohashi Bridge Damaged by Tohuku Tsunami using Applied Element Method Hamed Salem, Suzan Mohssen, Kenji Kosa, Akira Hosoda Journal of Advanced Concrete Technology, volume 12 ( 2014 ), pp. 388-402 The Micro Truss Model: An Innovative Rational Design Approach for Reinforced Concrete Hamed M. Salem Journal of Advanced Concrete Technology, volume 2 ( 2004 ), pp. 77-87 Computer-Aided Analysis of Reinforced Concrete Using a Refined Nonlinear Strut and Tie Model Approach Hamed M. Salem, Koichi Maekawa Journal of Advanced Concrete Technology, volume 4 ( 2006 ), pp. 325-336 Journal of Advanced Concrete Technology Vol. 12, 388-402, October 2014 / Copyright © 2014 Japan Concrete Institute 388 Scientific paper Collapse Analysis of Utatsu Ohashi Bridge Damaged by Tohuku Tsunami using Applied Element Method Hamed Salem1*, Suzan Mohssen2, Kenji Kosa3 and Akira Hosoda4 Received 1 March 2014, accepted 29 September 2014 doi:10.3151/jact.12.388 Abstract The 2011 Tohuku tsunami on the east coast of Japan resulted in killing more than 15,000 people and missing more than 2,500 people, washing away of more than 250 coastal bridges and loss of US$235 billion. Collapse of coastal bridges due to tsunami impact represents a huge obstacle for rescue works. Therefore, in the current study, the collapse of Uta- tsu Ohashi bridge is numerically studied. The analysis is carried out using the Applied element Method due to its advan- tages of simulating structural progressive collapse. The AEM is a discrete crack approach, in which elements can be separated, fall and collide to other elements in a fully nonlinear dynamic scheme of computations. The Utatsu Ohashi bridge collapse was successfully simulated using AEM. It was numerically found that the amount of trapped air be- tween deck girders during tsunami had a significant effect on the behavior of the bridge. This is attributed to the buoy- ant force accompanied with the trapped air. A simplified method for estimating trapped air was assumed and proved to give reasonable results compared to reality. Three different solution examples for mitigating collapse of similar existing bridges were introduced and applied to Utatsu Ohashi bridge case and found to be efficient for preventing collapse. 1. Introduction Bay suffered extensive damage by tsunami as shown in Fig. 1, where most of the bridge decks were washed On March 11th, 2011, a powerful tsunami, Tohuku tsu- away by the tsunami forces (Kawashima et al. 2011; Fu nami, with 10m-high waves swept over the east coast of et al. 2012). Japan. The tsunami was produced by a 9.0 Richter mag- The objective of the current study is to numerically nitude earthquake that reached depths of 24.4km mak- investigate the collapse mechanism of the Utatsu bridge ing it the fourth-largest earthquake ever recorded. The and propose structural design enhancements to avoid Japanese National Police Agency confirmed 15,884 collapses of similar bridges in future under tsunami ac- deaths, 6,150 injured, and 2,640 people missing across tion. The choice of the numerical method to do such twelve prefectures, as well as 126,631 buildings totally investigation was very important because of the signifi- collapsed, with further 272,653 buildings 'half col- cant need to simulate the collapse of different parts of lapsed', and 743,492 buildings partially dam- the bridge to the end. Although the FEM is a robust and aged. Approximately 452,000 people were relocated to well-established structural analysis method, it is not the shelters. The violent shaking resulted in a nuclear emer- optimum solution for the scope of the current study. gency, in which the Fukushima Daiichi nuclear power Many drawbacks are associated with the FEM progres- plant began leaking radioactive steam. The World Bank sive collapse analysis; the element damage separation, estimates that it could take Japan up to five years to falling and collision with other elements are very diffi- financially overcome US$235 billion damages. cult (Hartmann et al., 2008). Therefore, in the current The 2011 Tohuku tsunami also caused extensive and study, the numerical analysis was carried out using the severe structural damage to various infrastructures in Applied Element Method. The Applied Element Method north-eastern Japan, especially in the coastal area of is based on discrete crack approach and is capable of Iwate, Miyagi, Fukushima and Ibaraki Prefectures. following the structure's behavior to its total collapse More than 250 bridges were washed away. As an exam- (Tagel-Din and Meguro 2000; Meguro and Tagel-Din ple, Utatsu Bridge at Minami-Sanriku Town over Irimae 1Professor, Structural Engineering Department, Cairo University, Egypt. *Corresponding author, E-mail: [email protected] 2Structural engineer, Applied Science International, Cairo, Egypt. 3Professor, Department of Civil Engineering, Faculty of Engineering, Kyushu Institute of Technology. 4Associate professor, Faculty of Urban Innovation, Fig. 1 Destroyed Utatsu Ohashi bridge in Miyagi Prefec- Yokohama National University, Japan. ture due to Tohuku Tsunami. H. Salem, S. Mohssen, K. Kosa and A. Hosoda / Journal of Advanced Concrete Technology Vol. 12, 388-402, 2014 389 2001; Tagel-Din 2002; Meguro and Tagel-Din 2003; original position. It is noted that S3 and S4, and S5, S6 Tagel-Din and Rahman 2004; Galal and ElSawy 2010; and S7 flowed out together. This was explained that Sasani and Asgitoglu 2008; Salem et al. 2011; Park et al. they were tied by cable restrainers for preventing exces- 2009; Helmy et al. 2009; Helmy et al. 2012; Helmy et sive superstructure response under a large seismic exci- al. 2013; Sasani 2008; Wibowo 2009; Salem 2011; Sa- tation as shown in Fig. 3. On the other hand, S8, S9 and lem and Helmy 2014) S10 overturned during being floated as shown in Fig. 4. Figure 5 shows the top of a pier after superstructures 2. Collapse of Utatsu Ohashi bridge were washed away. Two types of steel devices were set as an unseating prevention device in this column; one is Utatsu Ohashi Bridge consisted of 12 spans with the devices aiming to increasing seat length, and the prestressed simply supported girders. It included 3 types other is the devices which were set for preventing ex- of superstructures with spans ranging from 14.4m to cessive deck displacement in the longitudinal direction. 40.7m as shown in Fig. 2. Piers consisted of both circu- It is important to observe that none of those devices lar and rectangular RC columns supported on pile foun- were detached from the pier, which must have happened dations. Bridge columns have been retrofitted by RC if the decks were simply washed away laterally. Only jacketing and an extension for the seat length was in- some of those devices were rotated, as shown in Fig. 6, stalled at the top of pier. The superstructures from S3 to and therefore, It is likely that the decks were uplifted by S10 were completely washed away from their supports tsunami buoyancy force and then they were washed in the transverse direction due to tsunami while the su- away. Steel plate bearings used in this bridge was very perstructures S1, S2, S11 and S12 were not. It was simple as shown in Fig. 7 such that both uplift and lat- found that concrete and steel shear keys, installed at the eral force capacities were limited. This is also the case pier girder, were damaged and some damage took place at a column shown in Fig. 6, in which four stoppers did at the land side of the pier girders. not tilt. Nevertheless, a RC side stopper at the land side The outflow displacements of S3~S10 are shown in collapsed probably due to a transverse force which ap- Fig. 2. The spans located at the center such as S5-S7 plied from the deck. It is likely that due to tsunami force and S8 were flowed 28 m and 41 m away from the the deck uplifted at the sea side first being supported only at the land side, which resulted in larger tsunami force. Thus the side stopper at the land side collapsed due to excessive concentration of tsunami force. Fig. 2 Outflow of Superstructure of Utatsu Ohashi bridge in Miyagi Prefecture due to Tohuku Tsunami (Kawashima et al. 2011). Fig. 4 An overturned superstructure in Utatsu Ohashi bridge. Fig. 5 Steel devices for extending seat length (short) and Fig. 3 Effective Restrainers to tie adjacent decks to- steel stoppers for preventing excessive longitudinal deck gether in Utatsu Ohashi bridge (Kawashima et al. 2011). response due to ground motions (tall). H. Salem, S. Mohssen, K. Kosa and A. Hosoda / Journal of Advanced Concrete Technology Vol. 12, 388-402, 2014 390 Fig. 7 An upper steel bearing after superstructure col- Fig. 6 Failure of a RC side stopper, with non-damaged lapse (Kawashima et al. 2011). four steel stoppers used for preventing excessive longi- tudinal deck response. springs are responsible for transfer of normal and shear stresses among adjacent elements. Each spring repre- 3. The applied element method (AEM) sents stresses and deformations of a certain volume of the material as shown in Fig. 8. Each two adjacent ele- The AEM is an innovative modeling method adopting ments can be completely separated once the springs the concept of discrete cracking. In AEM, structures are connecting them are ruptured. modeled with elements assembly as shown in Fig. 8. Fully nonlinear path-dependant constitutive models The elements are connected together along their sur- are adopted in the AEM as shown in Fig. 8. For con- faces through a set of normal and shear springs. Those crete in compression, elasto-plastic and fracture model Fig. 8 Modeling of a structure with the AEM. H. Salem, S. Mohssen, K.