Study Trip Report on
TOHOKU UNIVERSITY: INSPECTION OF DAMAGED BUILDING
By: Sergio Sunley (E-Course)

Tohoku University is located at Sendai city, at the north region of Honshu island. After the March
11th 2011 Earthquake, some facilities of the university were damaged. This report summarizes themost important damages presented in the buildings of Aobayama campus of the university.

AB(Google)(Google)The most damaged buildings where we visited are shown in the figure. The inspected buildings are:A) Department of Information and Intelligent SystemsB) Research Building of Department of Civil Engineering and Architecture
Department of Information and Intelligent Systems was qualified as unsafe, and damages were
presented in structural and not structural elements.
Figure 1 shows some damages presented on the building, such as the separation of the window
panel from the main RC walls. Sliding was presented in 7th and 8th floors.

Figure 1. Elevation view of department of information and Intelligent systems.
Figure 2 shows the most critical damage on the same building. The building had a discontinuity inelevation for levels higher than the 8th where the worst damages were presented.
As can be seen, shear failure was presented in RC wall’s main sections and also the concrete wascollapsed and completely shattered in the small sections close to openings. In the figures it can beseen that only the main vertical reinforcement uses deformed bars, but the horizontal reinforcement
bars are smooth, due to the fact that reduces the anchorage significantly.

Figure 2. Damage at the top floor of the Department of Information and intelligent systems
building

Figure 3 shows the collapse of the walls around openings.
The concrete in those walls was also shattered but somesteel reinforcing bars were not buckled. This failure seems
like the walls behaved as short columns, this is evidenced
because the walls without opening didn’t show concretecollapse.
The amount of horizontal reinforcement bars in thecollapsed sections was poor to carry the shear force by thewalls in the concrete sections.
Damages were also presented in the columns of the firstfloor. Figure 4 shows the collapse of the columns of the firstfloor. Main observed damage was due to the shear cracks.
The distribution of the steel reinforcement can be seen in
the figure showing a long separation of the stirrups thatallow the formation of shear cracks along columns and theconsequent failure.

Figure 3. Collapse of walls
around openings

Figure 4. Damage in columns at the first floor

Figure 5. Research Building of Department of Civil Engineering and Architecture
The research building of Department of civil engineering and architecture was classified as unsafe.
This is a 9-story building (non-full web Steel Encased Reinforced Concrete Building according toProfessor Motosaka). It was damaged in the past by the 1978 Miyagi-ken Oki earthquake. Thisbuilding was discontinuous in the third floor with a smaller cross section in plane from the 3rd to the9th level. The main damage occurred in the base columns of the 3rd level because of the collapse
generated by the axial force due to the overturning moment as is shown in Figure 6. Horizontal
cracks were also developed at the base of the wall showing sliding, however this sliding damage
was slight according to the commentary of Professor Motosaka .

Figure 6. Damage on the walls of 3rd floor
The structural health was observed and analyzed with the help of BRI Tsukuba using strong motion
records taken from the first, the fifth and the ninth floors. According to the record, the acceleration
at the 9th floor was 908cm/s2 and at the 1st floor 333 cm/s2. Important changes in the 1st natural
frequency were found according to the analysis of the structural health. Comparing the microtremor
and the earthquake frequencies, considerable difference was found after the March 11th 2011 mainshock.
Seismic retrofitting had been performed on the building before the earthquake due to past damages.
It consisted of the replacement of side walls, installation of steel braces, reinforcement of beams
and reinforcement of the slab.
After the 2011 earthquake, a provisional retrofitting has been performed as shown in Figure 7. This
retrofitting consists of the installation of new pretensed columns, with steel bolts able to resist theaxial load at the bottom corners of the wall, andprestressed concrete to support large compression
forces.
The permanent retrofit of the building or
reconstruction has not been performed because
the information about the damages and structural
health is still being analyzed.

Figure 7. provisional retrofit of the base ofwalls of 3rd floor.

Conclusion and final comments
The observation of damaged buildings in Tohoku University was performed. The main damages
were caused in old buildings constructed without the use of the newest design provisions forseismic structural safety such as the reinforcement detail and the dimensions. The building
irregularity was one important factor of the damages in the inspected structures. On the other hand,the change of natural period of the affected buildings due to the main shock of the 2011 earthquake
has been evidenced on the Research Building of Department of Civil Engineering and Architecture,and it remarks the importance of the structural health observation in order to expect the damages ofbuildings and to take countermeasures to guarantee the structural safety.