Isao Nishiyama

Damage to Steel Buildings

The Committee of Steel Structures of AIJ conducted earthquake damage reconnaissance over cities where severe ground shaking was recorded among Miyagi Prefecture and Fukushima Prefecture. Tsunami damage reconnaissance was also performed along the coastlines of Iwate, Miyagi, and Fukushima. The observed damage to steel buildings is categorized into that caused by ground motion and that caused by tsunami. Steel buildings exhibited excellent seismic performance. Buildings that used older cladding construction methods sustained damage to their claddings even though their structural performance was excellent. In some older buildings, severe ground motion caused damage to structural members and connections, which are the same modes of damage observed from past earthquakes. A unique feature is the damage caused by tsunami. In the most extreme cases, buildings were displaced from their original location and completely destroyed. In other cases, fracture of connections and members caused the building to tilt or collapse. In buildings whose claddings were completely washed away by tsunami, structural damage was minor. The extent of tsunami damage varied substantially depending on the locality of tsunami attack.

Seismic Performance of Steel Braces Jointed with High Performance Fiber Reinforced Cementitious Composites and Steel Bars

Steel-braced frames have been widely used for retrofitting due to their effectiveness in terms of their light weight and short construction period. The steel-braced frame retrofitting method is difficult to apply, however, to the inner frames of buildings. Consequently, there has been a demand for a braced frame retrofitting method that can be broadly and easily applied to both the inner and outer frames of buildings. In this study, a retrofitting method using steel-braced frames with HPFRCC and steel bars is proposed. The pre-fabricated upper and lower segments of the brace member are connected on-site with HPFRCC, meaning that the proposed method is applicable to the inner frames of buildings as a seismic retrofitting method that has the advantage of simple and rapid installation. The tension force is transmitted only through the steel bars, which transmit the compression force to the HPFRCC of the joint that connects the three brace units. The results of cyclic tests of four specimens clearly showed that steel braces using HPFRCC and steel bars ensure stable structural performances and improve construction efficiency.