抄録
One of the most remarkable fact recognized at the Tokachi-Oki earthquake was the collapse of reinforced concrete buildings by the shear failure of their columns, which were designed by ordinary aseismic design and performed by ordinary building technics with normal standards. The important fact is that they were destroyed in spite of the aseismic design and ordinary construction. In this report the author would like to present the data on the deformation characteristics of the reinforced columns, which were gotten in his laboratory, in order to present the materials to analyse the destroyed buildings. One of the most important factor to determin the ductility of reinforced concrete columns is the shear span ratio (a/d). In the range (a/d)>2, the column shows mainly the bending deformation with a relative sway angle of 20/1000 or more and it shows bending fracture, so it is usually very ductile. (See Fig. 1. (d), 2). On the contrary, in the range (a/d)<2, the column shows mainly the shear deformation with a relative sway angle of only 1/1000〜3/1000 and then it shows very brittle fracture even explosive. (See, Fig. 1 (a) (b) (c), Photo. 1). From this fact, one can recognize the reason of the shear fracture (Photo 3) and the bending fracture (Photo 4) in the destroyed buildings at Tokachi-Oki earthquake. To protect against this shear explosion it must be applied sufficient hoops with a hoop reinforcement ratio of 0.8% or more (See, Fig. 4).
