The seven floors in the 30 meter tall Asan building suddenly tilted 20 degrees just before completion of the construction. Judging from the photo and news articles, it would be safe to say that the building failed by a differential settlement of foundation which had created a concentrated load on the columns at the tilting side of the structure, which further caused shear failure in those columns. The basic physical theory of the building leaning on the land is about the same as the listing and capsizing of the ferry Sewol occurred a month ago at sea.
A differential settlement of foundation occurs when the subsoil is weak or has a different layer of soil pressures or contrasting classification of soils or change of flow of underground water. This can be prevented by pre-soils exploration and analyses of the earth and consequent foundation design against the dead and live loads of proposed structure.
Both architects for the leaning Tower of Pisa and the Asan building in the years 1173 and 2013 respectively neglected to do so. Some old traces at Pisa reveal, however, that the Italian architect might have had a hidden intention to attract tourists, so they didn't demolish the leaning tower.
Most building defects are avoidable; they occur, in general, not through a lack of basic knowledge but by non-application or misapplication of it. Knowledge seems to become mislaid from time to time. Current training in design tends to concentrate on what to do rather than what not to do. A similar situation exists in training in constructional techniques, where the craftsmen are instructed how best to undertake a particular operation as fast as possible but, to lesser extent, in the dangers of deviation from an accepted technique.
Nam Sang-so
Architect/engineer in Seoul