Old Houses without Diagonal Bracings

Houses built in small-scaled development totally collapsed due to the lack of earthquake-resistant walls (Ashiya city)

Many of the collapsed wooden houses were structurally old without diagonal bracings installed. They collapsed because the framework members had already been damaged by termites and dilapidation, and also because the traditional construction method to have horizontal members such as crosspieces and mud walls against the horizontal force was not sufficient for the house to withstand such a big earthquake.

Many new houses with bracings also collapsed or were damaged because the fixing of the bracings had not been perfect, they were dislocated at the joint or broken, or the location of the bracings had been inadequate in the first place.

Importance of Structural Planning, Diagonal Bracings and Horizontal Rigidity

There are four points in the improvement of structural defects in the conventional construction method for wooden housing as follows.

First, strict and detailed structural planning, like the one in two-by-four construction, should be adopted.

Second, diagonal bracings need improving to work efficiently against compression and/or tension without easily dislocating by a huge horizontal force. Nailing up a sheet of plywood to fix to horizontal members is effective and fairly easy to do with little error.

Third, horizontal rigidity at the floor and the roof faces should be increased. Installment of horizontal angle braces, as presently regulated by law, is nothing more than a comfort. Far much greater strength is required.

Lastly, the above-mentioned reinforcement of the rigidity of the wall and horizontal faces means not only to make the building resistant to earthquakes and typhoons but also to improve energy saving performance and livability by improving the impregnability and airtight performance of the building.

(TAKEYAMA Kiyoaki)