ISSUES RELATED TO EARTHQUAKES

RELATIVE DISPLACEMENT BETWEEN STORIES

Different Building Standards vary regarding how much buildings can move, but this can be up to 3% of the

height of the building. Therefore, if a building is 200 metres tall, it can move laterally +/-6 metres at the top.

Among other concerns, this movement can have serious consequences for the stairs in the building.

The difference in horizontal displacement between two stories can create a significant change to the length of

the diagonal line spanned by the stairs.

Figure 2 illustrates a straight stair with a mid-height landing. With a typical story height of 3 metres, the

horizontal distance between the anchorage points can vary +/- 90mm (3000mm x 3%).

In one deformation cycle, the relative displacement between stories causes the stair to compress, which

potentially causes plastic (permanent) deformation of the stair. In the next cycle the span length of the stair

increases which may result in an insufficient support width of the stair and the stair collapses.

Figure 2: Relative displacement between stories gives a permanent shortening followed by a collapse /1/.

Figure 2, right side, illustrates a typical stair shaft with “scissor” stairs, where the stair turns back 180 degrees
at the mid-height landing. Assuming a storey height of 3m, means the distances between the supports may
vary +/- 45mm (1500mm x 3%). The sliding mechanism at the bottom of the stair must allows for the relative
displacement.

Technical information download

Seismic zones TSS - RVK

Memo no	Name/download	Format
	Calcyl, Earthquake.	Excel
Des Bull	Des Bull Report.	PDF
	Analyses of stairwells performace and damage during Wenchuan earthquake.	PDF
Memo no 70	Memo 70 i C SOLUTION FOR EARTHQUAKE AND STAIRS 2	PDF
Memo no 71	iC solution for earthquake and stairs spreadsheet.	PDF
Memo no 72	iC solution for earthquake and stairs additional reinforcement.	PDF