Trigonometric Calculation of Twisting Angle in Spiral Stair from beech wood

In this study, twisting angle of wooden spiral stairs from beech wood (fagus orientals) on the scale of 1/6 and according to SMA-R311 has been calculated using trigonometry, and the effect of radius (in two levels as 11.5 and 42.5 cm), handrail width (in two levels as 4.5 and 8cm, and rake angle (in two levels as 15 º and 33º) on twisting angle was determined. The results showed that decreasing the diameter increases stair rake angle. While increasing the rake angle increases twisting angle of the handrail, an increase in the handrail width have not any significant effect on the twisting angle. The results also showed that there was a non-linear relationship between the rake angle and the twisting angle by radius of the circle.