Example: L shaped column section

Accompanying this is a file called dezi.xsf. It is in metric units with small dimensions.


This example was taken from a published paper:-

Andrea Dall’Asta and Luigino Dezi, “Design of RC sections with generic shape under biaxial bending“, Journal of Structural Engineering, ASCE, v118 n4 p1138-1143, April 1992.

In the published paper the axes on the cross-section are called ‘Y’ and ‘Z’; Y being left to right and ‘Z” being up. To fit with the language used in the application the axes names were changed to ‘X’ and ‘Y’; X being left to right and Y being up.

Thus the given loading is:

Axial load = -500 kN

The bending moment about the X axis = -400 kNm

The bending moment about the Y axis = 200 kNm

These bending moments can be viewed as components of one bending moment that expressed in polar co ordinates is:

Magnitude = 447.21 kNm

Orientation = 153.43 degrees

The objective is to obtain the diameter of the steel bars for which the ultimate bending moment is at least this given bending moment.

In the application the reference angle was set to 153.43 degrees and the other axis restrained checkbox (Mac & PC) or switch (iPhone) set to off. This meant that in a result from the “Ultimate bending moment” method the bending moment about the other axis would be negligible and the bending moment about the reference axis could be compared with the 447.21 kNm requirement.

Various diameters were tried. The bar diameter can be input on the point component edit dialog (Mac & PC) or first display (iPhone). After each time the diameter was changed the “compute area from diameter” button was pressed. (The main computations use the area and ignore the diameter.)

It was found 18.4 mm gave 445.81 kNm and 18.5 mm gave 448.73 kNm showing that 18.5 mm diameter would suffice.

The paper stated that the minimum necessary reinforcement is 5348 mm2. That is the total area of the twenty bars. To satisfy this each bar would have 267.4 mm2. This bar area was entered directly into the application; the bar diameter being ignored. The resulting bending moment from the application was 447.32 kNm which satisfied the requirement 447.21 kNm nicely.