Reinforced Concrete Slab & Wall Design

by Helmut Schmidhofer

This spreadsheet was developed in conjunction with Earth Pressure on Buildings, where a bending moment and shear forces are calculated.

The project came about as a result of checking a building with 100 thick concrete walls that had 1.2 m of soil piled up against it on the high side (the default values in both spreadsheets).

The design is based on Australian Standard AS 3600, which should apply in most cases. A rectangular stress block of depth gamma*ku*d is assumed, where:

gamma = 0.85 - 0.007*(f'c-28) within the limits of 0.65 to 0.85 and

ku = neutral axis factor, obtained from the following equation:

PHIm*.85*f'c*b*gamma*ku*d*(d-gamma*ku*d/2) - M*10^6 = 0 where:

PHIm = strength reduction factor for moment (0.8);

f'c = 28-day concrete strength in MPa;

b = width of section (1000 mm);

d = depth to centroid of reinforcement in mm;

M = given bending moment in kNm/m.

With ku found and yield strength of reinforcement, fy, given, the required area of reinforcement is:

Ast = M*10^6/(PHIm*fy*d*(1-gamma*ku/2)) in mm2/m

The shear capacity of the slab is then:

PHIs*Vuc = PHIs*beta1*b*d*(Ast*f'c/(b*d)^(1/3)/1000 in kN/m

where beta1 = 1.1*(1.6 - d/1000) but not less than 1.1 and

PHIs = strength reduction factor for shear (0.7).

You should do at least one calculation manually, for two reasons:
1. to check the spreadsheet so you can have confidence in its results; and
2. to appreciate how much time the spreadsheet saves.

Please support the ongoing maintenance of this site. Donate $7 and I shall send you the Excel spreadsheet so you can satisfy yourself that the program uses the equations correctly.

Reinforced Concrete Slab & Wall Design
Given:
ultimate moment, M				kNm/m
ultimate shear force, V				kN/m
depth to reinforcement, d				mm
yield stress of reinforcement, fy				MPa
concrete strength, f'c				MPa
strength reduction factor for moment, PHIm
strength reduction factor for shear, PHIs
Then:
0.85 - 0.007*(f'c-28) between 0.65 and 0.85
neutral axis factor (must be <= 0.4), ku
required reinforcement, Ast				mm2/m
shear capacity of slab, PHIs*Vuc
where factor beta1 =