RC walls are calculated according to the principles given in:
- DTU 23.1 'Murs en béton banché'
- PS 92
- Henry Thonier 'Conception et calcul des structures de bâtiment'
- Victor Davidovici 'Formulaire du beton béton armé'.
There are two methods of RC wall calculations available in the French code:
- simplified method
- classic method.
SIMPLIFIED METHOD
The simplified method of RC Wall Design is based on a diagram of stresses resulting from loads applied to the wall. It assumes that linear distribution of stresses due to vertical loads and moments is adopted. The stress diagram is divided into bands for which an average stress (for compression) and the maximal or average stress (for tension, depending on the option selected) is assumed. You carry out stress analysis and design with three verification levels: under the floor, at the midpoint of the wall height, and at the base of the wall.
Calculations are performed in two paths.
- It is assumed that a wall is made of unreinforced concrete
- Calculations of stresses on the relevant verification levels are performed assuming the distribution of gravitational loads in unreinforced concrete.
- Load capacity of an unreinforced wall is calculated.
- The load capacity condition is checked. If load capacity is sufficient, calculation of reinforcement distributed in the wall is unneccesary and only the constructional reinforcement is generated. If the load capacity condition is not fulfilled, the wall is considered reinforced (see point 2).
- It is assumed that a wall is a reinforced wall.
- Recalculation of stresses on the relevant verification levels assume the distribution of loads in reinforced concrete (see also The method of load distribution and calculation of stresses in RC walls)
- Based on the required load capacity, reinforcement distributed in the wall is generated as is the constructional reinforcement according to the relevant requirements.
CLASSIC METHOD
The wall design, according to the classic method, is based on the assumption that the wall works in its plane as an RC section. Parabolic-linear distribution of compressive stresses in the section is adopted here.
Calculations are performed for an unreinforced wall and, if needed, for one with reinforcement. The design process is focused on the bottom section of the wall.
The calculation algorithm for the classic method is as follows.
- For load reduction, linear loads are reduced to the system N - M.
- For calculations of the load capacity of an unreinforced wall, refer to the descriptions of algorithms of wall calculations for non-seismic and seismic loads.
- If load capacity of an unreinforced wall is less than the impact due to the vertical reduced forces N, then uniform reinforcement distribution is assumed.
- Based on distributed reinforcement (the greater of individual seismic and non-seismic combinations is adopted), load capacity of a reinforced wall is calculated (separately for seismic and non-seismic structures).
- If stress in the wall exceeds the allowable stress in concrete ςbc=0,85fcj/(θ*γf), calculations are interrupted. Dimensions of the wall section should be increased
- Calculations of compression with bending are performed, assuming the section resistance from concrete strength or concrete with distributed reinforcement, taking into account wall buckling (the a coefficient)
- Shear calculations and sliding calculations for seismic walls are carried out.
- Reinforcement for compression with bending is arranged near wall edges (with hidden zones). Distributed vertical reinforcement is calculated to be able to carry the N force and possible reinforcement resulting from the verification of shear and sliding. Both are generated along the whole section.
Note: Currently openings are disregarded in calculations by means of the classic method. Reduction of the section is taken into account in neither calculations due to bending with compression nor in tangent stress calculations. Only constructional reinforcement is generated near the opening (for seismic walls it is the minimal edge reinforcement CV).
See also:
The algorithm of wall calculations (non-seismic loads)
The algorithm of wall calculations (seismic loads)
Application of wall calculation methods - recommendations
Arrangement of reinforcement generated for both methods differs considerably. Calculations of the simplified method lead to reinforcing a wall along the entire section length in zones with a varying amount of reinforcement. The amount of reinforcement is proportional to the value on the stress diagram. It also takes account of loads due to forces and openings (distribution of loads from lintels).
In the classic method, strong reinforcement near edges Af is generated. Along the section length there is less uniformly-distributed reinforcement as compared to the simplified method.
The simplified method is advisable when walls have to transfer vertical loads from floors (including walls with openings). The classic method is recommended for walls which work as cores and are loaded with a moment (working as an RC section subjected to compression with bending).