Wall 2:
Wall 3:
Wall 4:
Wall 5:
| Structural load on foundation | t | kN |
| Wall mass | ||
| Floor mass | ||
| Roof mass | ||
| Finish mass | ||
| Building self-weight | ||
| Live load | ||
| Snow load | ||
| Design foundation load | ||
| Load on soil | t | kN |
| Foundation mass | ||
| Design load on soil | ||
| Load on soil for pressure calculation | ||
| Number of piles | pcs | |
| Design load per pile | ||
| Foundation bearing area | m² | |
| Foundation volume | m³ | |
| Bearing pressure | kPa (kN/m²) | |
| Allowable pressure (maximum) | kPa (kN/m²) | |
| Soil bearing capacity utilization | % | |
About Structural Load on Foundation Calculation
This Structural Load on Foundation calculator determines the building self-weight, loads from floors, roof and finishes, live load and snow load, and then calculates the total building load on the foundation and ground. For strip, slab and column foundations, it also calculates foundation mass and volume, bearing area, average ground pressure and the percentage of allowable soil pressure used. For pile foundations, it determines the total pile mass and the design load on one pile.
The calculation is performed sequentially: first, the geometry and self-weight of structural elements are determined, then live and snow loads are added, after which load combinations with coefficients are formed and the action on the foundation or ground is calculated.
Guidelines and recommendations
Wall mass
Wall geometry. The length of the external walls is taken from the external perimeter of the building. The lengths of the selected internal walls are determined from the plan dimensions and the position of wall C, taking into account the thickness of intersecting walls. The entered storey height is used for each floor.
Wall mass. For each wall, the material volume is calculated from its length, thickness and height, after which the volume is multiplied by the material density and the number of storeys.
m = L × t × H × n × ρ × k
Here L is the wall length, m; t is the thickness, m; H is the storey height, m; n is the number of storeys; ρ is the material density, kg/m3; k is the factor accounting for openings.
Openings in walls. A factor of 0.85 is used for external walls, meaning that windows and doors are assumed to occupy 15% of the wall area. A factor of 0.95 is used for internal walls, corresponding to an assumed 5% opening area. These factors reduce both the structural wall mass and the wall finish area and are not safety factors.
Wall material density. The built-in values are: insulated frame construction - 450 kg/m3, timber - 520 kg/m3, aerated concrete D400/D500/D600 - 400/500/600 kg/m3, porous ceramic block - 800 kg/m3, expanded-clay concrete block - 1000 kg/m3, brick - 1600 kg/m3, structural concrete - 2400 kg/m3. If the actual material density is known, it can be entered directly.
Floors
Number of floor structures. A one-storey building includes 2 horizontal floor structures, a two-storey building includes 3, and a three-storey building includes 4. The mass of each floor structure is calculated by multiplying the building plan area by its mass per unit area in kg/m2.
mfloor = A × q
Reinforced concrete floor. For cast-in-place reinforced concrete, a density of 2500 kg/m3 is used, so the mass per unit area is calculated from the entered thickness.
q = 2500 × t
The thickness t in this formula is used in metres. For example, at a thickness of 200 mm, the mass per unit area is 500 kg/m2.
Hollow-core slabs. Their mass per unit area is determined by interpolation between the built-in values: 150 mm - 250 kg/m2, 200 mm - 285 kg/m2, 220 mm - 310 kg/m2, 265 mm - 365 kg/m2, 320 mm - 430 kg/m2. For an intermediate thickness, the value changes proportionally between the nearest points.
Other floor types. A value of 350 kg/m2 is used for a steel floor structure and 200 kg/m2 for a timber floor structure. If the actual mass of the structure per unit area is known, it can be entered directly.
Roof and snow load
Roof area. The roof structure weight and snow load are applied to the horizontal projection. To account for roof overhangs, the calculator adds 0.5 m on each side of the building, so each projection dimension is increased by 1 m.
Aroof = (A + 1) × (B + 1)
Roof mass. The roof structure mass per unit area in kg/m2 is multiplied by the horizontal roof projection.
mroof = Aroof × qroof
Snow load. The entered snow load in kg/m2 or kN/m2 is also multiplied by the horizontal projection including the overhangs. When entered in kN/m2, the calculator converts the units internally.
Interior and facade finishes
Internal walls. Both faces of internal walls are included. Their total area is determined from the lengths of the selected walls, the storey height and the number of storeys, after which the opening factor 0.95 is applied.
Inside face of external walls. It is calculated from the internal building perimeter, with the external wall thickness deducted. A factor of 0.85 is applied to this area.
Floor and ceiling. The finish area is calculated from the internal building dimensions. The area occupied by internal walls is deducted, so the thickness of external and internal walls is not included in the finished floor and ceiling area.
Afinish = [(A - 2text) × (B - 2text) - Apartitions] × n
Facade. The external finish area is determined from the external perimeter and the total wall height of all storeys. A factor of 0.85 is used to account approximately for windows and doors.
Strip foundation
Concrete volume. The external strip is calculated along the external perimeter of the building, while the internal strip is included only below the selected internal walls. Different widths can be used for the external and internal strips.
V = Lext × s1 × h + Lint × s2 × h
Bearing area. The foundation base area is calculated in the same way, but without the strip height.
Ab = Lext × s1 + Lint × s2
Slab foundation
Slab volume. The external building dimensions and the specified foundation slab thickness are used.
V = A × B × h
Bearing area. For a slab foundation, it is equal to the building plan area A × B.
Column foundation with grillage
Number of columns. First, the external perimeter and the length of the selected internal grillage lines are added together. The resulting length is divided by the specified column spacing, and the result is rounded up to the next whole number.
N = ceil(Ltotal / s)
Foundation volume. The grillage volume and the total volume of all columns are added together.
V = Ltotal × bg × hg + N × a × b × h
Bearing area. Ground pressure is distributed over the total base area of the columns.
Ab = N × a × b
Pile foundation
Reinforced concrete piles. For a square pile, the volume is determined from its length and cross-section width and then multiplied by the number of piles. A reinforced concrete density of 2500 kg/m3 is used to calculate the mass.
V = N × b2 × L
Steel piles. For tubular and screw piles, the entered mass of one pile in kilograms is used. The total mass is equal to the mass of one pile multiplied by the number of piles.
Load per pile. The design load on the ground, including the self-weight of the piles, is divided equally by the specified number of piles.
Fpile = Fd,ground / N
Foundation mass
Material density. A density of 2500 kg/m3 is used for reinforced concrete and 2400 kg/m3 for concrete. Foundation mass is calculated by multiplying the calculated volume by the density.
mfoundation = V × ρ
Live load
Loaded area. The live load is applied to the area of each storey. For a building with n storeys, the area A × B × n is used.
Q = A × B × n × qlive
The value represents the variable load from occupants, furniture, equipment and other imposed actions as one equivalent load per 1 m2.
Load combinations
Permanent load. The building self-weight includes walls, floors, roof and finishes. When calculating the load from the building directly on the foundation, the self-weight of the foundation is not included. When calculating the load on the ground, the foundation self-weight is added.
Design factors. The calculator uses a factor of γG = 1.35 for permanent load and γQ = 1.50 for the leading variable load. The accompanying variable load is additionally multiplied by the combination factor ψ0 = 0.70.
Combination selection. Two cases are checked: in the first, live load is the leading variable action; in the second, snow load is the leading variable action. The larger result is used.
Fd = max(1.35G + 1.50Q + 1.50 × 0.70S; 1.35G + 1.50S + 1.50 × 0.70Q)
For the “Design load on foundation” result, G contains the building self-weight without the foundation. For the “Design load on ground” result, the foundation mass is additionally included in G.
Load used for ground pressure. To determine average ground pressure, loads are used without the 1.35 and 1.50 factors, but the same two leading-variable-load cases are checked with the 0.70 combination factor.
Fservice = max(G + Q + 0.70S; G + S + 0.70Q)
Ground pressure
Average pressure. The load is converted from tonnes to kilonewtons using 1 t = 9.80665 kN and divided by the foundation bearing area. Since 1 kPa = 1 kN/m2, the result is obtained directly in kPa.
p = Fservice × 9.80665 / Ab
Allowable pressure utilization. The calculated average pressure is compared with the allowable soil pressure.
η = p / pallow × 100%
At η = 100%, the calculated pressure is equal to the specified allowable value. A value below 100% means that the average calculated pressure is lower than the specified allowable soil pressure.
Built-in soil values
Allowable pressure. When a soil type is selected, the calculator inserts the following value in kPa. The user can replace it with a known value for the actual ground conditions.
- dense sand or gravel - 392 kPa;
- medium-dense sand - 294 kPa;
- loose sand - 196 kPa;
- medium-dense fine or silty sand - 147 kPa;
- medium sandy clay - 245 kPa;
- stiff sandy clay - 245 kPa;
- stiff loam - 147 kPa;
- plastic loam - 147 kPa;
- stiff clay - 392 kPa;
- plastic clay - 147 kPa.
Related European standards
EN 1990 “Eurocode: Basis of structural design”. This standard is related to the general logic of combining permanent and variable actions. The calculator uses fixed values of γG = 1.35, γQ = 1.50 and ψ0 = 0.70; the ψ0 factor is taken as the same for accompanying live and snow loads as a unified calculation assumption of the calculator.
EN 1991-1-1 “Eurocode 1: Actions on structures. Part 1-1: General actions. Densities, self-weight, imposed loads for buildings”. This standard is related to determining permanent loads from structural elements and imposed loads in buildings.
EN 1991-1-3 “Eurocode 1: Actions on structures. Part 1-3: General actions. Snow loads”. This standard is related to the snow load input, which the calculator applies to the horizontal roof projection.
EN 1997-1 “Eurocode 7: Geotechnical design. Part 1: General rules”. This standard is related to geotechnical design of foundations and ground. The calculator compares the average pressure below the foundation base with the specified allowable soil pressure.
FAQs
Why is the building load on the foundation lower than the load on the ground?
The building load on the foundation includes the self-weight of walls, floors, roof and finishes together with live and snow loads, but it does not include the mass of the foundation itself. When calculating the total building load on the ground, the foundation mass is added to the permanent load, so the resulting value is higher.
Why does the calculator check two combinations of live load and snow load?
Live and snow loads are variable actions, and either of them may become the governing load. The calculator therefore treats each one in turn as the leading variable action, while the other is treated as accompanying with a factor of 0.70, and then selects the larger result.
How are windows and doors accounted for when calculating wall mass?
A factor of 0.85 is applied to external walls, so the calculated material mass and finish area are reduced by 15%. A factor of 0.95 is used for internal walls, which means that 5% of the area is excluded.
Why is the floor finish area smaller than the external building area?
The floor and ceiling finish calculation uses the internal floor area. The thickness of the external walls is deducted from the external dimensions, and the area occupied by the selected internal walls is then subtracted, so the wall structures are not included in the finish area.
How is the percentage of allowable soil pressure used calculated?
The average pressure below the foundation is divided by the specified allowable soil pressure and multiplied by 100%. For example, a result of 75% means that the calculated average pressure is three quarters of the specified allowable value.