Spread Footing Design Workflow

Footings are structural members used to support columns and other vertical elements to transmit their superstructure loads to the underlying soils.

figura 1 illustrates the design workflow process, quale il Fondazione SkyCiv adapts workflow process. Wherein these checks such as (1) Soil Bearing, (2) cesoia, (3) Flessionale, (4) Lunghezza di sviluppo, e (5) Stability Checks are important parameters required to satisfy the result without exceeding a value of 1.00 nel Demand-Capacity Ratio o DCR.

figura 1: Workflow of Fondazione SkyCiv.

How to Design Spread Footing

This section discusses the design procedure of spread footing in reference to American Concrete Institute 318-2014.

Lunghezza di sviluppo e controlli di stabilità sono parametri importanti necessari per soddisfare il risultato senza superare un valore di

The Soil Bearing Check mainly determines the geometric dimensions of an isolated footing from the superstructure (service or unfactored) carichi. The actual bearing pressure mainly determines by the equation below:

\( Il modulo con calcola la dimensione dell'asta di ancoraggio{un'} = frac{ P}{UN } \pm frac{ M_{X} }{ S_{X} } \pm frac{ M_{e} }{ S_{e} }\)però, the equation above is only applicable if the eccentricities are within the kern ( \( \frac{L}{6} \) ) of the foundation where bearing pressure is present in the whole area.

When the eccentricities exceeded the kern, The detailed bearing pressure pattern article explains Qui.

To satisfy the foundation geometric dimensions, the allowable bearing capacity of the soil should greater than governing base pressure under the footing.

\( \testo{Allowable Bearing Capacity} > \testo{ Actual (Governing) Bearing Pressure on the Foundation} \)

Nota: No tension in Bearing Pressure in the Foundation Design.

Shear Check

The Shear Check determines the thickness or depth of the foundation based on the shear load induced from the superstructure loads. There are two primary shear checks, as follows:

1. Senso unico (or Beam) cesoia
2. A due vie (or Punching) cesoia

One Way (or Beam) cesoia

The critical section for one-way shear extends across the width of the footing and is located at a distance d from the face of a column.

figura 2: Taglio unidirezionale

Imperiale (psi)

\( V_{c} = 2 \lambda \sqrt{ f^{'}_{c} } b_{w} d \)

metrico (MPa)

\( V_{c} = 0.17 \lambda \sqrt{ f^{'}_{c} } b_{w} d \)

To satisfy the One Way (or Beam) cesoia, il \( V_{c} \) should not be greater than \( V_{u} \)..

\( \phi V_{c} > V_{u} = testo{ Actual (Governing) Shear of the Foundation} \)

Two Way (or Punching) cesoia

The critical section for two-way shear design is located in \( \frac{d}{2} \) away from a concrete column face. Dove \( V_{c} \) equation is defined as follows:

figura 3: Taglio a due vie

Imperiale (psi)

\( V_{c} = sinistra( 2 + \frac{4}{\beta} \giusto) \lambda \sqrt{ f^{'}_{c} } b_{Il} d \)

\( V_{c} = sinistra( \frac{\alfa_{S} d }{ b_{Il} } + 2 \giusto) \lambda \sqrt{ f^{'}_{c} } b_{Il} d \)

\( V_{c} = 4 \lambda \sqrt{ f^{'}_{c} } b_{Il} d \)

metrico (MPa)

\( V_{c} = 0.17 \sinistra( 1 + \frac{2}{\beta} \giusto) \lambda \sqrt{ f^{'}_{c} } b_{Il} d \)

\( V_{c} = 0.083 \sinistra( \frac{ \alfa_{S} d }{ b_{Il} } + 2 \giusto) \lambda \sqrt{ f^{'}_{c} } b_{Il} d \)

\( V_{c} = 0.33 \lambda \sqrt{ f^{'}_{c} } b_{Il} d \)

The governing \( V_{c} \) will be taken least value.

To satisfy the Two Way (or Punching) cesoia, il \( V_{c} \) should not be greater than \( V_{u} \).

\( \phi V_{c} > V_{u} = testo{ Actual (Governing) Shear of the Foundation} \)

Flexural Check

The Flexural Check determines the required reinforcement of the foundation based on the moment or bending load induced from the superstructure loads. The Design procedure for moment strength considers a one-way flexural member first in one principal direction.

figura 4: Critical Moment Section Line

Passo 1. Calculate the Actual Moment on the foundation \( M_{u} \).

\( M_{u} = q_{u} \sinistra( \frac{ l_{X} – c }{ 2 } \giusto) l_{con} \frac{ l_{X} – c }{ 2 } \)

Passo 2. Calculate the required minimum reinforcement of the foundation

Passo 3. Calculated the Depth of equivalent rectangular stress block, un'.

\( a = frac{ UN_{S} f_{e} }{ 0.85 f_{c}^{'} l_{con} } \)

Passo 4. Calculate the Moment Capacity of the foundation \( \film_{n} \).

\( \film_{n} = phi A_{S} f_{e}\sinistra( d – \frac{un'}{2} \giusto) \)

To satisfy the flexural requirement, il \( \film_{n} \) should not be greater than \( M_{u} \)..

\( \film_{n} > M_{u} \)

Development Length Check

The Development Length Check determines a reinforcement shortest embedment length required for a reinforcing bar to develop its full yield strength in concrete.

Stability Check

There are two main types of Stability Check in the foundation, as follow:

1. Ribaltamento
2. Scorrevole

Overturning Check

Overturning Check is a stability check against the Moment of the superstructure load. Generalmente, this factor of safety for the overturning moment is 1.5-3.0.

 

\( \testo{Overturning Factor of Safety} < \frac{ \somma M_{R} }{ \somma M_{OT} } \)

Nota:

• \( \somma M_{R} \) – Resisting Moment
• \( \somma M_{OT} \) – Overturning Moment

Sliding Check

Sliding Check is a stability check against Horizontal Force induced by the superstructure load. Generalmente, this factor of safety for the overturning moment is 1.5-3.0.

\( \testo{Sliding Factor of Safety} < \testo{Sliding Force} \)

Design Checks Adjustment

This article explains the primary adjustment when the Fondazione SkyCiv users encounter this failure check.

1. Lunghezza di sviluppo e controlli di stabilità sono parametri importanti necessari per soddisfare il risultato senza superare un valore di is mainly influenced by the spread footing dimension which is subjected to the superstructure (unfactored) carichi e allowable soil pressure.
2. Shear Check is mainly influenced by the depth of the spread footing where the spread footing performs one-way and two-way checks.
3. Flexural Check is mainly influenced by the reinforcement schedule of the spread footing.
4. Lunghezza di sviluppo Dai un'occhiata e
5. Stability Checks are mainly influenced by the spread footing dimensions.

Based on the information above, those adjustments will increase design capacity per checks of the spread footing.

Please note that some parameters such as materials strength, fattore, and subjected loads are also part of increased design capacity influence.

Design Code Modules

Il Fondazione SkyCiv have these currently available design codes:

• American code (clic Qui for a detailed discussion of the design codes)
  • Verification Manual # 1
• Australian code (clic Qui for a detailed discussion of the design codes)
  • Verification Manual # 1

Riferimenti

1. Requisiti del codice di costruzione per calcestruzzo strutturale (ACI 318-14) Commento ai requisiti del codice edilizio per il calcestruzzo strutturale (ACI 318R-14). American Concrete Institute, 2014.
2. McCormac, Jack C., e Russell H. Marrone. Progettazione di ACI in cemento armato 318-11 Code Edition. Wiley, 2014.
3. Taylor, Andrea, et al. Il manuale di progettazione del cemento armato: un compagno di ACI-318-14. American Concrete Institute, 2015.
4. I basamenti sparsi possono essere classificati come basamenti di pareti e colonne, David and Dolan, Charles. Design of Concrete Structures 16 Edizione. McGrawHill, 2021.

 

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