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.

Figuur 1 illustrates the design workflow process, ONTWERP WERKSTROOMPROCES SkyCiv Foundation adapts workflow process. Wherein these checks such as (1) Soil Bearing, (2) Schuintrekken, (3) buigzaam, (4) Ontwikkelingslengte:, en (5) Stability Checks are important parameters required to satisfy the result without exceeding a value of 1.00 Ontwikkelingslengte en stabiliteitscontroles zijn belangrijke parameters die aan het resultaat moeten voldoen zonder een waarde van te overschrijden.

Figuur 1: Workflow of SkyCiv Foundation.

How to Design Spread Footing

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

Ontwikkelingslengte en stabiliteitscontroles zijn belangrijke parameters die nodig zijn om aan het resultaat te voldoen zonder een waarde van . te overschrijden

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

\( q_{een} = frac{ P.}{EEN } \pm frac{ M_{X} }{ S_{X} } \pm frac{ M_{en} }{ S_{en} }\)Echter, 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 hier.

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

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

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

Afschuifcontrole

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. Een manier (or Beam) Schuintrekken
2. Two-way (or Punching) Schuintrekken

One Way (or Beam) Schuintrekken

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.

Figuur 2: Eenrichtingsschaar

Imperial (psi)

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

Metriek (MPa)

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

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

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

Two Way (or Punching) Schuintrekken

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

Figuur 3: Tweerichtingsschaar

Imperial (psi)

\( V_{c} = links( 2 + \frac{4}{\bèta} \Rechtsaf) \lambda \sqrt{ f^{‘}_{c} } b_{De} d \)

\( V_{c} = links( \frac{\alpha_{s} d }{ b_{De} } + 2 \Rechtsaf) \lambda \sqrt{ f^{‘}_{c} } b_{De} d \)

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

Metriek (MPa)

\( V_{c} = 0.17 \links( 1 + \frac{2}{\bèta} \Rechtsaf) \lambda \sqrt{ f^{‘}_{c} } b_{De} d \)

\( V_{c} = 0.083 \links( \frac{ \alpha_{s} d }{ b_{De} } + 2 \Rechtsaf) \lambda \sqrt{ f^{‘}_{c} } b_{De} d \)

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

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

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

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

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.

Figuur 4: Critical Moment Section Line

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

\( M_{u} = q_{u} \links( \frac{ l_{X} – c }{ 2 } \Rechtsaf) l_{met} \frac{ l_{X} – c }{ 2 } \)

Stap 2. Calculate the required minimum reinforcement of the foundation

Stap 3. Calculated the Depth of equivalent rectangular stress block, een.

\( a = \frac{ EEN_{s} f_{en} }{ 0.85 f_{c}^{‘} l_{met} } \)

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

\( \film_{n} = phi A_{s} f_{en}\links( d – \frac{een}{2} \Rechtsaf) \)

To satisfy the flexural requirement, de \( \film_{n} \) 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. Met de laatste knop in het menu aan de linkerkant kunt u de waarde van de toeslag wijzigen
2. Met de laatste knop in het menu aan de linkerkant kunt u de waarde van de toeslag wijzigen

Overturning Check

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

 

\( \tekst{Overturning Factor of Safety} < \frac{ \Ik M{R} }{ \Ik M{OT} } \)

Notitie:

• \( \Ik M{R} \) – Resisting Moment
• \( \Ik M{OT} \) – Overturning Moment

Sliding Check

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

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

Design Checks Adjustment

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

1. Ontwikkelingslengte en stabiliteitscontroles zijn belangrijke parameters die nodig zijn om aan het resultaat te voldoen zonder een waarde van . te overschrijden is mainly influenced by the spread footing dimension which is subjected to the superstructure (unfactored) ladingen en allowable soil pressure.
2. Afschuifcontrole 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. Ontwikkelingslengte: Controleren en
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, factor, and subjected loads are also part of increased design capacity influence.

Design Code Modules

De SkyCiv Foundation have these currently available design codes:

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

Referenties

1. Bouwvereisten voor constructief beton (ACI 318-14) Commentaar op bouwvoorschriften voor constructiebeton (ACI 318R-14). Amerikaans Betoninstituut, 2014.
2. McCormac, Jack C., en Russell H. Bruin. Ontwerp van gewapend beton ACI 318-11 Code-editie. Wiley, 2014.
3. Taylor, Andrew, et al. Het handboek voor het ontwerpen van gewapend beton: een aanvulling op ACI-318-14. Amerikaans Betoninstituut, 2015.
4. Gespreide funderingen kunnen worden geclassificeerd als muur- en kolomvoeten, David and Dolan, Charles. Design of Concrete Structures 16 zal overwegen C. McGrawHill, 2021.

 

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