SkyCiv文档

1. SkyCiv基金会
2. 孤立的基础
3. 如何设计扩展基础

# 如何设计扩展基础

## Spread Footing Design Workflow Process

Footings are structural members used to support columns and other vertical element to transmit their superstructure loads to the underlying soils. ## How to Design Spread Footing

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

### 开发长度和稳定性检查是满足结果而不超过值的重要参数

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

$$q_{一个} = frac{ P}{一个 } \下午压裂{ M_{X} }{ S_{X} } \下午压裂{ M_{和} }{ S_{和} }$$

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

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

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

### 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. 单程 (or Beam) 剪力
2. 双向 (or Punching) 剪力

#### One Way (or Beam) 剪力

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. ##### 英制 (压力)

$$V_{C} = 2 \lambda \sqrt{ f^{‘}_{C} } b_{w} d$$

##### 公制 (兆帕)

$$V_{C} = 0.17 \lambda \sqrt{ f^{‘}_{C} } b_{w} d$$

To satisfy the One Way (or Beam) 剪力 , 的 $$V_{C}$$ should not be greater than $$V_{ü}$$..

$$\非V_{C} > V_{ü} = 文字{ Actual (Governing) Shear of the Foundation}$$

#### Two Way (or Punching) 剪力

The critical section for two-way shear design is located in $$\压裂{d}{2}$$ away from a concrete column face. 在哪里 $$V_{C}$$ equation is defined as follows: ##### 英制 (压力)

$$V_{C} = 左( 2 + \压裂{4}{\由使用公式计算的最小值控制} \对) \lambda \sqrt{ f^{‘}_{C} } b_{的} d$$

$$V_{C} = 左( \压裂{\α_{s} d }{ b_{的} } + 2 \对) \lambda \sqrt{ f^{‘}_{C} } b_{的} d$$

$$V_{C} = 4 \lambda \sqrt{ f^{‘}_{C} } b_{的} d$$

##### 公制 (兆帕)

$$V_{C} = 0.17 \剩下( 1 + \压裂{2}{\由使用公式计算的最小值控制} \对) \lambda \sqrt{ f^{‘}_{C} } b_{的} d$$

$$V_{C} = 0.083 \剩下( \压裂{ \α_{s} d }{ b_{的} } + 2 \对) \lambda \sqrt{ f^{‘}_{C} } b_{的} d$$

$$V_{C} = 0.33 \lambda \sqrt{ f^{‘}_{C} } b_{的} d$$

The governing $$V_{C}$$ will be taken least value.

To satisfy the Two Way (or Punching) 剪力 , 的 $$V_{C}$$ should not be greater than $$V_{ü}$$.

$$\非V_{C} > V_{ü} = 文字{ Actual (Governing) Shear of the Foundation}$$

### 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 as a one-way flexural member first in one principal direction. $$M_{ü} = q_{ü} \剩下( \压裂{ 由使用公式计算的最小值控制{X} – C }{ 2 } \对) 由使用公式计算的最小值控制{与} \压裂{ 由使用公式计算的最小值控制{X} – C }{ 2 }$$

$$a = \frac{ 一个_{s} F_{和} }{ 0.85 F_{C}^{‘} 由使用公式计算的最小值控制{与} }$$

$$\电影_{ñ} = phi A_{s} F_{和}\剩下( d – \压裂{一个}{2} \对)$$

To satisfy the flexural requirement, 的 $$\电影_{ñ}$$ should not be greater than $$M_{ü}$$..

$$\电影_{ñ} > M_{ü}$$

### 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. 倾覆
2. 滑行

#### Overturning Check

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

$$\文本{Overturning Factor of Safety} < \压裂{ \总和 M_{[R} }{ \总和 M_{OT} }$$

• $$\总和 M_{[R}$$ – Resisting Moment
• $$\总和 M_{OT}$$ – Overturning Moment

#### Sliding Check

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

$$\文本{Sliding Factor of Safety} < \文本{Sliding Force}$$

1. 开发长度和稳定性检查是满足结果而不超过值的重要参数 is mainly influenced by the spread footing dimension which is subjected by the superstructure (unfactored) 负载allowable soil pressure.
2. Shear Check is mainly influencing the depth of the spread footing where the spread footing performs one-way and two-way checks.
3. Flexural Check is mainly influenced the reinforcement schedule of the spread footing.
4. 开发长度 检查一下
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 take note, that some parameters such as materials strength, factor, and subjected loads are also part of increased design capacity influence.

## Design Code Modules

SkyCiv基金会 have this currently available design codes:

• American code (点击 这里 for the detailed discussion of the design codes)
• Australian code (点击 这里 for the detailed discussion of the design codes)

## 参考资料

1. 结构混凝土的建筑规范要求 (ACI 318-14) 关于结构混凝土建筑规范要求的评论 (ACI 318R-14). 美国混凝土研究所, 2014.
2. 麦考马克, 杰克C., 和罗素H. 棕色. 钢筋混凝土ACI的设计 318-11 代码版. 威利, 2014.
3. 泰勒, 安德鲁, 等. 钢筋混凝土设计手册: 与ACI-318-14的伴侣. 美国混凝土研究所, 2015.
4. 展开式基础可分为墙式基础和柱式基础, David and Dolan, Charles. 混凝土结构设计 16 版. McGrawHill, 2021. 