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.
数字 1 illustrates the design workflow process, 设计工作流程 SkyCiv基金会 adapts workflow process. Wherein these checks such as (1) Soil Bearing, (2) 剪力, (3) 弯曲的, (4) 开发长度, 和 (5) Stability Checks are important parameters required to satisfy the result without exceeding a value of 1.00 设计工作流程.
数字 1: Workflow of SkyCiv基金会.
How to Design Spread Footing
This section discusses the design procedure of spread footing in reference to 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:
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.
\( \文本{Allowable Bearing Capacity} > \文本{ Actual (Governing) Bearing Pressure on the Foundation} \)
注意: 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:
- 单程 (or Beam) 剪力
- 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.
数字 2: 单向剪切
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:
数字 3: 双向剪切
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 a one-way flexural member first in one principal direction.
数字 4: Critical Moment Section Line
步 1. Calculate the Actual Moment on the foundation \( M_{ü} \).
\( M_{ü} = q_{ü} \剩下( \压裂{ 由使用公式计算的最小值控制{X} – C }{ 2 } \对) 由使用公式计算的最小值控制{与} \压裂{ 由使用公式计算的最小值控制{X} – C }{ 2 } \)
步 2. Calculate the required minimum reinforcement of the foundation
步 3. Calculated the Depth of equivalent rectangular stress block, 一个.
\( a = \frac{ 一个_{s} F_{和} }{ 0.85 F_{C}^{‘} 由使用公式计算的最小值控制{与} } \)
步 4. Calculate the Moment Capacity of the foundation \( \电影_{ñ} \).
\( \电影_{ñ} = phi A_{s} F_{和}\剩下( d – \压裂{一个}{2} \对) \)
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:
- 倾覆
- 滑行
Overturning Check
Overturning Check is a stability check against the Moment of the superstructure load. 通常, this factor of safety for the overturning moment is 1.5-3.0.
\( \文本{Overturning Factor of Safety} < \压裂{ \总和 M_{[R} }{ \总和 M_{OT} } \)
注意:
- \( \总和 M_{[R} \) – Resisting Moment
- \( \总和 M_{OT} \) – Overturning Moment
Sliding Check
Sliding Check is a stability check against Horizontal Force induced by the superstructure load. 通常, this factor of safety for the overturning moment is 1.5-3.0.
\( \文本{Sliding Factor of Safety} < \文本{Sliding Force} \)
Design Checks Adjustment
This article explains the primary adjustment when the SkyCiv基金会 users encounter this failure check.
- 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 to the superstructure (unfactored) 负载 和 allowable soil pressure.
- Shear Check is mainly influenced by the depth of the spread footing where the spread footing performs one-way and two-way checks.
- Flexural Check is mainly influenced by the reinforcement schedule of the spread footing.
- 开发长度 检查一下 和
- 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
的 SkyCiv基金会 have these currently available design codes:
- American code (点击 这里 for a detailed discussion of the design codes)
- Australian code (点击 这里 for a detailed discussion of the design codes)
参考资料
- 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.
- 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.
- 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.
- 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.
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