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擁壁の設計プロセス

擁壁の設計

The process of running a Concrete Retaining Wall Design comprises three main stages:

  • Preliminary dimensioning: Set the baseline dimension for each of the components using some recommended proportions.
  • Stability checks: Make sure that the geometry of the wall will be stable under the load conditions it will be subjected to. Basically lateral earth pressure and surcharge loads.
  • 設計: For the material properties and the calculated internal actions (shear and flexure) make sure the resistance requirements are satisfied by the wall as per a Design code.

記事上で, we will focus on describing each of the steps to successfully design a Retaining Wall with examples.

Preliminary dimensioning

The first step before checking the retaining wall for stability is to assign preliminary dimensions to the different components of the retaining wall system, this is a very important stage in the design of a retaining wall since not assigning the right proportionate dimensions from the beginning to each component may lead to the need of iterating a lot to get the retaining wall to be compliant with the stability requirements or have an oversized system that complies all of the requirements but it using a lot more material than the theoretical minimum. ACI に従って擁壁の寸法を決定するための推奨事項は次のとおりです。:

  • 全体の高さ (\(h )): It is the first parameter that depends only on the needs of the project (measured from the bottom of the base to the top of the stem).
  • ベース幅 (\(=最も近いサポートの面までのせん断が考慮されているセクションの距離{メンバーがいます}\)): 間 0.4 そして 0.7 of the overall height
  • Toe width (\(=最も近いサポートの面までのせん断が考慮されているセクションの距離{つま先}\)): 間 1/4 そして 1/3 of the base width
  • Base thickness (\(t_{メンバーがいます}\)): 間 0.07 そして 0.1 of the overall height and greater than \(0.3 メートル (12 デッドロードからの反応)\)
  • ステム底厚 (\(t_{蒸気, \; btm}\)): 間 0.07 そして 0.12 of the overall height
  • Stem top thickness (\(t_{蒸気, \; 上}\)): 最小 \(0.2 メートル (8 デッドロードからの反応)\), \(0.25 メートル (10 デッドロードからの反応)\) preferred

Skyciv Concrete Retaining Wall Design Example showing recommended ACI dimensions

Stability checks

The stability of a Retaining Wall is ensured once certain requirements are satisfied. Each of those requirements and the recommended factor of safety as per ACI are as follows:

  • Overturning failure: The retaining wall may overturn about the bottom-left corner of its base. This effect is due to the moment generated by the applied loads against the stem (horizontal components of the soil pressure and the surcharge effect) すべての垂直荷重によって打ち消されます (self-weight and vertical components of pressure). 以前の記事で, we fully worked on an example of 転倒モーメントの計算. 伝統的に推奨される安全係数は:

\(FS_{転覆} \ゲク 2.0\)

転倒に対する安全率が低すぎる場合, the geometry of the wall must be modified by increasing its dimensions so that the vertical load is higher.

  • Sliding failure: The retaining wall may slide along its base. This is driven by the same horizontal loads that tend to overturn the wall, and are withstood by the friction force generated between the bottom surface of the base and the substructure soil. 以前の記事で, we fully worked on an example of calculating the Sliding Factor of Safety. 伝統的に推奨される安全係数は:

\(FS_{スライディング} \ゲク 1.5\)

In the case that the factor of safety against sliding is too low, one possibility is to lengthen the base but in case there are limitations to do that, せん断キーを追加すると役立つ場合があります.

  • Bearing failure: The maximum allowable pressure of the substructure soil might be exceeded by the pressure that the wall applies to the soil. 伝統的に推奨される安全係数は:

\(FS_{ベアリング} \ゲク 3.0\)

この場合, if the factor of safety is too low, the option is to lengthen the base for the pressure to distribute better.

Another article describes in detail these stability requirements and the stability checks of any retaining wall can be performed using SkyCiv’s Retaining Wall Calculator Software.

Skyciv Concrete Retaining Wall Design Example Showing Stability Checks Results

 

Design checks

The basic principle for the design of the Retaining Wall is that the reinforced concrete stem and footing flexure and shear design strength must e at least equal to the factored moment and shears determined from the analysis.

  • ウォールステム is designed as a cantilever, fixed at the footing. The loads considered for the design of this component include the axial load due to its weight and frictional forces of the backfill that act on the wall stem. さらに, the bending due to eccentric vertical loads, surcharge loads, and lateral earth pressure also needs to be considered. Ignoring the axial loads acting on the wall stem can be conservative since small loads in that direction tend to increase the moment strength of the wall according to the interaction equation.
  • wall base normally extends on both sides of the stem if there are no physical constraints such as the property line or an existing structure. The footing’s projection underneath the retained soil is known as the heel and is designed to support the entire weight of the soil above it, surcharge loads and if the backfill is inclined, the vertical component of the soil pressure is also supported by the footing. In the case that the footing extends also away from the retained soil, that portion is known as the toe. The critical sections for calculating the flexural strength of the toe and the heel are the front and back face of the wall stem, およびせん断強度の計算用, the critical sections are taken a distance d from the front and back face of the stem.

参考文献

鉄筋コンクリート設計ハンドブック, ACI SP-17(14), 巻. 2

擁壁計算機

SkyCiv offers a Free Concrete Retaining Wall Calculator that will check overturning moment and perform a stability analysis on your retaining walls.

Retaining Wall Software

SkyCiv Retaining Wall Software helps engineers design Cantilever and Gravity retaining walls and is suitable for the calculation of block or concrete walls. の場合、ベースの下部から壁の高さの半分, の場合、ベースの下部から壁の高さの半分, 転倒に対する擁壁の安定性を計算する方法, スライディング, とベアリング!

OscarSanchez製品開発者
オスカーサンチェス
製品開発者
ベン (民事)
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