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杭基礎設計の簡単なガイド

How to Design Pile Foundation?

A deep 財団, such as a pile, is a structural member that transmits loads from the superstructure to bedrock or a stronger layer of soil. SkyCivレンダラAPI です type of foundation that can be made of steel, コンクリート, or timber. In terms of cost, piles foundation costs are higher than shallow foundations. Despite its cost, piles are often necessary for structural safety purposes.

図杭の基礎, how to design pile foundation, pile foundation design
図 1: Piles foundation

When can we use Piles?

Weak soils

If the upper soil layers are too weak or highly compressible to support the loads transmitted by the superstructure, piles are used to transfer these loads into a stronger layer of soil or onto a bedrock. 岩盤に荷重を伝達する杭は、エンドベアリングパイルと呼ばれます。. このタイプのパイルは、パイルの先端にある下にある材料の耐荷重能力のみに依存しています。. 一方, 岩盤が深すぎる場合, 杭は、摩擦によって徐々に周囲の土に荷重を伝えることができます. このタイプのパイルは摩擦パイルと呼ばれます.

Horizontal forces

Piles are a more suitable foundation for structures subjected to horizontal forces. 杭は、上部構造からの垂直方向の力を伝達できる一方で、曲げによって水平方向の動きに抵抗することができます. This is a typical situation for designing earth-retaining structures and tall structures subjected to high wind or seismic forces.

Expansive or collapsible soils

Swelling or shrinking of soils may add a considerable amount of pressure to the foundation. It occurs on expansive or collapsible soils due to the increase or decrease in moisture content. It may also cause more damage for shallow foundations; この場合, piles can be used to extend the foundation beyond the active zone or where the swelling and shrinking might occur.

Uplift forces

Uplift forces are developed as a result of hydrostatic pressures, seismic activity, overturning moments, or any forces that may cause the foundation to be extracted from the ground. It is common on structures such as transmission towers, オフショアプラットフォーム, and basements. この状況では, pile foundation is considered to resist these uplift forces.

Soil erosion

Soil erosion at the ground surface may cause the loss of bearing capacity of the soil.This may severely damage structures with shallow foundations.

How Do We Estimate the length of the pile?

Soil investigation plays a significant role in the selection of pile type and estimation of the necessary length of the pile. Estimating the length of pile requires good technical judgement on the geotechnical site data. It can be classified depending on the load-transfer mechanism from the structure to the soil: (a) エンドベアリングパイル. (b) 摩擦杭, そして (c) 締固め杭.

エンドベアリングパイル

The ultimate load capacity of end-bearing pile depends on the load-bearing capacity of the underlying material at the tip of the pile. The necessary length of this type of pile can easily be estimated by determining the location of bedrock or a strong layer of soil as long as it is at a reasonable depth. For instances where a hard stratum is present rather than bedrock, the length of the pile can be extended for a few more meters into the soil layer, as shown in Figure 2b.

Friction piles

Friction piles (Figure 2c) are used when the bedrock layer or hard stratum doesn’t exist or located at unreasonable depth. In that case, the use of end-bearing piles become very long and uneconomical. The ultimate load capacity of friction piles is derived from the skin friction developed along the length of the pile and the surrounding soil. Length of friction piles is relative to the shear strength of soil, 適用荷重, and pile size.

Compaction piles

Compaction piles are a type of piles which are driven through granular soils to achieve proper compaction of soil near the ground surface. Length of compaction piles depends mainly on the relative density before and after the compaction, and the required depth of compaction. Compaction piles are generally shorter than the other types of piles.

how to design pile foundation, pile foundation design
図 2: (a) そして (b) エンドベアリングパイル, (c) Friction Piles

 

Load Transfer Mechanism for Piles

Consider a loaded pile with length L and diameter D, 図に示すように 2. The load Q on the pile shall be resisted mainly by the soil at the bottom of the pile Qp., and partly by skin friction developed along the shaft Qs. 一般的に, の ultimate load-carrying capacity (Qu) of a pile can be represented by the sum of the load resisted at the tip of the pile and the load resisted through skin friction, または式に示すように 1.

Qあなた = Qp + Qs (1)

Qあなた =究極の負荷容量

Qp =エンドベアリング耐荷重

Qs =皮膚摩擦抵抗

しかしながら, エンドベアリングパイル用, load Q is mostly resisted by the soil below the tip of the pile and skin frictional resistance is minimal. 一方, the load Q on friction piles is mostly resisted only by the skin friction rather than the end-bearing capacity Qp. Ultimate load capacities for end-bearing and friction piles are on equations 2 そして 3, それぞれ.

Qあなた Qp (2)

Qあなた Qs (3)

杭の設計方法?

The design and analysis of deep foundations such as piles is somehow a form of art because of all the uncertainties involved in interpreting geotechnical data. Although numerous theoretical and experimental approach was conducted to analyze the behavior and estimate the load-carrying capacity of piles in various soil types, まだ, パイルズファンデーションのメカニズムについては、まだまだ解明すべきことがたくさんあります. 幸運なことに, 構造工学の進歩とともに, これらの不確実性を最小限に抑え、計算時間を短縮するために使用できるさまざまなソフトウェアがあります.

以下は、杭基礎を設計するために従うことができるプロセスの一部です。:

Geotechnical report data

前述のように, pre-foundation design data, パイルタイプなど, 長さ, and size, are pre-determined based on geotechnical report data. Some of the critical parameters which are necessary for further piles foundation design and analysis are the soil types, unit weight, shear strength, modulus of subgrade reaction, and groundwater data

構造解析

Recent developments in structural engineering include structural design software which aims to enhance our skills as structural engineers and produce safe designs, especially with complex structures. There is various FEA software that we can use to model our structures and generate reactions, 既知の値を使用してソルバーの結果をテストする, および上部構造からのサポートの曲げモーメント. 得られたデータは、基礎の設計と分析に使用されます。.

Foundation design

Similar to the FEA software we used to analyze and generate support reactions of the superstructure, there is also numerous foundation design software which we can use to design piles foundation in accordance with different design codes. (注意: 簡略化された計算機の場合, 無料でお試しください コンクリート基礎計算機).

Foundation design software for piles requires various input to perform design checks. ジオメトリデータが含まれています, 土壌プロファイル, コンクリートおよび鉄筋の材料特性, 補強レイアウト, design parameters specified by the design codes, および構造解析ソフトウェアからエクスポートされた反応データ.

図 3: Foundation design software

Some of the standard design checks that are performed for the design of piles foundation:


Geotechnical capacity check is completed when the end-bearing capacity of the soil is determined by dividing the applied vertical loads by the load-carrying capacity of the soil. The ratio should not exceed a value of 1.0. Laterally loaded piles are also checked by estimating the values of the ultimate and allowable lateral loads.

Structural capacity checks are performed by determining axial, 剪断, and flexural capacities in accordance with the chosen design code. Although for a pile foundation, geotechnical failure is more likely to occur than structural failure, it is still necessary to perform this check for safety measures.

最適化

A structural engineer should always prioritize safety in designing any type of structure. しかしながら, engineers may also optimize their design by experimenting with different pile sizes, and reinforcement layouts, resulting in a reduced total amount of materials and the overall cost of the structure without compromising safety and still maintaining the minimum standards required by the code.

概要

The process of designing piles foundation generally involves good interpretation of geotechnical site data, modeling and analysis of the superstructure through an FEA software, generating support reactions, foundation design checks, and optimization to come up with a safe and economical design.

無料のコンクリート基礎計算機

I hope this tutorial has helped you understand more about pile foundation design. 私たちをチェックしてください 無料のコンクリート基礎計算機, a simplified version of SkyCivFoundationデザインソフトウェア, または今すぐサインアップして、SkyCiv ソフトウェアを使い始めましょう!

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