目录

• Understanding Rebar Development Length in Pad Footings
• 压缩展开长度
• 张力发展长度
• SkyCiv 基础设计模块

This documentation explores the significance of rebar development length in concrete footings and its role in ensuring structural integrity. You can gain insights into design code requirements, factors that influence development length, and practical approaches for incorporating them into your footing designs. Plus, discover how the SkyCiv Foundation Design module simplifies the process of verifying rebar development length for your projects.

Understanding Rebar Development Length in Pad Footings

Proper anchorage and reinforcement are essential for the stability and longevity of concrete structures, especially in pad footings. Development length is the minimum length of rebar embedded in the concrete necessary to achieve the required bond strength between steel and concrete. A development length check ensures that reinforcement is adequately embedded to resist loads without slipping, maintaining structural integrity and enabling safe load transfer to the ground. Verifying development length is a key part of footing design, assuring performance under static and dynamic loads and safeguarding overall structure stability.

Different design standards provide specific guidelines for determining these lengths to ensure that reinforcing bars are securely anchored within the concrete. This article provides an overview of the footing development length requirements as specified by various design standards, 包括ACI 318-14 (美国混凝土研究所), 如 3600 (澳大利亚标准), CSA (加拿大标准协会), 和EN (欧洲规范). By examining the distinct approaches and criteria set forth by each standard, engineers can better understand how to apply these guidelines effectively in practice, ensuring robust and compliant structural designs.

压缩展开长度

The compression development length of a footing is a crucial factor in determining its required thickness to ensure proper anchorage of reinforcing bars. This length is calculated based on the need to embed the bars sufficiently within the concrete to achieve adequate bond strength and prevent slippage under compressive loads. Incorporating the correct development length allows engineers to design footings with optimal thickness for reinforcement, ensuring structural stability and durability and enhancing overall safety.

美国混凝土研究所 (ACI 318 部分 25.4.9)

公制:

\(由使用公式计算的最小值控制{直流} = MAX \left[ \压裂{0.24 F_{和} \psi_{[R}}{\lambda \sqrt{F'_{C}}} \d_{b}, 0.042 F_{和} \psi_{[R} d_{b}, 200mm \right]\)英制:

\(由使用公式计算的最小值控制{直流} = MAX \left[ \压裂{F_{和} \psi_{[R}}{50 \λ sqrt{F'_{C}}} \d_{b}, 0.0003 F_{和} \psi_{[R} d_{b}, 8inch \right]\)在哪里:

F_和 = Rebar yield strength (兆帕, 压力)
F’_C = Concrete strength (兆帕, 压力)
d_b = Dowel bar diameter (毫米, 在)
ѱ _[R = Confinement reinforcement factor (桌子 25.4.9.3)
ƛ = Concrete type factor (桌子 25.4.9.3)

澳大利亚标准 (如 3600 部分 13.1.5)

Basic development length:

\(由使用公式计算的最小值控制{他的,CB} = MAX \left[ \压裂{0.22 F_{他的}}{ \sqrt{F_{C}’}} \d_{b}, 0.0435 F_{他的} d_{b}, 200mm \right]\)在哪里:

F_他的 = Rebar yield strength (兆帕)
F_C‘ = Concrete strength
d_b = Starter bar diameter (毫米)

Canadian Standard Association (CSA Section 12.3)

\(由使用公式计算的最小值控制{D b} = MAX \left[ \压裂{0.24 F_{和}}{ \sqrt{F_{C}’}} \d_{b}, 0.045 F_{和} d_{b}, 200mm \right]\)在哪里:

F_和 = Rebar yield strength (兆帕)
F_C‘ = Concrete strength
d_b = Dowel bar diameter (毫米)

欧洲规范 (EN Section 8.4)

Basic anchorage length (8.4.3)

\(由使用公式计算的最小值控制{b,rqd} = frac{\φ}{4} \时代 frac{\sigma_{sd}}{F_{bd}} \)在哪里:

F_和 = Rebar yield strength (兆帕)
F_bd = Ultimate bond stress (兆帕)
σ_sd = Design stress of the bar at the position from where the anchorage is measured from (兆帕)
ɸ = Dowel bar diameter (毫米)

Design anchorage length (8.4.4)

\(由使用公式计算的最小值控制{bd} =\alpha_{1} \α_{2} \α_{3} \α_{4} 由使用公式计算的最小值控制{b,rqd} \)在哪里:

一种₁, 一种₂, 一种₃, 一种₄ = 1.0 for Compression (桌子 8.2)

Minimum anchorage length (8.4.4)

\(由使用公式计算的最小值控制{b, 分} =MAX \left[ 0.6 由使用公式计算的最小值控制{b,rqd}, 10ɸ, 100mm \right]\)Anchorage length in compression

\(由使用公式计算的最小值控制{bd,压缩} =MAX\left[ 由使用公式计算的最小值控制{b, 分}, 由使用公式计算的最小值控制{bd}\对]\)

张力发展长度

The tension development length is key to ensuring that a footing’s dimensions are adequate to anchor reinforcement against tensile forces. This length, calculated to achieve the necessary bond strength between concrete and rebar, directly impacts the footing’s size and design. Properly determining the tension development length allows engineers to design footings capable of securely anchoring the reinforcement, enabling the structure to withstand tensile stresses and maintain stability and performance.

美国混凝土研究所 (ACI 318 部分 25.4)

Straight bars (部分 25.4.2.3)

公制:

\(由使用公式计算的最小值控制{d} = MAX \left[ \剩下( \压裂{F_{和}}{1.1 \λ sqrt{F'_{C}}} \时代 frac{\psi_{!} \psi_{2} \psi_3}{\剩下(C_{b} + K_{tr} \对) / d_{b}} \对)\d_{b}, 300mm \right]\)英制:

\(由使用公式计算的最小值控制{d} = MAX \left[ \剩下( \压裂{3 F_{和}}{40\λ sqrt{F'_{C}}} \时代 frac{\psi_{!} \psi_{2} \psi_3}{\剩下(C_{b} + K_{tr} \对) / d_{b}} \对) \d_{b}, 12in\right]\)

在哪里:

ѱ_Ť = Casting position factor (桌子 25.4.2.4)
ѱ_Ë = Bar coating factor (桌子 25.4.2.4)
ѱ_s = Bar size factor (桌子 25.4.2.4)
C_b = Minimum bar clear distance (毫米, 在)
ķ_tr = Transverse reinforcement index (毫米, 在)
(C_b + ķ_tr) / d_b ≤ 2.5

Standard hooked bars (部分 25.4.3.1)

公制:

\(由使用公式计算的最小值控制{d} = MAX \left[ \剩下( \压裂{0.24 F_{和} \psi_{Ë} \psi_{C} \psi_{[R}}{\λ sqrt{F'_{C}}} \对)\d_{b}, 8d_{b}, 150 mm \right]\)英制:

\(由使用公式计算的最小值控制{d} = MAX \left[ \剩下( \压裂{F_{和} \psi_{Ë} \psi_{C} \psi_{[R}}{50 \λ sqrt{F'_{C}}} \对)\d_{b}, 8d_{b}, 6 在右]\)

在哪里:

ѱ_Ë = Bar coating factor (桌子 25.4.3.2)
ѱ_C = Bar concrete cover factor (桌子 25.4.3.2)
ѱ_[R = Confining reinforcement factor (桌子 25.4.3.2)

澳大利亚标准 (如 3600 部分 13.1.2.2)

Basic development length:

\(由使用公式计算的最小值控制{他的,tb} = MAX \left[ \压裂{0.5 钢底板设计欧洲规范{1} 钢底板设计欧洲规范{3} F_{和} d_{b}}{钢底板设计欧洲规范{2} \sqrt{F'_{C}}}, 0.058 F_{和} 钢底板设计欧洲规范{1} d_{b} \对]\)在哪里:

ķ₁ = 1.3 for rebar with more than 300 mm concrete cast below the bar (1.0 否则)
ķ₂ = (132 – d_b)/100
ķ₃ = 1-[0.15(C_d – d_b)/d_b]
C_d = Minimum bar clear distance (毫米)

Straight bar:

\(由使用公式计算的最小值控制{他的,Ť} = l_{他的,tb}\)

Standard hook or cog:

\(由使用公式计算的最小值控制{他的,Ť} =0.5 \times l_{他的,tb}\)

Canadian Standard Association (CSA Section 12)

Straight bars (部分 12.2.3)

\(由使用公式计算的最小值控制{d} = MAX \left[ 0.45 钢底板设计欧洲规范{1} 钢底板设计欧洲规范{2} 钢底板设计欧洲规范{3} 钢底板设计欧洲规范{4} \压裂{F_{和}}{\sqrt{F'_{C}}} d_{b}, 300 mm \right]\)在哪里:

ķ₁ = Bar location factor (12.2.4)
ķ₂ = Coating factor (12.2.4)
ķ₃ = Concrete density factor (12.2.4)
ķ₄ = Bar size factor (12.2.4)

Standard hooked bars (部分 12.5)

\(由使用公式计算的最小值控制{d} = MAX \left[ \压裂{100 d_{b}}{\sqrt{F'_{C}}}\时代左(0.7 \压裂{F_{和}}{40}\对), 8 d_{b}, 150 mm \right]\)

欧洲规范 (EN Section 8.4)

Basic anchorage length (8.4.3)

\(由使用公式计算的最小值控制{b,rqd} = frac{\φ}{4} \时代 frac{\sigma_{sd}}{F_{bd}} \)Design anchorage length (8.4.4)

\(由使用公式计算的最小值控制{bd} =\alpha_{1} \α_{2} \α_{3} \α_{4} 由使用公式计算的最小值控制{b,rqd} \)在哪里:

一种₁, 一种₂, 一种₃, 一种₄ = values shown in Table 8.2 for bars in tension

Minimum anchorage length (8.4.4)

\(由使用公式计算的最小值控制{b, 分} =MAX \left[ 0.3 由使用公式计算的最小值控制{b,rqd}, 10ɸ, 100mm \right]\)Anchorage length in compression

\(由使用公式计算的最小值控制{bd,紧张} =MAX\left[ 由使用公式计算的最小值控制{b, 分}, 由使用公式计算的最小值控制{bd}\对]\)

For a detailed guide on how the SkyCiv Design module verifies development length, refer to the following links:

• 美国混凝土研究所 (ACI 318)
• 澳大利亚标准 (如 3600)
• Canadian Standard Association (CSA A23.3)
• 欧洲规范 (在 1992)

SkyCiv 基础设计模块

The latest update to the SkyCiv Foundation Design module enhances its functionality by introducing the ability to incorporate standard hooked reinforcements, enabling more precise and detailed development length checks. This new feature provides users with greater flexibility by allowing them to customize the reinforcement detailing at each end of the footing bars. Users can now specify reinforcement ends as straight bars, 90-degree hooks (cogs), or 180-degree hooks, catering to various design requirements and standards.

The module also features updated graphics that visually aid in inspecting reinforcement detailing checks. Column dowel or starter bars are now also visible in the 3D graphics. With the newly added solver settings under the Miscellaneous tab, users can toggle to ignore specific design checks, such as development length checks and other advanced solving options.

 

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