Оглавление

• Understanding Rebar Development Length in Pad Footings
• Длина развития сжатия
• Длина развития напряжения
• Модуль проектирования SkyCiv Foundation

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, включая ACI 318-14 (Американский институт бетона), ТАК КАК 3600 (Австралийские Стандарты), CSA (Канадская ассоциация стандартов), и EN (Еврокод). 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.

Длина развития сжатия

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.

Американский институт бетона (ACI 318 Раздел 25.4.9)

метрический:

\(l_{Округ Колумбия} = MAX \left[ \гидроразрыва{0.24 f_{и} \psi_{р}}{\lambda \sqrt{f'_{с}}} \раз д_{б}, 0.042 f_{и} \psi_{р} d_{б}, 200mm \right]\)имперский:

\(l_{Округ Колумбия} = MAX \left[ \гидроразрыва{f_{и} \psi_{р}}{50 \лямбда sqrt{f'_{с}}} \раз д_{б}, 0.0003 f_{и} \psi_{р} d_{б}, 8inch \right]\)куда:

е_и = Rebar yield strength (МПа, фунтов на квадратный дюйм)
е’_с = Concrete strength (МПа, фунтов на квадратный дюйм)
d_б = Dowel bar diameter (мм, в)
ѱ _р = Confinement reinforcement factor (Стол 25.4.9.3)
ƛ = Concrete type factor (Стол 25.4.9.3)

Австралийский стандарт (ТАК КАК 3600 Раздел 13.1.5)

Basic development length:

\(l_{его,cb} = MAX \left[ \гидроразрыва{0.22 f_{его}}{ \SQRT{f_{с}'}} \раз д_{б}, 0.0435 f_{его} d_{б}, 200mm \right]\)куда:

е_его = Rebar yield strength (МПа)
е_с‘ = Concrete strength
d_б = Starter bar diameter (мм)

Canadian Standard Association (CSA Section 12.3)

\(l_{db} = MAX \left[ \гидроразрыва{0.24 f_{и}}{ \SQRT{f_{с}'}} \раз д_{б}, 0.045 f_{и} d_{б}, 200mm \right]\)куда:

е_и = Rebar yield strength (МПа)
е_с‘ = Concrete strength
d_б = Dowel bar diameter (мм)

Еврокод (EN Section 8.4)

Basic anchorage length (8.4.3)

\(l_{б,rqd} = frac{\фи}{4} \[object Window]{\сигма_{sd}}{f_{bd}} \)куда:

е_и = Rebar yield strength (МПа)
е_bd = Ultimate bond stress (МПа)
σ_sd = Design stress of the bar at the position from where the anchorage is measured from (МПа)
ɸ = Dowel bar diameter (мм)

Design anchorage length (8.4.4)

\(l_{bd} =\alpha_{1} \альфа_{2} \альфа_{3} \альфа_{4} l_{б,rqd} \)куда:

а ₁, а ₂, а ₃, а ₄ знак равно 1.0 for Compression (Стол 8.2)

Minimum anchorage length (8.4.4)

\(l_{б, мин} =MAX \left[ 0.6 l_{б,rqd}, 10ɸ, 100mm \right]\)Anchorage length in compression

\(l_{bd,сжатие} =MAX\left[ l_{б, мин}, l_{bd}\право]\)

Длина развития напряжения

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.

Американский институт бетона (ACI 318 Раздел 25.4)

Straight bars (Раздел 25.4.2.3)

метрический:

\(l_{d} = MAX \left[ \осталось( \гидроразрыва{f_{и}}{1.1 \лямбда sqrt{f'_{с}}} \[object Window]{\psi_{!} \psi_{2} \psi_3}{\осталось(c_{б} + Ниже приведены различные способы определения коэффициентов давления грунта для расчета удельного сопротивления трения свай в песке.{tr} \право) / d_{б}} \право)\раз д_{б}, 300mm \right]\)имперский:

\(l_{d} = MAX \left[ \осталось( \гидроразрыва{3 f_{и}}{40\лямбда sqrt{f'_{с}}} \[object Window]{\psi_{!} \psi_{2} \psi_3}{\осталось(c_{б} + Ниже приведены различные способы определения коэффициентов давления грунта для расчета удельного сопротивления трения свай в песке.{tr} \право) / d_{б}} \право) \раз д_{б}, 12in\right]\)

куда:

ѱ_T = Casting position factor (Стол 25.4.2.4)
ѱ_е = Bar coating factor (Стол 25.4.2.4)
ѱ_s = Bar size factor (Стол 25.4.2.4)
с_б = Minimum bar clear distance (мм, в)
К_tr = Transverse reinforcement index (мм, в)
(с_б + К_tr) / d_б ≤ 2.5

Standard hooked bars (Раздел 25.4.3.1)

метрический:

\(l_{d} = MAX \left[ \осталось( \гидроразрыва{0.24 f_{и} \psi_{е} \psi_{с} \psi_{р}}{\лямбда sqrt{f'_{с}}} \право)\раз д_{б}, 8d_{б}, 150 mm \right]\)имперский:

\(l_{d} = MAX \left[ \осталось( \гидроразрыва{f_{и} \psi_{е} \psi_{с} \psi_{р}}{50 \лямбда sqrt{f'_{с}}} \право)\раз д_{б}, 8d_{б}, 6 в справа]\)

куда:

ѱ_е = Bar coating factor (Стол 25.4.3.2)
ѱ_с = Bar concrete cover factor (Стол 25.4.3.2)
ѱ_р = Confining reinforcement factor (Стол 25.4.3.2)

Австралийский стандарт (ТАК КАК 3600 Раздел 13.1.2.2)

Basic development length:

\(l_{его,tb} = MAX \left[ \гидроразрыва{0.5 к_{1} к_{3} f_{и} d_{б}}{к_{2} \SQRT{f'_{с}}}, 0.058 f_{и} к_{1} d_{б} \право]\)куда:

К₁ знак равно 1.3 for rebar with more than 300 mm concrete cast below the bar (1.0 иначе)
К₂ знак равно (132 – d_б)/100
К₃ знак равно 1-[0.15(с_d – d_б)/d_б]
с_d = Minimum bar clear distance (мм)

Straight bar:

\(l_{его,T} = l_{его,tb}\)

Standard hook or cog:

\(l_{его,T} =0.5 \times l_{его,tb}\)

Canadian Standard Association (CSA Section 12)

Straight bars (Раздел 12.2.3)

\(l_{d} = MAX \left[ 0.45 к_{1} к_{2} к_{3} к_{4} \гидроразрыва{f_{и}}{\SQRT{f'_{с}}} d_{б}, 300 mm \right]\)куда:

К₁ = Bar location factor (12.2.4)
К₂ = Coating factor (12.2.4)
К₃ = Concrete density factor (12.2.4)
К₄ = Bar size factor (12.2.4)

Standard hooked bars (Раздел 12.5)

\(l_{d} = MAX \left[ \гидроразрыва{100 d_{б}}{\SQRT{f'_{с}}}\раз осталось(0.7 \гидроразрыва{f_{и}}{40}\право), 8 d_{б}, 150 mm \right]\)

Еврокод (EN Section 8.4)

Basic anchorage length (8.4.3)

\(l_{б,rqd} = frac{\фи}{4} \[object Window]{\сигма_{sd}}{f_{bd}} \)Design anchorage length (8.4.4)

\(l_{bd} =\alpha_{1} \альфа_{2} \альфа_{3} \альфа_{4} l_{б,rqd} \)куда:

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

Minimum anchorage length (8.4.4)

\(l_{б, мин} =MAX \left[ 0.3 l_{б,rqd}, 10ɸ, 100mm \right]\)Anchorage length in compression

\(l_{bd,напряжение} =MAX\left[ l_{б, мин}, l_{bd}\право]\)

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

• Американский институт бетона (ACI 318)
• Австралийский стандарт (ТАК КАК 3600)
• Canadian Standard Association (CSA A23.3)
• Еврокод (В 1992)

Модуль проектирования SkyCiv Foundation

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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