Inhoudsopgave

• Understanding Rebar Development Length in Pad Footings
• Compressie Ontwikkelingslengte
• Spanningsontwikkeling Lengte
• SkyCiv Foundation-ontwerpmodule

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, volledige ACI 318-14 (Amerikaans Betoninstituut), ALS 3600 (Australische normen), CSA (Canadese Standards Association), and EN (Eurocode). 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.

Compressie Ontwikkelingslengte

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.

Amerikaans Betoninstituut (ACI 318 Sectie 25.4.9)

Metriek:

\(l_{dc} = MAX \left[ \frac{0.24 f_{j} \psi_{r}}{\lambda \sqrt{f'_{c}}} \keer d_{b}, 0.042 f_{j} \psi_{r} d_{b}, 200mm \right]\)Imperial:

\(l_{dc} = MAX \left[ \frac{f_{j} \psi_{r}}{50 \lambda sqrt{f'_{c}}} \keer d_{b}, 0.0003 f_{j} \psi_{r} d_{b}, 8inch \right]\)Waarbij:

f_j = Rebar yield strength (MPa, psi)
f’_c = Concrete strength (MPa, psi)
d_b = Dowel bar diameter (mm, in)
ѱ _r = Confinement reinforcement factor (Tafel 25.4.9.3)
ƛ = Concrete type factor (Tafel 25.4.9.3)

Australische standaard (ALS 3600 Sectie 13.1.5)

Basic development length:

\(l_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak,cb} = MAX \left[ \frac{0.22 f_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak}}{ \sqrt{f_{c}’}} \keer d_{b}, 0.0435 f_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak} d_{b}, 200mm \right]\)Waarbij:

f_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak} = Rebar yield strength (MPa)
f_c‘ = Concrete strength
d_b = Starter bar diameter (mm)

Canadian Standard Association (CSA Section 12.3)

\(l_{db} = MAX \left[ \frac{0.24 f_{j}}{ \sqrt{f_{c}’}} \keer d_{b}, 0.045 f_{j} d_{b}, 200mm \right]\)Waarbij:

f_j = Rebar yield strength (MPa)
f_c‘ = Concrete strength
d_b = Dowel bar diameter (mm)

Eurocode (EN Section 8.4)

Basic anchorage length (8.4.3)

\(l_{b,rqd} = frac{\phi}{4} \[object Window]{\sigma_{sd}}{f_{bd}} \)Waarbij:

f_j = Rebar yield strength (MPa)
f_bd = Ultimate bond stress (MPa)
σ_sd = Design stress of the bar at the position from where the anchorage is measured from (MPa)
ɸ = Dowel bar diameter (mm)

Design anchorage length (8.4.4)

\(l_{bd} =\alpha_{1} \alfa_{2} \alfa_{3} \alfa_{4} l_{b,rqd} \)Waarbij:

een₁, een₂, een₃, een₄ = 1.0 for Compression (Tafel 8.2)

Minimum anchorage length (8.4.4)

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

\(l_{bd,compressie} =MAX\left[ l_{b, min}, l_{bd}\Rechtsaf]\)

Spanningsontwikkeling Lengte

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.

Amerikaans Betoninstituut (ACI 318 Sectie 25.4)

Straight bars (Sectie 25.4.2.3)

Metriek:

\(l_{d} = MAX \left[ \links( \frac{f_{j}}{1.1 \lambda sqrt{f'_{c}}} \[object Window]{\psi_{!} \psi_{2} \psi_3}{\links(c_{b} + Hieronder volgen de verschillende manieren om de gronddrukcoëfficiënten te bepalen om de eenheidswrijvingsweerstand van palen in zand te berekenen{tr} \Rechtsaf) / d_{b}} \Rechtsaf)\keer d_{b}, 300mm \right]\)Imperial:

\(l_{d} = MAX \left[ \links( \frac{3 f_{j}}{40\lambda sqrt{f'_{c}}} \[object Window]{\psi_{!} \psi_{2} \psi_3}{\links(c_{b} + Hieronder volgen de verschillende manieren om de gronddrukcoëfficiënten te bepalen om de eenheidswrijvingsweerstand van palen in zand te berekenen{tr} \Rechtsaf) / d_{b}} \Rechtsaf) \keer d_{b}, 12in\right]\)

Waarbij:

ѱ_t = Casting position factor (Tafel 25.4.2.4)
ѱ_e = Bar coating factor (Tafel 25.4.2.4)
ѱ_s = Bar size factor (Tafel 25.4.2.4)
c_b = Minimum bar clear distance (mm, in)
K_tr = Transverse reinforcement index (mm, in)
(c_b + K_tr) / d_b ≤ 2.5

Standard hooked bars (Sectie 25.4.3.1)

Metriek:

\(l_{d} = MAX \left[ \links( \frac{0.24 f_{j} \psi_{e} \psi_{c} \psi_{r}}{\lambda sqrt{f'_{c}}} \Rechtsaf)\keer d_{b}, 8d_{b}, 150 mm \right]\)Imperial:

\(l_{d} = MAX \left[ \links( \frac{f_{j} \psi_{e} \psi_{c} \psi_{r}}{50 \lambda sqrt{f'_{c}}} \Rechtsaf)\keer d_{b}, 8d_{b}, 6 in rechts]\)

Waarbij:

ѱ_e = Bar coating factor (Tafel 25.4.3.2)
ѱ_c = Bar concrete cover factor (Tafel 25.4.3.2)
ѱ_r = Confining reinforcement factor (Tafel 25.4.3.2)

Australische standaard (ALS 3600 Sectie 13.1.2.2)

Basic development length:

\(l_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak,tb} = MAX \left[ \frac{0.5 zodat ingenieurs precies kunnen nagaan hoe deze berekeningen zijn gemaakt{1} zodat ingenieurs precies kunnen nagaan hoe deze berekeningen zijn gemaakt{3} f_{j} d_{b}}{zodat ingenieurs precies kunnen nagaan hoe deze berekeningen zijn gemaakt{2} \sqrt{f'_{c}}}, 0.058 f_{j} zodat ingenieurs precies kunnen nagaan hoe deze berekeningen zijn gemaakt{1} d_{b} \Rechtsaf]\)Waarbij:

k₁ = 1.3 for rebar with more than 300 mm concrete cast below the bar (1.0 anders-)
k₂ = (132 – d_b)/100
k₃ = 1-[0.15(c_d – d_b)/d_b]
c_d = Minimum bar clear distance (mm)

Straight bar:

\(l_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak,t} = l_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak,tb}\)

Standard hook or cog:

\(l_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak,t} =0.5 \times l_{de opwaartse bodemdruk veroorzaakt bidirectionele buiging met trekspanningen aan het bodemoppervlak,tb}\)

Canadian Standard Association (CSA Section 12)

Straight bars (Sectie 12.2.3)

\(l_{d} = MAX \left[ 0.45 zodat ingenieurs precies kunnen nagaan hoe deze berekeningen zijn gemaakt{1} zodat ingenieurs precies kunnen nagaan hoe deze berekeningen zijn gemaakt{2} zodat ingenieurs precies kunnen nagaan hoe deze berekeningen zijn gemaakt{3} zodat ingenieurs precies kunnen nagaan hoe deze berekeningen zijn gemaakt{4} \frac{f_{j}}{\sqrt{f'_{c}}} d_{b}, 300 mm \right]\)Waarbij:

k₁ = Bar location factor (12.2.4)
k₂ = Coating factor (12.2.4)
k₃ = Concrete density factor (12.2.4)
k₄ = Bar size factor (12.2.4)

Standard hooked bars (Sectie 12.5)

\(l_{d} = MAX \left[ \frac{100 d_{b}}{\sqrt{f'_{c}}}\keer links(0.7 \frac{f_{j}}{40}\Rechtsaf), 8 d_{b}, 150 mm \right]\)

Eurocode (EN Section 8.4)

Basic anchorage length (8.4.3)

\(l_{b,rqd} = frac{\phi}{4} \[object Window]{\sigma_{sd}}{f_{bd}} \)Design anchorage length (8.4.4)

\(l_{bd} =\alpha_{1} \alfa_{2} \alfa_{3} \alfa_{4} l_{b,rqd} \)Waarbij:

een₁, een₂, een₃, een₄ = values shown in Table 8.2 for bars in tension

Minimum anchorage length (8.4.4)

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

\(l_{bd,spanning} =MAX\left[ l_{b, min}, l_{bd}\Rechtsaf]\)

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

• Amerikaans Betoninstituut (ACI 318)
• Australische standaard (ALS 3600)
• Canadian Standard Association (CSA A23.3)
• Eurocode (IN 1992)

SkyCiv Foundation-ontwerpmodule

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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