Tabella dei contenuti

• Understanding Rebar Development Length in Pad Footings
• Lunghezza di sviluppo della compressione
• Lunghezza dello sviluppo della tensione
• Modulo di progettazione della Fondazione SkyCiv

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. Più, 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, compreso ACI 318-14 (American Concrete Institute), AS 3600 (Standard australiani), CSA (Associazione canadese per gli standard), e e (Eurocodice). 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.

Lunghezza di sviluppo della compressione

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.

American Concrete Institute (ACI 318 Sezione 25.4.9)

metrico:

\(l_{dc} = MAX \left[ \frac{0.24 f_{y} \psi_{r}}{\lambda \sqrt{f’_{c}}} \volte d_{b}, 0.042 f_{y} \psi_{r} d_{b}, 200mm \right]\)Imperiale:

\(l_{dc} = MAX \left[ \frac{f_{y} \psi_{r}}{50 \Lambda sqrt{f’_{c}}} \volte d_{b}, 0.0003 f_{y} \psi_{r} d_{b}, 8inch \right]\)Dove:

f_y = Resistenza alla snervamento dell'arredamento (MPa, psi)
f’_c = Forza concreta (MPa, psi)
d_b = Diametro barra di centraggio (mm, pollici)
ѱ _r = Confinement reinforcement factor (tavolo 25.4.9.3)
ƛ = Concrete type factor (tavolo 25.4.9.3)

Standard australiano (AS 3600 Sezione 13.1.5)

Basic development length:

\(l_{il suo,cb} = MAX \left[ \frac{0.22 f_{il suo}}{ \sqrt{f_{c}'}} \volte d_{b}, 0.0435 f_{il suo} d_{b}, 200mm \right]\)Dove:

f_{il suo} = Resistenza alla snervamento dell'arredamento (MPa)
f_c‘ = Forza concreta
d_b = Starter bar diameter (mm)

Associazione standard canadese (Sezione CSA 12.3)

\(l_{db} = MAX \left[ \frac{0.24 f_{y}}{ \sqrt{f_{c}'}} \volte d_{b}, 0.045 f_{y} d_{b}, 200mm \right]\)Dove:

f_y = Resistenza alla snervamento dell'arredamento (MPa)
f_c‘ = Forza concreta
d_b = Diametro barra di centraggio (mm)

Eurocodice (Nella sezione 8.4)

Lunghezza di ancoraggio di base (8.4.3)

\(l_{b,richiesta} = frac{\phi}{4} \volte frac{\sigma_{SD}}{f_{bd}} \)Dove:

f_y = Resistenza alla snervamento dell'arredamento (MPa)
f_bd = Stress di legame ultimo (MPa)
σ_SD = Sollecitazione di progetto della barra nella posizione da cui viene misurato l'ancoraggio (MPa)
ɸ = Dowel bar diameter (mm)

Lunghezza di ancoraggio di progetto (8.4.4)

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

un'₁, un'₂, un'₃, un'₄ = 1.0 for Compression (tavolo 8.2)

Minimum anchorage length (8.4.4)

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

\(l_{bd,compressione} =MAX\left[ l_{b, min}, l_{bd}\giusto]\)

Lunghezza dello sviluppo della tensione

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.

American Concrete Institute (ACI 318 Sezione 25.4)

Barrette dritte (Sezione 25.4.2.3)

metrico:

\(l_{d} = MAX \left[ \sinistra( \frac{f_{y}}{1.1 \Lambda sqrt{f’_{c}}} \volte frac{\psi_{!} \psi_{2} \psi_3}{\sinistra(c_{b} + K_{tr} \giusto) / d_{b}} \giusto)\volte d_{b}, 300mm \right]\)Imperiale:

\(l_{d} = MAX \left[ \sinistra( \frac{3 f_{y}}{40\Lambda sqrt{f’_{c}}} \volte frac{\psi_{!} \psi_{2} \psi_3}{\sinistra(c_{b} + K_{tr} \giusto) / d_{b}} \giusto) \volte d_{b}, 12in\right]\)

Dove:

ѱ_t = Casting position factor (tavolo 25.4.2.4)
ѱ_e = Bar coating factor (tavolo 25.4.2.4)
ѱ_S = Bar size factor (tavolo 25.4.2.4)
c_b = Distanza chiara della barra minima (mm, pollici)
K_tr = Indice di rinforzo trasversale (mm, pollici)
(c_b + K_tr) / d_b ≤ 2.5

Barre agganciate standard (Sezione 25.4.3.1)

metrico:

\(l_{d} = MAX \left[ \sinistra( \frac{0.24 f_{y} \psi_{e} \psi_{c} \psi_{r}}{\Lambda sqrt{f’_{c}}} \giusto)\volte d_{b}, 8d_{b}, 150 mm \right]\)Imperiale:

\(l_{d} = MAX \left[ \sinistra( \frac{f_{y} \psi_{e} \psi_{c} \psi_{r}}{50 \Lambda sqrt{f’_{c}}} \giusto)\volte d_{b}, 8d_{b}, 6 in destra]\)

Dove:

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

Standard australiano (AS 3600 Sezione 13.1.2.2)

Basic development length:

\(l_{il suo,tb} = MAX \left[ \frac{0.5 Eurocodice di design con piastra di base in acciaio{1} Eurocodice di design con piastra di base in acciaio{3} f_{y} d_{b}}{Eurocodice di design con piastra di base in acciaio{2} \sqrt{f’_{c}}}, 0.058 f_{y} Eurocodice di design con piastra di base in acciaio{1} d_{b} \giusto]\)Dove:

K₁ = 1.3 for rebar with more than 300 mm concrete cast below the bar (1.0 altrimenti)
K₂ = (132 – d_b)/100
K₃ = 1-[0.15(c_d – d_b)/d_b]
c_d = Distanza chiara della barra minima (mm)

Straight bar:

\(l_{il suo,t} = l_{il suo,tb}\)

Standard hook or cog:

\(l_{il suo,t} =0.5 \times l_{il suo,tb}\)

Associazione standard canadese (Sezione CSA 12)

Barrette dritte (Sezione 12.2.3)

\(l_{d} = MAX \left[ 0.45 Eurocodice di design con piastra di base in acciaio{1} Eurocodice di design con piastra di base in acciaio{2} Eurocodice di design con piastra di base in acciaio{3} Eurocodice di design con piastra di base in acciaio{4} \frac{f_{y}}{\sqrt{f’_{c}}} d_{b}, 300 mm \right]\)Dove:

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)

Barre agganciate standard (Sezione 12.5)

\(l_{d} = MAX \left[ \frac{100 d_{b}}{\sqrt{f’_{c}}}\volte sinistra(0.7 \frac{f_{y}}{40}\giusto), 8 d_{b}, 150 mm \right]\)

Eurocodice (Nella sezione 8.4)

Lunghezza di ancoraggio di base (8.4.3)

\(l_{b,richiesta} = frac{\phi}{4} \volte frac{\sigma_{SD}}{f_{bd}} \)Lunghezza di ancoraggio di progetto (8.4.4)

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

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

Minimum anchorage length (8.4.4)

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

\(l_{bd,tensione} =MAX\left[ l_{b, min}, l_{bd}\giusto]\)

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

• American Concrete Institute (ACI 318)
• Standard australiano (AS 3600)
• Associazione standard canadese (CSA A23.3)
• Eurocodice (NEL 1992)

Modulo di progettazione della Fondazione SkyCiv

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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