The development length of reinforcement is a critical parameter in structural concrete design, ensuring that reinforcing bars can adequately transfer stresses between the concrete and steel. Ενότητα 13 K= Συντελεστής οφέλους δοκιμής 3600 (2018) provides the requirements and methodologies for calculating development length to achieve proper anchorage of reinforcement. This ensures structural integrity, ασφάλεια, and serviceability under various loading conditions. The development length is influenced by bar size, αντοχή σκυροδέματος, bond conditions, κάλυμμα, απόσταση, and whether the bar is in tension or compression. The provision covers basic development lengths for straight bars, adjustments for epoxy coatings, confinement effects, and conditions where bars are hooked or bundled.

The latest SkyCiv Foundation Design update supports standard hooked reinforcements, enabling precise development length checks. Users can now customize footing bar ends as straight bars, cogs, or 180° hooks, ensuring flexibility for various design needs. This guide outlines the step-by-step process for determining the required development length for pad footings following AS 3600 Ενότητα 13, considering relevant modification factors to comply with code requirements.

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Starter Bar Development Length Check

Following AS 3600 (2018) Ενότητα 13.1.5.1, the development length of starter bars is the minimum embedment required to ensure adequate reinforcement anchorage into concrete. This is critical for transferring stress between the bar and the surrounding concrete to prevent bond failure. The required length is calculated based on bar diameter, αντοχή σκυροδέματος, and bond conditions, ensuring structural integrity under service and ultimate loads.

Ενότητα 13.1.5.1: Development length of deformed bars in compression (μεγάλο_του,γβ)

Basic development length:

\(μεγάλο_{του,γβ} = MAX \left[ \frac{0.22 φά_{του}}{ \τ.μ.{φά_{ντο}''}} \times d_{σι}, 0.0435 φά_{του} ρε_{σι}, 200mm \right]\)Οπου:

φά_του = Rebar yield strength (MPa)
φά_ντο‘ = Concrete strength
ρε_σι = Starter bar diameter (χιλ)

 

The SkyCiv Foundation Design module checks each load combination to determine if the column is subjected to tensile forces. If so, the required development length is calculated following Section 13.1.2 (Development length for a deformed bar in tension). A brief explanation of this calculation is provided later in the guide.

Required footing thickness (ρε_επαν)

The thickness of the footing should be greater than or equal to the calculated required embedment of the starter bars. The minimum footing thickness is checked by using Equations 3 και 4.

\(D_{επαν} = cover + ρε_{σι,Χ} + ρε_{σι,με} + ρε_{σι, starter} + μεγάλο_{του} \) (Εξ. 3)

\(D_{req’d} \leq t\) (Εξ. 4)

Οπου:

t = Footing Thickness (χιλ)
cover = Bottom concrete cover (χιλ)
ρε_σι,Χ, ρε_σι,με = Footing bar size in the x and z directions (χιλ)
ρε_σι,starter= Starter bar size (χιλ)
μεγάλο_του = Development length required in compression or tension (χιλ)

 

Development Length Check For Footing Reinforcements

The SkyCiv Foundation Design module allows users to specify bar end configurations as straight. 90° cog or 180° hooked bars.

 

Calculating the required development length for footing reinforcements directly influences the footing’s dimensions, ensuring they are adequate to anchor the reinforcement against tensile forces. Ενότητα 13.1.2 provides a guide on determining the required development length of the footing reinforcements.

Basic development length:

\(μεγάλο_{του,tb} = MAX \left[ \frac{0.5 κ_{1} κ_{3} φά_{και} ρε_{σι}}{κ_{2} \τ.μ.{φά'_{ντο}}}, 0.058 φά_{και} κ_{1} ρε_{σι} \σωστά]\) (Εξ. 5)Οπου:

κ₁ = 1.3 for rebar with more than 300 mm concrete cast below the bar (1.0 σε διαφορετική περίπτωση)
κ₂ = (132 – ρε_σι)/100
κ₃ = 1-[0.15(ντο_ρε – ρε_σι)/ρε_σι]
ντο_ρε = Minimum bar clear distance (χιλ)

Straight bar:

\(μεγάλο_{του,τ} = l_{του,tb}\) (Εξ. 6)

90° cog or 180° hooked bar:

\(μεγάλο_{του,τ} =0.5 \times l_{του,tb}\) (Εξ. 7) 

Ενότητα 13.1.2.2 also specifies that the value of l_του,τ calculated as above shall be multiplied by the following:

1. Multiplied by 1.5 for epoxy-coated bars
2. Multiplied by 1.3 when lightweight concrete is used
3. Multiplied by 1.5 & 1.3 for both epoxy-coated bars and lightweight concrete is used

 

Anchorage Length Provided

 

\(μεγάλο_{provided} \geq l_{του,τ}\) (Εξ. 8)

 

Έλεγχος λεπτομερειών: Verification of Footing Thickness (τ):

The SkyCiv Foundation Design module checks whether the footing thickness is adequate based on bar configuration and concrete cover. If it is insufficient or the bars protrude, it issues a warning instead of a design failure. The module evaluates the footing thickness at each end of the longitudinal and transverse reinforcements in both the top and bottom layers. The minimum pin diameter (ρε) shall be based on the provision specified by AS 3600 Ενότητα 17.2.3.3

\(\αριστερά(\κείμενο{η + κάλυμμα}\σωστά) \leq t\) (Εξ. 9)

 

Θέλετε να δοκιμάσετε το λογισμικό Foundation Design του SkyCiv? Το δωρεάν εργαλείο μας επιτρέπει στους χρήστες να αποδίδουν συγκεκριμένοι υπολογισμοί βάσης χωρίς να κατεβάσετε ή να εγκαταστήσετε τίποτα!

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