Instantaneous Deflections (TS500)

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Last updated: Oct 24, 2022 by Zeynep Aladağ
3 min read

  • For beams, Instantaneous Deflection is calculated automatically according to TS500 13.2.2

  • For slabs, Immediate Deflection is calculated automatically according to TS500 13.2.2

  • The deflection limit is determined by the user.

Notation

Ec = Modulus of elasticity of concrete,
fctd = Design tensile strength of concrete
Icr = Moment of inertia of cracked section transformed to concrete
Ief = Effective moment of inertia for calculation of deflection
Ic = Moment of inertia of gross concrete section about controidal axis
ln = span length of beam or one-way slab;
Mcr = cracking moment
Mmax = maximum moment in member due to service loads at stage deflection is calculated
y = distance from centroidal axis of gross section, neglecting reinforcement, to tension surface
δt = Total deflection
δi = Instantaneous deflection
δig = Instantaneous deflection due to permanent loads
γt = time-dependent favtor for sustained load
λ = multiplier used for additional deflection due to long-term effects
ρ' = compression reinforcement ratio

According to TS500 13.2.2 Immediate deflections of reinforced concrete bending members under dead and live loads is calculated in accordance with the conditions given below.

  • If Mmax ≤ Mcr moment of inertia of gross concrete section Ic is used for deflection.

  • If Mmax > Mcr Effective moment of inertia Ief is used for deflection.

It is calculated using and taking into account the support conditions. Mmax ≤ Mcr corresponds to no cracking in the element and therefore the entire moment of inertia of gross concrete section Ic, is used. In the case of Mmax > Mcr, it corresponds to the cracking of the element and the deflection is calculated using Effective moment of inertia Ief.

Effective moment of inertia Ief is calculated in accordance with TS500 13.1.

Allowable maximum deflections for flexural members are given in TS500 Table 13.3.

 

Deflection limits can be adjusted in the Cracking / Deflection tab of the Beam Settings window .

The deflection limits conditions can be adjusted in the Deflection tab of the Tiling Settings window .

Deflection results can be examined in the Deflection & Crackings tab of the Beam Reinforcements window .

 

The results of Instantaneous deflection and time-dependent deflection of beams can be examined from the Beam Deflection and Crack Control report.

The results of Instantaneous deflection and time-dependent deflection of the slabs can be examined from the Slab Deflection Control report.