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CALCULATIONS OF EARLY THERMAL CRACKING BA 24/87 & BD 28/87
BS 8007
Appendix A. Smax= (fct/fb). φ/2ρ Then 0.5εult] ρ= (fct/fb). φ/2Smax (1) May be Assume w = S Rα(T1+T2) max max εcs = 0.5εult , R=Rmax=1 Then Then 1/Smax= Rα(T1+T2)/wmax (2) ρ= (fct*/fb).φ/2wmax.Rεte From (2) in (1) we get From 5.7 BA εte=0.8α(T1+T2) where α=12E-6 ρ= (fct/fb).φ/2wmax. Rα(T1+T2) where R is the restraint factor, being the Then * ρ=(fct /fb).φ/2wmax.R.(0.8α(T1+T2)) restrained proportion of the theoretical linear thermal or Form 5.11 in BA shrinkage movement, taken as 0.5 Restraint Restraint Condition for immature concrete with rigid Factor® end restraints. Base cast onto 0.2 Rmax=0.5 blinding Then Edge restraint ρ=(fct/fb).φ/2wmax.[0.5α(T1+T2)] 0.5 in box type >ρcrit deck cast in stages Wall cast onto 0.6 base ρ= (fct*/fb).φ/2wmax.[R(εcs + εte)-
ρ= (fct*/fb).φ/2wmax.[0.8 α(T1+T2)] >Fct/Fy BS 8110 Section 3. εr=0.8Δt αR (EQ 14) Rmax=1 Table 3.3 — Values of external restraint recorded in various structures Pour configuration Restraint factor (R) Thin wall cast on to massive concrete base
0.6 to 0.8 at base 0.1 to 0.2 at top
Massive pour cast into blinding
0.1 to 0.2
Massive pour cast on to existing mass concrete
0.3 to 0.4 at base 0.1 to 0.2 at top 0.2 to 0.4 0.8 to 1.0
Suspended slabs Infill bays, i.e. rigid restraint
CIRIA _REPORT_91 Section 6.6 ρ= (fct*/fb).φ/2wmax.[kR(εcs + εte)0.5tsc] (EQ 11) Where tsc=εult (tensile strain capacity of concrete). K=0.5 & Rmax=1 ((εcs + εte)-0.5tsc)≈ εte=α(T1+T2) Then ρ= (fct/fb).φ/2wmax.[0.5α(T1+T2)] >ρcrit
Finally the ratio of RFT to cross section (surface zone) (ρ) to control the early thermal cracking. ρ= (fct/fb) .f/2w.aR (T1+T2) ≥ fct/fy Where Rmax=0.5 according to Bs8007 Or ρ'= (fct/fb) .f/2w.0.8aR' (T1+T2) ≥ fct/fy where R'max=1 according to BA 24/87 or BD 28/87 Or ρ"= (fct/fb) .f/2w.aKR" (T1+T2) ≥ fct/fy where k=0.5 & R"max=1.06 according to CIRIA report So ρ=ρ"<ρ' when we use Rmax with each code or report
