TOTAL LOSSES AT SERVICE LOADS

An estimate of relaxation loss taken as 2.5ksi for low relaxation strand, 10.0 ksi for stress relieved strand, and in accordance with manufacturers recommendation for other type of strand.

{Δ f}_{p t} + Δ_{E S} + {E G}_{p r e c a s t} + {R G}_{c o m p o s i t e} + {E G}_{l i v e} + Δ f_{{E G}_{p r e c a s t}}^{a d j u s t} + Δ f_{{E G}_{c o m p o s i t e}}^{a d j u s t} + Δ f_{{E G}_{l i v e}}^{a d j u s t} + {Δ f}_{C R} + Δ f_{S H} + Δ f_{p r}

= 7.76 - 0.28 - 1.75 - 4.39 + 0.02 + 0.38 + 9.02 + 10.9092 + 2.5 = 24.2 k s i

Stress in tendon after all losses:

f_{p c} = f_{p i} - f_{p l} = 202.5 - 24.2 = 178.3 k s i

Check Prestressing Limit At Service Limit State [LRFD Table 5.9.3-1]

LRFD Table 5.9.3-1 states that prestressing stress limit after all losses should be such that:

f_{p e} = 178.3 k s i < 0.8 f_{p y} = 0.8 \times 243 = 194.4

Force per strand = (Stress in tendon after all losses) (strand area)

= 178.3 \times 0.153 = 27.28 k i p s

Therefore, total prestressing force after all losses is:

P_pe = 27.59 x 27 = 744.985 kips

\frac{{Δ f}_{p T O T A L}^{A A S H T O}}{f_{p i}} = \frac{24.2}{202.5} = 11.95 %