Lightweight Concrete for High Strength - Expanded Shale & Clay

Table 6.1 Comparison between experimental and estimated prestress losses of HPLC prestressed
girders
8,000-psi HPLC
Girders
Measured
AASHTO
refined
AASHTO
Lump sum PCI ACI 209
(ksi) (%) (ksi) (%) (ksi) (%) (ksi) (%) (ksi) (%)
Stress After Jacking 202.5 100.0 202.5 100.0 202.5 100.0 202.5 100.0 202.5 100.0
Elastic Shortening 17.0 8.4 11.2 5.5 10.4 5.2 10.5 5.2 12.0 5.9
Creep not measured 16.4 8.1 14.1 7.0 14.8 7.3
Shrinkage separately not estimated
6.5 3.2 5.1 2.5 11.3 5.6
separately
CR+SH 8.8 4.3 22.9 11.3 19.2 9.5 26.1 12.9
Relaxation 11.5* 5.7 18.7 9.2
3.8 1.9 5.6 2.8
Total Timedependent
20.2 10.0 41.5 20.5 24.2 12.0 23.0 11.3 31.7 15.7
Total Losses 37.2 18.4 52.8 26.1 34.7 17.1 33.5 16.5 43.7 21.6
AASHTO AASHTO
10,000-psi HPLC Measured
refined Lump sum PCI ACI 209
Girders
(ksi) (%) (ksi) (%) (ksi) (%) (ksi) (%) (ksi) (%)
Stress After Jacking 202.5 100.0 202.5 100.0 202.5 100.0 202.5 100.0 202.5 100.0
Elastic Shortening 12.0 5.9 10.1 5.0 9.8 4.8 9.0 4.4 10.9 5.4
Creep not measured 16.1 7.9 13.0 6.4 12.7 6.3
Shrinkage separately 6.5 3.2 not estimated 5.1 2.5 11.2 5.6
CR+SH 3.0 1.5 22.6 11.2 separately 18.1 8.9 24.0 11.8
Relaxation 14.6* 7.2 19.2 9.5
3.9 1.9 5.6 2.8
Total Losses 29.6 14.6 51.9 25.6 33.3 16.4 31.0 15.3 40.5 20.0
* Relaxation was determinate with Equation 6.1 using experimental ES, CR and SH.
∆f
2
where
( ∆f
+ ∆f
)
pR2 = 20 − 0.4 ⋅ ∆f
pES
− 0. ⋅
pSR pCR
(6.1)
∆f pR2 : after transfer steel relaxation loss (ksi)
∆f pES : elastic shortening loss (ksi)
∆f pCR : creep of concrete loss (ksi)
∆f pSR : shrinkage of concrete loss (ksi)
Experimental “total losses” for 8,000-psi girders made with HPLC was 37.2 ksi. The
AASHTO-LRFD refined and ACI-209 method overestimated total losses by 15.6 and 6.5 ksi,
respectively. The AASHTO-LRFD lump sum and PCI methods were close to experimental data,
but they underestimated total losses by 2.5 and 3.7 ksi, respectively. The experimental prestress
6-2