ABSTRACT
Bonded tendons have been used in reactor buildings of heavy water reactors and the light water reactors of some nuclear power plants operating in Korea. The assessment of prestressed forces on those bonded tendons is becoming an important issue in assuring their continuous operation beyond their design life. In order to assess the effective prestressed force on the bonded tendon, indirect assessment techniques have been applying to the test beams which were manufactured on construction time.
Therefore, this research mainly forced to establish the assessment methodology to measure directly the effective prestressed force on the bonded tendon of containment buildings using System Identification (SI) technique. To accomplish this purpose, simple SI method was proposed and adapted three dimensional finite element analysis of the 1:4 scale prestressed concrete containment vessel (PCCV) tested by Sandia nation Laboratory in 2000.
PCCV MODEL
General Description
The PCCV test model uniformly scaled at 1:4 represents the containment building of an actual pressurized water reactor (PWR) plant OHI unit 3 in Japan. The objectives of the internal pressurization tests were to obtain measurement data on the structural response of the model to pressure loading beyond design basis accident in order to validate analytical modeling, find pressure capacity of the model and observe its failure mechanisms.
The schematic of the test model is shown in Fig. 1 and the design pressure is 0.39 MPa. The pressure at which the local analysis computed liner strains that reached the failure limits was 3.2 times the design pressure which is 1.27 MPa and the catastrophic rupture occurred at 3.6 Pd during the SFMT (Structural Failure Mode Test)
Fig. 1 1:4 scale PCCV model geometry (mm)
Material Properties
The material properties for concrete, steel rebar, post-tensioned tendons and steel liner are prepared by using the experiment data provide by Sandia National Laboratories (SNL).
Concrete
Two Type of concrete such as a normal strength concrete and a high strength concrete were used to construct the SNL PCCV test model. In the present finite analysis, the material property data for the trial mix concrete based on a field curing are used. The material properties adopted in the finite element analysis are described in Table 1.
Table 1. Material data for trial mix concrete (MPa)
 |
fc=29.42 (basemat) |
fc =44.13 (dome & wall) |
||
|
Standard curing |
Field curing |
Standard curing |
Field curing |
|
|
Compressive strength |
51.39 |
41.68 |
60.21 |
48.84 |
|
Tensile strength |
3.93 |
3.37 |
4.21 |
3.45 |
|
Flexural strength |
5.37 |
4.00 |
5.58 |
5.51 |
|
Young’s modulus |
29,030 |
27,950 |
31,970 |
26,970 |
|
Poisson’s ratio |
0.20 |
0.18 |
0.20 |
0.18 |
|
Density (ton/m3) |
2.25 |
2.21 |
2.26 |
2.19 |
Steel rebar
The material properties for each type of rebar are selected from the test data. The material properties are summarized in Table 2 and the test data for steel rebar is illustrated in Fig. 2. In the finite element analysis, we adopt the mean value for the material properties of rebar: (a) SD490 is used for the basematn part; (b) SD390 is used for the cylinder wall and dome parts.
|
- Elastic modulus |
: 1.86E5 MPa (basemat), 1.848E5 MPa (wall and dome) |
|
- Yield stress |
: 512.2 MPa (basemat), 479.9 MPa (wall and dome) |
|
- Ultimate stress |
: 709.7 MPa (basemat), 628.7 MPa (wall and dome) |
|
- Poisson’s ratio |
: 0.3 |
|
- Elongation(%) |
: 17.8 MPa (basemat), 21.32 MPa (wall and dome) |
Table 2. rebar material properties (unit:MPa)
 |
D10 (SD390) |
D13 (SD390) |
D16 (SD390) |
D19 (SD390) |
D22 (SD390) |
D19 (SD490) |
|
Elastic modulus |
1.83E5 |
1.83E5 |
1.83E5 |
1.84E5 |
1.91E5 |
1.86E5 |
|
Poisson’s ratio |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
|
Yield stress |
482.0 |
490.1 |
476.6 |
491.9 |
459.0 |
512.2 |
|
Ultimate stress |
613.6 |
640.4 |
606.2 |
630.4 |
653.2 |
709.7 |
|
Elongation (%) |
20.5 |
24.2 |
22.1 |
21.1 |
18.7 |
17.8 |
Fig. 2 Stress-strain relationship for steel rebar
Prestressing tendon
TAISE performed the calibration test of six samples of a three-strain tendon assembly. The stress-strain data are calculated by the division of the measured forces by the initial cross section area (339mm ) as shown in Fig. 3. The ultimate stress and strain test data are summarized in Table 3.
Fig. 3 Stress-strain relationship for tendons Table 3. Tendon material data
|
Test specimen |
Ultimate stress (MPa) |
Failure strain (%) |
|
Specimen 1 |
1,924 |
3.32 |
|
Specimen 2 |
1,912 |
3.51 |
|
Specimen 3 |
1,932 |
3.36 |
|
Specimen 4 |
1,921 |
No strain gages |
|
Specimen 5 |
1,934 |
No strain gages |
|
Specimen 6 |
1,924 |
3.3 |
|
Mean |
1,924.5 |
3.3 |
* Estimate based on surviving strain gages
Steel liner plate
Two sets off material samples for the steel liner plate were tested to evaluate their material properties. The stress-strain data is illustrated in Fig. 4.
