seismic response and numerical verification for a 1/25 scaled

SEISMIC RESPONSE AND NUMERICAL VERIFICATION FOR A 1/25 SCALED-DOWNREINFORCED CONCRETE REACTOR BUILDING SPECIMEN

Wei-Ting Lin1, Yuan-Chieh Wu2, An Cheng1 and Hui-Mi Hsu11Department of Civil Engineering, National Ilan University, Ilan, Taiwan, R.O.C.

2Institute of Nuclear Energy Research, Atomic Energy Council, Executive Yuan, Taoyuan, Taiwan, R.O.C.E-mail: [email protected]; [email protected]; [email protected]; [email protected]

ICETI-2014, T1038_SCINo. 15-CSME-26, E.I.C. Accession 3801

ABSTRACTIn recent years, full-scale specimens for seismic test were important to safety assessment of the structure innuclear power plants but the full-scale tests were not easy to realize due to the limited capable of the existingshaking table capacity. In Taiwan, it was first time to construct a 1/25 scale-down reinforced concrete reactorbuilding specimen in a nuclear power plant and conduct to study the dynamic properties using shaking tabletest. The specimen was with a length of 2.9 m, width of 2.9 m, height of 2.9 m and weight of 28 tons and castusing the non-demoulding technology and self-consolidating concrete. The entirety structure was composedof a primary containment (thickness of 10 cm), a secondary containment (thickness of 7.5 cm) and threefloors (thickness of 30 and 15 cm). The comparison of measured and calculated results demonstrate thatETABS numerical model was satisfactory and can be further used for numerical shaking table tests and reallife structures.

Keywords: shaking table test; scale-down reinforced concrete specimen; finite element model.

RÉPONSE SISMIQUE ET VÉRIFICATION NUMÉRIQUE D’UN SPÉCIMEN EN BÉTON ARMÉÀ ÉCHELLE RÉDUITE 1/25

RÉSUMÉAu cours des dernières années, les spécimens à pleine échelle pour des tests sismiques sont importants pourl’évaluation de la sécurité des structures dans les usines d’énergie nucléaire. Mais les tests à pleine échellen’étaient pas faciles à réaliser à cause de la capacité limitée des tables à secousse existantes. À Taiwan, pourla première fois, on a construit un spécimen de réacteur en béton armé à échelle réduite 1/25 dans une usined’énergie nucléaire, et on en a étudié les propriétés dynamiques au moyen de tests avec la table à secousse.Les dimensions du spécimen sont de 2,9 m de longueur, 2,9 m de largeur, 2,9 m de hauteur et d’un poidsde 28 tonnes, et il est moulu selon la technologie de béton non-démoulable et auto-consolidant. La totalitéde la structure est composé d’un réservoir de confinement primaire de 10 cm d’épaisseur, d’un confinementsecondaire de 7.5 cm, et trois planchers de 30 et 15 cm d’épaisseur. La comparaison des résultats mesuréset calculés démontrent que le modèle numérique ETABS est satisfaisant et peut être utilisé pour des tests detable de secousse et des structures réelles.

Mots-clés : test de table de secousse; spécimen de béton renforcée à échelle réduite; modèle d’élément fini.

Transactions of the Canadian Society for Mechanical Engineering, Vol. 39, No. 3, 2015 479

1. INTRODUCTION

Since the Tohoku earthquake and subsequent tsunami struck northern Japan in 2011, the primary structure ofnuclear power plants caused severe and fatal damages as well as nuclear disaster triggered immediately [1–3]. It has become necessary to perform seismic analysis and calculate the seismic capacity of safety-relatedstructures, such as seismic category I structures, for the safety assessment of the nuclear power plants. InTaiwan, there are three nuclear power plants located near themetropolis, Taipei, and the safety assessmentof nuclear power plants is paramount missions to authorities and the general public [4].

In order to understand the seismic analysis on those safety-related nuclear structures, a shaking tabletest was frequently used in the civil engineering field and this testing method was useful to learn the dy-namic properties and seismic responses under the historical or artificial earthquakes However, a full-scalespecimen for seismic test was not easy to be realized due to the limited capable of the existing shakingtable capacity. Based on the reason, the assistance of scale-down technique [5] was essential for such hugestructure in seismic test. In the shaking table test, the micro-concrete, finer wires or rebars and copperplatewere used to cast the scale-down specimen due to the thinner members. In this study, the non-demouldingtechnology replaced traditional wooden molds and self-consolidating concrete replaced ordinary portlandcement concrete were used to cast the specimen. The mechanical performance of non-demoulding moldsand self-consolidating concrete was studied first and confirmed as the same as traditional building materials[6].

Few experimental study of the seismic performance of a scale-down reactor building on a shaking tabletest has been reported. Tomomi was the first to report a seismic proving test of a 1/10 scale-down prestressedconcrete containment vessel with the boiling water reactor [7]. And then Hirama reported a seismic prooftest of a 1/8 scale-down reinforced concrete containment vessel, which was an important seismic category Istructures in the plant with advanced boiling water reactor [8]. Wang presented the latest study on theshaking table test of a 1/15 scale-down reinforced concrete containment vessel [9]. Next, many seismictests were performed on the scaled model in US, Japan and other countries and it is feasible to realize thetechnology in the near further.

This study is aimed to carry out to cast a 1/25 scale-down reinforced concrete reactor building and conductto study the dynamic properties using the shaking table test at National Center for Research on EarthquakeEngineering in Taiwan. The displacement response, acceleration response and seismic spectrums of thescale-sown specimen using seismic test was summarized and discussed. Further, a finite element modelof the test was generated using commercially available software as known ETABS. Those results obtainedfrom the suggested numerical model were compared with the experimental measurements in terms of dis-placements, accelerations and spectral curves.

2. EXPERIMENTAL AND PROGRAM

2.1. SpecimenThe scale-down reactor building specimen (R/B) is made by reinforced concrete and the dimension of typicalspecimen is 290 cm high, 290 cm wide, 290 cm deep and the net weigh is approximately 28 tf. The R/Bspecimen composed of a square foundation, an outer wall as secondary containment, an inner wall as maincontainment (reinforced concrete containment vessel), two floors and one roof. The dimensions of thosecomponents are by following: the length is 330 cm and the thickness is 10 cm for the square foundation;the thickness is 7.5 cm and the height is 290 cm for the rectangular secondary containment; the thicknessis 10 cm, the height is 290 cm and the inner diameter is 85 cm for the rectangular main containment, thethickness is 30 cm for the floor and the thickness is 15 cm for the roof with three rectangular openings. Inaddition, an attached mass with 2 tf was to simulate the weight of water for the spent fuel pool. Additionally,the test specimen was at 1/25 scale in diameter and story height based on the original structure of an advanced

480 Transactions of the Canadian Society for Mechanical Engineering, Vol. 39, No. 3, 2015

Fig. 1. Drawing of the R/B specimen.

Fig. 2. Appearance of the R/B specimen.

boiling water reactor. Moreover, the self-consolidating concrete of 280 kg/cm2 was used to cast the specimenin accordance with ASTM C1611 and the embedded #3 and #4 rebar was made of medium carbon steelfollowing the specification of ASTM A615. The details and appearance of R/B specimen are shown inFigs. 1 to 2, respectively. Besides, the R/B specimen was connected to the shaking table by 29–30 bolts andthe non-demoulding technology was used in casting the specimen as shown in Fig. 3.

2.2. Shaking Table TestThe shaking table has 3 degree of freedom system with a frequency range between 0.1 to 50 Hz and themaximum specimen weight is 50 tons. In addition, the maximum acceleration for lateral, longitudinal andvertical direction is 3, 1 and 1 g, respectively. The testing cases of uniaxial white noise wave testing and aset of tri-axial artificial motion testing and impact pulse testing were implemented for each testing item. Thetesting programs and associated input motion were scheduled as shown in Table 1 and the acceleration time


Fig. 3. Appearance of the non-demoulding set-up.

Fig. 4. Acceleration time histories curves (PGA= 200 gal): (a) N–S direction; (b) E–W direction; (c) vertical direction.

Table 1. A schedule for shaking table tests.Test program

Case Input motion X direction (N–S) Y direction (E–W) Z directionPeak Ground Acceleration (g)

White noise-X 0.05White noise-Y 0.05White noise-Z 0.05

Test 1 to 4 N–S test 0.60E–W test 0.60Vertical test 0.60Three direction test 0.60 0.60 0.60


Fig. 5. 3D R/B specimen Model.

Table 2. Natural frequency results.X direction (N–S) Y direction (E–W) Z direction (vertial)

Experimental result 26.6 Hz 21.6 Hz –Numerical result 25.3 Hz 26.1 Hz –

histories of fictitious seismic input motion in N–S, E–W and vertical direction are shown in Fig. 4. Besides,the maximum artificial motion is 0.6 g, and the time history has a duration of 24 s by a factor of 1/

√25.

The accelerometers and laser doppler displacement meters were applied in the top of the specimen for themeasurement of the acceleration and displacement response of the RC specimen.

2.3. Finite Element ModelThe structural model for the scale-down R/B specimen was modeled using a finite element model by em-ploying the ETABS program. The major frames of the R/B specimen were represented by wall and floorelements and there were 139 nodes in the model. In order to model the connection between the bolts andshaking table, the nodes used as the location of the bolts were modeled using a vertical spring which stiff-ness was 500,000 kg/cm. Besides, the 3D R/B model was generated as the actual R/B specimen tested inshaking table as illustrated in Fig. 5.

3. RESULTS AND DISCUSSION

3.1. Natural Frequency AnalysisThe natural frequencies generated by white noise method and transfer function curves are shown in Table 2and Fig. 6, respectively. The natural frequency in the Y direction (N–S direction) was observed lowervalue than that in the X direction (E–W direction) for all cases. It indicated that the X axis was the statusand principal direction of the dynamic mode. From the sine sweeping frequency test, it can be found thatthe fundamental frequency in the X and Y directions are about 26.6 and 21.6 Hz (Fig. 6), respectively.The frequencies were different to the values from the numerical results, 25.3 and 26.1 Hz, for X and Ydirections, respectively. For the Z direction (vertical direction), the peak of the sweeping frequency curveswas not significant at the frequency domain from 10 to 50 Hz and hence it cannot confirm the predominantfrequency in the vertical direction.


Fig. 6. Transfer function curves of R/B specimen: (a) N–S direction; (b) E–W direction; (c) vertical direction.


Fig. 7. Analyzed and measured acceleration responses at top of R/B specimen: (a) X direction; (b) Y direction.

Fig. 8. Analyzed and measured Fourier spectrum at top of R/B specimen: (a) X direction; (b) Y direction.

Fig. 9. Analyzed and measured displacement responses at top of R/B specimen: (a) X direction; (b) Y direction.

3.2. Acceleration ResponseThe measured acceleration responses from the top of the R/B specimen in X and Y directions are shownin Fig. 7. The numerical results are also plotted in Fig. 7 for comparison. It is seem that the suggestednumerical model can well simulate the experimental records in time domain. The calculated and measuredacceleration responses with their corresponding Fourier spectrum of the sensor on the R/B specimen in Xand Y directions are illustrated in Fig. 8. For a frequency smaller than 23 Hz, the calculated accelerationresponses matched quite well with the measured acceleration responses. For a frequency greater than 23 Hz,the calculated acceleration responses were larger than the measured responses. It may be due to the naturalfrequency of the R/B scale-down specimen.


Fig. 10. Measured spectral acceleration curves of R/B specimen for three directions: (a) X direction; (b) Y direction;(c) Z direction.

3.3. Displacement ResponsesThe measured displacement responses from the top of the R/B specimen in X and Y directions and thenumerical results are illustrated in Fig. 9. It is seem that the displacements of the suggested numerical modelwere lower than that of the experimental records in all time domains for two directions. The maximummeasured and calculated displacements of the sensor in X direction were 0.99 and 0.56 mm, respectively.For Y direction, the maximum measured and calculated displacements were 1.07 and 0.44 mm, respectively.It may be due to the interaction between displacement meters in X and Y direction.


Fig. 11. Analyzed and measured spectral acceleration curves of R/B specimen: (a) first floor in X direction; (b) secondfloor in X direction; (c) roof in X direction; (d) first floor in Y direction; (e) second floor in Y direction; (f) roof in Zdirection.

3.4. Spectral Acceleration CurvesThe measured spectral acceleration curves of the R/B specimen in X , Y and Z directions are shown inFig. 10. In these figures, A0, A2W, A3W and A4WS represent the basemat, first floor, second floor and roofaccelerometers of the R/B specimen, respectively. The results show mostly good agreements with thosenodes in a frequency range from 1 to 8 Hz. Considering the peak values at 20 Hz frequency, a range from 77to 261% amplification can be observed for first floor, second floor and roof corresponding to the basemat. Itis indicated that the higher elevation shows higher acceleration especially at the second peak.

The measured and numerical spectral acceleration curves from the top of the R/B specimen in X and Ydirections are illustrated in Fig. 11. It is seen that the suggested numerical model can simulate the experi-mental records in the frequency domain well, especially for a frequency smaller than 18 Hz.

4. CONCLUSIONS

The performance of the reinforced concrete reactor building under specific earthquake excitation is investi-gated in this study through shaking table test and numerical simulations on a scale-down structural specimen.Furthermore, the designed scale-down R/B specimen tested in shaking table is a successful case of the civilengineering and nuclear energy industry field in Taiwan. Comparison of measured and calculated results


demonstrates that the suggested ETABS numerical model is satisfactory and can thus be further used fornumerical shaking table tests and numerical analysis of real life structures.

ACKNOWLEDGEMENTS

Support from the National Science Council (NSC) under grant no. NSC102-3113-P042A-009 in Taiwanand the National Center for Research on Earthquake Engineering (NCREE) is gratefully acknowledged.

REFERENCES

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7. Tomomi, S., Masayuki, S., Yoshihisa, Y., Hiroaki, E., Kazuaki, T., Katsumi, T. and Hiroshi, A., “Seismic provingtest of concrete containment vessels part 1: model tests of a curved shear wall for the PCCV”, in Proceedings of11th World Conference on Earthquake Engineering, Acapulco, Mexico, June 23–28, 1996.

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