Research Papers: Seismic Engineering

Evaluation of Inelastic Seismic Response of a Piping System Using a Modified Iterative Response Spectrum Method

[+] Author and Article Information
A. Ravikiran

e-mail: arkiran@barc.gov.in

P. N. Dubey

e-mail: pndubey@barc.gov.in

M. K. Agrawal

e-mail: mkagra@barc.gov.in

G. R. Reddy

e-mail: rssred@barc.gov.in

K. K. Vaze

e-mail: kkvaze@barc.gov.in
Reactor Safety Division,
Bhabha Atomic Research Centre,
Mumbai, 400085, India

1Present address: SO/E, R. No. 407, Eng. Hall-7, BARC, Trombay, Mumbai, 400085, India.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received May 21, 2012; final manuscript received January 24, 2013; published online June 11, 2013. Assoc. Editor: Chong-Shien Tsai.

J. Pressure Vessel Technol 135(4), 041801 (Jun 11, 2013) (8 pages) Paper No: PVT-12-1062; doi: 10.1115/1.4023730 History: Received May 21, 2012; Revised January 24, 2013

In pressurized piping systems, strain accumulation may take place due to cyclic loading during a seismic event. This incremental plastic deformation called ratcheting may lead to failure of the piping systems. There is no numerical method available to evaluate this accumulated strain in the piping system using response spectrum as input. In the literature, incremental hinge technique is available to predict the failure level conservatively by considering static collapse as the failure mode. However, it is observed from shake table tests that failure in the piping components, especially in elbows, is due to ratcheting. Considering this failure mode and design input as a response spectrum, a modified incremental hinge technique is developed and validated with experimental results. The strain predicted by this analysis closely matches with that of experimental results which are available up to an excitation of 0.75 g ZPA (zero period acceleration). In the experiment, the pressure boundary rupture occurred at 2 g ZPA, while the analysis predicts the failure of the piping system at 2.37 g ZPA. Details of these investigations are presented in the paper.

Copyright © 2013 by ASME
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Fig. 1

Test setup of the piping system

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Fig. 2

FE model of the piping system

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Fig. 3

Test input spectrum in X direction (horizontal, 100% TRS)

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Fig. 4

Test input spectrum in Z direction (horizontal, 100% TRS)

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Fig. 5

Test input spectrum in Y direction (vertical, 100% TRS)

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Fig. 6

Strain history at elbow-1

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Fig. 7

Strain history at anchor-2

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Fig. 8

Photograph of crack at weld location of elbow-1

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Fig. 9

FE model of the piping system by replacing elbow with springs

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Fig. 10

Schematic of spring model to replace elbow

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Fig. 11

Flow chart for iterative response spectrum method

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Fig. 12

FE model of the elbow

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Fig. 13

Determination of yield displacement of elbow

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Fig. 14

Variation of three components of back-stress with plastic strain

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Fig. 15

Comparison of stable hysteresis loop by Chaboche model with experiment

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Fig. 16

Load line displacement time history at the free end of the pipe

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Fig. 17

Hoop strain history at the crown of the elbow

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Fig. 18

Variation of moment with hoop strain at the crown of the elbow

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Fig. 19

Moment rotation hysteresis loops for the elbow

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Fig. 20

Cyclic envelope moment-rotation curve for the elbow

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Fig. 21

Variation of strain with moment in the elbow

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Fig. 22

Comparison of predicted strain accumulation with test results




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