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

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
A. Ravikiran ◽  
P. N. Dubey ◽  
M. K. Agrawal ◽  
G. R. Reddy ◽  
K. K. Vaze
Keyword(s):  
Failure Mode ◽  
Seismic Event ◽  
Response Spectrum ◽  
Experimental Results ◽  
Piping System ◽  
Strain Accumulation ◽  
Shake Table Tests ◽  
Accumulated Strain ◽  
Piping Systems ◽  
Inelastic Seismic Response

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.

Comparison of Failure Modes of Piping Systems With Wall Thinning Subjected to In-Plane, Out-of-Plane, and Mixed Mode Bending Under Seismic Load: An Experimental Approach

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Dynamic Behavior ◽  
Failure Modes ◽  
Seismic Load ◽  
Piping System ◽  
Shake Table ◽  
Shake Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Out Of Plane ◽  
Plane Bending

Pressurized piping systems used for an extended period may develop degradations such as wall thinning or cracks due to aging. It is important to estimate the effects of degradation on the dynamic behavior and to ascertain the failure modes and remaining strength of the piping systems with degradation through experiments and analyses to ensure the seismic safety of degraded piping systems under destructive seismic events. In order to investigate the influence of degradation on the dynamic behavior and failure modes of piping systems with local wall thinning, shake table tests using 3D piping system models were conducted. About 50% full circumferential wall thinning at elbows was considered in the test. Three types of models were used in the shake table tests. The difference of the models was the applied bending direction to the thinned-wall elbow. The bending direction considered in the tests was either of the in-plane bending, out-of-plane bending, or mixed bending of the in-plane and out-of-plane. These models were excited under the same input acceleration until failure occurred. Through these tests, the vibration characteristic and failure modes of the piping models with wall thinning under seismic load were obtained. The test results showed that the out-of-plane bending is not significant for a sound elbow, but should be considered for a thinned-wall elbow, because the life of the piping models with wall thinning subjected to out-of-plane bending may reduce significantly.

Fatigue-Ratcheting Behavior of 6 in Pressurized Carbon Steel Piping Systems Under Seismic Load: Experiments and Analysis

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
A. Ravi Kiran ◽  
G. R. Reddy ◽  
P. N. Dubey ◽  
M. K. Agrawal
Keyword(s):  
Carbon Steel ◽  
Response Spectrum ◽  
Thickness Variation ◽  
Seismic Load ◽  
Frequency Change ◽  
Shake Table Tests ◽  
Numerical Studies ◽  
Piping Systems ◽  
Earthquake Load ◽  
Steel Piping

This article presents the experimental and numerical studies of fatigue-ratcheting in carbon steel piping systems under internal pressure and earthquake load. Shake table tests are carried out on two identical 6 in pressurized piping systems made of carbon steel of grade SA333 Gr 6. Tests are carried out using similar incremental seismic load till failure. Wavelet analysis is carried to evaluate frequency change during testing. The tested piping systems are analyzed using iterative response spectrum (IRS) method, which is based on fatigue-ratcheting and compared with test results. Effect of thickness variation in elbow on strain accumulation is studied. Excitation level for fatigue-ratcheting failure is also evaluated and the details are given in this paper.

A Load Combination Method for Aseismic Design of Multiple Supported Piping Systems

1989 ◽  
Vol 111 (1) ◽  
pp. 10-16 ◽  
Author(s):  
K. Suzuki ◽  
A. Sone
Keyword(s):  
Structural Model ◽  
Response Spectrum ◽  
Reduction Factor ◽  
Combination Method ◽  
Piping System ◽  
Response Reduction Factor ◽  
Load Combination ◽  
Combination Scheme ◽  
Piping Systems ◽  
Reduction Effect

A new load combination scheme for seismic response calculation of piping systems subjected to multiple support excitations is presented. This scheme has an advantage, such that the cross-correlation among support excitations are properly taken into account by use of a stationary random vibration approach. The authors also present the idea of generating a “multi-excitation floor response spectrum.” First, using a simple analytical SDOF piping system to two support excitations and a simple Z-shaped piping model for shaking test, the combination law is supplied to various correlation cases of two support excitations and the maximum responses of piping in a fundamental mode is calculated. Second, nonlinear characteristics such as gap and friction appearing between piping itself and supports are specifically investigated. The response effect due to these nonlinearities is evaluated by the results through the shaking test with a piping-support structural model, and the amount of response reduction effect is represented by “a response reduction factor β.”

Comparison of Failure Modes of Piping Systems With Wall Thinning Subjected to In-Plane, Out-of-Plane and Mixed Mode Bending Under Seismic Load: An Experimental Approach

2007 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Seismic Load ◽  
Piping System ◽  
Shake Table ◽  
Shake Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Out Of Plane ◽  
Plane Bending ◽  
The Difference

In order to investigate the influence of degradation on the dynamic behavior and failure modes of piping systems with local wall thinning, shake table tests using 3-D piping system models were conducted. About 50% full circumferential wall thinning at elbows was considered in the test. Three types of models were used in the shake table tests. The difference of the models was the applied bending direction to the thinned wall elbow. The bending direction considered in the tests was either of the in-plane bending, out-of-plane bending, or mixed bending of the in-plane and out-of-plane. These models were excited under the same input acceleration until failure occurred. Through these tests, the vibration characteristic and failure modes of piping models with wall thinning under seismic load were obtained. The test results showed that the out-of-plane bending is not significant for a sound elbow, but should be considered for a thinned wall elbow, because the life of piping models with wall thinning subjected to out-of-plane bending may reduce significantly.

Passive Control of Seismic Response of Piping Systems

2005 ◽  
Vol 128 (3) ◽  
pp. 364-369 ◽  
Author(s):  
Y. M. Parulekar ◽  
G. R. Reddy ◽  
K. K. Vaze ◽  
K. Muthumani
Keyword(s):  
Passive Control ◽  
Response Spectrum ◽  
Time History ◽  
Time History Analysis ◽  
Nonlinear Time History Analysis ◽  
Equivalent Linearization ◽  
Piping System ◽  
Equivalent Damping ◽  
History Analysis ◽  
Piping Systems

Passive energy dissipating devices, such as elastoplastic dampers (EPDs) can be used for eliminating snubbers and reducing the response of piping systems subjected to seismic loads. Cantilever and three-dimensional piping systems were tested with and without EPD on shaker table. Using a finite element model of the piping systems, linear and nonlinear time-history analysis is carried out using Newmark’s time integration technique. Equivalent linearization technique, such as Caughey method, is used to evaluate the equivalent damping of the piping systems supported on elastoplastic damper. An iterative response spectrum method is used for evaluating response of the piping system using this equivalent damping. The analytical maximum response displacement obtained at the elastoplastic damper support for the two piping systems is compared with experimental values and time history analysis values. It has been concluded that the iterative response spectrum technique using Caughey equivalent damping is simple and results in reasonably acceptable response of the piping systems supported on EPD.

A Test and Analysis of the Multiple Support Piping Systems

1989 ◽  
Vol 111 (3) ◽  
pp. 291-299 ◽  
Author(s):  
T. Chiba ◽  
R. Koyanagi ◽  
N. Ogawa ◽  
C. Minowa
Keyword(s):  
Large Scale ◽  
Response Spectrum ◽  
Steel Structures ◽  
Response Spectra ◽  
Piping System ◽  
Multiple Response ◽  
Actual Behavior ◽  
Test Results ◽  
Piping Systems ◽  
Multiple Support

One of the current topics in the seismic design of piping systems is the overall reliability of them in earthquake events. Actual piping systems are generally supported by independent structures such as vessels and steel structures. So, it is very important to clarify the behavior of actual piping systems during the seismic events. For this purpose, the analytical method of multiple excitation problems is a preferable approach to not only evaluate the actual behavior of the piping systems, but also improve the reliability of piping systems. To clarify the dynamic characteristics of the piping systems and to assess the computational methods in the linear system subjected to multiple support excitations, an experimental study using a realistic large-scale piping model has been conducted. The equations for the multiple excitation problem have been validated and the adequacy of the multiple response spectra method has been confirmed by the comparison of the test results with the analytical one. This paper reports the results focusing on the analytical methods of the multiple support piping system. It is noted that the multiple response spectrum method is efficient for the multiple excitation problems.

Influence of Local Wall Thinning and Support Stiffness in Piping Systems on Safety Assessments for Dynamic Loading

2014 ◽  
Author(s):  
Klaus Kerkhof ◽  
Fabian Dwenger ◽  
Gereon Hinz ◽  
Siegfried Schmauder
Keyword(s):  
Stress Analysis ◽  
Response Spectrum ◽  
System Response ◽  
Piping System ◽  
Load Bearing ◽  
Wall Thinning ◽  
Safety Margins ◽  
Piping Systems ◽  
Bearing Behavior ◽  
Local Wall Thinning

The load bearing behavior of piping systems depends considerably on support distances and stiffness as well as cross section characteristics. Stiffness of supports can often be defined only with difficulty by applying simplified procedures or guidelines based on assumptions. Load cases can be estimated quite well, but the safety assessment of a piping system can only be as reliable as the system model can realistically describe the present support stiffness or imperfections e.g. local wall thinning. As a consequence, the prediction of the system response may be poor. It is likely that calculated frequencies differ from natural frequencies determined experimentally. These frequency shifts lead to unrealistic predictions of stress analysis. Examples for overestimations and underestimations of stress analysis are given regarding the load case earthquake, depending on whether the frequency shift runs into or out of the plateau of the applied floor response spectrum. The influence of local wall thinning on modal characteristics is investigated. Conservative estimations of the influence on the load bearing behavior regarding severe local wall thinning are given. For fatigue checks the linear response of an experimental piping system is calculated and safety margins are demonstrated by comparing calculated with experimental results.

Failure Mode and Failure Strengths for Wall Thinning Straight Pipes and Elbows Subjected to Seismic Loading

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Kunio Hasegawa ◽  
Katsumasa Miyazaki ◽  
Izumi Nakamura
Keyword(s):  
Cyclic Loading ◽  
Crack Initiation ◽  
Failure Mode ◽  
Seismic Event ◽  
Low Cycle Fatigue ◽  
Seismic Loading ◽  
Fatigue Curve ◽  
Wall Thinning ◽  
Piping Systems ◽  
Asme Code

It is important to assess the failure strengths for pipes with wall thinning to maintain the integrity of the piping systems and to make codification of allowable wall thinning. Full-scale fracture experiments on cyclic loading under constant internal pressure were performed for 4in. diameter straight pipes and 8in. diameter elbow pipes at ambient temperature. The experiments were low cycle fatigue under displacement controlled conditions. It is shown that a dominant failure mode under cyclic loading for straight pipes and elbows is crack initiation∕growth accompanying swelling by ratchet or buckling with crack initiation. When the thinning depth is deep, the failure mode is burst and crack growth with ratchet swelling. In addition, failure strengths were compared with the design fatigue curve of the ASME Code Sec. III. It is shown that pipes with wall thinning less than 50% of wall thickness have sufficient margins against a seismic event of the safety shutdown earthquake.

Failure Analysis of Piping Systems With Thinned Elbows on Tri-Axial Shake Table Tests

2011 ◽  
Author(s):  
Tadahiro Shibutani ◽  
Izumi Nakamura ◽  
Akihito Otani
Keyword(s):  
Plastic Strain ◽  
Failure Analysis ◽  
Seismic Loading ◽  
Fracture Analysis ◽  
Piping System ◽  
Shake Table ◽  
Loading History ◽  
Damage Factor ◽  
Shake Table Tests ◽  
Piping Systems

This paper presents a computational failure analysis of piping systems with and without thinned elbows on tri-axial shake table tests. In a previous experimental study, two piping models, a sound piping system and a degraded piping system with thinned elbows, were assessed. The sound piping system was found to failed at the elbow flank due to in-plane cyclic bending, whereas the degraded system failed at the end of the elbow due to excessive pipe ovalization. In the present study, finite element (FE) models of elbows were developed in order to carry out fracture analysis. The measured displacements of seismic motions were used as the boundary conditions for FE models. In the sound piping system, plastic strain concentrated at the flank of the elbow due to in-plane bending. The cumulative damage factor was calculated from the fatigue curve and Miner’s rule. The effect of ratcheting was also considered. In the failed elbow, the calculated cumulative damage factor showed good agreement with experimental results. On the other hand, for the fracture analysis of the thinned elbow, the entire seismic loading history on the tri-axial shake table was considered, since the effect of pipe ovalization depends on loading history. The ovalization occurred at the elbow due to cumulative seismic loading. Consequently, the principal plastic strain began to concentrate at the end of the elbow. These FE results offer quantitative explanation for the observed failure modes in the degraded piping system.

Passive Control of Seismic Response of Piping Systems

2004 ◽  
Author(s):  
Y. M. Parulekar ◽  
G. R. Reddy ◽  
K. K. Vaze ◽  
K. Muthumani
Keyword(s):  
Passive Control ◽  
Response Spectrum ◽  
Time History ◽  
Time History Analysis ◽  
Nonlinear Time History Analysis ◽  
Equivalent Linearization ◽  
Piping System ◽  
Equivalent Damping ◽  
History Analysis ◽  
Piping Systems

Passive energy dissipating devices like Elasto-plastic dampers (EPDs) can be used for eliminating snubbers and reducing the response of piping systems subjected to seismic loads. Cantilever and 3-dimensional piping systems were tested with and without EPD on shake table. Using a finite element model of the piping systems, linear and nonlinear time history analysis is carried out using Newmark’s time integration technique. Equivalent linearization technique such as Caughey method is used to evaluate the equivalent damping of the piping systems supported on Elasto-Plastic damper. An iterative response spectrum method is used for evaluating response of the piping system using this equivalent damping. The analytical maximum response displacement obtained at the Elasto-Plastic damper support for the two piping systems is compared with experimental values and time history analysis values. It has been concluded that, iterative response spectrum technique using Caughey equivalent damping is simple and results in reasonably acceptable response of the piping systems supported on EPD.

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