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Finite Element Analysis of Creep Buckling of CIPP Liners Martin Zhao 10/25/2006.

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Presentation on theme: "Finite Element Analysis of Creep Buckling of CIPP Liners Martin Zhao 10/25/2006."— Presentation transcript:

1 Finite Element Analysis of Creep Buckling of CIPP Liners Martin Zhao 10/25/2006

2 Mercer University2 Topics Personal Background An Introduction to Creep and Buckling Cured-In-Place (CIPP) Liners & Trenchless Technology Finite Element Model and Analysis Results and Discussions Q & A

3 10/25/2006Mercer University3 Training & Experiences in Mechanics Training in Solid Mechanics B.S. – University of Science & Technology of China (USTC) Training in Computer Aided Structural Analysis M.S. – Beijing Institution of Information & Control (BIIC) Experiences with Applied Computational Structural Dynamics at the Institute of Mechanics, under the Chinese Academy of Sciences Training in Applied & Computational Analysis & Modeling (ACAM) Ph.D. – Louisiana Tech University

4 10/25/2006Mercer University4 Verification and enhancement of a FEA package for offshore platforms with a wave and current load generator and result visualization tool (IM/CAS) Typical Projects in Mechanics Residual stress distribution around cold-worked fastener holes using laser speckle interferometry (USTC) Finite element analysis of passive vibration control for an aerospace structure with damping (BIIC) Long-term in-situ monitoring and structural dynamic analysis of a offshore production platform (W114A) located in South China Sea (IM/CAS) Finite element simulation of creep buckling of cured-in-place plastic (CIPP) liners under hydrostatic pressure (LaTech)

5 10/25/2006Mercer University5 Twin Towers : how did they collapse?

6 10/25/2006Mercer University6 Failure Mode The failure mode can be summarized as Local buckling (at the locale where they got hit), plus Dynamic loading (from the top portion of each building to the remain lower potion) What is buckling?buckling

7 10/25/2006Mercer University7 Models – Buckling in Columns Euler Formula (1744) Governing Equation Extended Euler Formula L eff = L/2 L eff = 2L Simply- Supported (hinged- hinged) cantilever (free- clamped) clamped- clamped

8 10/25/2006Mercer University8 What is Creep?Creep Why do we need to know this? Because it is the answer to the question “But why didn’t they buckle immediately after the collision?” Work hardening

9 10/25/2006Mercer University9 Creep Mechanism Dislocation: linear defect in the crystalline may help explain both work hardening and creep At low temperatures, a dislocation may become “jogged” by other interacting dislocations and hence hardens the material At higher temperatures, that jog or dislocation may become mobile and climb to a direction perpendicular to the normal stress applied

10 10/25/2006Mercer University10 Models for Creeping Bailey creep law – for both primary and secondary phase Findley long-term model – for plastics under room temperature and constant stress. Based on 1900- hour experiment, supported by test data over a continuous time span as long as 26 yearslong-term model The significance of creep-induced buckling: critical pressure needs to be replaced by critical time ( T cr )

11 10/25/2006Mercer University11 CIPP Application Purpose Trenchless, or no-dig Maintain utility of sewer pipes and sanity of underground water environment Problems Long-term buckling under hydrostatic pressure Design guidelines and criteria

12 10/25/2006Mercer University12 Design Practices Design code (ASTM-93) based on critical pressure for free standing pipe (Bresse, 1866) and enhancement effect of from the host pipe Free standing pipe Encased liner

13 10/25/2006Mercer University13 Analytical Approximation With the assumption that the buckled portion maybe expressed as Glock (1977) derived that the critical pressure of encased pipe will be which suggests an enhancement factor

14 10/25/2006Mercer University14 Short-term and long-term material characterization Instantaneous buckling tests Long-term (10,000-hr) buckling tests CIPP Research at TTC, LaTech

15 10/25/2006Mercer University15 Finite Element Method Minimum total potential energy principle The total potential energy,, is the sum of the elastic strain energy, U, stored in the deformed body and the potential energy, V, of the applied forces: This energy is at a stationary position when an infinitesimal variation from such position involves no change in energy:stationary positioninfinitesimal The equality between external and internal virtual work (due to virtual displacements) is: Governing equilibrium equation for the system

16 10/25/2006Mercer University16 FE Modeling of CIPP Liners Material properties Elastoplasticity Creep Buckling Contact: liner with the rigid confine

17 10/25/2006Mercer University17 Results: Instantaneous Buckling One- and two-lobe buckling modes are found to give lower and upper bounds for critical pressures Imperfections and yield limits have impacts on P cr

18 10/25/2006Mercer University18 Results: 1- to 2-lobe mode transition Start with a combined effect of the two competing collapse mechanisms, and end with transition into one-lobe mode

19 10/25/2006Mercer University19 Results: Creep Buckling A model relating critical time and dimensionless pressure ratio is proposed

20 10/25/2006Mercer University20 Result: Design Guidelines Critical time vs. critical pressure

21 10/25/2006Mercer University21 Q & A

22 10/25/2006Mercer University22 Other Training & Experience

23 10/25/2006Mercer University23 What’s Shared in Common? Using computing technologies to solve real world problems Result visualization – making real truth easy to see Game programming – make artificial images look real

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