Proposed Method to Map the Elastic Follow-Up 3D Distribution Time History Using Finite Element Methods

Elastic follow-up (EFU) is a complex and influencing phenomenon in pressure vessels and piping systems. It affects the performance of structural components at elevated temperatures. Quantification of elastic follow-up is challenging since it’s still not clearly defined in the ASME Boiler & Pressure Vessel Code. Pressure vessels and piping under operating load over time can exhibit mixed elastic follow-up trajectories due to inelasticity. Typically, secondary, and primary load are present at the onset which can redistribute over time due to strain accumulation and stress relaxation during elastic-follow-up. ASME Boiler & Pressure Vessel Code Div. 5, limits strain accumulation via criteria in regions outside of the elastic core. However, a method that directly addresses Elastic follow-up, would be advantageous in establishing actual margins against elastic follow-up during the design phase. The phenomenon has been well studied with various assemblages of uniaxial models, showing load and displacement controlled and mixed responses. This study will present a method of assessing elastic follow up in finite element models. The method is based on the R5 elastic follow-up factor (EFF) expression that has been readily derived in the uniaxial case and employed by authors. Essentially the Von Mises equivalent strains are obtained from both a linear elastic and inelastic 3D finite element models subject to thermal (secondary) and pressure (primary) loading. The linear elastic model establishes the hypothetical initial elastic stress and the inelastic model will map the inelastic response through time. The Von Mises equivalent strains are then substituted into R5 expression, which are obtained from the onset linear-elastic model and the time varying inelastic model to map the elastic follow up and through time. The results are benchmarked against uniaxial results having combined primary and secondary loading.

Seismic Responses of Zoned Earth-Fill Dam by Instrumentation and Finite Element Simulation

Natural disasters recently occurred in the northern region of Thailand have been increasingly becoming an important issue with emphasis on the alarm and caution for damage and frequency of disasters which may cause major losses of human lives and properties. In May 2014, six provinces in the northern region of Thailand were affected by the earthquakes (the main shock of Mw 6.1 (Moment Magnitude by USGS) and hundreds of aftershocks including the one Mw 5.9 at most) that had the epicenters at Phan District, Chiang Rai Province (19.656°N 99.670°E). This research aimed to study the distribution of seismic accelerations at Mae Ngad Somboon Chon Dam in Chiang Mai. The accelerometers were installed at 3 positions in the dam, consisting of the crest, middle and base of the dam. The collected data were compared and analyzed by the Finite Element Method. Analyses of the Linear Elastic Model, the Mohr-Coulomb Model and the Hardening Soil Model with using the acceleration actually recorded at the dam were conducted to determine an appropriate analytical model. The results indicated that the accelerations obtained from the Hardening Soil Model were more suitable for actual accelerations among others. Therefore the behavior of the Hardening Soil Model is more realistic than that of the Linear Elastic Model or the Mohr-Coulomb Model.