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Houston, TX, United States

Hu G.,2H Offshore Inc. | Engelhardt M.,University of Texas at Austin
Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) | Year: 2012

This paper summarizes the results of a recently completed research study on the behavior of simple beam end framing connections in steel buildings subjected to fire. Connections are critical elements in maintaining the integrity of a structure during a fire, but there are still many aspects of connection behavior in a fire that are not well understood. In the USA, one of the most common types of simple beam end framing connections is the single-plate connection, which was the subject of this study. In this research investigation, a series of experiments were conducted on connection subassemblies at elevated temperatures to understand and characterize connection stiffness, strength and deformation capacity, and to validate predictions of connection capacity developed by computational and design models. Three dimensional finite element (FE) connection models were developed and these models were evaluated by comparing with experimental data. The FE models were then used to conduct an extensive series of parameter studies that investigated the impact of several key variables on connection response to the heating and cooling stages of a fire. This paper describes key aspects of this study, including the experiments, development of FE models and parametric studies. The paper highlights the results of the study that provide important insights into connection behavior during a fire and the implications of these results for design. Source


Zhang H.,University of Toledo | Zhang H.,2H Offshore Inc. | Fatemi A.,University of Toledo
International Journal of Fracture | Year: 2010

Mixed-mode loading represents the true loading condition in many practical situations. In addition, most of the fatigue life of many components is often spent in the short crack growth stage. The study of short crack growth behavior under mixed-mode loading has, therefore, much practical significance. This work investigated short crack growth behavior under mixed-mode loading using a common medium carbon steel. The effects of load mixity, crack closure, and load ratio on short crack growth behavior were evaluated by conducting experiments using four-point bending specimens with several initial KII/KI mixed-mode ratios and two load ratios. Cracks were observed to grow along the paths with very small K II /K I ratios (i.e. mode I). The maximum tangential stress criterion was used to predict the crack growth paths and the predictions were found to be close to the experimental observations. Several parameters including equivalent stress intensity factor range and effective stress intensity factor range were used to correlate short crack growth rates under mixed-mode loading. Threshold values for short cracks were found to be lower than those for long cracks for all the mixed-mode loading conditions. Crack closure was observed for the entire crack length regime with all load mixity conditions at R ≈ 0.05 and for short crack regime under high load mixity condition at R = 0.5. Several models were used to describe mean stress effects and to correlate crack growth rate data. © 2010 Springer Science+Business Media B.V. Source


Patent
2HOffshore Inc., BP Exploration and Production Inc. | Date: 2014-12-22

A system and method is provided for determining curvature for subsea riser system, including but not limited to drilling risers, steel catenary risers, lazy-wave catenary risers and riser jumpers, comprising the steps of: periodically measuring acceleration in a first lateral direction at said vertical position to obtain a first acceleration timetrace processing said first acceleration timetrace to obtain a first acceleration spectra; applying a transfer function to said first acceleration spectra to obtain a first curvature spectra; and processing said first curvature spectra to obtain a first curvature timetrace. Preferably the transfer function is determined by a method comprising the step of modelling the riser as a Tensioned Timoshenko Beam. The curvature may be used to determine stress and fatigue damage in a structure from motions measured at a single location or a combination of motions measured at a single location with or without tension measurement. The method can be used to determine curvature and hence stress and fatigue damage from any source of excitation, for example the excitation at the tension ring by the top tensioner system, and the vortex induced vibration locked in at any water depth.


Akhtar W.,2H Offshore Inc. | Cerkovnik M.,2H Offshore Inc.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2013

A methodology is developed to account for the effect of crack face pressure on the reference stress in high pressure, thick walled, flowlines and risers. A detailed finite element analysis (FEA) is conducted over a range of crack depths (a/t) for long flaws (large crack aspect ratios (2c/a)) for a thick walled pipe (wall thickness/average radius = 0.28). The results from this analysis allows for the implementation of an accurate calculation of the reference stress, for thick walled pipes under high service pressures and temperatures, thereby, allowing an improved fracture prediction. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE). Source


Tran L.,2H Offshore Inc. | Cerkovnik M.,2H Offshore Inc.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2013

Risers, flowlines and other subsea components may be designed using limit state concepts, where displacement controlled loads are allowed to push stresses beyond yield. However, there can be consequences if the lines are damaged or degraded in service. This paper presents a case study comparing the damage tolerance capacity of a deepwater steel catenary riser (SCR) designed with allowable (working) stress criteria and another designed with limit load criteria. The exercise is also conducted for a production flowline. The damage scenario examines the effects of various levels of pitting corrosion and accounts for the potential of accelerated crack growth due to corrosive effects. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE). Source

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