Arc-length technique for nonlinear finite element analysis

Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ordinary solution techniques lead to instability near the limit points and also have problems in case of snap-through and snap-back. Thus they fail to predict the complete load-displacement response. The arc-length method serves the purpose well in principle, received wide acceptance in finite element analysis, and has been used extensively. However modifications to the basic idea are vital to meet the particular needs of the analysis. This paper reviews some of the recent developments of the method in the last two decades, with particular emphasis on nonlinear finite element analysis of reinforced concrete structures.

Progressive collapse resisting capacity of reinforced concrete load bearing wall structures

Reinforced concrete(RC) load bearing wall is widely used in high-rise and mid-rise buildings. Due to the number of walls in plan and reduction in lateral force portion, this system is not only stronger against earthquakes, but also more economical. The effect of progressive collapse caused by removal of load bearing elements, in various positions in plan and stories of the RC load bearing wall system was evaluated by nonlinear dynamic and static analyses. For this purpose, three-dimensional model of 10-story structure was selected. The analysis results indicated stability, strength and stiffness of the RC load-bearing wall system against progressive collapse. It was observed that the most critical condition for removal of load bearing walls was the instantaneous removal of the surrounding walls located at the corners of the building where the sections of the load bearing elements were changed. In this case, the maximum vertical displacement was limited to 6.3 mm and the structure failed after applying the load of 10 times the axial load bored by removed elements. Comparison between the results of the nonlinear dynamic and static analyses demonstrated that the "load factor" parameter was a reasonable criterion to evaluate the progressive collapse potential of the structure.

Simulation of 3D parachute fluid–structure interaction based on nonlinear finite element method and preconditioning finite volume method

A fluid–structure interaction method combining a nonlinear finite element algorithm with a preconditioning finite volume method is proposed in this paper to simulate parachute transient dynamics. This method uses a three-dimensional membrane–cable fabric model to represent a parachute system at a highly folded configuration. The large shape change during parachute inflation is computed by the nonlinear Newton–Raphson iteration and the linear system equation is solved by the generalized minimal residual（GMRES） method. A membrane wrinkling algorithm is also utilized to evaluate the special uniaxial tension state of membrane elements on the parachute canopy. In order to avoid large time expenses during structural nonlinear iteration, the implicit Hilber–Hughes–Taylor（HHT） time integration method is employed. For the fluid dynamic simulations, the Roe and HLLC（Harten–Lax–van Leer contact） scheme has been modified and extended to compute flow problems at all speeds. The lower–upper symmetric Gauss–Seidel（LUSGS） approximate factorization is applied to accelerate the numerical convergence speed. Finally,the test model of a highly folded C-9 parachute is simulated at a prescribed speed and the results show similar characteristics compared with experimental results and previous literature.

Numerical investigation of low cycle fatigue life for channel wall nozzles

The thermal-structural response and low cycle fatigue life of a three-dimensional(3D)channel wall nozzle with regenerative cooling were numerically investigated by coupling the finite volume fluid-thermal method,nonlinear finite element thermal-structural analysis and local strain methods.The nozzle had a high area ratio(nozzle exit area divided by throat area)under cyclic working loads.Parametric studies were carried out to evaluate the effects of channel structural parameters such as channel width,channel height,liner thickness and rib width.Results showed that the integrated effects of three-dimensional channel structure and load distribution caused serious strain,which mainly occurred at the intersectant regions of liner wall on the gas side and the symmetric planes of channel and rib.The cooling effect and channel structural strength were significantly improved as the channel width and height decreased,leading to substantial extension of the nozzle service life.On the other hand,the successive decrease in liner thickness and rib width apparently increased the strain amplitude and residual strain of channel wall nozzle during cyclic work,significantly shortening the service life.The present work is of value for design of the channel wall nozzle to prolong its cyclic service life.

Load Distribution on the Hull-Leg Connection Components of a Jack-Up

The jacking pinions and rack chocks of the fixation system of a jack-up sustain tremendous load in the elevated condition, especially when there exists a remarkable non-uniformity of the load distribution. Failures of these structural components may lead to disastrous consequence of the jack-up. Despite the importance of these components, it is difficult to give an accurate prediction of the load distribution on these components in engineering application due to the complex nonlinear interaction mechanism, which is influenced by the relative stiffness of the components, leg-guide clearance and backlash. Previous studies mainly focus on the global performance of the jack-up and pay little attention to the load distribution on the pinions and chocks. The strength of the jacking system is often guaranteed by the manufacturer for an estimate load level, which brings in uncertainty to the safety of the jack-up. The characteristics of the hull-leg interaction are discussed in this paper, and a simplified method using gap elements is proposed. The nonlinear structural analyses are carried out for a specific jack-up using the proposed method and the three-dimensional finite element method(FEM) with contact algorithm. The proposed method is proved accurate and effective for the engineering application. The characteristics of the load distribution of the specific jack-up are discussed, and the conclusions are presented.