Search results for "Elastic plastic"
showing 8 items of 18 documents
Evaluation of the shakedown limit load multiplier for stochastic seismic actions
2017
A new approach for the evaluation of the shakedown limit load multiplier for structures subjected to a combination of quasi-statically variable loads and seismic actions is presented. The common case of frame structures constituted by elastic perfectly plastic material is considered. The acting load history during the lifetime of the structure will be defined as a suitable combination of never ending quasi-statical loads, variable within an appropriate given domain, and stochastic seismic actions occurring for limited time interval. The proposed approach utilizes the Monte Carlo method in order to generate a suitable large number of seismic acceleration histories and the corresponding shake…
Optimization of continuous elastic perfectly plastic beams
2004
Abstract The optimal design of elastic plastic beams subjected to loads quasi-statically variable within a given domain is studied. A minimum volume formulation and a maximum load multiplier formulation are developed, both expressed on the grounds of a statical as well as of a kinematical approach. The search problems are formulated according to three different limiting criteria acting simultaneously. For each criterion a corresponding selected safety factor is imposed. The Euler–Lagrange equations related to the above described problems are deduced. A special iterative technique devoted to the solution of the above referenced problems is proposed. Some numerical examples conclude the paper.
Fixed strength and stiffness hinges for steel frames
2017
A new type of device able to connect steel beam elements is proposed. Specifically, the device is designed in such a way that the required bending stiffness and limit resistance can be independently imposed. To this goal, the device is realized as a "sandwich" section whose wings possess a particular geometry able to guarantee the required characteristics. Further technological requirement is that the device has to engage plan dimensions equal to those of the elements to which it is connected. The procedure to design the device is presented in the paper with reference to a simple plane steel portal constituted by appropriate profiles in such a way it behaves following an assigned force/disp…
Ideal Elastic-Plastic Oscillators Subjected to Stochastic Input
1999
Abstract The paper deals with the evaluation of the probabilistic response of an ideal elastic-plastic single degree of freedom oscillator subjected to a normal white noise. The analysis has been conducted on the hypothesis that accumulated plastic displacements are a compound homogeneous Poisson process independent of the external excitation. In this case plastic displacements can be treated as an additional external noise, to be identified, acting on a linear system. In the paper a time domain approach to obtain the two variable non stationary correlation function is proposed. Hence the evolutionary power spectral density function is also obtained. A numerical example is presented in orde…
Comparison among different dynamic shakedown approaches
2017
The paper concerns the search for the limit load multiplier of structures subjected to seismic actions under shakedown conditions. The search problem is treated referring to two fundamental different approaches: The unrestricted dynamic shakedown approach and a new stochastic one recently proposed. The comparison between the above cited approaches is effected with the aim of evaluate the goodness of the obtainable results and the related computational effort. The structure sensitivity with respect to shakedown is evaluated through the analysis of the shakedown limit load multiplier cumulative distribution function. This function is determined by means of the stochastic approach, adopting th…
An Approximate Technique for Dynamic Elastic-Plastic Analysis
1994
The possibility of obtaining an approximate sufficiently reliable response for elasticplastic discretized structures subjected to dynamic load (kinematical and/or mechanical), with alow computational effort, has been considered. A suitable technique to this effect comes from the form of the dynamic influence matrix of imposed plastic strains on self-stresses, which is shaped by adding up a sparse time-dependent matrix and a block diagonal time-independent matrix (which is the sum of two block diagonal matrices). Several cases of practical interest have been studied, among these cases a special one where all the degrees-of-freedom are dynamic. The technique is compared to other approximate t…
Computational procedures for plastic shakedown design of structures
2004
The minimum volume design problem of elastic perfectly plastic finite element structures subjected to a combination of fixed and perfect cyclic loads is studied. The design problem is formulated in such a way that incremental collapse is certainly prevented. The search for the structural design with the required limit behaviour is effected following two different formulations, both developed on the grounds of a statical approach: the first one operates below the elastic shakedown limit and is able to provide a suboptimal design; the second one operates above the elastic shakedown limit and is able to provide the/an optimal design. The Kuhn–Tucker conditions of the two problems provide usefu…
Bounds on plastic strains for elastic plastic structures in plastic shakedown conditions
2007
The problem related to the computation of bounds on plastic deformations for structures in plastic shakedown condition (alternating plasticity) is studied. In particular, reference is made to structures discretized by finite elements constituted by elastic perfectly plastic material and subjected to a special combination of fixed and cyclic loads. The load history is known during the steady-state phase, but it is unknown during the previous transient phase; so, as a consequence, it is not possible to know the complete elastic plastic structural response. The interest is therefore focused on the computation of bounds on suitable measures of the plastic strain which characterizes just the fir…