Distributed Plasticity Approach Research Articles

Nonlinear seismic response of mid-rise modular buildings subjected to near-field ground motions

In recent earthquakes, structures near seismic sources have suffered severe damage due to near-fault ground motions. When compared with ordinary ground motions, these ground motions create high demands on structures. The presence of a strong energy pulse has been observed in near-fault ground motions. This impulsive motion, propagating towards the site, will result in forward-directivity effects. This study is intended to assess the structural effects of mid-rise steel Modular Building Systems (MBSs) under the near-fault pulse-like and non-pulse-like records and to investigate design procedures that explicitly comprise near-fault effects. The main objective of this paper is the nonlinear seismic responses of MBSs to near-fault forward-directivity (FD) and non-forward-directivity (NFD) ground motions, as well as whether the equivalent pulse present in forward-directivity earthquake ground motions dominate the structural response. This paper discusses the key properties that can be used to characterize near-fault ground motions with forward-directivity effects and non-forward-directivity effects on the engineering demand parameters. For this purpose, using 72 pulse-like ground motions and 120 non-pulse-like ground motions, a Cloud analysis is conducted to obtain statistically significant results. Nonlinear time history analysis is performed using OpenSees based on distributed plasticity approach to develop a finite-element model of a 6-story mid-rise MBS. The results depict that near-field pulse-type ground motions generate larger demands to the MBS compared with the non-pulse ground motions. In addition, when correlated with simple intensity measures such as PGA, PGV, and spectral acceleration at the first mode period, the structural response to forward-directivity ground motions exhibits a higher dispersion than the structural response to non-forward-directivity ground motions. The representative equivalent pulses of the considered forward-directivity ground motions were decomposed using the continuous wavelet transform method to explore their effects on the MBS response. Finally, the influence of the pulse parameters, including period and amplitude of the forward-directivity, are ascertained.

Finite element model for advanced analysis of plane steel frames with hinged end conditions including von Mises criterion

Traditionally, the design of steel structures is carried out in two steps: first, the structural analysis is performed, and then the cross-sections and structural members are checked individually. In contrast, in the advanced analysis, the effects related to global (P-Δ) and local (P-δ) instabilities and to the degradation of material stiffness are incorporated; therefore, there is no need to verify the resistance capacity of the structural members separately, which allows a better use of the load capacity of the structural system. Generally, research developed in this area of study is based on the classical Euler-Bernoulli theory; however, in the case of short elements, an analysis that includes the shear effects and the interaction between normal and shear stresses on cross-section yielding becomes necessary. Thus, this work aims to study the behavior of plane steel frames considering the influence of shear deformations by using advanced analysis. A geometrically exact formulation for analysis of rigid-hinged and hinged-rigid elements is presented. The proposed numerical methodology is implemented in finite element software and takes into account Timoshenko’s kinematic hypothesis, the distributed plasticity approach, residual stresses, and second-order effects. To assess the plastification state of the structural elements, the von Mises yield criterion is applied. From numerical examples available in the literature, the efficiency of the software in predicting the nonlinear behavior of steel frames is assessed. It is concluded that for short beams, the adoption of the von Mises criterion during the analysis leads to lower load capacities, compared to the results obtained considering only the normal stresses in the evaluation of the plastification state of the cross-sections.

Distributed plasticity approach for nonlinear analysis of nuclear power plant equipment: Experimental and numerical studies

Numerical modeling for the safety-related equipment used in a nuclear power plant (i.e., cabinet facilities) plays an essential role in seismic risk assessment. A full finite element model is often time-consuming for nonlinear time history analysis due to its computational modeling complexity. Thus, this study aims to generate a simplified model that can capture the nonlinear behavior of the electrical cabinet. Accordingly, the distributed plasticity approach was utilized to examine the stiffness-degradation effect caused by the local buckling of the structure. The inherent dynamic characteristics of the numerical model were validated against the experimental test. The outcomes indicate that the proposed model can adequately represent the significant behavior of the structure, and it is preferred in practice to perform the nonlinear analysis of the cabinet.Further investigations were carried out to evaluate the seismic behavior of the cabinet under the influence of the constitutive law of material models. Three available models in OpenSees (i.e., linear, bilinear, and Giuffre-Menegotto-Pinto (GMP) model) were considered to provide an enhanced understating of the seismic responses of the cabinet. It was found that the material nonlinearity, which is the function of its smoothness, is the most effective parameter for the structural analysis of the cabinet. Also, it showed that implementing nonlinear models reduces the seismic response of the cabinet considerably in comparison with the linear model.

Distributed plasticity approach for the nonlinear structural assessment of offshore wind turbine

This study provides an insight of the nonlinear behavior of the Offshore Wind Turbine (OWT) structure using the distributed plasticity approach. The fiber section beam-column element is applied to construct the finite element model. The accuracy of the proposed model is verified using linear analysis via the comparison of the dynamic characteristics. For collapse risk assessment of OWT, the nonlinear effects considering the earthquake Incident Angle (IA) have been evaluated first. Then, the Incremental Dynamic Analysis (IDA) has been executed using a set of 20 near-fault records. Lastly, fragility curves are developed to evaluate the vulnerability of structures for different limit states. Attained results justify the accuracy of the proposed approach for the structural response against the ground motions and other environmental loads. It indicates that effects of static wind and wave loads along with the earthquake loads should be considered during the risk assessment of the OWT structure.

A Distributed Plasticity Approach for Steel Frames Analysis Including Strain Hardening Effects

This paper focuses on the creation and numerical application of physically nonlinear plane steel frames analysis problems. The frames are analysed using finite elements with axial and bending deformations taken into account. Two nonlinear physical models are used and compared – linear hardening and ideal elastic-plastic. In the first model, distributions of plastic deformations along the elements and across the sections are taken into account. The proposed method allows for an exact determination of the stress-strain state of a rectangular section subjected to an arbitrary combination of bending moment and axial force. Development of plastic deformations in time and distribution along the length of elements are determined by dividing the structure (and loading) into the parts (increments) and determining the reduced modulus of elasticity for every part. The plastic hinge concept is used for the analysis based on the ideal elastic-plastic model. The created calculation algorithms have been fully implemented in a computer program. The numerical results of the two problems are presented in detail. Besides the stress-strain analysis, the described examples demonstrate how the accuracy of the results depends on the number of finite elements, on the number of load increments and on the physical material model. COMSOL finite element analysis software was used to compare the presented 1D FEM methodology to the 3D FEM mesh model analysis.

Influence of repairable bolted dissipative beam splices (structural fuses) on reducing the seismic vulnerability of steel-concrete composite frames

After a strong earthquake, repair work of conventional steel-concrete composite buildings can be very expensive, and very often, impossible due to practical problems. Within the EU-funded research project FUSEIS, a new steel-concrete composite frame type has been developed, as a cost-effective and robust alternative to conventional earthquake resistant structures. In this new frame type, damage concentrates mainly in the bolted dissipative beam splices acting as “structural fuses”, which can be easily and inexpensively replaced after strong seismic events. After the replacement, the building can be restored to its original form. This paper studies a benchmark building frame with and without bolted dissipative beam splices. The performance of both innovative and conventional structures has been quantified in terms of energy dissipation, floor displacements and inter-story drifts, as a result of nonlinear transient dynamic analysis. Different than similar studies in the literature, the numerical models explicitly consider the presence of reinforced concrete slab by means of fiber-based distributed plasticity approach. They have been calibrated according to the experiments, both provided in the literature and performed in the FUSEIS research project. The models allowed the quantification of the energy dissipated by each component of a steel-concrete composite frame (structural fuses, steel elements, concrete slab and steel reinforcement), which gave an insight on redistribution of dissipated energy in the case of adopting the structural fuses with respect to the traditional steel-concrete composite buildings. Based on the results of the numerical analysis, the reparability aspect has been discussed.

Validation of Fiber-Based Distributed Plasticity Approach for Steel Bracing Models

Nonlinear analysis approach is not anymore limited only to research purposes, but becoming more popular as a tool that can be used during design, thanks to the increased efficiency of computer software and hardware. An accurately calibrated numerical model may simulate the behaviour of buildings in a quite realistic way, which helps designers understand better the performance of their structures. However, the feasibility of the nonlinear analysis approach is limited by the complexity of the numerical model, and the aim of any researcher or engineer is to obtain the most useful information in a reasonable amount of time. This study focuses on the validation of a simplified numerical modelling approach to simulate the nonlinear behaviour of steel bracings. The paper presents a comparison between two different modelling approaches; a refined finite element model using volumetric elements, and fiber-based model using beam elements with distributed plasticity. The numerical models calibrated with the experimental result from existing literature, reproduce the behaviour of cold formed square, and hot rolled open section steel elements under inelastic cyclic loading. The hysteresis loops obtained from two models show that the accuracy obtained by simpler fiber-element formulation is quite close to the more refined volumetric model. Finally, in order to assess the accuracy of the fiber-based modelling approach to estimate the nonlinear cyclic response of full-scale braced frame configurations, two real scale frames are analysed, and the results are compared with the results of the experiments performed on the test frames. In terms of computation time and accuracy, distributed plasticity model is much more efficient, and can be a good option to perform nonlinear analysis of multi-level buildings, which would be quite cumbersome with volumetric modelling approach. This study has been realized thanks to the research fund received from European commission with the contract MEAKADO RFSR-CT-2013-00022.

Seismic behavior of RC structures with absence of floor slab constraints and large mass turbine as a non-conventional TMD: a case study

This paper presents a case study on the influence of absence of floor slab constraints and large mass turbine as a non-conventional tuned mass damper (TMD) on the seismic behavior of the structure and members. The investigated structural system is a reinforced concrete (RC) shear wall-frame power plant structure with large slab openings and a large mass turbine. In RC structures, the existence of floor slabs can usually provide strong constraints on beams so as to greatly increase their bearing capacity. However, due to some special functional demands, large area of slabs may have to be removed so that some floor beams will lose the constraints provided by slabs. In such cases, beams could be subjected to complex internal forces and develop unexpected failure modes under earthquake actions. Nonlinear time history analyses are conducted by using the self-developed program COMPONA-MARC Version 1.0. The numerical model employs fiber beam-column elements with distributed plasticity approach which can elaborately simulate the complex seismic behavior of structural members without slab constraints including the significant transverse vibration damage mechanism. For the seismic effectiveness of the turbine as a TMD with large mass ratio, the optimized parameters are discussed and verified by extensive numerical examples under a wide selection of ground acceleration time histories. The acceleration responses of the turbine are analyzed and found to satisfy the corresponding requirements. The dynamic interaction between the structure and turbine is evaluated and the effects of mass ratio and multiple supporting springs on the dynamic response of the turbine are investigated. It is found that the acceleration response of the turbine modeled with multiple supporting springs is evidently larger than that modeled with a single degree-of-freedom system, and the floor response spectrum decreases significantly with the increase of the mass ratio.

Distributed plasticity approach for time-history analysis of steel frames including nonlinear connections

This paper presents a displacement-based finite element procedure for second-order spread-of-plasticity analysis of plane steel frames with nonlinear beam-to-column connections under dynamic and seismic loadings. A partially strain-hardening elastic–plastic beam-column element, which directly takes into account geometric nonlinearity, gradual yielding of material, and flexibility of nonlinear connections, is proposed. Three major sources of damping are considered at the same time. They are structural viscous damping, hysteretic damping due to inelastic material, and hysteretic damping due to nonlinear connections. A nonlinear solution procedure based on the combination of the Hilber–Hughes–Taylor method and the well-known Newton–Raphson equilibrium iterative algorithm is proposed for solving differential equations of motion. The dynamic behavior predicted by the proposed program compares well with those given by the commercial finite element software ABAQUS and previous studies. Coupling effects of three primary sources of nonlinearity, the bowing effect, geometric imperfections, and residual stress are investigated and discussed in this paper.