Simulation Of Structural Response Research Articles

Long-term solutions of calibrated and generalised Macdonald’s model for pedestrian-induced lateral forces

The inverted pendulum pedestrian model (IPM) for walking on laterally-oscillating structures, originally proposed by Macdonald, has been recently calibrated based on data from pedestrians walking on a laterally-oscillating instrumented treadmill. It was then generalised to be suitable for the application in a predictive manner, i.e. in simulations of lateral structural response for any population of pedestrians. The generalised IPM captures the fundamental pedestrian-structure interaction mechanism and pedestrian-generated lateral forces onto a structure, including the self-excited forces which are critical from the point of view of structural stability. However, since the closed-form solutions of the generalised IPM are currently unavailable, its application requires numerical integration. To address this shortcoming, closed form solutions for the long-term average lateral self-excited forces are derived in this study based on the framework introduced by McRobie. A parametric study is conducted revealing complex interdependencies between pedestrian and bridge behaviour and their influence on the self-excited forces. The presented results are related to the measurements from full-scale bridges and laboratory investigations.

Toward multivariate fragility functions for seismic damage and loss estimation of high‐rise buildings

AbstractData‐driven models for seismic damage and loss assessment of buildings have become more common in recent years due to the availability of large repositories of recorded and synthetic ground motions coupled with structural response simulation data. This paper explores the benefits of using bivariate and multivariate fragility functions to estimate earthquake‐induced damage and economic loss in high‐rise buildings. The dataset used in this study encompasses 15,000 simulations of modern high‐rise reinforced concrete shear wall buildings ranging from eight to 24 stories which are subjected to ground motion records at five different intensity levels. The proposed functions are conditioned on average spectral accelerations and ground motion significant duration. The results indicate that bivariate fragility functions improve damage state prediction success (Brier score) by 16%, and multivariate fragility functions by 24% relative to conventional univariate functions (standard of practice). To develop multivariate functions, nominal and ordinal probit regression models are fit to the dataset. While both models yield satisfactory predictive performance, ordinal functions can lead to a 15% reduction in misclassified collapse instances, that is, the minority class. Univariate functions tend to overestimate seismic losses at lower intensity levels while underestimating them at higher intensities. These loss estimates are significantly improved when bivariate or multivariate building fragility functions are used. Given the increase in the use of physics‐based ground motion simulations and/or multi‐variate ground motion models, from which multiple intensity measures can be extracted, a shift toward a more complex representation of fragility functions, for example, multivariate curves, is necessary and inevitable. The proposed functions are used to evaluate the performance of a portfolio of modern high‐rise reinforced concrete shear wall buildings at four sites across the Seattle, Washington metropolitan area under a potential magnitude‐9 Cascadia subduction zone earthquake scenario. The results indicate that the proposed functions can be beneficial in enhancing damage state predictions and loss estimates at a regional scale.

Quantification of Equivalent Strut Modeling Uncertainty and Its Effects on the Seismic Performance of Masonry Infilled Reinforced Concrete Frames

ABSTRACT Quantifying aleatory and epistemic uncertainty in nonlinear structural response simulation is key to robust performance-based seismic assessments. This paper focuses on the modeling parameters that are used to describe the nonlinear force-deformation response of the equivalent infill struts used in models of reinforced concrete frames with infills. The variability in several parameters is characterized by developing empirical and theoretical multivariate probability distributions based on the deduced-to-predicted ratios derived using data from 113 physical experiments. The effect of the uncertainty in the infill strut modeling parameters on maximum story drift ratios and associated limit state fragility functions is investigated for a 3-story reinforced concrete frame building with infills. Multiple stripe analysis is performed using hazard-consistent ground motions. Relative to when only record-to-record variability is considered, modeling parameter uncertainty has a non-negligible effect on the dispersion of the maximum story drift ratios, and affects both the median and dispersion of the limit state fragilities.

Uncertainty quantification and probabilistic performance-based assessment of nonlinear behavior of moment resisting frames under design and extreme wind loads

Recent advancements in performance-based assessment and design of buildings subjected to wind loads call for the incorporation of uncertainties in the simulation of both loading and structural response. Additionally, they require a better understanding of nonlinear wind-induced response of buildings. Probabilistic analysis approaches are commonly used for the incorporation of uncertainties in performance-based assessment of building response. These approaches, however, focus more on the wind loading side as opposed to incorporating detailed nonlinear models for the structures. This study leverages SimCenter's newly developed tool WE-UQ to integrate a detailed nonlinear structural model of a 20-story 2D building frame into larger probabilistic simulations. The detailed structural model is created in finite element software OpenSEES and can simulate complex behavior such as stiffness and strength degradation and provide reasonably accurate predictions of yield and collapse. Simulation results are then utilized for probabilistic performance-based assessment of the building frame using the new guidelines proposed by the ASCE pre-standard for performance-based wind design. Additionally, performance of the frame under higher wind speeds that would lead to yielding or collapse of the building is also assessed. The results obtained from the probabilistic simulations are compared with pure deterministic simulation outcomes to investigate the effects and necessity of adding uncertainties into the response prediction of buildings subjected to wind loads.

Development and Application of a Platform for Multidimensional Urban Earthquake Impact Simulation

Earthquakes can be devastating to cities. Therefore, accurate and efficient simulation of the potential seismic damage to buildings has become an indispensable part of worldwide efforts to mitigate earthquake hazards. Precise simulation results can highlight potential seismic damage and serve as a reference in urban development and for planning post-earthquake rescue operations. In urban areas, simulation of the structural dynamic response during an earthquake is key for planning an appropriate emergency response. Multidimensional visualization of the effects of earthquakes is a popular technique in current earthquake simulation research. In the present study, a dynamic multidimensional simulation method was developed for analyzing the impact of an earthquake on buildings. This method involved conducting three-dimensional (3D) dynamic analysis of data from a seismic capacity database. Polygonal models and seismic capacity data were used in a high-performance computing process to calculate the seismic response of each building in an urban environment. On the basis of the calculations, a platform was developed for multidimensional urban earthquake impact simulation (MDUES). The developed MDUES platform enables analysis of the impact of long-period earthquakes, simulation of the 3D seismic responses of buildings, and visualization of the disaster risk and earthquake impact in a specified area. In summary, simulation of structural seismic responses in an urban setting necessitates a careful examination of the characteristics of ground and building motion, and the results of this simulation can provide a crucial reference for city planning, post-earthquake rescue operations, and seismic damage assessments.

Large deformations and failure of clamped circular steel plates under uniform impulsive loads using various phenomenological damage models

Paper presents numerical models based on a detailed characterization of various uncoupled damage models in a finite element analysis (FEA) setup to assess their results and comparative performance in simulation of structural response and failure of clamped circular plates subjected to a wide range of uniform impulse loading. The significance of numerical modeling of ductile fracture in simulating the various observed modes of failure in steel structures under intense blast loading has also been presented along with an overview of various phenomenological damage models in the published domain. Numerical schemes presented in the paper are founded on a detailed and well-defined material model using mechanical uniaxial tension tests (UTT) and its inverse FEA simulations. Elaborate UTT experiments have been conducted to establish the mechanical strength and ductile fracture characteristics of a particular grade of mild steel for its usage in the calibration of the discussed damage models. Relative performance of various simple as well as complex phenomenological damage models in simulating/ predicting the experimentally observed structural response and different failure modes of fully clamped circular steel plates over a broad range of uniform impulsive loads has also been presented. Published results based on extensive experimental works by various authors on response of thin walled clamped circular plates under transversely applied uniform air blast loads, manifesting in plastic deformations of large magnitude, inception of thinning and tearing under various ductile fracture modes, have been utilized in the validation of the numerical model and procedure. Based on the evaluated performance of the discussed numerical models, a hybrid damage model adopted within the FEA setup has been proposed, demonstrating a very good correlation of numerical predictions with experiments. The validated FEA setup incorporating the calibrated hybrid damage model has further been gainfully utilized towards critical insights in the evolution of plastic deformations, progression of damage and their correlation with experimentally observed failure modes over a wide range of loading, involving varying stress states and tri-axiality.

Seismic Response Meta-model of High-Rise Fame Structure Based on Time-Delay Neural Network

To make structural seismic response simulation more efficient, a meta-model method which is based on the time delay neural network is proposed. And an accuracy evaluation method that considers the drift peak amplitudes and maximum amplitudes in each intensity as performance parameters is also proposed, this method can make a balance between accuracy and training time. Exampled by 4 frame structures which are all 20 stories, and accuracy evaluating results show that more than 80% of samples, which include training models and testing models of these performance parameters can be explained by meta models' fitting. The average time to simulate by this method is 0.08s and faster than the finite element method which spends 24 min averagely.

Optimization and performance assessment of tuned mass damper inerter systems for control of buildings subjected to pulse-like ground motions

Optimal tuned mass damper inerter (TMDI) systems in controlling displacement demands on structures affected by pulse-like near fault ground motions is presented. Simplified mathematical models of three buildings and many recorded near-fault ground motions, all containing a dominant velocity pulse, are used to make this investigation valid for a wide range of structural vibration periods and ground motion frequency content. For each of these ground motions, optimal parameters of TMDIs are estimated by minimizing structural displacement demand. Time history analysis is used for structural response simulation and Genetic Algorithm is used for minimizing the structural displacement demands. The performance or lack of it of the TMDIs are investigated and explained in relation to important properties of ground motions such as the frequency and oscillatory nature of the dominant pulse contained in the ground motion. The results indicate that properly optimized TMDIs can effectively control structural response under certain circumstances. When the structure resonates with the ground motion pulse, the less impulsive the ground motion, the more effective is the control scheme. An interesting finding is that TMDIs can be very effective in controlling response of structures which are not resonating with the pulse but nevertheless experience high demands due to other frequency components of near-fault ground motions. It is found that TMDI solutions obtained by minimizing the H2 norm of the elastic transfer function are not optimal when the fundamental period of vibration of the structure is lower than the period of the dominant pulse carried by the ground motion. Such solutions also result in unnecessarily high damping in the TMDI dashpot, without any benefit in controlling structural response.

Simulation of Shape and Structure Response of Nonspherical Magnetosensitive Vesicles Subjected to Magnetic Fields

Molecular dynamics simulation is performed to study coupled magnetic, structural, and mechanical response of magnetosensitive vesicles to quasistatic on/off switching of external magnetic field. The vesicle membrane filled with magnetic nanoparticles is modeled in the coarse-grained bead-spring representation. In detail it is shown, how discocyte- and stomatocyte-like vesicles respond to uniform magnetic field. Notably, having undergone an on/off switching cycle, a vesicle does not always restore in full its shape.

Estimating collapse risk and reliability of concrete moment frame structure using response surface method and hybrid of artificial neural network with particle swarm optimization algorithm

Structural collapse performance assessment has been at the center of many researchers’ interest due to complications of this phenomenon and uncertainties involved in modeling the simulation of the structural collapse response. This research aims to predict the structural collapse responses including mean collapse capacity, collapse standard deviation, and collapse drift by considering modeling uncertainties and then estimating collapse fragility curves, collapse risk, and reliability using Response Surface Method (RSM) and Artificial Neural Network (ANN). Modeling uncertainties for evaluating collapse responses are the parameters of the modified Ibarra-Krawinkler moment-rotation curve. Moreover, to analyze the structural uncertainty, the correlation between the model parameters in one component and between two structural components was considered. The Latin Hypercube Sampling (LHS) method and Cholesky decomposition were used to produce independent and dependent random variables, respectively. To predict the collapse responses of the structure, taking into account the uncertainties, as the number of uncertainties increases, the number of simulations for the uncertainties also increases, leading to a significant increase in the computational effort to estimate the structural responses, in the presence of a limited number of samples for uncertainties, a hybrid of ANN with PSO algorithm was used to reduce the computational effort in order to estimate the collapse fragility curves, collapse risk, and structural reliability. The results show that structural collapse responses can be predicted with appropriate accuracy by producing a limited number of samples for uncertainties and using an ANN-PSO algorithm.

Flow-Induced Vibration Analysis of Topside Piping at High Pressure

Flow-induced vibration (FIV) from high-velocity multiphase flow is a common source of vibration concern in process piping, potentially leading to fatigue failures and hydrocarbon leaks. A combination of computational fluid dynamics (CFD) and finite element (FE) modeling offers a potentially powerful tool for assessing and diagnosing multi-phase FIV problems in hydrocarbon-production piping systems. Global energy consultancy Xodus Group performed FIV studies on an Equinor-operated topside production system, carrying multiphase flow at high-pressure (approximately 69 bara) conditions, where significant vibration was measured. The study assessed different vibration-simulation methodologies, combining FE analysis with forcing functions based on both correlations and CFD simulations. The aim was to gain a better understanding of the accuracy and limitations of calculation methods typically used to assess fatigue. Calculating Multiphase FIV in Operational Pipework While CFD FIV modeling methods have been well validated against low-pressure water-airflow under laboratory conditions (Emmerson et al. 2016a and 2016b), little has been published to show how well these techniques perform for operational hydrocarbon-production systems. As these systems usually operate at higher pressures with complex, live hydrocarbon fluids and water, the process conditions are often not well defined. They typically incorporate sev-eral features that could complicate the vibration-generation mechanisms such as long upstream pipelines, chokes, and convoluted combinations of pipe bends with complex support arrangements. As part of the development of a new Energy Institute guidance document for subsea pipework, the project with Equinor was instigated following a joint industry project (JIP) established by Xodus, in collaboration with TNO and funded by six major operators, to improve techniques for estimating forcing functions in liquid-gas flows. Vibration measurements were taken at various locations on a section of piping carrying multiphase flow at high-pressure conditions (approximately 69 bara) (Fig. 1). The forces were applied in harmonic, transient, and fluid structural interaction (FSI) simulations (directly coupled FE and CFD). The topside piping arrangement consists of 16-in. schedule-100 piping, with a tee at the top of a riser section followed by six 90° and four 45° 1.5 R/D elbows and is reasonably well supported (as shown in Fig. 1). The measurements provided the vibration velocity of the piping structure, and frequency spectra analysis was performed for comparison with the structural-response simulations. The main locations of interest are V4 and V5 as the measured vibration was the highest here. The peak vibration velocity at V4 is 4.7 mm/s and this occurs at 5.1 Hz in the EW-Y direction (Fig. 2), while at V5 the peak is 6.4 mm/s at 5.2 Hz.

Numerical simulation of structural response during propeller-rudder interaction

The propeller wake can cause vibrations on the rudder surface, which worsen the noise and reliability. The vibration monitoring of the rudder operating in the propeller wake with fluid-structure interaction (FSI) method is still challenging. In the present study, the structural response during propeller-rudder interaction is investigated using detached eddy simulation. Three-dimensional distributions of loads, stresses, and deformations are discussed. The leading and trailing edges exhibit the strongest deformations in opposite directions, which are S-shaped. The strongest lateral deformation occurs between the tip vortex and hub vortex regions. In the tip vortex region, the dominant lateral vibrations fluctuate at the blade passing frequency (BPF) and shaft frequency (SF). However, the 75 Hz-fluctuation becomes significant at the trailing edge of the rudder. In the hub vortex region, the lateral deformation fluctuates mainly at 75 Hz except the area near the leading edge. There are weak vibrations occurring at the natural frequencies of the rudder when the natural frequencies of the rudder are much higher than the SF and BPF. However, the plate in the propeller suffers intense vibrations at the frequencies near the natural frequencies, where the natural frequencies of the plate are close to SF and BPF.

Structural response and wall thickness design of pulse detonation combustor

This paper deals with the structural response and wall thickness design of pulse detonation combustor. The pulse detonation combustor is a chamber with cylindrical shell structure, which is loaded with internal moving detonation pressure and thermal load. Much higher strain and stress can be excited under moving pressure load than static load. How to choose the attenuation coefficient during detonation pressure were discussed. The results of structural response simulation based on finite element method were compared with analytical result in the literature. The multi-cycle detonation pressure load and thermal load were measured on a pulse detonation engine principle prototype initialed through deflagration-to-detonation transition for the first time. The structural response characteristics of the detonation chamber were studied based on the measured load under different working frequencies. A series of comparison between numerical simulation and experimental measurement were carried out. The wall thickness of the chamber was designed based on the fatigue load spectrum under real detonation load and the chamber’s target fatigue life. Special attention was paid to the mutual influence between the dynamic amplification factor and the wall thickness.

Repowering Steel Tubular Wind Turbine Towers Enhancing them by Internal Stiffening Rings

This paper presents a robust repowering approach to the structural response of tubular steel wind turbine towers enhanced by internal stiffening rings. First, a structural response simulation model was validated by comparison with the existing experimental data. This was then followed with a mesh density sensitivity analysis to obtain the optimum element size. When the outdated wind turbine system needs to be upgraded, the wall thickness, the mid-section width-to-thickness ratio and the spacing of the stiffening rings of wind turbine tower were considered as the critical design variables for repowering. The efficiency repowering range of these design variables of wind turbine towers of various heights between 50 and 250 m can be provided through the numerical analysis. Finally, the results of efficiency repowering range of design variables can be used to propose a new optimum design of the wind turbine system when repowering a wind farm.

Simulation of fire and structural response in the Brenner Base Tunnel by means of a combined approach: A case study

We present and discuss, as a case study, the results of the fire safety analysis of the Brenner Base Tunnel structures. In particular we investigate the behavior of the main cross section of the tunnel using a new coupling strategy between a structural-thermal code based on Multiphase Porous Media Mechanics – MPMM (also called COMES-HTC) and a CFD code (the Fire Dynamics Simulator – FDS). This allows us to define fire loads based on realistic fire scenarios rather than on the classical temperature-time profiles used in engineering practice. Such an advanced analysis is desirable for an infrastructure like the BBT which is one of the most important engineering works under construction in Europe in the field of civil engineering from economic, social and technical point of view. This first set of results shows that the behavior of the “tunnel system” (i.e. fire scenario evolution + structure response) is captured in a much more accurate way, despite of an increased complexity in the analysis.

Numerical simulation of plastic deformation and mechanical response of strip rolled aluminium alloys

During the optimal design and simulation of machining or forming processes, detailed simulation of structural response is typically required for use in Finite Element Analysis (FEA). In this study, the bulk temperature and rate dependent resistance to deformation of strip formed aluminium alloys is modelled using the Mechanical Threshold Stress model. The model is characterised to AA5182 alloy data and used in the FEA simulation of a strip rolling process. The effects of element choice, dynamic or quasi-static simulations and the use of particular modelling algorithms on the computational cost and overall accuracy associated with each simulation have to be considered. Given the correctly implemented material tangent, an implicit analysis is illustrated to allow larger stable time-steps. Dynamic and quasi-static solutions are very similar for the simulated process meaning inertia effects are negligible. It is further demonstrated that great care be given to the maximum allowable time step size in order to capture the expected interaction between temporal and spatial discretisation in a fully Lagrangian FEA simulation.

Numerical simulation of blast responses of ultra-high performance fibre reinforced concrete panels with strain-rate effect

Ultra-high performance fibre reinforced concrete (UHPFRC) is a promising construction material for protective structures due to its superior material characteristics. In this study, a finite element model is developed for the simulation of structural responses of UHPFRC panels subjected to blast loads. Based on the available experimental data, the procedures for the material model calibration are presented. The effect of strain rate on the dynamic material properties is reviewed, and the formula of dynamic increase factor is selected and proposed based on the steel fibre dosage and matrix strength. The developed finite element model is validated by comparing the numerical predictions with the test results from literature. In addition, a parametric study is carried out to investigate the effects of steel reinforcement ratios and the blast scenarios on the resistance of UHPFRC panels, and the advantages of using UHPFRC in protective structures are demonstrated by the comparison against high strength reinforced concrete panels.

Numerical simulation of nonlinear structural responses of an arch dam to an underwater explosion

Abstract This paper is a preliminary attempt to examine nonlinear structural responses of an arch dam to an underwater explosion (UNDEX) shock loading based on numerical simulation. The numerical simulation is based upon the explicit dynamics finite element program ABAQUS/Explicit. Both the dam-reservoir interaction and the contraction-joint non-linearity are considered. Our research has underlined the importance of the shear keys to the integrity of the arch dam. Failures of the shear keys make each monolith more independent and thus the dam structure as a whole more flexible. Two major failure modes of the arch dam have been identified: (a) a break-off failure of the monolith closest to the explosive source, and (b) tensile cracking of the dam base concrete. The presented simulation procedure based upon ABAQUS/Explicit is time-efficient and relatively undemanding owing to its cut-off computational strategy. We believe that it is more suitable for a large-scale three-dimensional UNDEX simulation involving an arch dam than the full-process simulation procedure.

A multi-physics methodology for the simulation of reactive flow and elastoplastic structural response

We propose a numerical methodology for the numerical simulation of distinct, interacting physical processes described by a combination of compressible, inert and reactive forms of the Euler equations, multiphase equations and elastoplastic equations. These systems of equations are usually solved by coupling finite element and CFD models. Here we solve them simultaneously, by recasting all the equations in the same, hyperbolic form and solving them on the same grid with the same finite-volume numerical schemes. The proposed compressible, multiphase, hydrodynamic formulation can employ a hierarchy of five reactive and non-reactive flow models, which allows simple to more involved applications to be directly described by the appropriate selection. The communication between the hydrodynamic and elastoplastic systems is facilitated by means of mixed-material Riemann solvers at the boundaries of the systems, which represent physical material boundaries. To this end we derive approximate mixed Riemann solvers for each pair of the above models based on characteristic equations. The components for reactive flow and elastoplastic solid modelling are validated separately before presenting validation for the full, coupled systems. Multi-dimensional use cases demonstrate the suitability of the reactive flow-solid interaction methodology in the context of impact-driven initiation of reactive flow and structural response due to violent reaction in automotive (e.g. car crash) or defence (e.g. explosive reactive armour) applications. Several types of explosives (C4, Detasheet, nitromethane, gaseous fuel) in gaseous, liquid and solid state are considered.

A damage model for structures with degrading response

SummaryThe paper presents a hysteretic damage model for the response simulation of structural components with strength and stiffness deterioration under cyclic loading. The model is based on 1D continuum damage mechanics and relates any 2 work‐conjugate response variables such as force‐displacement, moment‐rotation, or stress‐strain. The strength and stiffness deterioration is described by a continuous damage variable. The formulation uses a criterion based on the hysteretic energy and the maximum or minimum deformation for damage initiation with a cumulative probability distribution function for the damage evolution. A series of structural component response simulations showcase the ability of the model to describe different types of hysteretic behavior. The relation of the model's damage variable to the Park‐Ang damage index is also discussed. Because of its consistent and numerically robust formulation, the model is suitable for the large‐scale seismic response simulation of structural systems with strength and stiffness deterioration.