Simplified Modeling Strategy Research Articles

Design and modelling strategy for cold-formed steel exoskeletons for the seismic-energy retrofit of reinforced concrete structures

Recent seismic events have highlighted the vulnerability of reinforced concrete (RC) buildings constructed before the enforcement of seismic design codes. This study is focused on a cold-formed steel exoskeletons, known as the Resisto 5.9 Tube system, used to enhance both seismic and thermal performance of existing structures. The main focus is the application of a simplified design and modelling strategy to elementary reinforced concrete structures with different heights. The design strategy is aimed to optimize the elements of Resisto 5.9 Tube according to the specific building under investigation. The modelling strategy is developed to reduce the computational effort when implementing the reinforcement system in structural software without negatively affecting the reliability of the results.

Rational Simplification of High Fidelity Wind Turbine Models Used for Mooring Analysis

This study investigates the use of simplified turbine modelling in analysis of a soft mooring system (horizontal plane periods > 250 s). Two simplified turbine models are developed, tested and compared to a high fidelity turbine model in a case study of the INO WINDMOOR 12 MW FOWT with a soft mooring system. The chosen simplified modelling strategies are a drag disc model, a de-coupled approach where the aerodynamic loads are pre-calculated in a fixed turbine simulation and a model with reduced degrees-of-freedom. Corrections to the pre-calculated force model is also developed and compared. The results show that the pre-calculated force approach gives better comparisons to the full model than the drag disc model, and that applying a controller correction to account for the wind turbine controller’s response to floater motions improves the predicted response.

Investigating the effect of the structural interactions due to floors and lintels on the lateral response of multi-storey Cross-Laminated Timber shear walls

The lateral behaviour of multi-storey Cross-Laminated Timber (CLT) structures is significantly influenced by the effects of the structural interactions between primary and secondary structural elements and their connections. In case of platform-type structures, in addition to the connections placed at the base of the walls, other structural components including the floor diaphragms and the lintels above the openings influence the lateral performances of the CLT shear walls. However, it is common practice in structural design to model multi-storey CLT shear walls by considering the wall base connections, while neglecting the effects of these structural interactions. This study investigates in detail the lateral behaviour of multi-storey CLT shear walls, comparing the results of simplified modelling strategy, typically adopted in practical design, and more advanced modelling strategies that take into account the effects of these structural interactions. Different shear wall configurations, including different geometries, number of storeys, and connection properties were analysed by means of linear elastic and nonlinear static analyses. The results of the numerical analyses highlighted significant differences between the lateral behaviour of multi-storey CLT shear walls modelled with these different modelling strategies and suggest that simplified modelling strategies may not always be reliable to describe the behaviour of multi-storey CLT shear walls.

Simplified micro-model for brick masonry walls under out-of-plane quasi-static and blast loadings

Attributed to the discontinuous configurations and nonhomogeneous mechanical properties of brick and mortar in masonry wall, the numerical reproduction of the structural responses and damage evolution of masonry walls under out-of-plane (OOP) loadings still remains a challenging work. Firstly, a 3D simplified micro-model of masonry wall was developed by utilizing the commercial finite element program ANSYS/LS-DYNA, the masonry wall was simplified as a combination of expanded brick units with a series of joints, in which the expanded brick units and joints are described by Riedel-Hiermaier-Thoma (RHT) model and cohesive contacts, respectively. Then, the corresponding parameters determination approaches for the cohesive contact and RHT model are proposed by comparing with the test on brick-mortar-brick assemblages and regulation, respectively. Furthermore, by comparing with four sets of OOP quasi-static and field explosive tests data, the prediction accuracy and efficiency of the simplified modeling strategy, material model and parameters are fully validated. Finally, based on the parametric study, it indicates that the blast resistance of walls is enhanced with increasing the compressive strength of brick and mortar, and arranging the tie bars, while significantly degraded with increasing the aspect and slenderness ratios of walls. This work could provide a helpful reference for the blast-resistant evaluation and design of brick masonry walls.

Influence of vehicular movement on the seismic response and fragility of highway bridge structures

Recognising the criticality of highway bridges for the socio-economic development of a nation, multiple researchers have endeavoured towards quantifying the seismic fragility of these key infrastructure elements. Given the present boom in urbanisation, however, there may also be an appreciable likelihood of vehicle presence on the highway bridge deck during an earthquake event. This study focuses on the impact assessment of vehicle-bridge-interaction (VBI) on the seismic fragility of highway bridges by explicitly accounting for vehicular movement atop the bridge deck during seismic shaking. Addressing existing drawbacks in literature that typically adopts a simplified modelling strategy and static vehicle placement, this paper considers different types of moving vehicles (modelled as mass-spring-dashpot system analogies) for VBI assessment through a novel algorithm. The proposed framework also accounts for uncertainties involved in the moving vehicle analysis, pertaining to vehicle characteristics and driver’s perception of the earthquake. The framework is demonstrated on representative multi-span continuous steel girder bridges located in Central and Southeastern United States. A comparative assessment of hysteretic response of bridge components and seismic fragility curves indicate a considerable influence of vehicular movement on bridge damage, signifying the importance of considering moving VBI effects for thorough seismic assessment of highway bridge structures.

Non‐linear dynamic analysis of buildings founded on piles: Simplified modelling strategies for soil‐foundation‐structure interaction

AbstractThe paper investigates the problem of Soil‐Foundation‐Structure Interaction (SFSI) for buildings supported on piles through the comparative analysis between the fixed base and the compliant base assumptions. The structure, a nine‐storey residential building (with or without infills), is modelled in non‐linear regime while the piled foundation is idealized by means of independent lumped parameters models, either linear or non‐linear. In this last case, the soil‐foundation system is replaced by an assembly of viscous‐dampers, fictitious masses and non‐linear springs modelled according to the classical Bouc‐Wen formulation, so as to account for the hysteretic behaviour of the foundation. A detailed calibration procedure for both linear and non‐linear foundation models is also presented and discussed. Two different natural soil deposits are considered, a pyroclastic deposit and a deep layer of lacustrine clay. The results undertaken in the context of a probabilistic analysis show that SFSI may lead to a significant reduction of the seismic demand in infilled buildings at low and intermediate earthquake intensity levels. Conversely, at higher intensity earthquakes the seismic demand is not affected by the non‐linear springs. It is shown that a proper modelling of radiation mechanism at foundation level is crucial for a reliable and sustainable prediction of SFSI effects.

A Simplified FE Modeling Strategy for the Drop Process Simulation Analysis of Light and Small Drone

The numerical accuracy of drop process simulation and collision response for drones is primarily determined by the finite element modeling method and simplified method of drone airframe structure. For light and small drones exhibiting diverse shapes and configurations, mixed materials and structures, deformation and complex destruction behaviors, the way of developing a reasonable and easily achieved high-precision simplified modeling method by ensuring the calculation accuracy and saving the calculation cost has aroused increasing concern in impact dynamics simulation. In the present study, the full-size modeling and simplified modeling methods that are specific to different components of a relatively popular light and small drone were analyzed in an LS-DYNA software environment. First, a full-size high-precision model of the drone was built, and the model accuracy was verified by performing the drop tests at the component level as well as the whole machine level. Subsequently, based on the full-size high-precision model, the property characteristics of the main components of the light and small drone and their common simplification methods were classified, a series of simplified modeling methods for different components were developed, several single simplified models and combined simplified models were built, and a method to assess the calculation error of the peak impact load in the simplified models was proposed. Lastly, by comparing and analyzing the calculation accuracy of various simplified models, the high-precision simplified modeling strategy was formulated, and the suggestions were proposed for the impact dynamics simulation of the light and small drone falling. Given the analysis of the calculation scale and solution time of the simplified model, the high-precision simplified modeling method developed here is capable of noticeably reducing the modeling difficulty, the solution scale and the calculation time while ensuring the calculation accuracy. Moreover, it shows promising applications in several fields (e.g., structure design, strength analysis and impact process simulation of drone).

Experimental and numerical evaluation of conduction welded thermoplastic composite joints

The capability of joining two thermoplastic composite parts by welding is a key technology to reduce the weight and cost of assembled parts and enables high volume manufacturing of future aeronautical structures made of thermoplastic composite materials. However, there is not much experimental understanding of the mechanisms involving welded joint failure, and the computational tools available for the simulation of thermoset composites have not yet been completely assessed for thermoplastic materials. In this work, a numerical and experimental evaluation is performed to investigate the strength and failure behavior of conduction welded thermoplastic composite joints. A welded single lap shear joint is designed, manufactured, tested and analyzed proposing two distinct modeling approaches. A simplified modeling strategy which only accounts for damage at the weld is compared to a high-fidelity model which can take into account the physical failure mechanisms at the lamina level. The high-fidelity modeling methodology is able to predict the experimental failure mode of the investigated welded joints with high accuracy and is used to gain new insights into the key-variables that influence the strength of thermoplastic welded joints. It is also found that the joint strength is highly influenced by the failure mechanisms not only of the welded interface but also of the surrounding plies.

A simplified non-linear modelling strategy to generate fragility curves for old masonry buildings

In the context of historical seismology, studying the behaviour of historic masonry buildings is of great importance, as they are witnesses of past events. While interesting methods can be found in the literature to assess the seismic vulnerability of masonry structures subject to strong earthquakes, the topic of moderate seismicity, as encountered in many European countries, is still to be investigated. The present work proposes a global methodology to build fragility curves for existing masonry buildings. An efficient computational method to address the non-linear response of masonry structures is presented. The method is based on the modal decomposition of the structural response. An equivalent non-linear single degree of freedom oscillator is identified for the main modes. The modelling strategy enables to carry out numerous computations with a low computational effort, allowing for a probabilistic approach. To build fragility curves, a damage indicator based on the frequency shift is chosen. To validate the proposed approach, the simplified model of a real masonry building is compared to a full non-linear time history analysis. The method is eventually illustrated by the derivation of fragility curves for industrial masonry buildings.

Numerical modeling of the seismic performance of Romanian timber-framed masonry walls

Traditional architecture with timber-framed masonry (TFM) system was used in many countries prone to seismic events due to its earthquake-resistant performance. In this context, Romanian TFM buildings were constructed by local builders applying non-engineered measures to reduce seismic vulnerability. However, the seismic safety assessment of these buildings still presents open issues due to material modeling, and in simulating the complex interaction between structural elements. Although the seismic response at building scale depends on a combination of factors such as geometry, boundary conditions, quality of construction, structural connections and interactions, it is significantly influenced by the in-plane behavior of TFM walls. The present paper aims to investigate the seismic performance of Romanian TFM walls by using a simplified equivalent frame model, in OpenSEES software, with linear elastic elements and nonlinear behavior lumped at the connections. Indeed each joint is modeled with nonlinear springs, one per degree of freedom, for which the parameters were initially calibrated based on representative experimental tests in literature. After this calibration, the resulting parameters were updated to approach the local and global responses from the experimental campaign performed at the Technical University of Civil Engineering of Bucharest in terms of initial stiffness, maximum base shear, and total dissipated energy. The simplified modeling strategy requires limited computational efforts and provides information about the role of each connection.

Operating at High TemperaturesContribution to the Magneto-Thermal Modeling of SRM Operating at High Temperatures

In this paper, we present a simplified magneto-thermal modeling strategy for switched reluctance electrical machines (SRM) operating at high temperatures. In addition to the magnetic non-linearity, the variations of the electromagnetic and thermal properties of materials with the temperature are taken also into account. The rapidity of the proposed approach makes it compatible with a CAD approach.

Data assimilation with multiple types of observation boreholes via the ensemble Kalman filter embedded within stochastic moment equations

Abstract. We employ an approach based on the ensemble Kalman filter coupled with stochastic moment equations (MEs-EnKF) of groundwater flow to explore the dependence of conductivity estimates on the type of available information about hydraulic heads in a three-dimensional randomly heterogeneous field where convergent flow driven by a pumping well takes place. To this end, we consider three types of observation devices corresponding to (i) multi-node monitoring wells equipped with packers (Type A) and (ii) partially (Type B) and (iii) fully (Type C) screened wells. We ground our analysis on a variety of synthetic test cases associated with various configurations of these observation wells. Moment equations are approximated at second order (in terms of the standard deviation of the natural logarithm, Y, of conductivity) and are solved by an efficient transient numerical scheme proposed in this study. The use of an inflation factor imposed to the observation error covariance matrix is also analyzed to assess the extent at which this can strengthen the ability of the MEs-EnKF to yield appropriate conductivity estimates in the presence of a simplified modeling strategy where flux exchanges between monitoring wells and aquifer are neglected. Our results show that (i) the configuration associated with Type A monitoring wells leads to conductivity estimates with the (overall) best quality, (ii) conductivity estimates anchored on information from Type B and C wells are of similar quality, (iii) inflation of the measurement-error covariance matrix can improve conductivity estimates when a simplified flow model is adopted, and (iv) when compared with the standard Monte Carlo-based EnKF method, the MEs-EnKF can efficiently and accurately estimate conductivity and head fields.

Seismic analysis of soil-structure interaction: Experimentation and modeling

This paper presents a simplified modelling strategy to simulate the soil-foundation-structure interaction under seismic loadings. The interaction of soil and structure is modeled by a macro-element with the coupling of geometric and material non-linearities. The model consists of 4 degrees of freedom in which the superstructure is lumped as a single degree of freedom (DOF) while the soil-foundation is modeled by 3 DOFs. The dynamic equilibrium equations are solved by a Newmark time integration scheme and implemented in Matlab. To verify the numerical model, an experimental investigation based on shaking table method has been conducted in the present study. Five series of earthquake motions with maximum acceleration increased from 0.1 m/s^2 to 1.4 m/s^2were applied and the results of time-dependent accelerations and displacements are extracted. Based on the result comparisons, it is found that the numerical results were well validated against the experimental results.

The Roof Bracing as Minimum Intervention for the Reduction of the Seismic Vulnerability of Historical Industrial Buildings: Analytical and Numerical Simplified Strategies for the Assessment of the Performances

ABSTRACT The paper deals with the reduction of the seismic vulnerability of historical masonry buildings characterized by a wide room, of significant height, provided by a multi-sloping timber roof lying on perimeter walls and, internally, on columns or pillars (e.g. industrial buildings). Typically, these structures are extremely vulnerable to earthquakes but a minimum intervention, consisting in the bracing of the timber roof through wooden-based sheathing panels, can improve the seismic performances providing an adequate restraint against the walls overturning and fostering the box-behaviour of the entire structure. The case study of an ancient industrial building is analyzed. A smart analytical design strategy for the dimensioning of the bracings and the evaluation of the resisting ground acceleration is developed. A simplified numerical modelling strategy for pushover analysis, based on the equivalent frame method for the masonry walls and on equivalent diagonal springs for the roof bracings, is also presented.

A simplified continuum damage mechanics based modeling strategy for cumulative fatigue damage assessment of metallic bolted joints

Fatigue damage and consequent failure account for the majority of the failure in metallic bolted joints of aerospace and mechanical engineering applications. In this paper, we present a cumulative fatigue damage evaluation approach for metallic bolted joints based on a combined continuum damage mechanics (CDM) theory and the critical plane approach. The analysis approach is applicable to both proportional and non-proportional multiaxial loading conditions. A cycle jumping based algorithm with a fixed damage evolution rate is adopted for efficient numerical approximation. To further increase the computational efficiency, a simplified modeling strategy is developed to avoid the expensive calculation of the full loading-unloading cyclic stress history. The proposed approach is established based on the assumption that a linear relation can be established between the minimum and maximum stress tensors in high-cycle fatigue analysis and is thus only dependent on the maximum stress states. A set of examples including a notched specimen and a metallic bolted joint with pre-tension are simulated to demonstrate the simplified approach.

Numerical Modeling of Traditional Masonry Walls Strengthened with Grout Injection

ABSTRACT The main purpose of this article is to experimentally and numerically study the improvements introduced by the grout injection strengthening technique for the structural rehabilitation of traditional unreinforced masonry (URM) walls. In this context, four damaged URM walls with four different types of lime mortars under shear-compression are strengthened using grout injection method. Injection materials (Grout) which have same contents with existing mortar types are applied to all cracks in damaged walls. Besides, for the numerical simulations, a simplified micro modeling strategy is preferred combining the mortar and the mortar-unit interface behavior and then an elasto-plastic damage (EPD) approach is adopted calibrating the parameters of Oliver’s damage model and the modified von-Mises yield criterion for the masonry constituents. Results show that the proposed approach can be useful to describe the behavior of mortar and mortar-unit interface in strengthened masonry structures with grout injection.

Experimental and numerical assessment of the seismic response of steel structures with clutched inerters

Supplemental rotational inertia devices provide an efficient means of suppressing ground-induced vibrations over a large range of structural periods. The beneficial effects of the inerter can be further enhanced by coupling it with a clutch system that prevents it from driving the structural response and ensures that its supplemental rotational inertia is only employed to resist the motion. In this paper, we examine the behaviour of single-degree-of-freedom and multi-degree-of-freedom structures equipped with twin inerter-clutch devices subjected to strong ground-motion. The influence of the clutch stiffness, gears play, viscous damping and dry friction, on the non-linear dynamics of the system are explored first, by analysing the stable periodic solutions of a structure with inerters under harmonic-sweeps. We demonstrate that, for the range of parameters typically expected in earthquake engineering practice, the influence of dry-friction and clutch damping are limited, although the clutch stiffness and gear play may need to be accounted for when large inertances or defective clutches are considered. Based on these findings, we propose a simplified numerical modelling strategy suitable for implementation in conventional Finite Element simulations. Small scale experiments on bare elastic structures as well as structures equipped with 3D-printed inerter and inerter-clutch twins are presented and employed for concept demonstration and for the validation of the numerical model proposed. Finally, a series of studies on detailed numerical models of multi-storey steel frames under idealized and real pulse-like ground-motions are used to demonstrate the vibration absorbing capabilities brought about by the twin inerter-clutch system and to highlight practical aspects related to their structural implementation.

In-plane deformability of RC floors: assessment of the main parameters and influence on dynamic behaviour

In-plane floor deformability is an important issue for the correct assessment of the behaviour of Reinforced Concrete (RC) structures subjected to seismic loads. Several studies have demonstrated that in-plane floor deformability is often not negligible in structures with RC walls as vertical resistant elements, since it mainly depends on the relative stiffness of floor and vertical elements. In this paper, approximately 700 simple buildings constructed with RC walls were simulated in finite element models considering both two-dimensional and one-dimensional modelling strategies. First, the reliability of the simplified modelling strategy was evaluated. Then, the simplified model was used to assess the effects of building shape and number of walls on the in-plane floor deformability. The differences between the behaviour of the buildings under the assumption of deformable and rigid floors were examined in terms of both floor displacements, based on static analyses, and the main vibration periods of the building, based on linear dynamic analyses. Finally, based on the collected numerical results, reliable regression curves for both the maximum displacements and the periods evaluated under the assumption of deformable and rigid floors were obtained as function of a parameter significant of floor and walls stiffness. The curves may provide a tool for evaluating the error related to an incorrect assumption about the in-plane floor deformability.

Shaping hybrids – Form finding of new material systems

Form-finding processes are an integral part of structural design. Because of their limitations, the classic approaches to finding a form – such as hanging models and the soap-film analogy – play only a minor role. The various possibilities of digital experimentation in the context of structural optimisation create new options for the designer generating forms, while enabling control over a wide variety of parameters. A complete mapping of the mechanical properties of a structure in a continuum mechanics model is possible but so are simplified modelling strategies which take into account only the most important properties of the structure, such as iteratively approximating to a solution via representations of kinematic states. Form finding is thus an extremely complex process, determined both by the freely selected parameters and by design decisions.

Insights Into the Bifunctional Aphidicolan-16-ß-ol Synthase Through Rapid Biomolecular Modeling Approaches

Diterpene synthases catalyze complex, multi-step C-C coupling reactions thereby converting the universal, aliphatic precursor geranylgeranyl diphosphate into diverse olefinic macrocylces that form the basis for the structural diversity of the diterpene natural product family. Since catalytically relevant crystal structures of diterpene synthases are scarce, homology based biomolecular modeling techniques offer an alternative route to study the enzyme's reaction mechanism. However, precise identification of catalytically relevant amino acids is challenging since these models require careful preparation and refinement techniques prior to substrate docking studies. Targeted amino acid substitutions in this protein class can initiate premature quenching of the carbocation centered reaction cascade. The structural characterization of those alternative cyclization products allows for elucidation of the cyclization reaction cascade and provides a new source for complex macrocyclic synthons. In this study, new insights into structure and function of the fungal, bifunctional Aphidicolan-16-ß-ol synthase were achieved using a simplified biomolecular modeling strategy. The applied refinement methodologies could rapidly generate a reliable protein-ligand complex, which provides for an accurate in silico identification of catalytically relevant amino acids. Guided by our modeling data, ACS mutations lead to the identification of the catalytically relevant ACS amino acid network I626, T657, Y658, A786, F789, and Y923. Moreover, the ACS amino acid substitutions Y658L and D661A resulted in a premature termination of the cyclization reaction cascade en-route from syn-copalyl diphosphate to Aphidicolan-16-ß-ol. Both ACS mutants generated the diterpene macrocycle syn-copalol and a minor, non-hydroxylated labdane related diterpene, respectively. Our biomolecular modeling and mutational studies suggest that the ACS substrate cyclization occurs in a spatially restricted location of the enzyme's active site and that the geranylgeranyl diphosphate derived pyrophosphate moiety remains in the ACS active site thereby directing the cyclization process. Our cumulative data confirm that amino acids constituting the G-loop of diterpene synthases are involved in the open to the closed, catalytically active enzyme conformation. This study demonstrates that a simple and rapid biomolecular modeling procedure can predict catalytically relevant amino acids. The approach reduces computational and experimental screening efforts for diterpene synthase structure-function analyses.