Prediction Of Structural Response Research Articles

Prediction of the structural response of the femoral shaft under dynamic loading using subject-specific finite element models

The goal of this study was to predict the structural response of the femoral shaft under dynamic loading conditions using subject-specific finite element (SS-FE) models and to evaluate the prediction accuracy of the models in relation to the model complexity. In total, SS-FE models of 31 femur specimens were developed. Using those models, dynamic three-point bending and combined loading tests (bending with four different levels of axial compression) of bare femurs were simulated, and the prediction capabilities of five different levels of model complexity were evaluated based on the impact force time histories: baseline, mass-based scaled, structure-based scaled, geometric SS-FE, and heterogenized SS-FE models. Among the five levels of model complexity, the geometric SS-FE and the heterogenized SS-FE models showed statistically significant improvement on response prediction capability compared to the other model formulations whereas the difference between two SS-FE models was negligible. This result indicated the geometric SS-FE models, containing detailed geometric information from CT images with homogeneous linear isotropic elastic material properties, would be an optimal model complexity for prediction of structural response of the femoral shafts under the dynamic loading conditions. The average and the standard deviation of the RMS errors of the geometric SS-FE models for all the 31 cases was 0.46 kN and 0.66 kN, respectively. This study highlights the contribution of geometric variability on the structural response variation of the femoral shafts subjected to dynamic loading condition and the potential of geometric SS-FE models to capture the structural response variation of the femoral shafts.

Finite element modelling and model updating of small scale composite propellers

The application of composite materials in marine propellers is a relatively recent innovation. Methods have been presented to analyse the hydro-elastic behaviour of these type of propellers and in some studies these methods have been validated as well. Differences between measured and predicted responses are typically explained from inaccuracies in structural or fluid modelling. It is beyond all doubt that for an accurate finite element (FE) model a correct modelling of the fibre orientations and material properties is required. Both subjects are addressed in this work. An approach is presented in order to accurately define the element dependent fibre orientations in doubly curved geometries like (marine) propeller blades. In order to improve the structural response prediction this paper presents an inverse method based on experimental and numerical results which can be used for structural identification and FE model updating. In the developed approach the residual between measurement results obtained with static experiments and results obtained with an FE model is minimized by adapting the stiffness properties in the FE calculation. This method has been successfully applied to two small scale composite propellers. The obtained material properties have been determined with a relatively high confidence level. A verification by means of measured and calculated eigenfrequencies show also that accurate results are obtained with the inverse method. Therefore, this paper gives a positive answer on the research question whether it is possible to determine the stiffness properties of small scale composite marine propeller blades from a static experimental data.

Interaction Between Compliant Structures and Boundary-Layer Transition in Hypersonic Flow

The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This interdependence implies that accurate structural response prediction of a hypersonic vehicle necessitates an aerothermoelastic analysis that accounts for boundary-layer stability in regions where transition is likely to occur. This study focuses on this problem by coupling a time-varying boundary-layer state to the aerothermoelastic response of a structural panel in hypersonic flow. Results indicate that the structural response shifts the transition onset location upstream by more than a quarter of the panel length. The forward movement of the transition front is found to be strongly dependent on the panel deformation and is related to a region of adverse pressure resulting from the panel bowing into the flowfield. Additionally, the response of the panel with clamped structural boundary conditions is highly dependent on the transition onset location due to its sensitivity to the spatial variation in the thermal moment.

Bottom structural response prediction for ship-powered grounding over rock-type seabed obstructions

This paper presents a simplified analytical method for predicting the resistance of ship bottom structures when a ship runs aground over rock-type seabed obstructions. During the powered grounding scenario, the structural damage caused by sharp seabed obstructions may lead to earlier penetration and serious consequences, such as compartment flooding, oil leakage and environmental pollution. Therefore, it is of great importance to rapidly and accurately analyse the response of a ship's bottom structure during powered grounding scenarios. A new simplified kinematically admissible analytical model is built to capture the dominant failure modes of the bottom transverse floor, which include plastic bending and membrane stretching, and the analytical expression of the resistance of the bottom floor is derived from a plastic mechanism analysis. The failure mechanisms of the bottom plating are also analyzed to provide insight into the main deformation mechanisms with reasonable predictive accuracy. The analytical prediction method is verified by numerical simulation using the code LS-DYNA. The simulation cases cover a wide range of indentations and semi-apex angles of the cone-shaped rocks. The results agree well, proving that the proposed analytical method can be used to predict the ship bottom structure crashworthiness during the structural design phase.

Prediction of Structural Response Based on Ground Acceleration Using Artificial Neural Networks

This study utilizes Artificial Neural Network (ANN) to predict structural responses of multi-storey reinforced concrete building based on ground acceleration. The strong ground acceleration might cause catasthropic collapse of multi-storey building which leads to casualties and property damages. Therefore, it is imperative to properly design the multi-storey building against seismic hazard. Seismic-resistant building design process requires structural analysis to be performed to obtain the necessary building responses. Modal response spectrum analysis is performed to simulate ground acceleration and produce structural response data for further use in the ANN. The ANN architecture comprises of 3 layers: an input layer, a hidden layer, and an output layer. Ground acceleration parameters from 34 provinces in Indonesia, soil condition, and building geometry are selected as input parameters, whereas structural responses consisting of acceleration, velocity and displacement (story drift) are selected as output parameters for the ANN. As many as 6345 data sets are used to train the ANN. From the overall data sets, 4590 data sets (72%) are used for training process, 877 data sets (14%) for the validation process, and 878 data sets (14%) for testing. The trained ANN is capable for predicting structural responses based on ground acceleration at (96%) rate of prediction and the calculated Mean-Squared Errors (MSE) as low as 1.2.10−4. The high accuracy of structural response prediction can greatly assist the engineer to identify the building condition rapidly and plan the building maintenance routinely.

Prediction of Structural Response Based on Ground Acceleration using Artificial Neural Networks

Prediction of Structural Response Based on Ground Acceleration using Artificial Neural Networks

The damage-induced bi-modulus characteristic of C/SiC materials and experimental validation

Abstract The credibility of structural stress response predictions is critical in the design and analysis of increasingly used C/SiC structures. The complexities of the damage mechanisms pose a challenge to the accuracy of the predictions. In this paper, the bi-modulus characteristic of C/SiC, which is induced by the micro cracks opening and closing under tensile and compressive load respectively, were studied. A phenomenological macroscopic approach based on irreversible thermodynamics was applied to model the constitutive behavior of C/SiC. Four-point flexure experiments were conducted on C/SiC specimens to validate the model. A simulation model analogous to the experimental setup was built and the effects of the bi-modulus were analyzed. The strain responses in the experiments and the simulation corresponded well with each other. In both the experiments and the simulations conducted, neutral planes of the specimens were deviated from the geometric center due to the bi-modulus characteristic of the material. Compared to the simulation results using the developed constitutive law, the model employing a linear elastic law over-predicts the tensile stress by 31.6% and underestimates the compressive stress by 15.2% of the C/SiC specimen under a four-point flexural load of 1600 N.

Experimental investigation on the stress-strain behavior of steel fiber reinforced concrete subjected to uniaxial cyclic compression

The behavior of steel fiber reinforced concrete (SFRC) under cyclic loading plays an important role in prediction of SFRC structural response. This paper deals with the stress-strain behavior and damage evolution of SFRC under uniaxial cyclic compression. A total of 36 specimens are tested for different fiber volume fractions and aspect ratios. Acoustic emission (AE) technique is used to characterize the damage progression and reveal the failure mechanism of SFRC during the whole loading process. The results show that slight strength degradation for SFRC specimens under cyclic loading is observed in comparison with monotonic loading cases. The increase in volume fraction of steel fiber can lead to a remarkable decrease in the plastic strain accumulation as well as an increase in the elastic stiffness ratio, while the effect of fiber aspect ratio is undiscernable. In addition, it is indicated from the AE parameters analysis that the total AE activities of SFRC specimens are higher than that of plain concrete specimen and become greater with an increase in the fiber volume fraction, while the opposite is true for increasing the fiber aspect ratio. Meanwhile, as substantiated by AE, the failure of SFRC mainly demonstrates a shear cracking mode that is induced by fiber pull-out and fiber sliding events, the amount of which is proportional to both fiber volume fraction and aspect ratio. Finally, based on the test results of stiffness degradation, an analytical formulation for the damage evolution law of SFRC is developed and the prediction yields a close estimation of SFRC damage progression.

Collapse resistance assessment through the implementation of progressive damage in finite element codes

Different procedures for assessing the robustness of a reinforced concrete (RC) frame under progressive damage are proposed and compared. The removal of a column in a RC frame structure is modeled with a commercial nonlinear finite element software according to three alternative strategies: (i) reduction of mechanical properties of the damaged column, (ii) incremental loading of the structure after total removal of the damaged column, and (iii) incremental unloading of internal forces on the damaged column. Nonlinear analysis is performed under a prescribed load combination on three RC frames designed with three Italian building codes in force in different periods. Despite the differences in the strategies for damage modeling, similarities between structural response predictions are highlighted. In addition, it is shown that seismic design provisions for RC structures increase the ductility of the structure but do not necessarily guarantee robustness to progressive collapse scenarios.

Observation of wind fields over different terrains and wind effects on a super-tall building during a severe typhoon and verification of wind tunnel predictions

Wind effects are of major concern in the design of super-tall buildings, especially those located in tropical cyclone-prone regions. In July 2012, Hong Kong encountered one of the most severe typhoons in the history, Vicente (1208). This study investigates the impact of Vicente to Hong Kong with emphasis on the wind fields over different terrain conditions and the wind effects on a 420-m-high super-tall building. Within a time period of 18h that covered the passage of Vicente in Hong Kong, six sets of wind data were collected from five meteorological stations and a structural health monitoring (SHM) system installed in the super-tall building. In this study, the typhoon wind fields over varied types of terrains are revealed, the structural dynamic properties of the super-tall building as well as its serviceability are evaluated, and finally wind tunnel predictions of structural responses are validated by the field measurements from SHM system. This study aims to investigate the typhoon-generated wind characteristics over different terrains and the wind effects on a super-tall building located in a metropolis during a severe typhoon as well as verification of the accuracy of wind tunnel testing results, so as to provide useful information for the wind-resistant design of high-rise buildings in tropical cyclone-prone regions.

On Shock Response of Marine Sandwich Structures Subjected to UNDEX Loading

Survivability at sea in a hostile environment is the last line of hope for naval platforms. Research today has seen advancement of underwater explosion science along with the delivery systems such as torpedoes and underwater missiles. The evaluation of the structural response to such explosive loading and designing structures to attenuate the loading effects is of prime concern. The structural response to various impulsive loads specifically to blast loads in the elasto-plastic region will be in the form of large deformation, crack initiation and tensile tearing. The above failure modes can be predicted reasonably accurately at the design stage based on finite element modelling employing nonlinear shock analysis. In the prediction of structural response beyond elastic limit, both material and geometric nonlinearity are to be considered. The material non-linearity is generally modeled by Von Mises yield criteria and associated flow rules with isotropic hardening. The material models such as rigid plastic, elastic perfectly plastic and elasto-plastic can be used to represent the material behaviour. The geometric non-linearity is based on total or updated Lagrangian formulation. Cole [1] established useful empirical relations to model the underwater explosion (UNDEX) loading, which were the outcome of numerous experimental investigations done by the military agencies. In the present study the UNDEX load profile has been modeled as an exponentially decaying shock wave which varies spatially and transiently. An elasto-plastic model with isotropic hardening, strain rate effects and fracture criterion has been developed was used to predict and establish the failure modes in high strength (HS) and WELDOX Steel rectangular plates sandwiched with a metallic core structure, under clamped edge conditions. These models were implemented in the non-linear finite element code ABAQUS/Explicit. The present study establishes empirical relationships derived from numerical analysis of stiffened and un-stiffened plates subjected to UNDEX.

Damage Assessment of Two-Way RC Slab Subjected to Blast Load Using Mode Approximation Approach

Significant research efforts have been invested on studying the response and damage of structures subjected to blast loads for better life and property protections. The single-degree-of-freedom (SDOF) approach has been widely adopted to simplify the structural response analysis for engineering design purpose. However, such an approach under certain circumstances oversimplifies the structural behavior and might not give reliable predictions of structural responses to blast loads. On the other hand, although detailed high fidelity finite element (FE) approach is able to give relatively accurate predictions of structural response, it is unfortunately not straightforward for application and very time-consuming, which impedes its application among engineers. Therefore, a method that can assure not only reliability but also efficiency is highly needed for design practice. In the present study, mode approximation method with Pressure–Impulse (P-I) diagrams is applied to analyze response and damage of RC slab due to blast load. Slab under analysis is assumed rigid-plastic and simply supported. Shear failure, bending failure and combined failure modes are considered based on different failure modes. Critical equations for structural shear and bending failures are derived respectively with appropriate failure criteria. P–I diagrams are then developed for quick damage assessments. The analytical results are verified by comparing with high fidelity numerical simulations. The reliability and efficiency of using this approach for design and analyzing RC slab response under blast loads are demonstrated.

Seismic performance of reinforced concrete frame buildings in Bhutan based on fuzzy probability analysis

Seismic performance of reinforced concrete (RC) frame buildings is mostly assessed based on the distinct interstorey drift limits defined by many existing guidelines. In reality, damage of a structure is a continuous process under the action of the load and also depends on a number of factors. Therefore damage can be more logically defined with a fuzzy performance level than a distinct interstorey drift limit. In this paper, probability and fuzzy set theory are used to estimate the realistic failure probabilities of the RC buildings in Bhutan by considering randomness in material and geometrical parameters and fuzziness in the damage criteria. Three typical RC frame buildings in Thimphu, Bhutan and the ground motions predicted at the generic soil sites in Thimphu are used for the structural response prediction. Rosenbluth Point Estimate Method is used for modelling the statistical variation of the input parameters and the computer program Perform 3D is used for carrying out the dynamic nonlinear analysis of the buildings. Monte Carlo Simulation is employed to validate the accuracy of the Rosenbluth Point Estimate Method and determine the statistical distribution of the response quantities. Soil structure interaction (SSI) is considered at the soft soil site using the uncoupled spring model. Based on the mean and standard deviation of the intersotrey drifts obtained from the analyses, the fuzzy failure probabilities of the buildings are estimated. It is found that under the 475 year return period ground motions, typical buildings experience a high probability of irreparable and severe damages, while the high probability of severe damage and complete collapse are predicted under the 2475 year return period ground motions. SSI is found to be detrimental to the 3 storey building, while no significant effect is observed to the 6 storey building.

Human-structure interaction effects on the maximum dynamic response based on an equivalent spectral model for pedestrian-induced loading

This paper investigates the effects of the human-structure interaction (HSI) on the dynamic response based on a spectral model for vertical pedestrian-induced forces. The spectral load model proposed in literature can be applied for the vibration serviceability analysis of footbridges subjected to unrestricted pedestrian traffic as well as in crowded conditions, however, in absence of HSI phenomena. To allow for a more accurate prediction of the maximum structural response, the present study in addition accounts for the vertical mechanical interaction between pedestrians, represented by simple lumped parameter models, and the supporting structure. By applying the classic methods of linear random dynamics, the maximum dynamic response is evaluated based on the analytical expression of the spectral model of the loading and the frequency response function (FRF) of the coupled system. The most significant HSI-effect is in the increase of the effective damping ratio of the coupled system that leads to a reduction of the structural response. However, in some cases the effect of the change in the frequency of the coupled system is more significant, whereby this results into a higher structural response when the HSI-effects are accounted for.

Prediction of structural response of naval vessels based on available structural health monitoring data

Structural health monitoring (SHM) can be beneficial in reducing epistemic uncertainties associated with fatigue life prediction. For naval ships, available SHM data can be discretized into operational cells, each referring to a certain navigation speed, heading angle, and sea condition. Cell-based approaches for predicting future fatigue life can be applied if monitoring information is known for all cells. However, available SHM data may populate some, but not all, potential cells. Moreover, since SHM data is only available for a given set of operating conditions, potential changes in climate or operational profiles cannot be accounted for. Accordingly, there is a need for an approach to predict structural responses in unmonitored cells as a function of limited available monitoring data. This paper proposes a methodology to predict the responses of naval vessels in unobserved cells by incorporating data from the limited number of observed cells. The power spectral density (PSD) of the SHM data is fit using generalized functions, based on sea wave spectra, and integrated into the prediction of the PSD for unobserved cells. The proposed methodology enables both spectral and time-domain fatigue methods. The methodology is illustrated on the SHM data from a high speed aluminum catamaran.

Structural response of fire-exposed cross-laminated timber beams under sustained loads

Cross-laminated timber (CLT) is a popular construction material for low and medium-rise construction. However an architectural aspiration exists for tall mass timber buildings, and this is currently hindered by knowledge gaps and perceptions regarding the fire behaviour of mass timber buildings. To begin to address some of the important questions regarding the structural response of fire-exposed CLT structures in real fires, this paper presents a series of novel fire tests on CLT beams subjected to sustained flexural loading, coincident with non-standard heating using an incident heat flux sufficient to cause continuous flaming combustion. The load bearing capacities and measured time histories of deflection during heating are compared against predicted responses wherein the experimentally measured char depths are used, along with the Eurocode recommended reduced cross section method and zero-strength layer thickness. The results confirm that the current zero-strength layer value (indeed the zero-strength concept) fails to capture the necessary physics for robust prediction of structural response under non-standard heating. It is recommended that more detailed thermo-mechanical cross-sectional analyses, which allow the structural implications of real fire exposures to be properly considered, should be developed and that the zero-strength layer concept should be discarded in these situations. Such a novel approach, once developed and suitably validated, could offer more realistic and robust structural fire safety design.

An integrated approach for non-periodic dynamic response prediction of complex structures: Numerical and experimental analysis

In this paper, a combined numerical and experimental method, called Extended Load Confluence Algorithm, is presented to accurately predict the dynamic response of non-periodic structures when little or no information about the applied loads is available. This approach, which falls into the category of Shape Sensing methods, inputs limited experimental information acquired from sensors to a mapping algorithm that predicts the response at unmeasured locations. The proposed algorithm consists of three major cores: an experimental core for data acquisition, a numerical core based on Finite Element Method for modeling the structure, and a mapping algorithm that improves the numerical model based on a modal approach in the frequency domain. The robustness and precision of the proposed algorithm are verified through numerical and experimental examples. The results of this paper demonstrate that without a precise knowledge of the loads acting on the structure, the dynamic behavior of the system can be predicted in an effective and precise manner after just a few iterations.

Effects of internal acoustic coupling on the response of a base-excited hollow structure

Traditionally, structural dynamic simulation predictions for hollow structures do not include internal acoustic volumes. This is the case for two reasons. First, it can be difficult to create a volume mesh of complicated internal cavities, and this additional volume would drastically increase the size of the model. Second, it is often blindly assumed that acoustic coupling is not important for structures with anything but thin walls. However, if the structural and acoustic modes are compatible, that is, the modes have similar frequencies and shapes, then the interaction between the structure and the enclosed acoustic volume will occur and can have an effect on structural response. The magnitude of this coupling effect is demonstrated here by examining the structural response predictions for a finite element model of a hollow structure with and without the acoustic volume in place. When a base excitation is applied at a frequency and location to excite compatible modes, the response predictions are seen to be drastically different if the acoustic volume is included. The frequency response results of the coupled finite element simulations will be compared with those of the classic two degree of freedom dynamic vibration absorber, showing the effect of frequency ratio and damping on the structural response.

Wind power spectra for coastal area of East Jiangsu Province based on SHMS

A wind velocity power spectrum (WVPS) with high fidelity is extremely important for accurate prediction of structural buffeting response. WVPS heavily depends on the geographical locations, local terrains and topographies. Hence, field measurement of wind characteristics may be the unique way to obtain the accurate WVPS for a specific region. In this paper, a systematic analysis and discussions of existing WVPSs were performed. Six recorded strong wind data from the structural health monitoring systems (SHMS) of Runyang Suspension Bridge (RSB) and Sutong Cable-stayed Bridge (SCB) in Jiangsu Province of China were selected for analysis. The measured and pre-processed wind velocity data was first transformed from time domain to frequency domain to obtain the measured spectrum. The spectrum for each strong wind was then fitted using the nonlinear least square method and compared with both the fitted spectrum from statistical analysis and the recommended spectrum in specifications. The modified Kaimal spectrum was proved to be the best choice for the coastal area of East Jiangsu Province. Finally, a suitable WVPS formula fit for the coastal area of East Jiangsu Province was presented based on the modified Kaimal spectrum. Results in this study provide a more accurate and reliable WVPS for wind-resistant design of engineering structures in the coastal area of East Jiangsu Province.

Rapid prediction of structural responses of double-bottom structures in shoal grounding scenario

This study presents a simplified analytical model for predicting the structural responses of double-bottom ships in a shoal grounding scenario. This solution is based on a series of analytical models developed from elastic-plastic mechanism theories for different structural components, including bottom girders, floors, bottom plating, and attached stiffeners. We verify this simplified analytical model by numerical simulation, and establish finite element models for a typical tanker hold and a rigid indenter representing seabed obstacles. Employing the LS-DYNA finite element solver, we conduct numerical simulations for shoal-grounding cases with a wide range of slope angles and indentation depths. In comparison with numerical simulations, we verify the proposed simplified analytical model with respect to the total energy dissipation and the horizontal grounding resistance. We also investigate the interaction effect of deformation patterns between bottom structure components. Our results show that the total energy dissipation and resistances predicted by the analytical model agree well with those from numerical simulations.