Finite Element Model Calibration Research Articles

Response surface-based model updating to detect damage on reduced-scale masonry arch bridge

Response surface (RS) methods, a combination of mathematical and statistical techniques, have been widely used in design optimization, response prediction, and model validation in structural engineering systems. However, its usage in structural damage identification, especially for historic structures has not been quite common. For this purpose, this study attempts to investigate damage detection in a masonry arch bridge. Within the scope of this, a reduced-scale model of a one span historical masonry arch bridge was built in a laboratory environment. To determine the modal parameters of the reduced-scaled bridge model, operational modal analysis (OMA) was performed under ambient vibrations. Signals originated by sensitive accelerometers were collected to quantify the vibratory response of the reduced-scaled model bridge. The experimental natural frequencies, mode shapes, and damping ratios resulting from these measurements were figured out by using the Enhanced Frequency Domain Decomposition (EFDD) technique. The three-dimensional model of the reduced-scale bridge was created in the ANSYS finite element (FE) software program to expose the analytical dynamic characteristics of the bridge model. The results obtained in the experimental application were compared with those of the finite-element analysis of the bridge model. The calibration of the numeric model was utilized depending on the experimental modal analysis results of the reduced-scale bridge by using the RS method. Design of experiments was constructed by using central composite design, and the RS models were generated by performing the genetic aggregation approach. The optimum results between the experimental and numerical analyses were found by using the RS optimization. Then, regional damages created on the scaled model and the changes of dynamic properties of the damaged case were evaluated. The damage location was approximately identified by using the RS method in the calibrated finite-element model. The results demonstrated that the RS-based FE updating approach is an effective way for damage detection and localization in masonry type structures.

Finite Element Model Calibration of Sandwich Structure Based on Mixed Numerical Experimental Technique

This paper presents the implementation of the mixed numerical experimental technique for the finite element (FE) model calibration of a sandwich structure by using modal data. Model calibration is conducted by minimizing the difference between the numerical and experimental dynamic parameters. In this study, instead of the direct minimisation of the response discrepancy, the experiment design and the response surface method is employed to solve the inverse (calibration) problem. Numerical eigenfrequencies are obtained by performing FE calculations in sample points derived by Latin Hypercube experiment design where each sample point represents a unique engineering constant configuration in the FE model of the sandwich panel. Using the information on the dynamic responses of the panel in the sample points, response functions describing the relationship between the engineering constants and the calculated eigenfrequencies are obtained by means of response surface method. Genetic algorithm is employed to solve the minimisation of the response discrepancy where the response functions instead of FE calculations are used to obtain the numerical modal frequencies. The verification results show that proposed method is capable to calibrate a numerical model with a good prediction accuracy and small uncertainties.

Numerical study for structural performance evaluation of adhesively bonded aluminum dynamic message signs

Adhesively bonded joints used for the fabrication of an aluminum dynamic message sign (DMS) have increasingly gained popularity in the transportation signage manufacturing industry. However, in-depth numerical studies on the structural performance of DMSs are tremendously limited. The main goal of this study was to numerically examine the structural performance of the adhesively bonded DMSs. In this study, the performance of DMS specifically refers to the maximum strength resisted by the DMS under ultimate loadings. In pursuit of this goal, this study proposed a three-dimensional finite element (FE) analysis approach to delve into the performance of a full-scale adhesive DMS tested with ultimate loads. The FE model for the tested DMS was generated using ABAQUS software and calibrated with the testing data. A parametric study was conducted via the calibrated FE model associated with variation in key design parameters, such as damage factor and area of adhesive, in order to not only quantify their effects on the performance of adhesive DMSs, but also determine its optimized performance. Finally, a parametric equation in conjunction with the key parameters was developed in a statistical manner for the efficient prediction of the adhesive DMS performance. Significant findings revealed that the overall structural behavior of the generated FE model was observed analogous to that found in the DMS testing, and the ultimate strength from the FE analysis was only 1.26% lower than that gained from the testing. Additionally, it was found that the optimized FE model exhibited 8.32% higher ultimate strength than the tested DMS, and the proposed equation was capable of estimating the strength with an average error of 9.58% compared to the FE analysis.

О состоянии и развитии системы мониторинга инженерных конструкций башни «Эволюция». Часть 2. Рекомендации по развитию

Во второй части статьи[1] представлены обоснованные рекомендации по дополнению системы мониторинга в части пространственно-координатного мониторинга с помощью ГЛОНАСС/GPS-датчиков, а также контроля за фасадными кон­струкциями (контрольные параметры для светопрозрачных фасадных систем; оборудование для мониторинга фасадных систем). В завершении сформулированы рекомендации по разработке и интеграции адаптивных конечноэлементных моделей несущих и фасадных конструкций. Даны указания на разработки авторов, посвящённые оригинальной расчётно­экспериментальной методике динамического мониторинга несущих конструкций высотных зданий в части её общих положений и структурной схемы, параметризируемых конеч­ноэлементных моделей, адаптации (калибровки) конечноэле­ментных моделей по данным инструментальных наблюдений, оценки несущей способности для фактического состояния и планирования измерений по результатам мониторинга.
 
 [1] Первая часть статьи «О состоянии и развитии системы мониторинга инженерных конструкций башни "Эволюция"» опубликована в № 1 журнала «Academia. Архитектура и строительство» за 2020 год.

A hybrid method for the calibration of finite element models of punching-shear in R/C flat slabs

The paper is focused on the calibration of non-linear 3D finite element (FE) analyses to simulate punching failure of R/C flat slabs. The calibration procedure is developed with reference to the code ABAQUS, which is one of the most used computer codes in nonlinear modelling of R/C structures. Generally, the calibration of a nonlinear FE model is grounded on one test only, so its reliability could be limited. Here a hybrid method for the calibration of FE models of R/C flat slabs failing in punching is proposed and discussed. The method consists in calibrating input data by comparison of finite element model (FEM) results with both experimental data and predictions provided by analytical models. The procedure allows for a consistent calibration to be performed, valid for a wide range of longitudinal reinforcement ratios, from 0.5% to 2.00%, and concrete grades, from C20/25 to C50/60. A case study is investigated using the proposed method. Results show that calibrated values of the fracture energy lie between those provided by Model Code 1990 and Model Code 2010. From the new calibration procedure, a relationship between fracture energy and concrete compressive strength is also derived and blind analyses are performed to check its reliability against experimental results.

Dynamic behavior and vulnerability analysis of bridge columns with different cross-sectional shapes under rockfall impacts

Rockfall disasters pose a significant threat to bridge structures in mountainous areas. Most of the destroyed bridge structures in mountainous regions are impacted by rockfalls to different degrees. Reinforced concrete (RC) columns with circular and square cross-sections are extensively used in bridge structures as typical alternatives, because of their advantages of easy construction and good performance. Although their seismic behaviors have been extensively investigated, limited studies have been devoted to exploring their dynamic responses and vulnerability to rockfall impacts. To this end, detailed finite element (FE) models were established in this study, to investigate the dynamic behavior and vulnerability of bridge structures with different cross-sections subjected to rockfall impact loading. Key modeling issues, such as modeling RC columns under both impact loading and the initial permanent loads prior to impact, were examined and addressed by high-resolution FE simulations. The effects of the rockfall diameter, impact velocity, and impact height on the dynamic behaviors of the columns, such as the impact force, lateral displacement, and residual axial capacity, were carefully investigated by using the calibrated FE models. Comparison of the dynamic behaviors of the circular and square columns indicated that the impact-resistance performance of the former was remarkably superior to that of the latter, for the same amount of materials used. A vulnerability analysis procedure based on the response surface model and Monte Carlo simulations was proposed, to investigate the probability of various damage levels for both the circular and square columns under rockfall impacts. Good agreement was achieved for the impact-induced responses obtained from the high-resolution FE simulations and the surrogate response surface models. The vulnerability analysis results further confirmed the disadvantage of the square columns for application in mountainous areas, owing to a relatively high risk of rockfall impact. The vulnerability analysis procedure proposed in this paper will assist researchers to investigate the damage and vulnerability of RC column structures subjected to impact loading.

Bridge Load Testing for Identifying Live Load Distribution, Load Rating, Serviceability and Dynamic Response

In this article, dynamic and static load tests of a concrete highway bridge, which is a deteriorated and repaired, are presented depending on displacement and strain data for engineering decision making about the operation of a critical bridge. Static load test was carried out to determine the live load distribution factor (DF) and load-rating (RF) as well as serviceability by means of deflection limits. Modal characteristics in terms of structural frequencies and mode shapes and impact factor (IM) were identified from the dynamic load test for different truck-load and speed cases, and FE model. The distribution factor (DF) and load rating factor (RF) were also compared with those calculated according to AASHTO standard and FE model. The results showed that the distribution factor (DF) calculated by AASHTO standard gave more conservative results when compared with the experimental and FEM approaches. Similarly, the load-rating factor (RF) calculated by AASHTO standard yielded to more conservative results comparing with the experimental FEM approaches using practical distribution factors. Maximum deflections in static cases and dynamic cases were found to be within the limit calculated by (L/800) given in the AASHTO code. Impact factors among all the cases were obtained much smaller than the one recommended by AASHTO standard (33%). The modal properties were obtained to track changes in dynamic behavior due to stiffness and boundary effects as well as for finite element model calibration. The calibrated FE model of the bridge also indicated that the load carrying capacity of the bridge is adequate after repair. Finally, the results from the current study reveal that use of experimental data can be utilized to obtain load rating with minimum interruption to bridge operations through computer vision technology and methods.

Response surface-based finite element model calibration of a one-span historical masonry bridge

Response surface-based finite element model calibration of a one-span historical masonry bridge

О состоянии и развитии системы мониторинга инженерных конструкций башни «Эволюция»

Настоящая статья посвящена текущему и перспективному состоянию системы мониторинга инженерных конструкций (СМИК) башни «Эволюция» Московского международного дело­вого центра (ММДЦ) «Москва-Сити». Данный объект выполнен в форме закрученного вокруг собственной оси 255-метрового 54-этажного небоскрёба, расположенного на трёхуровневом стилобате. В статье представлены результаты анализа научно­методической, проектной и исполнительной документации по объекту, проведён анализ действующей системы мониторинга инженерных конструкций (СМИК). В частности, приведены сведения о СМИК в части несущих конструкций, о контрольно­измерительной аппаратуре высотного здания, о действующей системе мониторинга несущих конструкций, о критериях оценки технического состояния несущих конструкций, о фасадных конструкциях, о результатах анализа достоверности объёма контролируемых параметров, оперативности и достоверности (точности и надежности) смонтированной МИК. Далее на основе изложенного даются обоснованные рекомендации по дополнению системы мониторинга в части пространственно­координатного мониторинга с помощью ГЛОНАСС/GPS-датчиков, а также контроля за фасадными конструкциями (предложения в части контрольных параметров для светопрозрачных фасадных систем, оборудования для мониторинга фасадных систем). В завершении сформулированы рекомендации по разработке и интеграции адаптивных конечноэлементных моделей несущих и фасадных конструкций. Даются необходимые ссылки на пу­бликации авторов, посвящённые разработанной оригинальной расчётно-экспериментальной методике динамического мони­торинга несущих конструкций высотных зданий. В основе этой методики лежит построение и последующее использование параметризируемых конечноэлементных моделей, адаптация (калибровка) этих моделей по данным инструментальных на­блюдений с целью адекватной оценки несущей способности для фактического состояния и планирования измерений по результатам мониторинга.

Seismic response evaluation of monuments based on ambient vibrations: the case studies of a Byzantine basilica and an Ottoman bath in Thessaloniki (Greece)

The present work focuses on the seismic response and damage distribution studies on two Thessaloniki monuments with different structural systems. The first one is the Acheiropoietos basilica—a Byzantine monument included in the World Heritage List of UNESCO—with a flexible structural system consisted of internal colonnades and perimeter walls. The second one is the Bey hamam, an Ottoman bath with a stiff structural system. Its successive square or rectangular functional spaces are organized in such a way as to obtain both spatial and structural (bearing structure) autonomy; thick internal and external walls in two directions bear the domes directly or through single or double arches. Both monuments were subjected to the June 20, 1978 Thessaloniki earthquake ground motion (EQ) (M6.5) with significant damage which were accurately recorded and demonstrated in the Ephorate of Antiquities of Thessaloniki (EFAPOTH) archives. Sets of ambient vibration measurements were performed before any intervention work at the basilica. For the present study, similar measurements were performed at both monuments. Their eigen-properties were then calculated based on this data. Both monuments were modeled in details by finite element method; the analytical models were calibrated for the optimum approach of the eigen-properties resulted by the measurements. The main calibration parameter was the modulus of elasticity of the masonry walls. These calibrated models were also analytically subjected to the recorded acceleration time history of the Thessaloniki 1978 EQ. The findings of this work are related to the appropriately documented material properties and factors of these monuments that are unique. The result of this procedure was the calibration of reliable finite element models for response evaluation of the structures to potential ground motions in future earthquakes. These models were capable to quantitatively explain the damage patterns observed in the monuments. The monument with higher stiffness (Ottoman bath) exhibited damage concentrated to fewer elements than the more flexible monument (Byzantine basilica) where the damages were distributed to many structural elements.

Experimental tests and finite element simulations of a new SMA-steel damper

Owing to their outstanding recentering capability, shape memory alloy (SMA) dampers are emerging as promising passive dampers for seismic applications. However, compared to typical seismic dampers, the inherent energy dissipation capability of SMAs is often deemed barely satisfactory. To enhance the damping capacity of SMA dampers, this study suggests combining SMA elements with steel dampers based on bending steel plates. In this new SMA-steel damper, the steel dampers are mainly responsible for absorbing seismic energy, whereas the SMA bars primarily play the role of recovering inelastic deformation. Experimental tests were conducted at room temperature to verify the cyclic behavior of the proposed damper. The hysteretic parameters, such as strength, stiffness, equivalent damping ratio, and residual deformation, are of particular interest and quantified as a function of the loading amplitude. According to test results, the new damper is confirmed to possess desirable recentering capability and high damping. To further understand the damper, numerical simulations were carried out in the finite element (FE) analysis software ABAQUS. The numerical results validated the experimental data. Based on the calibrated FE model, the thickness of the bending steel plate of the steel damper and the diameter of the SMA bars were varied in the parametric analysis to examine its effect on the recentering tendency and damping mechanism.

Earthquake-induced damage localization in an historic masonry tower through long-term dynamic monitoring and FE model calibration

This paper presents an enhanced version and the validation of a recently proposed methodology for earthquake-induced damage detection and localization in masonry towers by using long-term vibration monitoring data. The proposed enhanced method is based on continuous operational modal analysis through stochastic subspace identification, dynamic multiple linear regressive analysis to remove the effects of changing environmental conditions and finite element (FE) model updating. Any anomalous frequency deviation from normal conditions resulting from an earthquake triggers the damage localization process. This task is performed by solving an inverse FE model calibration problem, where equivalent elastic properties of macrostructural elements are identified by minimizing an objective function considering experimentally identified and numerically predicted damage-induced decays in natural frequencies and changes in eigenvector components. To minimize the computational effort of this calibration procedure, a quadratic surrogate model is constructed using a tuned numerical FE model of the structure. The methodology is validated through application to the “Sciri Tower”, an historic civic masonry tower located in Perugia, Italy, that has been continuously monitored by the authors for more than 1 year. The validation is carried out by using simulated damage scenarios and a set of real far-field earthquake data and is based on a FE model of the tower including surrounding buildings, calibrated on the basis of the measured data from ambient vibration tests. The results demonstrate that the proposed procedure is capable of correctly detecting and localizing earthquake-induced damages.

Automated modal identification using principal component and cluster analysis: Application to a long‐span cable‐stayed bridge

Obtaining timely information about the health of civil infrastructure is critical to ensuring safe and reliable operation. Structural health monitoring has been proposed as a means to provide such information; however, most structural health monitoring systems provide only raw data, rather than actionable information. It is necessary to develop automated modal analysis strategies that can provide near real-time dynamic information regarding the in-service state of a bridge, which is essential to vibration control, finite element model calibration, and damage detection for safety and serviceability condition assessment. This study presents an automated framework to extract structural modal parameters from the stabilization diagram using a parametric modal identification method such as stochastic subspace identification. The framework focuses on the automated modal analysis issues of an in-service long-span bridge with close-frequency modes. The presented framework is validated using experimental tests of a 1.8-m 18-story laboratory model. Subsequently, data from Sutong Cable-Stayed Bridge are employed to demonstrate its potential usage in the field. Finally, an application of the automated framework is presented to identify and track the modal parameters of the deck of Sutong Cable-Stayed Bridge for 20 days. Results show that the presented framework can successfully extract the structural modal parameters with good accuracy and robustness, hence can provide a reliable technical support for in-service monitoring of long-span bridges.

Assessment of progressive collapse potential of special moment resisting RC frames – Experimental and FE study

The catastrophic collapse of the Twin-towers has further prompted structural engineers to understand and investigate the progressive collapse of multi-story buildings. This paper aims to simulate the response of reinforced concrete (RC) special moment resisting frame (SMRF) assemblies under column-loss scenarios through nonlinear finite element (FE) modeling. Besides the modeling of nonlinear rate dependent material behavior, bond-slip effects at the concrete-to-steel rebar interface have been considered. The FE model was calibrated against a scaled, single-story, two-bay by one-bay, RC SMRF model specimen with reinforcement detailing conforming to ACI 318-11 code. The specimen was tested under a middle column removal scenario. The calibrated FE model was subsequently employed for some parametric studies of interest wherein the effect of different parameters such as: type of assembly, column continuity, development of beam rebars at exterior joints, applied axial loads on columns and beam continuity at exterior joints, on the behavior of SMRF under a middle column removal scenario was studied. A simple procedure is also proposed for the progressive collapse assessment of RC SMRFs caused by sudden column removal.

Synergistic and combinatorial optimization of finite element models for monitored buildings

This paper investigates the use of rank aggregation strategies for the finite element model calibration of monitored masonry structures subjected to earthquakes. Ranking is used to obtain optimal results from several competing optimization strategies, with the final aim of establishing a numerical model of reference to support the existing monitoring systems installed on the structures. For the tuning of the model, different optimization methods are currently employed (i.e., genetic optimization, particle swarm optimization, and simulated annealing optimization), which can provide an initial nonunique definition of the structural parameters. Starting from the results obtained from selected updating methods, a combinatorial parameter selection is proposed to define the best finite element model among several optimal results. In this case, the ranking problem is solved by using a Plackett-Luce model-based strategy. The calibrated model is a useful tool to investigate the dynamic response of the structure, allowing a preliminary structural assessment at the same time. The data recorded by the permanent dynamic structural health monitoring system installed on a masonry building, the Town Hall of Pizzoli in central Italy, are used to demonstrate the proposed model calibration strategy.

Dynamic Characterization and Vibration Analysis of a Four-Story Mass Timber Building

Mass timber construction has been gaining momentum in multi-story residential and commercial construction sectors in North America. As taller mass timber buildings are being planned and constructed, in-situ dynamic tests of this type of construction can be performed to further validate their design and use. As part of this larger effort, an in-situ dynamic characterization testing campaign based on ambient vibration measurements was conducted on a recently constructed four-story mass timber building located in Portland, Oregon. The building features cross-laminated timber (CLT) floors, a glued laminated timber (GLT) framing gravity system, and light-frame shear walls and steel HSS hold-downs that compose the lateral resisting system of the building. Ambient vibration acceleration testing data were collected using 18 accelerometers that were wired to a portable data acquisition system in two experimental setups. Approximately two hours of bi-directional horizontal acceleration data were recorded. In this paper, two operational modal analysis methods are used for estimating the modal parameters (frequency, damping, and mode shapes) based on the data collected. In addition, a multi-stage linear Finite Element (FE) model updating procedure is presented for this building type and the FE estimates of frequencies and mode shapes are compared to estimates from the collected data. The calibrated FE model provides confidence to the operational modal results, and presents a comprehensive modal characterization of the building. At ambient levels of excitation, the developed FE model suggests that stiffness of the non-structural elements, such as the exterior wall cladding and glazing affects the modal response of the building considerably. Lessons learnt on this unique and first of a kind four-story structure constructed in the United States and implications for taller mass timber buildings are summarized and provide valuable insight for the design and assessment for this building type under future dynamic excitation events.

Multiple Heat Source Thermal Modeling and Transient Analysis of LEDs

Thermal transient testing is widely used for LED characterization, derivation of compact models, and calibration of 3D finite element models. The traditional analysis of transient thermal measurements yields a thermal model for a single heat source. However, it appears that secondary heat sources are typically present in LED packages and significantly limit the model’s precision. In this paper, we reveal inaccuracies of thermal transient measurements interpretation associated with the secondary heat sources related to the light trapped in an optical encapsulant and phosphor light conversion losses. We show that both have a significant impact on the transient response for mid-power LED packages. We present a novel methodology of a derivation and calibration of thermal models for LEDs with multiple heat sources. It can be applied not only to monochromatic LEDs but particularly also to LEDs with phosphor light conversion. The methodology enables a separate characterization of the primary pn junction thermal power source and the secondary heat sources in an LED package.

Behavior of concrete beam-column frame joints with DfD connections: A simulation study with interface modelling

This paper presents a simulation study on the seismic behavior of newly developed concrete beam-column frame joints with design for deconstruction (DfD) connections. A two-dimensional nonlinear finite element (FE) analysis was carried out using ABAQUS software. Material constitutive laws for concrete and steel, interaction behavior for smooth concrete-concrete interface, interaction behavior for concrete-steel bond, and element type were presented. The FE model was calibrated using experimental data and simulation results were found to be comparable with experimental results. Particularly, the cracking pattern and failure mode can be well predicted by this FE model. Parametric studies were carried out subsequently based on the calibrated FE model. Results show that the condition of concrete-concrete interface has very limited effect on the overall capacity of concrete frame joint with DfD connections but will influence the cracking pattern and ductility of joints.

A Procedure for the Structural Identification of Masonry Towers

Historic masonry towers, as well as bell towers, minarets and chimneys, represent an important part of the Mediterranean basin architectural heritage. Widely spread out on the Italian peninsula, the bell towers reflect cultural, social and religious aspects of the communities, thus, their conservation remains an open challenge for scientists, governments and local communities. The seismic behavior of slender masonry structures is, generally, characterized by the combination, of the static vertical loads with dynamic loading. However, the determination of the structural behavior of masonry structures is always a complex challenge due to the material inhomogeneity, manufacturing imperfections, geometric configuration or structural interaction between the layers in the case multi-leaf masonry structures. In this research, an expeditious and low-cost procedure for the structural identification of historic masonry towers is proposed. The procedure, based on experimental measurements and numerical modeling, aims at the estimation of the average mechanical characteristics under service loads. In particular, the procedure proposes the acquisition of the fundamental frequency by means of a single compact digital tromograph and successive finite element model calibration starting from the experimental data. The whole identification procedure has been at first verified on an elementary laboratory specimen, then applied on the historic bell tower of Basilica dei Frari located in the historic city center of Venice.

Experiment-based reliability analysis of structural joints in a steel lattice tower

The main aim of this paper is to present a reliability estimation procedure for steel lattice telecommunication towers based on tensioned joint reliability. The experiment, which involved doing a full-scale pushover test of a 40 m high lattice tower, constituted the starting point for further analyses. Experimental data served as bases for finite element model calibration and assignment of steel mechanical properties based on tensile tests. A computational investigation was performed for random wind loads. Numerical considerations included a detailed dynamic analysis with respect to the specific wind velocity–time function, modeling of two particular tower joints by shell finite elements, and elastic-plastic range determination of joint reliability using the first-order and second-order reliability methods.