Showing papers in "Engineering Structures in 2018"
TL;DR: Techniques concerning applications of the noted AI methods in structural engineering developed over the last decade are summarized.
Abstract: Artificial intelligence (AI) is proving to be an efficient alternative approach to classical modeling techniques. AI refers to the branch of computer science that develops machines and software with human-like intelligence. Compared to traditional methods, AI offers advantages to deal with problems associated with uncertainties and is an effective aid to solve such complex problems. In addition, AI-based solutions are good alternatives to determine engineering design parameters when testing is not possible, thus resulting in significant savings in terms of human time and effort spent in experiments. AI is also able to make the process of decision making faster, decrease error rates, and increase computational efficiency. Among the different AI techniques, machine learning (ML), pattern recognition (PR), and deep learning (DL) have recently acquired considerable attention and are establishing themselves as a new class of intelligent methods for use in structural engineering. The objective of this review paper is to summarize techniques concerning applications of the noted AI methods in structural engineering developed over the last decade. First, a general introduction to AI is presented and the importance of AI in structural engineering is described. Thereafter, a review of recent applications of ML, PR, and DL in the field is provided, and the capability of such methods to address the restrictions of conventional models are discussed. Further, the advantages of employing such algorithmic methods are discussed in detail. Finally, potential research avenues and emerging trends for employing ML, PR, and DL are presented, and their limitations are discussed.
TL;DR: This review paper is intended to summarize the collective experience that the research community has gained from the recent development and validation of the vision-based sensors for structural dynamic response measurement and SHM.
Abstract: To address the limitations of current sensor systems for field applications, the research community has been actively exploring new technologies that can advance the state-of-the-practice in structural health monitoring (SHM). Thanks to the rapid advances in computer vision, the camera-based noncontact vision sensor has emerged as a promising alternative to conventional contact sensors for structural dynamic response measurement and health monitoring. Significant advantages of the vision sensor include its low cost, ease of setup and operation, and flexibility to extract displacements of any points on the structure from a single video measurement. This review paper is intended to summarize the collective experience that the research community has gained from the recent development and validation of the vision-based sensors for structural dynamic response measurement and SHM. General principles of the vision sensor systems are firstly presented by reviewing different template matching techniques for tracking targets, coordinate conversion methods for determining calibration factors to convert image pixel displacements to physical displacements, measurements by tracking artificial targets vs. natural targets, measurements in real time vs. by post-processing, etc. Then the paper reviews laboratory and filed experimentations carried out to evaluate the performance of the vision sensors, followed by a discussion on measurement error sources and mitigation methods. Finally, applications of the measured displacement data for SHM are reviewed, including examples of structural modal property identification, structural model updating, damage detection, and cable force estimation.
TL;DR: A methodology is described for global and local health condition assessment of structural systems using ambient vibration response of the structure collected by sensors using synchrosqueezed wavelet transform, Fast Fourier Transform, and unsupervised deep Boltzmann machine to create a structural health index.
Abstract: A methodology is described for global and local health condition assessment of structural systems using ambient vibration response of the structure collected by sensors. The model incorporates synchrosqueezed wavelet transform, Fast Fourier Transform, and unsupervised deep Boltzmann machine to extract features from the frequency domain of the recorded signals. A probability density function is used to create a structural health index (SHI). This index can be used to assess both the global and local health conditions of the structure. A beauty of the proposed model is that it does not require costly experimental results to be obtained from a scaled version of the structure to simulate different damage states of the structure. Only ambient vibrations of the healthy structure are needed. In the absence of ambient vibrations, they can be simulated stochastically using structural properties and the probability theory. The effectiveness of the proposed model is illustrated employing experimental data obtained on a shake table in Hong Kong.
TL;DR: In this paper, the authors present an ambitious review that describes all the main advances that have taken place since the beginning of the 21st century in the field of progressive collapse and robustness of buildings.
Abstract: Extreme events (i.e. terrorist attacks, vehicle impacts, explosions, etc.) often cause local damage to building structures and pose a serious threat when one or more vertical load-bearing components fail, leading to the progressive collapse of the entire structure or a large part of it. Since the beginning of the 21st century there has been growing interest in the risks associated with extreme events, especially after the attacks on the Alfred P. Murrah Federal Building in Oklahoma in 1995 and on the World Trade Center in New York in 2001. The accent is now on achieving resilient buildings that can remain operational after such an event, especially when they form part of critical infrastructures, are occupied by a large number of people, or are open to the public. This paper presents an ambitious review that describes all the main advances that have taken place since the beginning of the 21st century in the field of progressive collapse and robustness of buildings. Widely diverse aspects are dealt with, including: (1) a collection of conceptual definitions, (2) bibliometric details, (3) the present situation and evolution of codes and design recommendations, (4) quantification of robustness, (5) assessing the risk of progressive collapse, (6) experimental tests, (7) numerical modelling, and (8) research needs. Considering the comprehensive range of these aspects, this paper could be of great use to professionals and researchers who intend to enter the field of the progressive collapse of building structures and also to other experts who require an extensive and up-to-date view of this topic.
TL;DR: In this article, the effects of the graded properties on their crashworthiness are discussed, and the authors demonstrate that thin-walled structures and cellular materials could exhibit more efficient and effective energy-absorbing performance by introducing graded properties.
Abstract: In the past decades, there has been a constant aspiration for light-weight and highly efficient energy-absorbing structures and materials in vehicle and other industries. A large number of publications have shown that advanced configurations with functionally graded properties could collapse in a more controlled manner and have a remarkable energy-absorbing efficiency when compared with traditional uniform structures and materials. This paper mainly covers the state of the art of energy absorption of graded structures and materials, and discusses the effects of the graded properties on their crashworthiness. Those advanced energy-absorbing structures and materials include primarily thin-walled structures with variable diameter/width/wall thickness/strength, cellular materials with variable density and their filling structures, and other hybrid structures with multiple graded properties. It demonstrates that thin-walled structures and cellular materials could exhibit more efficient and effective energy-absorbing performance by introducing graded properties. Additionally, some advanced manufacturing and modeling technologies such as the 3D printing, multi-scale computation, etc. provide a much wider and more feasible conceptual design for graded structures and materials.
TL;DR: An autoencoder based framework for structural damage identification, which can support deep neural networks and be utilized to obtain optimal solutions for pattern recognition problems of highly non-linear nature, such as learning a mapping between the vibration characteristics and structural damage.
Abstract: Artificial neural networks are computational approaches based on machine learning to learn and make predictions based on data, and have been applied successfully in diverse applications including structural health monitoring in civil engineering. It is difficult to optimize the weights in the neural networks that have multiple hidden layers due to the vanishing gradient issue. This paper proposes an autoencoder based framework for structural damage identification, which can support deep neural networks and be utilized to obtain optimal solutions for pattern recognition problems of highly non-linear nature, such as learning a mapping between the vibration characteristics and structural damage. Two main components are defined in the proposed framework, namely, dimensionality reduction and relationship learning. The first component is to reduce the dimensionality of the original input vector while preserving the required necessary information, and the second component is to perform the relationship learning between the features with the reduced dimensionality and the stiffness reduction parameters of the structure. Vibration characteristics, such as natural frequencies and mode shapes, are used as the input and the structural damage are considered as the output vector. A pre-training scheme is performed to train the hidden layers in the autoencoders layer by layer, and fine tuning is conducted to optimize the whole network. Numerical and experimental investigations on steel frame structures are conducted to demonstrate the accuracy and efficiency of the proposed framework, comparing with the traditional ANN methods.
TL;DR: The efficiency of various machine learning techniques is evaluated using extensive experimental data from 536 experimental tests, and it has been seen from the comparison that lasso regression has a better efficiency and reasonable accuracy in the classification and prediction.
Abstract: Beam-column joints are one of critical components that control the oveerall performance of reinforced concrete building frames under seismic loadings. To identify the response mechanism, including the classification of failure mode and the prediction of associated shear strength, of beam-column joints, this paper introduces the application of machine learning techniques. The efficiency of various machine learning techniques is evaluated using extensive experimental data from 536 experimental tests, all of which exhibited either non-ductile joint shear failure prior to beam yielding or ductile joint shear failure after beam yielding. It has been seen from the comparison that lasso regression has a better efficiency and reasonable accuracy in the classification and prediction. The suggested formulations as a function of influential input variables can be easily used by structural engineers to provide an optimal rehabilitation strategy for existing buildings and to design new structures.
TL;DR: A multi-parameter fragility methodology using artificial neural network to generate bridge-specific fragility curves without grouping the bridge classes is suggested.
Abstract: Recent researches are directed towards the regional seismic risk assessment of structures based on a bridge inventory analysis. The framework for traditional regional risk assessments consists of grouping the bridge classes and generating fragility relationships for each bridge class. However, identifying the bridge attributes that dictate the statistically different performances of bridges is often challenging. These attributes also vary depending on the demand parameter under consideration. This paper suggests a multi-parameter fragility methodology using artificial neural network to generate bridge-specific fragility curves without grouping the bridge classes. The proposed methodology helps identify the relative importance of each uncertain parameter on the fragility curves. Results from the case study of skewed box-girder bridges reveal that the ground motion intensity measure, span length, and column longitudinal reinforcement ratio have a significant influence on the seismic fragility of this bridge class.
TL;DR: This study summarises a part of the activities conducted by the Working Group 2 of COST Action FP1402, by presenting an in-depth review of the research works that have analysed the seismic behaviour of CLT structural systems.
Abstract: Cross-Laminated Timber (CLT) structures exhibit satisfactory performance under seismic conditions. This is possible because of the high strength-to-weight ratio and in-plane stiffness of the CLT panels, and the capacity of connections to resist the loads with ductile deformations and limited impairment of strength. This study summarises a part of the activities conducted by the Working Group 2 of COST Action FP1402, by presenting an in-depth review of the research works that have analysed the seismic behaviour of CLT structural systems. The first part of the paper discusses the outcomes of the testing programmes carried out in the last fifteen years and describes the modelling strategies recommended in the literature. The second part of the paper introduces the q-behaviour factor of CLT structures and provides capacity-based principles for their seismic design.
TL;DR: In this article, the authors present the test results of an experimental study consisting of nine large-scale rectangular reinforced concrete columns, including eight FRP-confined RC columns and one RC column without FRP jacketing as the control specimen, tested under axial compression.
Abstract: Fiber-reinforced polymer (FRP) jacketing has become an attractive technique for strengthening/retrofitting reinforced concrete (RC) columns. Extensive research has been conducted on FRP-confined rectangular columns under axial compression, leading to a significant number of stress-strain models for FRP-confined concrete in these columns. However, most of these models have been developed based on test results of small-scale columns, so their applicability to large FRP-confined rectangular RC columns has yet to be properly validated. To this end, the present paper first presents the test results of an experimental study consisting of nine large-scale rectangular RC columns, including eight FRP-confined RC columns and one RC column without FRP jacketing as the control specimen, tested under axial compression. The experimental program examined the sectional corner radius and the FRP jacket thickness as the key test variables. Five representative design-oriented stress-strain models for FRP-confined concrete in rectangular columns, identified from critical reviews of the existing literature, are then assessed using the test results to examine their validity for these large-scale columns.
TL;DR: In this paper, the authors used a numerical model verified against some experimental testing data to investigate the dynamic responses and failure modes of reinforced concrete bridge columns under vehicle collision and showed that the peak impact force from the collision is governed by the vehicle engine and the vehicle velocity while the impulse of the impact force is influenced by the initial momentum of the total mass.
Abstract: The dynamic responses and failure modes of reinforced concrete bridge columns under vehicle collision have been numerically investigated in this study by using a numerical model verified against some experimental testing data. The numerical results show that the Peak Impact Force (PIF) from the collision is governed by the vehicle engine and the vehicle velocity while the impulse of the impact force is influenced by the initial momentum of the total mass. It is, therefore, suggested that not only the total vehicle mass and the vehicle velocity but also the engine’s weight need to be considered to determine the impact force on structures under vehicle collision. The engine’s mass significantly affects the peak impact force, the moment, the shear force and thus the damage of the column. The lateral impact force considerably affects the column axial force and a relation between the PIF and the increase of the axial force is proposed for the design purpose. The numerical model is able to reproduce and provide an explanation of most of the common failure modes observed in real impact events including flexural failure, shear failure, and punching shear damage. In addition, the influences of four different methods of the superstructure modelling, i.e. uniformly distributed load, lumped mass, simplified beam model, and 3D detailed model on the behaviour of the bridge column under vehicle impact are also investigated.
TL;DR: In this article, an experimental investigation on the seismic behavior of a novel steel-concrete composite beam-to-column connections reinforced by outer-annular-stiffener is presented.
Abstract: This paper presents an experimental investigation on the seismic behavior of a novel steel-concrete composite beam-to-column connections reinforced by outer-annular-stiffener. This type of connection consists of beams with varying depths in opposite sides, and a concrete filled steel tubular (CFST) column. Four cruciform connection specimens with varying beam depth ratios (1, 0.75 and 0.5) were tested under monotonic and cyclic loading protocols to investigate shear capacity, hysteretic behavior, deformation capacity and failure modes within the irregular joint panel zone. From the test results, two types of failure modes were identified as global shear failure occurred in the panel zones 1 and 2 on the side of large depth beam when subjected to positive loading direction, and partial shear failure only in the panel zone 1 under the negative loading direction. The global shear failure was characterized by plastic deformation in the panel zones 1 and 2 prior to out-of-plane instability arose in the column flange near the outer-annular-stiffener. On the other hand, shear failure of panel zone under negative direction loading, the deformation of steel part was similar to that under the positive loading direction. While, the concrete panel zone located in the web of column only connecting with small depth beam, showed an arch mechanism. There was no fatigue fracture throughout the test, and all the specimens behaved in a ductile manner. All the tested specimens demonstrated good plastic deformation and energy dissipation capacity.
TL;DR: In this paper, the seismic behavior of the beam-column connections in concrete frame is studied, including five precast specimens and one cast-in-place specimen, and the results reveal that the seismic performance of the precast connection is similar to that of the cast in-place connection, but the distribution of cracks, the strain of reinforcements and the deformation of joint are different.
Abstract: The seismic behavior of the beam-column connections in concrete frame is studied in this paper, including five precast specimens and one cast-in-place specimen. For the precast specimens, the column, joint and part of the beam away from the joint are prefabricated, while the part of beam close to the joint is cast-in-place. The rebar is connected by grout sleeve. The specimens were tested under low-reversed cyclic loading, and were evaluated in terms of failure mode, skeleton curves, stiffness, energy dissipation, and drift capacity. Differences in seismic performance between these specimens were also revealed. From the test results, the seismic performance of the precast connection is similar to that of the cast-in-place connection. However, the distribution of cracks, the strain of reinforcements and the deformation of joint are different. The strength ratio between column and beam is an important factor on the failure mode of the precast connections. For precast connection, the seismic behavior of the plastic hinge as well as the core region of the joint are clearly affected by the grout sleeve, the cast-in-place region and the rebar hole. Also in the core region of the joint, slippage of longitudinal rebar is observed.
TL;DR: In this paper, the geometrically nonlinear harmonically excited vibration of third-order shear deformable functionally graded graphene platelet-reinforced composite (FG-GPLRC) rectangular plates with different edge conditions is examined.
Abstract: The geometrically nonlinear harmonically excited vibration of third-order shear deformable functionally graded graphene platelet-reinforced composite (FG-GPLRC) rectangular plates with different edge conditions is examined. The considered plate with N L -layers is made from a mixture of an isotropic polymer matrix and graphene platelets (GPLs) in each layer. The weight fraction of GPLs changes in a layer-wise manner. The modified Halpin-Tsai model and rule of mixture are utilized to compute the effective material properties of FG-GPLRCs. To mathematically model the vibrations of FG-GPLRC plates, the displacement field, strain tensor and constitutive relations as well as the energy functional of system including strain and kinetic energies and external work are represented in matrix forms as a function of the displacement components. Then, by simultaneous use of Hamilton’s principle and an efficient numerical scheme namely, the variational differential quadrature (VDQ) technique, the weak form of discretized nonlinear equations of motion is obtained. The present model includes the influences of geometric nonlinearity, rotary inertia and transverse shear deformation. Furthermore, a multistep numerical approach based on the Galerkin method, time periodic discretization method and pseudo arc-length continuation technique in conjunction with the modified Newton-Raphson method is employed to solve the problem of nonlinear harmonically excited vibration of FG-GPLRC rectangular plates. Results are plotted in the form of frequency-response and force-response curves to indicate the effect of various parameters such as GPL distribution pattern, weight fraction, geometry of GPL nanofillers and boundary constraints of FG-GPLRC plates.
TL;DR: In this paper, an existing dilation model for concrete-filled FRP wraps is combined with a biaxial stress analysis of the FRP tube so that the effect of the Poisson's ratio of the tube is properly accounted for.
Abstract: The use of FRP with seawater and sea sand concrete (SWSSC) holds great potential for marine and coastal infrastructure, and concrete-filled FRP tubular columns are among the attractive forms of structural members for such applications. This paper presents a theoretical model for the compressive behaviour of seawater and sea sand concrete-filled circular FRP tubular stub columns. FRP tubes can be manufactured to possess considerable strength and stiffness in the longitudinal direction, so the behaviour of concrete-filled FRP tubes differed substantially from that of concrete columns with an FRP wrap (also referred to as “concrete-filled FRP wraps”) which commonly contains fibres only in the hoop direction. Many theoretical models have been proposed for concrete-filled FRP wraps, but very limited work has been conducted on the theoretical modelling of concrete-filled FRP tubes. In the present study, an existing dilation model for concrete-filled FRP wraps is combined with a biaxial stress analysis of the FRP tube so that the effect of the Poisson’s ratio of the FRP tube is properly accounted for. In order to predict the buckling of the FRP tube, a maximum strain buckling failure criterion is proposed and is shown to be in reasonable agreement with the experimental results. Moreover, the load carried by the FRP tube is studied, and a simplified model is proposed to determine the load shared by the FRP tube during the entire loading process. Finally, a theoretical model for SWSSC-filled FRP tubular columns is proposed, in which the behaviour of both the concrete and the FRP tube as well as their interactions are explicitly modelled (i.e., an analysis-oriented model). The proposed model gives reasonably close predictions of the existing experimental data.
TL;DR: Numerical simulations of the application of inerter to a barge-type floating offshore wind turbine for the purpose of mitigating loads of the wind turbine structures induced by wind and wave show that the overall performance can be improved, except the tower-top fore-aft load and the TMD working space.
Abstract: This paper investigates the application of inerter to a barge-type floating offshore wind turbine for the purpose of mitigating loads of the wind turbine structures induced by wind and wave. An inerter-based structural control system, consisting of a parallel connection of a spring, a damper, and an inerter-based network, is proposed. A nonlinear aeroelastic simulation tool for wind turbines called FAST-SC is employed for evaluating the performances of the inerter-based structural control system. Due to the inefficiency of implementing FAST-SC in optimizing the element parameters (spring stiffnesses, damping coefficients, inertances), a time-efficient parameter optimization method is proposed based on a simplified linear design model, where a mixed performance objective function including the tower-top fore-aft deflection and the TMD working space is minimized with respect to the element parameters. It is shown that there exists a tradeoff between the tower-top fore-aft deflection and the TMD working space. Moreover, numerical simulations based on the nonlinear FAST-SC code show that the overall performance can be improved by using an inerter, except the tower-top fore-aft load and the TMD working space. The inerter-based configurations tend to demand more TMD working space than the system with no inerter. Furthermore, it is demonstrated that the overall performance can be improved while maintaining similar TMD working space as the system with no inerter.
TL;DR: In this paper, the feasibility of using the ultra-high ductility cementitious composites (UHDCC) for construction without steel reinforcement, the mechanical properties of UHDCC was experimentally tested at material, structural member and structure levels.
Abstract: To verify the feasibility of using the ultra-high ductility cementitious composites (UHDCC) for construction without steel reinforcement, the mechanical properties of UHDCC was experimentally tested at material, structural member and structure levels. The tensile strength of UHDCC was from 5 MPa to 20 MPa, the average tensile strain capacity was 8% with the maximum value up to 12%. Four-point bending tests demonstrated that the plain UHDCC beams can match the loading capacity of conventional reinforced concrete beams with the steel reinforcement ratio of 0.5–1.5%. The deflection-span ratio of all the plain UHDCC beams exceeded 1/50 at the peak load. The eccentric compressive loading tests showed that the loading capacity of plain UHDCC column was close to that of RC column with a steel ratio of 0.8%. Additionally, shaking table tests were implemented on a RC frame (steel reinforcement ratios of columns were about 2.0%) and a plain UHDCC frame. The UHDCC frame survived 3 kinds of earthquakes with the peak ground acceleration from 0.105 g to 1.178 g, and exhibited excellent inter-story drift control under extremely strong earthquakes. The performance of the UHDCC frame fulfilled the requirements of various seismic codes. The feasibility of non-steel reinforced UHDCC structure was preliminarily confirmed by this study.
TL;DR: In this paper, a study on long-term properties of concretes manufactured with recycled aggregates of different parent concrete strengths was presented to establish the longterm compressive strength, elastic modulus, splitting tensile strength, workability, drying shrinkage, and creep of each batch.
Abstract: It is now accepted that replacement of natural aggregates in concrete with recycled concrete aggregates obtained from construction and demolition waste is a promising technology to conserve natural resources and reduce the environmental impact of concrete. This paper presents a study on long-term properties of concretes manufactured with recycled aggregates of different parent concrete strengths. A total of six batches of recycled aggregate concretes (RACs) were manufactured. Tests were undertaken to establish the long-term compressive strength, elastic modulus, splitting tensile strength, workability, drying shrinkage, and creep of each batch. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) characterizations were performed to explain the mechanisms behind the observed time-dependent and mechanical properties of RACs. Test parameters comprised the replacement ratio and parent concrete strength of the recycled aggregates used in the preparation of the new concrete mixes. The results indicate that the parent concrete strength of the recycled aggregates significantly affects the time-dependent and long-term mechanical properties of RACs. It is shown that concrete mixes containing lower strength recycled concrete aggregates develop lower mechanical properties and higher shrinkage strain and creep deformation compared to mixes prepared with higher strength recycled concrete aggregates. Normal-strength RAC mixes containing higher strength recycled concrete aggregates develop slightly lower splitting tensile strength at all curing ages but similar compressive strength and elastic modulus in longer term (i.e. over 90 days) compared to those of the control mix. It is also shown that high-strength RACs, prepared with full replacement of natural aggregates with recycled concrete aggregates having a higher parent concrete strength, exhibit time-dependent and long-term mechanical properties that are similar to or better than those of companion natural aggregate concretes.
TL;DR: In this paper, the in-plane experimental response of external masonry infills constructed with tongue and groove clay units has been studied, with particular attention devoted to the infill performance, the related damage distribution, the lateral stiffness, strength and dissipation capacity and a possible definition of performance limit states.
Abstract: In line with the current European building practice, clay masonry infills are commonly adopted for the construction of enclosures and partitions in RC frame structures. In order to improve further the understanding of the seismic response of masonry infills in newly designed RC structures, within the scope of a systematic numerical and experimental research program, the in-plane experimental response of external masonry infills constructed with tongue and groove clay units has been studied. Particular attention has been devoted to the infill performance, the related damage distribution, the lateral stiffness, strength and dissipation capacity and a possible definition of performance limit states for future developments in the current design approach. This paper reports the framework and discusses the results of in-plane static cyclic tests on full-scale, single-storey, single-bay RC frame specimens with strong masonry infills with and without opening designed following European seismic design provisions, carried out at the laboratory of the Department of Civil Engineering and Architecture of the University of Pavia. Based on the observations during the tests, drift levels at the different limit states have been evaluated, with the attainment of large values for the solid specimen (0.30%, 0.50% and 1.75% at the operation, damage limitation and ultimate limit state, respectively), but lower performance for the panel with opening. The experimentally obtained lateral stiffness and strength have been compared with the results of some of the most common analytical models based on single diagonal equivalent strut, underlining the formulations that better fit the test outcomes.
TL;DR: The most significant conclusion of the investigation is that the ANNs can reliably approach the seismic damage state of r/c buildings in real time after an earthquake.
Abstract: The present paper deals with the investigation of the ability of Artificial Neural Networks (ANN) to reliably predict the r/c buildings’ seismic damage state. In this investigation, the problem was formulated as a problem of approximation of an unknown function as well as a pattern recognition problem. In both cases, Multilayer Feedforward Perceptron networks were used. For the creation of the ANNs’ training data set, 30 r/c buildings with different structural characteristics, which were subjected to 65 actual ground motions, were selected. These buildings were subjected to Nonlinear Time History Analyses. These analyses led to the calculation of the buildings’ damage indices expressed in terms of the Maximum Interstorey Drift Ratio. The influence of several configuration parameters of ANNs to the level of the predictions’ reliability was also investigated. In order to investigate the generalization ability of the trained networks, three scenarios were considered. In the framework of these scenarios, the ANNs’ seismic damage state predictions were evaluated for buildings subjected to earthquakes, neither of which are included to the training data set. The most significant conclusion of the investigation is that the ANNs can reliably approach the seismic damage state of r/c buildings in real time after an earthquake.
TL;DR: The FE results show that both AISC and European design procedures can guarantee the formation of a plastic hinge in the beam under cyclic loading and that under column loss scenarios the European connections are more ductile than those designed according to both Aisc 358-16 and AISC 341-16.
Abstract: Extended stiffened end-plate bolted joints are widely used in seismic resistant steel frames. In the United States of America (USA) this type of joint is seismically pre-qualified according to AISC 358-16. At the present time, prequalification criteria for different types of bolted joints are also under development in Europe within the framework of the EQUALJOINTS (i.e. European pre-QUALified steel JOINTS) research project. The design criteria and detailing rules proposed by this European project for extended stiffened end-plate joints differ from AISC criteria in some respects. Therefore, the aim of this work is to verify and to compare the effectiveness of both design procedures through the results of a comprehensive parametric study based on finite element (FE) simulations. The FE results show that both AISC and European design procedures can guarantee the formation of a plastic hinge in the beam under cyclic loading. However, under column loss scenarios the European connections are more ductile than those designed according to both AISC 358-16 and AISC 341-16. In addition, it is investigated the possibility to use heavy columns satisfying the resistance requirements without stiffeners (i.e. continuity plates and supplementary web plates). The comparison between the response of the joints with and without stiffened columns shows that heavy unstiffened columns can be adopted without appreciably modifying the joint response.
TL;DR: In this paper, a finite element method (FEM) analysis framework is introduced for the free and forced vibration analyses of functionally graded porous (FGP) beam type structures, where both Euler-Bernoulli and Timoshenko beam theories have been adopted such that the explicit stiffness and mass matrices for 2-D FGP beam element through both beam theories are explicitly expressed.
Abstract: A finite element method (FEM) analysis framework is introduced for the free and forced vibration analyses of functionally graded porous (FGP) beam type structures. Within the proposed computational scheme, both Euler-Bernoulli and Timoshenko beam theories have been adopted such that the explicit stiffness and mass matrices for 2-D FGP beam element through both beam theories are explicitly expressed. Both Young’s modulus and material density of the FGP beam element are simultaneously considered as grading through the thickness of the beam. The material constitutive law of a FGP beam is governed by the typical open-cell metal foam. Furthermore, the damping effects of the FGP structures can be also incorporated within the proposed FEM analysis framework through the Rayleigh damping model. Consequently, the proposed approach establishes a more unified analysis framework which can investigate simple FGP beams as well as complex FGP structural systems involving mixture of different materials. In order to demonstrate the applicability, accuracy, as well as the efficiency of the proposed computational scheme, both FGP beams and frame structures with multiple porosities have been rigorously explored.
TL;DR: A Modified Cornwell Indicator (MCI) is proposed that performs more efficient in damage detection than the standard Corn well indicator (CI) and is combined with Genetic Algorithm for further quantification of the detected damage.
Abstract: This paper presents a new methodology for damage identification and quantification in two- and three-dimensional structures. The application of the proposed methodology is investigated numerically using Finite Element Method (FEM) and Matlab program. We propose a Modified Cornwell Indicator (MCI) that performs more efficient in damage detection than the standard Cornwell Indicator (CI). Furthermore, MCI is combined with Genetic Algorithm (GA) for further quantification of the detected damage. In GA, MCI, is used as an objective function to compare between measured and calculated indicators. The results of the analysis show that the proposed technique is accurate and efficient, when compared with other techniques in the literature, to estimate the severity of structural damage.
TL;DR: In this paper, the structural responses of steel moment resisting and self-centring braced frames under pulse-like near-fault earthquakes are analyzed. And the influence of varying brace properties on the key engineering demand parameters such as maximum inter-storey drift (MID), residual inter-boardy drift and peak absolute floor acceleration (PA) is revealed.
Abstract: This paper presents the behaviour of steel moment resisting and braced frames under pulse-like near-fault earthquakes. The key properties for characterizing near-fault ground motions with forward directivity and fling step effects are discussed, and the influence of varying brace properties on the key engineering demand parameters such as maximum inter-storey drift (MID), residual inter-storey drift (RID) and peak absolute floor acceleration (PA) is revealed. Among other findings, it is shown that the structural responses are related to spectral accelerations, PGV/PGA ratios, and the pulse period of near-fault ground motions. The moment resisting and self-centring braced frames (MRFs and SC-BRBFs) generally have comparable MID levels, while the buckling-restrained braced frames (BRBFs) tend to exhibit lower MIDs. Increasing the post-yield stiffness of the braces decreases the MID response. The SC-BRBFs generally have mean residual drifts less than 0.2% under all the considered ground motions. However, much larger RIDs are induced for the MRFs/BRBFs under the near-fault ground motions, suggesting that these structures may not be economically repairable after the earthquakes. From a non-structural performance point of view, the SC-BRBFs show much higher PA levels compared with the other structures. A good balance among the MID, RID, and PA responses can be achieved when “partial” SC-BRBs are used. To facilitate performance-based design, RID prediction models are finally proposed which enable an effective evaluation of the relationship between MID and RID.
TL;DR: In this paper, a machine-learning based condition assessment method for stay cables by using the monitored cable tension force was proposed, which is based on the correlation of cable tension response between cable pairs (defined as the two cables at the upriver side and the opposite downriver side in the double cable planes).
Abstract: The stay cables are one of most critical elements for cable-stayed bridges. This paper proposes a machine-learning based condition assessment method for stay cables by using the monitored cable tension force. First, based on the correlation of cable tension response between cable pairs (defined as the two cables at the upriver side and the opposite downriver side in the double cable planes), cable tension ratio is extracted as the feature variable, and the cable tension ratio is defined as the ratio of vehicle-induced cable tension between a cable pair. It is found that cable tension ratio is only related with cable properties and the transverse position of a vehicle over the deck. Vehicles on the bridge naturally cluster themselves into a few clusters that correspond to the traffic lanes, i.e. the vehicles in one lane form a cluster. Consequently, the vehicle-induced cable tension ratio forms the corresponding clusters or patterns. Gaussian Mixture Model (GMM) is employed for modelling the patterns of cable tension ratio, and each pattern (corresponds to a certain traffic lane) is modelled by a mono-Gaussian distribution. The Gaussian distribution parameters of tension ratio are used as condition indicator of stay cables because they are only related to cable conditions (the information of vehicle transverse location is presented in the number of tension ration patterns). The number of patterns which represents the model complexity are determined by Bayesian Information Criteria (BIC), while other parameters of GMM are estimated by using Expectation-Maximization algorithm under the Maximum Likelihood criteria, based on the monitored cable tension force. The cable condition is then evaluated according to the variation in estimated parameters of GMM. It is noted that pre-process of source separation is conducted to make the cable tension ratio independent from vehicle weight, environmental variant, and possible sensor errors. An FE model analysis is carried out to qualitatively illustrate the principle of the proposed method and physical sense of the cable tension ratio.
TL;DR: A case study application quantifying the EAL and collapse safety for three school buildings representative of the Italian school building stock and a comparison is made with the seismic classification guidelines recently introduced in Italy to provide further insight into how these can be used to identify existing buildings vulnerable to excessive damage and potential collapse during earthquakes.
Abstract: Extensive damage to school buildings has been observed during past earthquakes in Italy and there is a need to better understand their potential vulnerability. As part of a national project to assess seismic risk in Italian schools, a database was compiled in terms of characteristics such as school location and construction typology. This paper examines a number of these buildings considered to be a representative sample of the Italian school building population. To quantify their seismic vulnerability, the induced damage with respect to increased shaking intensity need to be quantified. This characterisation of the building vulnerability, in combination with the seismic hazard, allows more informed, risk-based decisions to be made using performance metrics such as expected annual loss (EAL). This article outlines a case study application quantifying the EAL and collapse safety for three school buildings representative of the Italian school building stock. Detailed numerical models were developed using information collected during in-situ inspections in order to accurately represent the dynamic response of the school structures. To estimate economic losses, a structural and non-structural element inventory was compiled using in-situ survey information. This case study application is conducted in a systematic fashion to clearly illustrate the various details required to implement more advanced seismic assessment studies. Finally, a comparison is made with the seismic classification guidelines recently introduced in Italy to provide further insight into how these can be used to identify existing buildings vulnerable to excessive damage and potential collapse during earthquakes.
TL;DR: In this article, the seismic performance of a sea-crossing cable-stayed bridge is comprehensively evaluated based on the fragility function methodology, and the effect of seawater on the bridge seismic responses is modeled using the hydrodynamic added mass method.
Abstract: As key components in the transportation networks at coastal areas, sea-crossing cable-stayed bridges play a very important role in the development of regional economy. These bridges may be subjected to severe earthquakes during their life-cycles. Owing to the lack of actual seafloor earthquake recordings and approaches in synthesizing offshore seismic motions, the onshore seismic motions are commonly utilized as inputs in the seismic design of sea-crossing cable-stayed bridges. However, this approach may lead to erroneous structural response predictions since the characteristics of onshore and offshore seismic motions are different. In this paper, the seismic performance of a sea-crossing cable-stayed bridge is comprehensively evaluated based on the fragility function methodology. A novel approach is presented to theoretically calculate the ground motion transfer function at any location within an offshore site and stochastically synthesize the offshore multi-support ground motions at different depths (MGMDDs). The OpenSees analysis platform is employed to develop the three-dimensional finite element model of the example bridge, in which the p-y, t-z and q-z elements are installed at the pile nodes to simulate the interaction between the bridge piles and surrounding soils. Moreover, the effect of seawater on the bridge seismic responses is modeled using the hydrodynamic added mass method. The seismic fragility curves of the example bridge are generated by using the synthesized MGMDDs as inputs. The influences of spatial and depth varying offshore seismic motions, soil-structure interaction (SSI) and seawater added mass on the bridge component and system fragilities are investigated and discussed. Numerical results show that the seismic fragility of the example sea-crossing cable-stayed bridge is affected by the above mentioned influencing factors with different extents. The proposed approach can rationally and effectively assess the seismic fragilities of sea-crossing cable-stayed bridges.
TL;DR: Tests on seven full-scaled tee-shape connections made of hollow structural section (HSS) members were conducted under monotonic and cyclic load, indicating that the proposed connection can be classified as “semi-rigid” connection and will provide useful references for expanding the application of MSCs.
Abstract: Attributable to the superiority in construction speed and quality, modular steel constructions (MSCs) have been increasingly used for mid-to-high rise buildings with repetitive units. An architecturally pleasing bolted connection with welded cover plate was proposed in this paper to settle the current research limit. Tests on seven full-scaled tee-shape connections made of hollow structural section (HSS) members were conducted under monotonic and cyclic load. The results indicated that all the specimens under monotonic load were capable of developing the full plastic strength of the twin-beams. The twin-beams were found to have individual bending behavior. The current seismic design code GB 50011-2010 and AISC 341-10 were used to evaluate the seismic performance and verify the applicability for seismic design of the proposed connection, demonstrating the satisfactory deformation capacity and ductility. Furthermore, EC3 Part 1–8 was adopted to evaluate the stiffness characteristic of the proposed connection, indicating that the proposed connection can be classified as “semi-rigid” connection. In addition, the design consideration was recommended to predict the bending capacity of the proposed connection. The presented research work will provide useful references for expanding the application of MSCs.
TL;DR: In this article, the impact resistances of UHPFRC-strengthened columns were extensively investigated using the appropriate simplified model, and three different simplified models, as published in current studies, were investigated to replace the whole bridge model.
Abstract: Bridge columns made of normal concrete are evidenced to be susceptible to vehicle collisions. Particularly in the United States, vehicle collision has become one of the primary causes of bridge failures. This is largely due to the low crashworthiness of a conventional reinforced concrete (RC) column. Ultra-high-performance fiber-reinforced concrete (UHPFRC) as one of advanced concrete materials has been experimentally demonstrated to possess excellent strength, durability, impact resistance and energy-absorbing capacity. Accordingly, one type of UHPFRC-strengthened columns was proposed in this study as an alternative to RC columns that may be at risk for vehicle collision incidents. High-resolution finite element (FE) models were developed to investigate the performance of UHPFRC-strengthened columns subjected to vehicle collisions. In the high-resolution FE model, a three-span simply-supported girder bridge (including girder, pier column, column cap, bearing, etc.) was adopted and modelled. Material models regarding normal concrete and UHPFRC as well as the vehicle model were carefully calibrated by experimental data. The influence of initial gravity loads on impact responses was found to be pronounced, and a damping-based method was proposed to efficiently exert permanent loads on pier columns prior to a collision. Three different simplified models, as published in current studies, were investigated to replace the whole bridge model. Two single-column models with different boundaries were shown to have low accuracy. The pier-bent model considering the superstructure gravity was demonstrated as capable of predicting collision-induced responses that are in good agreement with the high-resolution FE model. The impact resistances of both RC and UHPFRC-strengthened columns were extensively investigated using the appropriate simplified model. The crashworthiness of UHPFRC-strengthened column was found to be considerably superior to that of RC column. An extensive parametric study was performed using response surface methodology to explore the influences of reinforcement ratios, thickness of UHPFRC jacket, UHPFRC strength and initial impact speed. The impact-resistant performance is mostly sensitive to changes in the thickness of UHPFRC jacket when the impact speed is not very high. On the contrary, the residual capacity of the bridge column is hardly increased by thickening UHPFRC jacket. In addition, the developed response surface models provided easy estimation of impact-induced responses of an UHPFRC-strengthened column, which have potential use as the surrogates of time-consuming FE simulations to efficiently examine the reliability and optimization of bridge columns under impact loadings.
TL;DR: In this paper, the impact responses of UHPC targets with 3 volumetric% ultra-high molecular weight polyethylene (UHMWPE) fibres and UHMC targets with steel fibres are experimentally investigated subjected to high-velocity projectile penetration, and plain concrete targets under the same loading scenarios are also tested as control specimens for comparative purpose.
Abstract: Ultra-high performance concrete (UHPC) which is known for high strength, high toughness, excellent ductility and good energy absorption capacity can be adopted as an ideal material in the impact resistant design of structures. In the present study, impact responses of UHPC targets with 3 vol-% ultra-high molecular weight polyethylene (UHMWPE) fibres and UHPC targets with 3 vol-% steel fibres are experimentally investigated subjected to high-velocity projectile penetration, and plain concrete targets under the same loading scenarios are also tested as control specimens for comparative purpose. In addition, numerical studies are conducted to simulate the projectile penetration process into UHPC targets with the assistance of a computer program LS-DYNA. The numerical results in terms of the depth of penetration (DOP) and crater diameter as well as projectile abrasions and damages are compared with the experimental results. Moreover, DOPs of these two types of UHPC targets obtained from tests are compared with the previously proposed empirical model.