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A bounded stochastic optimal semi-active control strategy for random excited hysteretic systems by using MR damper is proposed and illustrated by an example of a single degree-of-freedom hysteretic system. First, the dynamics of MR damper and the hysteretic force are expressed by using the Bouc-Wen model. Then, the system is converted into an equivalent nonlinear non-hysteretic stochastic system, from which the optimal bounded semi-active control law consisting of optimal unbounded control and bang-bang control is derived by using stochastic averaging method and stochastic dynamical programming principle. Finally, the response of optimally controlled system is predicted from solving the Fokker-Planck-Kolmogorov (FPK) equation associated with the fully averaged Itô equation. Numerical results show that the proposed control strategy has high control effectiveness and efficiency. [ABSTRACT FROM AUTHOR]

Double-I built-up columns are used extensively in low and medium rise steel structures. These sections have inherent compression, torsion and bending strength in all directions. The open sides of this type of column are covered with plates. When I beams are connected to double-I built-up columns through the column cover plate, the load transfer at the joint becomes a disturbing problem. To modify the connection, the authors propose a special type of connection using side plates. In this method the end of a beam is connected to the column by full depth side plates instead of direct welding of the beam ends to the column. The new geometry eliminates the traditional welded connection between the end of the beam and the face of the column. A series of eight non-linear, three dimensional finite elements models were developed to study the behaviour of the connection under cyclic loadings. The results obtained from the numerical analyses indicate that the proposed connection geometry has sufficient strength and ductility to be applied in 'special moment frames (SMF)' as a 'full strength' connection. [ABSTRACT FROM AUTHOR]

This paper shows current trends in testing and numerical analysis of dynamic loading in relation to a real frame foundation for a turbogenerator set. The analysis of the machine's foundations, which are subjected to static and dynamic loads, is a complex problem combining the issues of geotechnics, structural engineering, and vibration theory. The authors present a case study of the assessment of the foundation's technical condition. The main objective of this study is to perform and compare experimental and numerical dynamic analysis which includes the measurement of the acceleration, speed, and amplitude of the natural vibrations of the foundation during the operational speed of the turbogenerator. In addition, auxiliary material tests were carried out to fully diagnose the foundation and obtain the material properties required for the numerical analysis. They included both destructive and non-destructive of concrete strength, the evaluation of the degree of its carbonation, and the scanning of the reinforcement distribution. The research presented in the paper is intended to facilitate the preparation of appropriate data for the design of the foundation renovation and strengthening. [ABSTRACT FROM AUTHOR]

Welded tubular joints are integral components in various engineering structures, subject to cyclic loading conditions throughout their operational lifespan. This paper investigates the evolution of welding residual stresses within the CHS X-joint and CHS double K-joint under cyclic loading, shedding light on their intricate behavior and potential implications for structural integrity. The advanced XRD experimental technique enables the characterization and monitoring of residual stress variations over multiple loading cycles. Assisted by the non-destructive XRD measurements, this study validates the optimization-improved thermal-mechanical simulation method for predicting not only the as-welded residual stresses in the tubular joints but also the residual stress evolutions during the cyclic loading tests. The most pronounced relaxation of peak residual stresses in the tubular joints occurs within the first cycle and then maintains a relatively stable magnitude in subsequent cycles. The findings of this research contribute to the enhancement of structural reliability and serve as a foundation for mitigating the adverse effects of welding residual stresses in welded tubular joints under cyclic loading scenarios. • This paper reports the experimentally measured residual stress during cyclic loads. • The residual stresses in both X and DK CHS joints relax significantly within 1st cycle. • Numerical analyses predict closely the evolution of residual stresses under cyclic actions. [ABSTRACT FROM AUTHOR]

Laboratory research of wood–CFRP (carbon fiber reinforced polymer) structural elements, especially beams, is a scientific issue undertaken by many scientists. Research is often complemented with numerical analysis with the use of complex finite element method (FEM) models. Modern FEM software offers models that can reproduce such properties and phenomena as orthotropy and plasticity of wood and CFRP, delamination and mechanical behavior of adhesive layers, and damage of a strengthened element. The author of the paper reproduces numerical laboratory research of a four-point bending test of a glulam beam strengthened with CFRP tape. The main goal of the numerical research is an analysis of how the complexity of the FEM model influences the results of calculations, especially stress, deflection, and bearing capacity of the glulam beam. In some cases, a simpler model can be satisfactory, especially for a structural engineer, who takes into account serviceability limit states (permissible deflection of a structural member) and assumes that stress should not exceed the yield stress of timber. [ABSTRACT FROM AUTHOR]

In nature, soil layers possess large variability during their geological process. This variability may also lead to differences in the location and thickness of nonliquefiable and liquefiable soil layers. In practice, the impact of liquefaction on the pile can be ignored at depths greater than 20 m due to high confining stress levels and a lack of liquefaction triggering data. On the other hand, this approach may underestimate design loads in many cases, especially in deep-seated and embedded engineering structures. This paper presents the bending response of piles installed through liquefiable layers located at depths beyond 20 m, and parametric analysis was conducted for a wide range of liquefiable layer thicknesses and depths by using OpenSeesPL (version 3.0.2) software. The numerical results were evaluated considering the inelastic concrete pile behavior under different earthquake records and different peak ground accelerations. The findings show that liquefaction can lead to a failure of piles even at depths greater than 20 m, and thus, a design consideration of piles may require a more comprehensive view considering the liquefiable layer depth and thickness effect. [ABSTRACT FROM AUTHOR]

As one kind of jacketed vessels, half‐pipe jacketed vessels are widely used in engineering owing to the structural and heat transfer advantages. But for the design of half‐pipe jacketed vessels, there are limitations in codes ASME VIII‐1 and ASME VIII‐2. In this paper, a new design method based on numerical limit‐load analysis is proposed to design half‐pipe jacketed vessels. The scheme and advantages of the method are presented through a design of half‐pipe jacketed vessel. It is found that by performing limit‐load analysis, problems of the codes ASME VIII‐1 and ASME VIII‐2 about the structural limitation of the half‐pipe jacketed vessels and loading limitation are solved. In addition, by performing limit‐load and parametric analysis, the strength weakness areas on the vessels can be found, and the rational strength design of a structure can be achieved. [ABSTRACT FROM AUTHOR]

This paper provides a simplified design approach for estimating the lateral–torsional buckling (LTB) strength of the pultruded glass fiber-reinforced polymer (GFRP) composite I-beams. A detailed finite element (FE) model based on ABAQUS incorporating more realistic parameters for pultruded GFRP I-beam is developed and verified against the test results available in the relevant literature. After achieving a reliable FE model (through high degree of accuracy in the numerical validation), detailed parametric studies were undertaken by varying the section geometries as well as the span of pultruded I-beams. The selection of the sectional dimensions was based on the composite manuals available in the market, to ensure ease in the practical application of the outcomes of this study. In this analysis, simply supported beam with a uniform bending moment is considered. In accordance with the results of the FE parametric analysis, the accuracy of the theoretical LTB strengths predicted by the equations proposed for pultruded GFRP beams available in the literature is assessed. This comparison indicates that the existing method results in an over-conservative LTB strength estimates for pultruded GFRP I-beams, especially in the low and medium slenderness range. This is primarily due to a comparatively lesser impact of section imperfections on LTB resistance than high slenderness range. Therefore, to address this shortcoming, new simplified design formulations were proposed to have high accuracy of the LTB strength predictions for pultruded GFRP I-beams especially in the low and medium slenderness range. The proposed equations have been provided that might aid the structural engineers in economically designing the pultruded GFRP I-beams in the future. [ABSTRACT FROM AUTHOR]

Aim of the paper is to present a one dimensional simple model for the study of the bond behavior of Fabric Reinforced Cementitious Matrix (FRCM) strengthening systems externally applied to structural substrates. The equilibrium of an infinitesimal portion of the reinforcement and the mortar layers composing the strengthening systems allows to derive the governing equations. An analytical solution is determined solving the system of differential equations. In particular, in the first part of the paper a nonlinear shear-stress slip law characterized by a brittle post-peak behavior with a residual shear strength in the post peak phase is introduced for either the lower reinforcement-mortar interface (approach 1) or both the lower and the upper interface (approach 2). In the latter approach, a calibration of the shear strength of the upper interface is proposed in order to implicitly account for the effect of the damage of the mortar on the bond behavior. In the second part of the paper it is presented the solution of the problem in the case of softening behavior by approximating the shear-stress slip law throughout a step function. Comparisons with experimental data, available in literature, are presented in order to assess the reliability of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper presents a customised beam finite element and analysis formulation for structures in fire, where structures are modelled as skeletal frames, even for composite frames. This provides a simple and fast approach, suitable for design office analyses, with the objective of making structural fire design more accessible for consulting engineers. The methodology proposed has a generic formulation so is suitable for concrete, steel or composite structures. A single, resultant bending and axial stiffness is calculated for a generic cross-section. Stiffnesses are calculated about updated neutral axis positions, which can change during analyses. Thermal effects are applied using resultant pseudo forces. Three case studies are investigated with predicted and experimental deflections showing good correlation. Case Study 1 presents a concrete slab subjected to a standard fire, and deflections predicted by the proposed methodology are between 4.7% and 16.9% different from experimental results, comparable to an advanced modelling system. Two composite beams are considered in Case Study 2. Results for the first composite beam are almost indistinguishable from deflections predicted by a significantly more complicated 3D analysis method in the literature. The runaway failure that occurs during the second composite beam experiment is anticipated by the proposed formulation. In Case Study 3 a full composite floor slab subjected to a real fire is investigated. A novel contribution of the paper is demonstrated in that a slab experiencing tensile membrane action can be modelled using a series of beam elements. Predicted deflections are typically in the order of 12.7% different from experimental results (with both over and under predictions occurring), closer to experimental results than a contemporary full 3D analysis. The aforementioned case studies are carried out using subroutines coupled with a simple, commercially available, finite element program to demonstrate the effectiveness of the approach. [ABSTRACT FROM AUTHOR]

The paper concerns thin-walled corrugated steel profiles used as arched roofing in architectural structures. Corrugation formed on the profile surface when the profiles are shaped affects their rigidity and load capacity. The complicated geometry of a profile surface prevents the creation of an analytical description based on the thin film theory. A loss of stability in this kind of profile is related to the formation of local instabilities in the early stage of local plastic mechanisms development. To that end, it is more relevant to identify the lower limit of load capacity to estimate the overall load capacity of the profile. The results obtained by the numerical calculations demand a thorough analysis of the map of strain, which is difficult because there are no clear quantitative criteria describing the beginning of plasticisation formation. The paper presents a method of analysing the results of numerical calculations based on the identification of a perturbation component of displacement in selected points of the profile. The method is based on a discrete Fourier transform and allows the establishment of an estimation criterion for the lower limit of a profile's load capacity. [ABSTRACT FROM AUTHOR]

The Seismic Microzonation of level 3 (SM3) is nowadays a world-wide accepted tool for the mitigation of seismic risk. The SM3 is a complex process involving different disciplines ranging from Geology and Applied Seismology to Structural and Geotechnical Engineering. The outcome of a SM3 is presented on a zoning map in terms of a selected ground shaking intensity parameter and susceptibility to main ground instability (soil liquefaction, settlements, landslides, fault ruptures). In an advanced SM3 study for a given area, four main interdisciplinary steps can be recognized: (1) definition of the reference input motions, (2) construction of the subsoil model, (3) performing of numerical analyses and computing of amplification factors, (4) identification of zones with different geotechnical hazard potential and drawing up of the SM3 map. After the 2016–2017 Central Italy seismic sequence, intensive studies have been performed to obtain SM3 maps in 137 municipalities most damaged by the earthquakes. The aim of these studies has been to obtain a clear background on site effects to perform a correct reconstruction of the municipalities. In the paper, main results and critical issues of the above-mentioned steps of SM3 procedure are discussed together with some remarks on the use of SM3 output in supporting seismic design for reconstruction. [ABSTRACT FROM AUTHOR]

The paper deals with composite structures in the field of advanced and modern structures in engineering design and according to high specification of composite materials such as high strength to weight ratio use in various industries such as aerospace, marine. One of the most important fields that Researchers have paid less attention to that is to investigate the effect of stacking sequence on the strength of mechanical joints under impact loading. In view of changing the mechanical properties of composite materials by changing the arrangement of layers, in this study, the effect of different orientation of layers on the strength of pin joints in glass-epoxy composites under low-velocity tensile impact has been investigated. Using the Abaqus software and the finite element method, the impact simulation and the force applied to the mechanical joint were analyzed. To evaluate the simulations, the results of the finite element method have been compared with the experimental results. By observing the results, the introduced finite element model is well-considered and is well-matched with the result of the experimental dataset, which made it a valuable tool for predicting the strength of multi-layer composite materials under impact loadings. Using the results of the model, one can analyze the distribution and type of stress and strain in each layer of composite. [ABSTRACT FROM AUTHOR]

The Tensairity principle is a recent concept for lightweight structures. Until now, mainly linear beam elements have been developed and investigated. To broaden the range of Tensairity applications, Tensairity arches are investigated experimentally and numerically. This paper focusses on the validation of the numerical approach for Tensairity arches. The results shows that a good agreement is found between the numerical and experimental approach when the manufacturing imperfections are included in the numerical model. This paper also documents a basic parameter study on the validated numerical model to prove the usefulness and effectiveness of this numerical approach. Finally, the Tensairity arch is up-scaled to spans of 8 m where it is compared to other inflatable arches currently used. These results clearly show the added advantage the Tensairity principle can bring for inflatable arch structures. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a new high-performance, fine-scale damage analysis method using three techniques. Firstly, efficient and detailed mesh discretization is performed via octree, which can easily accomplish cross scale and thus significantly alleviate the burden of fine modelling using octant cubes. Secondly, the introduction of coupled scaled boundary finite element (SBFEs) into FEM can offer more generality, flexibility and conveniences. Thirdly, the parameter matrices (e.g. stiffness, mass, damping) of geometrically similar elements generated by octree are proportionable and can be pre-computed. Therefore, by leveraging the similarity among elements for elasto-plastic problems will significantly improve computational efficiency. In order to demonstrate the effectiveness of the new approach, a fine-scale damage evolution of DaiKai subway was comprehensively modelled using different mesh sizes. Plastic damage and generalized plasticity models for soil and interfaces were used. Results from the case study demonstrated that octree possesses the advantages of high robustness, ability for automation and capacity to work with fewer elements during mesh generation. The coupled SBFEM-FEM and the use of element similarity markedly improved the computation cost (50% computation time was reduced). The presented method bypasses the need for undesired compromise between simulation accuracy and solver efficiency. [ABSTRACT FROM AUTHOR]

The paper presents an effective two-stage approach based on modal strain energy change and Jaya algorithm for damage assessment in plate-like structures. In the first stage, a newly developed damage indicator, named as normalized modal strain energy-based damage index (nMSEBI), is proposed to help locate potential damage elements more effectively. After eliminating most of the healthy elements, the actual damaged sites and its extent in plate structure are determined in the second stage by minimizing an objective function, which is solved using Jaya algorithm. For finding a suitable objective function used in optimization process, two different objective functions are considered to examine their effects on the performance of the utilized optimization algorithm. The efficiency and accuracy of the proposed two-stage damage detection method are investigated by two numerical examples comprising a concrete plate and a four-layer (0°/90°/90°/0°) laminated composite plate with multiple damage locations. All of the obtained results indicate that even under measurement noise, the proposed method can identify the actual damage sites and estimate the extent of damage with high precision. In addition, the numerical results also show that the computational cost of the optimization process using the objective function based on modal flexibility change is much lower than that using the objective function based on mode shapes change. [ABSTRACT FROM AUTHOR]

Highlights • Analysis of RC panels with different transverse reinforcement are presented. • The conventional RC panel with T-bar is used for the purpose of comparison. • Effects of transverse reinforcement arrangement and its ratio are presented. • Efficient design of RC panel is recommended. Abstract The effects of transverse reinforcing rebar on the penetration resistant capacity of the reinforced concrete (RC) panel still remains a challenging problem in the field of civil and structural engineering. In the present paper, we numerically analyze the penetration resistant capacity of three proposed panels with different transverse reinforcing rebar arrangements. The obtained results are then compared with reference solutions derived from the conventional RC panel using T-bars. The components of the RC panel, missile, and support system are fully developed. Material nonlinearity, which considers erosion damage, is employed in this simulation. The IRIS Punching tests are used for validating the numerical modeling of the RC panel subjected to impact loading. Parametric studies with varying transverse reinforcing rebar arrangements and ratios are performed to investigate the penetration response of RC panels. The present numerical result shows that the proposed panels offer a better penetration resistant capacity than that of conventional panels using T-bars. We thus recommend an efficient design of RC panels with a proposed transverse reinforcing rebar arrangement. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a novel numerical form-finding method is presented based on a dynamic relaxation algorithm for cable nets in mesh reflectors. To obtain a shape with high profile efficiency, structural forces are assumed to be constant values during the computational iterations, so a perfectly uniform distribution of structural forces can be achieved. An initial shape, normally not in equilibrium, is given in advance, and nodes of the network are forced to vibrate by the unbalanced forces. Parameters of dynamic relaxation algorithms, such as the type of damping and the time interval, are tested to ensure the speed and stability of the computation process. Finally, two different types of Astromesh reflectors are used as examples to verify the developed method. [ABSTRACT FROM AUTHOR]

In this paper a macro-block model accounting for frictional resistances is presented to assess the lateral strength of a multi-storey masonry block wall. The kinematic approach of limit analysis is used to define the load factor causing the onset of rocking-sliding mechanism under in-plane horizontal loading. A dry frictional contact condition is assumed at the rigid block interfaces, according to the Coulomb's law with non-associated flow rule. The key aspect of the proposed approach is the introduction of a criterion to evaluate the contribution of the actual frictional resistances depending on the inclination angle of the crack line. An accurate assessment of the frictional resistances is also obtained by distinguishing two different contributions (the wall own weight and additional vertical loads) and their application points. Hence, a sensitivity analysis is performed with respect to the overloading condition, the friction coefficient, and geometrical parameters such as the shape ratios of the wall and of the unit block and the number of rows. The analytical results of the proposed model are also validated against results from other existing macro and micro-block modelling approaches in terms of load factor. The comparison confirms the reliability of the proposed model that allows, with similar results, great simplification of the computational effort with respect to micro-block models. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic behaviour of a family of piecewise linear structures, namely the vibration of beams on block-and-tackle suspension system is analysed. The regularity of the vibration modes in one of the linear states induces non-harmonic, yet periodic free vibration modes. The periodicity constraint of the continuous structure is formulated using modal analysis in the regular state. The required number of modes in the finite modal analysis is specified so that the numerical damping caused by the omitted modes does not change the periodic or non-periodic nature of the free vibration of the continuous structure. It is shown, that the application of five excess passive modes allows to draw conclusions about the behaviour of the continuous structure. The periodic behaviour depends on the number and position of the suspension points and the number of the active vibration modes. Analysis of the limits of the periodic behaviour reveals that suspension points close to the middle of the beam, or first few active vibration modes result in periodic vibration of the nonlinear system. [ABSTRACT FROM AUTHOR]

In the modern building construction, openings in beams are necessary to accommodate several service pipes and ducts. Due to these openings, high stress concentration occurs at its edges. Local cracks also appear around the openings as a result of the reduction in the beam stiffness, the load carrying capacity and the shear capacity. There are many studies which were conducted to develop and test different strengthening methods for the beams opining to increase the ultimate load capacity of the beams. However, from a practical point of view, it is better to have one strengthening method having the same specifications to be used in both; shear and flexural zones for circular opining beams in buildings. In spite of the prior studies, no study has addressed this issue; therefore, there is a need to study such a case. In this paper, an analytical study was conducted to investigate the behavior of the reinforced concrete (RC) beams with circular openings in flexural and shear zones strengthened by steel plates. A 3D FE modeling (ABAQUS 6.12) software was used to simulate five different specimens of RC beams. The study results showed that when the openings were strengthened by steel plates, the ultimate load carrying capacity increased, but the deflection was decreased when compared to the openings without strengthening. In addition, the model reliability was verified via good agreements between the experimental and numerical results. [ABSTRACT FROM AUTHOR]

Timber-concrete composite floors represent an efficient possibility for strengthening timber beam ceilings and stiffening timber frame structures. The results of this construction method are higher stiffness and load bearing capacity, improved sound insulation, and better fire resistance. Replacing conventional RC with an innovative and efficient material, such as fiber RC, leads to improvements in the construction progress, material properties, and load transfer and to a reduction in the slab thickness. The subject of this paper is the numerical simulation of the behavior of composite timber-fiber concrete floor, consisting of a fiber concrete slab and timber beams. The primary point of this work is to explore the membrane action of the fiber concrete slab with timber beams and investigate the behavior of the load floor structure by using finite-element (FE) models. This paper presents a three-dimensional FE model developed to predict the mechanical behavior of timber-fiber concrete composite floors, to derive simpler models for representing the partially protected composite floors in fire. The analysis of these structures is nonlinear and considers the orthotropic behavior for timber and isotropic behavior for concrete. The description of the model, general parameters, and values are given in this paper. All modeling was prepared by using an FE software program. The numerical models are validated against the results of full-scale furnace, material property, push-out, and beam tests. [ABSTRACT FROM AUTHOR]

In parallel with the experimental study described in the companion paper (Zhao et al., submitted for publication), a numerical modelling programme has been carried out to investigate further the structural behaviour of stainless steel cross-sections under combined loading. The numerical models, which were developed using the finite element (FE) package ABAQUS, were initially validated against the experiments, showing the capability of the FE models to replicate the key test results, the full experimental load–deformation histories and the observed local buckling failure modes. Upon validation of the FE models, parametric studies were conducted to generate additional structural performance data over a wide range of cross-section slenderness and combinations of loading. The experimental and numerical results were then compared with the design capacity predictions from the current European Standard EN 1993-1-4 (2006) and American Specification SEI/ASCE-8 (2002) for stainless steel structures. The comparisons revealed that the current design standards can significantly under-estimate the resistance of stainless steel cross-sections subjected to combined loading; this under-prediction of capacity can be primarily attributed to the lack of consideration of strain hardening of the material under load. The Continuous Strength Method (CSM) is a deformation-based design approach that accounts for strain hardening and has been shown to provide accurate predictions of cross-sectional resistance under compression and bending, acting in isolation. In the present paper, proposals are made to extend the scope of the CSM to the case of combined loading. Comparisons between the CSM design proposals and the test and FE results indicated a high level of accuracy and consistency in the predictions. The reliability of the proposals was confirmed by means of statistical analyses according to EN 1990 (2002). [ABSTRACT FROM AUTHOR]

The present paper describes a design approach for textile-reinforced concrete (TRC) shells which reflects the interaction between normal forces and bending moments based on the cross-sectional strength characteristics of the material determined experimentally. The influence of oblique loading on the composite strength of TRC elements with flexible reinforcement is included in a normalized interaction diagram for combined loading. As an example, the design approach is applied to the ultimate limit state assessment of a TRC shell in double curvature. Furthermore, the general applicability of the design approach is discussed in the light of the non-linear loadbearing behaviour of TRC. Due to its strain-hardening tensile response, stress redistributions within the shell result in loadbearing reserves. Details of the structural design and production solutions developed and applied during the realization of the TRC shell structure are described in the companion paper (Part I). [ABSTRACT FROM AUTHOR]

This paper deals with comparisons of numerical results of reinforced high strength concrete corbels and experimental results obtained from the literature. The application of precast structures and high strength concrete have increased in the last years and taking into account the possibility of brittle failures using this solution, specific investigations are demanded to some structural details, as for example, corbels. It should be mentioned that brittle failures and complex regions are difficult to be analyzed by means of computational resources and for that reason it is argued if the available packages software are able to correctly describe the behavior of high strength concrete, specifically for corbels. In this way, the numerical simulations described in this paper have been conducted using the Finite element method. A parametric study was then carried out using the validated model to investigate the effect of the shear span-to-effective depth ratio, the main reinforcement rate and the compressive strength of concrete in the failure load and the contribution of secondary reinforcements. The main conclusions are: the numerical and experimental results showed a very close agreement, not only in the cracking and failure modes, but also in the load-deflection and load-reinforcement strain responses; there is a strong linear correlation of the failure load and shear span-to-effective depth ratio, the main reinforcement rate and the compressive strength of concrete; the horizontal secondary reinforcement improves the load capacity and could be considered in the design models; and the vertical secondary reinforcement only affects in the cracking distribution and ductility of the corbels. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a new time reversal imaging (TRI) algorithm with noise suppression is developed for the application of imaged based structural damage detection of plate‐like structures. The conventional TRI method suffers from performance degradation in high noise condition. The proposed method addresses the aforementioned issues. First, an array of detection transducers is used and is divided into several subgroups. Then, the echo signals of the subgroups are time reversed and reemitted via numerical computation. Finally, the cross‐correlation functions of the summation of refocused time reversed signals in each subgroup are obtained to locate damages. The time reversed signals at the reference time are irrelevant to the noise, meanwhile, the multiple refocused signals in each subgroup are first added and then cross‐correlated. Therefore, the proposed method can effectively suppress noise. To validate the effectiveness of proposed method, 2 experiments were performed. The 2 experiments involved 2 aluminum plate specimens. Each specimen was equipped with 4 surface‐bonded lead zirconate titanate transducers. One specimen involved a simulated damage (an addition of a mass), and the other one involved an actual through‐hole damage. The experimental performances of the proposed method are compared to those of the conventional TRI method. The imaging results demonstrated that the damage on both specimens was clearly displayed with high spatial resolution by the proposed method even under the low signal‐to‐noise ratio condition. On the contrary, the location of the damage computed by the conventional TRI method was submerged in noise and cannot be distinguished. [ABSTRACT FROM AUTHOR]

Corrosion growth analysis is a vital part of the integrity and risk assessment of corroded pipelines. The results are used to schedule pipeline inspections and maintenance actions. Corrosion growth is often determined from noisy in-line inspection results where the sizing errors can have a significant impact on the measured size and growth of the corrosion features. If the inspection results are on average unbiased, the top percentiles of measured features have a statistical trend of being oversized as shown in the paper. This trend has been confirmed in pipeline practice. The statistical bias effect leads to suboptimal inspection and maintenance requirements if it is not removed in the corrosion growth analysis. Three deterministic and probabilistic models, which account for the sizing bias inherent in in-line inspection data, are introduced for the corrosion growth analysis. The models are tailored toward pipelines subject to internal corrosion with high feature densities. A numerical example is provided based on a subsea pipeline to demonstrate the ramifications of the oversizing bias and the proposed corrosion growth models. [ABSTRACT FROM AUTHOR]

Cable-arch structures, having features of the flexibility of cable and rigidity of arch, have often been used in structural and bridge engineering. It is important to fully understand the behavior of such a structure under various conditions. For this purpose, in this paper, linear and nonlinear elastic buckling analysis of four cable-arch related structures, including tied cable-arch structure, pure arch, tied arch and cable-arch, were conducted using the finite element methods under different boundary and load conditions with the stability of these structures compared. Furthermore, the parametric analysis was carried out to investigate the influence of numbers and inclined angles of hangers and cables, materials of cables and stiffness of tie beam on the buckling behavior of tied cable-arch. The results indicate that the stability of pure arch and tied arch can be enhanced by anchoring cables on the arch rib due to the increase in stiffness. Moreover, the weaker the stiffness of an arch, the greater the cable's contribution to structural stiffness. The stability of a tied cable-arch is quite sensitive to the inclined angle of hangers and cables, the number and materials of cables, and tie bar, but not to the fracture of two hangers. The study gives us a complete understanding of the elastic buckling behavior of circular tied cable-arch structures. [ABSTRACT FROM AUTHOR]

The present study sheds light on geometric nonlinear static analysis of prismatic shells using the semi-analytical finite strip method. A new computational model, which includes a fully nonlinear compound strip with a longitudinal and transverse stiffener, has been presented. Furthermore, strips with non-uniform characteristics in the longitudinal direction have been used in nonlinear analysis. This has, to the best knowledge of authors, never been reported. Also, this paper describes the design and implementation of eighteen ideal boundary conditions using three different longitudinal and six well-known transverse displacement interpolation functions. The results of the presented study were obtained using an open-source software and multi-purpose software Abaqus. Moreover, the accuracy of the applied computational approach has been verified by comparison with results from the literature. An excellent agreement of displacement fields is achieved for large deflection analyses of plates with a hole and stiffeners as well as for shells with a stepped thickness in the longitudinal direction. Additionally, results from post-buckling analyses of thin-walled structures, a snap-through and snap-back behavior of shallow shells, are matched. The work presented here has profound implications for future studies of the finite strip deployment. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this paper is to provide a new theoretical basis to identify localized damage in structures using incomplete modal information, such as a subset of the spectrum. The paper expands upon well-established ideas from sensitivity-based model updating and offers a new perspective on the problem by using l 1 norm minimization to solve the inverse problem. It is shown that in contrast with the more traditional l 2 (Euclidean) norm minimization, the proposed l 1 norm minimization approach enables accurate examination of a set of potentially damaged locations significantly larger than the subset of the spectrum used in the formulation of the sensitivity matrix. The main prerequisite is that the damage must be sparse, i.e. occur in a small portion of the domain, no other information regarding the damage is required. The computational effort necessary to solve the l 1 optimization is larger than in traditional Euclidean norm minimization and requires the use of convex optimization methods. However, given the results that can be obtained, the computational effort is justified. [Copyright &y& Elsevier]

Abstract: The development of predictive models for plate end debonding failures in beams strengthened with thin soffit plates is a topic of great practical relevance. After the early stress-based formulations, fracture mechanics approaches have become increasingly established. More recently, the cohesive zone (CZ) model has been successfully adopted as a bridge between the stress- and fracture mechanics-based treatments. However, the few studies of this nature propose complex formulations which can only be implemented numerically. To date, the only available analytical solution based on CZ modeling for the prediction of interfacial stresses/debonding in plated beams is limited to the determination of interfacial shear stresses and thus neglects the mixed-mode effects generated by the presence of interfacial normal stresses at the plate end. This paper presents a new analytical formulation based on the CZ modeling approach for the prediction of plate end debonding in plated beams. A key enhancement with respect to the previous solution is the use of a coupled mixed-mode CZ model, which enables a full account of mixed-mode effects at the plate end. The model describes the evolution of the interface after the end of the elastic regime, and predicts the value of the load at incipient debonding. The achievement of a closed-form solution for this quite complex case entails the introduction of a crucial simplifying assumption, as well as the ad hoc modeling of an effective cohesive interfacial response. The paper presents the analytical theory and compares its predictions with numerical and experimental results. [Copyright &y& Elsevier]

This paper revisits from a nonsmooth dynamics perspective the contact process encountered in two archetypal rocking structures: the rigid rocking block and the flexible rocking oscillator. The analysis assumes impact is an instantaneous (unilateral) contact, and models the behavior along the normal direction with a set-valued Newton's law. In the tangential direction it assumes that sliding is prevented. The study formulates both impact and uplifting phenomena as linear complementarity problems (LCPs). The proposed LCP formulation encapsulates all post-impact states and liberates from the need for additional ad-hoc assumptions. The results show that the proposed nonsmooth approach verifies the corresponding results of other studies with reference to the rigid rocking block. Focusing on the flexible rocking oscillator, the proposed model is compared with pertinent analytical, numerical and experimental results from literature. The present study offers original analytical solutions describing all physically feasible post-impact states and confirms, as a special case, existing solutions of rocking initiation. Importantly, the analysis unveils that a given rocking oscillator might choose a different post-impact state (e.g. bouncing, full contact, or immediate rocking) depending on its flexural deformation at the time of impact. Further, it shows that in the case of immediate rocking after impact, the post-impact flexural velocity of the rocking oscillator is not equal with its pre-impact value. The results also reveal the dominant role of the assumed value of the Newton's coefficient of restitution on the response-history of the rocking oscillator. [ABSTRACT FROM AUTHOR]

Foundation settlement is a common issue for bridges, which not only generates additional static stresses in continuous bridge members but also may affect the dynamic interaction between the bridge and vehicle traveling over it. In this paper, a new bridge-vehicle model with consideration of foundation settlement effect is created through the principle of virtual works to investigate the settled bridge and vehicle interaction responses. The correctness and accuracy of the model are validated with theoretical and numerical results. Based on the proposed model, numerical simulations have been conducted using the Newmark’s β method to investigate the effects of settlement mode, vehicle traveling speed, road surface roughness and boundary condition. It is shown that foundation settlement has a significant effect on impact factors of the bridge at high vehicle speeds, and road surface roughness may act together with the settlement to have a coupling effect, which needs special attentions in bridge design. [ABSTRACT FROM AUTHOR]

Accurate modal analysis is the basis to evaluate the dynamic performance of inflated membrane structures, however, it is still a challenge to analyze and testify due to strong nonlinearity of geometry deformation, initial stress and the air-elastic effects. This paper presents modal characteristics of inflated beam and flexible airship envelope. Firstly, an approach to numerically simulate modal behaviors of a plane membrane in the air was validated by testing natural vibration behaviors of plane membranes. This was followed with modal analysis of inflated tube in experimental and numerical methods. The influencing factors for the modal performance of the inflated tube were estimated in terms of boundary condition, internal pressure, elastic modulus and air. Based on this outcome, the verified simulation method was employed to investigate the natural vibration behaviors of flexible airship including dry and wet modal analysis. Thirdly, pressure difference, geometric dimension, welding seam were considered as influencing factors to study their effects on modal characteristics of non-rigid airship hull. Lastly, modal analysis of airship with suspended curtain in self-equilibrium configuration and self-weight and buoyancy was to investigate close practical engineering structural behavior of large airship. [ABSTRACT FROM AUTHOR]

Finite element model (FEM) is a broadly used numerical tool in structural damage detection. In such applications, damage parameters in FEM are estimated by minimizing the differences between experimental modal analysis data and the corresponding FEM model prediction. Very limited works exist on analyzing the identifiability of the FEM used in such applications. In this paper, the identifiability of FEM-based structural damage detection is investigated for undamped elastic beams. We theoretically proved that damage severity at a given location in a uniform beam is identifiable by reformulating the FEM into a linear time invariant (LTI) system. A numerical algorithm is also proposed for checking the identifiability issue of multiple damage locations. Numerical case studies are provided to validate the effectiveness and usefulness of the proposed framework. [ABSTRACT FROM AUTHOR]

Abstract: This paper is primarily focused on the identification of structural forces, with the objective of localizing forces injected into structures in the mid-high frequency range. An energy method, called the simplified energy method (MES), has already been introduced for the purpose of predicting an energy density distribution for structural acoustic problems in the mid-high frequency range. The present paper proposes using this same energy method to solve inverse structural problems. More specifically, the injected forces are to be estimated and localized through knowledge of a set of energy densities within the structure. The 2D formulation of this inverse approach, known as inverse MES (or IMES), is first expressed. Both the boundary and internal sources can then be detected by applying the proposed formulation. Numerical test results are processed using a 2D Kirchhoff plate, and a number of conclusions are also drawn regarding IMES capabilities. Moreover, this paper offers a numerical comparison with another energy-based method. [Copyright &y& Elsevier]

Abstract: The effect of structural boundary conditions and explosive spalling on performance of concrete elements in fire is still an area of interest within the research community. This paper presents the results of experimental research executed on 30 high strength concrete columns. The parametric study investigated the high strength concrete columns under five loading levels (0.2, 0.3, 0.4, 0.5 and 0.6) subjected to two heating rates, with special attention directed towards explosive spalling. The second part of the paper represents a three-dimensional finite element (FE) model of the reinforced concrete columns, taking into account exposure to high temperatures. The effects of tension softening are included in the model and are based on the Hordjik, Cornelissen and Rienhardt curve. The concrete columns were modelled taking into account the embedded reinforcement and crack formation and propagation using the smeared cracks model, which allowed a nonlinear transient structural analysis to be conducted. The comparison of the results of the FE analysis and the tests performed showed a reasonable agreement and a divergence in some cases due to concrete spalling. An assessment of stresses generated in the high strength concrete columns under fire using the FE model is also presented in the paper. The evaluation shows that mechanical and thermal tensile stresses could reach up to 8.69 MPa, which is high enough to cause concrete spalling. [Copyright &y& Elsevier]

Abstract: The paper presents a case study of progressive collapse analysis of a selected multistory building. The subject of the numerical study is an existing 8-story steel framed structure built for fire tests in the Cardington Large Building Test Facility, UK. The problem is investigated using nonlinear dynamic finite element simulations carried out following the GSA guidelines. The paper focuses on model development for global models subject to increasing vertical loading and notional column removal. Taking advantage of parallel processing on multiprocessor computers, a detailed 3D model with large number of finite elements has been developed for the entire structure. The objective of the presented feasibility study is to identify modeling parameters affecting the final result (potential of progressive collapse) and propose a hierarchical verification and validation program for reducing outcome uncertainties. [Copyright &y& Elsevier]

Abstract: The paper proposes a new approach for shape optimisation with fatigue life as the design objective. Conventional designs often incorporate stress optimisation that aims at reducing stress concentrations around a structural boundary by minimising the peak stress. However, this is only an effective and sufficient measure for an ‘ideal’ or ‘flaw-less’ structure. It is a well-known fact that flaws (cracks) are inevitably present in most structures. This emphasises the need to investigate the influence of cracks on optimised shapes. Numerical modelling of cracks using the Finite Element Method requires a fine mesh to model the singularity at crack tips, which makes fracture calculations computationally expensive. Furthermore, for a damage tolerance based optimisation, numerous cracks are to be considered at various arbitrary locations in a structure, and fatigue life evaluation needs to be repeated for each crack at every iteration. This makes the optimisation process extremely computationally inefficient for practical purpose. Moreover, the lack of information concerning crack size, orientation, and location makes the formulation of the optimisation problem difficult. As a result, there has been inadequate research to consider fracture parameters, such as fatigue life, in the optimisation objective. To address this, the paper presents an approach for the shape optimisation of damage tolerant structures with fatigue life as the design constraint. The damage tolerance based optimisation was performed using a number of nonlinear programming algorithms, namely the Broydon–Fletcher–Goldfarb–Shanno (BFGS) method, the Fletcher Reeves (Conjugate Direction) method, and the Sequential Unconstrained Minimisation Technique (SUMT). These methods were extended for optimising the fatigue life in the presence of numerous surface cracks. A significant enhancement in fatigue life was achieved for various crack cases consisting of different initial and final crack sizes. It is shown that the fatigue life optimised shapes can be considerably different from the corresponding stress optimised solution. This emphasises the need to explicitly consider fatigue life as a distinct design objective when optimising damage tolerant structures. A fatigue life optimisation leads to the generation of a ‘near uniform’ fatigue critical surface. The design space near the ‘optimal’ region was found to be relatively flat. This means that the precise identification of the local/global optimum solution is not critical, because a significant structural performance enhancement can be achieved in the ‘near’ optimal region. An additional benefit of fatigue life optimisation is that the resulting optimised shapes may even be lighter than the stress optimised designs. To verify the optimal solutions obtained using the nonlinear programming algorithms, the results were compared with those obtained using a heuristic optimisation method (Biological algorithm). The solutions predicted by both the methods, employing inherently different (gradient-based and gradient-less) algorithms, were found to agree very well. [Copyright &y& Elsevier]

Abstract: The paper presents an efficient numerical procedure for materially and geometrically nonlinear FE analysis of segmentally erected structures, including time dependent effects due to load history, creep, shrinkage and aging of the concrete. The main attribute of this procedure is its generality: the procedure is applicable to any kind of structure and does not require heavy coding. Modification of structure topology is carried out using an efficient procedure for creating/removing elements. The problem data are the reference configuration of the structure and the construction stages represented by an adding and removal time for each element. This procedure, presented here for beam elements, can be extended to any kind of finite element and allows the transforming of any standard FE code to deal with evolutionary structures. Besides, time effects have a strong influence, especially for concrete structures. These effects must be taken into account in the design process. To meet the demand of design offices, the model must be simple, efficient and scientifically sound. The approach presented in this article, is a good balance between these two objectives. This method is based on the fictitious loading age method with improvements to take into account recovery and to yield back the same final strain as superposition. The method requires only six variables at each Gauss point. At intermediate stages, the maximum discrepancy in strain observed is 5%. This method is applied to a complex stress history and compares favourably with results obtained by superposition. Application to the erection of a two-span cable stayed bridge is discussed at the end of the paper. [Copyright &y& Elsevier]

Abstract: In this paper a Romanesque masonry church is analysed in order to assess its structural behaviour and its seismic vulnerability with respect to the actual state of conservation. Starting from a specific case study, a contribution to the issue of modelling and analysis of monumental masonry buildings under seismic action is provided. A finite element methodology for the static and dynamic nonlinear analysis of historical masonry structures is described and applied to the case study. A quasi-static approach (the seismic coefficient method) for the evaluation of the seismic loads has been used (as indeed is common in many analyses of the seismic behaviour of masonry structures). The comparison demand vs. capacity confirms the susceptibility of this type of building to extensive damage and possibly to collapse, as frequently observed. Moreover the actual efficiency of current techniques for repairing and strengthening are analyzed in order to evaluate their benefits. The analysis of repairing and strengthening techniques show the effectiveness of the usual structural reinforcement in terms of increased seismic capacity. The paper advocates that significant information can be obtained from advanced numerical analysis, namely with respect to the understanding of existing damage and to the minimum and adequate design of strengthening. A clear understanding of the structural behaviour and reliable strengthening, based on sophisticated tools of structural analysis, can therefore reduce the extent of the remedial measures in the restoration of ancient structures. [Copyright &y& Elsevier]

Dynamic crack propagation in non-plane strain (or 3D) slate blocks under wedge impact loads was investigated numerically in this part of the paper. A parabolic-shaped crack trajectory was taken into consideration to model the crack propagation in slate blocks for analyzing the impact splitting of layered slate rock. Major and minor axes of the parabola were determined from the condition of equal mode I stress intensity factors (SIFs) along the crack front. Mode I SIFs were determined for experimental breaking loads for each increment of crack growth in a manner similar to that mentioned in part I of this paper. These values were compared with the plane strain material fracture toughness value obtained from experimental studies and very good agreement was obtained between them, for the case of actual load applied on the specimen. Numerical analysis of a field problem, i.e., separation of a large-sized slate slab from the rock strata in a slate quarry using wedge impacting, was also carried out in this paper. It can be observed that a large magnitude of load is required to break large-sized slate blocks; but this load is applied through a number of smaller load-capacity actuators-in-parallel, requiring large power capacity for the hydraulic pumps. However, this required power could be reduced considerably if the load applied on the line of hydraulic actuators is cascaded across the (line of) actuators (starting from centrally placed actuators) with a small time delay (equal to the initial crushing time in slate rock). [ABSTRACT FROM AUTHOR]

Study of the dynamic properties of a monolayer cable net is described in this part II of the paper. The linear vibration properties of a cable net are analyzed in the form of a lumped-mass system based on the assumption of small-amplitude vibration. The respective influence of two vital factors: geometric shape and cable pretension on the dynamic properties of cable nets at different deflected positions under load is especially focused upon. Results show that when the geometric shape has a small displacement, the displacement influence on frequencies of vibration is almost the same as that of pre-tension, otherwise, the influence of geometric shape is far greater than that of pre-tension. Dynamic tests on the cable net model mentioned in Part I were also carried out at each pre-stretching stage. The results of experiments agree well with those of finite element analysis (FEA). In addition, a modified method called ‘MML’ based on Rayleigh's approach for the calculation of fundamental frequency is put forward in this paper, since it was found that Rayleigh's approach may sometimes introduce large errors. The nonlinear dynamic properties of the cable net were also analyzed. Different from the linear vibration case, nonlinear cases are to some extent amplitude-dependent. Thus explicitly approximate formulae for the first and second nonlinear modal frequencies are derived from continuous theory assuming the cable net to act as a continuous membrane. Transient dynamic analysis using the finite element software ANSYS was carried out to validate the formulae. The results given by the formulae and those via numerical analysis agree with each other well. [ABSTRACT FROM AUTHOR]

Integrated structural designs, with consideration of system reliability for steel portal frames comprising tapered members, are studied in this paper. The reliability-based integrated design (RID) directly checks the structural system limit states and the corresponding system reliability, based on structural nonlinear analysis. The nonlinear integrated analysis model, the semi-analytical simulation method employed for system reliability assessment, the development processes of RID format and the design application of RID formula and curves are presented in this paper. Design examples and comparisons among three different design formats demonstrate that RID proposed in this paper is of certain and consistent system reliability levels, and provides a feasible way for structural engineers to improve the design quality and flexibility of steel frame structures. [Copyright &y& Elsevier]

A hot gas duct is an indispensable component for the nuclear-process heat applications of the Very-High-Temperature Reactor (VHTR), which has to fulfill three requirements: to withstand high temperature, high pressure, and large pressure transient. In this paper, numerical investigation of pressure transient is performed for a hot gas duct under rapid depressurization. System depressurization imposes an imploding pressure differential on the internal structural elements of a hot gas duct, the structural integrity of which is susceptible to being damaged. Pressure differential and its imposed duration, which are two key factors to evaluate the damage severity of a hot gas duct under depressurization, are examined in regard to depressurization rate and insulation packing tightness. It is revealed that depressurization rate is a decisive parameter for controlling the pressure differential and its duration, whereas insulating-packing tightness has little effect on them. [ABSTRACT FROM AUTHOR]

The mathematical models applied to real-life engineering structures result into large-scale dynamical systems. The efficient computation of their dynamical characteristics requires the usage of advanced numerical methods with parallel algorithms. The shooting method, in combination with a continuation method, presents a powerful tool for analyzing and investigating the dynamical characteristics of such systems. The efficiency and scalability of the shooting method are analyzed in the current paper for linear and nonlinear equations. Its applicability to large-scale systems is demonstrated by structural component of bridge discretized by three-dimensional finite elements. [ABSTRACT FROM AUTHOR]

The use of structural lightweight concrete (LWC) has the potential to substantially reduce construction costs as its lower density allows for longer spans, reduced self-weight and a reduction in foundation size. Despite its usefulness, LWC with natural aggregates sees limited use in design due to a lack of design guidelines. This lack of guidance arises primarily due to the highly empirical nature of the design standards in predicting behaviour at all load levels i.e. empirical equations are used at the serviceability limit to predict for flexural rigidities and crack widths as well as at the ultimate limit to predict hinge rotation and moment redistribution. It is thus costly and time-consuming to conduct large scale member testing for a particular type of LWC in order to establish design guidelines. To address this, a generic, mechanics based, segmental moment–rotation ( M / θ ) approach has been proposed to simulate the flexural behaviour of reinforced concrete at all load levels, in which the only empiricisms required are the definition of fundamental material properties. In this paper, it is shown that the M / θ approach and the subsequent existing closed-form solutions derived based on the approach can predict the full range of flexural behaviours of oil palm shell (OPS) LWC beams such as load–deflection and crack width at all load levels. The successful application of the M / θ approach suggested that the approach can be used as a basis for developing design guidelines for LWC. This was further enforced by the good agreement between the predicted response using the M / θ approach and the published test results for other types of LWC material. [ABSTRACT FROM AUTHOR]

This paper deals with the vibration control of existing structures forced by earthquake induced ground motion. To this aim it is proposed for the first time to exploit the structure–soil–structure mechanism to develop a device, hosted in the soil but detached from the structure, able to absorb part of the seismic energy so to reduce the vibration of neighbourhood structures. The design of the device is herein addressed to protect monopile structures from earthquake induced ground motion. By modelling the ground motion as zero-mean quasi-stationary response-spectrum-compatible Gaussian stochastic process, the soil as visco-elastic medium and the target monopiled-structure as a linear behaving structure the device, herein called Vibrating Barrier (ViBa), has been designed through an optimization procedure. Various numerical and experimental results are produced to show the effectiveness of the ViBa. Remarkably, a significant reduction of the structural response up to 44% has been achieved. [ABSTRACT FROM AUTHOR]