Search

Abstract: In a recent paper (Computer Aided Geometric Design 23 (3), 243–260), Yang presented a novel kind of nonlinear and geometry driven subdivision scheme for curve interpolation. The author declared that this scheme was shape preserving when all free parameters were explicitly selected by some specific rules. In this note, we demonstrate that the author (a) ignored the consistency of the definition to straight edges, and also (b) did not give a perfect scheme and proof for the shape preserving subdivision. [Copyright &y& Elsevier]

In ultra-high-field (UHF) magnetic resonance imaging (MRI) applications, the design and analysis of high-frequency radio frequency (RF) coils requires full-wave electromagnetic (EM) methods that can handle complex field-tissue interactions. Using a Huygens' equivalent surface, the Method of Moments (MoM) and the Finite-Difference Time-Domain (FDTD) algorithm can be combined to accurately model the high-frequency RF coils. In previous research, a uniform FDTD mesh structure was considered, providing a compromised solution for coil-tissue interactions. This paper proposes a hybrid FDTD/MoM algorithm with non-uniform meshes. The fine mesh domain is set at the Huygens' surface, and the other domain uses coarse meshes. The proposed algorithms are strictly validated, and their computational performance is compared against conventional methods. Results show that the new algorithm can improve the calculation efficiency without losing accuracy. Specifically, compared with the uniform FDTD method, the numerical difference between both hybrid methods remains at 3.2%. Still, the calculation time of the non-uniform grid algorithm is reduced by 64.2%, demonstrating the effectiveness of the new algorithm for modeling RF coils for UHF-MRI applications. [ABSTRACT FROM AUTHOR]

• Investigate assigning shipping requests to crowdsourcees with time and capacity constraints • Propose a centralized, deep reinforcement learning-based approach • Present new state space representation encompassing spatial-temporal and capacity information • Embed heuristics-guided action choice in DRL to preserve tractability and enhance efficiency • Integrate rule-interposing into DRL to further enhance training and implementation efficiency This paper investigates the problem of assigning shipping requests to ad hoc couriers in the context of crowdsourced urban delivery. The shipping requests are spatially distributed each with a limited time window between the earliest time for pickup and latest time for delivery. The ad hoc couriers, termed crowdsourcees, also have limited time availability and carrying capacity. We propose a new deep reinforcement learning (DRL)-based approach to tackling this assignment problem. A deep Q network (DQN) algorithm is trained which entails two salient features of experience replay and target network that enhance the efficiency, convergence, and stability of DRL training. More importantly, this paper makes three methodological contributions: 1) presenting a comprehensive and novel characterization of crowdshipping system states that encompasses spatial-temporal and capacity information of crowdsourcees and requests; 2) embedding heuristics that leverage information offered by the state representation and are based on intuitive reasonings to guide specific actions to take, to preserve tractability and enhance efficiency of training; and 3) integrating rule-interposing to prevent repeated visiting of the same routes and node sequences during routing improvement, thereby further enhancing the training efficiency by accelerating learning. The computational complexities of the heuristics and the overall DQN training are investigated. The effectiveness of the proposed approach is demonstrated through extensive numerical analysis. The results show the benefits brought by the heuristics-guided action choice, rule-interposing, and having time-related information in the state space in DRL training, the near-optimality of the solutions obtained, and the superiority of the proposed approach over existing methods in terms of solution quality, computation time, and scalability. [ABSTRACT FROM AUTHOR]

• Numerical methods used for the estimation of the RMS. • Simpson's 1/3 rule and Simpson's 3/8 rule modified for the purpose of general application. • Modified Simpson's rules do not necessitate more complex mathematical calculations than those used in the existing methods. • Modifications provide better measurement results for some a lower ratio of the frequency of sampling and the frequency of the signal. • Modified methods do not require the manufacturers of commercial measurement equipment to additionally invest in it. This paper demonstrates that direct changes in the algorithm for the estimation of the root mean square value of a voltage signal of an arbitrary waveform can lead to improved performances and lower measurement uncertainty of commercially available instruments without requiring any upgrade of their existing hardware. The research conducted and presented here is an original contribution to the development of estimation techniques and mathematical models for measurement oriented purposes regardless of the number of samples in the given period relying on mathematical calculation of the equal complexity as in the methods already in use. The theoretical approach examines the problem of numerical integration focusing on modified Simpson's 1/3 rule and modified Simpson's 3/8 rule used for the purpose of the estimation of the root mean square value when a small number of samples per period is available. It highlights the limitations of Simpson's 1/3 rule and Simpson's 3/8 rule, and shows that the newly proposed algorithm is optimal with respect to measurement accuracy and precision even in cases when the ratio of the sampling frequency and the signal's fundamental frequency is low. All theoretical results have been validated experimentally. [ABSTRACT FROM AUTHOR]

• An algorithm of dexterity evaluation for continuum robots based on IK is proposed. • An IK model for continuum robots is established using an oval curve equation. • Length distribution of the robot is optimized based on dexterity indices. Performance evaluation and inverse kinematics (IK) for continuum robots are always hard and time-consuming. In this paper, an efficient dexterity evaluation algorithm based on IK (DEAIK) for continuum robots is proposed. The IK model is established using an oval curve equation to improve computational efficiency. The relationship between length distributions and dexterity distribution is obtained by the simulation in this paper. Length distribution of the two-segment continuum robot is optimized under the guidance of the dexterity indices using the fruit fly algorithm. Theoretical analysis and numerical simulations demonstrate that the dexterity of the structure-optimized continuum robot is better than that of the traditional continuum robot. The simulation shows that the DEAIK algorithm is 3.68 times faster than the algorithm based on forward kinematics. The IK algorithm in this paper is 3 203 times faster than the IK algorithm based on the Levenberg-Marquardt algorithm in the same accuracy. This work is significant for designing a high-performance continuum robot. [ABSTRACT FROM AUTHOR]

Abstract A Boolean Finite Synchronous Dynamical System (BFDS, for short) consists of a finite number of objects that each maintains a boolean state, where after individually receiving state assignments, the objects update their state with respect to object-specific time-independent boolean functions synchronously in discrete time steps. The present paper studies the computational complexity of determining, given a boolean finite synchronous dynamical system, a configuration, which is a boolean vector representing the states of the objects, and a positive integer t , whether there exists another configuration from which the given configuration can be reached in t steps. It was previously shown that this problem, which we call the t -Predecessor Problem, is NP-complete even for t = 1 if the update function of an object is either the conjunction of arbitrary fan-in or the disjunction of arbitrary fan-in. This paper studies the computational complexity of the t -Predecessor Problem for a variety of sets of permissible update functions as well as for polynomially bounded t. It also studies the t -Garden-Of-Eden Problem, a variant of the t -Predecessor Problem that asks whether a configuration has a t -predecessor, which itself has no predecessor. The paper obtains complexity theoretical characterizations of all but one of these problems. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes a simplified reproducing kernel method to solve the linear Volterra integral equations with variable coefficients. The main idea of the method is to establish a reproducing kernel direct space that can be used in Volterra integral equations. And in the first time, this paper analyzes the convergence order and stability of the approximate solution. Then the uniform convergence of the numerical solution is proved, and the time consuming Schmidt orthogonalization process is avoided. The proposed method is proved to be stable and is not less than the second order convergence. The algorithm is proved to be feasible and stable through some numerical examples. [ABSTRACT FROM AUTHOR]

Highlights • The mathematical model of corrugated shells with special shapes is presented. • Effect of corrugation parameters on critical load is investigated. • Linear and nonlinear buckling analyses are conducted. • Critical load of corrugated shells is compared to smooth ones. • Specific range of corrugation parameters significantly increase the value of relative critical load. Abstract The problem of elastic stability of the shells with special shapes with corrugated middle surfaces under external pressure is debated in the presented paper. Solution of the problem is based on FEM study. Corrugated barrelled, pseudo-barrelled, and cylindrical shells of constant mass are considered. Geometrical modification of the middle surface geometry is based on sine wave along principal directions. Middle surface of the corrugated shells are described referring to differential geometry of surfaces by parametric functions in three-dimensional Euclidean space. Linear and nonlinear buckling analyses are conducted. Examples of buckling modes are presented, which differ significantly from those typical for shells of revolution with positive or zero Gaussian curvature. It is proven that corrugation may lead to serious increase or decrease of critical load for all types of presented shells. [ABSTRACT FROM AUTHOR]

The number of failed components in a failed or operating system is a very useful quantity in terms of replacement and maintenance strategies. These quantities have been studied in several papers for a system consisting of identical components. In this paper, the number of failed components at the time when the system fails and the number of failed components when the system is working are considered for a well-known and widely applicable k -out-of- n structure. The system is assumed to have multiple types of components. That is, the system consists of components having nonidentical failure time distributions. Optimization problems are also formulated to find optimal values of the number of components of each type, and the optimal replacement time. [ABSTRACT FROM AUTHOR]

• The improved PSO was employed to calibrating the micro-parameters. • Different combinations of micro-parameters of DEM model can be obtained. • More macro-parameters should be used to calibrate the micro-parameters of DEM model. The discrete element method (DEM) is commonly used for simulating the mechanical characteristics of rock materials; however, constructing a DEM model requires the specification of a number of microparameters. In this paper, to obtain the microparameters of the DEM model, the improved particle swarm optimization (PSO) calibration method was presented. Based on numerical simulation examples, the new approach is considered valid for calibrating the microparameters of the DEM model. Moreover, it is concluded that different sets of microparameters can be determined when few macroparameters are used, which indicates that the empirical formula between microparameters and macroparameters is not reliable. From the analysis of the numerical simulation results, it is suggested that more macroparameters should be used to calibrate the microparameters of the DEM model, and the corresponding numerical simulation results could be more reliable; otherwise, the generated numerical model may not accurately simulate the mechanical characteristics of rock materials. [ABSTRACT FROM AUTHOR]

• We derive the Hamiltonian formulation of the fractional sine-Gordon equation. • A linearly implicit energy-preserving scheme based on the IEQ method is developed for the equation. • An optimal l ∞ -error estimate for the proposed scheme is established without any restriction on the grid ratio. • A fast algorithm based on the FFT technique is used to reduce the computational complexity. • Remarkable performances in the energy preservation and computational efficiency are obtained with the new scheme. This paper aims to develop a linearly implicit structure-preserving numerical scheme for the space fractional sine-Gordon equation, which is based on the newly developed invariant energy quadratization method. First, we reformulate the equation as a canonical Hamiltonian system by virtue of the variational derivative of the functional with fractional Laplacian. Then, we utilize the fractional centered difference formula to discrete the equivalent system derived by the invariant energy quadratization method in space direction, and obtain a conservative semi-discrete scheme. Subsequently, the linearly implicit structure-preserving method is applied for the resulting semi-discrete system to arrive at a fully-discrete conservative scheme. The stability, solvability and convergence in the maximum norm of the numerical scheme are given. Furthermore, a fast algorithm based on the fast Fourier transformation technique is used to reduce the computational complexity in practical computation. Finally, numerical examples are provided to confirm our theoretical analysis results. [ABSTRACT FROM AUTHOR]

Let B be a set of b blue points and R be a set of r red points in the plane. In this paper we study the problem of finding rectangles that contain the maximum number of blue points without containing any red points, known as the maximum-box problem . First we study this problem for axis-aligned rectangles, and propose an exact worst-case optimal O ( r 2 + r b + b log ⁡ b ) time algorithm using O ( r + b ) space to find all maximum boxes. We also provide a 2-approximation algorithm running in O ( ( r + b ) log ⁡ ( r + b ) ) time and using O ( r + b ) space to find a single maximum box in the axis-aligned case. Then we generalize the exact algorithm for the axis-aligned case to find all arbitrarily oriented maximum boxes leading to a worst-case optimal O ( ( r + b ) 2 ( r + log ⁡ b ) ) time algorithm using O ( ( r + b ) 2 ) space to solve the problem. We conclude the paper by discussing time and space trade-offs. Our results improve the previously best known solutions to the maximum-box problem. [ABSTRACT FROM AUTHOR]

This paper proposes a weighted averaging filter procedure combined with a Riemannian geometry method to carry out a target detection in sea clutter. In particular, the weighted averaging filter, conceived from a philosophy of the bilateral filtering in image denoising, is presented on a Riemannian manifold of Hermitian positive-definite matrix. This filter acts as a clutter suppression procedure in the detection framework of the algorithm proposed in this paper, and can improve the detection performance. The principle of detection is that if a location has enough dissimilarity from the Riemannian mean or median estimated by its neighboring locations, targets are supposed to appear at this location. Numerical experiments and real sea clutter data are given to demonstrate the effectiveness of the proposed target detection algorithm. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel density-based fuzzy clustering algorithm based on Active Learning Method (ALM), which is a methodology of soft computing inspired by some hypotheses claiming that human brain interprets information in pattern-like images rather than numerical quantities. The proposed clustering algorithm, Fuzzy Unsupervised Active Learning Method (FUALM), is performed in two main phases. First, each data point spreads in the feature space just like an ink drop that spreads on a sheet of paper. As a result of this process, densely connected ink patterns are formed that represent clusters. In the second phase, a fuzzifying process is applied in order to summarize the effects of all members of each cluster. Finding arbitrary shaped clusters, noise robustness and proposing fuzzy clusters are some of the advantages of our proposed clustering algorithm. The algorithm is described in full details and its performance is evaluated and compared with well-known clustering algorithms on synthetic and real-world datasets. [ABSTRACT FROM AUTHOR]

In computer aided geometric design a polynomial is usually represented in Bernstein form. This paper presents a family of compensated algorithms to accurately evaluate a polynomial in Bernstein form with floating point coefficients. The principle is to apply error-free transformations to improve the traditional de Casteljau algorithm. At each stage of computation, round-off error is passed on to first order errors, then to second order errors, and so on. After the computation has been "filtered" (K − 1) times via this process, the resulting output is as accurate as the de Casteljau algorithm performed in K times the working precision. Forward error analysis and numerical experiments illustrate the accuracy of this family of algorithms. [ABSTRACT FROM AUTHOR]

In those oceans where measured wave data are not available, numerical wave models are usually adopted to hindcast wave parameters in order to define design waves for marine structures. To utilize these hindcating data, it is very important to perform error corrections of model results for accurate estimation of the appropriate wave parameters. In this paper, a new non-parametric correction model is established to improve wave model accuracy through modifying a previous approach released by Caires and Sterl in 2005. The new correction model introduces a kernel algorithm to learn error information from both value magnitude and series trend through training datasets, and utilizes the information to correct potential errors in model outputs. It is shown that the two-dimensional learning method is more effective than the previous one-dimensional which only learns error information from the value magnitude. Furthermore, an error constraint parameter is initially adopted in the new correction model to decrease the possibility of overcorrection. The new correction model performs better than its predecessor, especially when modeling wave period and altimeter synchronized wave height. Though this paper evaluates the model correcting performance with WAVEWATCH III outputs, the modified model can be adopted to correct other kinds of time-series data. [ABSTRACT FROM AUTHOR]

The paper presents a new algorithm to compute the LU-factorization of a matrix represented in a quasiseparable or semiseparable form (i.e., using generators). It obtains the quasiseparable representations of the factors L and U of an N × N block matrix via O ( N ) arithmetic operations on the block entries. The algorithm uses recursions based exclusively on unitary transformations which provide numerical stability even in singular cases. The method of the paper is based on the theory developed in [1] and provides an alternative to the approach proposed in [7] for strongly regular matrices. The algorithm presented here works also for some matrices with possibly singular principle submatrices. The results of numerical tests show that also for strongly regular matrices the new algorithm is comparable with the previous methods. [ABSTRACT FROM AUTHOR]

Highlights • The new algorithm is the second-order accurate, unconditionally stable (L-stable) and self-starting. • The new algorithm shares the identical effective stiffness matrices inside two sub-steps. • The new method does not involve any artificial parameters and additional variable, such as the Lagrange multipliers. • The new scheme achieves the same numerical properties as the Bathe algorithm, but requires less matrix-vector operations. Abstract This paper presents a new composite sub-steps algorithm for solving reliable numerical responses in structural dynamics. The newly developed algorithm is a two sub-steps, second-order accurate and unconditionally stable implicit algorithm with the same numerical properties as the Bathe algorithm. The detailed analysis of the stability and numerical accuracy is presented for the new algorithm, which shows that its numerical characteristics are identical to those of the Bathe algorithm. Hence, the new sub-steps scheme could be considered as an alternative to the Bathe algorithm. Meanwhile, the new algorithm possesses the following properties: (a) it produces the same accurate solutions as the Bathe algorithm for solving linear and nonlinear problems; (b) it does not involve any artificial parameters and additional variables, such as the Lagrange multipliers; (c) The identical effective stiffness matrices can be obtained inside two sub-steps; (d) it is a self-starting algorithm. Some numerical experiments are given to show the superiority of the new algorithm and the Bathe algorithm over the dissipative CH- α algorithm and the non-dissipative trapezoidal rule. [ABSTRACT FROM AUTHOR]

Abstract Distributions of Monge type are a class of strongly regular bracket-generating distributions introduced by I. Anderson, Zh. Nie and P. Nurowski. Their symbol algebras prolong to simple graded Lie algebras, thus allowing one to associate a parabolic geometry to any given Monge distribution. This article is devoted to the classification problem for homogeneous models of Monge distributions of type C 3 in dimension eight, and is complementary to a paper by I. Anderson and P. Nurowski. The general classification algorithm, as well as most of its application to the particular problem, are joint work with Ian Anderson. [ABSTRACT FROM AUTHOR]

Highlights • Dynamical analysis has been provided to describe nonlinear behavior of supercavitating vehicles. • Robust H∞ loop-shaping synthesis with modified PID algorithm is proposed to control the dive plane maneuver of the HSSV. • Multi-objective control problems are solved using BMI optimization of an equivalent Schur formula. • Control scheme has the low order structure and provides robustness against uncertainties. • Integrated robust controller can deal with high parametric uncertainties and suppress exogenous disturbances and sensor noises. Abstract The high-speed supercavitating vehicle (HSSV) utilizes advanced technology that enables an underwater vehicle to reach its unprecedented high speed. The vertical motion control of the HSSV is challenging problem because of its complex dynamics with nonlinear planing force, parametric uncertainties, external disturbances, actuator saturation, and sensor noises. This paper deals with dynamical analysis and a robust H∞ loop-shaping synthesis with modified PID (proportional-integral-derivative) algorithm to control the dive plane maneuver of the HSSV. Typically, the control scheme has the low order structure and provides robustness against dynamic uncertainties, which can be implemented using the bilinear matrix inequality (BMI) optimization of an equivalent Schur formula. Simulation results show that the controlled vehicle system provides good performance and high robustness against uncertainties, ensuring no-overshoot and fast in time-domain responses. In addition, the control algorithm can decouple the dynamic interactions in the multi-input multi-output (MIMO) system, overcoming parametric uncertainty, planing force, and actuator saturation while minimizing the effect of the strong external disturbances and measurement noises. [ABSTRACT FROM AUTHOR]

Abstract Future Mars missions may require improved landed accuracy to facilitate the landing site selection and finally access a region of complex terrain with high scientific return. This paper is to develop a novel, robust, and precision entry guidance algorithm for Mars entry vehicles with low lift-to-drag ratios. In the presence of large uncertainties, the entry terminal point controller algorithm can encounter severe performance degradation due to: (1) the small perturbation assumption, and (2) theoretically ignoring deviations in the atmospheric-density model, aerodynamic-force model, etc. Based on numerical technologies and the classical variation method (VM), this work develops a semi-analytical (SA) algorithm, in which combined effects of several dynamic uncertainties now can be addressed. The terminal-downrange error is predicted by a numerical predictor such that the dependence on the reference trajectory can be reduced and then the issue caused by the small perturbation assumption can be addressed. Such a predicted terminal-downrange error is finally corrected by an analytical corrector, which is designed by the VM. It is indicative that there can be no numerical iterations in the SA algorithm. Numerical results demonstrate the effectiveness of the SA algorithm. [ABSTRACT FROM AUTHOR]

• An automatic algorithm for generating polyhedral meshes was systematically developed. • Hexahedral elements near the given STL surface were categorized into polyhedral volume topologies based on the MC algorithm. • Topology ambiguities of the MC algorithm were effectively resolved to provide an appropriate mesh for complex geometry. • The effectiveness was demonstrated through numerical analysis using the smoothed finite element method. Hexahedral meshes that exhibit the superiority in terms of solution accuracy and convergence rate are preferred to other types of meshes in the finite element analysis. However, the construction of the hexahedral meshes for complex geometries is still considered troublesome due to their poor geometric adaptability. This paper presents an efficient grid-based scheme to automatically generate polyhedral meshes including the hexahedral elements, and thus to provide hexahedral-dominant meshes for three-dimensional geometry with complex shapes. On the basis of the marching cube algorithm with a background grid composed of a regular arrangement of cubes, surface topologies for the background cubes are defined to represent the three-dimensional boundaries of a given domain. Then, in order to generate a three-dimensional finite element mesh, the surface topologies of the marching cube algorithm are systematically expanded to polyhedral volume topologies. Meanwhile, a topology ambiguity problem inherent in the marching cube algorithm is effectively resolved to generate an appropriate polyhedral mesh even for an arbitrary complex geometry. Several examples including biostructure modeling demonstrate that the proposed mesh generation scheme can easily discretize complex three-dimensional domains with hexahedral-dominant meshes, which are composed of the polyhedral elements near the domain boundaries and the hexahedral elements that come from the background cubes inside the domains. Furthermore, to show the applicability and effectiveness of polyhedral meshes in the finite element analysis, some structural analyses are performed using the smoothed finite element method that can be straightforwardly adapted to polyhedral elements of arbitrary shape. [ABSTRACT FROM AUTHOR]

Abstract The paper considers a method for evaluation of reinforced concrete damage due to the bending of concrete beams reinforced with steel and fiberglass reinforcement. The evaluation procedure is based on measuring the electrical response to mechanical impact. Measurements of the electrical response are carried out periodically during a gradual increase in the external load. The analysis of signals in time and frequency is the basis for the algorithm for evaluating the damage processes in reinforced concrete structures subjected to four-point bending. On the basis of numerical simulation and experimental study of the load graphs, the stages of damage process in reinforced concrete beams under bending action were determined. A good correspondence between experimental and theoretical results is shown. As diagnostic parameters characterizing the stages of damage in reinforced concrete beams, it is proposed to use the energy decay coefficient of the electrical responses, the coefficient of cross-correlation of the signal spectrum in the process of loading with the signal spectrum from the same sample before loading, and the frequency shift at which the maximum coefficient of correlation can be observed. Most informative frequency ranges where the proposed diagnostic parameters relation to the degradation processes of reinforced concrete during bending is more reliable were determined. The proposed method can be used to monitor the development of damage in reinforced concrete under bending conditions. [ABSTRACT FROM AUTHOR]

Highlights • The damper has an excellent hysteretic energy dissipation capacity. • The damper exhibits a stable post-visible-rupture behavior. • The damper can be promptly repaired after a major earthquake. • The repaired damper behaved as the original one. • The model predicts acceptable results for yield and ultimate strengths of the damper. Abstract This research focused on a new type of seismic damper consisting of replaceable U-shaped steel plates. To investigate behavior of the damper, seven specimens were tested. The test parameters varied in these specimens included geometries and materials of the U-shaped steel plates and the loading protocols. Test results show that the specimens exhibited stable hysteretic behaviors and satisfactory energy dissipating capacities. In addition, this research provided clear evidence that the damper is robust and tolerant to the ruptures in the U-shaped steel plates. Some specimens continued to dissipate significant amounts of hysteretic energy even after formation of the visible ruptures in the U-shaped steel plates. Moreover, this research demonstrated that the damper repaired through replacement of the U-shaped steel plates following a severe earthquake remained satisfactory in a subsequent earthquake. Further, this paper presents the equations for estimating yield strength and ultimate strength of the damper. It was found that the derived equations provide reasonable predictions and can be used for future design. [ABSTRACT FROM AUTHOR]

Highlights • Analytical and numerical study results of Y-type self-centering eccentrically braced frame (SCEBF-Y) are presented. • Post-gap opening stiffness of SCEBF-Y depend on PT cable properties. • Finite element model of the SCEBF-Y is verified with analytical and experimental test data. • Post-gap-opening stiffness and equivalent yield strength of SCEBF-Y is adjustable. Abstract This paper presents the results from both analytical and numerical study of a Y-type self-centering eccentrically braced frame (SCEBF-Y) subjected to earthquake loading. In this study, a three-story SCEBF-Y frame building has been designed along with a three-story conventional D-type eccentrically braced frame (EBF-D) for a site located in Los Angeles, California. The analytical results reveal that initial stiffness and post-gap opening stiffness of SCEBF-Y depend on brace section properties and PT strand properties respectively. The finite element model of the SCEBF-Y frame has been verified with analytical results as well as experimental test data from a similar one-story one-bay D-type self-centering eccentrically braced frame specimen. The study results demonstrate that SCEBF-Y frame can be designed to the same strength and stiffness as conventional EBFs while it can re-center itself after design basis earthquake (DBE). In the SCEBF-Y system, replaceable energy dissipation devices termed RHD devices are installed to dissipate seismic energy, and the primary structural members are intended to remain elastic under the DBE earthquakes. The nonlinear time history analysis results for the prototype SCEBF-Y buildings show that not only the SCEBF-Y building has negligible residual drift, but also it has its major damage confined to replaceable energy dissipation devices. In the parametric study, three different levels of PT strands' initial stress along with different PT cable length has been considered and the parametric study suggests that by properly choosing cable length and cable's initial post-tensioning stress level, key structural system properties such as the post-gap-opening stiffness and the equivalent yield strength of SCEBF-Y can be adjusted accordingly. [ABSTRACT FROM AUTHOR]

Highlights • Partially bonded (PB)-FREBs can retain the same advantages of unbonded-FREBs. • No relative slip occurs under low-rate lateral displacements in a PB-bearing. • The influence of static rotations on the hysteresis loops of PB-FREBs has been investigated. • A new copolymer employed in the bearings, and its response was examined experimentally. • The PB-application of FREBs as seismic isolators/bridge bearings is feasible. Abstract There are two classical types of application for fiber reinforced elastomeric bearings (FREB), namely, "bonded (B)" and "unbonded (UB)" applications. Although the UB-application results in improved seismic isolation efficiency due to rollover deformations, UB-FREB are not capable of transferring tensile forces, and may experience slip under certain loading conditions. As such, a new application type called Partially Bonded (PB) has been introduced to overcome these two limitations. A PB-FREB is achieved by partially bonding the top and bottom surfaces of the bearing to its contact supports. This paper presents the results of a comparative experimental study between UB-FREB and PB-FREB. Heat accelerated deterioration tests based on Arrhenius law was also conducted on the PB-FREB. Additionally, the low-temperature horizontal response of the PB-FREB was investigated. Results show that the displacement characteristics and damping values, long-term performance, and low-temperature response of the PB-FREB investigated in this study comply with current standard requirements. [ABSTRACT FROM AUTHOR]

Highlights • Formulation of random field theory for the elastic properties of old concrete dams. • Evaluation of the correlation length effect on the frequency response dispersion and inter-correlation among vibrational modes. • First-time analysis of six arch dams in the context of a "dam class". • Proposal of an experimental design using a dam frequency analytical model. • Proposal of an iterative random field-based system identification technique for arch dams. Abstract Determining vibration characteristics constitutes the first step in calibrating the finite element model in an old arch dam analysis. These characteristics provide the required information for a proper dynamic analysis of the coupled fluid-structure system used for risk assessment purposes. This paper investigates the detailed vibration characteristics of arch dams with heterogeneous material by applying random field theory. A group of six double-curvature arch dams are studied herein. The spatial material distribution using different correlation lengths is compared, and the response dispersion is quantified. An experimental meta-model design is developed for a specific class of dams, with an approximate analytical solution being derived. Ultimately, an iterative, random field-based system identification technique is proposed for old arch dams. [ABSTRACT FROM AUTHOR]

Highlights • Investigated seismic performance of seismically isolated and non-isolated buildings. • Buildings designed using the minimum ASCE 7 criteria and enhanced design criteria. • Calculated annual rate of exceeding drift, residual drift and floor acceleration. • Probabilities of exceeding response limits that relate to damage are computed. Abstract Recent studies have shown that seismically isolated buildings designed by the minimum criteria of ASCE/SEI 7 may have unacceptable probabilities of collapse in the MCE R. Acceptable probabilities of collapse in the MCE R are achieved when the isolation system displacement capacity and the strength of the superstructure are increased. The same studies have shown that conventional buildings designed by the minimum criteria of ASCE/SEI 7 have acceptable probabilities of collapse in the MCE R , and that the collapse probabilities may be much lower than those of minimally designed seismically isolated buildings and may even be lower than those of seismically isolated buildings designed by enhanced collapse performance criteria. This paper investigates what isolated buildings offer in terms of performance criteria other than collapse performance. Based on a probabilistic approach, mean annual frequencies of exceedance of story drift, residual story drift and floor acceleration are computed for a number of isolated and non-isolated buildings that meet the minimum criteria of ASCE/SEI 7 and other enhanced criteria. Based on the mean annual frequencies, probabilities of exceeding response limits that relate to damage are computed for a lifetime of 50 years. It is shown that seismically isolated buildings designed by the minimum or enhanced criteria generally have lower probabilities to develop damage or to be in need of demolishing in 50 years of lifetime than any minimally designed non-isolated building. [ABSTRACT FROM AUTHOR]

Highlights • The rotation required by structural elements to perform a plastic design is evaluated. • The proposed approach allows to the failure mode of the structure to be predicted. • Information on the more efficient configuration of additional bolts are provided. • Theoretical results are applied to rack joints tested in an experimental campaign. Abstract The structural behaviour of beam-column joints plays a critical role in the seismic response of frame structures. In the case of steel rack systems, uprights (columns) are usually 3rd or 4th class open thin-walled cold-formed steel members according to Eurocode 3, as such, local buckling occurs before the plastic moment resistance (in the case of the 3rd class) or yield stress (4th class) is achieved. Beams are usually 1st or 2nd class, so they can form a plastic hinge with the rotation capacity required from plastic analysis without reduction of the resistance (1st class) or with a limitation on the rotation capacity due to local buckling (2nd class). For this reason, only beams and connections, which can be easily equipped with additional bolts to increase their structural performance, can provide a post-elastic behaviour with energy dissipation. This paper presents and develops a method capable of evaluating the rotational capacity, or ductility, required by beams and connections to perform a plastic design. The proposed approach allows for the failure mode of the structure to be predicted starting from mechanical properties of structural members, and it is valid for both service and seismic loads. The analytical method could be applied to different structural systems and materials; in the present work it is presented with reference to industrial pallet racks. Theoretical assessment herein of the required plastic rotation for beams and connections provides useful information for bolted connection design to increase capacity of the racks with minimal additional cost. [ABSTRACT FROM AUTHOR]

Abstract Assuming specific behavior models, the variety of design codes currently used for the design of concrete beams inevitably results in different solutions, ensuring service during the whole expected lifetime with a maximum functional quality and safety. However, from a sustainable design perspective, such differences may have remarkable environmental impacts. This paper analyses if the approach of the newest design code, i.e., the Model Code, leads to a reduction in resource consumption and greenhouse gas emissions (GHG) over the life-cycle of concrete beams. To do so, a comparative analysis of the environmental impact of concrete beams was carried out depending on the reference code used for its design (i.e., EHE-08 or Model Code). The results show that the reduction of reinforcing steel is a basic objective to minimize the life cycle environmental impacts of concrete beams. Every country may have its own design codes and, thus, the reinforcing steel use can vary for structures subjected to the same loads and with equivalent structural reliability. Hence, regulations play a key role in the sustainability of construction assets. Conclusions depend on the beam length (L) and height (h) and characteristic compressive strength (f ck). For short beams (4 m), the greater the h , the greater the reinforcement difference between the two codes. With regard to beams of 8 m, these differences can lead to varying steel and GHG savings, e.g., up to 5.0% with MC-2010 (h = 0.6 m and f ck ≤ 35 MPa), almost 40% with EHE – 08 (h = 1.0 m and 35 MPa < f ck ≤ 50 MPa) and more than 30% with EHE–08 (h = 0.6 m and 35 MPa < f ck ≤ 50 MPa). For long beams (L = 12.0 m), steel consumption is 0.3–19% lower when the beam is designed with EHE-08, and this difference decreases as f ck increases. [ABSTRACT FROM AUTHOR]

Highlights • Developed a moment connection for a progressive collapse resistant precast frame. • Experimental destructive testing was performed to obtain moment-rotation behavior. • 2 configurations were tested: higher strength with lower ductility and vice versa. • Experimental results were input into a system-level computational model. • Models show that both tested connections prevent collapse for a column removal. Abstract This paper documents the experimental development of a new spandrel-to-column moment connection detail for progressive collapse resistance in precast concrete building frames. This study focuses on a 10-story prototype precast concrete frame building with perimeter special moment frames (SMF) that are subjected to a ground-floor column removal. The experimental subassembly represents a spandrel-to-column connection on the perimeter SMF near the middle of the building face (i.e. not at the corners). The connection is non-emulative and utilizes unbonded high-strength steel post-tensioning (PT) bars which pass through ducts in the column and are anchored to the spandrels via bearing plates. The proposed design strives for construction simplicity, avoids field welding and/or grouting, and maximizes ductility by allowing the high strength steel bars to act as structural "fuses" when yielding. A full-scale quasi-static pushdown test is performed on two variants of the proposed connection: one with higher moment-rotation capacity and limited ductility, and another with lower capacity and higher ductility. The results show that the connection can reliably achieve its design yield capacity, performs well under service level demands, and can achieve moderate-to-high ductility. The experimental results are then applied to a system-level computational model of the prototype building frame under a column removal scenario. The results of a nonlinear dynamic analysis demonstrate that the system can arrest progressive collapse in the event of a single column loss scenario when either variant of the proposed connection is considered. [ABSTRACT FROM AUTHOR]

Highlights • DMF for the vertical pseudo- and absolute-acceleration response spectra based on 3198 earthquake records. • Effects of earthquake magnitude, epicenter distance, hypocenter depth, site condition, and PGA on the vertical spectral DMF. • The probabilistic properties of the vertical spectral DMF simulated by the normal distribution model. • Highly accurate models for the mean and the standard deviation of the vertical spectral DMF. Abstract This paper aims to establish a regional (Japanese) damping modification model for scaling the 5%-damped vertical seismic response spectra to other damping ratios. In doing so, 3198 strong vertical ground motion (VGM) records are selected from the Japanese seismic database, and their linear elastic response spectra are computed by the Newmark- β algorithm. Taking the 5%-damped vertical response spectra as benchmarks, the vertical spectral damping modification factors (DMFV) for ζ (damping ratio) = 0.5%, 1%, 2%, 3%, 4%, 6%, 7%, 8%, 9%, 10%, 12.5%, 15%, 17.5%, 20%, 25%, 30%, 35% and 40% are calculated. For structural design purpose, the DMFV s of both the vertical pseudo acceleration response spectra and the vertical absolute acceleration response spectra are calculated. The DMFV spectra have their peaks (for ζ < 5%) or valleys (for ζ > 5%) at T = 0.12 s (here T indicates spectral period), and their values get farther away from unity as earthquake magnitude or VGM epicenter distance increases. The effect of earthquake hypocenter depth, local site condition (represented by Vs30) and peak ground acceleration on DMFV generally shows no pattern. For each ζ , the mean DMFV -lg T curves are simulated by highly accurate piecewise functions. Moreover, it is revealed that the normal distribution model is feasible for representing the probabilistic properties of DMFV , especially in the short-to-medium period region where the skewness of the DMFV distribution is not quite pronounced. The standard deviations of DMFV are modeled by piecewise functions as well, yet it is emphasized that the variation of a damping-scaled spectral ordinate is jointly controlled by the probabilistic properties of DMFV and the uncertainties of the 5%-damped spectral ordinates. [ABSTRACT FROM AUTHOR]

Highlights • Eight slender RC columns were strengthened with steel tube and sandwiched concrete jackets. • The experimental results showed that the mechanical properties of the RC columns were enhanced. • An accurate FE model was developed to simulate the response of the retrofitted columns. • A modified load-bearing capacity prediction model was proposed. Abstract Steel tube and sandwiched concrete jacketing has been proved to be effective in improving the load-bearing capacity and ductility of deficient reinforced concrete (RC) stub columns. However, the effectiveness of this technique for slender RC columns remains to be validated due to instability problems. In this study, nine slender specimens, including one reference column and eight retrofitted columns, were tested under axial compression. The experimental results showed that the load-bearing capacity, stiffness and ductility of the slender RC square columns were significantly enhanced. The load enhancement was not only attributed to section enlargement, but also due to the confinement provided by the steel tube. Based on the experimental results, a finite element (FE) model was developed to simulate the structural response of the retrofitted slender columns under axial load. The FE results demonstrated that the sandwiched concrete shared a higher load than the steel tube for the cross-section of this paper, justifying the use of "steel tube and sandwiched concrete jacketing". Moreover, the confinement effects on the load-bearing capacity of the RC part and the sandwiched concrete part were quantitatively analyzed. A modified formula was subsequently proposed to predict the load-bearing capacity of the retrofitted columns, the results of which agreed well with the experimental and FE results. [ABSTRACT FROM AUTHOR]

Highlights • Descriptions of the experimental tests of two large-size RC containment specimens. • Descriptions of CSMM-based shell element for simulation of RC shell-type structures. • Nonlinear FE analysis of the RC containments using CSMM-based shell element. • Discussions and comparisons of experimental outcomes and analytical results. Abstract The nuclear containment structure is one of the most important infrastructure systems ensuring the safety of a nuclear power plant. The structural behavior of a cylindrical containment structure made of reinforced concrete (RC) with large dimensions and numerous rebars is complex and difficult to predict. The complex behavior of the RC containment structure has been investigated in an international collaboration project between the National Center for Research on Earthquake Engineering (NCREE) in Taipei, Taiwan and the University of Houston (UH), Houston, Texas. At NCREE two 1/13 scaled cylindrical RC containment specimens were tested under reversed cyclic loads [1]. At UH, a finite element simulation of the two tested specimens was developed using a finite element analysis (FEA) program SCS [2]. In the program, a new shell element, the so-called CSMM-based shell element, was developed based on the Cyclic Softened Membrane Model [3] and the formulation of an 8-node Serendipity curved shell element [4] with a multi-layer approach [5]. The UH simulated seismic behavior was close to the NCREE experimental results. This paper presents the theoretical development of the FEA program SCS and the comparisons of its predictions with the experimental structural behavior of the two RC containment specimens. This simulation model and the FEA program are excellent tools to develop effective performance-based design provisions. [ABSTRACT FROM AUTHOR]

Highlights • For precast concrete bridge decks, HSS-formed shear pockets should be designed to ensure ductile behavior. • Concrete strength and shear pocket dimensions are key parameters in the design of shear pocket connections. • Using HSS in forming shear pockets is an efficient way for confining pocket concrete/grout and controlling splitting cracks. • FEA can be utilized in modeling the predicting the behavior of HSS-formed shear pockets. Abstract Current bridge design codes do not provide adequate criteria/procedures for designing full-depth precast concrete deck systems, especially those with shear pocket connections. Instead, these systems and their connections are designed on a case-by-case basis by either conducting necessary testing or adopting the design criteria/procedures developed primarily for cast-in-place concrete deck systems. Shear pocket connections formed using steel hollow structural sections (HSS) provide a promising solution to connecting precast concrete deck panels to the supporting girders due to their superior structural performance and simplicity of panel fabrication. The main objective of this paper is to develop criteria/procedures for designing HSS formed shear pocket connections in full-depth precast concrete deck systems. These procedures will assist bridge designers in selecting pocket dimensions, HSS thickness, pocket anchorage and reinforcement necessary to maximize the connection capacity while allowing adequate construction tolerance. Experimental investigation (push-off testing) and finite element analysis (FEA) were performed to validate the developed design criteria/procedures. Analysis and testing results indicated that the developed design criteria/procedures for HSS formed shear pocket connections are satisfactory. [ABSTRACT FROM AUTHOR]

Highlights • Influence of the earthquake duration on damping reduction factor (DRF). • The displacement spectrum is obtained in stochastic way by mean of peak theory. • New DRF formulation considering effective duration, soil type, damping ratio, natural period. Abstract Damping Reduction Factor plays a key role in scientific literature and Technical Codes, but till now existing formulations present differences and inconsistences probably because obtained by integration of real recorded events, thus sensible to specific used data. This paper investigates the relation between damping reduction factor and earthquake duration by means of random vibration theory. A stochastic process, that is non-stationary and filtered, is used to model a seismic event. The modulation function is suitably chosen to describe earthquakes characterized by different durations. The stochastic process peak theory allows to calculate damping reduction factor after the definition of the probabilistic response of a simple linear visco-elastic oscillator. The variability with seismic duration for different soil conditions and damping ratios is investigated. The study points out that damping reduction factor is more sensitive to seismic duration in the range of high period and on rigid soil with respect to other conditions. The results show that, if damping ratio or effective duration values are increased, the damping reduction factor value diminishes. [ABSTRACT FROM AUTHOR]

Highlights • Fast 1D nonlinear dynamic model is validated to predict façade response. • External cladding systems influence stiffness and strength of high-rise structures. • Sensitivity to the façade typology is explored. • Locally, façades decrease stresses in structural key members up to 66.94%. • Globally, façades attenuate top displacements up to 4.94%. Abstract The dynamic interaction between glazed curtain wall stick systems and modern high-rise mega-frame buildings is investigated. In the present paper, four moment resisting frames (MRFs), consisting of thirty- and sixty-storey steel-based prototypes, are designed according to European standards: internal concentrically braced frame (CBF) core, outriggers and belt trusses are adopted to limit inter-storey drift and second order effects. Force-displacement relationships are derived from available full-scale test data performed on non-structural aluminium façade units. Therefore, 3D finite element (FE) models are developed to interpret the physical phenomena involved in façade dynamics: as a result, equivalent 1D nonlinear links are calibrated to simulate these phenomena independently. Nonlinear time history analyses (NLTHAs) are executed to investigate the potential combination of stiffness and strength of such hybrid systems, i.e. achieved through the integration of glazed curtain walls on the MRF lateral force resisting system (LFRs). Local and global performance will be shown in terms of inter-storey drifts and displacement peak profiles, forces and percentage peak variations, highlighting static-to-seismic load ratios in critical members and the sensitivity to the structural height. Conclusions point out that, even if accurately designed according to current standards, the façade omission from the seismic analyses of high-rise structures may lead to a crucial underestimation in the dissipation capacity of the building. [ABSTRACT FROM AUTHOR]

Highlights • SPSW in RCF with proposed connections improves load carrying capacity of RCF. • Initial stiffness and ductility is significantly influenced by connection types. • Three of proposed connections can be used for rehabilitation of RC structures. • One connection (type 4) proposed for new structures. Abstract In the reinforced concrete (RC) structures with steel plate shear walls (SPSWs) as a lateral resisting system, to obtain maximum capacity of SPSW, implementing proper connections play an important role to transfer force from wall to the frame. In this paper, four connection types are proposed and numerically investigated to transfer the tension field forces between SPSW and RC frame (RCF). Three types of connections are applicable for rehabilitating of existing RC structures and one type can be used for new construction. The behavior of connections has been evaluated using non-linear finite element analysis (NLFEA). Results of the specimens with different types of connections demonstrated that the use of SPSW in RCF with appropriate connections could provide excellent ductility as well as high load carrying capacity and initial stiffness by distributing the yielding zone in SPSW along the wall height. [ABSTRACT FROM AUTHOR]

Highlights • Efficient static and dynamic analysis of jointed Euler-Bernoulli beams. • Step changes in material and cross-section. • Internal rotational, internal translational and external translational springs. • Free and forced vibration of jointed Euler-Bernoulli damped beam. • Closed-form expressions of the four integration constants. Abstract Many engineering systems can be modelled as an assembly of beams with different material properties and cross-sections jointed at their edges. This paper presents an approach to analyse jointed Euler-Bernoulli (EB) beams with step changes in material and cross-section under static and dynamic loads. The standard approaches to tackle this type of problem are not completely satisfactory in terms of: (i) computational efficiency in dealing with step changes in material and cross-section, when the continuity conditions must be enforced with auxiliary equations (classic approach) or when a denser mesh has to be used at the discontinuity interfaces (Finite Element Method); (ii) taking into account efficiently internal and external springs at the discontinuity interfaces; (iii) numerical errors in the evaluation of high-order modes for jointed beams. An approach is proposed to overcome these limitations. This approach tackles an assembly of n piecewise homogenous EB beams jointed at their edges using the generalised functions to obtain a single expression of the solution which depends on the 4 integration constants associated with the boundary conditions. Closed-form expressions of the 4 constants are provided. Further, in the presence of internal or external springs, additional constants representing the discontinuities have to be taken into account. The latter are computed by considering one additional condition for each discontinuity. The proposed approach is particularized for the static and dynamic analysis (modal analysis and forced vibration analysis). The feasibility of the proposed approach is shown with two numerical applications. [ABSTRACT FROM AUTHOR]

Highlights • An optimal design procedure for nonlinear fluid viscous dampers is developed. • Nonlinear power law behavior is incorporated a priori in the optimal design process. • An improved stochastic linearization technique is used in the optimal design. • The procedure identifies the optimal dampers from an energy-based perspective. • Comparison with other methods proves key aspects and effectiveness of the procedure. Abstract The earthquake protection of structures equipped with energy dissipation devices in the form of nonlinear fluid viscous dampers (FVDs) is investigated. Most of the optimal design strategies from the literature either address a simplified linear (Newtonian) idealization of the devices, or identify the characteristics of the nonlinear FVDs in a later stage, by invoking the concept of "energy-equivalent" dampers to compromise between the nonlinear power law force-velocity behavior and a simplified (equivalent, in terms of energy dissipation) linear modeling. In this paper, the nonlinear power law behavior of the devices is incorporated a priori in the optimal design process. The proposed strategy, based upon a numerical approach to a constrained optimization problem, invokes a performance criterion that is derived from the energy balance equation of the system, expressed in stochastic terms. To handle the nonlinear constitutive behavior of the FVDs, a novel equal-energy non-Gaussian stochastic linearization technique is integrated in the optimal design process. For a given power-spectral-density function of the seismic excitation, the most effective set of nonlinear FVDs that maximize the energy dissipation behavior can be identified. By stochastic dynamic analysis and by nonlinear response-history-analysis with an ensemble of ground motions, the proposed energy-based design philosophy is found to be better able to control the overall seismic response of the structure than alternative procedures that are not based on energy concepts and that minimize other performance indices. [ABSTRACT FROM AUTHOR]

Highlights • A new type of anti-tension equipment used in isolation building is proposed. • The equipment with double column and steel brace may be more convenient and practicable after analyzed by FEA in detail. • A scale model was tested, test results have good agreement with that of FEA. Abstract When the height-width ratio of high-rise isolation buildings is excessively large, elastomeric isolators may suffer from tension in severe earthquakes. Because of the tension limits of isolators, an anti-tension equipment must be added to such buildings for safety. In this paper, a new type of anti-tension equipment is proposed. It consists of two steel frames: one is shape "□", and the other shape "∏", which are perpendicularly connected together. There are diagonal braces and short columns made of rebars on the top of shape "□" steel frame. A small-scale model was first tested, and then a series of parametric study were performed using FEA. In the FEA, the nonlinearity of material and geometry were considered. The yielding and ultimate loads, as well as the stress distribution of the equipment, were investigated for the vertical tensile load condition, considering different shapes of structure, steel materials, and constraint conditions. FEA results match well with the test results. Furthermore, FEA results show that the anti-tension equipment with double column is more effective than that with single column, especially in the case of eccentric tension state. The containment of the bar by the concrete is effective in increasing the ultimate load in the condition of eccentric tension state. Stiffening strips added to the vertical steel arms can significantly increase the ultimate capacity of the equipment. Mostly, as the state of eccentricity increases, the ultimate capacity of the anti-tension equipment decreases. [ABSTRACT FROM AUTHOR]

Highlights • The blast performance of concrete increases with material heterogeneity. • A compact material dissipates less energy within its structure. • Controlled heterogeneity predetermines blast damage zones. • Layer delamination increases blast energy dissipation. Abstract Because of the current geopolitical situation, research on improving the resistance of the civil and transport infrastructure to blast or impact loads has gained considerable attention. This paper presents the results of full-scale blast experiments designed to characterize the resistance of concrete-based composite bridge decks subjected to close-in blast loading. Three composite decks with different degrees of heterogeneity were proposed and tested: a slab with basalt fiber meshes in multiple layers along the depth of the specimen, a slab with recycled textile sheets 100 mm in total thickness, and a typical hollow-core prestressed slab. The dependence of the extent of the blast damage on the material characteristics of the composite material was studied. A detailed study of the damage to the specimen caused by the close-in explosion found apparent delamination of all tested composite specimens. The heterogeneity of the layered composite material converts the blast damage due to internal rebounds into layer delamination. [ABSTRACT FROM AUTHOR]

Highlights • Nonlinear finite element model of built-up section were developed and verified. • A proposed design approach is presented using direct strength method (DSM) • The proposed approach is evaluated by comparing with the current existing method and FEA data. • A parametric study showing the influence of D1/B ratio on the stability and strength of the built-up columns. Abstract This paper, based on new proposed approaches, is a numerical investigation of the behavior of thin-walled cold-formed steel built-up columns under a uniform compression. Two types of cross sections have been studied, built-up closed and open sections formed by two channels connected by battens plates. First, a nonlinear finite element model has been developed and the results obtained show a good agreement against experimental results, such as the ultimate strength, the type of deformed shapes at failure and the lateral displacement. Second, a new proposed approach based on the DSM approach where the local, distortional or global buckling has been obtained numerically, using finite element method software, the thickness at the contact area in the web is taken as 1.0 times the thickness of the plate "t", instead of 1.5 or 2.0 times "t". In this case, the compound section is acting as one rigidly connected section. Comparisons with experimental data give a satisfactory degree of accuracy in the proposed design method (DSM-t) and the results are more conservative than those found by the DSM-1.5 and DSM-2. The results, for either closed or open sections, are also slightly conservative for columns failing in global modes than in local ones, if compared with the AISI and EC3 specifications. Some parameters, such as the spacing channels-web length ratio (B1/D) influence the stability and strength of the built-up columns. [ABSTRACT FROM AUTHOR]

Highlights • A comprehensive and discussion of the pros and cons of the different approaches to deal with frame conditions in behavioral verification of UML/OCL models. • A description of conceptual ideas how to integrate frame conditions given by modifies only statements into a symbolic formulation as well as a precise SMT-LIB realization. • An evaluation of the actual implementation including a comparison with other approaches. Abstract Validation and verification of UML/OCL models is a crucial task in the design of complex software/hardware systems. The behavior in those models is expressed in terms of operations with pre- and postconditions. These, however, are often not precise enough to describe what may or may not be modified in a transition between two system states. This frame problem is commonly addressed by providing additional constraints in terms of so-called frame conditions and has already been considered in different research areas in the last decades—except for UML/OCL where corresponding approaches have been investigated only recently. Among these, the so-called modifies only statements constitute a very promising concept which is complementary to all other approaches. More precisely, instead of allowing arbitrary modifications in principle and prohibiting certain undesired behavior, the statements explicitly describe what is allowed to change. However, this approach to frame conditions has not been considered so far in any of the numerous approaches for the automatic validation and verification of the behavior in UML/OCL models that have been proposed in the last years. Most of these approaches rely on a symbolic formulation of all possible system states and transitions between them. Therefore, in this paper we explain how modifies only statements can be integrated into an existing symbolic formulation. Based on this, we evaluate the applicability of the presented concept and compare it to previous implementations of frame conditions. [ABSTRACT FROM AUTHOR]

Highlights • A combined model is proposed for multi-step ahead wind speed forecasting. • Data preprocessing technology is introduced to improve the forecasting performance. • Quasi-Newton algorithm is used to increase the particle diversity of water cycle algorithm. • The accuracy and stability of wind speed forecasting are improved simultaneously. • The simulation results are validated well in China. Abstract Owing to the complexity and uncertainty of wind speed, accurate wind speed prediction has become a highly anticipated and challenging problem in recent years. Researchers have conducted numerous studies on wind speed prediction theory and practice; however, research on multi-step wind speed prediction remains scarce, which hinders further development in this area. To improve upon the accuracy and stability of multi-step wind speed prediction, this paper proposes a combination model based on a data preprocessing strategy, an improved optimization model, a no negative constraint theory, and several single prediction models. To improve upon forecasting performance, an improved water cycle algorithm based on a quasi-Newton algorithm is proposed to optimize the weight coefficients of the single models. In the empirical research, 10-min and 30-min wind speed data from Shandong Province in China, collected for case studies, were used to assess the comprehensive performance of the proposed combination model. Finally, we used 10-fold cross-validation and multiple error criteria to evaluate the comprehensive performance of the proposed combination model. The simulation results indicate that (a) the quasi-Newton algorithm can effectively increase the diversity of the water cycle algorithm particles, resulting in improved water cycle algorithm optimization performance; (b) the combination model exhibits superior predictive performance to a single model by taking advantage of each single model; and (c) the proposed combination model can effectively improve multi-step wind speed prediction results. [ABSTRACT FROM AUTHOR]

The solution of discrete ill-posed problems has been a subject of research for many years. Among the many methods described in the literature, the Bregman algorithm has attracted a great deal attention and been widely investigated. Recently, a nonstationary preconditioned version of this algorithm, referred to as the nonstationary modified linearized Bregman algorithm, was proposed. The aim of this paper is to discuss numerical aspects of this algorithm and to compare computed results with known theoretical properties. We also discuss the effect of several parameters required by the algorithm on the computed solution. [ABSTRACT FROM AUTHOR]