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This paper presents a new discretize-then-optimize (DTO) method for dynamic force inversion in a two-dimensional (2D) linear elastic, damped solid based on Runge–Kutta (RK) explicit time integration. Previous literature on DTO modeling for force or material inversion has predominantly focused on inversion methods based on Newmark implicit time integration. However, because implicit time integration may not be suitable for a problem with a large number of degrees of freedom [e.g., third-dimensional (3D) wave problems], there is a need to study an alternative DTO force-inversion formulation that centers around the RK explicit time integration, leveraged by a diagonal mass matrix. This paper attempts to fill this gap and present the full detail of the new RK-DTO formulation for dynamic force inversion. Our computational examples demonstrate that the new RK-DTO inversion simulator effectively reconstructs moving dynamic forces on the upper surface of the solid. It excels in efficiency when dealing with a higher number of degrees of freedom (DOFs) and maintains accuracy even with increased DOFs and observation durations. A smaller sensor spacing enhances the accuracy of the inverted force profile in the RK-based inversion. The presented inversion method can effectively identify the profiles of dynamic moving loads even when measurement data include noise or when the values of material properties are not deterministic. [ABSTRACT FROM AUTHOR]

Origami-based structures have been widely implemented in the design of deployable systems. They possess desirable properties such as easiness in manufacturing, high transportability, programmability, and the capability to fold into complex three-dimensional (3D) structures starting from planar configurations. However, their geometric complexity poses major challenges in developing efficient design methods, in which optimizing their geometries and folding motions remains a challenging task. This paper investigates the motion and shape inverse design of a Miura-based origami deployable system for architectural applications. The proposed structure folds from a flat to different 3D shapes, has 1 degree of freedom, and can fold rigidly being also flat foldable. The capabilities of the structure to fold approximating symmetrical target shapes of different geometries and achieve tailored folding motions are investigated. Furthermore, an inverse computational design workflow is proposed. The structure showed good accuracy in approximating target shapes, folding within desired motion envelopes, and avoiding collisions with surrounding objects. The origami-based system could be designed to deploy in different scenarios at the architectural scale, and could find applications as deployable canopy for improving comfort in outdoor conditions. Although limited to early design stages, the proposed design workflow is a flexible tool that could be applied to shape and motion inverse design tasks by simply variating its objective function. The method could be further applied to different typologies of rigid-foldable origami-based structures at different scales. Current studies on origami-based deployable systems mainly cover geometries that can be deployed, function as static systems, and further folded after the end of their operation. Despite possessing desirable characteristics, such designs fail to take advantage of origami properties such as programmability and dynamic adaptability to different scenarios. In addition, the optimization of such structures and the conception of efficient design workflows remain challenging. This paper proposes a design that could be folded and unfolded dynamically adapting to its environment. Furthermore, a computational design workflow for the design of shape and motion is presented. The novel aspects of the study can be summarized as follows: (1) tailored design of complex 3D geometries using two-dimensional (2D) origami patterns, (2) design of both shape and motion, which extends the common only-shape design approach, (3) development of an efficient and flexible computational design workflow that could be adapted to diverse inverse design tasks with different objectives, and (4) development of the workflow in the Grasshopper interface, in which environmental simulations could be carried out. Thermal comfort, wind comfort, and acoustics are some of the topics of interest that could be evaluated without making any change in the proposed parameterization and optimization framework. [ABSTRACT FROM AUTHOR]

To overcome nonconvergence in the two-dimensional–three degrees of freedom (2D–3DOF) method, the practical modal-driven flutter analysis method (PMDFA) was proposed for the coupled flutter in long span bridges that used a genetic algorithm (GA). First, formulas in the 2D–3DOF method were updated when the assumed initial displacement was expressed as an exponential form for the frequency and damping. Then, the calculation results from the modified formulas proved to be identical to the exact solution that was calculated by the complex eigenvalue analysis (CEVA). However, due to the inherent defects in the iterative equations, the original fixed-point method (FPM) failed to converge when the frequencies of heaving and torsion were close. To overcome the convergence limitations in the FPM, a powerful GA without the restrictions of the iterative equation properties was introduced into the revised 2D–3DOF method. Then, the flutter analysis of suspension bridges with a main span from 1,000 to 5,000 m was carried out, and the numerical calculation showed that the FPM failed to complete the flutter calculation in most cases; however, the GA performed the analysis. In addition, a study on a suspension bridge showed that the numerical results obtained by the PMDFA were in reasonable agreement with the experimental results. Therefore, the proposed GA-based method has advantages of high accuracy and strong robustness and has wider application prospects in the flutter analysis of super long span bridges. Flutter instability can cause a large amplitude vibration and destroy a structure completely and it must be avoided during the service life of a structure. With an increase in the span, flutter performance has become an important index in the wind resistance design of long span bridges. The 2D–3DOF method can evaluate the flutter performance of structures effectively and establish a deep understanding between aerodynamic parameters and aerodynamic performance. Therefore, it plays an important role in the analysis of the flutter mechanism. However, due to the defect in the original convergence algorithm, sometimes it cannot calculate Ucraccurately in practical engineering applications. Therefore, to overcome this problem, a GA was introduced into this paper to calculate convergence. The case study showed that the proposed GA-based method has the advantages of high accuracy and strong robustness, and could deal with the problem perfectly. In addition, the iteration problem of nonconvergence might occur in the other methods, such as the CEVA or the multimodal flutter analysis and the solution idea in this paper might have a certain reference value for the convergence calculation. [ABSTRACT FROM AUTHOR]

When designing steel members with nonsymmetric cross sections, it is essential to consider twisting effects when performing stability checks via second-order analysis according to the ANSI/AISC 360-22. Existing line-element formulations for nonsymmetric sections are mostly derived based on thin-walled assumptions, leading to an overestimation of member strength due to the inaccurate prediction of member behavior, especially when the cross sections have moderate wall thickness. This paper proposes an efficient line-element method for second-order analysis of steel members with nonsymmetric thick-walled sections considering the warping degree of freedom (DOF) and the twisting effects along with the transverse shear deformations. Additionally, a two-dimensional (2D) finite-element cross section analysis method employing the constant strain triangle (CST) element is developed to calculate the section properties for arbitrary cross sections, including the Wagner and the shear coefficients. The proposed method is implemented in the educational structural analysis software MASTAN2 and verified through two sets of examples. [ABSTRACT FROM AUTHOR]

Knowing the extent of displacement experienced by railroad bridges when loaded is useful when evaluating the safety and serviceability of the bridge. However, measuring displacements under train crossing events is difficult. If simplified reference-free methods would be accurate and validated, owners would conduct objective performance assessment of their bridge inventories under trains. Researchers have developed new sensing technologies (reference-free) to overcome the limitations of reference point-based displacement sensors. Reference-free methods use accelerometers to estimate displacements, by decomposing the total displacement in two parts: a high-frequency dynamic displacement component, and a low-frequency pseudostatic displacement component. In the past, researchers have used the Euler-Bernoulli beam theory formula to estimate the pseudostatic displacement assuming railroad bridge piles and columns can be simplified as cantilever beams. However, according to railroad bridge managers, railroad bridges have a different degree of fixity for each pile of each bent. Displacements can be estimated assuming a similar degree of fixity for deep foundations, but inherent errors will affect the accuracy of displacement estimation. This paper solves this problem expanding the 1 degree of freedom (1DOF) solution to a new 2 degrees of freedom (2DOF), to collect displacements under trains and enable cost-effective condition-based information related to bridge safety. Researchers developed a simplified beam to demonstrate the total displacement estimation using 2DOF and further conducted experimental results in the laboratory. The authors assumed linearity on properties and connections and used real train crossing event data as input to evaluate the accuracy of the proposed 2DOF method. The estimated displacement of the 2DOF model is more accurate than that of the 1DOF model for ten train crossing events. With only one sensor added to the ground of the pile, this method provides owners with approximately 40% more accurate displacements. Future work includes the study of nonlinearities and parametric study of the effect of resonance in displacement estimation accuracy for practical field implementation. The main application of this research is the optimization of the number of sensors and the simplification of sensor location, for lateral displacement estimation. Infrastructure managers can install a minimum number of sensors in tall piers or structures and determine the transverse displacement. The main practical aspect of this work is that engineers can collect the rotation at the base of the pier by locating sensors in the base. Using both the rotation both at the bottom and the top of the pier, the total displacement at the top can be obtained. In the practical domain, timber railroad piers could demonstrate additional lateral displacement under train crossing events not associated with the rotation above ground. Engineers could observe or collect that lateral displacement and add it to the total estimated displacement to obtain the total transverse displacement. Based on the field observations of the main author of this paper the lateral separation between the timber pile at the base of the pier is small, however it can be a practical next step in further development of the proposed method for practical applications. [ABSTRACT FROM AUTHOR]

Due to the harsh space environment, burdensome tasks, and complex structure, space manipulators are vulnerable to joint failure, especially the free-swing joint failure during on-orbit operation. The unactuated units, including free-swing joint and free-floating base, lack driving source and need to be controlled by actuated joints. To determine the control input while executing the task, it is necessary to analyze the controllable degree of system input to the unactuated unit. In this paper, comprehensively considering the coupling effects of velocity and acceleration between free-floating base, fault joint, and actuated joint, the kinematic and dynamic coupling relationship of the space manipulator with free-swing joint failure is established first. Then, the controllability of the space manipulator is analyzed. Considering the factors affecting the coupling motion between the actuated joint and the unactuated unit, the controllable degree index of the actuated joint to the unactuated unit is constructed. Finally, taking a space manipulator with seven degrees of freedom as the object, the numerical simulation is carried out to analyze the influence of joint configuration, actuated joint combination, and joint velocity on the controllability of the space manipulator, so as to provide guidance for the subsequent fault-tolerant motion control of the space manipulator. [ABSTRACT FROM AUTHOR]

Many of the procedures used in bridge design are force-based and may be considered reasonable design approaches that will lead to safe structures. But they do not directly address performance criteria at the initial stage of the design. On the other hand, the previously presented displacement-based design procedures of isolated bridges only considered the displacement of the deck, which means the pier's seismic performance and the substructure mass effects are ignored. This paper presents a new performance-based design method for isolated RC bridges considering the contribution of substructure mass. This method allows the designer that selects the performance level of the superstructure and substructure at the beginning of the design procedure. In this respect, the two degrees of freedom analytical model of the isolated bridge containing substructure mass is presented to quantify its effect on the performance of the seismically isolated bridge. The proposed design method is applied to two continuous-span bridges with regular and irregular substructures, and different target performance levels, including elastic and yielded substructures. The results of the proposed design method have been compared with nonlinear time history analyses, AASHTO, and National Cooperative Highway Research Program simplified methods. The results showed that the seismic performances are close to the results of the nonlinear time history analyses. However, the other design approaches, which ignore the substructure mass, underestimate the responses of the substructure. [ABSTRACT FROM AUTHOR]

Existing nonlinear time series methods are mostly used to capture the conditional variance or volatility of hydrometeorological factors. Insufficient attention has been paid to the time-varying variance-covariance and dynamic conditional correlation among multivariate hydrometeorological time series. This paper introduces a type of multivariate generalized autoregressive conditional heteroscedasticity (MGARCH) model, named the dynamic conditional correlation (DCC) model, to characterize the time-varying relationship between rainfall (P), temperature (T), and streamflow (Q). For this purpose, the Yellow River basin is used as an example, and three association models are established, including the bivariate relationships of P-Q, T-Q, and the three-variable relationship of P&T-Q (rainfall and temperature jointly on streamflow). The results of the univariate generalized autoregressive conditional heteroscedasticity (GARCH) model show that the volatility of the temperature series is weaker than that of rainfall and streamflow. The conditional variance of the streamflow and temperature series has long-term persistence, while that of rainfall has short-term persistence, but the temperature has the lowest degree of variance memory. The bivariate DCC model shows that the streamflow is more sensitive to precipitation changes than temperature, and both rainfall-streamflow (P-Q) and temperature-streamflow (T-Q) associations have stronger long-term persistence and covariance memory. The P&T-Q correlation shows that the covariance of rainfall and temperature has stronger long-term persistence than streamflow fluctuations. In addition, the effectiveness of the P&T-Q relationship model is also stronger than that of the P-Q and T-Q relationship models. DCC, considering the combined effects of rainfall and temperature, can better represent the impact of environmental changes on streamflow than a single variable. [ABSTRACT FROM AUTHOR]

In the present paper, a semi-active damping control approach is proposed for the resilient design of façades subjected to extreme loads in the form of blast excitation. A 4 degrees of freedom (4DOF) model is developed to explore the effectiveness of the controlled variable damping, obtained by introducing magnetorheological (MR) dampers at the anchorage points of the curtain wall (CW). The modified Bouc-Wen model is incorporated into the multi-degree of freedom (MDOF) model and fuzzy logic control (FLC) is used to obtain continuously variable command voltage for damper coils, and thereby variable damping in the CW system. Dynamic displacement responses are evaluated for a specific system under different levels of blast loading to assess the structural integrity of the CW components, i.e., the glass and the frame. Pressure-impulse (PI) iso-damage curves are obtained for three damage states: glass cracking, membrane tearing, and frame yielding. Detailed parametric studies are carried out to demonstrate the versatility and superiority of the semi-active controlled variable damping approach toward the blast-resilient design of glass façades. [ABSTRACT FROM AUTHOR]

For the first time, a two-node beam element with nine degrees of freedom (DOFs) was developed in this paper using a combination of modified couple stress and k th-order shear deformation beam theory to analyze the free vibration and static buckling responses of rotating bidirectional functionally graded porous (BDFGP) microbeams resting on variable elastic foundations, in which the whole structure was exposed to a magnetic field in the hygrothermal condition. The mechanical properties and the length-scale parameters varied in both the thickness and length directions, which in the novel porosity model and power-law indexes of the material were considered to be a function of the x - and z -coordinates. The present method's accuracy was determined by comparing it with published findings. Additionally, extensive research was conducted to evaluate the effect of various parameters on the mechanical responses of the rotating BDFGP microbeam. The numerical results showed that porosity coefficient, elastic foundation parameters, and hygrothermal environment all significantly affect the rotating BDFGP microbeam's free vibration and static buckling behavior. [ABSTRACT FROM AUTHOR]

A novel quadrature element for performing plane stress elastoplastic analysis is introduced in this paper. Differing from the popular finite-element method, the quadrature-element method (QEM) first evaluates the integration in the weak-form statement of the problem by an integral quadrature scheme, and then approximates the differentiation at the discrete integration points by the differential quadrature analog. As a result, the QEM avoids construction of shape functions and obtains higher-order elements easily by just increasing the order of integration. The usage of higher-order elements leads to more accurate solutions and coarser geometric meshes without detriment to the computational scale because the number of degrees of freedom is maintained. In addition, the element nodes in the QEM are the same as the integration points that possess physical meanings such as strains and stresses, which is crucial in the elastoplastic analysis for determining the elastic/plastic state of the nodes. A straightforward elastoplastic quadrature-element formulation is developed. Incremental-iterative and return mapping solution schemes are adopted to implement the quadrature element for the elastoplastic analysis. Numerical examples are presented to demonstrate the effectiveness and high accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper reports an assessment of structure damages after the Richter magnitude 6.4 Puerto Rico earthquake that occurred on January 7, 2020. A review of the seismicity of the region and the postdisaster investigation of structural damages is first presented. The paper then focuses on explaining the failure modes of 2-story residential structures with open first story, which demonstrated the classical soft story behavior. The typological characterization of the failure modes is investigated using a nonlinear elastic dynamic analysis with a single degree of freedom model, which illustrates the contributions from partial to full construction of infill walls to the stiffness of the 2-story structures. The results indicate that the completion of the infill walls can significantly improve the stiffness of these structures and reduce damages to the structures. [ABSTRACT FROM AUTHOR]

This paper demonstrates the influence of pile head freedom on the thermomechanical performance of a belled pile. Field tests on the belled pile response to a cooling–heating cycle and incremental structural construction are carried out. The temperature changes, axial strain profiles, and pressures at the pile toe are recorded through the buried instruments. The variation in the degrees of freedom, tensile forces, and inferred pile head settlements along the pile depth for different test procedures are analyzed using the measured data. The degree of freedom close to the pile head calculated from strain rates decreases with the structure mass with a gradient of −2.8×10−5/kN. The reducing effect of the incremental superstructure on pile freedom decreases along with the orientation of the pile depth. Compared with the inferred thermal displacement of the pile without an applied structural load, the values decrease by about 10% when the pile was subjected to incremental floors, and an elastic recoverable characteristic response to cooling–heating-recovery phases is observed. Compared with the equal-diameter pile, the belled pile showed a significant constraint close to the toe. Mechanical loads can decrease the cracking risk because of a possible tensile force under cooling conditions. [ABSTRACT FROM AUTHOR]

Rebar cages are commonly used in reinforced concrete constructions. These cages consist of longitudinal and transverse reinforcing bars usually connected by tie wires. Numerous incidents of rebar cage failure and collapse have been reported at construction sites, often leading to injuries, fatalities, construction schedule delays, and added costs. Using mechanical connectors such as U-bolts instead of tie wires can improve stability and strength of rebar cages. This paper aims to investigate the mechanical behavior of U-bolt connections through experimental tests and to explore the potential application to rebar cages through analytical models. Experiments were conducted on U-bolt connectors to determine the force-deformation response behavior in different degrees of freedom and for different rebar conditions. Then, the data obtained from a previously completed experimental study on a full-scale tie-wired rebar cage were used to develop and calibrate a nonlinear finite-element model of the test specimen. The force-deformation response of U-bolt connections was then included in the model, replacing the tie wires, to investigate the effect of mechanical connectors on the lateral stiffness and strength of the rebar cage. The results showed that application of mechanical connectors for cross-bar connections in the rebar cages can increase the lateral strength of rebar cages, rendering U-bolt connectors as a potential solution to improve stability and safety of rebar cages. [ABSTRACT FROM AUTHOR]

Apprenticeship training is at the heart of government skills policy worldwide. Application of cutting-edge information and communication technologies (ICTs) can enhance the quality of construction training, and help in attracting youth to an industry that traditionally has a poor image and slow in uptaking innovation. This paper reports on the development of a novel mixed reality (MR) system uniquely targeted for the training of construction trade workers, i.e., skilled manual workers. From a general training viewpoint, the system aims to address the shortcomings of existing construction trades training, in particular the lack of solutions for enabling trainees to train in realistic and challenging site conditions, while eliminating occupational health and safety risks. From a technical viewpoint, the system currently integrates state-of-the-art virtual reality goggles with a novel cost-effective 6-degree-of-freedom (DOF) head pose tracking system supporting the movement of trainees in room-size spaces, as well as a game engine to effectively manage the generation of the views of the virtual three-dimensional environment projected on the VR goggles. Experimental results demonstrate the performance of the 6-DOF head pose tracking system, which is the main computational contribution of the research reported in this paper. Then, preliminary results reveal its value to enable trainees to experience construction site conditions, particularly being at height, in different settings. Details are provided regarding future work to extend the system into the envisioned full MR system whereby a trainee would be performing an actual task, e.g., bricklaying, while being immersed in a virtual project environment. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the thermal and mechanical behaviors of an energy pile–raft foundation under intermittent heating operation with forced heat recharge, with 16 h of pile cooling and 8 h of forced heat recharge (referred to as 16F, where F indicates forced). The forced heat recharge was found to increase the daily heat exchange rate to 180 W/m, which was 50% higher than the value under general intermittent heating operation without forced heat recharge. The raft and building load at the pile head imposed a significant restraint on the upper part of the energy pile, leading to a minimum degrees of freedom (0.27) near the pile head. The mechanical behaviors of the pile, including strains, stresses, and pile end displacements and stresses, followed reversible paths when plotted against the daily temperature cycles. A slight residual pressure stress (10 kPa) was observed at the bottom of the raft during the initial thermal cycles. [ABSTRACT FROM AUTHOR]

This paper examines the deflected shape assumptions built into the single-degree-of-freedom (SDOF) methodology used for analyzing structural components subject to blast loading. Design professionals use the SDOF models to analyze blast effects on components. It is common knowledge that the SDOF method is an approximation, and is not suitable for large charges with short distances (lower scaled distance -Z). Current design guidelines establish the limit of Z = 1.2 m=kg1/3 for using SDOF methodologies for blast-loaded components, which is equivalent to a peak pressure of 5,000 kPa; however, this paper shows that the limit may be significantly higher in Z value (or lower in peak pressure). Higher air-blast pressure and impulse combinations cause hinges toform before the assumed deflected shape dominates the response. Because transformation factors for SDOF are derived using static deflected shapes and the static collapse mechanism, the factors may not produce accurate or conservative responses for blast loading at lower scaled distances. Using the finite element multi-degree-of-freedom (FE-MDOF) model, the paper validates the accuracy of SDOF shape factors for large scaled distances, and shows that the static deflected shape assumptions do not apply at lower scaled distances with higher impulses. Limits to SDOF are established based on the equivalent shape factors, and the variability in the limits based on damping and mass are also discussed. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) coupling beams in pre-1970s coupled-wall structures often feature a small number of stirrups, and thus are susceptible to shear failure along inclined cracks. In short beams with a span-to-depth ratio smaller than about 2.5, the failure occurs along diagonal cracks and can limit the ductility of the member, which in turn limits the seismic performance of the entire coupled-wall system. To suppress diagonal tension failure, the coupling beams can be strengthened with externally bonded fiber-reinforced polymer (FRP) sheets. However, as the FRP sheets exhibit debonding and rupture, their contribution to the shear resistance cannot be evaluated without an explicit consideration of the compatibility of deformations with the existing beam. Therefore, this paper proposes a mechanical model based on deformations that predict the complete behavior of FRP-strengthened short coupling beams exhibiting diagonal tension failure, including the effects of debonding and rupture of the FRP. The model is an extension of a two-parameter kinematic theory (2PKT) for RC coupling beams and uses two degrees of freedom to evaluate the deformations of the beam. The extended 2PKT is validated with tests from the literature and is used to study the effect of FRP sheets. The model predicts the influence of existing diagonal cracks as well as the effect of the preparation of the beam edges prior to the application of the FRP sheets. According to the model, the effectiveness of FRP sheets to increase the shear resistance increases with the span-to-depth ratio of the beam. Furthermore, for the relatively short beams studied in the paper, it is predicted that U-sheets and side sheets are nearly as effective as fully wrapped FRP sheets. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of flexibly attached secondary systems (FSS) on the dynamic behavior of primary structures (PS) under harmonic and seismic ground excitations. An FSS affects the main structure during ground excitation differently than a secondary system that is rigidly attached to it. Small displacements in the FSS are used to derive the equations of motion that define the behavior of the PS and FSS. The analytical formulation presented is validated by a finite element (FE) study conducted in SAP2000. The influence of mass ratio, tuning frequency ratio, and excitation frequency ratio on the dynamic behavior of the PS is investigated. The results show that the combined system (PS+FSS) behaves as a modified single degree of freedom (SDOF) structure at higher tuning frequency ratios. The dynamic response of the structure is independent of the mass ratio at low tuning frequency ratio of FSS. Under seismic excitations, the flexible structure's response reduces considerably as the mass ratio increases, compared to a stiff structure at a higher tuning frequency ratio. When the tuning frequency ratio is equal to one, smaller mass ratios of FSS increase the seismic performance of the stiff structure. A design methodology is proposed to measure the spectral acceleration of the primary structure by incorporating the effect of FSS in the design response spectrum. An analysis of the tuning frequency ratio and mass ratio on the modified design spectrum is also presented. Finally, the proposed design methodology is validated with an existing study. [ABSTRACT FROM AUTHOR]

The maximum inelastic response of bilinear single-degree-of-freedom (SDOF) systems when subjected to ground motions without distinguishable pulses is revisited with dimensional analysis by identifying timescales and length scales in the time histories of recorded ground motions. The characteristic length scale is used to normalize the peak inelastic displacement of the bilinear system. The paper adopts the mean period of the Fourier transform of the ground motion as an appropriate timescale and examines two different length scales that result from the peak ground acceleration and the peak ground velocity. When the normalized peak inelastic displacement is presented as a function of the normalized strength and normalized yield displacement, the response becomes self-similar, and a clear pattern emerges. Accordingly, the paper proposes two alternative predictive master curves for the response that solely involve the strength and yield displacement of the bilinear SDOF system in association with either the peak ground acceleration or the peak ground velocity, together with the mean period of the Fourier transform of the ground motion. The regression coefficients that control the shape of the predictive master curves are based on 484 ground motions recorded at rock and stiff soil sites and are applicable to bilinear SDOF systems with a postyield stiffness ratio equal to 2% and an inherent viscous damping ratio equal to 5%. [ABSTRACT FROM AUTHOR]

Unreinforced masonry structures, particularly façade walls, are seismically vulnerable due to their weak connections with adjacent walls, floors, and/or roofs. During an earthquake, such walls formulate local mechanisms prone to out-of-plane collapse. This behavior has been largely investigated using classical rocking theory, which assumes the structure responds as a rigid body undergoing rocking motion, with energy dissipation at impact. Due to the complexity of the problem, however, e.g., number of degrees of freedom or boundary conditions, numerical block-based modeling is gaining momentum. However, numerical models lack a consistent and reliable treatment of the energy loss at impact. This paper bridges the gap between the well-established energy loss of classical rocking theory and the treatment of damping in numerical modeling. Specifically, it proposes an equivalent viscous damping model through novel ready-to-use predictive equations that capture the dissipative phenomena during both one-sided and two-sided planar rocking motion. The results reveal a satisfactory performance of the proposed model through comparisons with experimental results from literature and highlight its universality and robustness through applications of the model in fundamentally different block-based numerical modeling software. [ABSTRACT FROM AUTHOR]

Parallel structural systems and assemblies are challenging to erect, align and plumb on construction sites due to their complex geometries and current heuristic realignment strategies. Examples of parallel systems include complicated pipe modules and pipe racks in the industrial construction sector. This paper presents a generalized approach analogous to robotics and inverse kinematics for building parallel systems' realignment planning, introduced using a series approach. In addition to the calculation of a realignment strategy, feasible applications of such a strategy are also investigated in this paper. The framework for realigning parallel systems has two primary steps: (1) as-built status identification by capturing the geometric state of construction assemblies using three-dimensional (3D) imaging theories, and (2) realignment calculation and actuation based on degrees of freedom (DOFs) defined during the development of the kinematics chains of assemblies. A Quasi-Newton-Raphson (QNR) method is employed for solving the kinematics equation of the inverse kinematics analogy. Experimental results show that the developed algorithms are sufficiently accurate to capture any incurred geometrical discrepancies in parallel construction assemblies and proactively calculate and plan for efficient realignment strategies. Generalization of realignment calculation for parallel systems and realignment actuation are the key contributions of this work. [ABSTRACT FROM AUTHOR]

To investigate the performance of reinforced-concrete frames with buckling restrained braces (RCF-BRB) subjected to bidirectional earthquakes, a full-scale two-story RCF-BRB was tested using substructured pseudodynamic (PsD), quasistatic, and pushover techniques. This paper focuses on the structural modeling for the substructured PsD tests, and the control and measurement issues of the bidirectional loading system. To make a credible reproduction of the structural response using substructured PsD technique, an overlap modeling technique together with tuning the mass of the lamped-mass model and stiffness of the numerical substructure was employed to reduce errors caused by the incomplete boundary condition. The outer-loop control method based on Newton's iteration method was introduced for the loading system, with the data from external displacement sensors as the feedback to avoid errors caused by possible gaps in the connection parts of the loading system. The redundancy issue, caused by the actuators outnumbering the degrees of freedom of the floor to be controlled, is addressed with a force-displacement mixed control technique. The three of four actuators were controlled in displacement mode, whereas the redundant one was in force mode. The force command to the redundant actuator was determined with the optimization criteria to minimize the loads relative to the capacities of the actuators. The working range of the displacement sensors is investigated using numerical and geometric approaches. Failure examples from numerical simulation and experiment were shown to emphasize the importance of proper arrangement of displacement sensors. A rearrangement of the displacement sensors was proposed for the pushover test to enlarge the working range. Time-history results of the prototype structure using the calibrated finite-element model show that the PsD substructure test results could represent seismic responses of the prototype structure. The measured mass-center displacements accurately tracked the target displacements throughout the test, indicating the effectiveness of the loading control and measuring system. [ABSTRACT FROM AUTHOR]

The numerical simulation of a 3D complex reservoir has been an important but difficult problem. One of the biggest challenges is how to deal with the large number of natural fractures with consideration of hydromechanical coupling effect in those fractures. To address this problem, a 3D hydromechanical coupled element partition method (3D-EPM) is developed. The 3D-EPM allows a fracture to run through an element without any extra degree of freedom. It can embed any number of fractures in a background mesh without mesh modification. This brings great convenience to 3D reservoir simulation. To represent the permeability of a cracked element, the equivalent permeability of this cracked element is derived based on the cubic law. To account for the hydromechanical coupling effect in a fracture, the coupled equation of 3D-EPM is developed. It is verified by the analytical model. The simulation results suggest that this method can simulate the 3D hydraulic fracture propagation, its interaction with natural fractures and the impact of in-situ stresses. This paper provides an alternative method for the 3D hydraulic fracture simulation in a complex reservoir with consideration of hydromechanical coupling effect in a fracture. [ABSTRACT FROM AUTHOR]

The first two moments of the steady-state response of a dynamical random system are determined through a polynomial chaos expansion (PCE) and a Monte Carlo simulation that gives the reference solution. It is observed that the PCE may not be suitable to describe the steady-state response of a random system harmonically excited at a frequency close to a deterministic eigenfrequency: many peaks appear around the deterministic eigenfrequencies. It is proved that the PCE coefficients are the responses of a deterministic dynamical system-the so-called PC system. As a consequence, these coefficients are subjected to resonances associated to the eigenfrequencies of the PC system: the spurious resonances are located around the deterministic eigenfrequencies of the actual system. It is shown that the polynomial order required to obtain some good results may be very high, especially when the damping is low. These results are shown on a multidegree-of-freedom (DOF) system with a random stiffness matrix. A 1-DOF system is also studied, and new analytical expressions that make the PCE possible even for a high order are derived. The influence of the PC order is also highlighted. The results obtained in the paper improve the understanding and scope of applicability of PCE for some structural dynamical systems when harmonically excited around the deterministic eigenfrequencies. [ABSTRACT FROM AUTHOR]

Evaluating the mean-square response at the transient state of a single degree of freedom (SDOF) system to stationary random excitation has been extensively studied in the past, but the explicit closed-form solution has not been available unless the excitation was considered to be a physically unrealizable white noise process. In this paper, explicit closed-form solutions for the mean-square response are derived for arbitrary input power spectral density (psd) functions. While all existing solution methods for evaluating the mean-square response have always been conducted in the time and/or frequency domains, the proposed method is operated in the complex plane (Laplace domain) based on pole-residue formulations. Not only is the proposed approach is much more efficient than other existing approaches, but also meaningful physical and mathematical insights can be gained in its solution procedure. To demonstrate the procedure, this paper considers the excitation process characterized by a white and nonwhite psd, respectively, and the corresponding closed-form solutions for the transient mean-square response of SDOF systems are derived. The correctness of the closed-form solution for the nonwhite psd is verified by Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

It has been experimentally identified that a stationary crowd or an individual acts like a mass-spring-damper in structural vibration. However, experiments have shown that only one resonance frequency or damped natural frequency of human-structure systems are observed on structures, such as grandstands or floors with crowds. This paper studies the presence of the two resonance frequencies in a heavily damped, two-degree-of-freedom (TDOF) system in theory and in experiment. The invisibility, or nonpresence, of a resonance frequency is defined by investigating a heavily damped single-degree-of-freedom (SDOF) system subjected to a harmonic load. By using frequency response functions (FRFs) for acceleration, it is demonstrated that the observable presence of the two resonance frequencies of the TDOF system depends on the mass ratio and frequency ratio of the upper SDOF model to the lower SDOF model and the damping ratio of the upper SDOF model. The conditions for the presence of the two resonance frequencies are presented graphically based on a study of over 5,000 cases that covered reasonable ranges for these three parameters. Two sets of human-structure interaction experiments, whose design was based on the conditions for observing the resonance frequencies, demonstrated qualitatively the effect of the mass ratio of the system and damping ratio of the human body on the presence of the resonance frequencies, thus verifying the theoretical results. These limiting conditions are discussed and the observation of only one resonance frequency in experiments on some human-structure systems is explained. [ABSTRACT FROM AUTHOR]

An analytical method for responses of a class of nonlinear single degree-of-freedom (DOF) systems under nonstationary random excitations (NSREs) is presented. It is based on the transformation of the nonlinear stochastic differential equations that govern the vibrations of nonlinear systems under NSREs into a polynomial of which the exact roots are available, and therefore solutions without approximation of the nonlinear system can be evaluated. For demonstration purposes, the van der Pol-Duffing oscillator under a time-modulated zero mean Gaussian white noise process is considered. Representative solutions are verified by the Monte Carlo simulation (MCS) technique. The main conclusions are as follows. First, a simple and relatively straightforward method has been developed to transform the nonlinear stochastic differential equations of a class of nonlinear single DOF systems into polynomials for which exact solutions are available. The analytical solution developed in this paper is for the deterministic equation of motion for a specific realization of the input excitation function . The statistics of the displacement response are obtained using the expectation operator applied to the exact solutions computed for every realization of . Second, for the first time solutions without approximation are obtained for a nonlinear single DOF system with nonlinearities involving nonlinear velocity as well as displacement and under NSRE. Third, for solutions of the van der Pol-Duffing oscillator the computational time required by the present method is much more efficient than that using the MCS technique. [ABSTRACT FROM AUTHOR]

Soil nailing is an in situ soil reinforcement technique used for enhancing the stability of slopes, retaining walls, and excavations. Nails work predominantly in tension, but may also work in bending and/or shear under certain circumstances. To accurately simulate the interaction mechanism between soil mass and nails, it is necessary to study the behavior of their contact interface. The Goodman element is one of the interface elements used extensively in geotechnical contact problems. However, larger normal stiffness values are needed in the application of the Goodman element, which often leads to larger numerical error. In this paper, the Goodman element model was modified by adding two rotational degrees of freedom. Then, a finite-element program was written based on the modified Goodman element model and was applied in analyzing a foundation pit. Compared with the actual monitoring results, it shows that the modified Goodman element model developed in this paper is reasonable and feasible. [ABSTRACT FROM AUTHOR]

This paper presents new closed-form analytical approximations to the first-passage problem in structural reliability by using the exact closed-form solutions for the spectral characteristics of nonstationary random processes. The first-passage problem applied to a structural system possibly with random parameters and subjected to stochastic loading consists of computing the probability of a response quantity exceeding a deterministic threshold in a given exposure time. This paper also investigates, on the basis of benchmark problems, the absolute and relative accuracy of analytical approximations of the time-variant failure probability, such as Poisson, classical Vanmarcke, and modified Vanmarcke approximations, in the case of nonstationary random vibration. The classical and modified Vanmarcke approximations are expressed as time integrals of the closed forms of the corresponding hazard functions. These closed forms refer to linear elastic systems subjected to stationary and nonstationary base excitation from at-rest initial conditions, and they are obtained using recently developed exact closed-form solutions for the time-variant bandwidth parameter. These closed-form Vanmarcke's approximate solutions to the first-passage problem are compared with the well known Poisson approximation and accurate simulation results obtained via the importance sampling using elementary events (ISEE) method for two benchmark applications: (1) a set of linear elastic single-degree-of-freedom (SDOF) systems defined by different natural periods and damping ratios, and (2) an idealized, yet realistic three-dimensional asymmetric steel building model. The linear elastic SDOF systems are subjected to white noise base excitation from at-rest initial conditions, while the steel building model is subjected, from at-rest initial conditions, first to white noise and then to a time-modulated colored noise base excitation. The retrofit of this second benchmark structure with viscous dampers is also considered, illustrating (1) the use of the newly available closed-form approximations of the failure probability for nonclassically damped linear elastic systems, and (2) an example of practical use in structural engineering of the presented analytical solutions. The results presented in this study show that, for nonstationary random vibration problems, the two Vanmarcke approximations can improve considerably the estimates of the time-variant failure probability for the first-passage problem when compared with the simpler Poisson approximation. [ABSTRACT FROM AUTHOR]

This paper presents an application of multibody dynamics with unilateral contact to model the friction wedge interaction with the bolster and the side frame. The new friction wedge model is a three-dimensional, dynamic, stand-alone model of a bolster–friction wedge–side frame assembly. It allows the wedge four degrees of freedom: vertical displacement; longitudinal (between the bolster and the side frame) displacement; toe in and toe out; and yaw (rotation about the vertical axis). The dedicated train modeling software NUCARS (Transportation Technology Center, Inc., Pueblo, Colo.) has been used to run simulations with similar inputs and to compare—when possible—the results with those obtained from the new stand-alone MATLAB (MathWorks, Natick, Mass.) friction wedge model. The stand-alone model shows improvement in capturing the transient dynamics of the wedge better. Also, it can predict not only normal forces going into the side frame and bolster, but also the associated moments. Significant simulation results are presented and the main differences between the current NUCARS model and the new stand-alone MATLAB models are highlighted. [ABSTRACT FROM AUTHOR]

The dynamic flexibility (DF) and improved dynamic flexibility (IDF) methods can be applied to extract constrained structural modes from free-free modal test data. The residual flexibility method is also good for boundaries of constrained structure with rigid supports. Under elastic support boundary conditions both the DF and residual flexibility methods cannot produce accurate results. This paper expands the previously published IDF method to become a more general approach for structural design engineers. A new method called the general dynamic flexibility (GDF) method has been developed in this paper to extract constrained structural modes from free test data. The GDF method can always be applied as follows: (1) when the boundary support stiffness is very stiff, the GDF method can accurately obtain results from rigid support as by Liu et al. in 2001 and Zhang and Wei in 2003; (2) when the support stiffness is soft, the present method can produce results similar to those free-free modal parameters measured by hanging structures using rubber band; (3) when the support stiffness is zero, the method can reproduce true free-free modal parameters; and (4) when the support stiffness has any finite values, the GDF method can also achieve satisfactory results for engineering use. The algorithm included in the GDF method converges rapidly and is numerically stable in the analysis. This feature is very practical for many engineering applications for using the GDF method. [ABSTRACT FROM AUTHOR]

The vibration serviceability problems induced by the coupling vibration of lightweight footbridges is a research focus. Much research has been conducted in recent years, yet the attenuation of the coupling vibration subjected to a low-density crowd is still challenging. To investigate the coupling vibration between a moving crowd and aluminum alloy footbridge due to synchronous excitation, orthogonal crowd load tests were carried out on a simply supported aluminum alloy footbridge with a span of 34.8 m. Load tests with different numbers of pedestrians and step frequencies were conducted to obtain vibration frequency and peak acceleration of the footbridge. The comparative analysis reveals that vibration serviceability under certain conditions of synchronous excitation was not in accordance with German footbridges guidelines or British standards. Synchronous excitation of low-density crowds may lead to a marked decline in pedestrian comfort. A two degrees of freedom (TDOF) human dynamic model with a supporting mass of human body was applied to establish a crowd-footbridge coupling system. The numerical results are in agreement with experimental data, which validates the finite element model of the footbridge. Further numerical analysis was conducted to investigate the coupling vibration response of the footbridge subjected to low-density crowd below 1 person/m2. The results show that the coupling effect is minor when the mass ratio is 0.12–0.3. When the mass ratio is 0.3–0.46, the coupling vibration is significant. Therefore, the coupling vibration of lightweight aluminum alloy footbridge deserves attention in design when subjected to low-density crowds. The evaluation of vibration serviceability is advised to be conducted according to the requirements of peak acceleration given in footbridge specifications. [ABSTRACT FROM AUTHOR]

The distribution of internal defects in large-diameter steel pipes can be complicated. Due to the harsh working environments involved, the manual grinding method for correcting such defects is inaccurate, inefficient, and risky. Therefore, in this study, we designed a new internal pipe grinding robot with five degrees of freedom. The grinding trajectory was optimized, and dynamic and kinematic models of the robot were established for the internal space of a pipe with a diameter between 800 and 1,200 mm. The feasibility of the robot was verified by simulation. A trajectory optimization method that focuses on the time, energy, and impact of the trajectory of the grinding robot is proposed. The method uses modified multiobjective particle swarm optimization (MMOPSO) in the robot's trajectory planning module to obtain a Pareto solution set. The analytic hierarchy process is used with the minimum fuzzy entropy (AHP-MFE) method in the decision-making module to select the most appropriate trajectory according to the relevant working conditions. The experimental results validated the space accessibility and trajectory optimization performance. Compared with the original trajectory, operation time was shortened by 15.4%, energy consumption was reduced by 17.5%, and impact was reduced by 12.4%. The experimental error was less than 2.8%. The experimental results showed that the pipe grinding robot is safe and efficient. [ABSTRACT FROM AUTHOR]

This study investigated the seismic performance and self-centering behavior of a three-story steel frame equipped with self-centering brace (SCBs) using pseudodynamic tests aided by OpenSees version 2.5.7 and OpenFresco version 2.7.0. The three-story self-centering braced frame (SCBF) was simplified to a three-story shear building model, and a generic experimental element with three nodes with horizontal degrees of freedom was used to establish a two-dimensional (2D) numerical model. The input ground motions were scaled to a service level earthquake (SLE), design basis earthquake (DBE), maximum considered earthquake (MCE), and a very rare earthquake (VRE) with 63%, 10%, 2%, and 0.5% probability of exceedance in 50 years, respectively. The test results demonstrated the excellent seismic performance and self-centering behavior of the SCBF. The maximum story drift ratio and maximum residual story drift ratio of the SCBF under a VRE were 1.91% and 0.119%, respectively, below the thresholds of 2.0% and 0.5%. The SCBs provided more than 90% of the initial lateral stiffness of the SCBF and dissipated approximately 55% of the seismic input energy. The seismic performance of the SCBF satisfied the no-damage criterion under an SLE and DBE. Although the columns in Story 1 yielded under an MCE and VRE, no visible residual deformation of the column flanges was detected in Story 1 after the tests. In addition, the maximum residual drift ratio of Story 1 was only 0.066%. Therefore, the columns in Story 1 only required simple and quick reinforcements before being usable. Unexpected factors, such as the fit-up tolerances around the pins, out-of-sync activation of the SCBs in the same story, residual deformation of the SCBs, and the out-of-sync activation of the two groups of disc springs in the same SCB, did not affect the seismic performance and self-centering capacity of the SCBF. [ABSTRACT FROM AUTHOR]

This paper considers integrated guidance and control system with input saturation for homing missiles based on the three channels independence design idea. An auxiliary system is first introduced into the integrated guidance and control model for the pitch channel. Then, a smooth function and a Nussbaum type function are employed in the dynamic surface control design to deal with the problem of input saturation constraint. The proposed control scheme guarantees the desired interception performance and the stability of the missile dynamics. The similar control scheme is further applied to the yaw channel and roll channel respectively. Nonlinear 6-DOF simulations are carried out to demonstrate the effect of the approach. [ABSTRACT FROM AUTHOR]

This paper addresses the command tracking control system (CTCS) design problem for plants involving input quantization and input saturation. A novel approach is proposed and demonstrated to the angle of attack (AOA) CTCS and bank angle CTCS of hypersonic reentry vehicles (HRV) driven by a reaction control system (RCS). First, the six-degree-of-freedom (6-DOF) nonlinear dynamic model of HRVand the mathematical model of RCS are established, and dynamic analysis is conducted based on the linearized model of HRV. Second, a general CTCS for plants involving input quantization and saturation is designed by solving a convex optimization problem based on linear matrix inequalities (LMIs). Formulations of the domains of attraction and convergence of the closed loop CTCS are derived. Furthermore, input to state stability (ISS) of the closed loop system is analyzed. Finally, the proposed approach is applied to design the longitudinal AOA CTCS and lateral-directional bank angle CTCS of HRV driven by an RCS. Validation simulations are conducted by using the linear model and the 6-DOF nonlinear dynamic model of HRV, which indicate that the proposed LMIs based approach is well suited for CTCS design for static-unstable plants and multiaxis coupling plants driven by actuators with quantization and saturation. [ABSTRACT FROM AUTHOR]

A new beam element only having the translational displacement degrees of freedom is developed to analyze fracture and buckling behaviors of bilayer beams or columns with delamination using the multilayer modeling method. By comparing their degrees of freedom, it is found that the present beam element is equivalent to the conventional Timoshenko beam element. The upper and lower layers are both divided into one or several sublayers, which are modeled by the developed beam elements. The element stiffness matrix, load vector, and geometric stiffness matrix using the linear interpolation polynomial are derived by the principle of minimum potential energy. To illustrate the effectiveness, accuracy, and efficiency, both the fracture and buckling analyses are conducted. Four typical fracture specimens (i.e., homogeneous and asymmetric double cantilever beams, single leg bending, and asymmetric end-notched flexure specimens) are analyzed using the developed beam element, and the obtained energy release rate and its components using the virtual crack closure technique are compared with those of analytical and conventional two-dimensional (2D) finite element solutions. Further, buckling analysis of bilayer beam-columns with delamination is conducted, focusing on the effect of the number of sublayers. The results show that the developed beam element is capable of effectively and efficiently calculating the convergent stress intensity factor ratio, total energy release rate and its components, and critical buckling load of delaminated bilayer beams or columns with relatively few elements, but without introducing the interface continuity condition in comparison to the conventional modeling method. [ABSTRACT FROM AUTHOR]

This paper presents comparisons of the performances of three semiactive control algorithms for use with multiple magnetorheological (MR) dampers. The three controllers are (1) the clipped-optimal controller, (2) the decentralized output feedback polynomial controller, and (3) the simple passive controller. These controllers use different types of inputs to calculate control signals for the MR dampers, based on different control mechanisms. To investigate the advantages of each controller, a three-degree-of-freedom steel moment-resisting frame, designed using a performance-based design methodology, was developed. The performance was investigated by using four different earthquakes utilized during the design of the building frame. Comparisons of the controllers' performance were carried out in terms of reduction in the maximum interstory drifts, displacements, absolute accelerations, and control forces. Real-time hybrid tests were carried out to validate these comparisons. [ABSTRACT FROM AUTHOR]

Application of spline element and state-space approach in analyzing dynamic response of rectangular plates is presented in this paper. The proposed method is on the basis of state-space theory of control systems and spline element interpolation procedure to take advantage of both the time domain and the space domain analysis methods. A state-space recursive scheme is developed for analyzing the dynamic response, such as displacement and internal forces in the structure. The application of the proposed method is demonstrated by two numerical examples. [ABSTRACT FROM AUTHOR]

This paper proposes a derivative-free two-stage extended Kalman filter (2-EKF) especially suited for state and parameter identification of mechanical oscillators under Gaussian white noise. Two sources of modeling uncertainties are considered: (1) errors in linearization, and (2) an inadequate system model. The state vector is presently composed of the original dynamical/parameter states plus the so-called bias states accounting for the unmodeled dynamics. An extended Kalman estimation concept is applied within a framework predicated on explicit and derivative-free local linearizations (DLL) of nonlinear drift terms in the governing stochastic differential equations (SDEs). The original and bias states are estimated by two separate filters; the bias filter improves the estimates of the original states. Measurements are artificially generated by corrupting the numerical solutions of the SDEs with noise through an implicit form of a higher-order linearization. Numerical illustrations are provided for a few single- and multidegree-of-freedom nonlinear oscillators, demonstrating the remarkable promise that 2-EKF holds over its more conventional EKF-based counterparts. [ABSTRACT FROM AUTHOR]

This paper presents a method for simulating the flight of a passively controlled rocket in six degrees of freedom, and the descent under parachute in three degrees of freedom. Also presented is a method for modeling the uncertainty in both the rocket dynamics and the atmospheric conditions using stochastic parameters and the Monte Carlo method. Included within this, we present a method for quantifying the uncertainty in the atmospheric conditions using historical atmospheric data. The core simulation algorithm is a numerical integration of the rocket's equations of motion using the Runge-Kutta-Fehlberg method. The position of the rocket's center of mass is described using three dimensional Cartesian coordinates and the rocket's orientation is described using quaternions. Input parameters to the simulator are made stochastic by adding Gaussian noise. In the case of atmospheric parameters, the variance of the noise is a function of altitude and noise at adjacent altitudes is correlated. The core simulation algorithm, with stochastic parameters, is run within a Monte Carlo wrapper to evaluate the overall uncertainty in the rocket's flight path. The results of a demonstration of the simulator, where it was used to predict the flight of real rocket, show the rocket landing within the 1σ area predicted by the simulation. Also lateral acceleration during weather cocking, which was measured in the test, shows a strong correlation with simulated values. [ABSTRACT FROM AUTHOR]

This paper presents the basis of a procedure to estimate the explosive charge weight and stand-off distance to impose certain levels of damage on reinforced concrete (RC) structures. A series of experiments were also conducted to confirm its applicability for assessing the blast resistance capacity of RC slabs. Test results showed that the procedure was accurate in predicting the explosive charge weight and stand-off distance to impose a given damage level on the tested RC slabs. This main conclusion was derived because a reasonable agreement was observed between the damage levels selected for assessment and the damage levels observed during testing. [ABSTRACT FROM AUTHOR]

This paper presents an on-line learning failure-tolerant neural controller capable of controlling buildings subjected to severe earthquake ground motions. In the proposed scheme the neural controller aids a conventional H∞ controller designed to reduce the response of buildings under earthquake excitations. The conventional H∞ controller is designed to reduce the structural responses for a suite of severe earthquake excitations using specially designed frequency domain weighting filters. The neural controller uses a sequential learning radial basis function neural network architecture called extended minimal resource allocating network. The parameters of the neural network are adapted on-line with no off-line training. The performance of the proposed neural-aided controller is illustrated using simulation studies for a two degree of freedom structure equipped with one actuator on each floor. Results are presented for the cases of no failure and failure of the actuator on each of the two floors under several earthquake excitations. The study indicates that the performance of the proposed neural-aided controller is superior to that of the H∞ controller under no actuator failure conditions. In the presence of actuator failures, the performance of the primary H∞ controller degrades considerably, since actuator failures have not been considered for the design. Under these circumstances, the neural-aided controller is capable of controlling the acceleration and displacement structural responses. In many cases, using the neural-aided controller, the response magnitudes under failure conditions are comparable to the performance of the H∞ controller under no-failure conditions. [ABSTRACT FROM AUTHOR]

The differential settlement between the bridge abutment and the approach embankment produces the common “bump at the end of the bridge.” This paper conducts a theoretical study on the determination of the allowable differential settlement. The maximum transient vibration value of the acceleration is recommended as the vibration comfort index. A dynamic response analysis to Man-Vehicle-Road system is carried out by means of the Laplace transform in which the vehicle is modeled as a three-degree-of-freedom system, and the bridge approaches with and without approach-relative slopes are simplified as broken lines model and step model, respectively. Parametric studies are carried out to find out what kind of effects some parameters such as the driving direction and running speed may have on the allowable differential settlement. Finally, the method and computational procedures to determine the allowable differential settlement are presented. [ABSTRACT FROM AUTHOR]

In this paper, a new structure-dependent unconditionally stable time-integration method is presented for structural dynamic analysis. The proposed method not only benefits from a semiexplicit formulation, but also inherits the advantages of the Bathe composite scheme. In fact, numerical characteristics of the suggested algorithm are the same as those in the Bathe composite scheme, except that the proposed method does not require any time-step subdividing, which is one of the drawbacks of the composite scheme. A comprehensive stability and accuracy analysis, including numerical dissipation and dispersion, is carried out in order to gain insight into the spectral properties of the proposed method. For numerical verification, some problems with large numbers of degrees of freedom and geometrical nonlinearity as well as linear behavior are solved by the developed technique. Results demonstrate suitable capability, efficiency, and validity of the proposed method in comparison to other existing schemes. [ABSTRACT FROM AUTHOR]

Civil infrastructures are subjected to various loads over their lifetime, which leads to structural degradation. To understand and predict these dynamic behaviors of physical infrastructures, many mathematical structural models have been developed, such as subspace system identification. These models often require structural responses from all degrees of freedom (DOFs) to estimate structural parameters. However, in practice, it is often difficult, if not impossible, to make such measurements owing to sensing constraints, a lack of data, or an excessive number of DOFs as in large-scale civil structures. This lack of measurements in space results in ill-posed problems with nonunique solutions. To address this challenge, this paper presents a structural parameter estimation algorithm that incorporates spatially incomplete measurements and inaccurate prior information on structural parameters within a subspace system identification framework. Additional constraints are imposed using prior information, and the prior information is updated with a new estimation. To sequentially update the parameters, the process is repeated as more measurements are collected. The proposed method is evaluated using a numerical model of a 5-story shear building for two damage scenarios with measurement noise. The structural parameters are estimated with 85-99% accuracy with spatially incomplete measurements (40-80%), and the iterative updating further improves these accuracies. [ABSTRACT FROM AUTHOR]

Tests of deep concrete beams with internal fiber-reinforced polymer (FRP) reinforcement have shown that such members can exhibit lower shear strength than members with conventional steel reinforcement. To model this effect, the current paper proposes an approach based on a two-parameter kinematic theory (2PKT) for conventional deep beams. The 2PKT is built on a kinematic model with two degrees of freedom that describes the deformation patterns of cracked beams. Using this theory shows that large strains in FRP longitudinal reinforcement result in reduced shear resistance of the critical loading zones (CLZ) of deep beams. The original 2PKT is therefore modified by introducing a reduction factor for the shear carried by the CLZ. The extended 2PKT approach is then applied to a database of 39 tests of FRP-reinforced deep beams from the literature, resulting in an average shear strength experimental-to-predicted ratio of 1.06 and a coefficient of variation of 18.3%. The results show that the 2PKT adequately captures the effects of the stiffness of the reinforcement, section depth, concrete strength, and shear-span-to-depth ratio on the shear strength of FRP-reinforced deep beams. [ABSTRACT FROM AUTHOR]

This paper presents the results of a shake-table case study conducted on a proposed novel type of isolated floor system having special bidirectional spring units. This solution provides enhanced seismic performance for certain facilities where constraints may require isolation of select floors or spaces rather than the entire structure (typically for selected rooms in critical facilities). This system was tested on a 6-DOF shake table. The floor seismic excitations were obtained from nonlinear time history analyses of both single-degree-of-freedom and multidegree-of-freedom frames stiffened with buckling restrained braces and designed as a structural fuse frame, and subjected to synthetic ground motions. The test results show that the isolated floor system performs satisfactorily, but that system behavior differs from that of the spring units alone because correction must be made to account for sources of friction beyond those from the spring units alone. The mechanical properties of the isolated floor system are also obtained in terms of the acceleration–displacement relationship, which provides the foundation to better simulate these isolated floor systems in future parametric studies. [ABSTRACT FROM AUTHOR]

A finite element is developed for a piezoelectric beam theory whose displacement varies according to the Timoshenko assumption, and the electric potential varies quadratically through each piezoelectric patch thickness. The application of Gauss's law to patches in the sensing mode is treated as a constraint in order to eliminate electric degrees of freedom from the weak form of the problem and, thus, formulate a two-node element with the same degrees of freedom as its purely mechanical counterpart (i.e., two displacements and one rotation per node). As a result, the element can be easily included in any computer program by simply replacing the existing purely mechanical element with this piezoelectric one. Since the approximation space is the same as that of the general homogeneous solution of the piezoelectric beam theory, the element enjoys the superconvergence property and is completely free of locking. Simple numerical tests on linear static problems are presented to demonstrate the ability of the element to give exact nodal values for the displacements, rotations, and reactions, irrespective of the mechanical and electrical loadings applied and mesh used. Also, the ability of a postprocessing scheme, which is set up to recover the exact sensing voltages at the nodes, is demonstrated. The element is further employed in shape-control problems. [ABSTRACT FROM AUTHOR]