Flexible Structural Systems Research Articles

Geometry-force interactive design and optimization method of cable dome structures

Cable dome is a typical flexible structural system. Its initial geometry determines the prestress distribution and affects the structural performance. Using geometric parameters to establish the mechanical equation of initial state can effectively realize the geometric-force interactive design and optimization of cable dome structure. Consequently, a standardized equation is established in this paper to uniformly express the geometric-force relationship, utilizing a feasible prestress distribution function expressed by geometric parameters. Subsequently, an interactive design method for initial geometry and prestress is presented. The proposed method is theoretically expounded in terms of geometric design, prestress design and shape optimization. Two typical cable dome cases, Geiger and Levy, are successfully applied to accomplish the geometric-force design and optimization of the initial state. The results show that the efficient design of initial state can be completed by establishing the interaction between geometry and force without repeated algebraic calculation. The optimized initial geometry can significantly improve the Structural stiffness.

Exponential Stability for a Flexible Structure System with Thermodiffusion Effects and Distributed Delay

Exponential Stability for a Flexible Structure System with Thermodiffusion Effects and Distributed Delay

Seismic response of a RC structure with new self-centering metallic dampers under biaxial near-field ground motions: Shake table tests

A new metallic energy dissipation device (EDD) with self-centering capability is proposed, and its effectiveness in controlling the seismic response of buildings subjected to near-fault earthquakes is investigated experimentally in combination with an inherently very flexible structural system: the RC waffle-flat plate structure. The new EDD combines the high energy dissipation capacity of stainless steel with the super-elastic properties of shape memory alloys. EDDs are installed in a 2/5 scale portion of a prototype RC waffle-flat plate structure designed only for gravity loads and tested on a shake table. The specimen is subjected to two horizontal components of a ground motion scaled in amplitude to represent different levels of seismic hazard at the building site. The RC structure with EDDs performed basically elastic under frequent earthquakes, remained “operational” under the design-level earthquake, and performed within the limits of “operational” and “life safety” under maximum credible earthquakes. The new EDD substantially reduced the maximum residual inter-story drifts —up to 1/10 of those of a conventional metallic EDD without self-centering capability. The response was also compared with a counterpart conventional RC structure without EDDs. The importance of providing the metallic EDDs with self-centering capability is highlighted.

Shake table tests on a reinforced concrete waffle‐flat plate structure with new hybrid energy dissipation devices

AbstractThis paper presents a new hybrid energy dissipation device and investigates experimentally its capability to improve the seismic response of an inherently very flexible structural system: a reinforced concrete waffle‐flat plate structure. The new device combines in parallel within a single device a low‐cost viscoelastic (VE) component and a metallic yielding (MY) component. The device has a gap that prevents deformations on the MY component in the range of displacements caused by wind or low intensity earthquakes, to avoid high‐cycle fatigue damage. The MY component is expected to activate under the design or the maximum credible earthquake, providing the main structure with lateral stiffness, and a reliable and large source of energy dissipation capacity. Six new hybrid energy dissipation devices (energy dissipation system) were installed in a scaled two‐story portion of a prototype RC waffle‐flat plate structure (main structure) designed only for gravity loads, without considering special ductility detailing or capacity design rules for the columns. The VE component of the hybrid energy dissipation devices reduced the translational periods with largest effective modal mass along the horizontal directions X and Y to 60%, and increased the fraction of damping to about 12%. The main structure with the energy dissipation system was subjected to bidirectional shake table tests that represented frequent, design and maximum credible earthquakes. In the tests, the main structure remained basically undamaged under the frequent and the design earthquakes, whereas it suffered minor (reparable) damage under the maximum credible earthquake. The MY component remained undeformed under low intensity earthquakes.

Vibration Analysis and Human Comfort Assessment of Building Subjected to Wind Dynamic Loads

AbstractIn the last few decades, Brazilian cities have presented a substantial increasing associated to the design and construction of tall and slender buildings. However, this architectural trend has produced flexible structural systems, with low natural frequency values and, therefore, more susceptible to excessive vibrations problems, when subjected to the nondeterministic wind loadings. Having these ideas in mind, this research work aims to study the dynamic structural response and evaluate the human comfort of a 40‐storey reinforced concrete building with 150 m high and floor dimensions of 30 m by 60 m. In this research work the Spectral Representation Method (SRM) was adopted to generate the wind nondeterministic dynamic loadings, based on the use of pressure coefficients calculated through the use of different strategies such as the HFPI‐TPU and DEDM‐HRP databases, CFD modelling and the Brazilian design standard NBR 6123. The numerical model developed for the reinforced concrete building dynamic analysis, adopted the usual mesh refinement techniques present in finite element method simulations and implemented in the ANSYS program. The main conclusions obtained in this work aim to alert the civil engineers to the relevant modifications associated with the dynamic response, when different strategies are used to calculate the wind pressure coefficients on the building's facade.

Singular perturbation and initial layer for the abstract Moore-Gibson-Thompson equation

We investigate the singular limit of a third-order abstract equation in time, in relation to the complete second-order Cauchy problem on Banach spaces, where the principal operator is the generator of a strongly continuous cosine family. Assuming that an initial datum is ill prepared, the initial layer problem is studied. We show convergence, which is uniform on compact sets that stay away from zero, as long as initial data are sufficiently smooth. Our method employs suitable results from the theory of general resolvent families of operators. The abstract formulation of the third-order in time equation is inspired by the Moore-Gibson-Thompson equation, which is the linearization of a model that currently finds applications in the propagation of ultrasound waves, displacement of certain viscoelastic materials, flexible structural systems that possess internal damping and the theory of thermoelasticity.

Analysis and Design of the Accessory Structure under the Large Deformation of a Flexible Roof

An increasing number of large‐span space structures use flexible roofs to achieve a light and splendid architectural effect. When a flexible structural system such as a cable net is applied in a large‐span stadium, the roof will deform significantly under the self‐weight and wind load. Accessory structures of the roof such as catwalks, radial drainage pipes, circular drainage channels, and radial cable trenches need to cooperate with the large deformation of the roof to prevent damage caused by the large deformation of the roof. To thoroughly unveil the analysis and design method of an accessory structure, this paper first carried out the wind tunnel test to determine the wind load of the structure. Then, the gust response factors of each roof area and the dynamic amplification coefficient of the accessory structure considering the roof vibration were determined. Next, circular and radial catwalks were designed based on static analysis. A sliding joint was set in the accessory structure to adapt to the large deformation of the roof. Finally, a time history analysis of the catwalk was carried out to obtain the maximum deformation value of the sliding joint for the safety of the structure. The results demonstrate that the maximum deformation is less than the value given by the design and meets the specification.

Seismic Fragility Analysis of Self‐Anchored Suspension Bridge Considering Damping Effect

The self‐anchored suspension bridge is a kind of the flexible and redundant structural system. For this type of bridge, the current code only gives the overall seismic design principle, and there is little research on seismic fragility in the existing literature. Taking the three‐tower self‐anchored suspension bridge as the research object, the finite‐element dynamic models with and without damping are established, respectively. Based on the strong earthquake database of PEER (Pacific Earthquake Engineering Research), 10 ground motion records are selected, and the seismic fragility curves of piers, bearings, towers, and slings are established by using the incremental dynamic analysis (IDA) method. The fragility curves of the bridge system were established by first‐order reliability theory. In this study, the damage probability of bridge components under a seismic wave is studied. The results show that the damage exceedance probability of the damped connection system is reduced compared with the undamped fully floating structure system under the action of seismic waves. The damper device makes the seismic performance of the structure significantly improved, and the reduction effect of the damper device on high‐intensity earthquakes is more obvious than that on low‐intensity earthquakes.

Mathematical modelling, nonlinear dynamics, bifurcation, synchronization and control of mechanisms driven by power supply

The special issue entitled “Mathematical modelling, nonlinear dynamics, bifurcation, synchronization and control of mechanisms driven by power supply,” published by The European Physical Journal: Special Topics (EPJST), aims to bring into discussion works involving nonlinear and dynamic and chaotic behaviors, which are frequently found in mechanical and electromechanical systems, nonlinear circuits, and biologically inspired systems, stimulating the integration of findings on the nonlinear dynamics that can be observed in various systems in the physical sciences and engineering. This special issue presents 27 papers concerning the dynamics and control of flexible structure systems, nonideal systems, energy harvesting problems, and vibration absorbers. In addition, the papers address problems involving chaos control of nonlinear oscillations, phase-locked loops, synchronization of nonlinear oscillators, dynamics of bio-inspired and biostructural systems, nonlinear methods, and nonlinear circuits.

Behavior of Self Compacted Concrete Ferrocement Beams

Many researchers have been conducted on the ferrocement as a low cost construction material and a flexible structural system. This experimental investigation on the behavior of ferrocement beams after exposed to different type of ferrocement and different of ferrocement layer are presented in this paper. The experimental program consisted of seven simply supported beams tested up to failure under four-point load. The dimensions of 150mm×250mm×2000mm. Each beam was reinforced using steel 2 f 12 in top and 2 f10 in bottom and the stirrups was 10 f 10/m. In addition to six of them contains ferrocement different steel wire meshes and different of ferrocement layer. The test specimens are divided in three groups and the results of each one compared with the control specimen. The first group (A) which used the welded wire mesh. The second group (B) which used the expanded wire mesh. But the third group (C) which reinforced using woven wire mesh. The mid span deflection, cracks, reinforcement and concrete strains of the tested beams were recorded and compared. The performance of the test beams in terms of ultimate flexure load cracking behavior and energy absorption were investigated. The experimental results emphasized that high ultimate loads, better crack resistance control, high ductility, and good energy absorption properties could be achieved by using the proposed ferrocement beams. The cracks propagation decreased and its number and width decreased by using woven, expanded and welded wire mesh especially in specimens with two layers of wire mesh. Theoretical calculation was carried out to compare the oplained results with the theoretical ones, which show good agreement.

Modal-Based Nonlinear Model Predictive Control for 3-D Very Flexible Structures

In this article a novel nonlinear model predictive control (NMPC) scheme is derived, which is tailored to the underlying structure of the intrinsic description of geometrically exact nonlinear beams (in which velocities and strains are primary variables). This is an important class of partial differential equation (PDE) models whose behavior is fundamental to the performance of flexible structural systems (e.g., wind turbines, high-altitude long-endurance aircraft). Furthermore, this class contains the much-studied Euler–Bernoulli and Timoshenko beam models, but has significant additional complexity (to capture 3-D effects and arbitrarily large displacements) and requires explicit computation of rotations in the PDE dynamics to account for orientation-dependent forces. A challenge presented by this formulation is that uncontrollable modes necessarily appear in any finite dimensional approximation to the PDE dynamics. We show, however, that an NMPC scheme can be constructed in which the error introduced by the uncontrollable modes can be explicitly controlled. It is demonstrated that the asymptotic error can be made insignificant (from a practical perspective) using our NMPC scheme and excellent performance is obtained even when applied to a highly resolved numerical simulation of the PDEs. We also present a generalization of Kelvin–Voigt damping to the intrinsic description of geometrically exact beams. Finally, special emphasis is placed on constructing a framework suitable for real-time NMPC control, where the particular structure of the underlying PDEs is exploited to obtain both efficient finite-dimensional models and numerical schemes.

Applying negative imaginary systems theory to non-square systems with polytopic uncertainty

This paper aims to apply Negative Imaginary (NI) systems theory to non-square LTI systems, for example, flexible structure systems with redundant sensors and actuators. The paper proposes static pre- and post-compensation schemes to transform stable fat (i.e. no. of inputs more than the no. of outputs) and tall (i.e. no. of outputs more than the no. of inputs) LTI plants into the class of Strongly Strict Negative Imaginary (SSNI) systems, a subset of the Strictly Negative Imaginary (SNI) systems. The proposed compensators can also stabilise a non-square or a non-NI square plant in a positive feedback loop. Moreover, the compensators can be utilised to design a simple constant reference tracking scheme exploiting the integral controllability propoerty of SSNI systems. Subsequently, observer-based pre- and post-compensators are developed to handle the cases when some of the system states are not available for direct measurement. Then, the compensation schemes are extended to stable, non-square or non-NI square systems with polytopic uncertainty. Finally, the post-compensation technique is applied to stabilise a class of tall/square uncertain LTI plants preceded by a slope-restricted nonlinearity.

Nonlinear dynamics of viscoelastic flexible structural systems by finite element method

This article presents a nonlinear displacement based finite elements model to study and analyze the nonlinear dynamic response of flexible double wishbone structural vehicle suspension system considering damping effect which was not previously discussed elsewhere. Due to large deflection and moderate rotation encountered during passing over road bumps, the kinematic nonlinearity is included through von Karman strain component. Elastic undamped as well as viscous and viscoelastic damping mechanism are considered and compared. Considering the viscoelastic damping mechanism, the viscoelastic damping mechanism is modeled based on the integral constitutive form, which is recast into an incremental form suitable for finite element implementation. Additionally, the revolute joint element is adopted to incorporate the joint flexibility in the double wishbone system. The plane frame element is adopted to model the suspension links by using Timoshenko beam theory. The developed nonlinear finite element equations of motion are solved through the incremental iterative Newmark technique. The developed procedure is verified by comparing the obtained results with analytical solution and excellent agreement is observed. The applicability of the developed procedure is demonstrated by conducting parametric studies to show the effects of the road irregularities profiles, the vehicle speed, and the material damping coefficients on the nonlinear vibrations response of the double wishbone suspension systems. The obtained results are supportive in the design and manufacturing processes of these structural systems.

Physicochemical characteristics of bio‐based thermoplastic polyurethane/graphene nanocomposite for piezoresistive strain sensor

AbstractHerein, we report the physicochemical characteristics and piezoresistive strain sensing performance of flexible thin film comprising graphene and bio‐based thermoplastic polyurethane (TPU) prepared by solution cast method. A detailed analysis was carried to study the influence of graphene nanoplatelets on the morphological, thermal, mechanical, and electrical properties of TPU nanocomposite. Upon increasing the graphene nanoplatelets loading, the thermal stability and tensile properties improved remarkably, while glass transition temperature decreased slightly. Owing to better dispersion of graphene, the electrical conductivity was significantly increased, which broaden the utilization of the nanocomposite for various applications. The piezoresistive sensor was able to respond to various stress modes such as tapping, bending, and finger touch. The piezoresistive sensor was sensitive and achieved a gauge factor of 11. Sensor attached to finger, showed distinctive response upon bending at different angles and showed high stability and reproducibility even after >10,000 cycles under repetitive constant load. Also, the nanocomposite was able to detect any breakage or fracture in the form of change in electrical resistance. A combination of bio‐based TPU and graphene offered improved physical properties and high sensing performance, which could be a potential material in flexible electronics and structural health monitoring systems.

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

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

Control of second-order asymmetric systems with time delay: Smith predictor approach

Abstract The feedback control for systems modeled as second-order linear dynamics with time delays is a challenge that received crescent attention nowadays. Flexible structures and structural systems are some remarkable examples that can be modeled as second-order dynamics. In the presence of delays, the well-known pole/eigenvalue assignment may fail due to the infinite-dimensional nature of the characteristic polynomials: the dominant eigenvalues can be erroneously placed in positions near to the imaginary axis, or even in unstable locations, that is, in the right-half plane. Recently, the authors have proposed a receptance-based delay compensation strategy that merges remarkable properties of receptance description and Filtered Smith Predictor (FSP). The obtained results outperformed pure pole/eigenvalue assignment techniques since the undesired delay effect is removed from the nominal characteristic equation. Hence, standard design strategies can be directly applied to control second-order systems with time delay based on a receptance model with no delay. In this work, these results are extended to deal with unstable second-order systems, an issue widespread in aeroelastic or friction-induced vibration systems. The FSP structure design is carried out in the discretized models of the system receptance to ensure internal stability as a consequence of particular filter design and implementation strategy. This procedure is possible due to a stable implementation structure for the receptance-based predictor in its digital form. Two typical examples, namely, aeroelastic flutter control and friction-induced vibration control, are used as benchmarks to verify the efficacy of the proposal.

Design of Flexible Structural System for Building Customization

The main aim of this research work is to design a structural system for building customization, through simple industrialized components. The system is able to adapt to different orthogonal geometries and presents the necessary flexibility to allow modifications over the structure of the building throughout its life. The so‐named “flexible structural system” (FSS) is characterized by using only small industrialized components, handled by one person, which exhibit an easy and simple assembly. The new system proposes the use of just two different pieces named basic units (BUi) with only two possible thicknesses for any of them. The system is composed of only 5 different pieces. The generating process of the structural system is based on different combinations of the basic units (BUi) to obtain resistant members (RMn). These resistant members allow to build structural frames (F), and finally, the addition of structural frames allows to generate diaphanous volumes (DV) and obtain the desired structure for the building. The limit of structural length is set at 4.8 meters. Finally, an example is shown where a structure for a diaphanous volume is obtained, using the referred industrialized elements. This shows that the system is systematic and easy to understand by users. We want the users themselves to design and build their own home as well as make the necessary modifications throughout the useful life of the building. This is the final objective.

A New Scheduling Quantitative Feedback Theory‐Based Controller Integrated with Fault Detection for Effective Vibration Control

In this work, a new integrated fault detection and control (IFDC) method is presented for single‐input/single‐output systems (SISOs). The idea is centered on comparing the closed‐loop output between the faulty system and fault‐free one to schedule/switch the feedback control once the fault occurs. The problem addressed in this work is the output disturbance rejection. The set of feedback controllers are designed using quantitative feedback theory (QFT) for fault‐free and faulty systems. In the context of QFT‐based IFDC, the proposed active approach is novel, simple, and easy to implement from an engineering point of view. The efficiency of the proposed method is assessed on a flexible smart structure system featuring a piezoelectric actuator. The actuator and sensor faults considered are the multiplicative type with both fixed and time‐varying magnitudes. In the fixed magnitude fault case, the actuator/sensor output delivering capability is reduced by 50% (multiplying a factor of 0.5 to its actual output), while in the time‐varying magnitude case, it becomes 60% to 50% for a particular time interval. In both cases, the proposed control method identifies the fault and activates the required controller to satisfy the specification with less control effort as opposed to the passive QFT design featured by faulty system design alone.

C.13.03 Pharmacology of the D2 partial agonists – what they bring to the table

The feedback control for systems modeled as second-order linear dynamics with time delays is a challenge that received crescent attention nowadays. Flexible structures and structural systems are some remarkable examples that can be modeled as second-order dynamics. In the presence of delays, the well-known pole/eigenvalue assignment may fail due to the infinite-dimensional nature of the characteristic polynomials: the dominant eigenvalues can be erroneously placed in positions near to the imaginary axis, or even in unstable locations, that is, in the right-half plane. Recently, the authors have proposed a receptance-based delay compensation strategy that merges remarkable properties of receptance description and Filtered Smith Predictor (FSP). The obtained results outperformed pure pole/eigenvalue assignment techniques since the undesired delay effect is removed from the nominal characteristic equation. Hence, standard design strategies can be directly applied to control second-order systems with time delay based on a receptance model with no delay. In this work, these results are extended to deal with unstable second-order systems, an issue widespread in aeroelastic or friction-induced vibration systems. The FSP structure design is carried out in the discretized models of the system receptance to ensure internal stability as a consequence of particular filter design and implementation strategy. This procedure is possible due to a stable implementation structure for the receptance-based predictor in its digital form. Two typical examples, namely, aeroelastic flutter control and friction-induced vibration control, are used as benchmarks to verify the efficacy of the proposal.

Robust H ∞ Filtering for Neutral Systems with Multi-Delay and Application in the Flexible System

Abstract The residual vibrations in flexible structure system model can cause errors. In addition, the parameters in the system are also changed. For the problem of residual vibration, robust H∞ filter is designed for neutral systems with multi-delay. Based on Lyapunov stability theory, the sufficient condition for the existence of filter is given. For the permitted uncertainty and multi-delay, the designed filter can guarantee the robust asymptotically stability and satisfy H∞ performance index for the filtering error dynamic system. Finally, the designed filter is applied to the flexible system, and the result shows that the filter is effective.