Dissipation Capacity Research Articles

Performance-Based Multi-Objective Optimization of Four-Limb CFST Lattice Columns

In this paper, the low-cycle reciprocating load test was carried out on four-limb concrete-filled steel tubular (CFST) lattice columns with different slenderness ratios and axial compression ratios, and the seismic performance was studied. Two performance indicators, namely damage and hysteretic energy dissipation, were defined as the objective functions, and the axial compression ratio was used as an optimization variable to perform the multi-objective optimization analysis of four-limb CFST lattice columns. Optimization using the max–min problem approach aims to optimize the axial compression ratio to minimize damage and maximize the dissipation of hysteresis energy. The seismic performances before and after optimization were determined using a restoring force model and were evaluated by the finite element method under different axial compression ratios. The results show that, under low-cycle reciprocating loads, the load–displacement hysteresis curve is a bow shape (Members 1 and 2), inverse S-shape (Member 3), and approximate shuttle shape (Member 4). Through multi-objective optimization, the optimized axial compression ratio is 0.25 and the finite element analysis indicates that the optimal seismic performance is at an axial compression ratio of 0.25. Through the optimized design, the maximum horizontal load of lattice columns, the elastic stiffness, the dissipation capacity, and the seismic performance are all improved, under the premise of satisfying the structural safety.

Sunflower pith inspired dual-gradient cellular polyurethane architecture with amplified mechanical functions

Artificial cellular materials with various mechanical functions are attracting increasing attentions from aerospace, transportation, and industrialization. However, many artificial cellular materials, despite of the hierarchically ordered structures and even unique performance to some, still lag behind many natural ones in amplification of mechanical functions owing to the limitations in intrinsic mechanical performance and sophisticated structural design. Herein, inspired with lightweight and high strength of sunflower piths, we proposed a dual-gradient structure consisting of pore size gradient and wall thickness gradient to engineer cellular architectures with desirable mechanical performance by harnessing vat photopolymerization 3D printing of double crosslinking networks polyurethane elastomer. The double-gradient cellular polyurethane architecture displays more exceptional capability in load-bearing and energy absorption compared with non– and single gradient structures. Besides, the specific compressive strength and energy absorption of the dual-gradient cellular architectures are 4 times higher than those of traditional mechanical metamaterial structures such as octet-truss lattice, gyroid lattice, and porous structure prepared with the same material. Potential mechanisms such as dual-gradient cellular structures to obtain selective flexural deformation behaviour increasing their energy absorption and dissipation capacity are fully elucidated. As the potential paradigms, we demonstrated the mechanical functions of biomimetic mechanical cellular architectures for efficient impact protection and noise isolation, which offered a promising perspective toward developing soft metamaterials with excellent mechanical functions for potential soft machines and engineering applications.

Seismic performance of conrete‐filled steel tube column‐reinforced concrete beam frame using 100% recycled coarse aggregate

AbstractThis paper presents an experimental study of recycled concrete‐filled steel tube (CFST) columns with reinforced concrete (RC) beam frames using recycled aggregate under cyclic loading. A 1/3‐scale model of a CFST column‐RC beam frame with 100% recycled coarse aggregate was tested, the failure process and mode were monitored, and the hysteresis and skeleton curves were obtained. The seismic performance indexes were analyzed based on the test data, including the seismic force, plastic hinge sequence, ductility coefficient, inter‐story drift, dissipation capacity, and stiffness degeneration. The general behavior of the CFST column‐RC beam frame is discussed and compared with that of a normal aggregate concrete‐RC frame structure. The test results demonstrate that CFST column‐RC beam frames with 100% recycled coarse aggregate exhibit remarkable seismic performance and can be applied and popularized for construction in aseismic regions.

Limpet-inspired design and 3D/4D printing of sustainable sandwich panels: Pioneering supreme resiliency, recoverability and repairability

Sandwich panels, characterized by their solid exterior and thick, soft core, find extensive applications ranging from maritime to aerospace sectors due to their exceptional resilience and energy absorption/dissipation capabilities. The natural limpet, known for its resilience to mechanical loading, serves as inspiration in the present research to introduce innovative repairable core shells. Limpet-inspired shells with elasto-plastic and brittle behaviors are designed and 3D/4D printed using polylactic acid (PLA) filaments and resins via fused filament fabrication (FFF) and liquid crystal display (LCD) techniques. While PLA filament exhibits an elasto-plastic response with a shape-recovery feature, the resin results in brittle structures for LCD-printed design. The study demonstrates that the FFF-printed PLA shell can fully recover residual plastic deformations, while the LCD-printed PLA shell exhibits a mechanical fracture behavior very similar to the natural limpet with brittle properties. A nonlinear finite element model (FEM) is also developed to replicate the large deformations of the samples under quasi-static compression with a high level of accuracy. Experimental and numerical results reveal that the samples with material, mechanical behavior, and geometry close to the natural limpet result in the maximum energy dissipation per unit mass. Two bio-inspired cores are then tessellated to introduce a new class of sustainable sandwich panels with supreme recoverability, resiliency, and repairability. A three-point bending test is numerically carried out on sandwich panels using FEM, and their energy absorption and dissipation capacities are studied. Results demonstrate that the proposed sandwich panels can achieve almost 7.33 and 1.17 times higher energy dissipation per unit mass than those developed based on a recycled thermoplastic bottle cap core. This pioneering research sets a new benchmark for structural design in terms of resiliency, recoverability, repairability, and sustainability.

A Review of Friction Dissipative Beam-to-Column Connections for the Seismic Design of MRFs

The use of friction-based beam-to-column connections (BCCs) for earthquake-resistant moment-resistant frames (MRFs), aimed at eliminating damage to beam end sections due to the development of plastic hinges, has been prevalent since the early 1980s. Different technical solutions have been proposed for steel structures, and some have been designed for timber structures, while a few recent studies concern friction joints employed in reinforced concrete structures. Research aimed at characterizing the behavior of joints has focused on the evaluation of the tribological properties of the friction materials, coefficient of friction, shape and stability of the hysteresis cycles, influence of the temperature, speed of load application, effects of the application method, stability of preload, the influence of seismic excitation characteristics on the structural response, statistical characterization of amplitude, and frequency of the slip excursion during seismic excitation. Studies aimed at identifying the design parameters capable of optimizing performance have focused attention mainly on the slip threshold, device stiffness, and deformation capacity. This review compiles the main and most recent solutions developed for MRFs. Furthermore, the pros and cons for each solution are highlighted, focusing on the dissipative capacity, shape, and stability of hysteresis loops. In addition, the common issues affecting all friction connections, namely the characteristics of friction shims and the role of bolt preload, are discussed. Based on the above considerations, guidelines can be outlined that can be used to help to choose the most appropriate solutions for BCCs for MRFs.

Steel exoskeletons for integrated seismic/energy retrofit of existing buildings - General framework and case study

The implementation of strategies for the decarbonization of the existing buildings by 2050 and the reduction of polluting emissions is urgent, for energy, economic and environmental reasons. Moreover, the built heritage undergoes structural deterioration for which restoration interventions are required. Seismic and energy improvement strategies are usually treated separately. Conversely, this paper proposes a holistic approach to improve both structural and energy efficiency of existing buildings. The innovative aspect is to obtain a dual objective by exploiting a single element, i.e., the exoskeleton. This component is an external self-supporting structural system connected to the existing building structure for improving strength, stiffness, and/or dissipation capacity under seismic actions. Contemporarily, it defines a new building envelope with different functions, such as ventilated wall, solar greenhouse, shields, and support for insulating panels or solar panels. This approach is applied to a case study, a reinforced concrete building in central Italy. The exoskeleton is rigidly connected to the existing building and designed to absorb the seismic loads and prevent damage to the structure under seismic excitation. The exoskeleton is also used for energy retrofit, by combining active and passive solutions. A design procedure is illustrated step-by-step for the case study. The results show a significant improvement of thermal characteristics of the building envelope, with a relevant reduction of primary energy, and of the seismic capacity of the existing structure that preserves its elastic behaviour. Moreover, this approach is also convenient from an economic point of view compared to a total demolition and reconstruction.

Seismic performance of hybrid coupled shear walls

AbstractHybrid Coupled Shear Walls are an innovative seismic‐resistant system that aims at merging the advantages of the classical Coupled Shear Walls with the dissipative capacity and easy‐to‐repair characteristics of steel elements. They are constituted by a reinforced concrete wall connected to two side steel columns by dissipative steel links. Depending on the stiffness/strength of the links, it is possible to obtain different distributions of the seismic forces between the wall and the columns. As resulting from previous research activity on this topic, the seismic behavior of this structural system can be strongly influenced by the higher modes, especially for mid/high‐rise buildings, making classical pushover analyses unable to catch the correct behavior. In this regard, the paper presents the comparison between the results of Incremental Dynamic Analyses and of different Pushover Analyses, giving indications about a more reliable procedure for the assessment of the seismic performance through suitable pushover analysis.

Optimization methods for the design of advanced 3d‐printed metal seismic dissipation devices

AbstractIn recent years, the topic of passive building protection became increasingly relevant due to the intense seismic activity in many parts of the world, often impacting densely populated areas. In the meantime, modern additive manufacturing technologies enabled the introduction of devices for structural applications that are innovative both in terms of final shape and design methods. The aim of the research project is to develop metal energy dissipation devices (dampers) from conventional geometric shapes and then direct the design towards specific performance in terms of strength, stiffness and dissipative capacity through optimization algorithms, with the aim of optimizing their function when employed as damper for the seismic protection of buildings. The subsequent removal of parts in excess of the real structural needs makes it possible to pursue important goals such as saving material, and reducing weight and costs. The proposed study illustrates the results of the first dampers designed through advanced topological and geometric optimization algorithms, implemented within the Abaqus software. The early models, designed from a spherical shape, are conceived to withstand axial stresses, simulating the load that can be transferred through a diagonal brace during an earthquake.

Thermomechanical shape memory testing of 4D printed novel material rhombus-shape structure

4D printing of functional energy generation/absorption structures by material extrusion technique can capitalize on the exciting applications in intelligent damping devices and patterns to deform spontaneously. This paper investigated the capitalization of this acquired knowledge by studying the shape memory effects of a functional rhombus shape structure. Initially, the shape memory characteristics of energy absorption and dissipation capacity were analyzed using dynamic mechanical testing to develop databases to gather thermophysical data before expressing the material behavior and recovery performances of printed shape memory structures. Then a complete thermomechanical cycle (shape programming and recovery) on 4D printed amorphous and semi-crystalline shape memory polymers exhibited deep insights into shape memory performance. The performance factors (i.e., recovery and fixity ratios) are influenced by variable printing parameters (i.e., layer height, printing temperature, and speed) and stimuli-based testing conditions. Results reveal both materials have significant shape memory effects with a maximum recovery ratio of up to 92.30 ± 0.32% from the programmed configuration. The amorphous polymer was extremely affected by printing temperature, whilst the semi-crystalline was influenced heavily by the interaction of all three parameters. Finally, shape memory effects predicted by a high-order design model and compared with experimental results showed negligible error. The analyses and assessments presented in this paper are adequate to understand the shape memory behavior under process control parameters to establish a data-driven model of a 4D printed semi-crystalline and amorphous polymer reactive to thermal stimuli.

A Double-Tuned Pendulum Mass Damper Employing a Pounding Damping Mechanism for Vibration Control of High-Rise Structures

Recently, enhancing conventional tuned mass dampers (TMDs) with a pounding damping mechanism is demonstrated to be an efficient way for vibration control of flexible structures. In this paper, a double-tuned pendulum mass damper employing a pounding damping mechanism (DTPMD-PD) is proposed. DTPMD-PD dissipates energy through the collision between distributed balls with a smaller mass and viscoelastic (VE) boundary, which can effectively reduce noise during operation compared to conventional impact dampers. Moreover, DTPMD-PD utilizes a double-tuning mechanism, and its control performance is significantly enhanced. The motion equations of a multiple degree of freedom (MDOF) structure equipped with DTPMD-PD are formulated. Based on the H∞ optimization criterion, a numerical optimization is performed to obtain the optimal design parameters of DTPMD-PD. Additionally, the pounding dissipation capacity and the parametric identification of the impact force model are investigated through free pounding experiments, and the control performance and robustness of DTPMD-PD are experimentally studied in the laboratory. The results show that the proposed numerical modeling method has considerable accuracy through experimental verifications. The restitution coefficient of the pounding layer has a significant influence on the performance of proposed DTPMD-PD. Optimized DTPMD-PD has better effectiveness than conventional TMDs under harmonic and seismic loads.

Proof of Concept and Preliminary Validation of an Analytical Model of an Energy Dissipator for Tension Loads with Self-Centering Capacity

A novel energy dissipation device is proposed to protect structures against dynamic loads. A conceptual model of the device is presented, describing the fundamental components of its operation. This model has a linear elastic element and a frictional damper. The equilibrium equations that lead to the relationship that governs its behavior are proposed. A functional model of the device was built on a 3D printer with PLA filament. Experimental trials were carried out to characterize its elastic component and the coefficient of friction of the damping parts. Proofs of concept load-unload tests were also carried out on the device, subjecting it to cyclical movement sequences. The results of the first two types of tests allowed the parameters of the previously developed analytical model to be calibrated. The results of the load-unload tests were compared with the predictions of the analytical model using the calibrated parameters. Consistency was observed between the experimental and analytical results, demonstrating the basic attributes of the device: self-centering capacity, dissipation capacity and force proportional to the displacement demand. It is concluded that the proposed device has the potential to be used effectively in the protection of structures under dynamic loads.

Design for Seismic Resilient Cross Laminated Timber (CLT) Structures: A Review of Research, Novel Connections, Challenges and Opportunities

As a sustainable alternative to steel and concrete, cross laminated timber (CLT) shear wall systems are getting increasingly popular in mid-rise and high-rise construction, and that imposes new challenges on their seismic performance. The conventional connections used in this system, such as steel hold-downs and angle brackets, are, however, susceptible to brittle failures, thus being inappropriate for use in structures in seismic regions. A series of innovative connections have therefore been proposed in recent years for achieving better seismic behaviours in CLT structures, characterised by an adequate capacity, significantly improved ductility and dissipative capacity, as well as more controllable ductile failure modes. This paper first reviews the recent studies of CLT shear wall systems and conventional connections. Connection systems and shear wall reinforcement methods that have been recently proposed for seismic resilient CLT structures are then introduced, with their design strategies being summarised accordingly. The connections are then discussed comprehensively in terms of structural performance, manufacturability and constructability, employing similar criteria that have previously been proposed for steel modular connections. It is found that much improved ductility along with more predictable, ductile, timber damage-free deformation modes are achieved in most of the new connections. Some new connectors are designed with additional functionalities for optimised seismic performance or for easing the construction process, which, however, lead to complex designs that may add difficulties to the mass production. Therefore, comprehensive considerations are needed in connection design, and the discussion of this paper aims to assist in the future development of connection systems for seismic resilient multi-storey CLT buildings.

Seismic behavior and nonlinear analysis of Hybrid Coupled Shear Walls

Hybrid Coupled Shear Walls are an innovative seismic-resistant system that aims at merging the advantages of the classical Coupled Shear Walls with the dissipative capacity and easy-to-repair characteristics of steel elements. They are constituted by a reinforced concrete wall connected to two side steel columns by dissipative steel links. Depending on the stiffness/strength of the links, it is possible to obtain different distributions of the seismic forces between the wall and the columns. As resulting from previous research activity on this topic, the seismic behavior of this structural system can be strongly influenced by the higher modes, especially for mid/high-rise buildings, making classical pushover analyses unable to catch the correct behavior. In this regard, the paper presents the comparison between the results of Incremental Dynamic Analyses and of different Pushover Analyses, giving indications about a more reliable procedure for the assessment of the seismic performance through suitable pushover analysis.

A sub-assembly based technique for calibration of numerical models of infilled r.c. frames according to experimental tests

Most existing buildings in the Mediterranean area suffer from structural deficiencies and need to be retrofitted. However, a proper selection of the seismic upgrading technique stems from a reliable assessment of seismic response based on accurate numerical models. Furthermore, it is widely accepted that the effect of infill panels should be considered to properly reproduce the seismic response of buildings with r.c. framed structure. Indeed, several studies have demonstrated that infill panels significantly increase the lateral stiffness of the frame and influence its dissipative capacity and collapse mechanism. Unfortunately, despite all buildings are endowed with infill panels, the contribution of these non-structural elements to the structural response has been often “conservatively” neglected, in favour of computational simplicity. In this framework, this paper presents a technique for calibration of the finite element numerical model of r.c. frames with infill panels based on the results of a quasi-static cyclic experimental test of a prototype infilled frame. The proposed technique is based on a sub-assembly approach and relies of the fact that (1) the response of the system is mainly governed by the infill panel for small amplitude displacements, while (2) it becomes coincident with that of the bare r.c. frame for large amplitude displacements. Hence, the mechanical properties of the bare frame and those of the infill panel could be separately extracted from the same cyclic response of the infilled frame. This technique has been here applied for the calibration of the numerical model of a one-bay one-storey r.c. frame with infill panel. A full-scale cyclic test of the infilled frame is also executed and the obtained structural response is assumed as target to be fitted.

Preliminary analyses of an innovative solution for reducing seismic damage in steel-concrete hybrid-coupled walls

Hybrid steel-concrete structures used as earthquake-resistant systems are an interesting solution for buildings in seismic prone areas, combining in effective ways the benefits of concrete and steel. In this context, an innovative single-pier hybrid coupled wall (SP-HCW), made of a single reinforced concrete wall coupled to two steel side columns by means of steel link, was recently proposed. The system is conceived to reduce the damage in the reinforced concrete wall while concentrating dissipation to the replaceable links. Although the numerical analyses for this innovative solution showed encouraging seismic performances and the desired ductile global behaviour, bottom zones of the concrete wall might experience undesired damages. Starting from the first proposed SP-HCW, in this study a new solution for its base is presented and preliminary investigated, i.e., the wall is designed as pinned at the base and equipped with additional vertical dissipative devices. In this way, this new configuration is expected to achieve lower damage of the wall without reducing its dissipative capacity. In this article the results of preliminary pushover analyses are discussed to evaluate the expected performances of the proposed structural solution.

Development and experimental verification of self-centering disc slit damper for buildings

The damage avoidance design (DAD) philosophy is oriented towards the low-damage design of building structures compared to the previous conventional ductile design. Low-damage structures with supplemental damping and self-centering ability are one of the main aspects of the DAD philosophy to decrease irreparable damage and enhance the seismic performance of structures. This research proposes an efficient, double-acting self-centering hysteretic damper by combining the widely used steel slit dampers and prestressed disc springs for building structures. The proposed seismic protection device is called Self-Centering Disc Slit Damper (SC-DSD), which consists of two square standard hollow steel sections, nested together with an assembly of prestressed disc springs within the steel sections. The performance of SC-DSD is assessed experimentally through a static cyclic loading test to evaluate the global system's dissipation capacity, self-centering ability, and hysteresis loop. A simplified numerical model is developed to predict the self-centering force-displacement relationship of the proposed device. Finally, the seismic force bearing capacity of the proposed damper is compared with the conventional slit damper.

3D‐Printed Soft and Hard Meta‐Structures with Supreme Energy Absorption and Dissipation Capacities in Cyclic Loading Conditions

The main objective of this article is to introduce novel 3D bio‐inspired auxetic meta‐structures printed with soft/hard polymers for energy absorption/dissipation applications under single and cyclic loading–unloading. Meta‐structures are developed based on understanding the hyper‐elastic feature of thermoplastic polyurethane (TPU) polymers, elastoplastic behavior of polyamide 12 (PA 12), and snowflake inspired design, derived from theory and experiments. The 3D meta‐structures are fabricated by multi‐jet fusion 3D printing technology. The feasibility and mechanical performance of different meta‐structures are assessed experimentally and numerically. Computational finite element models (FEMs) for the meta‐structures are developed and verified by the experiments. Mechanical compression tests on TPU auxetics show unique features like large recoverable deformations, stress softening, mechanical hysteresis characterized by non‐coincident compressive loading–unloading curve, Mullins effect, cyclic stress softening, and high energy absorption/dissipation capacity. Mechanical testing on PA 12 meta‐structures also reveals their elastoplastic behavior with residual strains and high energy absorption/dissipation performance. It is shown that the developed FEMs can replicate the main features observed in the experiments with a high accuracy. The material‐structural model, conceptual design, and results are expected to be instrumental in 3D printing tunable soft and hard meta‐devices with high energy absorption/dissipation features for applications like lightweight drones and unmanned aerial vehicles (UAVs).

Investigating the seismic efficiency of buckling-restrained braced frame structures

The bracing systems have been considered a reliable solution for the seismic-resistant design of buildings, which has been widely applied in recent years. This article aims to investigate the performance of braced frame structures in the seismic-resistant design. Typical buckling restrained braced frames, represented by an approximate bilinear behaviour, are selected to perform nonlinear time-history analyses. The findings indicate that bracing systems are a potential solution for seismic-resistant design, as they significantly reduce the top displacement and internal force of the structures based on their dissipation capacities through inelastic behaviour. Furthermore, the performance of vertical bracing systems is recommended to calculate according to the distribution of shear forces along the height of structures, ensuring that they are effective solutions that meet the design philosophies.

Structural fuse design of bolted steel frame with low yield point angle steel connection components

In order to realize the urgent requirement for damage control and rapid recovery of structural function after earthquake excitations using more convenient strategies, a bolted steel frame equipped with replaceable dissipative angle steel connection components was proposed. These angle steels with designed free deformation length were made of low yield point steels (LYP) which have superior ductility, dissipation capacity and fatigue performance. The plastic deformation was expected to be circumscribed within the LYP angle steels, which behaved as structural fuses to protect the primary frame members and were easy to be demolished and replaced. To achieve this desired damage control objective, the quantitative influence of the key factors on the seismic performance and the structural fuse effect was evaluated via extensive numerical parametric analyses. The design procedure of the corresponding sizes of LYP connection components to act as structural fuses was further summarized on account of energy dissipation behavior. The analysis results demonstrated that the larger the strength reduction factor (the smaller design resistance capacity coefficient), free deformation length and height of beam section promoted the structural fuse action of the LYP connection components. In terms of comprehensive consideration of structural ductility, load-carrying capacity, structural fuse performance and material efficiency, the design resistance capacity coefficient (the strength reduction factor) was suggested as αd=0.8∼1.0, and the free deformation length ranged from 0.67 to 1.1 times of beam width. The critical value of the design resistance capacity coefficient to achieve desirable structural fuse effect was formulated by integrating above-mentioned key influencing factors. Consequently, the design resistance capacity coefficient was required to be less than this critical value to realize sufficient damage control objective.

Generalization of the Concept of Bandwidth

In the sciences and engineering, there is no generally accepted definition of bandwidth beyond those used to characterize low-loss linear time-invariant systems of low order operating at steady-state. In fact, the concept of bandwidth is often subject to interpretation depending upon context and the requirements of a specific community. The focus of this work is to formulate this concept for a general class of passive oscillatory dynamical systems, including but not limited to mechanical, structural, acoustic, electrical, and optical. Typically, the (linearized) bandwidth of these systems is determined by the half-power (-3 dB) method, and the result is often referred to as “half-power bandwidth.” The fundamental assumption underlying this definition is that the system performance degrades once its power decreases by 50%; moreover, there are restrictive conditions, rarely met, that render a system amenable to the use of this approach, such as linearity, low-dimensionality, low-loss, and stationary output. Here the concept of root mean square (RMS) bandwidth is considered, justified by the Fourier uncertainty principle, to generalize the definition of bandwidth to encompass linear/nonlinear, single/multi-mode, low/high loss and time-varying/invariant oscillating systems. By tying the bandwidth of an oscillatory dynamical system directly to its dissipative capacity, one can formulate a definition based solely on its transient energy evolution, effectively circumventing the previous restrictions. Further, applications are given that highlight the limitations of the traditional half-power bandwidth; these include a Duffing oscillator with hardening nonlinearity, and a bi-stable, geometrically nonlinear oscillator with tunable hardening or softening nonlinearity. The resulting energy-dependent bandwidth computations are compatible with the nonlinear dynamics of these systems, since at low energies they recover the (linearized) half-power bandwidth, whereas at high energies they accurately capture the nonlinear physics. Moreover, the bandwidth computation is directly tied to nonlinear harmonic generation in the transient dynamics, so that the contributions to the bandwidth of the individual harmonics and of inter-harmonic targeted energy transfers can be directly quantified and studied. The new bandwidth definition proposed in this work has broad applicability and can be regarded as a generalization of the traditional linear half-power bandwidth which is used widely in the sciences and engineering.