Complete Structural System Research Articles

Introducing a comprehensive methodology for optimizing the mass of realistic roofing structural systems using cold-formed steel profiles

This study aims to introduce a comprehensive methodology for optimizing complete real structural systems for roofs involving trusses, purlins, and bracing systems jointly, taking into account realistic loads and constraints dictated by technical codes, thereby offering a more accurate representation of practical scenarios. The objective is to achieve the minimum mass through size, shape, and topology optimization of both the main truss and purlin structural subsystems. To achieve this goal, the Enhanced Particle Swarm Optimization (EPSO) algorithm is implemented. An example of a realistic case, which takes into account multiple actual constraints such as stress, displacement, buckling, and natural frequency limits, is thoroughly evaluated. After that, 144 other interactions among dimensions of the building and loads applied are simulated, and the mass of the system is obtained for each one of them. The results indicated that the graphs generated from the various simulations allow for the determination of the optimized mass for different building dimensions. Consequently, the cost and raw material consumption can be estimated for common applications. Therefore, it is concluded that this work presents a significant contribution to structural designers, as the proposed methodology enables structural optimization quickly and easily for practical engineers.

Fuse replacement implementation by shaking table tests on hybrid moment-resisting frame

A seismic resilience enhanced structural system, called Hybrid Moment-Resisting Frame with Replaceable Energy Dissipation Angles (HMRF-REDA), is proposed with the advantage of cost-effective and easy replacement work. The system consists of energy dissipation bays (EDBs) featuring fuse connections and re-centering bays (RBs) constructed from high strength steel (HSS). The fuse connections are designed to concentrate damage on sacrificial and easy-to-repair elements in the presence of a concrete slab. The HSS members not only provide adequate load carrying capacity but also necessary re-centering capability essential for fuse replacement. In this research, shaking table tests were performed to investigate the seismic performance of HMRF systems and in particular, the feasibility of on-site fuse replacement within the complete structural system. The specimen was comprised of two parallel, three-story hybrid moment-resisting frames at a 1/2 scale. The results demonstrated that HMRF-REDA exhibited a multi-stage yielding sequence with damage restricted to the fuse elements for the expected deformation range. The HSS frame members were able to fully re-center the structure after it underwent an inner-story drift of up to 0.0235 rad. Furthermore, two on-site fuse replacement operations were successfully implemented within the structural systems, demonstrating the feasibility and ease of operation. The frames with replaced fuses exhibited similar elastic and inelastic performance when it experienced a preceding drift up to 0.0184 rad.

Surrogate model based on ANN for the evaluation of the fundamental frequency of offshore wind turbines supported on jackets

The design of the support structure of offshore wind turbines (OWT) requires the dynamic characterization of the complete structural system, including the soil-foundation subsystem. To minimize resonance phenomena, the structural natural frequencies should be sufficiently apart from those that characterize the different loads. The obtention of natural frequencies can be a computationally expensive procedure, more so if dynamic soil-structure interaction (SSI) phenomena are included. In order to reduce the computational cost, a surrogate model based on Artificial Neural Networks (ANN) is proposed to estimate the fundamental frequency of the assembly formed by the wind turbine, the jacket support structure and the pile foundation. The training dataset is obtained by a finite element substructuring approach in which the dynamic SSI is incorporated through impedance functions obtained from a continuous model. The ability of the proposed ANN-based surrogate model to reproduce the influence that the main variables of the problem have on the fundamental frequency in a sufficiently precise way is shown by comparing its predictions and the results of the finite elements model for new configurations. The high accuracy and significant computational cost reduction justify the use of the surrogate model in applications where a large number of evaluations is required.

Shaking table test of the effect of an enclosure structure on the seismic performance of a prefabricated subway station

The enclosure structure is an indispensable part of the construction system of the prefabricated subway station structure (PSSS), and has a significant impact on the overall mechanics and deformation performance, soil-structure interaction, seismic performance and damage characteristics of the PSSS. In order to study the effect of the enclosure structure on the seismic response of the PSSS, a series of large-scale shaking table tests of a PSSS with and without an enclosure structure were carried out to study in detail the seismic response characteristics of the model system, such as macroscopic phenomena, acceleration, strain, and joint deformation. Then the mechanism of the enclosure structure in strengthening the seismic performance of the PSSS was revealed. Finally, the seismic damage evolution mechanism of the PSSS with the enclosure structure was explained systematically. The results showed that the PSSS with the enclosure structure had good seismic performance, and the collaborative seismic design of the enclosure structure and PSSS should be paid attention to. The acceleration response of the foundation soil and PSSS increased due to the existence of the enclosure structure, but the enclosure structure effectively improved the deformation resistance and joint stiffness of the PSSS and reduced the local stress concentration of the structure. The enclosure structure and the prefabricated structure together constituted a complete structural system to resist earthquake action, and could effectively reduce the seismic damage to the PSSS. Under an extreme earthquake, the PSSS degenerated into a three-hinged arch structure, and still had a certain self-balancing performance, which made it less prone to serious damage such as overall collapse. The research conclusions could provide a scientific reference for the design and construction of PSSS.

Fire performance of earthquake-damaged reinforced concrete columns: an experimental study

PurposeEarthquake tremors not only increase the chances of fire ignition but also hinder the fire-fighting efforts due to the damage to the lifelines of a city. Most of the international codes have independent recommendations for structural safety against earthquake and fire. However, the possibility of a multi-hazard event, such as fire following an earthquake is seldom addressed.Design/methodology/approachThis paper presents an experimental study of Reinforced Concrete (RC) columns in post-earthquake fire (PEF) conditions. An experimental approach is proposed that allows the testing of a column instead of a full structural frame. This approach allows us to control the loading and boundary conditions individually and facilitates the testing under a variety of these conditions. Also, it allows the structure to be tested until failure. The role of parameters, such as earthquake intensity, axial load ratio and the ductile detailing of the column on the earthquake damage and subsequently the fire performance of the structure, is studied in this research. Six RC column specimens are tested under a sequence of quasi-static earthquake loading, followed by combined fire and axial compression loading conditions.FindingsThe experiment results indicate that ductile detailed columns subjected to 4% or less lateral drift did not lose significant load-carrying capacity in fire conditions. A lateral drift of 6% caused significant damage to the columns and reduced the load-carrying capacity in fire conditions. The level of the axial load acting on the column at the time of earthquake loading was found to have a very significant effect on the extent of damage and reduction in column load capacity in fire conditions. The columns that were not detailed for a ductile behavior observed a more significant reduction in axial load carrying capacity in fire conditions.Research limitations/implicationsThis study is limited to columns of 230 mm size due to the limitations of the test setup. The applicability of these findings to larger column sections needs to be verified by developing a numerical analysis methodology and simulating other post-earthquake-fire tests available in the literature.Originality/valueThe experimental procedure proposed in this paper offers an alternative to the testing of a complete structural frame system for PEF behavior. In addition to the ease of conducting the tests, the procedure also allows much better control over the heating, structural loading and boundary conditions.

Tissue-engineered esophagus: recellular esophageal extracellular matrix based on perfusion-decellularized technique and mesenchymal stem cells

Perfusion-decellularization was an interesting technique to generate a natural extracellular matrix (ECM) with the complete three-dimensional anatomical structure and vascular system. In this study, the esophageal ECM (E-ECM) scaffold was successfully constructed by perfusion-decellularized technique through the vascular system for the first time. And the physicochemical and biological properties of the E-ECM scaffolds were evaluated. The bone marrow mesenchymal stem cells (BMSCs) were induced to differentiate into myocytes in vitro. E-ECM scaffolds reseeded with myocytes were implanted into the greater omenta to obtain recellular esophageal ECM (RE-ECM), a tissue-engineered esophagus. The results showed that the cells of the esophagi were completely and uniformly removed after perfusion. E-ECM scaffolds retained the original four-layer organizational structure and vascular system with excellent biocompatibility. And the E-ECM scaffolds had no significant difference in mechanical properties comparing with fresh esophagi, p > 0.05. Immunocytochemistry showed positive expression of α-sarcomeric actin, suggesting that BMSCs had successfully differentiated into myocytes. Most importantly, we found that in the RE-ECM muscularis, the myocytes regenerated linearly and continuously and migrated to the deep, and the tissue vascularization was obvious. The cell survival rates at 1 week and 2 weeks were 98.5 ± 3.0% and 96.4 ± 4.6%, respectively. It was demonstrated that myocytes maintained the ability for proliferation and differentiation for at least 2 weeks, and the cell activity was satisfactory in the RE-ECM. It follows that the tissue-engineered esophagus based on perfusion-decellularized technique and mesenchymal stem cells has great potential in esophageal repair. It is proposed as a promising alternative for reconstruction of esophageal defects in the future.

Computer Digital Technology‐Based Educational Platform for Protection and Activation Design of Ming Furniture

Chinese Ming‐style furniture is the first of the three major furnitures in the world, which has high artistic value and complete structural system. The protection of Ming‐style furniture and making its design show vitality that has always been a research topic in China and even in the world. Based on 3D virtual simulation technology, this paper uses 3D scanning reverse data acquisition technology and intelligent operation of computer engine to realize big data simulation and develops the design software of Ming furniture. By means of computer information technology, we interpret and present the structural thinking and design concept of Ming furniture and transform it into design program software. This has formed a system‐wide educational software operation platform for knowledge reserve, thinking training, design and application, and achievement transformation. By applying the mechanism strategy of production and teaching to the talent training plan of colleges and universities, the underlying logic of talent training, technical management, and production management that can open up the innovative industry of Ming furniture is also constructed. After experimenting with the platform software, students are able to understand the relationship between the structure and form of Ming furniture and can design new styles that fit the logic of Ming furniture shapes as they prefer.

Decoupled model-based real-time hybrid simulation with multi-axial load and boundary condition boxes

Real-time hybrid simulation (RTHS) is a cost and space efficient alternative to shake table testing for seismic assessment of structural systems. In this method, complete structural systems are partitioned into numerical and physical components and tested at real earthquake velocities. Well-understood components of the structure are modeled in finite-element numerical models. Meanwhile, the physical substructure, which often contains the highly nonlinear and numerically burdensome components is fabricated and tested in a laboratory facility. Testing at real earthquake velocities is useful to obtain nonlinear rate-dependent material behaviors. Realistic reproduction of seismic conditions for structural assessment has required researchers to develop multi-axial RTHS capabilities. In such developments, multiple actuators are arranged at the boundary condition with the physical specimen to impose realistic displacements and rotations. But, varying degrees of dynamic coupling exist between the actuators in multi-axial boundary conditions. Controllers and kinematic transformations are developed for the tracking action of the actuators to compensate for the amplitude and phase discrepancies between target and measured displacement signals, otherwise stability issues are likely to result. In this paper, a multi-axial framework is introduced for RTHS testing, using a Load and Boundary Condition Box (LBCB) at the University of Illinois at Urbana-Champaign. The previously developed multi-axial RTHS framework for the LBCBs compensates for actuator dynamics in Cartesian coordinates; this approach lacked stability robustness when testing stiff specimens. The distinguishing feature of the proposed framework is that tracking compensation is executed in the actuator coordinates. The differences between the previous and proposed multi-axial RTHS frameworks are explored in detail herein. This paper presents the components of the framework and the describes a six-degree-of-freedom moment frame RTHS experiment. Finally, experimental results are discussed and directions for future research efforts are considered.

Cyber-physical structural optimization using real-time hybrid simulation

Traditionally, structural optimization is a numerical process; candidate designs are created and evaluated through numerical simulation (e.g., finite element analysis). However, when dealing with complex structures that are difficult to model numerically, large errors could exist between the numerical model and the physical structure. In this case, the optimization is less meaningful because the optimal results are associated with the numerical model instead of the physical structure. Experiments can be included in the optimization algorithm to represent complex structures or components. However, the time and cost limitations are prohibitive when iteratively constructing and evaluating complete structural systems. Real-time hybrid simulation (RTHS) is an efficient and cost-effective experimental tool that combines numerical simulation with experimental testing to capture the total structural performance. This paper proposes a framework for real-time hybrid optimization (RTHO); RTHS is used to evaluate the performance of candidate designs within the optimization process. The framework creates a cyber-physical optimization environment using RTHS, a modern experimental technique with roots in earthquake engineering. This paper outlines the framework for RTHO with accompanying proof-of-concept studies. In a preliminary study, the base isolation design of a two-story building was optimized for seismic protection. RTHO was further validated for the optimal selection of multiple semi-active control law parameters for an MR damper installed in the isolation layer of a five-story base-isolated building. Both cases used RTHS to evaluate the candidate designs and particle swarm optimization (PSO) to drive the optimization. RTHO is well-suited to evaluate nonlinear experimental substructures, in particular those that do not undergo permanent damage such as structural control devices. Structural damage, if of interest, can be modeled through the numerical component. This paper proposes and demonstrates the integration of state-of-the-art optimization algorithms with state-of-the-art experimental methods – a cyber-physical approach to structural optimization.

Homology Cycles and Dependent Cycles of Hypergraphs

In this paper, some new concepts for hypergraphs are introduced. Based on the previous results, we do further research on cycle structures of hypergraphs and construct a more strictly complete cycle structure system of hypergraphs.

Progressive cracking of masonry arch bridges

Numerous methods are available for the assessment of masonry arch bridges at the ultimate limit state. However, there is a lack of suitable methods for assessing behaviour at service levels of loading. To address this, non-linear three-dimensional finite element (FE) models that consider constitutive material models enabling progressive cracking and failure of the complete structural system were used to investigate the development of damage for three masonry arch bridges at both service levels and at the ultimate capacity. All of the elements contributing to the strength of the structure were represented in the models, including the arch barrel, spandrel, abutments, fill and surrounding soil. This allowed for consideration of the longitudinal and transverse capacities, the stiffening effects of the spandrel walls, the restraint and load distribution provided by the fill, the frictional behaviour between the masonry and fill, movement at the abutments and multiple causes of failure. While complex non-linear FE models are able to identify the ultimate load capacity there are alternative simpler approaches available for this, and it is the investigation of damage and crack propagation at service level loads where their use is of greatest benefit.

Dynamic and numerical issues relating to the control robustness of dynamically substructured systems

Summary Dynamically substructured system (DSS) techniques separate critical components of a complete structural system to be physically tested in full size; the remaining linear subsystems are tested numerically. Successful and robust DSS tests rely on a high-quality controller to cope with undesired disturbances surrounding the real-time environment and thus ensure synchronised responses of the numerical and physical substructure outputs. Three DSS control systems are compared in this paper, which use dynamics-based ordinary differential equations or geometry-based delay differential equations to model the systems. Even though the control designs are not new, a series of new experimental and analytical results capture the essence of DSS control problems in a simple way, showing that (i) reliable DSS tests depend on well-defined dynamics and numerical computational accuracy in the control design, (ii) dynamics-based methods lay a relatively transparent and systematic foundation for deeper investigation into robustness issues and (iii) an understanding of potential and fundamental real-time difficulties is important in order to give hints for accurate modelling, control redesign and quality improvement. Copyright © 2014 John Wiley & Sons, Ltd.

Dynamic response of tall buildings to wind loads by reduced order equivalent shear-beam models

Two equivalent beam models are proposed in order to estimate the dynamic response of tall buildings affected by wind loads. The first model is based on the Timoshenko beam, which assumes bending and shear stiffness to be in series. The second model considers bending and shear stiffness to be in parallel. The parameters of the two equivalent beams are calibrated using the data of a complete structural system and imposing both the value of suitable displacements (static approach) and the value of the first natural frequencies (dynamic approach). Numerical analyses are performed using wind tunnel loads and FEM models. The accuracy of the dynamic response of the two equivalent beam models is assessed by comparison to a complete FEM model describing the structural system of a case study tall building. Furthermore, the ability of the equivalent shear-beam models to describe the random features of dynamic response is assessed using the first four statistical moments of the dynamic response.

Pseudodynamic tests on a full-scale 3-storey precast concrete building: Behavior of the mechanical connections and floor diaphragms

A full-scale three-storey precast building was tested under seismic conditions at the European Laboratory for Structural Assessment in the framework of the SAFECAST project. The unique research opportunity of testing a complete structural system was exploited to the maximum extent by subjecting the structure to a series of pseudodynamic (PsD) tests and by using four different structural layouts of the same mock-up, while 160 sensors were used to monitor the global and local response of each layout. Dry mechanical connections were adopted to realize the joints between: floor-to-floor, floor-to-beam, wall-to-structure; column (and wall)-to-foundation and beam-to-column. Particular emphasis was given to the seismic behavior of mechanical beam–column connections, as well as to the response of floor diaphragms. Thus, the in-plane rigidity of three pretopped diaphragms with or without openings was assessed. In addition, two types of beam-to-column connections were investigated experimentally, namely hinged beam–column connections by means of dowel bar and emulative beam–column joints by means of dry innovative mechanical connections. Therefore, the seismic behavior of floor diaphragms and pinned beam–column connections in a multi-storey precast building was addressed experimentally. The results demonstrated that the proposed new beam-to-column connection system is a viable solution toward enhancing the response of precast RC frames subjected to seismic loads, in particular when the system is applied to all joints and quality measures are enforced in the execution of the joints.

Automated design studies: Topology versus One-Step Evolutionary Structural Optimisation

This paper presents the development of a virtual toolbox for the study of spatial–structural design processes. It will be able to transform a spatial design into a structural design. After structural optimisation, the structural design is interpreted as a spatial design. This spatial design is then modified to comply with the initial design requirements after which a new cycle starts. The transformation and optimisation processes within the toolbox can be altered, allowing automated design studies to be carried out. In this article, two processes for the structural optimisation are investigated to determine which is most suitable for specific conditions. These two processes are: (a) Topology Optimisation applied to complete structural systems for buildings; (b) Evolutionary Structural Optimisation for which only the first step is used. It can be concluded that: (a) although Topology Optimisation is formally more correct, One-Step Evolutionary Structural Optimisation will yield almost the same qualitative results, (b) quantitatively the methods cannot be compared exactly, however, it is likely that Topology Optimisation results in more efficient structures and (c) Topology Optimisation always leads to stable structures, whereas One-Step Evolutionary Structural Optimisation may yield a singular stiffness matrix, although this has no influence on the spatial design derived from the optimised structural design. It is intended to utilise the optimisation techniques in the virtual toolbox leading to design studies and to transcend additional transformation and optimisation processes in the virtual tool box via formal description. Fields of application are the academic study of spatial–structural design processes (i.e. design theory), the optimisation of all possible structural design types (i.e. design optimisation), and the generation of design instances (i.e. generative design).

Shake table testing and numerical simulation of a self‐centering energy dissipative braced frame

SUMMARYThe self‐centering energy dissipative (SCED) brace is a new steel bracing member that provides both damping to the structure and a re‐centering capability. The goal of this study was to confirm the behavior of SCED braces within complete structural systems and to confirm the ability to model these systems with both a state‐of‐the‐art computer model as well as a simplified model that would be useful to practicing engineers. To these ends, a three‐story SCED‐braced frame was designed and constructed for testing on a shake table. Two concurrent computer models of the entire frame were constructed: one using the opensees nonlinear dynamic modeling software, and a simplified model using the commercial structural analysis software sap2000. The frame specimen was subjected to 12 significant earthquakes without any adjustment or modification between the tests. The SCED braces prevented residual drifts in the frame, as designed, and did not show any significant degradation due to wear. Both numerical models were able to predict the drifts, story shears, and column forces well. Peak story accelerations were overestimated in the models; this effect was found to be caused by the absence of transitions at stiffness changes in the hysteretic model of the braces. Copyright © 2013 John Wiley & Sons, Ltd.

Nonlinear interaction behaviour of infilled frame-isolated footings-soil system subjected to seismic loading

The building frame and its foundation along with the soil on which it rests, together constitute a complete structural system. In the conventional analysis, a structure is analysed as an independent frame assuming unyielding supports and the interactive response of soil-foundation is disregarded. This kind of analysis does not provide realistic behaviour and sometimes may cause failure of the structure. Also, the conventional analysis considers infill wall as non-structural elements and ignores its interaction with the bounding frame. In fact, the infill wall provides lateral stiffness and thus plays vital role in resisting the seismic forces. Thus, it is essential to consider its effect especially in case of high rise buildings. In the present research work the building frame, infill wall, isolated column footings (open foundation) and soil mass are considered to act as a single integral compatible structural unit to predict the nonlinear interaction behaviour of the composite system under seismic forces. The coupled isoparametric finite-infinite elements have been used for modelling of the interaction system. The material of the frame, infill and column footings has been assumed to follow perfectly linear elastic relationship whereas the well known hyperbolic soil model is used to account for the nonlinearity of the soil mass.

Performance of Steel Moment Connections under a Column Removal Scenario. II: Analysis

AbstractThis paper presents a computational investigation of the response of steel beam-column assemblies with moment connections under monotonic loading conditions simulating a column removal scenario. Two beam-column assemblies are analyzed, which incorporate (1) welded unreinforced flange bolted web connections, and (2) reduced beam section connections. Detailed models of the assemblies are developed, which use highly refined solid and shell elements to represent nonlinear material behavior and fracture. Reduced models are also developed, which use a much smaller number of beam and spring elements and are intended for use in future studies to assess the vulnerability of complete structural systems to disproportionate collapse. The two modeling approaches are described, and computational results are compared with the results of the full-scale tests described in the companion paper. Good agreement is observed, demonstrating that both the detailed and reduced models are capable of capturing the predominan...

Study on the Spindle Error Test and Analysis System of Numerical Control Machine Tools

It’s always an important means of measuring and improving the performance of machine tools with spindle error test and error analysis. Based on the analysis of the dynamic and thermal performance of spindle, the study is focused on how to get thermal deformation and temperature field by experimental methods. First of all, spindle error analysis methods are researched. Furthermore, developed a spindle error test and analysis system, established a set of complete structure system for spindle error test and analysis. Finally, tests are performed to demonstrate the feasibility of the error test and analysis system of the spindle, which laid foundation for the further research on the experimental analysis of machine tools.

Improving the inverse compensation method for real‐time hybrid simulation through a dual compensation scheme

AbstractReal‐time hybrid simulation combines experimental testing of physical substructure(s) and numerical simulation of analytical substructure(s), and thus enables the complete structural system to be considered during an experiment. Servo‐hydraulic actuators are typically used to apply the command displacements to the physical substructure(s). Inaccuracy and instability can occur during a real‐time hybrid simulation if the actuator delay due to servo‐hydraulic dynamics is not properly compensated. Inverse compensation is a means to negate actuator delay due to inherent servo‐hydraulic actuator dynamics during a real‐time hybrid simulation. The success of inverse compensation requires the use of a known accurate value for the actuator delay. The actual actuator delay however may not be known before the simulation. An estimation based on previous experience has to be used, possibly leading to inaccurate experimental results. This paper presents a dual compensation scheme to improve the performance of the inverse compensation method when an inaccurately estimated actuator delay is used in the method. The dual compensation scheme modifies the predicted displacement from the inverse compensation procedure using the actuator tracking error. Frequency response analysis shows that the dual compensation scheme enables the inverse compensation method to compensate for actuator delay over a range of frequencies when an inaccurately estimated actuator delay is utilized. Real‐time hybrid simulations of a single‐degree‐of‐freedom system with an elastomeric damper are conducted to experimentally demonstrate the effectiveness of the dual compensation scheme. Exceptional experimental results are shown to be achieved using the dual compensation scheme without the knowledge of the actual actuator delay a priori. Copyright © 2009 John Wiley & Sons, Ltd.