Long-span Structures Research Articles

Experimental and Theoretical Studies on the Vibration Serviceability of Composite HCS Floors with RC Topping

Composite hollow–core slab floor with reinforced concrete topping (i.e. CHFT) is relatively new, which can be applied to various long-span structures. However, these systems are typically lightweight and exhibit low damping, posing potential serviceability concerns related to human vibrations. This paper presents a comprehensive vibration test on a 9[Formula: see text]m-long CHFT system. Natural frequencies, damping ratios, and mode shapes of the floor system were obtained through modal tests. The peak acceleration, root–mean–square acceleration, maximum transient vibration value, and perception factor of the floor under heel-drop excitation were obtained through the perceived vibration test and were checked against the available design codes and standards. Sensitivity studies using the finite element method were made to investigate the vibration performance of the CHFT system. Analytical formulas for the fundamental frequency and peak acceleration were derived, which are therefore suggested for practical use. Additionally, an approach for evaluating the vibration serviceability of CHFTs is described.

Modified plastic stress distribution method incorporating size effect for strength prediction of CFST members

Large-size concrete-filled steel tubular (CFST) members are widely applied in long-span and heavily-loaded structures due to increasing engineering demands. However, due to the size effect, applying the existing design methods to large-size CFST members may overestimate the load capacity, leading to unsafe designs. The plastic stress distribution (PSD) method is widely used as the primary method in typical design codes for calculating the strength of CFST members that are not susceptible to local buckling, while the PSD method was mainly used previously to evaluate the strength of CFST members with relatively small size. In this work, the experimental database of short CFST members with compact sections was complied, and the applicability of the PSD method was evaluated. The results showed that the test-to-calculated ratios decreased with increasing size of CFST members, and unsafe designs emerged for large-size CFST members. Based on the observations, the mechanics-based modified plastic stress distribution (MPSD) method was proposed, which not only considered the size effect at the material level similar to the way treated in most of the previous calculation methods, but also incorporated the size effect of the interaction action between the steel tube and concrete at the member level. Finally, the MPSD method was evaluated against the experimental database, and good agreement was achieved. These results provide strong justification for changes to the PSD method in design standards.

Safety evaluation for the dismantling of long-span spatial lattice structures based on deep learning and graph traversal

The demolition issue of long-span spatial lattice structures has become increasingly prominent with the rapid urban development and building renewal. Compared with traditional demolition techniques, building deconstruction offers superior economic and social benefits. Dismantling in blocks is one of the primary ways to realize the deconstruction of long-span spatial lattice structures, yet the safety is rarely studied. To fill this gap, a safety evaluation framework was established based on deep learning and graph traversal algorithm in this study. Hazardous configuration of the remaining structure is the basis of dismantling safety evaluation. To collect the hazardous configurations, an identification method in conjunction with deep neural network (DNN) and depth-first search (DFS) algorithm was proposed. The dismantling safety is measured by the improved structural well-formedness whose allowable range is determined by statistical analysis of hazardous configurations. The applicability of the framework was illustrated by the safety evaluation for the dismantling of single-layer reticulated domes. Results indicated that the dismantling safety is significantly affected by the configuration quality of the remaining structure, and the DNN-based prediction model is effective to classify the configuration state. Additionally, a large number of hazardous configurations were obtained through the identification method, and the allowable value of the safety evaluation index was determined to be 0.7. The configuration quality mainly depends on the geometry and boundary conditions. This novel framework provides scientific and effective methodological guidance for engineers, promoting the further application of building deconstruction.

A physical stochastic model of near-surface fluctuating wind fields

Modeling and simulation of atmospheric turbulence in coastal areas has emerged as a prominent area of research in recent years. This study presents a physical stochastic model to describe the horizontal coherence of fluctuating wind fields within the physical stochastic modeling frame. Based on the one-dimensional stochastic Fourier spectrum and isotropic turbulence theory, the horizontal coherence for fluctuating wind fields is expressed as a random function, with its probability information determined by the physical mechanism/background. The proposed physical stochastic model directly depicts the stochastic time series thereby enabling it to capture all probability information in detail comprehensively. The proposed model is numerically validated with the measured data obtained from an observation array constructed in Southeast China. This investigation holds significant potential for its application in wind-resistance design and reliability assessment of long-span structures.

Fragility analysis of long-span lightweight steel structures subjected to combined earthquake and non-uniform snow loads

Lightweight steel structures are commonly used in industrial facilities due to their low weight, high strength, and excellent performance. The design of these structures for cold regions not only has to consider the effects of earthquakes but also the negative impact of snow loads. Industrial structures often have long spans, and the effects of uneven snow loads cannot be underestimated. However, relatively few studies have focused on the performance of lightweight steel structures under the influence of combined earthquake and non-uniform snow loads. Therefore, this study assessed the seismic fragility of a typical single-span, double-sloped lightweight steel factory under combined earthquake and non-uniform snow loads using incremental dynamic analysis. Non-uniform snow loads, as compared to uniform snow loads, substantially increase the structural displacement responses, thereby increasing the structural failure risk. The improved structural design developed in this study effectively decreases the impact of adverse loading scenarios and enhances the multi-hazard resilience of the structure. Accordingly, these results can serve as an important theoretical guide for enhancing the safety of lightweight steel structures subjected to multiple hazards in cold regions.

Structural Design Considerations for a Large Single Span Reinforced Concrete Monolithic Beam-Column Structures

Large-span reinforced concrete structures present unique design challenges that necessitate meticulous consideration of load-bearing capacity, deflection control, reinforcement, and material choices. For spans exceeding 10 meters, structural engineers must carefully apply the principles and recommendations of Eurocode 2 to ensure that the structure is safe, functional, and durable. This paper explores the critical aspects of designing large single spans in reinforced concrete beam- column systems using Eurocode, with a focus on load distribution, reinforcement detailing, deflection limits, and material properties. Practical insights into the implementation of these guidelines are provided through examples, offering structural engineers in Nigeria a comprehensive approach to achieving safe and cost- effective long-span structures.

Assessing the Reliability of Truss Structures Based on the Bound Method and Collectively Exhaustive Events

Damage to long-span truss structures may cause structural deformation, load-capacity reduction, and even collapse. The design service life of truss structures is usually 50 years, so evaluating their reliability is of the utmost importance. Reliability considers the probability of failure as an analysis index. In calculating the probability of structural failure, important components are first selected to form a failure path, and then the failure probability corresponding to the failure path is calculated. A truss structure has many important components and failure paths, so calculating this probability requires extensive and thorough work. As a result, we propose selecting the important components via the approximation method to reduce the influence of the threshold of approximation. Collectively exhaustive events were established using the differential equivalent recursive algorithm to calculate the probability of structural failure. This process was considerably simplified, and validity was verified via a reliability analysis involving a three-bar truss structure, a plane truss structure, and a square pyramid truss structure. This method is suitable for selecting important components of regular flat truss structures.

Multimodal vortex-induced vibration mitigation and design approach of bistable nonlinear energy sink inerter on bridge structure

Large-scale structures, e.g., long-span bridge structures, are prone to induce multi-modal vibrations due to their densely spaced low modal frequencies. Due to the limited frequency bandwidth of linear dynamic absorbers, they are incapable of effectively mitigating vibrations across multiple modes. To this end, the bistable nonlinear energy sink inerter (BNESI) is used to mitigate the multimodal vortex-induced vibration (VIV) of the beam structure. The highly nonlinear equilibrium differential equations of the beam-BNESI system are numerically solved, and the simulated annealing (SA) algorithm is employed to determine the optimal VIV reduction ratio and BNESI parameters. In comparison to the cubic-type nonlinear energy sink inerter (CNESI), BNESI is found to possess more stable equilibrium positions, smaller stiffness coefficients, and higher VIV mitigation efficiency. The selection of design modes has been found to influence the efficiency of multimodal VIV mitigation, with the use of the intermediate modal order as the design mode resulting in the highest efficiency for multimodal VIV mitigation. The performance-based multimodal VIV mitigation design can be realized with three parameters, i.e., inertance ratio, damping coefficient, and stiffness coefficient. Moreover, the performance-based multimodal VIV mitigation approach and models proposed in this study demonstrate a high level of precision.

Nondeterministic High-Cycle Fatigue Macromodel Updating and Failure Probability Analysis of Welded Joints of Long-Span Structures

Nondeterministic High-Cycle Fatigue Macromodel Updating and Failure Probability Analysis of Welded Joints of Long-Span Structures

Development and engineering application of fiber bragg grating intelligent cable in large-span hyperbolic parabolic spatial cable network

In order to accurately control the prestress force of cables in long-span cable net structures, a new type of fiber Bragg grating (FBG) intelligent cable was developed. The FBG sensor was directly encapsulated inside the cable, and the sensing performance of the intelligent cable was verified by the cyclic tensile tests. The results show that the sensitivity coefficients of FBG monitoring are basically consistent, and the linearity deviation of the fiber Bragg grating is less than 4.67 %. Based on a real project Shunde Desheng Sports Center, a 114 m long-span saddle-shaped cable net structure model was established using finite element analysis, and the distribution and correlation of internal forces of cables in different tension stages were calculated and compared with the actual monitoring results of intelligent cables. The analysis results indicate that the force changes of intelligent cables is basically consistent with the value of finite element simulation. According to the data of long-term intelligent cable monitoring, the change of cable force caused by the temperature deformation of the steel ring beam is much greater than the influence of the temperature rise and fall of the cable itself on the cable force. Intelligent cables can provide a reference for cable force monitoring of long-span cable net structures.

Experimental study on seismic behaviour of thick-flange steel beam to square CFST column joints with internal diaphragms

Composite structures made of concrete-filled steel tubular (CFST) columns and steel beams have gained widespread usage in high-rise and long-span structures, and beam-to-column joints strengthened by an internal diaphragm (ID) are expected to be efficient joint patterns. However, the thickness ratio (ηbc) limit of beam-to-column flanges is not considered sufficiently in current design codes and existing studies. Moreover, the previous tests rarely included specimens with a beam flange thickness reaching 40 mm. Thus, three joint specimens were designed and tested under cyclic loadings to further investigate the mechanical properties of the ID-type joints and guide engineering applications. The effects of the thickness ratio of the beam-to-column flange were mainly considered in this study. All beam flange thicknesses were 40 mm. Two failure modes were observed, including excessive development of beam plasticity and failure of local connections. Specifically, as the thickness of column walls decreased, the seismic behaviour, such as the resistance, stiffness and ductility of the joints, deteriorated obviously. Two out of three joint specimens satisfied the AISC requirements for composite special moment frames (C-SMF). Based on the test results, the limit value of the thickness ratio of beam-to-column flange (ηbc) has been proposed for design purposes.

Research on the Performance of Prestressed High-Strengh Bolted Joints of Fully-Prefabricated Long-Span Spatial Structures

Research on the Performance of Prestressed High-Strengh Bolted Joints of Fully-Prefabricated Long-Span Spatial Structures

The prediction on non-Gaussian characteristics of wind pressure for the long-span roof in the mountainous area using proper orthogonal decomposition–deep learning framework

To make an accurate prediction of the non-Gaussian characteristics of wind pressure for the long-span roof, this study combines the proper orthogonal decomposition (POD) technique, convolutional neural network (CNN), and long short-term memory (LSTM) network to propose a novel POD-CNN-LSTM framework. Then, the proposed framework was well validated based on the wind tunnel testing of a long-span roof structure, and some error criteria, such as mean square root error and correlation coefficient, were adopted to evaluate the prediction accuracy of the non-Gaussian characteristics. Furthermore, two other methods, POD-CNN and POD-LSTM, were also used to conduct a comparative study. The obtained results illustrate that compared to POD-CNN and POD-LSTM, the proposed framework can achieve better performance on the pulsating wind pressure coefficient. For predictions of non-Gaussian characteristics, the output results of the proposed POD-CNN-LSTM show fewer errors, which means the predictions are close to the measured results, including skewness, kurtosis, and wind pressure probability density distributions. To summarize, the proposed POD-CNN-LSTM framework shows superiority over others, which means the proposed framework has good potential for the practical application of non-Gaussian prediction of the engineering structure.

Experimental study of the tension forming model of a long-span string-supported spoke-type truss structure

This paper investigates the structural response of the long-span string-supported spoke-type (LSSS) truss structure during the tension forming process, as well as the influences of the errors caused by initial defects of the structure. A 1:10 scaled test model was designed and fabricated with reference to the main hall structure of the Northwest University gymnasium. The mesh simplification and scaling-down of the design of the prototype were performed to obtain a test model with good similarity to the prototype. Subsequently, after the comparative analysis of different tensioning batches, numbers of tensioning stages, and tensioning sequences, a radial-cable-forming scheme of three-stage, five-batch, clockwise tensioning for each ring cables was determined to be superior for this type of system. The cable force, node vertical displacement, and rod stress were monitored during the test. SAP2000 finite element software was employed to establish a numerical model, which was then verified by the test results. The test results were found to be in good agreement with the simulation results. The outer-ring cables withstood a larger share of the load, which could provide more stiffness support for the structure. During the tensioning process, the tensioning of the inner-ring cables would further increase the vertical displacement of the outer-ring roof nodes, which increased the compressive stress of the upper-chord-rods near the outer-ring. After the tensioning was completed, the lower-chord-rods in the mid-span and at the ends of the truss were in tension. Comparative analyses of the variations of the position and geometry, as well as the cable force, in each ring of cables during the construction process demonstrated that initial defects in the installation of the upper roof will lead to the uneven distribution of the radial cable forces, and that the errors will gradually accumulate with the advancement of the tensioning stage. However, after the structure was formed, the verticality deviation of most struts was close to or less than 1/150, and the error between the measured value and the simulated value of the rod stress was basically kept below 10 %, which proved the rationality of the tension scheme adopted in the test.

Numerical investigation of wind-induced snowdrift on a long-span saddle-shaped roof based on the k-kl-ω model

Long-span structures are more vulnerable to the imbalanced distribution of snow loads, which is a primary factor contributing to structural failure. The development of snowdrifts is directly related to the shape of buildings, as it significantly affects turbulent characteristics and the process of snow drifting. This study explores the evolution of snowdrifts on a long-span saddle-shaped roof under various wind conditions. The numerical k-kl-ω model is validated against observation data by testing the flow field and snow distribution features of a stepped flat roof and a wind tunnel test. The snowdrift on a long-span saddle-shaped roof is simulated using the proven method, and the snowdrift's properties are studied at different wind speeds, wind angles, and threshold friction speeds. A comparative analysis of wind-induced snowdrift development on open and closed roofs is given, and the snow shape coefficients for each roof partition of the prototype roof are also provided. The findings indicate that the characteristics of snowdrifts on the roof vary with changing wind environmental factors, and the adverse inflow velocity and wind angle are identified. Snow morphology variation is more subject to an influence on changing inflow velocities compared to an alternation in wind-blowing time. The study reveals differences in how wind-driven fresh snow and long-deposited snow distribute themselves, with fresh snow producing more unevenness, potentially affecting roofs' load-bearing capacity.

Wind-induced interference effect of complex building clusters on long-span roof structures

The presence of complex buildings introduces interference effects and complicates the wind field around the long-span roof structure. The complexity of the problem makes it challenging to predict wind load of long-span roof structures, resulting in a scarcity of design data available to engineers and designers. Thus, the influence of interference effect on mean and peak pressure coefficients of a long-span tri-centered cylindrical roof structure was investigated through wind tunnel tests conducted in an atmospheric boundary layer wind tunnel. The study focused on the interference effects caused by two cooling towers, chimney, and some low-rise buildings, considering all wind directions. The results show that the interference effects are the result of a combination of amplification effects from the adjacent cooling towers and chimney and shielding effects from the surrounding low-rise buildings. Due to the shielding effect of low-rise buildings, the wind suction on the roof is mitigated compared to that of a single building, while at the end of the roof, wind suction is amplified by cooling tower effects. The interference effect of the building clusters, however, amplifies the fluctuating wind pressure coefficient and the peak pressure coefficient on the roof. To accurately estimate the wind load of building components and envelopes, furthermore, this study investigates the influence mechanism of interference effect on non-Gaussian characteristics of wind pressure combining with fluctuating wind pressure spectrum, spatial correlation of fluctuating wind pressure, and probability distribution characteristics of standardized wind pressure coefficient. The spatial correlation of wind pressure in the roof interference area exhibits a strong association, and the probability density distribution characteristics of the standardized wind pressure coefficient significantly deviate from the Gaussian curve, with a peak factor exceeding 3.5. Thus, it can be concluded that the wind pressure within this region demonstrates significant non-Gaussian characteristics. Hence, the zone values of peak pressure coefficients are determined using the peak factor approach to inform the wind resistance design of the envelope structure.

Numerical simulation and performance evaluation of compression members in long-span single-layer spatial grid structures constrained by steel bars

The collapse of long-span single-layer spatial grid structures can be triggered by the instability of compression members. To improve the stability of axially compressed members, this study proposes two novel compression members that are constrained using steel bars based on the design concept of existing constraint measures. A validated FE analysis is adopted to investigate the compressive mechanical behaviors, including parametric analysis. Members with different constraint measures are applied to single-layer latticed domes, and their feasibility in improving the progressive collapse resistance of the domes is evaluated. The results show that restraint measures using steel bars can significantly improve the stability of compression members, and when the ends of the restraint body are able to slide, the bearing capacity and ductility are greatly improved. The improvement can be maximized by reasonably designing various parameters of the constraint body. In addition, using different measures to constrain the compression members with higher key grades and thus improve the progressive collapse resistance of single-layer latticed domes is found to be feasible. However, the study finds that the failure mechanism of the constrained members sliding at the ends of the constraint body cannot be fully realized following dome collapse.

A novel symplectic geometry-based modal decomposition technique for accurate modal identification of tall buildings with close-spaced modes

The modal decomposition technique is of crucial importance for accurate modal parameter identification of tall buildings with close-spaced modes. However, most of the existing decomposition techniques are proposed for long-span structures, and the techniques specifically focused on tall buildings have rarely been explored. To this end, this paper proposes a novel modal decomposition technique called Symplectic Geometry Close-Spaced Mode Decomposition (SGCD) for the close-spaced modal identification of tall buildings. A numerical study conducted using a two-degree-of-freedom model is utilized to evaluate the effectiveness of the proposed approach. The results demonstrate that the SGCD method can effectively decompose close-spaced modes, and the modal parameters can be accurately identified with high robustness. Furthermore, the proposed modal decomposition technique is employed to analyze the field measurements obtained during a typhoon event on a 420-m-tall building. The results demonstrate the applicability and efficacy of the proposed modal decomposition technique to field measurement data. The main objective of this paper is to provide an effective modal decomposition technique for accurately identifying close-spaced modes of tall buildings.

Simplified calculation method of non-Gaussian wind pressure peak factor for large-span spatial roof structures

Based on the wind tunnel test data of a long-span spatial roof structure, the correlation between higher-order statistics and peak factors was obtained according to the time and frequency domain characteristics of wind pressure-time history, as well as the coincidence condition between wind pressure power spectra of measurement points and wind speed power spectra. A simplified peak factor calculation formula was proposed based on the moment-based Hermite polynomial model. The Gaussian part of the peak factor was calculated through the wind speed spectrum based on the zero-crossing theory, and the parameters related to higher-order statistics were considered as the non-Gaussian part of the peak factor. The simplified method was verified through the instantaneous extreme value method based on a coal shed structure with available long-term wind pressure-time history. It revealed that the results of the proposed simplified method correlate well with that of the instantaneous extreme value method, indicating its accuracy and potential value for engineering practice.

Seismic Response Analysis and Damage Calculation of Long-Span Structures with a Novel Three-Dimensional Isolation System

Seismic Response Analysis and Damage Calculation of Long-Span Structures with a Novel Three-Dimensional Isolation System