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In recent years, there have been more and more engineering examples of installing giant suspended equipment (e.g., central suspended LED display) in large-span space structures; however, there are fewer studies on the seismic response and strong-seismic failure process of large-span space structures after the addition of central suspended equipment. In this paper, changes in the nodal displacements of the reticulated shell structure before and after the addition of the central suspended equipment, the proportion and distribution characteristics of the plastic shell members, and the strong seismic deformation of the reticulated shell structures are taken as indexes under the different ground motions. This paper analyses the influence characteristics of the suspended equipment on the seismic response of Kiewitt K-8 single-layer spherical reticulated shell structures and reveals the influence laws of suspended equipment with different masses on the displacement of mounting nodes and the nodes in other rings in the reticulated shell structure. Based on the plastic degree development analysis of the structures under strong ground motion, the paper analyses the failure mechanism of the reticulated shell structures with central suspended equipment and summarizes two typical failure modes. The paper analyses the influence laws and characteristics of different factors (span, rise-to-span ratio, different seismic loads and the length of suspended cables) on the seismic response of the reticulated shell structures with central suspended equipment. [ABSTRACT FROM AUTHOR]

To explore the seismic response, influence mechanism, and failure of long-span spatial structures with three-dimensional seismic excitations in a strong earthquake, 1/6 -scale shaking-table tests of single-layer cylindrical reticulated shell structures with fixed hinged bearings, horizontal isolation bearings, and three-dimensional isolation bearings were conducted with three-dimensional seismic excitations. The accuracy of the numerical simulation method was verified by a numerical reconstruction analysis of the experiments. Dynamic time-history response analysis and incremental dynamic analysis of a full-scale single-layer cylindrical reticulated shell were conducted. The seismic response and failure states of the three-dimensional isolation structure were compared at different positions, different rise-span ratios, and different lower supporting structure heights. Studies have shown that horizontal isolation bearings cannot reduce the vertical vibration frequency and vertical seismic response of a structure; three-dimensional isolation bearings can effectively reduce the vertical vibration frequency and the vertical seismic response of the structure. The degree of plastic development is reduced by 82% in strong earthquakes; the initial plastic development position of the structure changes from the midspan to the four edges, and the ultimate bearing capacity of the structure increases by 40%. For a three-dimensional isolation structure, the natural frequency of the base-isolation structure is smaller, the ultimate bearing capacity is greater, and the isolation effect is better than with story isolation. With an increase in the rise-span ratio, the ultimate bearing capacity of the structure decreases. When the rise-span ratio is 1/2 , the bearing capacity is 0.9g , and the structure tends toward dynamic instability. A greater height for the lower support produces a greater ultimate bearing capacity and better isolation. [ABSTRACT FROM AUTHOR]

To investigate the variability of ground motion characteristics (GMC) with the angle of seismic incidence (ASI) and the impact of seismic incident directionality on structural responses, first, a large-scale database of recorded ground motions was used to analyze the causes of GMC variability due to the seismic incident directionality effect (SIDE). Then a single-mass bi-degree-of-freedom system (SM-BDOF-S) with different types of symmetrical sections was selected to explore the influence mechanism of SIDE on the seismic responses. The results illustrated that the GMC has substantial variability with the ASI, which is independent of the earthquake source, propagation distance, and site condition, and exhibits complex random characteristics. Additionally, a classification method for ground motions is proposed based on this GMC variability to establish a criterion for selecting ground motions in seismic analysis considering the SIDE. Moreover, for an SM-BDOF-S, the response spectral plane is proposed to explain the transition behavior of spectral responses that are very similar among different stiffness ratios, but divergent for different types of ground motions. The influence of SIDE on structures is determined by their stiffness and stiffness ratio in the x - and y -directions, as well as the type of ground motion. [ABSTRACT FROM AUTHOR]

Abstract The dynamic responses of large-span space structures are significantly associated with some higher structural frequency modes. A proper finite element model with accurate modal damping ratios is a key factor in obtaining precise structural seismic responses in numerical analyses. The complex damping model is often used in frequency domain structural analyses because of its characteristics of constant modal damping ratio with frequency and frequency-independent energy dissipation. Based on the five-parameter integer-order derivative method, a user subroutine of ABAQUS is developed to estimate the complex damping model in time-domain dynamic analyses. A shaking table test of a scaled and simplified single-layer reticulated dome is first conducted to validate the user subroutine. Detailed test data, including the identified natural frequencies and modal damping ratios, free vibration curves, and representative maximum responses, are summarized and compared with the corresponding finite element results using the complex damping model and a Rayleigh damping model. The comparisons indicate that the results of the complex damping model can yield a better estimation of the test data. Finally, the effect of the complex damping on the seismic responses of a single-layer reticulated dome is systematically studied by comparing the structural frequency properties and dynamic characteristic responses with those of Rayleigh damping. The results show that the complex damping model provides smaller structural modal damping ratio variation, lower ultimate seismic loading, and severer structural plastic developments. Highlights • A UMAT program is developed to take into account the complex damping in time-domain dynamic analyses. • A shaking table test is conducted to verify the five-parameter integer-order derivative method and the UMAT program. • The effect of complex damping in seismic responses of a reticulated dome is investigated and compared with Rayleigh damping. [ABSTRACT FROM AUTHOR]

The seismic performance of a single-layer spherical reticulated shell is the key problem to be solved in the design and analysis of this structure. In previous studies, the influences of roofing systems on the seismic performance of shells were usually ignored, resulting in large discrepancies between the results of analyses and the actual stress states of shells. In this paper, the finite element analysis method is applied to a shell with a roofing system, and the applicability of the method is proven by static loading experiments. The influences of roofing systems on the seismic performance of shells are obtained from seismic response curves, the proportions and distributions of plastic members and the failure behaviours of the shells during strong earthquakes. The mechanism of the influence of the roofing system on the seismic response of a shell is revealed by analysing the damage of purlin joints and the energy consumption of the components of the shell. The relationships that describe the influence of different parameters of reticulated shells and roofing systems on the seismic response of the shells are studied, and the results show that the roofing system can greatly change the seismic response and failure of a shell under strong earthquake conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Seismic incident directionality effect for OLF1000 was numerically evaluated. • Direction-to-direction and record-to-record uncertainties were derived. • 95% guarantee models for seismic responses of structures were proposed. • Prediction models by considering DEC-OLF1000-TLS and SIDE were established. As a typical and important supporting structure in ultra-high voltage substations, the 1000 kV outgoing line frame (OLF1000) bears the role of supporting electrical equipment and long-span transmission lines. The interaction between transmission towers, lines and OLF1000 makes it exhibit asymmetric stress and deformation states in normal use. For this kind of irregular coupling system (i.e., OLF1000-tower-line coupling system), the seismic incident directionality effect (SIDE) with high uncertainty may be a disadvantage. To investigate the effect of incident directionality on the seismic responses and ultimate bearing capacity of the OLF1000, and provide a reference for its seismic design, this study numerically evaluated the seismic responses of the OLF1000 by considering the dynamic coupling effect between a tower-line system and OLF1000 (DCE-TLS-OLF1000) under 40 multi-direction ground motions. According to our results, the seismic incident directionality significantly affects seismic responses, participation of vibration modes, plastic development law, failure modes, and ultimate bearing capacity of the OLF1000. In contrast, traditional approaches (i.e., 0° directional excitations) cannot ensure the seismic safety of the OLF1000 in arbitrary incident direction as the guarantee rate is less than 50%. Furthermore, the direction-to-direction (DTD) and record-to-record (RTR) uncertainties were theoretically derived; moreover, 95% guarantee models based on the two uncertainties and prediction models by considering the DCE-TLS-OLF1000 and SIDE were proposed to ensure the seismic safety of the OLF1000 under excitations exhibiting arbitrary incident direction and provide a helpful seismic design method for designers. [ABSTRACT FROM AUTHOR]

• Different with the traditional method that structural seismic responses were directly compared, in this study, through seismic fragility analysis, we investigated the aftershock influence on seismic performance of reticulated domes from probability perspective. • Existing researches have proved that the dominant vibration mode-based ground motion intensity measure S a , dom (Td 1 , Td 2 , ..., Td i , ..., Td N , ξ) was proposed as the most appropriate ground motion intensity measure for reticulated domes. However, it is not suitable for seismic study subjected to aftershocks, because the dominant vibration modes of damaged reticulated domes under main shocks would change. Therefore, in this study, we proposed the appropriate aftershock ground motion intensity measure for reticulated domes. • Based on the above ground motion intensity measure, we performed the fragility analysis of intact reticulated domes under main shock-aftershock sequences, and obtained the main shock-aftershock sequence fragility curves of structures for seismic design of reticulated domes considering multiple earthquake effects before earthquakes. • Different with the traditional seismic fragility analysis, we also performed the fragility analysis of damaged reticulated domes with different damage levels caused, which lead seismic fragility analysis not limited to intact structures and expanded the application scope of seismic fragility analysis. In this paper, single-layer and double-layer reticulated domes were taken as two typical research objects. Through the dynamic time history analysis of reticulated domes in full process domain, log-linear regression was performed with a large number of example results to compare the degrees of correlation and efficiency about 11 common ground motion intensity measures, and PGA was selected as the most applicable one for fragility analysis of reticulated domes with aftershock influence. Then, considering that main shock usually caused structural damage, with incremental dynamic analysis method, fragility analysis of reticulated domes under multiple earthquakes was conducted from two aspects as follows. One part was main shock-aftershock sequence fragility analysis of intact structures. The other part was aftershock fragility analysis of damaged structures with four different damage levels caused by main shocks. Based on the fragility curves, the aftershock influence on fragility of reticulated domes and the aftershock collapse probability of damaged reticulated domes with four different damage levels caused by main shocks were investigated. It was found that when the damage level reached severe damage under main shocks, the aftershock collapse probability of reticulated domes would increase significantly. The results expanded the application scope of traditional fragility analysis in seismic engineering and realized the prediction and evaluation of seismic performance of reticulated domes under aftershocks. [ABSTRACT FROM AUTHOR]

• The DCE between the suspended system and OLF1000 is investigated experimentally and numerically. • Transmission lines with different sag-span ratios are simplified based on the dynamic stiffness. • Seismic responses of the OLF1000 are reduced by the DCE owing to the energy consumption and elastic constraints. • The DCE is an attribute of the structure and irrelevant to external loads. Earthquake damage data show that substation long-span frames (LSFs) have remained intact under many strong earthquakes, even when electric power facilities and transmission towers had sustained serious damage. Therefore, the influence of the suspended system (SS) dynamic coupling effect (DCE) on LSF seismic responses is a matter of great concern. For that reason, this study focused on seismic responses of a 1000-kV outgoing line frame called OLF1000, which is a type of LSF, as it is subjected to the SS DCE. A scaled-down experimental model of a single-span OLF1000 was tested using a shaking table. An SS showing different sag–span ratios was applied to OLF1000 to determine how DCE influenced OLF1000 seismic responses. DCE was numerically simulated and analyzed according to different site classifications and ground motion intensities. Results showed that the DCE between the SS and OLF1000 was significant. In addition, the DCE reduced OLF1000 seismic responses owing to energy consumption and elastic constraints. Moreover, the DCE was found to be an SS structural attribute and was therefore unaffected by external loads. The DCE more significantly affected the single-span OLF1000 than the three-span OLF1000. [ABSTRACT FROM AUTHOR]

Abstract This paper aims to develop probabilistic seismic demand models (PSDMs), probabilistic seismic capacity models (PSCMs) and fragility curves for the widely-constructed reticulated structures using far-field earthquake records. The ground motion variability and prevailing uncertainties in structural design and modeling are considered, via performing incremental dynamic analyses (IDAs) on sample models of eighteen generic reticulated shells under forty far-field three-dimensional ground motions. A seismic energy demand-based damage index (DI E) is introduced and then employed together with the peak ground acceleration (PGA), to develop PSDMs and PSCMs for the reticulated shells considered, on the basis of statistical evaluation of the IDA results. The effects of two key structural design parameters, i.e., rise-to-span (or -width) ratio and roof load, on the PSDMs are investigated, and the normalized values for the PSCMs are also recommended. Fragility curves are derived and plotted to examine the difference among reticulated shells with different design parameters. It is concluded that DI E has strong correlation with PGA, and is more appropriate for developing PSDMs for the reticulated shells; and it also suggests that the reticulated shells with bigger rise-to-span (or -width) ratios or larger roof loads are more likely to damage or collapse during earthquakes. These results and conclusions will facilitate the performance-based seismic design and seismic vulnerability assessment of reticulated structures. Highlights • A seismic energy demand-based damage index is introduced for reticulated structures. • Probabilistic seismic demand and capacity models of reticulated structures are developed. • Seismic fragility curves are generated considering structural modeling uncertainties. [ABSTRACT FROM AUTHOR]

The transmission line is a vulnerable lifeline system when subjected to extreme loads, such as earthquakes and heavy ice loads. This study numerically investigates the structural performance of ultrahigh voltage long-span truss structures (LSTSs) under the multi-hazard action of earthquake and icing to mitigate disaster losses. A typical LSTS-3-tower-3-line system was selected as an analytical model. Its finite element model was established using a simplified spring model to simulate an ice-covered transmission conductor; it was excited by seven multi-component far-field ground motions. The natural vibration characteristics, structural responses, earthquake failure modes, and bearing capacities of LSTS affected by icing were comprehensively analyzed. The results showed that the seismic response of LSTS decreased, and its total response (induced by the tension of the conductor, ice load, and earthquake) increased with an increase in ice thickness. In addition, icing severely reduced the bearing capacity of LSTS with average reductions of 11.7% and 39.1% when the ice thicknesses were 15 and 50 mm, respectively. Moreover, the influence mechanism of icing on LSTS seismic responses and the failure mechanism of LSTS under the multi-hazard action of earthquake and icing were revealed. Specifically, the failure modes of LSTS, namely flexural (mode 1), mixed (mode 2), and shear failures (mode 3), were determined by the ice condition. Finally, prediction models for the structural responses and bearing capacity of LSTS were developed to facilitate the design of electrical equipment and LSTS and improve design efficiency. • Structural performance of UHV tower-line system under the multi-hazard action of earthquake and icing is studied. • Ice-covering conductor is simulated by a simplified spring model. • Icing influence mechanism is revealed by a theoretical method using SDOF. • Failure mechanism of long span truss structure is examined, including flexural, mixed, and shear failures. • Prediction models for structural responses and bearing capacity of long span truss structure are developed. [ABSTRACT FROM AUTHOR]

Single-layer reticulated shells are a type of spatial lattice structures with closely spaced natural frequencies and significant higher mode effects. An accurate calculation of the seismic responses of these structures necessitates the modal combination of dozens or even hundreds of modes when using mode superposition method. To precisely identify the modes that are significantly contributory to the seismic responses, the time-averaged modal strain energy ratio, denoted as TAMSER for brevity, is derived and then selected as the only evaluation metric, taking into account both the modal characteristics of a given structure and the spectral characteristics of an input ground motion. In terms of this metric, a methodology for identifying dominant modes is developed for structure systems under unidirectional or multi-directional seismic excitation. Based on this methodology, the dominant modes of two typical single-layer reticulated shells are identified and investigated, and then the responses resulting from the modal combination of these identified dominant modes are compared to that of the first 30 and 250 modes, as well as the time history analysis results. It is finally concluded that this proposed methodology is capable of accurately identifying the dominant modes of single-layer reticulated shells subjected to seismic excitations, and the incorporation of the identified dominant modes only into the modal combination is appropriate and sufficient to consider the higher modes effects and to get a satisfactory engineering accuracy in the mode superposition analysis. [ABSTRACT FROM AUTHOR]

Seismic ground motions are spatially varying when reaching the site of structures after long distance transmission. It is more realistic to consider the coherency effects by multi-support excitations than uniform excitations. The supporting structure of the five-hundred-meter aperture spherical telescope (FAST) is a new kind of cable net structure, thus it is necessary to investigate the seismic responses considering the spatial variations under multi-support excitations. Based on available excellent model of seismic ground motion, was used to simulate the seismic ground motions of 338 points within the area covered by FAST. The seismic ground motions at the 2 395 beamings of FAST were obtained via linear interpolation between the 338 points. The time-history responses of supporting structure of FAST under multiple-support excitations and uniform excitations were analyzed with ANSYS. The results show that the seismic coherency effects poses different influence on the supporting structure of FAST in three component directions. It is thus necessary to consider the seismic coherency of all three component directions in the analysis. Affected by the seismic coherency effect under three-dimensional seismic excitations, the stress in 94.08% of the main cables is increased by an average of 87.04%, the stress in 43.51% of the tie-down cables is increased by an average of 21.88%. Under three-dimensional multiple-support seismic excitations and three-dimensional uniform excitations, the maximum tensile stresses of the cable are 835.43 MPa and 671. 10 MPa, respectively, and both are smaller than the characteristic tensile strength of the cables of FAST. The supporting structure of FAST can withstand the expected seismic ground motions. [ABSTRACT FROM AUTHOR]