Effects Of Spatial Seismic Excitationson Single-layer Reticulated Domes

Seismic ground motions at a structural site are spatially correlated and coherent. It is more realistic to consider that the excitations at multiple supports of a structure are spatial coherency and correlation than to assume that the excitations are unifom. Since the available historical records that match match predefined inter-support distances of a structure for a specified seismic magnitude(or intensity) and site-to-source distance are unavailable, the simulated ground motion records are needed and used. The influence of the coherency on the seismic responses of structure has been investigated but the effect of the spatial correlation and coherency on the responses for the reticulated domes has not been studied. Furthermore, even under the uniform excitations, the number of records that is needed to carry out the analysis for the domes and to obtain statistically justifiable response quantities is unknown. The reticulated domes are light and with sufficient stiffness, they are often built for sports stadiums and gymnasiums. Seismic excitations are one of the possible natural loads that the reticulated dome needs to be designed to sustain during in service period. It is thus necessary to investigate the seismic responses of reticulated domes under multi-support excitations, as well as the minimum justifiable number of records to be used for design checking.The main contents in this paper are given below.1. Influence of wave-passage effect on seismic response of single-layer reticulated domesSeismic responses of single-layer reticulated dome, with different span, different roof mass, different rise-span ratio and different section, were calculated under uniform excitations and spatially varying excitations caused by wave-passage effect. The parametric investigation carried out indicates that the influence of spatially varying seismic excitations due to wave-passage effect on the structures depends on the structure as well as the excitation characteristics.2. Comparison of seismic responses of a reticulated dome under stochastic uniform and spatially correlated and coherent multiple-support excitationsApplication of the simulated records based on the extended stochastic point-source method for scenario events to a single-layer reticulated dome is presented. The application is aimed at investigating the differences between the responses under uniform excitation and under spatially correlated and coherent multiple-support excitations for a scenario seismic event, assessing the relative importance of the spatial coherency and spatial correlation on the responses, and evaluating the effect of the uncertainty in the spatially correlated and coherent records for a scenario event on the statistics of the seismic responses. The analys is results indicate that the spatial correlation of the Fourier amplitude spectrum has a predominant influence on the linear/nonlinear responses, and the consideration of spatially correlated and coherent excitations at multiple supports is very important. The consideration of the uniform excitation severely underestimate the seismic load effects as compared to those obtained under spatially correlated and coherent multiple-support excitations.3. Effect of support flexibility on seismic responses of a reti culated dome under spatially correlated and coherent excitationsEffect of the spatial correlation and coherency on the responses for the system with different flexibility of the substructure has not been studied. A parametric investigation is carried out to address this issue for a single-layer reticulated dome. The statistics of the responses of the dome with substructures of varying degree of flexibility are extracted from analysis, and compared with those obtained under uniform excitations. The results show the importance of considering spatially correlated and coherent excitations, especially as the stiffness of the substructure system increases. They also show that a flexible substructure system for the dome acts as a “base isolation” system for the dome under spatially correlated and coherent multiple-support excitations, and reduces the potential yielding and damage of the structure under large earthquakes. As the stiffness of the substructure system increases the consideration of uniform excitations instead of spatially correlated and coherent excitations can underestimate the seismic load effect by more than 25% for structural members in the rediculated dome and by more than 100% for the columns.4. Response analysis of reticulated dome under 3-component incoherent multiple-support excitationsModel parameters of an existing coherency model for excitations along the same direction is assessed using the ground motion records from SMART1 array and LSST array. The model parameters together with the adopted coherency model was used to simulate the seismic ground motions. Time history dynamic analysis of single-layer reticulated domes is carried out for spatial incoherent 3-component excitations. The results show that the spatial coherency in all the three directions(two horizontal directions and vertical direction) affects the seismic responses of reticulated domes. It is thus necessary to consider the seismic spatial coherency of all three component directions in the analysis. The analysis results also shown that substructure can act as isolator and reduce the incoherence of the excit5 ations at multiple supports.5. Influence of number of records and scaling on the statistics of seismic demand for lattice structureTo identify such an adequate ground motion intensity measure for Kiewitt 8 single-layer reticulated domes, we note that the ground motion intensity measure could be grouped as absolute intensity and relative intensity, by considering whether the dynamic characteristics of structures were taking into account. Sa(T1) is a adequate ground motion intensity measure for the horizontal excit ations for the considered dome. However, its use for vertical response is questionable as expected. Furthermore, the vibration period mode that control the peak ver tical displacements is usually unknown. A simple practical approach to remediate this drawback was suggested: it requires the use of harmonic analysis for horizontal and vertical excitations to identify the vibration periods at which the structural attends its peak responses; the spectral acceleration values at the identified periods can then be used as ground motion intensity measure.This study evaluates the statistics of seismic responses of the single-layer reticulated dome due to limited number of record components, and investigates the effect of the peak ground acceleration and spectral acceleration based scaling on the statistics of the responses. The time history analysis is carried out using 166 selected record components. Statistics of the maximum of seismic load effects on structural members and base shear forces are obtained based on the analysis results by considering all records, randomly sampled 3 and 7 records according to code criteria. The results are used to make recommendations on the preferred intensity for scaling the records and the number of record components(three or seven) to be used for analysing and designing such domes under seismic load.