Multi-scale Disaster Simulation Of Building Clusters Subjected To Sequential Ground Motion Fields

Urban building clusters are naturally interconnected in space and time.The historical experiences show that the collision between buildings,the site–cluster interaction,and the strong randomness of ground motions make it possible for individual buildings to be severely damaged or even collapse due to associated effects,even if they are designed according to seismic codes.In the background of the new generation of urban development strategies that serves the needs of urban renewal and is oriented to resilient cities,how to ensure the safety of building clusters under earthquake scenarios is a critical issue to be solved in the field of civil engineering and earthquake engineering.In this paper,the seismic disaster simulation of urban building clusters is the research object.Firstly,this paper summarizes and reviews the current research in the field of seismic disaster simulation of building clusters.Then,to address the lack of fineness and realism of the current simulation methods,in-depth studies on the seismic scenarios,the computational model of building clusters and the damage constitutive relationships are conducted respectively.Finally,a multi-scale seismic disaster simulation method for building clusters subjected to sequential ground motion fields is proposed to realize the seismic disaster simulation of building clusters at multiple scales of materials,sections,components,buildings,and building clusters.This paper aims to provide a scientific basis for disaster prevention decisions in resilient cities.In terms of seismic scenarios,a random field model of sequential ground motions is established.First,the effects and key factors of sequential ground motion and ground motion field on the nonlinear response of masonry,reinforced concrete and other structures are explored respectively.On this basis,the stochastic Fourier amplitude and phase spectra of the source,propagation path,local site and plane wave field are modeled from the physical mechanisms of earthquake,respectively.The correlation between mainshock and aftershock is inscribed by Copula theory,and the theoretical model of sequential random field is established accordingly.Then,the model parameters are identified by time histories of sequential ground motions and ground motion fields of the database of various countries.Accordingly,the marginal probability distributions and joint probability distributions of model parameters are determined.The comparison and validation show that the proposed model integrates the correlation between mainshock and aftershock,the non-stationarity of time history,and the spatial variability of ground motions on the local site(e.g.,traveling wave effect,attenuation effect,and dispersion effect).In terms of damage constitutive relationships,a plastic-damage constitutive model for quasi-brittle materials and an equivalent cyclic damage constitutive model for steel are developed in this paper,respectively.For quasi-brittle materials,within the framework of continuum damage mechanics,the two-scalar damage model for concrete is extended to an orthotropic stochastic damage model for quasi-brittle materials.This model can describe the mechanical behaviors of both concrete and masonry.First,a shear damage variable is introduced to enhance the description of the slipping failure along the bed joints,and the slip activation stress is proposed to drive the shear damage variables.Subsequently,meso-scale tensile,compressive and shear parallel systems are developed to explain and quantify the stochasticity of the mechanical properties of quasi-brittle materials,respectively.Then,the stress mapped tensor is introduced in the effective stress space to describe the orthotropy of masonry.Finally,two parameter identification methods are given and an efficient numerical implementation algorithm is established for the model.For steel,a two-scalar damage model is used to establish the theoretical framework of the constitutive model in this paper.First,the modified Giuffrè-Menegotto-Pinto model is used as the stress-strain relationship in the effective stress space.Subsequently,to describe the tensile fracture and compressive buckling behaviors of steel,the ductile damage model and the empirical buckling criterion are adopted to determine the damage initiation criteria and damage evolution laws for the tension and compression,respectively.Then,an efficient numerical implementation method is developed in combination with explicit algorithms.Accordingly,an equivalent cyclic damage constitutive model of steel for fiber beam elements is established.Finally,the validity of these two models is verified by numerical examples with different configurations and different loading conditions.In terms of computational model of building clusters,this paper proposes a multiscale seismic disaster simulation method based on fiber beam elements and multilayer shell elements,and gives an example of multi-scale seismic disaster simulation of building clusters subjected to sequential ground motion fields.This method uses regional electronic maps,structural layouts and structural design models of buildings.Firstly,the information of each single building in the clusters is extracted through several approaches to obtain the key information required for modeling.On this basis,the structural design model or building information model is converted into the FEM model with fiber beam elements and multi-layer shell elements through a conversion program.Then,the material constitutive relationships of the FEM model are assigned separately to make it a single computational model.Then,based on the spatial coordinates of each single building,the single computational models are assembled into a cluster computational model.Further,with the support of the high-performance computing platform,an explicit numerical algorithm is adopted to achieve efficient nonlinear time history analysis.Finally,the disaster scenario of the campus of Tongji University subjected to sequential ground motion fields is simulated,and the global reliability is assessed by applying the probability density evolution method.At the end,the issues to be further studied are discussed and prospected.In summary,the highlights of this paper are:(1)establishing a random field model of sequential ground motions,which achieves a breakthrough from single ground motion fields to a sequential ground fields,and provides a scientific and effective scenario basis for the seismic disaster simulation of building clusters;(2)proposing an orthotropic damage constitutive model for quasi-brittle materials and an equivalent damage constitutive model for steel,which solve the difficulties of describing the slip failure of masonry by macro damage model and simultaneously describing the fracture and failure of steel by one-dimensional constitutive model,and provides a solid analytical basis for multi-scale seismic disaster simulation;(3)developing a multiscale seismic disaster simulation method and a reliability assessment method for building clusters,which has made a breakthrough in the field of seismic disaster simulation in terms of fineness and realism,and provides a reliable theoretical support for disaster prevention decision-making in resilient cities.