Collapse Simulation and Response Assessment of a Large Cooling Tower Subjected to Strong Earthquake Ground Motions

Large cooling towers in thermal power plants and nuclear power plants are likely to suffer from strong earthquakes during service periods.The resulting destructions of the cooling towers would endanger the power plants and threaten the security of the related areas.It is important to use effective means to evaluate the safety status of the cooling towers and guide further precautions as well as retrofitting efforts.This paper is therefore focused on an elaborate numerical investigation to the earthquake-induced collapses of a large cooling tower structure.A complete numerical work for simulation of material failure,component fracture,structural buckling and system collapse is presented by integrating the stochastic damage constitutive model of concrete,refined structural element models,and some other key techniques.Numerical results indicate that the damage behavior and collapse mode of the cooling tower are affected notably by the randomness specification of ground motions.The collapse mechanisms of the cooling tower are studied from the energy absorption and dissipation points of view.An effective energy-based criterion is introduced to identify the collapse of the cooling tower under ground motion excitations.While distinct collapse modes are observed,the collapse criterion can predict well the damage and failure of the cooling tower.The proposed methodology is vital to better understanding the disastrous mechanisms and potential failure paths in optimal design of the cooling towers to ensure safety.

Upper bound limit analysis of roof collapse in shallow tunnels with arbitrary cross sections under condition of seepage force

The analytical solutions for predicting the exact shape of collapse mechanisms in shallow tunnels with arbitrary excavation profiles were obtained by virtue of the upper bound theorem of limit analysis and variation principle according to Hoek-Brown failure criterion. The seepage force was included in the upper bound limit analysis, and it was computed from the gradient of excess pore pressure distribution. The seepage was regarded as a work rate of external force. The numerical results of roof collapse in square and circular tunnels with different rock parameters were derived and discussed, which proves to be valid in comparison with the previous work. The influences of different parameters on the shape of collapsing blocks were also discussed.

Limit analysis of supporting pressure in tunnels with regard to surface settlement

The proliferation of Hoek-Brown nonlinear failure criterion and upper bound theorem makes it possible to evaluate the stability of circular tunnels with an original curved collapsing mechanism. The arch effect of shallow circle tunnel is not taken into consideration so that the mechanical characteristics can be easily described. Based on the mechanism, the upper bound solution of supporting pressure of tunnels under the condition of surface settlements and overloads on the ground surface is derived. The objective function is formed from virtual work equations under the variational principle, and solutions are presented by the optimum theory. Comparisons with previous works are made. The numerical results of the present method show great agreement with those of existing ones. With regard to the surface settlement and overloads, the influence of different rock parameters on the collapsing shape is analyzed.