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The slotting method is a nondestructive detection method based on the stress release principle to evaluate in-place stress in concrete. By measuring the change in strain of the slotting area using a strain gauge, the in-place stress within the concrete member can be calculated by elastic theory. This paper proposes a multi-step slotting method that combines experimental strain measurements with numerical simulation results. For concrete specimens under unidirectional stress, the effects of compressive stress, slotting spacing, slotting length, and slotting depth on the degree of stress release were analyzed using finite element analysis, and a normalized fitting equation was proposed that can be quickly and accurately applied in engineering detection. The excellent agreement between the experimental results and the numerical simulation (fitted equation) results shows that the slotting method can facilitate the accurate evaluation of the in-place stress in concrete, and the relative error can be reduced to less than 10% when it is calculated using the optimized multi-step experimental data. [ABSTRACT FROM AUTHOR]

The collapse processes of three typical long-span reticulated shell structures were simulated using nonlinear dynamic finite element analysis under strong seismic excitations. The plastic kinematic hardening model, which considers failure stain, was adopted for simulating steel. Both geometric and contact nonlinearities were considered in this study. The three failure states--i.e., dynamic local bucking, dynamic overall buckling, and whole collapse--were identified in accordance with the analysis results. Taking the Schwedler reticulated shell structure as an example, seismic waves were applied to the structure in three directions. The critical loads were obtained by the incremental dynamic analysis method (IDAM), and some critical state indices were obtained according to the dynamic responses. The results showed that all the critical indices need to be considered simultaneously in order to judge the dynamic collapse states. [ABSTRACT FROM AUTHOR]