No abstract

The estimation of structural robustness remains one of the most important stages of the design of structural systems. Recommended design strategies for the robustness assessment are based on the provisions specified in the actual EN 1991-1-7 and ISO 2394:2015. Currently, the EN 1991-1-7 and ISO2394:2015 allows the use of indirect tie-force method, but normally, non-linear pseudo-static analysis is widely used, because it is based on more realistic constitutive relations for basic variables, which enables a simulation of the real structural behaviour. Implementation of the non-linear pseudo-static analysis for the assessment of a structural system in accidental design situations requires to adopt a different approach to safety format. The paper presents an innovative approach to safety format calibration for non-linear analysis of RC-structures subjected to accidental loads. The proposed method of the robustness estimation is based on the joint energy-saving (conversion) approach and the full probabilistic method for the estimation of a safety format for pseudo-static non-linear response of modified (damaged) structural system. The proposed probabilistic considerations are based on the Order Statistic Theory.

In the case of accidental design situations, if accidental actions can be identified, one of the possible design strategies is checking the key element. This strategy minimizes the possibility of local failure and subsequent progressive collapse. The paper considers accidental action combinations and values of identified accidental loads according the various codes. The combination of actions for accidental design situation for checking of the “key-element” resistance was proposed. In addition, the values of the combination factors for variable loads and partial factors for permanent loads in accordance with required reliability class RC for structural element and values of accidental loads was proposed.

The present paper describes and critically analyses the most widely used safety formats (i.e., partial factor method, global resistance methods, and probabilistic method) for non-linear finite element analysis. It is shown that the global resistance approach initiated by the implementation of non-linear analysis, which is on a global structural resistance model and offers tools for the safety evaluation. In the general case, the global safety concept reflects the variability of the structural responses due to the random properties of basic variables. It concluded that all safety formats for non-linear analysis implemented in currently developed codes are contained many uncertainties, statistically incorrect and vague formulations.

Evaluation of the concrete compressive strength in existing structures is an important problem, which is associated with structural reliability estimation as well as a quality control procedure. In accordance with a new concept of EN 13791, reported by T.A.Harrison, one of the main targets of the standard is to determine not a class, but in-situ characteristic concrete compressive strength. Hereby proposed criterion for the estimation of the in-situ characteristic concrete compressive strength is based on the non-parametric confidence interval for quantile. This criterion was verified by the both Monte Carlo simulation and test results under the real concrete structures.