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Non-linear Probabilistic Assessment of Existing Bridge Considering Deterioration
(Brno University of Technology, Czech Academy of Sciences, 2024-05-14) Slowik, Ondřej; Sadílková Šomodíková, Martina; Novák, Drahomír
The integration of the non-linear finite element method with deterioration-based analysis represents a powerful approach for accurately simulating structural behaviors. However, conducting fully probabilistic analyses on large-scale models that incorporate numerous stochastic variables remains a significantly time-intensive task. As a result, structural designers and engineers frequently prefer semi-probabilistic methods, which significantly reduce the need for extensive non-linear computations. This paper concentrates on evaluating the reliability of an existing railway bridge constructed with cast-in steel beams. It employs an advanced numerical analysis through a non-linear finite element model, combined with established semi-probabilistic approaches, including the ECoV method and the newer eigen ECoV method. To accurately reflect the current state of the bridge's superstructure, the analysis models the carbonation of concrete and the ensuing corrosion of steel beams using analytical models that consider both the fundamental material properties and environmental factors.
Stress projection procedure for the form-finding analysis of membrane structures
(Elsevier, 2024-02-01) Lang, Rostislav; Němec, Ivan; Park, K. C.
This study examines the form-finding analysis of membrane structures and presents a new general method for determining prestress called stress projection. This method addresses several deficiencies while performing the form-finding analysis, especially in the case of conical membrane structures. A key feature of the proposed stress projection procedure is the adoption of a generally oriented projection plane, where finite elements are projected onto, and the determination of their stress states, which allows for a smooth adaptation of stresses over the membrane structures. Deformation gradients are then evaluated with respect to this projection plane, as opposed to the inertial reference frame used for the computation of stress tensors in subsequent form-finding processes. The proposed stress projection procedure efficiently modifies the stresses over the structures and significantly addresses intrinsic element distortion problems within the form-finding analysis. Thus, the proposed method allows for the maintenance of regularized finite element shapes and the smooth changing of stress states throughout form-finding iteration processes, especially for conical membrane shapes. Numerical experiments demonstrate the efficiency of the implemented stress projection scheme compared with two well-known stress adaptation schemes.
Two Stochastic Methods to Model Initial Geometrical Imperfections of Steel Frame Structures
(MDPI, 2024-01-12) Jindra, Daniel; Kala, Zdeněk; Kala, Jiří
The stochastic modeling of geometrically imperfect steel frame structures requires statistical inputs for imperfection parameters, often with specific mutual correlations. The stochastic input values of geometrical imperfections are derived from European Standard EN 1090-2:2018 tolerance criteria. Two advanced stochastic methods, #RSS (random storey sway) and #RSP (random storey position), are developed based on these criteria. This paper presents a verification study, using random sampling simulations, for these two stochastic methods (#RSS and #RSP) to directly model the initial global geometrical imperfections of steel frame structures. The proposed methods have been verified for structures with equidistant storey heights and for those comprising up to 24 storeys, making them applicable to a wide range standard steel frame structures. It has been found that the performance of the #RSS method is satisfactory. An advantage of #RSS is that the random parameters are statistically independent. On the other hand, the #RSP method requires the definition of these mutual correlations in order to satisfy the criterion that 95 percent of random realizations of initial imperfections fall within the tolerance limits of the corresponding European Standard. The #RSP method, however, might have certain advantages for structures with a larger number of storeys (above 24), as closely discussed in this study. Additionally, this study provides useful provisions for the advanced numerical analyses of multi-storey steel frames of various geometries.
Strain Energy and Entropy Based Scaling of Buckling Modes
(MDPI, 2023-12-06) Kala, Zdeněk
A new utilization of entropy in the context of buckling is presented. The novel concept of connecting the strain energy and entropy for a pin-ended strut is derived. The entropy of the buckling mode is extracted through a surrogate model by decomposing the strain energy into entropy and virtual temperature. This concept rationalizes the ranking of buckling modes based on their strain energy under the assumption of given entropy. By assigning identical entropy to all buckling modes, they can be ranked according to their deformation energy. Conversely, with identical strain energy assigned to all the modes, ranking according to entropy is possible. Decreasing entropy was found to represent the scaling factors of the buckling modes that coincide with the measurement of the initial out-of-straightness imperfections in IPE160 beams. Applied to steel plane frames, scaled buckling modes can be used to model initial imperfections. It is demonstrated that the entropy (scale factor) for a given energy roughly decreases with the inverse square of the mode index. For practical engineering, this study presents the possibility of using scaled buckling modes of steel plane frames to model initial geometric imperfections. Entropy proves to be a valuable complement to strain energy in structural mechanics.
Comparison of crack growth rates of IPE beams made from stainless steel in three-point bending
(Elsevier, 2023-11-24) Juhászová, Tereza; Miarka, Petr; Seitl, Stanislav
The main focus of research dealing with a fatigue of steel components is mostly performed by mechanical testing with focus set on small-scale components. On the other hand, from a civil engineering viewpoint, the steel load-bearing structures or their elements have much larger dimension, when comparing them to laboratory specimens. Therefore, the fatigue testing took place on IPE 80 specimens made from two different stainless steels AISI 304 and AISI 316, loaded in three-point bending with data collection of crack mouth opening displacement placed in mid-span using clip-on extensometer. This presented study focuses on the comparison of crack propagation rate in linear region of well-known Paris’ law. For the assessment of material constants from Paris’ equation C and m, two steel grades of stainless steel, AISI 304 and AISI 316 were experimentally obtained. To evaluate the experimental data, a three-dimensional (3D) numerical model, representing IPE 80 geometry, in a finite element method (FEM) software Ansys Mechanical APDL was created. The generated numerical results were used to evaluate stress intensity factor values, which serves as a main input to crack propagation Paris’ law.

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