Andrzej Garstecki

Damage detection using thermal experiments and wavelet transformation

Damage detection using the discrete wavelet transformation (DWT) of temperature field recorded on the surface of a plate structure is discussed. Defects in the form of voids and inclusions of various magnitude are considered. Computer-simulated experiments including the ones accounting for white noise and real thermal experiments are applied. Transient heat transfer problems are analysed. The efficiency of DWT in damage detection is studied by way of a number of examples. Haar, Daubechies 4, 6 and 8 wavelets in 1D and 2D DWT are used. The usefulness of the Lipschitz exponent evaluated with the use of DWT is discussed. The issue of denoising the thermal response signals using the soft threshold shrinkage procedure is also taken up.

Damage detection using parameter dependent dynamic experiments and wavelet transformation

Abstract The paper deals with a class of problems, where localised damage is detected using static and dynamic tests. Response of a structure is analysed employing discrete wavelet transformation as a tool for signal processing. The localised damage in beam structures was modelled as bending stiffness reduction. The efficiency of static and dynamic tests is studied. The minimal number of experimental measurement data and the precision of measurements required for the successful damage localisation is discussed by several numerical examples.

Snap-through Phenomenon of Imperfect Steel Structures

In the paper the stability analyses of steel members with initial imperfection are carried out. The results of experiments on steel girders with I section and very thin web are presented. In these experiments an unexpected phenomenon, namely the snap-through of the web was discovered. The authors assigned it to initial imperfections. This behavior is studied by introduction of a model structure composed of rigid bars connected by elastic hinges. Introducing various forms of geometric imperfections into the model structure the similar snap-through response as in experiments was observed and studied.

3.1 – Optimization of Steel Beams and Columns for Variable Rib Configuration

Optimal configuration of stiffening ribs in the steel welded I – beams and columns is studied. A wide class of designs with traditional orthogonal configuration implementing transverse and/or longitudinal ribs is considered and compared with a new configuration with diagonal ribs. The critical load and the total manufacturing cost, composed of costs of steel, cutting and welding are computed for all designs. The configuration with diagonal ribs proved to be more efficient than the traditional ones.

Reliability of Engineering Methods of Assessment the Critical Buckling Load of Steel Beams

In this paper the reliability assessment of buckling resistance of steel beam is presented. A number of parameters such as: the boundary conditions, the section height to width ratio, the thickness and the span are considered. The examples are solved using FEM procedures and formulas proposed in the literature and standards. In the case of the numerical models the following parameters are investigated: support conditions, mesh size, load conditions, steel grade. The numerical results are compared with approximate solutions calculated according to the standard formulas. It was observed that for high slenderness section the deformation of the cross-section had to be described by the following modes: longitudinal and transverse displacement, warping, rotation and distortion of the cross section shape. In this case we face interactive buckling problem. Unfortunately, neither the EN Standards nor the subject literature give close-form formulas to solve these problems. For this reason the reliability of the critical bending moment calculations is discussed.In this paper the reliability assessment of buckling resistance of steel beam is presented. A number of parameters such as: the boundary conditions, the section height to width ratio, the thickness and the span are considered. The examples are solved using FEM procedures and formulas proposed in the literature and standards. In the case of the numerical models the following parameters are investigated: support conditions, mesh size, load conditions, steel grade. The numerical results are compared with approximate solutions calculated according to the standard formulas. It was observed that for high slenderness section the deformation of the cross-section had to be described by the following modes: longitudinal and transverse displacement, warping, rotation and distortion of the cross section shape. In this case we face interactive buckling problem. Unfortunately, neither the EN Standards nor the subject literature give close-form formulas to solve these problems. For this reason the reliability of the cri...

STABILITY OF STEEL STRUCTURES WITH CLEARANCES AND IMPERFECTION

This paper deals with statics and stability problems of steel structures with the emphasis on their sensitivity to initial imperfections and clearances. The main aim is to performed an indication as the state of stress, displacement and the critical load. The paper presents theoretical studies involving linear and nonlinear behavior of thin-walled steel structures with a special reference to the interactive buckling, initial geometric imperfections and clearances which is in the scope of the modern approach to design. For this purpose authors proposed model structures composed of rigid bars where strains are concentrated in connecting elastic joints These model structures enable to derive nonlinear algebraic equilibrium equations which strictly describe preand post-buckling behavior of structures with various combinations of imperfections and clearances. Numerous examples demonstrate variable types of structural response depending on the modes and amplitudes of imperfections in relation with clearances. In the case of large clearances the model structure behaves like a typical Euler column characterized by a stable and symmetric bifurcation point. However, clearances combined with certain patterns of imperfections can result in unstable post buckling behavior and also in snap through phenomena. The developed model structures, which illustrate complex structural stability response accounting for initial geometric imperfections and clearances, due to its simplicity makes possibility to describe the exact close form solutions for both linear and nonlinear stability analysis. Based on the proposed model structure it is shown, that interaction between initial clearances and initial geometric imperfections can strongly affect the structural stability response.

Numerical evaluation of wrinkling stress in sandwich panels

Sandwich panels have been for years used as structural and cladding elements. Characteristic feature of these structures is that important role is played by temperature actions, creep of the core and local instability of thin faces of the panel [2]. Proper estimation of these phenomena has become a challenging issue because of strong tendency to optimize technical parameters and costs.