Simulations of Ultimate Limit States under Wind Loading by Combined Finite Discrete Element Method : Doctoral Thesis

U hrvatskom priobalju dominantni lokalni vjetrovi, Bura i Jugo, imaju izrazito različit karakter. Različitost njihovih karaktera manifestira se na njihovo djelovanje na konstrukcije. Analizom vremenskih serija zapisa vjetra na stupu „Bobani“ utvrđeni su parametri koji potvrđuju različitost ovih lokalnih vjetrova kao što su: koeficijent promjene srednje brzine po visini, faktor mahovitosti vjetra, intenziteta turbulencije, spektara turbulencije, gustoće zraka, parametara korelacije, odgovor konstrukcije u vidu akceleracija kritičnih točak te su uspoređeni sa odgovarajućim parametrima u Eurocode normama. Numerički model ponašanja rešetki, lančanica i membrana razvijen je na temelju numeričkog modela Y baziranog na kombiniranoj konačno-diskretnoj metodi. Za navedenu metodu razvijen je vlastiti set konačno-diskretnih elemenata kojima je moguće simulirati ponašanje konstrukcija do graničnih stanja. Za nove konačno-diskretne elemente, razvijene su metode za simulaciju opterećenje vjetrom koji su bazirani na parametrima dobivenim iz analize zapisa profila vjetra. Model uključuje sljedeće karakteristike: velike pomake, rotacije i deformacije elemenata, tranzijentna analiza uz eksplicitnu integraciju kojom se postiže zadovoljavajuća preciznost u svakom vremenskom trenutku, geometrijska i materijalna nelinearnost, aeroelastično prigušenje, opterećenje vjetrom bazirano na neosrednjenim zapisima vjetra. Valjanost numeričkog modela testirana je analitičkim verifikacijskim primjerima te usporedbom zapisa odgovora konstrukcije prikupljenog u tijeku terenskog eksperimenta Bobani. Usporedbom rezultata numeričkog modela i rezultata analitičkih rješenja i eksperimenata pokazano je da je model prihvatljiv za uporabu, te da sa zadovoljavajućom točnosti prati stvarno ponašanje konstrukcija.In Croatian coastal area dominant local winds Bora and Sirocco (Jugo) have significantly different regimes. Difference in their regimes is manifested onto their loading on constructions. Using analysis of time series of wind speeds collected at full scale field experiment “Bobani” the parameters that differs were deduced. Those parameters include wind shear factor, wind gust factor, turbulence intensity, and spectra of turbulence, air density, correlation parameters and construction response factor. Also, these parameters are compared to those given in Eurocode. Next, numerical model for simulation of truss structures, cables and membranes are developed from Y code software based on combined finite-discrete element method. For stated method, new element types are developed which can simulate stated constructions until ultimate limit state. For new element types, wind loading method is developed based on parameters deduced form wind time series analysis. The numerical model includes large displacements, strains and rotations of elements, transient analysis with explicit integration scheme, geometric and material nonlinearity, aeroelastic damping. Numerical model is verified with comparison to analytical solutions and experimental studies including full-scale field experiment “Bobani”. The verification shows extends of usage of model and confirm model accuracy

Simulations of Ultimate Limit States under Wind Loading by Combined Finite Discrete Element Method : Doctoral Thesis

U hrvatskom priobalju dominantni lokalni vjetrovi, Bura i Jugo, imaju izrazito različit karakter. Različitost njihovih karaktera manifestira se na njihovo djelovanje na konstrukcije. Analizom vremenskih serija zapisa vjetra na stupu „Bobani“ utvrđeni su parametri koji potvrđuju različitost ovih lokalnih vjetrova kao što su: koeficijent promjene srednje brzine po visini, faktor mahovitosti vjetra, intenziteta turbulencije, spektara turbulencije, gustoće zraka, parametara korelacije, odgovor konstrukcije u vidu akceleracija kritičnih točak te su uspoređeni sa odgovarajućim parametrima u Eurocode normama. Numerički model ponašanja rešetki, lančanica i membrana razvijen je na temelju numeričkog modela Y baziranog na kombiniranoj konačno-diskretnoj metodi. Za navedenu metodu razvijen je vlastiti set konačno-diskretnih elemenata kojima je moguće simulirati ponašanje konstrukcija do graničnih stanja. Za nove konačno-diskretne elemente, razvijene su metode za simulaciju opterećenje vjetrom koji su bazirani na parametrima dobivenim iz analize zapisa profila vjetra. Model uključuje sljedeće karakteristike: velike pomake, rotacije i deformacije elemenata, tranzijentna analiza uz eksplicitnu integraciju kojom se postiže zadovoljavajuća preciznost u svakom vremenskom trenutku, geometrijska i materijalna nelinearnost, aeroelastično prigušenje, opterećenje vjetrom bazirano na neosrednjenim zapisima vjetra. Valjanost numeričkog modela testirana je analitičkim verifikacijskim primjerima te usporedbom zapisa odgovora konstrukcije prikupljenog u tijeku terenskog eksperimenta Bobani. Usporedbom rezultata numeričkog modela i rezultata analitičkih rješenja i eksperimenata pokazano je da je model prihvatljiv za uporabu, te da sa zadovoljavajućom točnosti prati stvarno ponašanje konstrukcija.In Croatian coastal area dominant local winds Bora and Sirocco (Jugo) have significantly different regimes. Difference in their regimes is manifested onto their loading on constructions. Using analysis of time series of wind speeds collected at full scale field experiment “Bobani” the parameters that differs were deduced. Those parameters include wind shear factor, wind gust factor, turbulence intensity, and spectra of turbulence, air density, correlation parameters and construction response factor. Also, these parameters are compared to those given in Eurocode. Next, numerical model for simulation of truss structures, cables and membranes are developed from Y code software based on combined finite-discrete element method. For stated method, new element types are developed which can simulate stated constructions until ultimate limit state. For new element types, wind loading method is developed based on parameters deduced form wind time series analysis. The numerical model includes large displacements, strains and rotations of elements, transient analysis with explicit integration scheme, geometric and material nonlinearity, aeroelastic damping. Numerical model is verified with comparison to analytical solutions and experimental studies including full-scale field experiment “Bobani”. The verification shows extends of usage of model and confirm model accuracy

Behaviour of prestressed hollow core concrete slab under fire – experimental study

U radu je prikazan eksperiment u kojem je praćeno ponašanje prednapete šuplje betonske ploče pri djelovanju ISO krivulje razvoja požara. Analizirana šuplja ploča je dimenzija 1,2 × 8,0 m. U eksperimentu praćen je razvoj temperatura u nekoliko točaka: unutar ploče, u šupljinama i na površini ploče. Povećanje progiba ploče u vremenu praćeno je uz pomoć dva LVDT uređaja. Dva dodatna LVDT uređaja postavljena su na kraju ploče sa svrhom praćenja zaokreta ploče. Također, u eksperimentu je praćena promjena relativne uzdužne deformacije na sredini ploče uz pomoć dvije mjerne trakice. Rezultati eksperimenta pokazali su da nosivost i deformabilnost prednapete ploče uslijed djelovanja požara dominantno ovisi o razvijenoj temperaturi u prednapetim kablovima, te o degradaciji modula elastičnosti betona. Posmični lom nije imao utjecaja na ukupnu nosivost prednapete ploče.The paper presents an experimental study of behaviour of a prestressed hollow-core slab exposed to ISO fire curve. Dimensions of the slab are 1,2 × 8,0 m. The study includes measurements of temperature gradient inside the section of the slab, voids, and upper surface of the slab. Time dependent vertical deflection of the structure was recorded by using two linear variable differential transformers (LVDT). Two additional LVDTs were used for tracking the rotation at the end of the slab. In addition, measurements of the time dependent longitudinal deformation of the slab at midspan were also carried out with two strain gauges. The study has shown that the behaviour of slab under fire depends on the temperature of the prestressed strands, combined with the degradation of the modulus of elasticity of the heated concrete. Shear failure had no effect on the load bearing capacity of the slab

Multiplicative Decomposition Based FDEM Model for Membrane Structures

A finite strain large displacement model for membrane structures based on the combined finite-discrete element method (FDEM) has been developed. The model is implemented in the open source FDEM package - Yfdem. The paper also presents benchmark tests and numerical results

Experimental testing and numerical modelling of glued laminated timber

U ovom su radu prikazani eksperimentalni testovi i numeričko modeliranje lijepljenih lameliranih greda izrađenih od različitih vrsta mekog i tvrdog drva (hrast, bagrem i smreka). Lijepljene lamelirane grede promatrane su tijekom ispitivanja na savijanje u tri točke na kratkim uzorcima. Eksperimentalni testovi uključuju mjerenja primijenjenih sila te deformacija i pomaka pomoću linearnog varijabilnog diferencijalnog transformatora (LVDT). U radu su prikazane karakteristike ispitnih uzoraka, postupak i rezultati ispitivanja na savijanje te modeliranje istih uzoraka pomoću računalnog programa ANSYS 16.2. Cilj ovog istraživanja je opisati ponašanje svakog uzorka posebno. Posebna pozornost se posvećuje analizi tipa i mehanizma otkazivanja greda izrađenih od tvrdog i mekog drva. Mehanička svojstva dobivena iz eksperimenata uspoređena su s rezultatima dobivenim numeričkom analizom.This paper presents experimental testing and numerical modelling of glulam beams made from different softwood and hardwood species (oak, acacia and spruce). The glulam beams are observed during a 3-points bending tests on short samples. Experimental tests include measuring applied forces, deformations and displacements using the linear variable differential transducer (LVDT). The present report shows details of the test specimens, test set-up, results of the bending tests and numerical modelling using computer program Ansys. The aim of the current research is to describe the behaviour of each specimen individually. Particular attention is given to the accurate analysis of the type and mechanisms of failure of beams made of hardwood and softwood. The mechanical properties obtained from the experiments are compared with the results from numerical analysis software

New Screening tool for Obtaining Concentration Statistics of Pollution Generated by Rivers in Estuaries

Rivers represent an essential pathway for waterborne transport, and therefore estuaries are critical coastal areas for a pollution hazard that might lead to eutrophication and general water quality deterioration. When addressing these problems, the decision makers and coastal managers often need additional skills and specialists, so they engage consultants in developing models and providing potential solutions. Different stakeholders’ interests present a challenge in the implementation process of proposed solutions. Nevertheless, if the relevant institutions were presented with a screening tool, enabling them with a certain level of solution ownership, potentially more involvement would occur. There are numerous intertwined physical processes present in the estuary ecosystem, including river discharge, tidal forces, wind-induced stress and water density variations. This research utilizes an analytical model based on ensemble averaging and near-field approximation of the advective-diffusion equation for the case of continuous, steady, conservative solute transport in a stratified, river-dominated estuary. Such an approach significantly reduces the costs and time needed to obtain enough measured data required for common statistical analysis or the need for a more complex numerical model. The developed methodology is implemented into a simple software named CPoRT (Coastal Pollution Risk Tool) within a recently conducted research project funded by European Social Fund

Simulations of Ultimate Limit States under Wind Loading by Combined Finite Discrete Element Method : Doctoral Thesis

U hrvatskom priobalju dominantni lokalni vjetrovi, Bura i Jugo, imaju izrazito različit karakter. Različitost njihovih karaktera manifestira se na njihovo djelovanje na konstrukcije. Analizom vremenskih serija zapisa vjetra na stupu „Bobani“ utvrđeni su parametri koji potvrđuju različitost ovih lokalnih vjetrova kao što su: koeficijent promjene srednje brzine po visini, faktor mahovitosti vjetra, intenziteta turbulencije, spektara turbulencije, gustoće zraka, parametara korelacije, odgovor konstrukcije u vidu akceleracija kritičnih točak te su uspoređeni sa odgovarajućim parametrima u Eurocode normama. Numerički model ponašanja rešetki, lančanica i membrana razvijen je na temelju numeričkog modela Y baziranog na kombiniranoj konačno-diskretnoj metodi. Za navedenu metodu razvijen je vlastiti set konačno-diskretnih elemenata kojima je moguće simulirati ponašanje konstrukcija do graničnih stanja. Za nove konačno-diskretne elemente, razvijene su metode za simulaciju opterećenje vjetrom koji su bazirani na parametrima dobivenim iz analize zapisa profila vjetra. Model uključuje sljedeće karakteristike: velike pomake, rotacije i deformacije elemenata, tranzijentna analiza uz eksplicitnu integraciju kojom se postiže zadovoljavajuća preciznost u svakom vremenskom trenutku, geometrijska i materijalna nelinearnost, aeroelastično prigušenje, opterećenje vjetrom bazirano na neosrednjenim zapisima vjetra. Valjanost numeričkog modela testirana je analitičkim verifikacijskim primjerima te usporedbom zapisa odgovora konstrukcije prikupljenog u tijeku terenskog eksperimenta Bobani. Usporedbom rezultata numeričkog modela i rezultata analitičkih rješenja i eksperimenata pokazano je da je model prihvatljiv za uporabu, te da sa zadovoljavajućom točnosti prati stvarno ponašanje konstrukcija.In Croatian coastal area dominant local winds Bora and Sirocco (Jugo) have significantly different regimes. Difference in their regimes is manifested onto their loading on constructions. Using analysis of time series of wind speeds collected at full scale field experiment “Bobani” the parameters that differs were deduced. Those parameters include wind shear factor, wind gust factor, turbulence intensity, and spectra of turbulence, air density, correlation parameters and construction response factor. Also, these parameters are compared to those given in Eurocode. Next, numerical model for simulation of truss structures, cables and membranes are developed from Y code software based on combined finite-discrete element method. For stated method, new element types are developed which can simulate stated constructions until ultimate limit state. For new element types, wind loading method is developed based on parameters deduced form wind time series analysis. The numerical model includes large displacements, strains and rotations of elements, transient analysis with explicit integration scheme, geometric and material nonlinearity, aeroelastic damping. Numerical model is verified with comparison to analytical solutions and experimental studies including full-scale field experiment “Bobani”. The verification shows extends of usage of model and confirm model accuracy

Behaviour of Aluminium EN AW 6082 T6 Columns Exposed to Transient Heating—Experimental and Numerical Analysis

The paper presents an experimental and numerical analysis of EN AW 6082 T6 aluminium alloy columns exposed to high-temperature creep in transient conditions. Transient tests with columns subjected to a constant heating rate for a persistent external load in the form of the horizontal and transversal forces were carried out. A total of ten columns were examined with varying ratios of horizontal and transversal loads. The test results were compared to numerical results obtained from ANSYS 16.2. The coefficients for an ANSYS built-in Modified Time Hardening creep model were calibrated from the previously conducted tests on coupons and used as a base for the numerical analysis of the column. The study results reveal that creep reduces column load-bearing capacity, starting at temperatures above 150 °C. Furthermore, the level of reduction in the aluminium column capacity, which manifests itself as a runaway failure of the column between the creep and creep-free model, deviates with a difference exceeding 160% in vertical displacement upon failure, while the creep model correlates very well with the results obtained from the tested specimens in terms of failure time and the displacement ratio