Hrvoje Draganić

Numerical simulation of effect of explosive action on overpasses

Nadvožnjak nije moguce uciniti, projektiranjem i/ili izvedbom, apsolutno sigurnim na djelovanje eksplozije jer se ni sama kolicina eksploziva kojOverpasses can not be made absolutely safe to explosive action, regardless of interventions made during their design and/or realisation. This is due to the fact that the very quantity of explosive to be activated under the bridge during an attack can not be defined with an acceptable level of probability. Three quantities of explosives activated under the overpass structure are analysed. The load, behaviour, and damage to overpass superstructure are considered. It is stated in conclusion that all three quantities of explosive afflict considerable damage to usual overpasses, and cause their collapse. The nonlinear numerical analysis of the overpass was conducted using the Ansys Autodyn hydrocode software.

Stress–strain relationships and influence of testing parameters on coupon test results

Tensile steel-coupon testing qualifies as one of the more commonly used experiments for determination of basic parameters for structural design. Such

Analysis of Blast Wave Parameters Depending on Air Mesh Size

Results of numerical simulations of explosion events greatly depend on the mesh size. Since these simulations demand large amounts of processing time, it is necessary to identify an optimal mesh size that will speed up the calculation and give adequate results. To obtain optimal mesh sizes for further large-scale numerical simulations of blast wave interactions with overpasses, mesh size convergence tests were conducted for incident and reflected blast waves for close range bursts (up to 5 m). Ansys Autodyn hydrocode software was used for blast modelling in axisymmetric environment for incident pressures and in a 3D environment for reflected pressures. In the axisymmetric environment only the blast wave propagation through the air was considered, and in 3D environment blast wave interaction and reflection of a rigid surface were considered. Analysis showed that numerical results greatly depend on the mesh size and Richardson extrapolation was used for extrapolating optimal mesh size for considered blast scenarios.

Finite Element Mesh Size Optimization for Steel Bolted Connection

Bolted connections are important components of steel structures and they must be based on good design, with analytical descriptions of failure mechanisms that are thoroughly researched. A robust and reliable analytical description of a failure mode requires a large base of results, collected experimentally or numerically, usually via FEA. The modelling procedure in FEM simulations can significantly influence result accuracy, and one of the most important parameters is spatial discretization. Mesh size presents a delicate balance between accuracy, efficiency and convergence issues, especially in bolted connection analysis with contact, material and geometric nonlinearity. Due to increased complexity, sensitivity studies are difficult to interpret and time expensive, which is why in this study a mesh size optimization procedure is presented. This optimization is based on a previously verified and validated numerical model parametric study of a single-bolt lap connection. The first step included forming of an optimization model based on an artificial neural network, through which results were extrapolated and compared to experimental. However, estimated solving wall time was significantly longer. In the second step, a nonlinear optimization model was structured to determine a mesh size for which the difference between experimental and optimization results would be equal, whilst having a minimal solving wall time. The optimization model provided insights into mesh size quality to efficiency ratios and rendered that the minimal difference between experimental and numerical results is 1.57%, while having a solving wall time of 1.3 h, instead of the step one optimization modelling estimated 36 h.

COLLISIONS OF ROAD VEHICLES WITH BRIDGE COLUMNS

As speed limits and traffic on city roads continue to increase, collisions between road vehicles and bridge columns are becoming more common. Current

Usporedba osnovnih perioda modela zgrada s armiranobetonskim zidovima s empirijskim izrazima

Usporedba osnovnih perioda modela zgrada s armiranobetonskim zidovima s empirijskim izrazima Izvorni znanstveni clanka Empirijski izrazi za procjenu osnovnih perioda su sastavni dio propisa za proracun seizmickih djelovanja te uglavnom ovise o visini, materijalu (celik, armirani beton) i nosivom sustavu(okvir, posmicni zidovi, itd.) građevine. Ovi izrazi su obicno nastali iz empirijskih podataka kroz analizu mjerenih osnovnih perioda postojecih građevina pod djelovanjem potresa. Provedena je parametarska studija na 480 modela armiranobetonskih zgrada s posmicnim zidovima s razlicitim ulaznim podacima: visina zgrade, broj raspona i omjer povrsine posmicnih zidova i tlocrtne povrsine zgrade. Cilj ovog istraživanja je provjeriti empirijske izraze razlicitih autora i seizmickih propisa u svrhu provjere tocnosti izraza kao pocetnih pretpostavki kod projektiranja potresno otpornih građevina. Kljucne rijeci: EN1998-1; armiranobetonski posmicni zidovi; modeli zgrada; osnovni period; parametarska studija

NAJPOVOLJNIJI OBLIK OSI LUČNOG MOSTA

Predstavljen je proracun najpovoljnijeg oblika osi luka mosta, koristeci uvjet da moment savijanja od stalnog opterecenja iscezava u svim presje

KONTINUIRANO MOTRENJE MOSTOVA

Mostovi su važne infrastrukturne građevine i zbog toga ih je potrebno održavati. Održavanje obuhvaca preglede i popravak uocenih ostecenja. U radu je dan pregled nekih od metoda za kontinuirano motrenje i primjeri njihove primjene na izgrađenim mostovima. Metode koriste: GPS (Global Positioning System ; satelitski Sustav globalnog pozicioniranja), akcelerometre, opticka vlakna, anemometre, tenzometre. Iako je postavljanje opreme za kontinuirano motrenje mostova isprva skuplje od uobicajenih metoda, ono omogucuje uvid u stanje mosta u bilo kojem trenutku te pravodobno reagiranje.

UTJECAJ RASPOREDA LEŽAJEVA NA NAPREZANJA RASPONSKOGA SKLOPA PLOČASTOG MOSTA

Ležajevi su elementi kojima se prenose razlicita djelovanja s rasponskoga sklopa na potpore. Oni su veza gornjeg i donjeg ustroja mosta. Predviđen