Changes in dynamic properties of reinforced concrete frame experimentally tested on a shaking table

U radu je promatrana armiranobetonska konstrukcija eksperimentalno ispitana na potresnome stolu. Fizički je model konstrukcije ispitan u četiri faze, pri čemu je svaka faza uključivala potres snažnijega intenziteta. To je omogućilo istraživanje utjecaja oštećenja konstrukcije na njezina dinamička svojstva: prigušenje i osnovni period osciliranja. Za promatranu je konstrukciju napravljena procjena prigušenja i osnovnoga perioda osciliranja nakon svake završene faze ispitivanja primjenom vremenskih zapisa pomaka dostupnih autorima. Rezultati dobiveni na stvarnoj konstrukciji uspoređeni su s preporučenim vrijednostima prigušenja te proračunanim vrijednostima osnovnoga perioda osciliranja uz primjenu analitičkih izraza iz dostupne literature. Osim toga, u radu je prikazan i jednostavan način filtriranja i zaglađivanja vremenskih zapisa koji sadrži visoko frekvencijski šum.This paper observes reinforced concrete structure experimentally tested on a shaking table. The physical model of the structure was tested in four phases where each phase involved shaking of higher intensity. This allowed study of the influence of structural damage on its dynamic properties. For the observed structure an estimation of the damping and the natural period of oscillation was made after each completed phase of the test using displacement time history records available to the authors. The results obtained from the real structure were compared with the recommended values of damping and calculated values of the fundamental period of oscillation using analytical expressions provided in available literature. Besides that, the paper shows simple way of filtering and smoothing of time histories that comprises high frequency noise

PRELIMINARY DESIGN OF CABLE-STAYED FOOTBRIDGE

Rad prikazuje idejno rješenje pješačkog mosta preko rijeke Drave u Osijeku. Širina vodene prepreke koju je potrebno premostiti iznosi 195,0 m. Odabrano rješenje je ovješeni armiranobetonski most s jednim ekscentričnim kosim pilonom. Grafički prikaz mosta je izrađen u programskom paketu AutoCad, a numerički model mosta u programskom paketu SAP2000 v14.2. Na osnovi odabranih izmjera pojedinih dijelova konstrukcije, analize promjenjivog opterećenja prema EN1991-2 te odgovarajućih kombinacija opterećenja (EN1990), izvršena je modalna analiza i proračun odgovarajućih reznih sila mosta.This paper presents a preliminary design of a footbridge over the River Drava in Osijek. Width of the water obstacle is 195,0 m. The selected solution is cable-stayed reinforced concrete bridge with an eccentric inclined pylon. Graphical drawings of the bridge were made in AutoCad software package and numerical model in the SAP2000 v14.2 software package. Modal analysis and calculation of the section forces was performed on the basis of selected dimensions of certain parts of the bridge structure, the analysis of variable loads according to EN1991-2 and the appropriate combination of loads according to EN1990

EFFECT OF INFILLS MADE OF CONCRETE CONTAINING CRUSHED BRICKS/TILES ON SEISMIC RESPONSE OF SHORT COLUMNS

Mnoga izvješća načinjena nakon obilazaka potresom pogođenih područja pokazuju da su kratki stupovi vrlo osjetljivi elementi te da su izvor oštećenja na zgradama pogođenim potresom. Osim toga, pregledom literature je ustanovljeno da djelomični nekonstrukcijski zidani ispun, u usporedbi s betonskim ispunima, ima manje štetan utjecaj na kratke stupove. Ova spoznaja je ukazala na mogućnost primjene opekarskog loma (lom opeke i crijepa) kao agregata za beton, čime bi se dodatno podržao održivi razvoj. U radu je prikazano numeričko istraživanje utjecaja ispuna od betona s opekarskim lomom kao agregatom na potresni odziv kratkih armiranobetonskih stupova, kao i proračun i konstruiranje kratkih stupova, sličan onome za vezne grede zidova s otvorima. Linearno-elastični modalni proračun spektrima odziva proveden je na tropoljnim armiranobetonskim okvirima visine četiri i sedam katova. Mehanička svojstva betona s opekarskim lomom kao agregatom, opisana i korištena u ovom istraživanju, određena su laboratorijskim ispitivanjima provedenima na Građevinskom fakultetu Osijek.Various post-earthquake reports indicate that short columns are vulnerable structural members and significant source of serious earthquake damage. Furthermore, reviewing the literature, it was observed that nonstructural partial brick infills, comparatively to partial concrete infills, have less harmful effects on short columns. This put a new perspective on the use of crushed bricks and tiles as concrete aggregate with the additionally benefit of providing a sustainable management of such material. This paper discusses a numerical study on the effect of infills made of concrete containing crushed bricks and tiles on the response of short reinforced-concrete columns. In addition, this paper presents an approach for the analysis and design of short columns, similar to that of tie beams. Linear elastic analysis was carried out on four- and seven-story three-bay reinforced-concrete frames using modal response spectrum analysis. Mechanical properties of concretes containing crushed bricks and tiles determined by laboratory testing at Faculty of Civil Engineering Osijek are described and used in this study

Impact loading of a space nuclear powerplant

Preferred formulation of the problem in two space dimensions are described for solving the threefundamental equations of mechanics (conservation of mass, conservation of momentum, and conservation ofenergy). Models of the behavior of materials provide the closure to the three fundamentals equations forapplications to problems in compressible fluid flow and solid mechanics. Models of fracture and damage aredescribed. A caloric model of the equation of state is proposed to describe thermodynamic properties of solidmaterials with the phase transitions. Two-dimensional problems of a high-velocity impact of a space nuclearpropulsion system reactor are solved. High-velocity impact problems of destruction of reactor are solved for thetwo cases:1) at its crash landing on the Earth surface (the impact velocity being up to 400 m/s);2) at its impact (with velocity up to 16 km/s) with the space debris fragments

INFLUENCE OF THE RESPONSE OF A SHALLOW FOUNDED REINFORCED CONCRETE FRAME STRUCTURE ON SOIL LIQUEFACTION POTENTIAL

Nakon katastrofalnih posljedica potresa na Aljasci i u Niigati 1964. godine, Seed i Idriss su razvili i objavili metodu za procjenu otpornosti tla na likvefakciju pod nazivom „pojednostavljeni postupak“. Dugo vremena se smatralo kako prisutnost građevine smanjuje opasnost od pojave likvefakcije, no nakon nedavnih potresa (Kobe 1995. i Kocaeli 1999.) uočeno je kako se likvefakcija pojavila ispod temelja građevina, iako nije došlo do njezinog pojavljivanja na slobodnim površinama tla u okolici građevina. U ovome radu analiziran je i uspoređen likvefakcijski potencijal tla neopterećenog objektom i tla ispod građevine, za dva profila relativno mekog tla u Osijeku pri djelovanju dva potresa različitog frekventnog karaktera i magnitude. Linearno-elastične analize vremenskim zapisom provedene su koristeći računalni program SAP2000 za slučaj neopterećen objektom i za slučaj prisutnosti i utjecaja odziva plitko temeljene armiranobetonske okvirne konstrukcije. Dodatno su prikazani i osnovni dinamički odzivi same konstrukcije u interakciji s tlom, te je dana kratka usporedba s općeprihvaćenim modeliranjem apsolutno krutih oslonaca konstrukcije.Following disastrous earthquakes in Alaska and in Niigata in 1964, Seed and Idriss developed and published a method for evaluating liquefaction resistance of soils termed the ‘‘simplified procedure’’. For a long time it has been considered that the presence of the building reduces the risk of liquefaction, but after the recent earthquakes (Kobe 1995. and Kocaeli 1999.) it was observed that the liquefaction occurred under the foundations of buildings, although it has not been observed in the free field around buildings. This paper analyzes and compares soil liquefaction potential in the free field and beneath the building, for two relatively soft soil profiles under the influence of two strong motions with different frequency character and magnitude. A linear-elastic time history analysis was conducted using computer program SAP2000 for the free field case and case with presence and response impact of a shallow founded reinforced concrete frame structure. In addition, basic dynamic response of the structure in interaction with the soil is presented and a short comparison is made opposite to the widely accepted rigid-base structure assumption

SEISMISCHE BERECHNUNG DES STAHLBETONRAHMENS NACH EN 1998-1

Prikazan je proračun armiranobetonskog okvira izloženog djelovanju potresa kako bi se pokazalo da ne vrijedi uvriježena pretpostavka o seizmičkom proračunu koji daje velike unutarnje sile, a time i velike količine čelika za armiranje i/ili velike dimenzije pojedinih konstrukcijskih elemenata. Odabrani okvir konstrukcije proračunan je s plastičnim zglobovima na krajevima greda i bez njih. Dobiveni su odzivi na djelovanje potresa, a izrađena je i usporedba utroška čelika za armiranje.The analysis of a reinforced-concrete frame subjected to seismic action was undertaken so as to demonstrate invalidity of the widely accepted assumption about the seismic design resulting in great internal forces, and hence in great quantities of reinforcing steel and/or great dimensions of individual structural elements. The selected structural frame was analyzed with plastic hinges at beam ends, and without such hinges. The seismic response values were obtained, and a comparative analysis of reinforcing steel consumption was made.L'analyse du cadre en béton armé soumis à l'action sismique a été réalisée afin de démontrer l'invalidité de la supposition répandue sur l'étude sismique résultant en des grandes forces internes et, de cela, en des grandes quantités de ferraillage et/ou en des grandes dimensions des éléments structurels individuels. Le cadre structurel choisi a été analysé avec les rotules plastiques aux extrémités de la poutre, et sans ces rotules. Les valeurs de la réponse sismique ont été obtenus, et une analyse comparative de la consommation de ferraillage a été faite.Приведен расчет железобетонной рамы, подверженной сейсмическому воздействию, для того, чтобы опровергнуть общепринятую предпосылку о том, что сейсмический расчет дает большие внутренние силы и, следовательно обуслoвливает большие количества стали для армирования и/или большие размеры отдельных конструкционных элементов. Произведен расчет выбранной рамы конструкции с пластичными шарнирами на краях балок и без них. Получены реакции на сейсмическое воздействие, произведено сравнение расходов стали для армирования.Dargestellt ist eine Berechnung des der Erdbebeneinwirkung ausgesetzten Stahlbetonrahmens um zu zeigen dass die eingebürgerte Annahme über die seismische Berechnung welche grosse innere Kräfte, somit auch grosse Stahlmengen und/oder grosse Abmessungen einzelner Konstruktionselemente verlangt, nicht gilt. Den ausgewählten Rahmen der Konstruktion berechnete man mit plastischen Gelenken und ohne denselben. Man erreichte Antworten auf die Einwirkung des Erdbebens, und auch der Vergleich des Stahlaufwands für die Bewehrung wurde erarbeitet

PRORAČUN ARMIRANOBETONSKE OKVIRNE KONSTRUKCIJE SUKLADNO OČEKIVANOM POMAKU U SKLADU S PROPISIMA EUROCODE 8

The new concept in designing structures to achieve a specified performance limit state was first introduced in New Zealand, in 1993. Over the following years, USA and Europe have put a great effort focused on research and development of the concept as a viable and logical alternative to the current forcebased code approaches. The paper presents the theory and application of this method using a reinforced concrete frame structures as an example. The frame structure is designed with implementing Eurocode 8 regulations. Furthermore, results obtained using direct displacement based design method are compared to the ones obtained using multimodal response spectrum method. Among other things, significant differences are highlighted in regard to current design regulations.Novi koncept oblikovanja konstrukcija s ciljem postizanja određenog graničnoga stanja prvi puta je predstavljen u Novom Zelandu, 1993. Tijekom narednih godina u SAD-u i Europi se ulaže veliki napor usmjeren na istraživanje i razvoj ovoga koncepta kao održivog i logički alternativnog trenutnom pristupu proračuna preko sile. U ovom je radu prikazana osnovna teorija i primjena metode proračuna sukladno očekivanom pomaku na primjeru armiranobetonske okvirne konstrukcije. Okvirna konstrukcija je proračunata koristeći Eurocode 8 propise. Nadalje, rezultati dobiveni koristeći proračun sukladno očekivanom pomaku, uspoređeni su s rezultatima dobivenim koristeći višemodalnu spektralnu analizu. Između ostaloga naglašene su bitne razlike u odnosu na trenutno propisane postupke proračuna, kao i nedostatci istih

SPEKTRI POTRESNOG ODZIVA PLITKO TEMELJENIH KONSTRUKCIJA NA MEKIM TLIMA

Rad obrađuje potresni odziv plitko temeljenih konstrukcija na mekim tlima. Istraživanje u okviru rada je pokrenuto uz glavnu pretpostavku da europski normirani spektri odziva za meka tla nisu dobro definirani te da ne uključuju učinke međudjelovanja tla i konstrukcije. S ciljem definiranja poboljšanog spektra odziva kao osnovnog alata za proračun sigurnih i potresno otpornih konstrukcija, izrađene su i funkcije impedancije i prijenosne funkcije koje omogućuju uključivanje učinaka međudjelovanja tla i konstrukcija u proračunima primjenom metode spektara odziva. Oslonac studiji daju rezultati eksperimentalnih istraživanja provedenih na potresnom stolu na Sveučilištu u Bristolu te u geotehničkoj centrifugi na institutu IFSTTAR. Numerički modeli korišteni za provedbu parametarske studije su uspješno kalibrirani s obzirom na rezultate spomenutih eksperimentalnih istraživanja. U radu je dan prijedlog primjene funkcija impedancije, nastalih u okviru ovog rada, u klasičnim računalnim programima koji primjenu nalaze u znanosti i praksi. Osim toga, dan je prijedlog za primjenu funkcija impedancije u okviru N2 metode.This thesis deals with seismic response of shallow founded structures on soft soils. Research within the thesis is initiated with the main assumption that the European code-based response spectra for soft soils are ill-defined and that they do not include soil-structure interaction effects. With the aim to provide improved response spectrum, as a key engineering tool for design of earthquake resistant structures, both impedance and transfer functions were developed. Those functions enable incorporation of both soil compliance and its capability that dissipates earthquake energy. Parametric study was conducted using numerical models calibrated with regards to experimental results obtained both from testing performed in enhanced gravitational field using geotechnical centrifuge at the IFSTTAR institute and on shaking table of the University of Bristol at 1g. Numerical modelling, and thus parametric study, was governed using equivalent linear method. The last chapter of the work provides proposed methodology for including the developed functions into classical program packages mostly used by engineering practice and academia for structural analysis and design. Also, proposal for application of impedance functions within the framweork of N2 method is provided