Numerical model of fluid-structure interaction for water tower analysis of vibrations

This paper deals with the aspects of vibration analysis of 3D numerical water tower models with the explicitly generated 3D finite element (FE) solid fluid model that simulates the fluid-structure interaction (FSI). The development and implementation of the 3D FE solid fluid model in modelling and analysing the system response is extremely important, both in terms of determining the impulsive and convective hydrodynamic pressure, and in terms of overall sizing of the water tower. Vibration of the water tower is calculated based on the analysis of its eigenvibrations, analysis of eigenvibrations occurring when charging and discharging the water tower reservoir (SFA - Staged Fluid Analysis), Steady-State Analysis (SSA) in the frequency domain and the analysis of the system response in the time domain (THA - Time History Analysis), followed by the transformation of the frequency domain response using the Fast Fourier Transform (FFT). The analysis of eigenvalues using the Ritz vectors (Ritz analysis) and the Power Spectral Density Analysis (PSDA) are carried out as the means of additional control and with the purpose of identifying vibration periods. The system's stiffness matrix and mass matrix are corrected using the 3D FE solid fluid model for analysing the water tower vibrations. Effects of the system's increasing vibration period are determined for the partially charged reinforced concrete (RC) water tower reservoir, given the strong action of the fluid mass that is excited for convective hydrodynamic action (sloshing) due to the water tower dimensions and the amount of fluid contained in the reservoir in this case

Buckling analysis of 3D model of slender pile in interaction with soil using finite element method

U radu je prikazano modeliranje i analiza rezultata stabilnosti vitkih šipova primenom metode konačnih elemenata. Formulisan je koncept za modifikovanu analizu stabilnosti 3D modela šip-naglavna ploča-tlo formiran od solid konačnih elemenata za dva tipa modela tla: jednoslojni i dvoslojni. Veza šip-tlo je modelirana primenom kontaktnih link elemenata. Izrazi za nivo normalizovane vrednosti kritične sile Pcr/PE 3D modela šip-naglavna ploča-tlo izvedeni su primenom regresionih analiza za stepenu funkciju. Na osnovu sprovedenih numeričkih testova i regresionih analiza izvedeni su izrazi za koeficijent dužine izvijanja b u funkciji dužine šipa, krutosti šipa i krutosti tla. Istraživanjem je pokazano da je primena sofisticiranih matematičkih modela i numeričkih analiza opravdana i neophodna u cilju kvalitetnijeg uvida u ponašanje vitkog šipa sa aspekta stabilnosti. Ukazano je na kompleksan oblik izvijanja vitkog šipa sa većim brojem polutalasa.The paper describes the modelling and stability analysis of slender piles using finite element method. The concept of a modified stability analysis of 3D model pile-soil-pile cap is formulated; it is formed from solid finite element models for the two types of soil, and a single-pile. Connection in pile-soil contact is modelled using link elements. The terms of the level of normalized critical load Pcr/PE 3D model of pile-soil-pile cap are derived using regression analysis of the power function. On the basis of performed numerical tests and regression analyses expressions are derived for the buckling length coefficient b as a function of pile length, pile stiffness and soil stiffness. Research has shown that the use of sophisticated mathematical models and numerical analysis is justified and necessary in order to gain better insight into the behaviour of slender piles in terms of stability. The paper points to the complex shape of the buckling of slender piles with a number of half waves

Buckling analysis of 3D model of slender pile in interaction with soil using finite element method

U radu je prikazano modeliranje i analiza rezultata stabilnosti vitkih šipova primenom metode konačnih elemenata. Formulisan je koncept za modifikovanu analizu stabilnosti 3D modela šip-naglavna ploča-tlo formiran od solid konačnih elemenata za dva tipa modela tla: jednoslojni i dvoslojni. Veza šip-tlo je modelirana primenom kontaktnih link elemenata. Izrazi za nivo normalizovane vrednosti kritične sile Pcr/PE 3D modela šip-naglavna ploča-tlo izvedeni su primenom regresionih analiza za stepenu funkciju. Na osnovu sprovedenih numeričkih testova i regresionih analiza izvedeni su izrazi za koeficijent dužine izvijanja b u funkciji dužine šipa, krutosti šipa i krutosti tla. Istraživanjem je pokazano da je primena sofisticiranih matematičkih modela i numeričkih analiza opravdana i neophodna u cilju kvalitetnijeg uvida u ponašanje vitkog šipa sa aspekta stabilnosti. Ukazano je na kompleksan oblik izvijanja vitkog šipa sa većim brojem polutalasa.The paper describes the modelling and stability analysis of slender piles using finite element method. The concept of a modified stability analysis of 3D model pile-soil-pile cap is formulated; it is formed from solid finite element models for the two types of soil, and a single-pile. Connection in pile-soil contact is modelled using link elements. The terms of the level of normalized critical load Pcr/PE 3D model of pile-soil-pile cap are derived using regression analysis of the power function. On the basis of performed numerical tests and regression analyses expressions are derived for the buckling length coefficient b as a function of pile length, pile stiffness and soil stiffness. Research has shown that the use of sophisticated mathematical models and numerical analysis is justified and necessary in order to gain better insight into the behaviour of slender piles in terms of stability. The paper points to the complex shape of the buckling of slender piles with a number of half waves

Fragility and reliability analyses of soil -pile -bridge pier interaction

U radu je prikazana procedura evaluacije seizmičkih performansi interakcije šip-tlo inkrementalnom nelinearnom dinamičkom analizom (INDA -Incremental Nonlinear Dynamic Analysis). Ulazni signal u sistemu je tretiran preko generisanih veštačkih akcelerograma, a koji su dodatno procesirani po slojevima tla do osnovne stene. Postprocesiranje INDA analiza izvršeno je posebno za stub, a posebno za šip, tako da su konstruisane krive PGA=f(DR) u kapacitativnom domenu. Za ovako konstruisane krive određeni su performansni nivoi, a na osnovu određenih DR i PGA parametara sprovedene su regresione analize. Krive povredljivosti su konstruisane na osnovu rešenja regresione analize i teorije verovatnoće log-normalne raspodele. Takođe, konstruisane su i krive pouzdanosti na osnovu rešenja analize povredljivosti. Metodološki postupak za analizu seizmičkih performansi, prezentovan u ovom istraživanju, omogućava integrisano kvantitativno-kvalitativno razmatranje i evaluaciju kompleksne interakcije konstrukcija-tlo (SFSI -Soil-Foundation-Structure Interaction).The purpose of this paper is to present the methodology for performance-based seismic evaluation of soil-pile-bridge pier interaction using the incremental nonlinear dynamic analysis (INDA). The system's input signal was treated through the generated artificial accelerograms which were subsequently processed by soil layers and for the bedrock. The INDA analysis was post processed separately for the pier and for the pile, so that the constructed PGA=f(DR) curves are in the capacitive domain. For these curves the authors identified the performance levels, while the regression analyses were conducted based on the specific DR and PGA parameters. Fragility curves were constructed based on the solutions of regression analysis and the probability theory of log-normal distribution. Based on the results of fragility analysis, reliability curves were also constructed. The methodological procedure for seismic performance analysis presented in this study provides an integrated quantitative-qualitative consideration and evaluation of the complex soil-foundation-structure interaction (SFSI)

Performance -based nonlinear static and dynamic seismic analysis of framework buildings

U ovoj doktorskoj disertaciji su sprovedena istraživanja 2D i 3D modela okvirnih sistema zgrada prema performansama za uslove seizmičkog dejstva, a u skladu sa PBEE (Performance-Based Earthquake Engineering) metodologijom. Istraživanja se mogu klasifikovati u četiri bitno različite celine: istraživanja na polju akcelerograma i spektara odgovora, istraživanja na polju nelinearnog odgovora 2D modela okvirnih sistema koji participiranju u konstruktivnom sistemu okvirnih zgrada (dekomponovani ili tretirani kao nezavisne celine), istraživanja na polju nelinearnog odgovora 3D modela okvirnih zgrada i istraživanja na polju odnosa kapacitet konstrukcije/seizmički zahtev 2D i 3D modela okvirnih zgrada. Istraživanja na polju akcelerograma zasnivaju se na primeni akcelerograma realnih zemljotresa i akcelerograma veštačkih zemljotresa. Prethodno su dvokomponentalni akcelerogrami realnih zemljotresa selektovani i preuzeti iz PEER GMDB baze. Veštački akcelerogrami su razmatrani kao nepotpuni i potpuni nestacionarni veštački akcelerogrami, pri čemu je pri kreiranju potpunih nestacionarnih veštačkih akcelerograma uzeta u obzir i analiza seizmičkog hazarda. Procesiranje akcelerograma je sprovedeno po teoriji signala kroz analize: formatiranje, konvertovanje, skaliranje, kalkulacija, procesiranje, kompatibilizacija, filtriranje, generisanje i transformacija. Postupak generisanja međukomponenata akcelerograma po uglovima je sproveden rotacijom komponenata akcelerograma u pravcu raseda i upravno na pravac raseda. Integracijom međukomponenata akcelerograma kreirana je površ akcelerograma (ground motion record surface). Na osnovu generisanih međukomponenata akcelerograma razvijeni su spektri odgovora i integrisani u površ spektra odgovora (response spectra surface). Za sve akcelerograme i spektre odgovora su analizirane mere intenziteta i kreirane anvelope mere intenziteta (intensity measure envelope). Istraživanjem su razmatrani aspekti skaliranja i kompatibilizacije akcelerograma i njihov uticaj na formu površi spektra odgovora. Istraživanja na polju nelinearnog odgovora 2D modela okvirnih sistema zasnivaju se na primeni linijskih konačnih elemenata, čiji je poprečni presek diskretizovan na vlakna i kod kojih se uzimaju u obzir razvoj neelastičnih deformacija. Definisani su opšti modeli pushover krivih koji su poslužili kao podloga za dalja razmatranja u doktorskoj disertaciji: visoko duktilno, visoko ili srednje duktilno, nisko ili neduktilno ponašanje zgrada i prelazna kategorija. Takođe, sprovedena je i klasifikacija pushover krivih varijacijom duktilnosti, duktilnosti u zoni ojačanja/omekšanja i koeficijenta odnosa krutosti u nelinearnom i linearnom domenu. Primenom ova tri parametra generisan je set tipoloških modela pushover krivih kod okvirnih 2D i 3D modela zgrada. Istraživanje tipa raspodele lateralnog seizmičkog opterećenja kod NSPA pushover analize sprovedeno je razmatranjem rešenja dobijenih iz INDA analiza zemljotresa. Predložena je parabolična raspodela kao alternativa ravnomernoj i ekvivalentnoj. Prednost ovakve raspodele je dokazana upoređujući sa rešenjem dobijenim iz regresione analize za grupu zemljotresa, odnosno diskretne vrednosti INDA analiza. Takođe, istraživanjem je utvrđeno da se primenom pushover krive za ravnomernu raspodelu lateralnog seizmičkog opterećenja postiže dosta dobro pokrivanje INDA anvelope u kapacitativnom domenu. Istraživanje uticaja TU (total updating), IU (incremental updating) i HU (hybrid updating) korekcije je razmatrano na 2D modelu okvira, pri čemu se najkvalitetnija rešenja dobijaju primenom NSAPA-DBA analize, u odnosu na INDA analizu. U cilju određivanja potrebnog broja NDA analiza u okviru jedne INDA analize, razvijena je metoda koja se bazira na rešenju dobijenom iz NSPA analize. Sa druge strane, u cilju predikcije rešenja koje se dobija iz INDA analize 2D i 3D modela okvirnih zgrada sa mogućnošću razmatranja odgovora sistema u kapacitativnom domenu, a pri tome ne povećavajući znatnije vreme potrebno za procesiranje, razvijena je hibridna inkrementalna nelinearna statička-dinamička analiza (HINSDA - Hybrid Incremental Nonlinear Static-Dynamic Analysis). Istraživanjem su dobijene veće vrednosti driftova u slučaju primene PGA-IDRmax parametara, nego kod primene PGA-DR parametara. Najmanje odstupanje HINSDA krive od INDA krive dobija se primenom trećeg UBEPKHS konstitutivnog modela, dok se najveće odstupanje dobija primenom prvog UBEPKHS konstitutivnog modela. Istraživanja na polju nelinearnog odgovora 3D modela okvirnih sistema zasnivaju se na primeni linijskih konačnih elemenata, dok se na krajevima štapova apliciraju plastični zglobovi u kojima se omogućava razvoj nelinearnih deformacija. Efekti egzistencije tavanica modelirani su primenom elemenata veze. S obzirom da se kod 3D modela zgrada nelinearan odgovor razmatra primenom pushover krivih za različite uglove dejstva zemljotresa, to je integracijom istih dobijena pushover površ (pushover surface) za NSPA i za INDA (IDA) analizu. Razmatranjem je prikazan opšti model pushover površi i ukazano je na neke specifične modele pushover površi. Tipološki modeli NSPA pushover površi su definisani u funkciji varijacije duktilnosti, duktilnosti u zoni ojačanja/omekšanja i koeficijenta odnosa krutosti u nelinearnom i linearnom domenu za jedan i dva glavna pravca. Generalno razmatrajući identifikovane su četiri grupe pushover površi: rotaciono polisimetrične u osnovi, monosimetrične u osnovi, bisimetrične u osnovi i asimetrične u osnovi. Uvedenim koeficijentom površi duktilnosti (ductility area coefficient) moguće je analizirati performanse 3D modela zgrada uzimajući u obzir duktilnost za sve pravce, odnosno uglove dejstva zemljotresa. Istraživanjem je pokazano da INDA (IDA) pushover površ ima drugačiji oblik, u odnosu na NSPA pushover površi, s obzirom da je primenjena druga mera intenziteta i inženjerski parametar zahteva. U cilju analize performansi 4x6x3, 4x6x5-13, 15x4x4, 15x4x4-6 i 9x6x5-12 3D modela zgrada sproveden je monitoring razvoja plastičnih zglobova po inkrementalnim fazama, a koji je prezentovan preko izopovrši u polarnim koordinatama. Takođe, razmatrane su realizovane krive u polarnim koordinatama za driftove, relativnu vrednost ukupne smičuće sile u osnovi zgrade i duktilnost. Istraživanjem je utvrđeno da su kod svih modela zgrada realizovani manji ili nešto veći maksimalni globalni driftovi DRmax od globalnog drifta DRIO, za IO performansni nivo prema FEMA propisima. Kod zgrada veće spratnosti se lakše realizuje viša klasa duktilnosti, a da se povećanjem neregularnosti u osnovi ova duktilnost redukuje. Razmatrajući realizovane NSPA pushover površi u prostornim koordinatama utvrđeno je da je kod svih 3D modela zgrada krutost u nelinearnom domenu gotovo horizontalna Kn≈0 ili blago pozitivna, osim u pojedinim slučajevima, gde sa povećanjem nelinearnih deformacija krutost postaje negativna Kn<0. Kod 9x6x5-12 3D modela zgrade su realizovane znatno manje maksimalne relativne vrednosti ukupne smičuće sile, u odnosu na relativne vrednosti ukupne smičuće sile kod 4x6x3, 4x6x5-13, 15x4x4 i 15x4x4-6 3D modela zgrada, a što je direktna posledica proračuna seizmičkog dejstva prema SRP propisima. U odnosu na krive relativne vrednosti ukupne smičuće sile u osnovi zgrade (V/W)adeq za maksimalni globalni drift DRmax određene NSPA analizama koje su kružnog ili približno kružnog oblika, krive relativnog spektralnog ubrzanja Sa/Sa,y određene IDA analizama su elipsoidnog oblika ili složenije forme. U početnom delu istraživanja odnosa kapacitet konstrukcije/seizmički zahtev 2D i 3D modela okvirnih zgrada definisani su opšti modeli odnosa pushover krivih i krivih zahteva (BR/SD), a koji su poslužili kao podloga za dalja razmatranja ciljnih pomeranja. U drugom delu je razvijena iterativna metoda koeficijenata pomeranja (IDCM - Iterative Displacement Coefficient Method) kojom su određeni nivoi ciljnih pomeranja. Na osnovu IDCM metode i sprovedenih numeričkih testova na pushover krivama standardizovanih modela odgovora i random funkcija odgovora, utvrđeno je da se postiže veoma zadovoljavajuće slaganje vrednosti driftova realizovanih prema IDCM i NDA analizi. Takođe, minimalna su odstupanja relativne vrednosti ukupne smičuće sile u osnovi objekta realizovana IDCM metodom, u odnosu na rešenja dobijena NDA metodom pri nivoima ciljnih pomeranja (V/W)t. U trećem delu je sprovedeno istraživanje za nivo seizmičkog zahteva 3D modela zgrada, a prezentovano je preko anvelope ciljnog pomeranja (target displacement envelope) i driftova za: performansne nivoe, srednju vrednost, medijanu ciljnog pomeranja i maksimalno pomeranje. Takođe, prikazane su i relativne vrednosti ukupnih smičućih sila u osnovi zgrade za ciljna pomeranja i za maksimalni globalni drift. Na osnovu definisane anvelope ciljnog pomeranja razvijen je niz koeficijenata kojima se ocenjuju performanse 3D modela zgrada. Takođe, performanse zgrada su analizirane i primenom razvijene površi globalnog drifta (drift surface) i površi međuspratnog drifta (interstorey drift surface). U četvrtom delu je, na osnovu razvijene NSPA analize zasnovane na principu projektovanja zgrada prema mehanizmima loma (NSPA-DMBD - Nonlinear Static Pushover Analysis - Damage Mechanisms-Based Design) i istraživanjem na modelu okvirnog sistema, ukazano da je čak kod inicijalne NSPA analize indikator nepovoljnog mehanizma loma bio preko graničnih dilatacija betona. Kod nižih spratova, prema NSPA-DMBD metodi, vrednosti međuspratnih driftova se redukuju, dok se kod viših spratova povećavaju uravnotežujući na taj način odgovor konstrukcije.Research of 2D and 3D models of frame building system according to the performances for the seismic action, and in accordance with the Performance-Based Earthquake Engineering (PBEE) methodology is presented in this doctoral dissertation. Research can be classified into four distinctly different areas: research in the field of ground motion record and response spectra, research in the field of nonlinear response of 2D model system frameworks that participate in building structural system framework (decomposed or treated as independent entities), research in the field of nonlinear response of 3D model frameworks and research in the field of the relationship of building capacity/seismic demand of 2D and 3D model frameworks. Research in the field of ground motion record is based on the application of natural earthquakes and artificial earthquakes. Previously, the two-componential ground motion records of natural earthquakes are selected and downloaded from the PEER GMDB database. Artificial ground motion records were considered as incomplete and complete non-stationary artificial accelerograms, whereby when creating complete non-stationary artificial accelerograms the analysis of seismic hazard is taken into consideration. The signal processing theory is used for analysis of accelerograms: formatting, converting, scaling, calculation, processing, spectral matching, filtering, generating and transformation. The process of generating inter-components of accelerograms by angles is carried out by rotating components of accelerograms in the fault parallel and fault normal direction. The ground motion record surface is created integrating inter-components of accelerograms. Based on the generated inter-components of the accelerograms the response spectra are developed and integrated into the response spectra surface. For all accelerograms and response spectra intensity measures were analyzed and the intensity measure envelopes were created. The research examined the aspects of scaling and spectral matching of accelerograms and their impact on the form of the response spectra surface. Research in the field of nonlinear response of 2D model system frameworks is based on the application of the beam finite elements, whose cross-section is discretized into fibers and which take into account the development of inelastic deformations. The general models of the pushover curves are defined, which served as a basis for a further consideration in this doctoral dissertation: highly ductile, highly or medium ductile, low or brittle behavior of buildings and transitional category. Also the classification of the pushover curves is implemented by variation of ductility, ductility in the field of stiffening/softening and coefficient of the relation of stiffness in nonlinear and linear domain. By applying these three parameters the set of typological model of the pushover curves is generated for 2D and 3D models of framework buildings. Research the type of distribution of lateral seismic loads for the NSPA pushover analysis was conducted considering the solutions obtained from the INDA analysis of earthquakes. The parabolic distribution is proposed as an alternative to the uniform and equivalent. The advantage of this distribution is demonstrated by comparing with the solution obtained from the regression analysis for a group of earthquakes or discrete values of the INDA analysis. Also, research has found that the application of the pushover curve for the uniform distribution of the lateral seismic loads is achieved quite good coverage of the INDA envelope in the capacity domain. Exploring the impact of the TU (total updating), IU (incremental updating) and HU (hybrid updating) is discussed for 2D model system frameworks, where the highest quality solutions are obtained for the NSPA-DBA analysis, compared to the INDA analysis. In order to determine the required number of the NDA analysis within one INDA analysis, a method is developed based on the solution obtained from the NSPA analysis. On the other hand, in order to predict a solution that is obtained from the INDA analysis of 2D and 3D models of framework buildings with the possibility of considering the response of the system in the capacity domain, but not significantly increasing the time required to process, the Hybrid Incremental Nonlinear Static-Dynamic Analysis (HINSDA) is developed. Higher values of drifts are obtained in a case of application of PGA-IDRmax parameters, than in a case of application of PGA-DR parameters. The least deviation of the HINSDA curve to the INDA curve is obtained using the third UBEPKHS constitutive model, while the maximum deviation is obtained using the first UBEPKHS constitutive model. Research in the field of non-linear response of 3D models of framework buildings is based on the application of the beam finite elements, while at the ends of the beams and columns are applied plastic hinges which enable the development of inelastic deformations. Effects of existence of interstorey plates were modeled using the link elements. Given that in 3D models of framework buildings nonlinear response is considering using the pushover curves for different angles of seismic actions, the pushover surface is obtained by integrating the pushover curves for the NSPA and the INDA (IDA) analysis. The general model of the pushover surface is shown and some specific models of the pushover surfaces are pointed. The typological models of NSPA pushover surfaces are defined as a function of variations in ductility, ductility in the field of stiffening/softening and coefficient of the relation of stiffness in nonlinear and linear domain for one and two main directions. Generally considering, the four groups of pushover surfaces are identified: rotationally polysymmetrice at a base, monosymmetric at a base, bisymmetric at a base and asymmetric at a base. Introducing the ductility area coefficient it is possible to analyze the performance of 3D models of framework buildings taking into account the ductility in all directions or angles of seismic actions. Research has shown that the INDA (IDA) pushover surface has a different shape, compared to the NSPA pushover surface, since the different intensity measure and engineering demand parameter are applied. In order to analyze the performance of 4x6x3, 4x6x5-13, 15x4x4, 15x4x4-6 and 9x6x5-12 3D models of framework buildings, monitoring of the plastic hinges development at incremental stages was conducted, which is presented as isosurfaces in polar coordinates. Also, the implemented curves are discussed in polar coordinates for a drift, the relative value of the total base shear force of building and ductility. Research found that in all models of buildings are realized smaller or something larger maximum global drifts DRmax from global drifts DRIO, for the IO performance level according to the FEMA regulations. The higher ductility class is easier to realize for buildings with a larger number of storeys, and increase in irregularities at a base reduces ductility. Considering the realized NSPA pushover surface in spatial coordinates, for all 3D models of framework buildings, was found that stiffness in the nonlinear domain Kn≈0 is almost horizontal or slightly positive, except in certain cases where with increasing nonlinear deformations stiffness becomes negative Kn<0. For 9x6x5-12 3D model of framework building was realized significantly lower maximum relative value of the total base shear force of building in relation to the relative value of the total base shear force of building for 4x6x3, 4x6x5-13, 15x4x4 and 15x4x4-6 3D models of framework buildings. It is a direct consequence of calculation of the seismic action according to the SRP regulations. In relation to the curve of the relative value of the total base shear force of building (V/W)adeq for maximum global drift DRmax calculated by the NSPA analyses that are circular or nearly circular in shape, curve of the relative spectral acceleration Sa/Sa,y calculated by the IDA analyses are ellipsoidal or more complex forms. In the initial part of research of the relationship of building capacity/seismic demand of 2D and 3D model frameworks the general models of relations for the pushover curves and the demand curves (BR/SD) were defined, which served as a basis for further consideration of target displacements. In the second part of research the Iterative Displacement Coefficient Method (IDCM) was developed, which was used for analyses of the target displacements. Based on the IDCM method and numerical tests conducted on the pushover curves for standardized models of responses and the random response function, it is found that the values of drifts are in very satisfactory agreement according to the IDCM and the NDA analyses. Also, the minimum deviation of the relative value of the total base shear force of building realized by the IDCM method, compared to the solutions obtained by the NDA method at levels of target displacements (V/W)t. In the third part of research the level of seismic demands of 3D models of framework buildings were conducted, and is presented through the target displacement envelope and drifts: for performance levels, mean, median of target displacement and maximum displacement. Relative values of the total base shear force of building for target displacements and maximum global drift are also shown. Based on the defined target displacement envelope a series of coefficients were developed which are used to assess the performance of 3D models of framework buildings. The performances of buildings are analyzed also using the developed global drift surface and interstorey drift surface. In the fourth part, based on the Nonlinear Static Pushover Analysis - Damage Mechanisms-Based Design (NSPA-DMBD) and research on the model of framework system, indicated that even at the initial NSPA analysis unfavorable fracture mechanism was through the ultimate concrete strain. At lower storeys, according to the NSPA-DMBD method, the values of interstorey drifts are reduced, while at the higher storeys are increased thus balancing the response of the structure

Pile integrity testing: Testing and results analysis

U radu su prikazani karakteristični primeri ispitivanja integriteta šipova sa analizom rezultata, pri čemu se metodologija ispitivanja oslanja na postojeće ASTM standarde, ali i na metodologiju ispitivanja prikazanu u naučnom radu "Ispitivanje integriteta i nosivosti šipova: metodologija i klasifikacija", koji je publikovan u ovom časopisu. Ispitivanja šipova sprovedena su primenom licenciranih oprema za test integriteta šipa sa senzorom (SIT) i test integriteta šipa sa sondama (CSL). Ispitivanjima su prikazane korektne i problematične situacije, koje se pojavljuju prilikom analize integriteta šipova. Ukazano je na aspekte primene talasne teorije, ali i na procesiranja signala i numeričke analize. Takođe, posebno je skrenuta pažnja na potrebu izrade plana ispitivanja integriteta šipova kod objekata s velikim brojem šipova.The paper presents typical examples of pile integrity testing and the results analysis, whereby the testing methodology relies on existing ASTM standards, as well as on the testing methodology presented in the scientific paper Pile Integrity and Load Testing: Methodology and Classification, published in this journal. The pile tests were conducted using licensed equipment for Sonic Integrity Test (SIT) and Crosshole Sonic Logging (CSL). The tests have shown the correct and problematic situations that arise when analyzing pile integrity. Some aspects of the wave theory implementation, but also of signal processing and numerical analysis have been indicated. Also, the need to develop a plan for testing the integrity of piles in structures with a large number of piles has been emphasized

Multidisciplinary Approach to the Assessment of Seismic Performances and Rehabilitation of Bridges: Nonlinear Analyses, Probability Theory and Optimization Theory

AbstractThe paper presents a multidisciplinary approach to the assessment of seismic performances based on the Performance-Based Earthquake Engineering (PBEE), taking into account the multi-criteria optimization theory in analyzing the priority methods for bridge rehabilitation/strengthening. One bridge model was subjected to nonlinear static pushover analyses (NSPA), target displacement analyses using the spectrum capacity method (CSM), vulnerability analyses, and reliability analyses, while for a damaged bridge, in addition to be considered using the above methods, was also analyzed using the VIKOR method of multi-criteria optimization. Seismic performances were determined based on monitoring the system's plastification and analyzing the relevant parameters for the level of target displacement, such as target displacement, total shear force, spectral displacement, spectral acceleration, vibration period, damping and ductility. The phases of damage were considered using the probabilistic analysis of vulnerability and reliability: slight, moderate, extensive and complete, as a function of system ductility

HE DEVELOPMENT OF CONTROLLED DAMAGE MECHANISMS-BASED DESIGN METHOD FOR NONLINEAR STATIC PUSHOVER ANALYSIS

Abstract. This paper presents the original method of controlled building damage mechanisms based on Nonlinear Static Pushover Analysis (NSPA-DMBD). The optimal building damage mechanism is determined based on the solution of the Capacity Design Method (CDM), and the response of the building is considered in incremental situations. The development of damage mechanism of a system in such incremental situations is being controlled on the strain level, examining the relationship of current and limit strains in concrete and reinforcement steel. Since the procedure of the system damage mechanism analysis according to the NSPA-DMBD method is being iteratively implemented and designing checked after the strain reaches the limit, for this analysis a term Iterative-Interactive Design (IID) has been introduced. By selecting, monitoring and controlling the optimal damage mechanism of the system and by developed NSPA-DMBD method, damage mechanism of the building is being controlled and the level of resistance to an early collapse is being increased.Key words: damage mechanisms, strains, Capacity Design Method, Nonlinear Static Pushover Analysis, Iterative-Interactive Design

Analiza performansi oštećenih objekata, primenom scenarija povezanih nelinearnih analiza i koeficijenta oštećenja

U radu je razvijena i prikazana metodologija za analizu oštećenja objekata koji su izloženi incidentnom i seizmičkom dejstvu. Procedura se bazira na nelinearnim numeričkim analizama, uvažavajući principe projektovanja konstrukcija prema seizmičkim performansama (PBSD). Matrica krutosti za uticaje vertikalnog dejstva koristi se kao inicijalna matrica krutosti prilikom nelinearne analize kojom se simulira kolaps pojedinačnih stubova prizemlja, formirajući nekoliko mogućih scenarija. Matrica krutosti na kraju analize, kojom se simulira kolaps pojedinačnih stubova, koristi se kao inicijalna matrica krutosti prilikom nelinearne statičke pushover analize (NSPA) za bidirekciono seizmičko dejstvo (X i Y pravac). Analize ciljnog pomeranja sprovedene su prema metodi spektra kapaciteta (CSM). Procena stanja zgrade je sprovedena na osnovu proračunatih globalnih i međuspratnih driftova i razvijenog koeficijenta oštećenja. Razmatranje stanja oštećenja zgrade utvrđeno je integralnim pistupom i preko globalnih i preko međuspratnih driftova, tako da se - u zavisnosti od nivoa pomeranja za koji se driftovi određuju - dobija pouzdaniji odgovor. Primenom koeficijenta oštećenja može se dobiti veoma brz, pouzdan i dovoljno precizan odgovor kada je reč o nivou oštećenja kompletne zgrade u kapacitativnom domenu, od elastičnog, preko nelinearnog, pa sve do stanja kolapsa

Metodologija pripreme i obrade akcelerograma za linearne i nelinearne seizmičke analize konstrukcija

U radu je dat prikaz metodologije za pripremu i obradu akcelerograma koji se koriste za seizmički proračun konstrukcija. Definisani su termini i detaljnije obrazložene procedure koje se sprovode nad akcelerogramima kao što su: selekcija, formatiranje, konvertovanje, skaliranje, kalkulacija, procesiranje, kompatibilizacija, normalizacija, filtriranje, generisanje i transformacija. Ove procedure se izvršavaju u vremenskom, frekventnom, FFT frekventnom, FFT frekventno- vremenskom i kapacitativnom domenu. Jasno su postavljene granice između procedura definisanjem termina za svaku po na osob, tako da su pojedine procedure međusobno autonomne, ali sa druge strane matematičke formulacije i fizikalnost problema određenih procedura se preklapaju ili su komplementarne