Comparative nonlinear analysis of a RC 2D frame soil-pile interaction

U radu je sprovedena komparativna nelinearna statička (NSA) i nelinearna dinamička analiza (NDA) seizmičkog ponašanja rama kao dela skeletne konstrukcije AB zgrade fundirane na šipovima. Da bi se dobila realnija slika ponašanja ramovske konstrukcije u analizu je uključena interakcija konstrukcija - temelj - tlo. Pri tome u proračunski model je uključena i linearno-nelinearna dinamička interakcija šip-tlo korišćenjem link elemenata. Konstrukcija temelja sastoji se od bušenih šipove prečnika 60cm. Tlo je modelovano sa više (linijskih) plastičnih veznih elemenata, kao p-y krivama, sa obe strane šipa, za potopljen krut pesak, i uz pretpostavku da p-y krive (eksperimentalno određene nelinearne krive zavisnosti: pomeranje/pritisak, u tlu po dubini šipa) primaju samo pritisak. Analizom je ukazano na probleme, koje prate izdvajanje 2D ramova kao reprezenta regularne prostorne 3D konstrukcije. Proučen je uticaj pojave i lokacije pojedinih plastičnih zglobova na seizmičke performanse analiziranog konstruktivnog sistema, i analizirana relativna spratna pomeranja (driftovi). Zaključeno je da se analizom 2D rama u interakciji sa temeljom i tlom, mogu dobiti dovoljno tačni rezultati ponašanja i ocene seizmičkih performansi skeletne AB višespratne zgrade. To je značajno jer uvođenje prostorne konstrukcije u ovakve analize je veoma kompleksno i zahtevno.Comparative non-linear static (NSA) and non-linear dynamic analyses (NDA) of 2D frames (as parts of skeletal 3D structures) of RC buildings founded on piles are presented in this paper. In order to produce a more realistic presentation of behaviour of a frame structure, the analysis involves a structure-foundation-soil interaction. Also, the model involves a linear-non-linear dynamic pile-soil interaction, using link elements. The foundation consists of drilled piles having 60 cm in diameter. The soil is modelled using Multi-linear plastic link elements, as well as with p-y curves, on both sides of the pile, assuming that p-y curves transfer only compression (p-y curves are experimentally determined non-linear relationships of displacement/pressure in soil, along the depth of a pile). The analysis shows the problems which accompany extraction of a 2D frame, as a representative of a regular 3D space frame. The impact of onset and location of individual plastic hinges on seismic performances of the analyzed structural system are investigated, and relative floor drifts are analyzed. It was concluded that the analysis of 2D frame, in the interaction with the foundation and soil, may provide sufficiently accurate results of behaviour and assessments of seismic performances of skeletal RC multi-storey building. It is important, because introduction of a spatial structure in such analyses is very complex and challenging

Multidisciplinary approach to the assessment of seismic performances and rehabilitation of bridges: nonlinear analyses, probability theory and optimization theory

The 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

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)

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

Deciding the order of interventions on the structure of reinforced concrete (RC) bridges for earthquake conditions

A multitude of existing bridges fail to meet the criteria of seismic resistance, as designed according to inadequate regulations, which eventually led to the reduction in their resistance. This practice requires interventions (rehabilitation or strengthening) conducted on their structure, which in turn requires developing methods of assessment of seismic performances of existing reinforced concrete (RC) girder bridges. Due to budget constrains it is impossible to strengthen all the bridges, so that a list of priorities is necessary to be drawn. The rank of a specific bridge in this list is stated by the importance of the road, age of the bridge, technical regulations according to which the bridge was designed and the condition of vital support elements. Ranking requires conducting multi-criteria optimization. This paper is focused on overpass, which is used to demonstrate the developed methodology

Seismic performances of the structures at variation of artificial accelerograms

U radu je proučen utjecaj promjene parametara umjetnih akcelerograma na seizmičke karakteristike konstrukcija. Pri tome su analizirani seizmički odziv i seizmičko oštećenje. Nelinearni odziv sustava je određivan inkrementalnom dinamičkom analizom (IDA), dok je analiza oštećenja sustava razmatrana na osnovi indeksa oštećenja. Istraživanjem je utvrđeno da je za kreiranje umjetnih akcelerograma potreban znatan broj ciklusa kojim se poboljšava usklađenost spektra odziva zapisa u odnosu na spektar odziva prema EN 1998-1, a što je mjereno na osnovi odstupanja krivulja spektralnih ubrzanja u funkciji duktilnosti sustava.The impact of changes to artificial-accelerogram parameters on the seismic performance of structures is examined in this paper. The seismic response and seismic damage are analysed in this respect. Nonlinear response of the system is determined by the incremental dynamic analysis (IDA), while the damage analysis of the system is considered using the damage index. The study has shown that generation of artificial accelerograms requires a considerable number of cycles, which improves the correspondence between the range of recorded response spectra and the range of the response spectra according to EN 1998-1, which is measured based on deviation of spectral acceleration curves as a function of the ductility of the system

The strut – and – tie model for analysis of some RC foundation design

Technical beam theory is not applicable for the analysis of non-standard reinforced concrete structural elements (D-region), especially when members are exposed to significant shear stress and/or torsion. In this case strut – and – tie models (STM), which give reliable results, are used. In this paper we present a review of theoretical bases and application of STM for design. The focuse is also on the detailing of pile caps for diferent numbers of piles (2, 3 and 4) in the foundation. Some international recommendations are also commented (ACI, EN 1992, etc.).Tehnička teorija savijanja nije primenljiva kod analize nestandardnih armiranobetonskih (AB) nosača, naročito kada su izloženi znatnim smičućim naponima i/ili torziji. U takvim slučajevima se koriste uprošćene analize, koje daju dovoljno tačne rezultate, za praktične probleme. Rad je usmeren na primenu štapnih modela (pritisnuti kosnici i zatege) kod analize i oblikovanja detalja temeljnih kapa („jastuka“) kod fundiranja na šipovima. Pri tome korišćene su i komentarisane neke međunarodne preporuke (ACI, EN 1992, i dr.).ЗБОРНИК РАДОВА 6. МЕЂУНАРОДНЕ КОНФЕРЕНЦИЈЕ САВРЕМЕНА ДОСТИГНУЋА У ГРАЂЕВИНАРСТВУ 2018 ГРАЂЕВИНСКИ ФАКУЛТЕТ СУБОТИЦА Проф. др Мирослав Т. БЕШЕВИЋ, декан Проф. др Илија М. МИЛИЧИЋ Доц. др Огњен ГАБРИЋ UDK: 624.072.2.012.4

Developing a methodology for the integrated numerical evaluation and performance assessment of soil-pile-pier

In the paper is developed a discrete numerical solid pile model with a discontinuity and defects. Model included performance-based seismic evaluation of the soil-pile-bridge pier interaction. The pile discontinuity and defects are modelled by reducing the specific finite elements and elastic modulus of concrete. The wave-propagation response of the pile was analyzed based on a step-by-step numerical integration using the Hilber-Hughes-Taylor (HHT) method in time domain (THA). The response analysis is performed with an integration of individual reflectograms into a reflectogram surface, which is generated in a 3D cylindrical coordinate system. Non-linear response of the system is considered using the incremental-iterative Newton-Raphson`s method, while the stability analysis is performed according to the modified geometrical nonlinearity analysis of stability. Determination of critical load and effective length of the pile are performed based on numerical solution and using regression analysis of the power function. The procedure of the soil-pile-bridge pier performance evaluation is based on the incremental nonlinear dynamic analysis (INDA). The system's input signal is treated through the generated artificial accelerograms, which were subsequently processed by soil layers and for the bedrock. Fragility curves were constructed based on solutions of the regression analysis and the probability theory of log-normal distribution, while the generation of reliability curves is based on a solution of vulnerability

Fragility and robustness analysis of a multistorey RC building

U radu je analizirana robusnost armiranobetonske (AB) peteroetažne zgrade (okvir ukrućen zidovima). Konstrukcija visoke klase duktilnosti dimenzionirana je u skladu s nizom konstrukcijskih norma Eurokod. Analiziran je odziv konstrukcije za osam scenarija gubitka pojedinih vertikalnih elementa u prizemlju. Za analizu robusnosti primijenjene su metoda nelinearne statičke (NSA) i dinamičke analize (NDA). Statističkom obradom konstruirane su krivulje oštetljivosti zgrade. Uspoređene su vrijednosti dobivene primjenom NSA i NDA, granična stanja oštećenja sistema i krivulje oštetljivosti. Proučen je i utjecaj položaja uklonjenoga elementa na robusnost.The robustness of a reinforced concrete (RC) five-storey building (frame system stiffened by walls) is analysed in the paper. A high ductility class structure is designed in accordance with structural Eurocodes. The response of the structure to eight different scenarios of the ground floor vertical element loss is analysed. Nonlinear Static Analysis (NSA) and Nonlinear Dynamic Analysis (NDA) methods are used for the robustness analysis. Fragility curves of the building are derived from statistical analysis of these results. The values obtained through NSA and NDA, damage limit states of the system, and fragility curves, are compared. The influence of the position of the removed element on robustness of the structure is also analysed

Effects of selection and scaling methods used for ground motion data on determination of seismic response of RC bridge

In this paper two different methods of selection and scaling ground motion data were investigated in order to examine their effect on accuracy predicting seismic response of RC bridge. First method used is one proposed in EN 1998-2 and second method is scaling of earthquakes based on calculated conditional mean spectrum (CSM) related known parameters of earthquake scenario for certain location. For both methods certain limitations upon scaling factor were implemented in order to examine its effect on accuracy. Totally 4 sets consisted of 7 records were selected, and average seismic response were obtained from nonlinear dynamic analysis. Responses were compared to calculated real response of bridge, so called point of comparison. Conclusions were made about investigated methods accuracy and effect on imposed limitation of scaling factor on realistic prediction of seismic bridge response