Performance evaluation of reinforced concrete buildings with softer ground floors

Određivanje seizmičkog ponašanja je važan zadatak seizmičke analize prema zahtijevanom ponašanju konstrukcije. Podudaranje rezultata dobivenih prema različitim normama od velike je važnosti u postupku seizmičkog ocjenjivanja konstrukcija. U radu je opisana nelinearna analiza ponašanja triju armiranobetonskih zgrada s mekim prizemljem primjenom metode konačnih elemenata prema normama FEMA-356 i FEMA-440, te turskim potresnim normama iz 2007. Za svaku konstrukciju je prikazano stanje oštećenosti, modalna svojstva, međukatni pomaci i globalne razine ponašanja te su dani odgovarajući prijedlozi.Determination of seismic performance is a significant task in the performance-based seismic analysis of structures. The consistency between analysis results obtained according to various codes is highly significant for seismic evaluation of structures. Non-linear performance of three reinforced concrete buildings having a soft storey irregularity is studied based on the finite elements analysis according to FEMA-356, FEMA-440, and Turkish Earthquake Code - 2007. Damage situations, modal properties, storey drift ratios, and global performance levels are comparatively presented for each structure, and appropriate suggestions are given

FSI ANALYSIS OF SUBMARINE OUTFALL

In the scope of this study, main pipe of the diffuser, risers, ports, internal and external environments forming the discharge system which is used in application are modelled by Finite Elements Analysis (FEA) program to obtain discharge and structural behaviour. The last two spans of the system (20 m) and four ports on these spans are investigated. While the diameter and geometry of the risers and ports remain constant, the diffuser pipe is modelled in three different ways. These are constant sectioned (Model 1), contracting with sharp edge entrance sectioned (Model 2) and gradually contracting sectioned (Model 3) respectively. Among them, only Model 1 is treated as Single Degree of Freedom (SDOF) system and it is simulated by FEA to verify FEA solver in the first place. After structural suitability is confirmed, rest of the models are analysed to determine reaction forces and stresses. The discharge is performed as unsteady external flow as well as steady external flow assumption which is widely used in external flow model in the literature. The discharge analyses are performed in two different ways to verify FEA program. Iterative method is accompanying to FEA program. As a result of this study, proper model for structural and discharge behaviour and external flow effects on discharge velocities are obtained

Performance assessment and strengthening proposal of an existing building

Kao odgovor na pojavu snažnih potresa u seizmičkim se propisima provode revizije metoda za projektiranje građevina otpornih na seizmička djelovanja. Poznato je da su mnoge postojeće građevine smještene u seizmički aktivnim područjima diljem svijeta. Potresi uzrokuju znatna oštećenosti elemenata konstrukcije, te djelomično ili potpuno rušenje građevina. Zbog toga se, u okviru različitih seizmičkih propisa, diljem svijeta provodi ocjenjivanje seizmičkog ponašanja i postupaka pojačanja postojećih građevina. Zahvaljujući razvoju računalne tehnologije, nelinearne metode danas nude sve pouzdanije postupke za određivanje ponašanja građevina. U ovom se radu najprije provodi nelinearna analiza ponašanja postojeće tipične armiranobetonske građevine srednje visine prema turskom seizmičkom propisu – 2018 te prema američkoj normi ASCE. Nakon ocjene oštećenosti konstrukcijskih elementa, građevina je pojačana čeličnim razuporama te je zatim analiza ponovljena. U postupku je korišten računalni program za analizu konačnih elemenata SAP2000. Koeficijenti oštećenosti konstrukcijskih elemenata te modalna svojstva i međukatni pomaci, određeni su i uspoređeni prema oba spomenuta propisa, te je zaključeno da predložena metoda pojačanja može biti prihvatljivo alternativno rješenje za takve građevine.Due to major-scale earthquakes, revisions of earthquake resistant structural design methods have periodically been made in seismic codes. It is known that many existing buildings are located in active seismic zones in all parts of the world. Severe damage to structural members, with partial or total collapse of buildings, has been observed in past earthquakes. Consequently, the evaluation of seismic performance and strengthening techniques of the existing buildings according to various seismic codes has become a global issue in structural engineering. With the development of computer technology, non-linear methods have been offering increasingly reliable evaluation procedures in the performance-based assessment of buildings. In this study, non-linear performance analysis of an existing typical mid-rise reinforced concrete building is first performed according to Turkish Building Earthquake Code-2018 and American Standard, ASCE. After evaluation of damage to structural members, the building is strengthened by steel braces and the analysis is performed once again. The SAP2000 finite elements analysis software is utilized in the solutions. Damage ratios of structural members as well as modal properties and storey drift ratios are determined and compared according to both codes, and it is concluded that the proposed strengthening method could be a significant alternative in such buildings

Numerical modelling of floating structure with coupled Eulerian–Lagrangian technique

Plutajuće konstrukcije složeni su sustavi sastavljeni od platforme (pontona), priveznih elemenata i konopa. U ovom radu istražuje se ponašanje pontona koji se koristi kao plutajuća konstrukcija i četiri privezna elementa pod utjecajem različitih uvjeta opterećenja valovima. Kombinirana analiza se numerički provodi između kretanja pontona, konopa za privez i morskog okoliša. Konopi za privez modelirani su kao mrežni elementi, a ponton je modeliran kao kruto tijelo sa šest stupnjeva slobode kretanja. Stanje opterećenja valovima predstavljeno je pomoću dva različita valna spektra. Prvi se spektar (slučaj I) generira iz jednog sinusoidnog vala korištenjem Jonswapovog spektra, drugi (slučaj II) se generira iz superponiranog višesinusoidnog vala. Vremenski promjenjivo kretanje pontona i napetosti konopa za privez određeni su numeričkom analizom za slučaj I i slučaj II. Na temelju rezultata oba slučaja određene su kritične vrijednosti. U numeričkim rješenjima primijenjena je dvosmjerna analiza interakcije fluid-konstrukcija (FSI). U analizi se provodi potpuno nelinearna simulacija slobodne površine pomoću tehnike spregnute Euler-Lagrangeove formulacije. Uz to, numerički rezultati uspoređeni su s rezultatima dobivenim analitičkim rješavanjem kota slobodnih površina.Floating structures are complex systems composed of superstructure, floating-mooring components, and anchors. In this study, the behaviours of a pontoon, which is used as a floating structure, and four mooring elements under different wave loading conditions were investigated. A numerical analysis of the coupled motions of the pontoon, mooring lines, and marine environment was performed. While the mooring lines were modelled as wire elements, the pontoon was modelled as a rigid body with six degrees of freedom. Wave loading conditions were represented using two different wave spectra. The first spectrum (Case I) was generated based on a single sinusoidal wave utilising the JONSWAP spectrum, whereas the second one (Case II) was generated based a superimposed multi-sinusoidal wave. Time-varying motions of the pontoon and tensions of the mooring lines were determined based on the numerical analyses for Cases I and II. Critical values were determined using the results of both cases. The numerical solutions were based on bidirectional fluid–structure interaction (FSI) analysis. A fully non-linear free surface simulation was performed using the coupled Eulerian–Lagrangian (CEL) technique. Furthermore, numerical results were compared with the results obtained from analytical solutions of free surface elevations

Non-linear analysis of reinforced concrete slabs under impact effect

Većina postojećih konstrukcija projektirana je tako da se odupre samo statičkim opterećenjima. Brojni istraživači ukazuju da u projektnoj fazi treba razmotriti i iznenadna opterećenja. Površine mnogih građevina izvedene su ab pločama koje su pod utjecajem iznenadnih opterećenja poput iznenadnih padova različitih elemenata, odrona kamenja ili vojnih djelovanja. Nelinearna analiza ab ploča u radu je provedena primjenom računalnog programa ABAQUS. Određeni su i detaljno analizirani parametri udara kao što su ubrzanja, brzine, pomaci, udarne sile i energetski kapaciteti za svaku ploču.Most of the existing structures are designed to resist static loads only. Various researchers indicate that sudden loads affecting structural members should also be considered in the design phase. Surfaces of many structures are covered with concrete slab members that are under the effect of sudden loads such as accidental drops, rock falls, or military attacks. A non-linear analysis of RC slabs is performed in this study using the Abaqus software. Impact parameters such as accelerations, velocities, displacements, impact forces, and energy capacities, are determined for each slab

Analyses of damaged effects on jacket type offshore platform

U ovom je istraživanju izvanobalna platforma, koja je podvrgnuta dinamičkom opterećenju za različite slučajeve oštećenja, modelirana analizom interakcije fluida i konstrukcije (engl. fluid-structure interaction - FSI). Razmatrani su različiti modeli oštećenja u slučaju kada je jedan stup bio oštećen, a Youngov modul oštećenog elementa smanjen je s četiri različita omjera intenziteta. Osim pet oštećenih konstrukcija, neoštećena je konstrukcija modelirana prema dva različita uvjeta razmaka stupova. Na taj su način oštećeni modeli uspoređivani i međusobno i s neoštećenim modelima. U ovom su radu modeli ispitivani primjenom numeričkog FSI postupka. Numerički postupak potvrđen je poluanalitičkim modeliranjem. U ovoj je fazi jednadžba gibanja jednog od konstrukcijskih modela riješena poluanalitičkom metodom temeljenom na sustavu s više stupnjeva slobode. Osim toga, numerički model okoline potvrđen je primjenom poluanalitičkog rješenja jednadžbe gibanja slobodne površine i krivulje valna brzina-valna sila. Za modeliranje konstrukcija i njihove okoline upotrijebljen je program Abaqus, utemeljen na metodi konačnih elemenata. Konstrukcije su modelirane primjenom Lagrangeova postupka, fluidno okruženje je modelirano primjenom Eulerova postupka. Modelirani su i uvjeti razmaka stupova i različiti omjeri intenziteta, te je zabilježen najnegativniji tip oštećenja.In this paper, an offshore platform subjected to dynamic loading for different damage cases was modelled via fluid-structure interaction (FSI) analysis. Different damage models were considered in the case where one leg was broken, and the Young’s modulus of the damaged member was reduced with four different severity ratios. In addition to the five damaged structures, the undamaged structure was modelled according to two different leg spacing conditions. Thus, the damaged models were compared among themselves as well as with undamaged models. In this study, models were investigated using a numerical FSI technique. The numerical technique was verified using semi-analytical modelling. At this stage, the equation of motion of one of the structural models was solved using a semi-analytical method based on a multi-degree-of-freedom system. In addition, the numerical environment model was verified using a semi-analytical solution of the free-surface motion equation and the wave velocity-wave force curve. An Abaqus finite-element analysis program was used to model the structures and their surroundings. While the structures were modelled using the Lagrangian technique, the fluid surroundings were modelled using the Eulerian technique. Both the conditions of leg spacing and different severity ratios were modelled, and the most negative damage type was revealed

Experimental study on hollow section joints under impact loading

U ovom se radu analizira udarna otpornost čeličnih profila s četiri različite vrste priključaka. Za te je potrebe razvijeno ispitivanje uređajem s padajućim teretom. Ispitivanja otpornosti na udarno opterećenje provedena su za dvije razine energije. Izrađeni su i prikazani dijagrami ubrzanja i vremena, pomaka i vremena, udarnog opterećenja u vremenu te odnosa udarnog opterećenja i pomaka. Utvrđeno je da na ponašanje uzoraka utječe vrsta priključka i nanesena udarna energija. Do sloma oštećenjem dolazi ranije kod niže krutosti uzoraka te pri nanošenju više razine udarne energije.Steel sections with four different joint types, subjected to sudden impact, are investigated in this study. A drop weight test setup was developed for this purpose. Impact tests were performed for two different energy levels. Acceleration-time, displacement-time, impact load-time, and impact load-displacement graphs were developed and presented. It was established that the behaviour of test specimens is affected by joint types and impact energy applied. Failure damage situation occurs earlier when rigidity of specimens decreases and when higher level of impact energy is applied

Experimental and Numerical Investigation of Steel Sections under Impact Effect

U radu se analizira eksperimentalno i numeričko ponašanje čeličnih ispitnih uzoraka s različitim vrstama priključaka. U tu svrhu korišten je uređaj s padajućim utegom. Kako bi se primijenila ista količina udarne energije na ispitne uzorke, masa i visina udarnog utega uzete su kao konstante. Eksperimentalnim istraživanjem dobivene su vrijednosti ubrzanja, pomaka, udarnog opterećenja, broja ispusta i trajanja pada. Tijekom ispitivanja pratilo se i širenje oštećenja na ispitnim uzorcima. Provedena je i numerička analiza ponašanja uzoraka uslijed udarnog opterećenja pomoću računalnog programa Abaqus te je napravljena usporedba rezultata.Experimental and numerical behaviour of steel test specimens with various types of joints is investigated in this study. A drop weight test setup with necessary test equipment is used for this purpose. The mass and drop height of the hammer is taken to be constant so that the same impact energy can be applied on test specimens. The acceleration, displacement, impact load, drop numbers and drop durations, are obtained through experimental study. In addition, development of damage to test specimens is observed during tests. Numerical analyses of behaviour of test specimens under impact load are also conducted to verify test results using the Abaqus software, and a comparison of results is made

Comparative analysis of tripod offshore structure

Pomorske se konstrukcije u današnje vrijeme koriste za razne namjene. U ovom se radu analizira odobalna građevina tronožnog tipa ukupne visine šezdeset metara. Uz opterećenja vezana za samo funkcioniranje, konstrukcija građevine podvrgnuta je i opterećenjima uslijed djelovanja vjetra i valova. Za proračun sile vjetra korišten je profil brzine prema europskoj normi, a za određivanje sile valova Airyeva brzina valova. Model je izrađen pomoću programa za analizu konačnih elemenata, a sastoji se od fluidnog i konstrukcijskog dijela. Interakcija između tih dijelova postignuta je kombiniranim Euler-Lagrangeovim postupkom (CEL).Marine structures are nowadays used in a variety of ways. The analysis of a tripod-type offshore structure sixty m in total height is performed in this study. In addition to operation-related loads, the structure is also under the effect of wind and wave loads. While the Eurocode velocity profile is used to calculate wind forces, the Airy wave velocity profile is utilized to determine wave forces. The model is created by a finite elements analysis program, and is composed of fluid and structural parts. The interaction of the parts is ensured by Coupled Eulerian Lagrangian (CEL) technique

Experimental Study on Pipe Sections against Impact Loading

Pipelines are significant structural systems that transfer necessary materials from one place to another. They are under the effect of static and dynamic loads during their service lives. Investigations have become important to determine the effects of sudden dynamic loads with technological developments. Researchers study the mechanical properties of different materials and structural members under dynamic effects such as earthquake, wind, blast, rock falling and vehicle crushing. For this purpose, different test setups have been developed to investigate the behaviour of test members. In this study, galvanized and water filled galvanized pipe sections having three different diameter values are produced in a laboratory to perform tests under impact loading. The behaviour of the pipes is determined by free falling test apparatus. In addition, measurement devices as accelerometer, dynamic force sensor, lvdt, and data logger are used in the experimental program. So, acceleration, impact force, and displacement values are obtained during the tests. Besides, damage developments of the pipes are also observed to determine the impact resistances of test members. The results are compared to each other and it is stated that while acceleration and impact force values decrease, displacement values increase as the test members approach to collapse damage situation