{"title":"Damage detection in steel fiber reinforced concrete using resonant method","authors":"N. T. Malic, N. Bede, I. Kožar","doi":"10.5592/CO/YODA.2019.2.4","DOIUrl":"https://doi.org/10.5592/CO/YODA.2019.2.4","url":null,"abstract":"Main aim of this work was to experimentally investigate steel fiber distribution in concrete, i.e. fiber segregation and nonuniform distribution, as well as possible internal cracks, with resonant frequency method (RFM). The RFM is based on determination of resonant frequencies of vibration on specimens excited by impact hammer, which is basis for determination of dynamic modulus of elasticity of FRC. Based on the reduction of dynamic modulus of elasticity and change of frequency response curve some conclusions about presence of local damage or defect are made. These conclusions are verified with x-ray scans of FRC prisms. Ključne riječi: steel fiber reinforced concrete, resonant frequency, impulse excitation method, dynamic modulus of elasticity Detekcija oštećenja u mikroarmiranom betonu primjenom rezonantne metode Sažetak Cilj je rada primjenom metode rezonantne frekvencije (MRF) eksperimentalno proučiti raspored čeličnih vlakana u betonu, odnosno defekte nastale ugradnjom, kao što su segregacija i nehomogena raspodjela vlakana. Istražena je i mogućnost detekcije unutarnjih pukotina. MRF se zasniva na određivanju rezonantnih frekvencija uzoraka pobuđenih na vibracije udarnim čekićem, iz kojih se dalje određuje dinamički modul elastičnosti. Na osnovi redukcije dinamičkog modula elastičnosti i promjene oblika frekvencijske krivulje odgovora doneseni su zaključci o prisutnosti lokalnih oštećenja. Zaključci su potkrijepljeni rendgenskim slikama uzoraka.","PeriodicalId":101599,"journal":{"name":"Numerički postupci. Zbornik radova mini - simpozija","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120997507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Effect of dynamic loading on concrete properties","authors":"N. Bede, J. Ožbolt","doi":"10.5592/CO/YODA.2019.2.5","DOIUrl":"https://doi.org/10.5592/CO/YODA.2019.2.5","url":null,"abstract":"Concrete is very strain rate sensitive material, especially in tension. In this work the effect of dynamic loading on concrete properties in terms of rate dependent failure mode, resistance, tensile strength and fracture energy will be presented. Through own experiments and numerical modeling of L-specimen it is shown that inertia effects are responsible for progressive increase of resistance and rate dependent failure mode. Numerical results and their comparison with experiments show that the true fracture energy and tensile strength increases approximately linear in semi-log scale with strain rate and that approximately follow rate dependent constitutive law used in the computation.","PeriodicalId":101599,"journal":{"name":"Numerički postupci. Zbornik radova mini - simpozija","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125166349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Fragility curves of reinforced concrete frame without earthquake resistance design","authors":"M. Hadzima-Nyarko, G. Pavić, Dijana Nikić","doi":"10.5592/CO/YODA.2019.4.1","DOIUrl":"https://doi.org/10.5592/CO/YODA.2019.4.1","url":null,"abstract":"Although newer buildings are designed in accordance with the requirements of HRN EN 1998-1:2011 for the design of earthquake resistant buildings, there are still a significant number of older buildings built without following any standards. The study carried out in this paper is based on the assessment of earthquake vulnerability of an elementary school building in Osijek designed in the 1970’s, with a bearing system which is reinforced concrete frame. For the assessment of the earthquake vulnerability, “step by step” dynamic analysis was performed on the numerical model of the building a reinforced concrete frame with low ductility.","PeriodicalId":101599,"journal":{"name":"Numerički postupci. Zbornik radova mini - simpozija","volume":"40 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133073828","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}