Experimental Research and FE Model of a Bolted Steel-CLT Composite Connection

Steel-timber composite structures have numerous advantages compared to steel only and timber only structures. One of the most important parts of a composite structure is the composite connection. Object of this research was a steel-CLT composite connection consisting of a steel profile, a cross-laminated timber (CLT) panel and a bolt with nut and washer. Aim of the research was to develop an efficient finite element (FE) model of a bolted steel-CLT composite connection and to validate it experimentally. The research process consisted of several steps: experimental testing of the considered connection using asymmetrical push-out test, numerical modelling and analysis of the connection using Finite Element Method (FEM), validation of the numerical model using experimental results, and parametric study of the proposed numerical model. For numerical analysis, an innovative method for timber modelling has been proposed. The comparison between the experimental and numerical research results demonstrated that the proposed numerical model was convenient for practical application in structure analyses. The parametric study showed that, in some cases, atypical failure modes of the connection occurred. Based on registered behavior, a recommendation is given to calculate the load capacity of the connection integrally, taking into account both the primary (Johansen’s) and the secondary (rope effect) part of the connection strength, instead partially, as proposed by EN standards

Application of industrial by-products as mineral admixtures for self-compacting concrete

Upotreba otpadnih materijala kao mineralnih dodataka samozbijajućem betonu može pridonijeti rješavanju problema njihovog odlaganja, ali je potrebno utvrditi njihovu djelotvornost. Ispitan utjecaj elektrofiltarskog pepela, mljevenih otpadnih opekarskih elemenata – crjepova, flotacijske jalovine i silicijske prašine na konzistenciju betona i njihove tlačne čvrstoće, vlačnu čvrstoću pri savijanju i vlačnu čvrstoću pri cijepanju. Dobiveni rezultati ispitivanja mješavina samozbijajućeg betona su uspoređeni s mješavinom konvencionalnog betona.Although the use of waste materials as mineral admixtures for self-compacting concrete can contribute to solving the problem of their disposal, the effect of such use should be further explored. The influence of fly ash, powdered waste brick elements - roof tiles, flotation tailing and silica fume, on the consistency, compressive strength, bending tensile strength, and tensile splitting strength of concrete, is studied. Self-compacting concrete mixtures test results are compared to a common concrete mixture

Macrophages, the main marker in biocompatibility evaluation of new hydrogels after subcutaneous implantation in rats

Biocompatibility of materials is one of the most important conditions for their successful application in tissue regeneration and repair. Cell-surface interactions stimulate adhesion and activation of macrophages whose acquaintance can assist in designing novel biomaterials that promote favorable macrophage–biomaterial surface interactions for clinical application. This study is designed to determine the distribution and number of macrophages as a means of biocompatibility evaluation of two newly synthesized materials [silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/ Gr) nanocomposite hydrogels] in vivo, with approval of the Ethics Committee of the Faculty of Veterinary Medicine, University of Belgrade. Macrophages and giant cells were analyzed in tissue sections stained by routine H&E and im munohistochemical methods (CD68+ ). Statistical relevance was determined in the statistical software package SPSS 20 (IBM corp). The results of the study in terms of the number of giant cells localized around the implant showed that their number was highest on the seventh postoperative day (p.o.d.) in the group implanted with Ag/PVA hydrogels, and on the 30th p.o.d. in the group implanted with Ag/PVA/Gr. Interestingly, the number of macrophages measured in the capsular and pericapsular space was highest in the group implanted with the commercial Suprasorb© material. The increased mac rophage number, registered around the Ag/PVA/Gr implant on 60th p.o.d. indicates that the addition of graphene can, in a specific way, modulate different biological responses of tissues in the process of wound healing, regeneration, and integration

PRORAČUN VEZE DRVO-BETON IZVEDENE EKSEROM PREMA EVROKODU I PRIMENOM MKE

During rehabilitation of residential buildings built in the first half of the 20th century, it is necessary to strengthen timber floors so they can fulfill the requirements of strength and serviceability according to contemporary regulations. Floors made of monolithic timber girders can be most easily strengthened by forming a composite structure with a reinforced concrete slab supported on a trapezoidal steel sheeting, with appropriate connections between different materials. In the paper, the procedure of calculation of nails used as shear connectors for composite action of timber and concrete is presented. The procedure is based on equations given in Eurocode 5, and besides that, a calculation applying FEM has been conducted, and a comparison of results is presented.Prilikom sanacije stambenih objekata građenih u toku prve polovine prošlog veka, potrebno je ojačati drvene međuspratne konstrukcije kako bi ispunile zahteve nosivosti i upotrebljivosti prema savremenim propisima. Međuspratne konstrukcije od monolitnih drvenih nosača se najjednostavnije ojačavaju sprezanjem sa armirano-betonskom pločom koja se izrađuje na trapeznom čeličnom limu, a spajanje se vrši odgovarajućim spojnim sredstvima. U radu je prikazan postupak proračuna eksera koji se koristi kao moždanik za sprezanje drveta i betona. Postupak je zasnovan na jednačinama datim u Evrokodu 5, a pored toga je sproveden i proračun primenom MKE i dato je poređenje rezultata

Macrophages, the main marker in biocompatibility evaluation of new hydrogels after subcutaneous implantation in rats

Biocompatibility of materials is one of the most important conditions for their successful application in tissue regeneration and repair. Cell-surface interactions stimulate adhesion and activation of macrophages whose acquaintance can assist in designing novel biomaterials that promote favorable macrophage-biomaterial surface interactions for clinical application. This study is designed to determine the distribution and number of macrophages as a means of biocompatibility evaluation of two newly synthesized materials [silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) nanocomposite hydrogels] in vivo, with approval of the Ethics Committee of the Faculty of Veterinary Medicine, University of Belgrade. Macrophages and giant cells were analyzed in tissue sections stained by routine H&E and immunohistochemical methods (CD68(+)). Statistical relevance was determined in the statistical software package SPSS 20 (IBM corp). The results of the study in terms of the number of giant cells localized around the implant showed that their number was highest on the seventh postoperative day (p.o.d.) in the group implanted with Ag/PVA hydrogels, and on the 30th p.o.d. in the group implanted with Ag/PVA/Gr. Interestingly, the number of macrophages measured in the capsular and pericapsular space was highest in the group implanted with the commercial Suprasor

Procena regenerativnih procesa mekih tkiva nakon supkutane implantacije srebro / poli (vinil alkohol) i novog srebro / poli (vinil alkohol) / grafenskog hidrogela na animalnom modelu

A newly produced biomaterial is necessarily subject of standards, which are performed in vivo on animal models. For the evaluation of soft tissue regenerative possibilities after subcutaneous implantation of biomaterials – silver/poly(vinyl alcohol) (Ag/PVA) and novel silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) provided for clinical use, sixteen rats were used, according to the instructions of international standards, ISO 10993-6, 2007. Histological sections were observed 7, 15, 30 and 60 days after grafting. These hydrogels were produced by in situ electrochemical synthesis of silver nanoparticles in the polymer matrices, which enabled obtaining completely safe and biocompatible materials, free from any additional toxic chemical reducing agents. Surgical implantation of hydrogels was done according to the permission of the Ethical Committee of the Faculty of Veterinary Medicine, University of Belgrade. Immunohistochemical (IHC) studies included the assessment of smooth muscle expression actin in blood vessels (α-SMA), the expression of laminin and type I and type III collagen in the skin structures, and, the determination of cell proliferation marker expression (Ki-67) keratinocytes. The results were assessed in a semiquantitative manner. The data were analyzed in the statistical software package IBM SPSS 20. The conclusions indicated that Ag/PVA/Gr might be used as wound dressings to enhance the tissueBilo koji novoproizvedeni biomaterijal nužno podleže standardima, po čijim se protokolima sprovode in vivo istraživanja na životinjskim modelima. Za procenu mogućnosti regeneracije mekog tkiva nakon potkožne implantacije biomaterijala - srebra/poli(vinil alkohola) (Ag/PVA) i novog materijala srebra/poli(vinil alkohola)/grafena (Ag/PVA/ Gr) predviđenog za kliničku upotrebu, šesnaest pacova je korišćeno, po uputstvima međunarodnog standarda, ISO 10993-6 2007. Histološki uzorci su sakupljeni 7, 15, 30 i 60 dana nakon implantacije. Ovi hidrogelovi su proizvedeni in situ elektrohemijskom sintezom nanočestica srebra u polimernim matricama, što je omogućilo dobijanje potpuno sigurnih i biokompatibilnih materijala, bez ikakvih dodatnih toksičnih hemijskih sredstava za redukciju. Hirurška implantacija hidrogela urađena je prema dozvoli Etičkog komiteta Fakulteta veterinarske medicine Univerziteta u Beogradu. Imunohistohemijske (IHC) studije uključivale su procenu ekspresije aktina glatkih mišića u krvnim sudovima (α-SMA), ekspresiju laminina i kolagena tipa I i III u strukturama kože i određivanje ekspresije markera proliferacije (Ki-67) keratinocita. Rezultati su procenjeni semikvantitativnom analizom. Podaci su analizirani u statističkom softverskom paketu IBM SPSS 20. Zaključci su ukazali da se Ag/PVA/Gr može koristiti kao obloga za rane kako bi se povećao potencijal zarastanja tkiva i uspostavila brža integracija i kraće zadržavanje u tkivu

In vivo investigation of soft tissue response of novel silver/poly(vinyl alcohol)/ graphene and silver/poly(vinyl alcohol)/chitosan/graphene hydrogels aimed for medical applications - the first experience

In this paper, we have shown for the first time the soft tissue response of novel silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) and silver/poly(vinyl alcohol)/chitosan/graphene (Ag/PVA/CHI/Gr) nanocomposite hydrogels aimed for medical applications. These novel hydrogels were produced by in situ electrochemical synthesis of silver nanoparticles in the polymer matrices as described in our previously published works. Both Ag/PVA/Gr and Ag/PVA/CHI/Gr, as well as controls Ag/PVA, Ag/PVA/CHI and commercial Suprasor