Roger Owen – Eminent Scientist and Extraordinary Friend

With profound sadness we heard that Professor Roger Owen passed away on Monday 13th January 2020. He was eminent scientist, researcher, lecturer, teacher, mentor, engineer, and above all beloved husband and father, good man and reliable, altruistic, genial and extraordinary friend. With this review we want to describe, after conventional curriculum vitae, his connections with researchers and professors from the University of Split, Faculty of Civil Engineering, Architecture and Geodesy, as well as some common projects

An overview of some characteristic numerical models for concrete

On the basis of experimental testing of behaviour of concrete, reinforced concrete and prestressed concrete structures, various phenomena were observed; in the first place, highly non-linear and inelastic behaviour of concrete. Since it is hard to include all the phenomena and changes that occur in concrete, a large number of numerical models for concrete were developed to describe different states of the problem under consideration, with the tendency to include in these analyses the changes that are dominant in the observed problem. This paper will give a brief overview of some characteristic numerical models for concrete, developed so far, with a short overview of their advantages and disadvantages, i.e. possibilities and limitations. The models were classified depending on the formulation of the constitutive laws. Models were chosen to demonstrate the diversity of modelling and specifics of their application

Mathematical formulation of the space curvature of the tendon in the PC structures

This paper presents the mathematical formulation of the space curvature of the prestressing tendon in the nonlinear analysis of prestressed concrete (PC) structures. The nonlinear behaviour of prestressed tendons is described by the one dimensional elasto-viscoplastic model. The tendon element geometry is described by the second order space function which is determined by its projections. These elements make it possible to model arbitrarily curved prestressing tendons in space, thus they can be determined independently of the three-dimensional (3D) finite element mesh. This is very important in the case when the prestressing tendon can not be located in a plane. The transfer of prestressing force on the concrete was modelled numerically. The developed model makes it possible to compute prestressing structures in phases: before prestressing, during prestressing and after prestressing. The described models are implemented in the computer programme for a 3D analysis of the prestressed concrete structures where the structures are discretized by three-dimensional finite elements with an embedded one-dimensional element of prestressed tendons

Comparison of two-dimensional and threedimensional analysis of reinforced and prestressed concrete structures

This paper presents the comparison of two-dimensional and three-dimensional analysis of the reinforced and prestressed concrete structures. The curved prestressing tendons and reinforcing bars, which are modelled by onedimensional finite element, are embedded into adequate two-dimensional and three-dimensional finite elements. The influence of the prestressing tendons on the concrete is modelled by distributed normal and tangential forces along the tendons and two concentrated forces at the anchors. The computation of the post-tensioned prestressed structures is organized in three phases: before, during and after prestressing of the tendons. A few numerical examples are given to compare the results obtained by these two analyses

Validation of the developed triaxial nonlinear material model for concrete

This paper presents a validation of newly developed material model for concrete. The model is based on a combination of elasto-fractureplastic formulation, considering all dominant influences in concrete: yielding in compression, fracture in tension, softening and hardening. The modified Mohr-Coulomb criterion for dominant compression stresses, the modified Rankine criterion for dominant tension stresses, exponential softening and the function for hardening are considered in this model. All constitutive equations are defined by elementary material parameters (Young’s modulus of elasticity, Poisson’s coefficient, maximal uniaxial tensile and compression stresses, the coefficient of tensile correction, maximal tensile and maximal compression strains). A multi-surface presentation of the model is implemented which permits the rapid convergence of the mathematical procedure. The model uses return-mapping algorithm for the integration of the constitutive equations with associated and non-associated flow rules. Considering triaxial stress state, the paper presents the structural validation of a developed numerical model, which is incorporated into computer programme PRECON3D, illustrated on four examples, both experimental and numerical, taken from the literature: (i) four point bending of normalstrength and high-strength reinforced concrete beams with four different constant-zone lengths and two different reinforcement ratios; (ii) three point bending of reinforced concrete beam; (iii) prestressed concrete beam; (iv) prestressed Π-beam

Numerical testing of prestressed reinforced concrete structures with PRECON3D material model

Some time ago, we have developed a computer programme called PRECON3D for a three-dimensional non-linear analysis of reinforced and prestressed concrete structures where the structures are discretized by three-dimensional finite elements with an embedded one-dimensional element of reinforcement and prestressed tendons. Non-linear triaxial behaviour of concrete is involved in the material model, including all dominant influences in concrete (yielding in compression, fracture in tension, softening and hardening). The non-linear behaviour of reinforcement and prestressed tendons is described by the one-dimensional elasto-viscoplastic model. The tendon element geometry is described by the second order space function which is determined by its projections. Programme PRECON3D can be used very simple because the material model is defined by elementary material parameters (Young’s modulus, Poisson’s coefficient, maximal uniaxial tensile and compression stresses, coefficient of tensile correction, maximal tensile and maximal compression strains). Furthermore, the developed model makes it possible to compute prestressing structures in phases including losses caused by friction and the losses which result from the concrete deformation. In the described analyses we have performed the numerical testing of the prestressed concrete girders from the engineering practice (prefabricated element), which were reinforced with various cross-sectional area of prestressed reinforcement and various tendons geometry. During analyses next parameters were observed: deflections of the girders, concrete stresses and strains at the top and bottom of the girders, compressive and tensile strains of the reinforcement. The paper presents the structural validation of developed numerical model, PRECON3D, on a few examples and the obtained results are compared with the known numerical and experimental ones. It is concluded that the presented programme and numerical model can be effectively used in nonlinear analysis of reinforced and prestressed concrete structures

Numerical Simulation of Saturated and Unsaturated Consolidation Behaviour of Marl Residual Soil

Consolidation tests were performed on reconstituted marl samples under saturated and unsaturated conditions in the geomechanical laboratory at the Faculty of Civil Engineering, Architecture and Geodesy (FCEAG). Reconstituted marl samples were used to simulate the behaviour of marl residual soil as a final product of weathering. The experimental results were implemented in the Plaxis 2D finite element software, and saturated and unsaturated consolidation tests were simulated using hydro-mechanical coupling analysis. Material parameters for the Mohr-Coulomb and Hardening Soil models were calculated from the obtained experimental results. The validity of above mentioned constitutive models for marl residual soil was evaluated using the consolidation tests results and considering the values of axial displacement and void ratio as deformation indicators for saturated and unsaturated conditions. The validity of the input parameters for unsaturated analysis (i.e. the obtained SWCC fitting parameters) and the applied boundary conditions were evaluated considering the achieved degree of saturation value for each calculation phase

Three-dimensional model of a prestressed tie

Prikazane su osnove numeričkog modeliranja prednapete natege za analizu prostornih prednapetih armiranobetonskih konstrukcija. Natege su modelirane jednodimenzionalnim krivocrtnim elementima ukomponiranim u trodimenzijski konačni element betona. Razvijeni model je uključenu program PRECON3D. Primjena modela prikazana je na numeričkim primjerima, a njezina valjanost provjerena je usporedbom dobivenih rezultata s numeričkim i eksperimentalnim rezultatima poznatima iz literature.Basic notions of numerical modelling of prestressed ties, as used in the analysis of spatial prestressed reinforced-concrete structures, are presented. The ties are modelled by one-dimensional curvilinear elements contained in a three-dimensional finite element of concrete. The model developed in this way is entered in the PRECON3D program. The use of the model is presented through numerical examples, and its validity is checked by comparing the results with numerical and experimental results taken from literature

Degradation of inkjet ink by greensand and ultrasonic sonification

The study describes the degradation of inkjet ink at low frequency ultrasound (US) and greensand to compare their reactivity. Environmental sonochemistry is a rapidly growing area and an example of the advanced oxidation process (AOP) that deals with the destruction of organic species in aqueous solutions. Greensand is a granular material coated with a thin layer of manganese dioxide (MnO2) which is among the strongest natural oxidants. In our study magenta inkjet water-based printing ink was dissolved in distilled water and the solutions obtained after degradation were analysed in terms of total organic compound (TOC) and absorption curves in the visible spectra. Also used for the process monitoring was high performance liquid chromatography (HPLC). The efficiency of discoloration is significantly affected by the effluent pH. The efficiency of discolouration was higher when the pH of initial solution was 2 with respect to the initial solution pH of 5.5. In all solutions, irrespective of the initial pH value and the processing method the oxidation of polyhydric alcohols occurs. Although the decomposition is significant, surface peaks resulting from HPLC analysis are very small. Decolourization is closely related to the cleavage of the – C=C and -N=N- bonds, and oxidation of polyhydric alcohol to the formation of monosaccharides, carboxylic acids or other low molecular weight compounds with a lesser number of unsaturated double bonds. These compounds have low UV absorbance or they absorb below 200 nm and therefore their detection is impossible. Thus, the obtained total organic compound results indicate a small degree of mineralization. The effectiveness of the low-frequency ultrasound (20 kHz) oxidation is similar to the effectiveness of oxidation by greendsand

The Position of Women in the Labour Market of Split

Autorice predstavljaju dio rezultata sociološkoga istraživanja kojim su nastojale ustvrditi položaj žena na tržištu rada grada Splita. Istraživanje je provedeno metodom ankete, pomoću konstruiranog upitnika, tijekom srpnja i kolovoza 2008. na uzorku od 680 zaposlenih žena na području grada Splita (340 zaposlenih u državnim i 340 u privatnim tvrtkama). Potvrđena je hipoteza o prisutnosti rodne diskriminacije na tržištu rada u gradu Splitu. Zaposlene žene slažu se s tvrdnjom kako u Hrvatskoj postoji podjela na muške i ženske poslove i mišljenja su da je emancipacija tek djelomično ostvarena. Ispitanice smatraju kako u usporedbi s muškarcima nisu jednako plaćene, te iako prevladavaju one koje drže kako muškarci i žene posjeduju iste sposobnosti za obavljanje jednakih poslova, jedna trećina smatra kako nisu sposobne jednako dobro obavljati iste poslove kao i muškarci. Tako je analiza, pored ostalog, ukazala i na postojanje duboko ukorijenjene predrasude o rodnim grupama i to samih žena prema vlastitim vrijednostima i sposobnostima. U kontekstu tranzicijskih i globalizacijskih promjena kao i globalne ekonomske krize, autorice zaključuju kako su rezultati istraživanja u skladu s nalazima koji ukazuju na potrebu nužne prilagodbe tržišta rada na svim razinama stvarnim potrebama žena, kao njegovim bitnim i nezaobilaznim sudionicama.The authors present some results of sociological research in which they tried to examine the position of women in the labour market of Split. The study was conducted by using the surveys and designed questionnaires during July and August 2008 on the sample of 680 employed women in the area of Split (340 employees in state and 340 women employees in private companies). They have confirmed the hypothesis about the presence of gender discrimination in the labour market in the city of Split. Employed women have agreed with the statement that in Croatia there is a division into men\u27s and women\u27s jobs and that emancipation has only been partially achieved. Respondents believe that , compared with men, they are not equally paid. Although the majority believe that men and women possess equal abilities, one third of them think that they are not capable of doing the same jobs as men. Therefore, the analysis has also pointed to the existence of a deeply rooted gender prejudice and the fact that women themselves doubt their own values and abilities. In the context of transition and globalisation changes, such as the global economic crisis, the authors conclude that research results are consistent with findings that indicate the need for immediate adjustments to the labour market at all levels according to the real needs of women who are its essential and imperative actors