Proceedings of Faculty of Civil Engineering
“Proceedings of works“ is annual publication of the Faculty of Civil Engineering of University in Rijeka. It is published continuously since 2008 (Book XI), carrying forward the publishing practice started in 1972 which lasted until 1994. Since the edition of 2016 (Book XIX), the journal is augmented by a new section which covers highlighted events and persons which had, in the year of publishing, marked the activity of Faculty and are therefore important for its visibility and recognition in the scientific and social community. The main purpose for the publishing of “Proceedings of works” of the Faculty of civil engineering of University in Rijeka is to enable the publication of co-authored papers of students in the finishing years of University and Professional studies and their mentors, as well as course teachers and collaborators, of independent and co-authored papers of teachers and students of Post-graduate doctoral study, external Faculty collaborators, other scientists from University of Rijeka and Republic of Croatia, and experts for industry and close social community. The indirect purpose of the publication is encouragement of acquisition of writing skills and paper editing and motivation for research work in young colleagues. The papers must contain noticeable results that were not previously published, and to refer to existing knowledge and topics connected to the areas of activity, mission, and vision of the Faculty. Every paper is reviewed by at least two scientists in scientific/scientific-teaching position for the corresponding discipline, chosen from the employees of the University, Faculty of civil engineering and other institutions of higher education, components of other universities in Republic of Croatia and outside Croatia, recognised experts from local, and wider academic and business community. Reviewers are chosen by the main and responsible editor from the reviewers base, suggested by the members of editorial board in which all scientific areas of technical and natural sciences within the activities of the Faculty are represented. The journal uses the Universal decimal classification (UDK). “Proceedings of works“ is published in black and white, whereas an overall text, with original illustrations in colour, is available on the internet page of Publishing activities of the Faculty, since Book XI in 2008. Reviews: external reviewers, mostly national reviews, double review, all papers, double blind reviews First year of publishing: 1977 Publishing frequency (annually): 1
University of Rijeka, Faculty of Civil Engineering
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Triangular 2D linked-interpolation finite elements for micropolar continuum
Triangular finite elements for linear micropolar continuum theory are developed using linked interpolation. In order to satisfy convergence criteria, the newly presented finite elements are modified using the Petrov-Galerkin method, which uses different interpolation for the test and trial functions. The elements are tested through several numerical examples consisting of a set of patch tests, and a stress concentration problem, and compared to the analytical solution and membrane micropolar finite elements with standard Lagrangian interpolation. All the presented elements faithfully reproduce the micropolar effects in the stress concentration analysis, but the enhancement is negligible with respect to standard Lagrangian elements.
Planning a sanitary wastewater drainage system for Drivenik settlement
The settlement of Drivenik is located in the hinterland of the City of Crikvenica, within the administrative boundaries of the Vinodol Municipality. Currently, there is no systematic solution for sanitary wastewater drainage system in this area; instead, wastewater is managed individually through septic tanks, which is not sustainable in the long term from the perspective of environmental protection and public health. As part of this study, a conceptual design for a sanitary wastewater drainage system for the settlement of Drivenik has been proposed. The objective of the proposed solution is to meet the technical requirements related to the construction of connections, as well as overcoming of terrain obstacles along the planned collectors route, while simultaneously optimizing the length of the sewer collectors, reducing pipe diameters, and minimizing the need for construction of additional installations. In accordance with the Spatial Plan of the Vinodol Municipality proposal, the sanitary wastewater from Drivenik is intended to be conveyed to the central wastewater treatment plant serving the City of Crikvenica. Implementation of the proposed sewage system would enable efficient and environmentally acceptable collection, transport, treatment, and discharge of wastewater, while maintaining costeffectiveness in terms of construction and maintenance. As part of the study, a layout scheme of the sanitary wastewater drainage system for the settlement of Drivenik, all relevant hydraulic and structural calculations for the collectors, as well as calculations for the pumping stations were developed. Additionally, a corresponding approximate bill of quantities for the planned works required for the implementation of the system was prepared.
orizontal management of the sewer network
Computation of Euler's critical buckling load for a rod with stepwise varying cross-section using analytical approach and the finite difference method
This paper presents the computation of Euler’s critical buckling load for rods with stepwise varying cross-section using both an analytical method and the finite difference method. A comparison of results shows that the numerical method yields slightly lower, conservative values. The results contribute to the analysis of buckling in geometrically complex elements and can be used to validate numerical models.
Design of T-shaped reinforced concrete retaining wall and seawall according to Eurocode 7
This paper presents a practical example for the design of a reinforced-concrete (RC) T-section retaining wall and a T-section seawall in accordance with Eurocode 7 (EC7). The objectives are: a) in the context of Design Approach 3 (DA3), which is applied in Croatia, examine the sensitivity of stability verifications with respect to different classifications of structural and geotechnical actions and to where the corresponding partial factors are applied, and b) to compare the stability of retaining and seawalls of identical geometry. After a brief overview of EC7 and DA3, design calculations are carried out for an RC T-wall under several alternative definitions of actions, and the results of the sliding, overturning, and foundation bearing capacity checks are compared. Finally, the obtained utilization ratios for the retaining and seawall T-walls are compared to highlight the influence of seawater actions (hydrostatic pressure and uplift) on the design.
Theoretical and mathematical basis of computational fluid dynamics application in modeling wastewater treatment processes
The article examines the application of Computational Fluid Dynamics (CFD) in the analysis of physical, chemical and biological processes in wastewater treatment. The use of CFD in wastewater treatment enables detailed simulation and visualization of fluid flow, mixing, and chemical reactions within treatment units, which helps optimize design and operational parameters. CFD can identify inefficiencies, such as dead zones or short-circuiting in tanks, and support improvements in aeration, sedimentation and chemical dosing. By reducing the need for physical prototyping and trial-and-error adjustments, CFD contributes to cost savings, enhanced treatment performance, and more sustainable system development. The aim of the paper is to highlight the application of CFD in the design, optimisation and analysis of wastewater treatment plants and to encourage wider application in professional and educational settings.
Experimental investigation of superplasticizer effect on mortar properties
This paper investigates the influence of superplasticizers on the workability and mechanical properties of cement mortar at the ages of 2 and 7 days. The aim of the study was to examine how different dosages and timing of superplasticizer incorporation affect the properties of fresh and hardened mortar, with focus on compressive and flexural strength as well as workability. Superplasticizer was added in proportions of 0%, 0.5%, and 1% by cement mass, while the water-cement ratio was kept constant in all mixtures. The results show that mixtures containing superplasticizer achieved higher compressive and flexural strengths, as well as improved workability, compared to the reference mixture without admixture. It was particularly observed that the effectiveness of the admixture is significantly higher when added together with water during the initial mixing phase of the mortar components, while adding the admixture after initial mixing of the fresh mortar resulted in a smaller increase in strength. These findings highlight the importance not only of correct dosing but also of the timing of superplasticizer application. This indicates that the addition of superplasticizer has a positive impact on the workability and mechanical properties of mortar, where proper mix design and the choice of the optimal timing for admixture addition play the key role in achieving the desired properties.
Assessment of real and inevitable losses in water supply systems
Water losses in water supply systems cause significant economic and environmental damage. In addition to increasing the costs of drinking water distribution, they also negatively affect water resources, which is particularly critical in areas with limited water availability. Despite efforts to reduce them, water losses in the Republic of Croatia still account for a significant share of total consumption, averaging up to 50% of abstracted water volumes. The assessment of water losses is based on specific performance indicators of the water utility infrastructure, among which the Infrastructure Leakage Index (ILI), proposed by the International Water Association, is particularly important. ILI is defined as the ratio of current real losses to unavoidable losses. This paper presents the theoretical basis for the assessment of the ILI indicator, with emphasis on the key parameters influencing it (real and unavoidable losses, pipeline length, average system pressure, and the number of consumers). A practical example of ILI assessment was also provided, based on a hydraulic model of a selected District Metered Area (DMA). Using the EPANET software, pressures within the given DMA zone were modeled, and the obtained data were used to estimate real and unavoidable water losses. The analysis identified areas within the DMA zone that require the implementation of measures to reduce water losses and improve the operational efficiency of the system. It was concluded that reducing the ILI indicator to a target value can only be achieved through the iterative application of numerical analyses and field measurements.
Load-bearing capacity of T-joints with self-tapping screws in thin-walled C-profile
This paper investigates the mechanical behaviour of T-joints made from cold-formed steel C-profiles connected with self-tapping screws, with a particular emphasis on the influence of profile thickness and hole design on the joint’s load-bearing capacity. Joints with two sheet thicknesses, 0.95 mm and 1.15 mm, as well as two hole variants, without reinforcement and with reinforcement, achieved by plastic forming, were analysed. Numerical simulations were performed using ABAQUS software, and the validity of the models was confirmed by comparison with relevant results from the literature. The results show that increasing the sheet thickness by approximately 21% results in a 15.2% increase in the maximum load capacity of the joint, accompanied by a change in the failure mechanism, where the critical failure location shifts from the steel profiles to the screw. Introducing hole reinforcement significantly improves stress distribution and reduces local deformations around the screw holes. For thinner profiles, reinforcement leads to a 19.8% increase in load capacity, while for thicker sheets, the increase is considerably more pronounced, reaching 46.7%. Thus, hole reinforcement enhances the joint’s resistance to local deformations and enables better utilization of the steel profiles’ capacity without exceeding their yield limit. Proper selection of sheet thickness, screw quality, and hole design proves crucial to ensuring optimal load capacity and safety of T-joints in thin-walled steel structures. The obtained results provide a valuable contribution to the understanding and optimization of joints in modern cold-formed steel constructions.
Analytical solution for thermal effects in laminated glass with a compliant interlayer
This paper analyses the thermal effects in composite beams using an analytical solution for a two-layer beam across three types of models: fully composite (no slip between layers), partially composite (limited slip) and non-composite beams (free slip). Laminated glass is selected as a representative example of a composite beam. The applicability and accuracy of the analytical solution are verified by a comparison to experimental results from the literature, taking into account that rising temperatures cause gradual softening of the interlayer in laminated glass.
Parametric analysis of out-of-plane façade overturning
Masonry structures show great vulnerability during earthquakes. In this paper, emphasis is placed on the out-of-plane failure mechanisms, which occur due to inadequate wall-to-wall and wall-to-floor connections. The following out-of-plane façade overturning mechanisms are analysed: i) vertical overturning of the façade and ii) overturning of the façade with one side wing. A parametric analysis was carried out and diagrams of the activation factors of the mechanism and spectral acceleration were created. The analysis is based on defining the geometry of the blocks included in the mechanism, the boundary conditions and the loads acting on the wall. The activation factor of the mechanism can be obtained by applying the principle of virtual work or by using the equilibrium equation of the overturning and the stabilizing moment. Based on the activation factor of the mechanism, the value of the spectral acceleration of the activation of the mechanism is obtained, which should meet the criteria of limit states. The effect of stabilizing horizontal forces in the form of ties installed in the floor plane was also considered.
Vibration analysis of a 2D micropolar continuum using finite elements with enhanced fixed-pole interpolation
In this paper, newly developed quadrilateral finite elements of arbitrary order are presented for the linear vibration analysis of a 2D micropolar continuum. For the displacement field interpolation, two types of interpolation functions based on the fixed-pole concept are considered: the original and the enhanced (linked) interpolation. The developed finite elements with 4 and 9 nodes were subsequently employed to discretise several geometrical domains. Their convergence curves for the first two natural frequencies of the selected numerical examples are critically assessed against the results obtained using standard Lagrange interpolation.
Analysis of the infrastructure of the City of Opatija for the purpose of tourism
This study examines the pivotal role of construction infrastructure in the development of tourism, using the City of Opatija as a case study. Through an analysis of geographic location, urban planning factors, tourist assets and events, as well as historical tourism, the research focuses on the importance of infrastructure projects for a destination’s attractiveness and competitiveness. By analyzing hotel accommodation, projects under construction, spatial planning and the significance of tourist infrastructure, the study provides insight into how Opatija leverages its construction assets to meet tourist demands year‑ round. Emphasis is placed on maintaining a balance between preserving cultural heritage and adapting to contemporary trends. The analysis demonstrates the importance of continuous investment in both developing and maintaining construction infrastructure so that the tourist city of Opatija retains its status as an attractive tourist destination and stimulates the local community’s economic development. The paper lays the groundwork for further research on the impact of construction infrastructure on tourism and suggests a need for ongoing monitoring and adjustment of urban planning and projects to ensure the destination’s sustainability and competitiveness.
Numerical and experimental analysis of the dynamic response of a blocky portal frame with elastic joints
This paper investigates the dynamic response of a block-based portal frame with elastic joints. A nonlinear numerical model based on discrete kinematics was developed and implemented in Python using the Newmark method. Experimental tests were conducted to validate the model. Results confirm its suitability for analyzing block systems and form a basis for future extension to nonlinear joint behavior.
Price changes of reinforced concrete works in the Republic of Croatia
The topic of this paper is related to major changes and price increases in the construction sector, which have seriously disrupted the implementation of construction projects in the period from 2019 to 2024. The paper analyses the price trends of reinforced concrete works for the specified period using a real example of the construction of a family house in the Republic of Croatia. This paper aims to investigate how market movements impact the prices of selected construction works, as well as to identify the key elements that contribute most to changes in the total price. The project documentation of the selected project served as the basis for calculating prices by year, and the price itself was determined using the standard additional calculation method, applying a calculation factor. According to the results obtained, the total price of reinforced concrete works increased by approximately 93 % within the observed period. The largest share of the total price of works is accounted for by material costs, which amount to as much as 84 %. The causes of price changes include various geopolitical, health and natural disasters, such as the coronavirus pandemic, earthquakes, war in Europe and other consequential events. To mitigate the effects of market instability, more flexible contracting of works, along with improved planning and management of construction projects, is recommended.
Analysis of mechanical properties of fiber reinforced concrete
Since its invention, concrete has been one of the most used structural materials in the world, if not the most used. Today, there are many types of concrete, such as reinforced concrete (RC), ultra-high-performance concrete (UHPC), high-strength concrete (HSC), self-consolidating concrete (SCC), lightweight concrete, recycled aggregate concrete, etc. Among these different types of concrete, fiber-reinforced concrete (FRC) is the subject of numerous studies. These fibers serve as reinforcement of concrete in a similar way like reinforcing bars – they bridge cracks in concrete. Regardless of the good properties of concrete as a material, it has some weaknesses such as low tensile strength. Reinforcing concrete with fibers aims to improve its tensile strength. Different types of fibers are used for this purpose: steel, glass, synthetic, carbon and natural fibers. This paper provides an overview of the use of these fibers for the purpose of obtaining UHPC with a focus on their influence on the mechanical properties of the resulting material: compressive, tensile and flexural strengths.
In Memoriam prof. dr.sc. Edvard Pavlovec
Presentation of companies from the Professional Base of the University of Rijeka - Faculty of Civil Engineering
Comparation of flow calculations using the population load coefficient method and population distribution by individual sections of the water supply network
The paper presents a comparison and analysis of the flow calculation using the population load coefficient method K and population distribution by individual sections of the branched water supply network. The hydraulic design is based on the laid water supply network for the community of Ližnjan in Istria. Using the population coefficient load method K, a characteristic section of the water supply network is defined, and then the population load coefficient is defined for the remaining sections. After that, the virtual lengths and specific flow for sections of the water supply network are defined in l/s/m, based on which the own flows for individual sections of the water supply network are calculated. The second method defines the number of inhabitants on individual sections of the water supply network, based on which the specific flow for sections of the water supply network is defined in l/s/inhab. After that, own flows are calculated for individual sections of the water supply network. Hydraulic design is made based on the calculated total flows covered by the given methods, and also the comparison and analysis of total flows, pipe diameters, velocities and pressures on individual sections and nodes of the water supply network is given. The conducted comparisons of hydraulic calculations did not reveal any significant differences in the flows, and therefore not in the pipe diameters and velocities in individual sections of the system, nor in the pressures calculated in the calculation nodes of the water supply network. When used properly, both methods give reliable results.
Excavation protection of the Paromlin city library construction pit in Zagreb
The choice for the construction pit protection is extremely important in order to ensure the safety of workers, neighboring buildings and the environment during construction. The specific conditions of the construction site, geological conditions, the depth of the pit and the nearby infrastructure are crucial for the selection of the stabilization method of the construction pit. The paper provides an insight into several variant solutions for securing the construction pit of the Paromlin city library in Zagreb, for which a calculation was made in the PLAXIS 2D software package based on numerical analysis, i.e. the finite element method, taking into account the geotechnical characteristics of the soil determined by investigation work, the depth of the pit, environmental conditions, project requirements, legal and safety aspects, and economic feasibility. In order to choose the most suitable method of pit stabilization, a calculation was carried out for seven variant solutions on the relevant cross-section, all of which can be classified into three types of the construction pit protection: steel sheet piles, pilot rock design, and reinforced concrete diaphragm design.
numerical modeling, finite element method
Modeling the inflow and outflow dynamics of retention/detention basin
The paper presents a calculation method that can be used to model the dynamics of emptying and filling retention basins intended for the temporary retention of water, i.e. to achieve the necessary transformation of the flood wave hydrograph. The calculation method is based only on the principle of mass conservation and is therefore very simple and attractive for practical application (assuming that dynamic phenomena can be reasonably neglected). To verify the effectiveness of retention for the relevant hydrological extreme conditions, the temporal change in water level must be determined by solving the mass conservation equation, which correlates the resulting change in water volume in the retention and the difference in mass flows at the inlet and outlet of the retention in the same time period. The presented procedure takes into account the inflow of water from the surface flow and the inflow of water resulting from precipitation above the retention basin. Therefore, for water flows at the outlet, the following are taken into account: the water flow under pressure through the outlet, the water flow over the spillway crest and the infiltration flow at the bottom of the retention basin. The calculation method was reduced to a simple numerical solution of an ordinary and non-linear differential equation of the first order.
Genesis and development phases of coastal settlements on the example of Milna on Brač
The paper analyses the development of the urban structure of coastal settlements on the example of Milna on Brač, whose prosperity was marked by shipbuilding. The development stages of the place that gave Milna its characteristic features were examined, which can be observed in the changes in the settlement's fabric. Given the rapid increase in the built environment of almost all coastal settlements, including Milna on Brač, it is imperative to investigate the development processes and changes in the morphology of these settlements to preserve their characteristic features and develop quality guidelines for further development.