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Elektronički časopis Građevinskog fakulteta Osijek, e-GFOS je online časopis otvorenog pristupa koji objavljuje znanstvene i stručne članke u svim područjima građevinarstva i arhitekture.
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Number 22 - July, 2021.


    

EXPERIMENTAL AND ANALYTICAL STUDY ON THE IMPACT BEHAVIOR OF STEEL–CONCRETE COMPOSITE SLAB

Autori: Sangeetha P., Ramanagopal S., Manjula R., Hema Naga Sri Pushpa Swetha T.

Sažetak: Concrete structures have been widely used for many years to resist impact loads. Steel–concrete composite structures may be considered efficient structures in the emerging modern construction field. Hence, the main objective of this research was to study the impact behavior of steel concrete composite slabs with different shear connectors and compare them with conventional slabs. Seven specimens of dimensions 500 × 500 × 50 mm were cast, which included plain cement concrete slabs, two reinforced cement concrete slabs with steel mesh and steel rebars as reinforcement, and four steel-concrete composite slabs with four different shear connectors: stud, tee, angle, and channel connectors. The composite action was achieved using a steel decking sheet welded with connectors on which the concrete layer was poured at the top. The test setup was fabricated with slots provided for specimens with simply supported end conditions and a mild steel drop weight. The specimens were impacted at the center of the span by dropping a steel mass from a free fall height of 1 m. The number of blows corresponding to the initial cracking and ultimate failure stages was recorded. The parameters that were used to compare the specimens were the impact energy absorbed, crack pattern, crack width, and increase in impact energy from the first blow to the last blow. The experimental results were very close to the analytical results obtained using ANSYS. The experimental and analytical results showed that the composite slabs with channel connectors performed better than the others, and it was proven that the composite slabs performed better under impact loading than conventional slabs.

Ključne riječi: Composite slab, shear connectors, impact strength, energy dissipation, crack pattern, ANSYS

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PEDESTRIAN BRIDGES AS ELEMENTS OF THE NEW URBAN IDENTITY OF CITIES

Autori: Željka Jurković, Željko Koški, Danijela Lovoković

Sažetak: By the start of the 21st century, the majority of the world’s population was living in cities. Therefore, a top priority has been solving the problem of connecting parts of the city divided by traffic infrastructure in the shortest possible manner by using pedestrian paths. The aim of this study was to analyze, systematize, and typologically define the specific types of structures that make this possible, specifically pedestrian bridges located above roads and railway corridors. The primary and secondary requirements that must be met when designing a pedestrian bridge were identified, and an analysis and comparison of examples of constructed pedestrian bridges in Croatia and the world are herein presented. The results of this study enable the conclusion that, in recent times, in the age of the spectacle society and spectacle architecture, pedestrian bridges are simultaneously deemed architecture, engineering, and infrastructure projects. They are becoming new elements in a city’s image and contribute to the creation of a new urban identity. The original design of pedestrian bridges fosters the use of different construction systems and materials in accordance with technical and technological advancements in construction.

Ključne riječi: Pedestrian bridges, typology, architectural design, urban identity

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ANALYTICAL CALCULATIONS OF THE VIBRATIONS OF VERTICAL STRUCTURES CONSIDERING THEIR DEAD WEIGHT

Autori: Yurii KRUTII, Victor VANDYNSKYI, Petr Konstantinov

Sažetak: This paper presents the results of studies on the analytical dependence between the value of a longitudinal distributed load and the frequency of free vibrations in a uniform rod. Based on the exact solution of the corresponding differential equation, a method for calculating vibrations in rod structures, while considering their dead weight, is implemented. The method algorithm is shown using the example of a rod with both ends clamped. This article contains graphs and analytical formulas for displaying dependencies. A table is provided that contains all the necessary coefficients to perform similar calculations for other boundary conditions. These results allow the physical and mechanical characteristics of a system to be used to determine the natural frequency of rod structures without using approximate methods.

Ključne riječi: Rod structure, variable longitudinal force, bending vibration, natural frequency

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APPLICATION OF PRINCIPAL COMPONENT ANALYSIS TO DROUGHT INDICATORS OF THREE REPRESENTATIVE CROATIAN REGIONS

Autori: Lidija Tadić, Tamara Brleković, Kristina Potočki, Marija Leko-Kos

Sažetak: Drought has become a very frequent hydrological event globally, including in Croatia. It can generally be explained by air temperature and precipitation changes on an annual and seasonal basis, owing to climate change. To contribute to the knowledge on drought phenomena in Croatia, the changes in air temperature and precipitation over a relatively long period between 1951 and 2018 were analyzed. The meteorological stations included in the research were Osijek, Zagreb, and Split, which represented the climate of the entire country. Drought was estimated using the standardized precipitation evapotranspiration index, which is one of the most comprehensive drought indices. Furthermore, the drought severity and duration were calculated using run theory. These parameters were tested for homogeneity using the standard normal homogeneity test. Only the air temperature exhibited inhomogeneity, with a break year in 1991 (Zagreb and Split) and 1998 (Osijek). The existence of significant temporal trends was tested using the non-parametric Mann–Kendall trend test. The probability of drought occurrence with a certain duration and severity was calculated using the copula function. Finally, principal component analysis was applied to the computed standardized Mann–Kendall test statistic (ZMK) to define the relevance of each parameter change and their combination in drought occurrence on a seasonal basis. Drought occurrence was less recognizable from 1951 to 1991 (1998). In the second sub-period, the impact of an increasing air temperature was the most significant variable, particularly in Zagreb.

Ključne riječi: Drought, SNHT, PCA, copula function

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DURABILITY STUDY OF CONCRETE WITH ELECTRONIC WASTE PLASTIC AGGREGATE

Autori: Alena Sičáková, Erika Figmigová

Sažetak: This study aims to determine the durability of concrete, in which plastic chips originating from the casing and enclosures of small electronic items are used as a part of coarse natural aggregate. The following three amounts were used: 50%, 70%, and 90% of the aggregate by volume. The concretes were tested after 28 days of standard curing as well as after exposure to physical (25 freeze-thaw cycles and 25 wet-dry cycles) and chemical (HCl, MgSO4, and NaOH) aggressive influences. Durability was evaluated based on changes in both flexural and compressive strength after exposure. The results of the corrosion resistance tests confirm the different types of behavior of the samples, depending on the relative proportion of the plastic aggregate. In terms of a comprehensive evaluation of the experiment, the greatest potential was found in concrete with 50% plastic chips, which can be defined as lightweight-low strength concrete. However, the specific compressive strength (strength to density ratio) increased with increasing amounts of plastic aggregate, which is a good standpoint for recycling this waste if specific applications are identified that can accept the technical limits of this material while using the positive parameters that could be useful for the application.

Ključne riječi: Electronic waste plastic aggregate (EWPA), durability, freeze-thaw resistance, wet-dry resistance, chemical resistance

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WETTING AND DRYING RESISTANCE OF LIME-STABILIZED EXPANSIVE SOILS MODIFIED WITH NANO-ALUMINA

Autori: Jijo James, Sivapriya, S.V., Sajid Ali, Madhu, T.R., Basudev Singh

Sažetak: Weak soil at construction sites necessitates ground improvement. Chemical stabilization is typically carried out using either lime or cement. The primary objective of this study was to assess the strength and durability of lime-stabilized soils modified with nano-alumina (NA). This study adopted the scientifically established initial consumption of lime (ICL) content for soil stabilization. In addition, nano-alumina was added in varying percentages as an auxiliary additive. It was observed that 0.5% of nano-alumina was optimal with respect to the ICL for maximizing the soil stabilization. The stabilized soils were cured for 0, 7, 14, and 28 days. Post-curing testing revealed that the strength increased six fold for the optimal combination, compared with the virgin soil. To understand the durability behavior of the optimal combination, the stabilized soil specimens were subjected to wetting and drying cycles after 28 days of curing. The optimal combination was nearly as durable as that of the lime-stabilized soil subjected to five cycles of wetting and drying.

Ključne riječi: Expansive soil, lime, unconfined compressive strength, nano-alumina, durability, wetting-drying

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