This study presents a complex experimental research of a damaged steel railway bridge. Before the reconstruction, the elastic behavior of the material was evaluated using the hole-drilling strain gauge method of determining residual stresses at the relevant cross-sections. During the reconstruction project (lifting of the structure), a short-term monitoring system was installed at the critical cross-sections for continuous recording of strain. The aim was to evaluate the quality of the reconstruction intervention and prevent further damages. Following a successful reconstruction, a diagnostic load testing was performed according to Croatian standards. The purpose of the load testing (static and dynamic) was to evaluate the ability of the bridge to carry the design loads and calibrate the finite element models. During static load testing vertical displacement was measured as well as strain. Dynamic load testing of the bridge was performed in order to determine the main dynamic parameters of the structure and to calculate the dynamic factor. In order to select the appropriate measurement parameters and methods used during this experimental research it was necessary to consider the bridge type, materials and reconstruction or strengthening interventions. Especially, since this bridge was an example of insufficient inspection and maintenance during service. A well-designed monitoring and diagnostic load testing needed to be performed in order to obtain useful results for the decision makers involved.

In light of various initiatives taken around the world to convert waste materials into new products, the objective of this paper is to promote the use of steel fibers from recycled car tyres in the concrete industry. Hybrid steel fiber reinforced concrete (HSFRC) is a material that combines two or more types of steel fibers, in this case: manufactured steel fibers and recycled steel fibers from waste car tyres in equal proportions. The main objective of the presented research was to investigate the possible application of HSFRC in structural elements with conventional reinforcing bars in order to improve the flexural behavior and to investigate the possibility of partially replacing the conventional reinforcement with steel fibers in terms of service performance. For this purpose, eight slab specimens with different reinforcement ratios were subjected to a four‐point bending test to measure displacements, strength, and crack widths. The addition of a hybrid fiber mix to a conventionally reinforced concrete slab significantly reduced crack widths by up to 53%. The addition of fibers compensated for a conventional reinforcement reduction of 20% by reducing crack widths by up to 38%. It was observed that slightly more cracks opened with smaller widths and at smaller distances from each other in these slab types than in the conventionally reinforced reference slabs. Slabs with hybrid fiber mix and 44% reinforcement reduction showed no improvement in crack control compared to the conventionally reinforced concrete reference slabs. Using numerical models in ABAQUS simulating the flexural test on notched prismatic specimens, a calibration of the material models of plain concrete, and HSFRC was performed based on the test results. These validated material models were used for numerical modeling of slabs. The results of the analyses compared with the experimental results showed good agreement and confirmed the ability of the proposed material model of HSFRC to predict the flexural behavior of slabs with conventional reinforcement.

In general, 20–25% of the original fibre weight is considered waste in the production of high-quality textiles for the construction sector. A market analysis has shown that in the Republic of Croatia alone, up to 327 tonnes of this waste is produced annually, which is enough to reinforce 50 to 150 thousand m³ of cementitious composites. This preliminary study aims to evaluate the contribution of glass, basalt and carbon fibres generated as waste in the local production of high-performance technical textiles, to the fresh and hardened properties of fibre reinforced mortars. In order to investigate the influence of fibres, three types of fibres in two different lengths (5 and 10 mm) were used, while the amount of fibres was constant. The obtained results show that due to the fibre presence, workability is reduced regardless of the type and length of the fibre. The tested fibres have a negligible effect on compressive strength, but the use of basalt and carbon fibres increases the tensile strength. Furthermore, all three types have positive influence on the toughness and volumetric deformations, although to a greater extent in the use of 10 mm long fibres and carbon fibres.

The recent seismic activity in Croatia has inflicted significant damage upon numerous buildings, with masonry structures being particularly affected. Consequently, experimental investigations and structural condition assessments’ have garnered increased attention, as they have become integral to the renovation process for such buildings. Additionally, assessing the structural condition prior to seismic events is vital for determining the extent to which earthquakes impact the stiffness of systems, such as masonry structures. This paper presents the results of experimental investigations and numerical analysis conducted on a damaged high school building in Sisak, Croatia. The experimental investigation involved shear testing, flat jack analysis, and operational modal analysis. Utilizing the available drawings and mechanical properties determined experimentally, an initial numerical model was developed. Subsequently, through the iterative process of finite element model updating, the initial numerical model was refined based on the structural dynamic properties. The updated numerical model was then employed to assess the structural condition prior to the earthquake event. This study contributes to the field by providing insights into the post-earthquake estimation of dynamic properties in intact masonry buildings, utilizing a comprehensive approach that combines experimental investigations and finite element model updating. By quantifying the changes in dynamic parameters, such as natural frequencies and mode shapes, the study provides valuable insights into the response characteristics of damaged masonry building. The observed differences in natural frequencies between the damaged and undamaged states are as follows: 9% for the first mode shape, 6% for the second mode shape, and 2% for the third mode shape.

This study investigates how high-strength, self-compacting concrete beams reinforced with polypropylene fibres behave under shear loading. While this topic is interesting and important for the development of better concrete materials, the manuscript...