Beam-to-column joints are one of the most common types of joints in metal structures. In the design of load-bearing aluminium structures, welding, as a joining method, is often avoided because of ...localised degradation of mechanical properties in the heat-affected zone (HAZ). However, recent experimental studies on the extent and strength of the HAZ show a significant difference compared to very conservative design rules when modern welding techniques are used. Therefore, the numerical study conducted in this paper addresses the influence of HAZ on the mechanical behaviour of the welded aluminium beam-to-column joint. Parametric numerical analyses were performed varying the aluminium alloys, the reduced mechanical properties of the HAZ, and different definitions of the HAZ extent. The obtained results show that the highest stress concentration occurs at the connection between the top beam flange and the column flange, resulting in plastic softening in this region. Different joint capacities were observed by varying the mechanical properties of the HAZ. A detailed overview of numerical models as well as the obtained moment–rotation curves show that the behaviour of some models is not as conservative as assumed in the design standards considered.
In this paper, numerical optimisation of aluminium prefabricated halls is made considering different wind and snow load zones in the Republic of Croatia. The main structural system is a portal frame ...with a tension-tie element. Standard frame spans of 10 to 20 meters and heights of 3 to 6 meters were analysed. Beams and columns were made of EN AW-6005 A aluminium alloy using extruded rectangular profiles 230 x 90 x 3 mm with slots. In the joint zones, aluminium profiles were connected using 180 x 80 mm tubular steel knee inserts with thicknesses varying from 3 to 6 mm made of structural steel S 235 or S 355. Parametric analyses were performed to find the optimal geometry of steel inserts in terms of uniform utilisation of aluminium and steel cross-sections for all considered frame geometries and load zones. Also, the material consumption is discussed. Based on the performed analyses, the preliminary geometry of the frame with their maximum allowable distances is proposed. These results can be used for cost estimations of the optimal disposition of aluminium halls in the Republic of Croatia.
Fatigue of welded steel details is a very complex phenomenon influenced by many factors. To improve its fatigue strength by extending the crack initiation period in total fatigue life, high-frequency ...mechanical impact (HFMI) method can be employed. The previously developed two-stage model (TSM), which considers the crack initiation and propagation periods separately, can take all HFMI improvement parameters. High cycle fatigue tests have been conducted to collect the necessary data for the calibration of the TSM. This paper presents fabrication, HFMI treatment, geometry inspection, monotonic tensile tests of the base material, and fatigue tests of as-welded and HFMI-treated details with longitudinal and transverse attachments. HFMI treatment’s quality control is emphasized, extending from the HFMI gauge’s standard application to the 3D scan of specimens. Additionally, the continuous monitoring system for crack initiation and propagation data collection is also presented. The obtained results and the observations during the tests are described in detail. It is shown that the HFMI method significantly extends the fatigue life of welded steel details, and data for the calibration of the TSM are presented.
The 2020 Zagreb earthquake caused extensive damage to historically significant buildings, including the Cathedral of the Assumption of Mary, a key monument of Croatian cultural heritage. The ...earthquake rendered the cathedral unsafe due to significant damage to its towers and numerous cracks in its vaults and walls. Urgent measures were necessary to ensure safety and facilitate planned reconstruction and strengthening efforts. A specialised scaffolding design was developed to support inaccessible and unstable areas, involving over 1000 tonnes of steel. This paper details the structural concepts and specific scaffolding design implemented for the urgent restoration and seismic retrofitting of Zagreb Cathedral, ensuring it meets high earthquake resistance requirements.
The complex nature of the fatigue strength of welded steel details, which is influenced by a multitude of factors, can be improved by extending the crack initiation phase of the total fatigue life. ...This enhancement can be achieved through the use of the High-Frequency Mechanical Impact (HFMI) method. This study discusses the fabrication and laboratory cyclic testing of as-welded and HFMI-treated transversal and longitudinal attachments made from S690QL steel. Assessment of a two-stage model (TSM) for the evaluation of their fatigue life, previously developed by the authors, is also performed. The TSM's estimated fatigue lives of the details under consideration align well with the fatigue test results. Moreover, both the TSM model results and the corresponding fatigue test results demonstrate that the HFMI method significantly prolongs their fatigue life. The fatigue resistance of HFMI-treated details compared to as-welded details increased by 1.67 and 1.91 times for longitudinal and transversal attachments, respectively.
•Fabrication and cyclic tests of AW and HFMI treated S690QL steel details.•Application of the previously developed Two-Stage model for the fatigue life assessment.•Fatigue lives estimated with the Two-Stage model align well with the experimental results.•HFMI treatment significantly extends the fatigue life of S690QL steel details.
It is known that steel–concrete composite systems are very efficient. However, such steel–concrete composite systems can be optimised using cold-formed steel elements and innovative shear ...connections. In other words, by considering demountability and reusability, the negative impact of the built environment on the whole ecosystem can ultimately be reduced. This paper, therefore, presents a numerical study of an innovative solution for a composite floor system consisting of built-up cold-formed sections and concrete slabs. Through parametric numerical analysis, parameters such as the diameter and quality of bolts, the concrete class, the type of concrete slab, and the steel quality of sections and bolts were varied. The numerical analysis results show that the system with a solid concrete slab had a higher shear resistance and ductility than the system with a concrete slab made with profiled sheeting and showed different failure modes. The presented results form the basis for push-out tests for the proposed shear connection types.
The vast majority of existing structures in Croatia, as well as in other European countries, are made of unreinforced masonry. The seemingly ideal building material presents a great challenge for ...engineers in earthquake-prone zones. Given that structural failure can have significant consequences in terms of loss of human lives as well as financial losses, a comprehensive structural reliability assessment is needed. Old existing masonry structures often do not have design documentation, and even when they do, the initial mechanical properties have almost certainly degraded over time. That is why in situ testing is of great importance, but masonry is also characterized by a large scattering of results. After recent severe earthquakes in Croatia, more than ever, there is a need for a more reliable assessment of existing masonry structures. This paper presents reliability approaches for resistance evaluation of existing masonry in a real case study where basic failure modes of the masonry were observed. First, the data recommended in standards were used, followed by the updated data obtained from the flat-jack test. Finally, the design value method (DVM) and the adjusted partial factor method (APFM) were used. These methods align with Eurocode standards for new structures but are also adaptable for the assessment of existing structures. Differences in the results between the existing and the new version of the standard were observed, as well as an increase in the obtained resistances with an increase in the complexity of the methods used. Also, the influence of in situ testing proved to be an important factor in the analysis.
This paper investigates the bending resistance of an innovative lightweight composite floor system, LWT-FLOOR. The system consists of built-up cold-formed steel elements that are spot-welded and ...connected to the concrete slab using demountable shear connectors. As the system under investigation is new, the existing standards do not provide guidelines for calculating its bending resistance. This paper gives an overview of different analytical approaches and a comparison of calculated results using bending capacities from the numerical parametric study. Within the numerical parametric study, the influence of the height of the steel beam, the type and degree of shear connection, the connection between the steel elements, and the thickness of the corrugated web used for the bending capacity are investigated. Numerical results for the full shear connections resulted in lower bending capacities than the analytically calculated plastic bending resistances. However, numerically obtained bending capacities for partial shear connections were found to exceed the calculated characteristic non-linear bending resistances and bending resistances for partial shear connections. The obtained results will comprise the basis for further experimental tests, which will support the search for an optimal analytical approach for the bending resistance of the proposed composite system.
In the last decades, the post-earthquake assessment and strengthening of existing structures are becoming one of the most critical fields of civil engineering. Most parts of Europe, as well as many ...existing buildings in Croatia, are built in masonry. For that reason, the main objective of this paper is to show the role of updating knowledge in the decision analysis process of existing masonry assessment. Collecting information through condition assessment can be performed on multiple levels with different precision and quality of the obtained data. Several alternative maintenance strategies and corresponding outcomes usually represent decision problems regarding the assessment of existing structures. Regarding existing buildings, decision analysis proved the benefits of updating knowledge in the building post-earthquake assessment process. As case studies, two existing masonry buildings were selected and different assessment procedures and decision scenarios were presented. The Value of Information (VoI) analysis showed that the applied method is feasible from the perspective of owners and users, as its implementation resulted in a reduction in the overall strengthening and maintenance costs.
The application of tubular columns in steel structures offers many advantages. However, this potential has not been fully utilized due to a lack of access for the installation of standard bolts in ...end-plate beam-to-column joints. Blind bolts are an alternative way of connecting the beam end-plate to hollow section column, for they can be installed and tightened from outside of the column. Standard high strength bolts can be directly screwed into the threaded hole tapped in the column hole wall. Bolts in threaded holes (BTH) - use threads on the bolt hole wall as an anchorage instead of nuts used in standard bolt assemblies. Provisions regarding BTH can be found in the draft version of new Eurocode 3, Part 1 -8, including the definition of minimum thread engagement lengths. Parametric study of beam-to-tubular column joint with extended end-plate was conducted in order to analyse the influence of BTH and specific failure modes on overall joint resistance. Minimum thread engagement length limitations were checked for all considered combinations of parameters, and based on these results, an overview of the general applicability of bolts in threaded holes was gained.
