Papers by Keyword: Experimental Testing

Abstract: Recent research on the progressive collapse of buildings has mainly focused on load redistribution following member failure, commonly referred to as “re-distributional progressive collapse”. However, “impact-type progressive collapse” remains less explored. This mechanism, often triggered by dynamic events such as falling debris or fire scenarios, introduces complex interactions that are difficult to capture using traditional quasi-static models, leaving a significant gap in our understanding of how impact-type progressive collapses occur. This study aims to bridge that gap by investigating the impact forces generated between concrete bodies of various geometries through an experimental campaign. Spherical, semi-spherical, and cubic concrete samples were dropped onto a fiber-reinforced concrete plate from controlled heights. A high-speed camera captured the impact for detailed analysis, while parameters such as impactor mass and velocity, contact radius, and concrete compressive strength were systematically varied. Using advanced data processing techniques, namely Variational Mode Decomposition (VMD), results showed that a 73% increase in impact velocity led to a 75% rise in maximum contact force. Geometry had a significant influence, with spherical and semi-spherical specimens generating up to 64% higher forces than cubes of equal mass. In contrast, compressive strength had a minor effect, raising contact force by only 9% despite a 50% strength increase. High-speed camera footage confirmed more concentrated impacts for spherical shapes, while no notable differences were found between spherical and semi-spherical specimens of equal weight but different contact radii.

Abstract: When investigating the heterogeneous properties of welded joints, mechanical testing of certain Heat Affected Zone (HAZ) regions, using standard approach test specimens, is very difficult or sometimes even impossible. Inability to precisely position and extract mechanical test specimens, even ones of the subsize dimensions, from the narrow HAZ regions is a limiting factor in the mechanical testing implementation. Detailed investigation of the HAZ is made possible by the use of thermo-mechanical simulations on the Gleeble welding simulator. In scope of this paper several characteristic HAZ microstructures of S690QL grade High Strength Steel (HSS) are being simulated. Multi-pass welding simulations are done on special 10x10 mm square section bar specimens in order to reproduce thermal gradients and characteristic microstructures at any location in a weld. Such simulated HAZ microstructures are of a sufficiently large volume, with homogeneous and repeatable properties, that standard specimen methods for mechanical testing can be readily implemented. Metallographic optical examinations, as well as hardness measurements were done initially. Mechanical properties are focused on determining stress-strain curves for each characteristic weld region. The paper investigates whether the mechanical properties of Gleeble simulated hard-soft combined HAZ regions are better in comparison to exclusively hard or soft HAZ regions. The obtained results can subsequently be used for the material model development.

Abstract: This study focuses on the experimental analysis of concrete-filled double-skin tubular (CFDST) short columns with double circular inner steel tubes under concentric axial loading. This cross-section layout promises to increase the ductile behavior of the compressive element and its energy absorption capacity, not to mention its ultimate axial strength. This research analyses main twofold variables: (i) Hollow ratio and (ii) eccentricity ratio (i.e., distance ratio between the inner tube’s separation and the sandwiched concrete width). As a result, load Vs. Axial deformation, load Vs. Axial strain curves, ductility index, strength index, energy absorption capacity, and ultimate axial capacity formulae for square CFDST columns with double circular inner tubes are reported. Key findings of this study show that (a) ductility is an intrinsic property of these types of sections; (b) the variation effect of hollow ratio influence inversely in the confined concrete strength of the element, (c) Eccentricity ratio has proved to be the least ultimate strength capacity influencer. However, its impact increases when it is jointly analyzed with the hollow ratio values. (d) The formulae proposed for predicting the ultimate capacity of CFDST columns showed good agreement with the experimental results. Thus, these expressions could be extended to the design of composite CFDST elements, provided a resistance factor based on a reliability analysis is incorporated.

Abstract: The paper presents a structural survey of the arch bridge from the 17^th century located in Portz Insel near Mikulov. The purpose of the research was to analyze service life and reliability of the bridge structure including long-term functional durability. There were performed probes in order to search for the original frame foundation and defining a shape of particular arches buried in the ground for decades. The probes also helped to check up the structure of the bridge deck in several places. Currently, throughout 2019 and 2020, the bridge will undergo major reconstruction work in the context of the project „Mikulov, Portz Insel – restructuralisation of the historic countryside“.

Abstract: The paper deals with a structural survey of the historic drainage and ventilation system discovered recently in the Prague Castle area. Based on in-situ inspection the remedial works in the context of historic importance of the area are presented. The experimental testing is used for the assessment of the efficiency of remedial technologies, but also for a deeper investigation of moisture transport phenomena in heterogeneous materials. The data collected for the investigated aspects should allow foresight of the behavior of existing structures providing damage prediction models and help in the design of remedial measures.

Abstract: Buckling restrained braces are increasingly used as structural fuse elements due to their stable and quasi-symmetric cyclic behaviour and capacity to dissipate a large amount of energy. However, a wider adoption of buckling restrained braced frames is often precluded by the proprietary character of most buckling restrained braces, need for their experimental qualification and sometimes lack of experience of designers. To overcome these problems, a set of typical buckling restrained braces were developed in view of their pre-qualification. Both "conventional" and "dry" devices were considered, with capacities corresponding to typical steel multistorey buildings in Romania. Detailing of buckling restrained braces aimed at investigating the core aspect ratio, gap size, strength of the buckling restraining mechanism, and the unbonding material. The paper presents the results of the experimental program, and recommended design parameters of qualified specimens.

Abstract: Cladding details which span the building envelope are particularly susceptible to forming thermal bridges, where heat is transferred between interior and exterior, resulting in loss of energy. To prevent these thermal bridges, thermal breaks inserted in the cladding detail connection to the building interior are necessary. This paper summarizes recent work on the design, validation, and implementation of thermal break strategies. Fiber-reinforced polymer (FRP) shims were used to provide thermal breaks in steel connections of cladding details. The use of these shims was due to their combination of favorable thermal properties and promising structural performance. While several cladding details were examined, this paper will concentrate on the cyclic performance of roof posts (under axial and cyclic lateral loads) and canopy beams (under cyclic lateral loads only), representing their anticipated performance during earthquakes. The impact of FRP shims at the bolted base plate connection to the building interior is discussed. Recommendations for design are also presented.

Abstract: Steel links inside Eccentrically Braced Frames (EBFs) can be classified as either short, intermediate or long. The more commonly used short links yield primarily in shear and dissipate incoming energy inside the web of the link. Advances in shear link research and industry practice, particularly the increased use of bolted links, have allowed greater freedom in the design of the link section, as the section used can be decoupled from the collector beam section. Seven shear link specimens were tested inside a full scale EBF set up, and were subjected to AISC’s 2005 shear link loading protocol. Increasing levels of rotation were applied to links of varied cross-sections and intermediate stiffener spacings. Links with low web aspect ratios performed to a higher rotation than past research would have suggested, and when intermediate stiffeners were removed, they performed to an even higher rotation. Recommendations for design are presented, including a relaxation of the stiffener spacing equations when web aspect ratio criteria are met. A provision is also included to allow greater rotational ductilities in EBF frames with low web aspect shear links.

Abstract: The determination of the blast protection level of civil engineering buildings components against explosive effects represents a design topic of crucial importance, in current practice. However, some key aspects of blast resistant structures design have been only marginally considered in the last decade, and currently still require appropriate regulations. This is especially true in the case of glass windows and facades, where the intrinsic material brittleness is the major influencing parameter for blast-resistant assemblies. While blast assessment of buildings and systems is usually achieved by means of experimental investigations, as well as Finite-Element numerical simulations, general regulations and guidelines are currently missing. In this regard, the European Reference Network for Critical Infrastructure Protection - Task Group (ERNCIP-TG) “Resistance of Structures to Explosion Effects” attempts to develop guidelines and recommendations aimed to harmonise test procedures in experimental testing of glass windows under blast, as well as standardized approaches for their vulnerability assessment via Finite Element numerical modelling. In this paper, major ERNCIP-TG outcomes and next challenges are briefly summarized.

Abstract: A slender steel arch supporting textile membranes in a complex membrane structure with respect to in-plane and out-of plane stability is investigated. In the last decades the textile membranes are widely used to cover both common and exclusive structures due to progress of new membrane materials with eminent properties. In comparison with use of a traditional roof decking these structures are much more economical and attractive. However, the complex analysis and computational design methods are demanding and still not codified. The real physical model of a membrane structure supported by two inner steel arches and covering a concert stage was constructed and tested in laboratory of CTU in Prague. The membrane used was the Précontraint 702S Ferrari¹ prestressed textile membrane with PVC coating. The arches were hot-formed in a workshop from Grade S355J0 steel. The paper presents experimental results for: i) isolated inner arch, ii) complex structure of the membrane with supporting arches, both under symmetrical and asymmetrical loading. Furthermore the numerical nonlinear FEM model created in SOFiSTiK software package and its validation for the above structural configurations and loading is presented. Subsequent parametrical studies cover various levels of the membrane prestressing to show its significance for nonlinear behaviour and stability of the inner arch. Finally some recommendations concerning numerical modelling are presented.