Search

Design of long-span and lightweight building floors has increasingly been governed by vibration criteria, and cross-laminated timber (CLT) floors are no exception. Due to their high stiffness to-mass ratio, CLT floors are highly susceptible to pedestrian-induced vibrations. The paper presents extensive experimental research designed to study modal properties and pedestrian induced vibration response of numerous long-span multi-panel CLT floors. The tested floor specimens include a wide range of bare CLT floors, as well as CLT hybrids with concrete and FRP bars to improve their vibration performance.

Cross-laminated timber (CLT) floors are typically an assembly of prefabricated panels connected together on the site. CLT offers a wide range of configuration possibilities, as it can be easily pre-cut into various shapes and sizes, making it suitable for use in different architectural design requirements. However, available CLT design guidelines do not apply to complex-shaped CLT floors, i.e. unconventional geometry of floor plans including concave polygons, arches and openings. This paper presents a numerical vibration analysis of such a floor with openings, which represents a standard floor structure for residential and commercial buildings. Influence of panel orientation and inter-panel connections on modal properties and vibration response induced by a single pedestrian walking is analysed and discussed.

This paper discusses vibration serviceability assessment of cross-laminated timber (CLT) floors induced by human activities, with special emphasis on vibrations induced by walking. In the first part current design criteria for vibration serviceability check of timber and CLT floors were analyzed in line with the more general vibration performance-based approach applicable to any floor structure regardless of the material used. The second part focuses on the ongoing research achievements in the design of vibration resistant CLT floors carried out at the Faculty of Civil Engineering, University of Belgrade. In addition, challenges for future research were formulated as well.

Cross-laminated timber (CLT) floors have gained in popularity due to their outstanding strength, aesthetic appeal, good fire resistance, and high level of prefabrication. However, due to their high stiffness-to-weight ratio, CLT floors are highly susceptible to pedestrian-induced vibrations. In design practice, vibration serviceability is usually assessed by assuming a floor as a set of CLT panels with no inter-panel connections, which leads to overestimation of the vibration response. In this paper, an experimental dynamic testing was carried out to identify modal properties and pedestrian-induced response of two CLT floors with different number of panels in a floor assembly. Influence of the inter-panel connections on the floor modal properties and pedestrian-induced vibration response is particularly studied and discussed.

Zbog svojih izuzetnih materijalnih karakteristika u pogledu čvrstoće i krutosti, male sopstvene težine, otpornosti na koroziju i niskih troškova održavanja, kompozitni laminati imaju potencijal za upotrebu u građevinarstvu. Sa porastom svesti o zaštiti životne sredine u 21. veku, sve je češća upotreba prirodnih materijala..., Laminar composites are extensively used in civil engendering due to their exceptional strength, stiffness, corrosion resistance, and cost-effectiveness...

U ovoj doktorskoj disertaciji istraživani su osnovni i dodatni temperaturni naponi u kontinualno zavarenim šinama primenom numeričke analize zasnovane na metodi konačnih elemenata. Glavni ciljevi istraživanja su: (1) određivanje temperaturnog polja šine i osnovnih temperaturnih napona usled neravnomerne raspodele temperature, (2) kvantifikovanje preraspodele temperature i osnovnih temperaturnih napona usled prenosa toplote između šine i praga, kao i između nožice šine i zastora od tucanika, (3) uporedna analiza osnovnih temperaturnih napona određenih korišćenjem numeričke analize sa osnovnim temperaturnim naponima određenim u skladu sa inženjerskom praksom, (4) kvantifikovanje uticaja parametara koloseka i mosta na dodatne temperaturne napone u kontinualno zavarenim šinama na mostu i definisanje smernica za integralno projektovanje konstrukcija koloseka i mosta..., In this doctoral dissertation basic and additional temperature stresses in continuously welded rails were investigated using numerical analysis based on the finite element method. The main aims of the research are: (1) determination of the rail temperature field and basic temperature stresses due to uneven temperature distribution, (2) quantifying the redistribution of temperature and basic temperature stresses due to heat transfer between the rail and the sleeper, as well as between the rail foot and the ballast, (3) comparative analysis of basic temperature stresses determined by using numerical analysis with the basic temperature stresses determined in accordance with engineering practice, (4) quantifying the influence of track and bridge parameters on the additional temperature stresses in continuously welded rails on the bridge and defining guidelines for the integral design of track and bridge structures...

Laminar composites are extensively used in civil engendering due to their exceptional strength, stiffness, corrosion resistance, and cost-effectiveness. They are ideal for high-reliability applications. The 21st century’s focus on environmental protection has led to increased use of natural-based materials like cross-laminated timber (CLT) in building construction. CLT panels have a high stiffness-to-weight ratio, making them well-suited as load-bearing elements, such as walls and floors. The optimal design of laminar composites is often hindered by uncertainties in failure prediction and the computational costs associated with progressive failure analysis (PFA), particularly for larger structures. This study introduces a novel prediction model that combines the smeared crack band (SCB) damage model with the full layerwise theory (FLWT). The aim is to enhance the computational efficiency of PFA in laminar composites while maintaining the accuracy of 3D finite element models. The SCB model accurately captures the response of damaged lamina in both fiber and matrix directions using distinct strain-softening curves, ensuring a precise representation of post-failure behaviour. The damage law is derived based on the assumption that the total energy required to cause failure in an element (released strain energy) is equivalent to the energy necessary to create a crack passing through it. To alleviate mesh dependency, the fracture energy is scaled by a characteristic element length. Failure initiation and modes are determined using the Hashin failure criterion. Furthermore, the model is extended to consider different failure behaviour of timber in tension and compression. This extension enhances the computational framework’s applicability to the field of computational mechanics for bio-based composites, such as CLT. The validity of the model is then confirmed through an extensive experimental program carried out at the Faculty of Civil Engineering, University of Belgrade., Zbog svojih izuzetnih materijalnih karakteristika u pogledu čvrstoće i krutosti, male sopstvene težine, otpornosti na koroziju i niskih troškova održavanja, kompozitni laminati imaju potencijal za upotrebu u građevinarstvu. Sa porastom svesti o zaštiti životne sredine u 21. veku, sve je češća upotreba prirodnih materijala. U skladu sa tim, u građevinarstvu sve veću popularnost stiče kompozitni laminat na bazi drveta - unakrsno-lamelirano drvo (CLT). Zbog visokog odnosa krutosti i sopstvene težine CLT-a, moguće je projektovati elemente male težine i velikog raspona. Nepouzdanost u predviđanju ponašanja oštećenih kompozitnih laminata, kao i kompleksnost proračuna progresivnog loma znatno otežavaju njihovo projektovanje. U okviru ove disertacije je razvijen numerički model za analizu progresivnog loma kompozitnih laminata, koristeći model razmazane pukotine (eng. "smeared crack band" - SCB) i slojevitu teoriju ploča. Model poseduje kapacitet trodimenzionalnih numeričkih modela uz smanjeno trajanje proračuna, čime se povećava efikasnost numeričke analize. Kod SCB modela, ponašanje oštećene lamine je opisano različitim krivama loma u naponsko-deformacijskom prostoru, kako bi se u makroskopskom pogledu opisala propagacija oštećenja koje nastaje usled kidanja vlakana i matrice, respektivno. Zakon omekšavanja materijala je određen na osnovu pretpostavke da je oslobođena energija deformacije jednaka energiji potrebnoj da dođe do loma vlakana, odnosno kidanja matrice. Inicijacija i oblici loma su određeni primenom Hashin-ovog kriterijuma loma. Nakon toga, izvršena je modifikacija modela kako bi se opisalo različito ponašanje drveta pri zatezanju i pritisku. Na taj način, mogućnosti razvijenog numeričkog modela su proširene i na analizu progresivnog loma prirodnih kompozitnih laminata, kao što je CLT. Validnost predloženog modela je potvrđena kroz detaljna eksperimentalna ispitivanja na Građevinskom fakultetu Univerziteta u Beogradu. Upotreba slojevitih konačnih elemenata u an

Cross-laminated timber (CLT) floors have gained in popularity due to their outstanding strength, aesthetic appeal, good fire resistance, and high level of prefabrication. However, due to their high stiffness-to-weight ratio, CLT floors are highly susceptible to pedestrian-induced vibrations. In design practice, vibration serviceability is usually assessed by assuming a floor as a set of CLT panels with no inter-panel connections, which leads to overestimation of the vibration response. In this paper, an experimental dynamic testing was carried out to identify modal properties and pedestrian-induced response of two CLT floors with different number of panels in a floor assembly. Influence of the inter-panel connections on the floor modal properties and pedestrian-induced vibration response is particularly studied and discussed.

With advancements in structural modelling and construction techniques, contemporary footbridges have become increasingly susceptible to vibrations induced by human activities, such as walking, jogging and jumping. This study aims to evaluate pedestrian-induced vibrations of a stress-ribbon footbridge. A three-dimensional finite element model of the footbridge was developed, considering nonlinear behavior of the structure and staged construction. Vibration serviceability assessment was carried out using HIVOSS design guidelines. Numerical modal analysis showed that the lateral modes of vibration cannot be excited in resonance by pedestrians walking. However, the footbridge is prone to vertical pedestrian-induced vibrations. The first torsional mode shape is the most critical. It can be excited in resonance by the first harmonic of the vertical pedestrian loading, yielding vibration response beyond the suggested acceleration limit in some extreme scenarios of pedestrian loading.

Additional temperature stresses in continuously welded rails (CWRs) are caused by track/bridge interaction (TBI) due to thermal actions. Exceeding permissible stresses in CWRs on the bridge can lead to track buckling or rail cracking, compromising the safety of railway traffic. The main aim of the conducted study is to determine the effects of the key parameters such as rail cross-sectional area, track longitudinal resistance, bridge expansion length, and longitudinal stiffness of the fixed bridge support on the reduction of additional temperature stresses in CWRs on steel truss railway bridges. To quantify the effects of these parameters, two steel railway bridges with CWRs and the maximum expansion lengths according to UIC Code 774-3 were analyzed: (1) simply supported truss bridge with expansion length of 60 m and (2) continuous truss bridge with expansion lengths of 2 × 60 m. According to the obtained results, the track longitudinal resistance had the most significant impact on additional temperature stresses in CWRs, leading to their reduction of up to 72%. The bridge expansion length and the rail cross-sectional area led to reductions of up to 25% and up to 18%, respectively. Considering the deformation criteria of TBI, the longitudinal stiffness of the fixed bridge support had a minor effect on the reduction of additional temperature stresses in CWRs.

This paper considers the dynamic analysis of a spatially curved Bernoulli-Euler beam subjected to a moving load. The isogeometric approach is used for the spatial discretization of the weak form of the equation of motion. Both the reference geometry and the solution space are represented using the same NURBS basis functions that guarantee an accurate description of the beam centerline. The time integration is done by the explicit technique. The presented formulation is validated by the comparison with the existing results from the literature for the curved beam subjected to a constant load moving with a constant velocity. In addition, the influence of the moving load velocity on the dynamic response of a spatially curved beam has been investigated.

Dynamic analysis of a spatially curved Bernoulli-Euler beam subjected to the moving load is considered in this paper. The isogeometric approach is used for the spatial discretization of the weak form of the equation of motion. Both the reference geometry and the solution space are represented using the same NURBS basis functions that guarantee an accurate description of beam’s centerline. The time integration is done by the explicit technique. The presented formulation is validated by the comparison with the existing results from the literature for the curved beam subjected to the constant load moving with the constant velocity.

Trends in contemporary architecture towards open-plan spaces in commercial and residential buildings have created problems with excessive vibrations of large-span floors induced by active people. Solving vibration serviceability problems of as-built structures is costly and time-consuming. Therefore, such a problem is the most efficiently and economically addressed at the design stage. This paper presents software developed by the authors for assessing pedestrian-induced vibrations of floors. The software is designed as a user-friendly graphical interface that could be utilised in everyday design practice., Trendovi u savremenoj arhitekturi, koji diktiraju projektovanje komercijalnih i stambenih zgrada sa otvorenim prostorom, prouzrokovali su problem prekomernih vibracija međuspratnih konstrukcija velikih raspona usled aktivnosti ljudi koji se po njima kreću. Saniranje prekomernih vibracija već izgrađenih konstrukcija je skupo i vremenski zahtevno. Zbog toga je najefikasnije i najekonomičnije ovaj problem eliminisati već u fazi projektovanja. U radu je predstavljen softver za procenu vibracija međuspratnih konstrukcija izazvanih pešačkim opterećenjem, jednostavnog grafičkog okruženja i pogodan za svakodnevnu upotrebu u projektovanju.

U ovom radu primenjena je metoda dinamičke krutosti za analizu slobodnih vibracija sistema koji se sastoji od kružne cilindrične ljuske i kružnih i/ili prstenastih ploča. Pri formulaciji dinamičkih matrica krutosti korišćena je Flügge-ove teorija ljuski, kao i Kirchoff-ova teorija tankih ploča. Na osnovu razvijenog programa u Matlab okruženju, urađeno je nekoliko numeričkih primera. Rezultati za sopstvene frekvencije dobijeni primenom metode dinamičke krutosti upoređeni su sa rezultatima dobijenim pomoću komercijalnog programa Abaqus zasnovanog na metodi konačnih elemenata., In this paper, the dynamic stiffness method is used for the free vibration analysis of assemblies built up of circular cylindrical shells and circular and/or annular plates. Flügge's shell theory as well as Kirchoff's theory of thin plates were used in the formulation of dynamic stiffness matrices. Based on the Matlab code, developed for this particular purpose, several numerical examples were presented. The results for natural frequencies obtained using the dynamic stiffness method are compared with the results obtained using the commercial finite element method - based software Abaqus.

As a result of rapid development of cities and construction of high-speed rail/road infrastructure, vibration serviceability of buildings due to traffic-induced vibrations has become a growing issue that affects the comfort of living and health of building occupants. In this paper a numerical study in which the influence of soil stiffness on the traffic-induced vibrations of an eight-story residential building is investigated considering soil-structure interaction and applying the substructuring approach and transfer function method. The results are presented in terms of transfer functions for selected points of interests inside the building. The results show that the resonant response of the structure occurs at lower frequencies for soft soil and at higher frequencies for stiff soil, indicating that soil-structure interaction can significantly affect the vibration response of the building.

Accurate numerical modeling of curved beams is of significant importance in different engineering fields. Several challenges can be present during the curved beam formulation, primarily due to the issues regarding the beam geometry, discretization and beam theory assumptions. In this dissertation, the isogeometric approach is applied in the dynamic analysis of spatial curved beams. A novel beam element was formulated using the Bernoulli - Euler hypothesis and the fundamental relations of the differential geometry, as well as the Cauchy continuum beam model. The geometry of the beam, as well as the displacement, velocity and acceleration fields, were defined using the Non-Uniform Rational B-Spline (NURBS) basis functions, which present the basis concept of the isogeometric approach. Complex geometry of the curved beams can be modeled accurately using NURBS - based isogeometric approach. Formulation of the spatial beam is conducted for the linear case, while the geometrically nonlinear formulation is conducted only for the plane curved beam using an explicit integration procedure. Free and forced vibration analyses of the curved beams are studied. In the latter, the influence of the moving mass on the curved beams is analyzed. The presented approach had shown that, in comparison to the classical finite element method (FEM), a less number of degrees of freedom are required in order to obtain accurate results. Consequently, fewer computational resources are needed to reach the appropriate level of accuracy for the curved beams. This makes the presented approach competitive with the conventional FEM, especially in the analysis of the flexible spatial engineering structures with complex geometry., Tacno numericko modelitanje krivolinijskih gredna nosac je od izuzetnog znacaja u mnogim inženjerskim oblastima. Geometrija krivolinijskog grednog nosaca, diskretizacija grede kao i potrebne pretpostavke grede, predstavljaju poteškoce prilikom formulacije krivolinijskog grednog elementa. U ovom radu je primenjen izogeometrijski pristup u dinamickoj analizi prostornih krivolinijskih grednih nosaca. Novi gredni element je definisan primenom Bernuli - Ojelerove pretpostavke, kao i osnovnih relacija diferencijalne geometrije i mehanike kontinuuma Košijeve grede. Geometrija grede, kao i polje pomeranja, brzine i ubrzanja su definisani primenom NURBS baznih funkcija, što predstavlja fundamentalnu osobinu isogeometrijskog pristupa. Složena geometrija krivolinijskog grednog nosaca može se tacno modelirati primenom izogeometrijskog pristupa zasnovanog na NURBS baznim funkcijama. Formulacija prostornog krivolinijskog grednog nosaca je izvedena u uslovina linearne teorije, dok je geometrijski nelinearna teorija primenjena samo na ravanskom krivolinijskom grednom nosacu, primenom eksplicitne metode integracije. Izvšena je analiza slobodnih i prinudnih vibracija. Analiza prinudnih vibracija je fokusirana na uticaj pokretnog opterecenja na krivolinijski gredni nosac. Primenom date formulacije dobijeni su rezultati zadovoljavajuce tacnosti sa manje stepeni slobode u poredjenju sa klasicnom metodom konacnih elemenata. U sladu sa tim, u cilju dobijanja rezultata zadovoljavajuce tacnosti krivolinijskog grednog nosaca nepohodna je primena manje resursa. Ovo cini prikazani pristup konkurentnijim klasicnoj metodi konacnih elemenata u analizi fleksibilnih inženjerskih konstrukcija sa složenom geometrijom.

Variety of wood species and complexity of their structure make the reliable material properties of cross-laminated timber (CLT) difficult to obtain, which can lead to inaccurate prediction of CLT behavior. Due to high stiffness-to-weight ratio, CLT floors can suffer from vibration serviceability issues. This paper aims to quantify the uncertainties induced by material properties and investigate their effect on vibration performance of CLT floors. Analysis based on Monte Carlo simulations, considering material properties as random variables, is developed. Based on the conducted analysis, appropriate conclusions have been derived., Raznolikost u vrstama drveta, kao i kompleksnost njegove strukture otežava pouzdanu procenu materijalnih karakteristika elemenata od unakrsno lameliranog drveta (CLT), što dovodi do nedovoljno tačnog predviđanja njihovog ponašanja. Problem koji se neretko javlja i narušava funkcionalnost CLT tavanica su vibracije. U ovom radu je izvršena analiza uticaja nepouzdanosti materijalnih karakteristika na vibracije CLT tavanica. Sprovedena je analiza zasnovana na Monte Karlo simulacijama, gde su karakteristike materijala usvojene kao slučajno promenljive veličine. Na osnovu dobijenih rezultata izvedeni su odgovarajući zaključci.

Cross-laminated timber (CLT) panels have an increasing market share and extensive application in civil engineering practice, as full size walls or floor structures. CLT provides a compelling alternative to the concrete and steel (as conventional building materials), providing a low carbon footprint and comfortable living conditions. However, the orthotropic elastic material behavior of wood and the crosswise lay-up yield a relatively complex kinematics of CLT, characterized by high shear deformation across the thickness. This complicates the appropriate and accurate kinematic description of CLT and further prolongs the design phase of the real engineering structure. Due to the relatively low weight, CLT floors are particularly prone to human-induced vibrations, causing vibration serviceability issues such as annoyance to human occupants and dysfunction of vibration sensitive equipment. Therefore, for the accurate response prediction of CLT under dynamic loading, its fundamental dynamic properties should be derived first. In the paper, dynamic stiffness-based FREEVIB software, previously developed by the authors, has been used for modeling and prediction of the free vibration characteristics of CLT floor structures. Frequency curves taking into account: (i) span-to-thickness (a/h) ratio, (ii) plate aspect (a/b) ratio and (iii) different combinations of end constraints, have been developed using FREEVIB and systematized to be easy for use in engineering practice, especially in the conceptual design phase of CLT-based buildings. The results have been compared against the current CLT design recommendations.

In the paper, an overview of the development of the dynamic-stiffness-method-based computational model for the free vibration analysis of plates has been presented. Starting from several formulations of the so-called dynamic stiffness elements, formulated at the Institute for Numerical Analysis and Design of Structures (INP) at the Faculty of Civil Engineering, University of Belgrade in the last decade, a novel software framework FREEVIB has been developed and validated. FREEVIB is object-oriented software in Python environment, designed to predict free vibration characteristics in a wide range of possible structural problems (stepped, stiffened and folded plate structures, implying isotropic or orthotropic material formulations). The presented methodology still serves as a strong basis for further improvements through the extensive research efforts of authors, their collaborators and students.

A framework for free vibration analysis of plate-like structures is presented in the paper. Based on the previously formulated dynamic stiffness elements, FREEVIB object-oriented software in Python environment has been created. Software design and structure as well as a wide range of possible structural problems that could be analyzed using the FREEVIB are presented. Through several illustrative examples including free vibration analysis of stepped, stiffened and folded plate structures, implying isotropic or orthotropic material formulations, the efficiency and accuracy of the FREEVIB is demonstrated. The possibilities of further extensions and improvements of the software are discussed.