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Analiza progresivnog loma kompozitnih laminata u uslovima prostornog stanja napona primenom slojevitih konačnih elemenata
Get PDFLaminar 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.
Application of layered finite elements for continuum damage modelling in laminar composites
remains largely unexplored in literature, particularly when combined with the SCB damage
model. The FLWT-based model accurately captures the 3D stress state within each lamina,
including continuous transverse stresses between adjacent layers, crucial for accurate prediction
of failure initiation. Furthermore, the FLWT demonstrates a weak correlation between the size
of the considered domain and the mesh, presenting a notable difference from standard finite
element models. The developed FLWT-SCB prediction model is integrated into an original
FLWTFEM framework, offering a user-friendly graphical environment for easy visualization
of input and output data. The proposed model’s efficiency has been verified using numerous
benchmark examples during progressive failure analyses of laminar composites and CLT panels
with arbitrary geometries, loading and boudary conditions and stacking sequences. The model
has demonstrated its accuracy in predicting the response of both intact and damaged laminar
composites, and valuable recommendations for future research in this field are included.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 analizi progresivnog loma je u velikoj meri neistražena
u literaturi, posebno u kombinaciji sa SCB degradacijskim modelima, gde slojeviti model
ploče treba objediniti sa fenomenima mehanike loma. Numerički model, zasnovan na slojevitoj
teoriji ploča, omogućava precizno određivanje prostornog stanja napona, zadovoljavajući uslove
ravnoteže međulaminarnih napona, što je veoma bitno prilikom predviđanja inicijacije loma.
Takođe, pri modeliranju većih konstrukcija, primenom slojevite teorije ploča omogućava se
znatno smanjenje broja konačnih elemenata u poređenju sa postojećim numeričkim modelima.
Razvijeni numerički model je implementiran u FLWTFEM kod, čime je obezbeđeno puno
grafičko okruženje, pogodno za vizualizaciju ulaznih podataka i rezultata proračuna. Efikasnost
predloženog modela je verifikovana korišćenjem brojnih referentnih numeričkih primera, prilikom
analize progresivnog loma kompozitnih laminata i CLT panela sa proizvoljnom geometrijom,
opterećenjem, graničnim uslovima i orijentacijom slojeva. Potvrđena je tačnost predloženog
modela u predviđanju odgovora kako neoštećenih tako i oštećenih kompozitnih laminata, a date
su i važne preporuke za buduća istraživanja u ovoj oblasti
Project on erosion monitoring of Devils Town ”DEMONITOR”
No full textОво саопштење је сажет приказ пројекта "DEMONITOR", одобреног од стране Фонда за науку Републике Србије кроз програм ПРИЗМА. Пројекат је фокусиран на Ђавољу варош, заштићено природно добро у јужној Србији, које се састоји од око 200 земљаних стубова, формираних селективном ерозијом. У оквиру пројекта је предвиђен иновативан приступ праћења Ђавоље вароши и њене околине у периоду од три године, коришћењем најсавременијих неинвазивних метода, укључујући терестрички LiDAR, снимке из ваздуха са фотогтраметријском обрадом и сателитску радарску интерферометрију, а такође обухвата и геофизичка истраживања геоелектричним методама. Циљ истраживања је квантификација промена између сваке епохе снимања у периоду од три године, укључујући ерозију, одроне и слегање тла, као и дефинисање подповршине и истраживање потенцијала за стварање нових облика. Очекује се да ће резултати не само приказати промене, већ и омогућити предвиђање еволуције форми у будућности, као и њихове прошлости и настанка. Ефекат који би могао да се постигне резултатима пројекта укључује повећање туристичке вредности Ђавоље вароши, што би донело економску корист за локалну заједницу, али и њену афирмацију у научним и стручним круговима, као и могућу промоцију на UNESCO-вој листи природног наслеђа
COVID-19 Struggle and Post-COVID-19 Recovery: Exploring the Governance, Success, and Digital Transition in Construction Projects in Serbia
No full textConstruction, one of the largest global economic sectors, has been severely challenged by the economic uncertainties brought on by COVID-19. Since 2020, pandemic-related disruptions and remedial measures have made its historically low performance even more difficult. As a result, recent research mainly addressed these negative consequences on the construction sector. In contrast, this paper aims to identify mitigation strategies recognised as good practices on construction projects in Serbia, in addition to detecting disruptions and quantifying their effects on cost and time overruns. A particular emphasis is given to how the pandemic hastened digital transition and encouraged the adoption of modern project management practices. The research was carried out through a survey of two rounds, conducted one year apart, to obtain an in-depth overview. The findings indicated that, although it had an impact on construction projects, the pandemic was not particularly harmful, because of widely used remedial measures and modern project management techniques. However, the pandemic did not modernise project implementation substantially nor significantly increase the use of cutting-edge digital technologies. Nevertheless, it encouraged project managers to think about introducing new approaches in project management, where digitisation is the new normal. The research findings may indicate to academia and practitioners what strategies may assure a project’s implementation even in enormously changed conditions, such as during a pandemic
Impact of surroundings on the local peak pressure in high-rise building clusters
No full textThis study contributes to the field of wind engineering by evaluating the local peak pressure coefficients in a generic high-rise building cluster. Unlike previous studies that have focused on isolated buildings or buildings in tandem arrangements, this research considers the impact of four buildings when surrounding the principal one. Both experimental and numerical techniques are applied, demonstrating the capabilities of the LES method in predicting the local peak pressure. The obtained results offer new insights into the complex interplay between buildings and the wind
environment in high-rise building clusters, especially in the roof zone. The experiments reveal higher peak suction for the building in the group than the isolated at all wind angles. The minimum negative peak pressure coefficient of 5.8 is recorded at a 45° wind angle. Validation of the obtained numerical results shows the promising potential of the LES as a design tool in wind engineering, providing higher resolution of the quantities of interest.Proceedings on C
Analiza efekata prirodom inspirisanih rešenja na ugroženost grada Krupnja od poplava
No full textU ovom radu se razmatra primena prirodom inspirisanih rešenja na slivu reke Likodre uzvodno od Krupnja radi ublažavanja ugroženosti od bujičnih poplava i erozije na slivu. Razmatrane mere uključuju čeone retenzije, buji-čne pregrade, konzervaciju zemljišta, pošumljavanje sliva i melioraciju postojećih šuma. Uticaj navedenih mera je ispitan kroz hidrološki model sliva formiran pomoću programa HEC-HMS. Poređenje rezultata dobijenih sa merama i bez njih pokazalo je da svaka od mera ima pozitivne efekte na smanjenje ugroženosti od poplava i erozije na slivu, pri čemu su najefikasnije čeone retenzije i melioracija šuma
Research, testing and application potential of steel fiber reinforced ultra-high performance concrete
Get PDFThis paper deals primarily with research and testing of ultra-high performance concrete (UHPC) made with or without the addition of steel fibers. Two stages of research are presented and discussed in detail: first - UHPC based mostly on local component materials and produced in the form of a premix with a commercial name ForteCrete150®, and second – modified UHPC, made with a partial cement substitution by limestone filler, as a more eco-friendly and sustainable solution. The obtained results indicate that there is a great potential for application of ultra-high performance concrete, especially in the form of premix that can be prepared on-site. The addition of limestone filler (and potentially other types of mineral additives) as SCM, could generally contribute to improvement of a negative agenda surrounding the cementitious composites
Contribution of strain-hardening cementitious composites (SHCC) to shear resistance in hybrid reinforced concrete beams
Get PDFStrain Hardening Cementitious Composite (SHCC) is an innovative type of fibre-reinforced cement-based composite that has superior tensile properties. Because of this, it holds the potential to enhance the shear capacity of reinforced concrete (RC) beams, if applied properly. This paper presents the general and distinctive properties of SHCC as well as a literature review of topics related to the contribution of SHCC layers to the shear resistance of RC beams with and without shear reinforcement. Based on the analysed results, it is concluded that the main characteristics of SHCC are its microcracking behaviour, high ductility, and increased tensile strength (between 2 and 8 MPa) at large deformations. When used in structural elements, SHCC develops multiple parallel cracks compared to concentrated cracks in conventionally reinforced concrete. The biggest disadvantage of SHCC is its significant drying shrinkage. Although showing high variability, using SHCC as laminates with a thickness of 10 mm improves the shear capacity of hybrid RC beams, but debonding of interfaces in a hybrid system occurs in some cases
Carbonation of limestone powder concrete: state-of-the-art overview
Get PDFRecently, research into finding long-term solutions to CO2 mitigation in the cement and
concrete sectors was initiated since commonly used supplementary cementitious materials
are not globally available in sufficient amounts. One of the possible solutions to that problem
is to develop concrete with a higher percentage of limestone in the powder phase. This work
presents a critical overview of the state-of-the-art in the field of the carbonation resistance of
limestone powder concrete. Experimental research performed so far has shown that if the
simple replacement of cement with limestone powder is applied in the standard mix design, a
maximum of 10-15% of cement (clinker) could be replaced to maintain similar carbonation
resistance. It has also been proven that the dilution effect of weakly inert limestone powder
can be compensated for with several measures in the mix design of concrete. By adjusting the
cement, limestone, and water content and their particle size distribution, it is feasible to design
concrete formulations with up to 50% limestone in the powder phase that are comparable to
referent Portland cement concrete in terms of rheological and mechanical performance and
carbonation resistance. This is an environmentally significant reduction in the clinker content,
but it comes at the cost of a larger superplasticizer content. Prediction models for the
carbonation resistance of the limestone powder concrete are poorly developed. Amongst
them, the fib MC 2010 prediction model is considered relatively simple and robust; however, it
has not yet been proven that the model is applicable to concrete with a higher content of
limestone powder (>15-20% of the powder phase). The future research should be oriented
towards further optimization of the concrete mix design and implementing this model on the
middle- and high-content limestone concrete carbonation
Teaching computing for complex problems in civil engineering and geosciences using big data and machine learning: synergizing four different computing paradigms and four different management domains
No full textThis article describes a teaching strategy that synergizes computing and management, aimed at the running of complex projects in industry and academia, in the areas of civil engineering, physics, geosciences, and a number of other related fields. The course derived from this strategy includes four parts: (a) Computing with a selected set of modern paradigms—the stress is on Control Flow and Data Flow computing paradigms, but paradigms conditionally referred to as Energy Flow and Diffusion Flow are also covered; (b) Project management that is holistic—the stress is on the wide plethora of issues spanning from the preparation of project proposals, all the way to incorporation activities to follow after the completion of a successful project; (c) Examples from past research and development experiences—the stress is on experiences of leading experts from academia and industry; (d) Student projects that stimulate creativity—the stress is on methods that educators could use to induce and accelerate the creativity of students in general. Finally, the article ends with selected pearls of wisdom that could be treated as suggestions for further elaboration