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Faktori koji doprinose kašnjenju projekta iz perspektive izvođača radova: studija slučaja - građevinski projekti putne infrastrukture u Srbiji
Get PDFInfrastrukturni projekti su kapitalni projekti koji su veoma složeni u pogledu obima,
trajanja i velikog broja učesnika. Prema postojećim studijama, prekoračenje vremena
građevinskih projekata je jedan od najčešćih problema. Cilj ovog istraživanja je da se
identifikuju uzroci kašnjenja u cilju razvoja mera za ublažavanje ili otklanjanje
potencijalnih rizika i uspešnog završetka projekta u planiranom roku. Da bi se postigao
definisani cilj, sprovedeno je empirijsko istraživanje kako bi se identifikovali glavni
uzroci kašnjenja na projektima putne infrastrukture iz perspektive izvođača radova.
Anketa je obuhvatila 53 uzroka kašnjenja grupisanih u 8 kategorija. Ukupno 35 izvođača
je učestvovalo u empirijskom istraživanju. Rezultati su pokazali da su najčešći uzroci koji
prouzrokuju prekoračenje vremena problemi sa projektnom dokumentacijom i tenderske
procedure. Doprinosi ovog istraživanja mogu biti od koristi u cilju poboljšanja
vremenskih performansi na projektima putne infrastruktur
Vibration serviceability assessment of a stress-ribbon footbridge
Get PDFWith 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
Modelovanje Etveševog tenzora primenom normalnog polja potencijala teže i digitalnih modela terena
Get PDFПредмет овог рада је истраживање могућности моделовања градијената убрзања теже
Земље, елемената тзв. Етвешевог тензора. Анализирани концепт подразумијева
моделовање које се врши без коришћења било каквих резултата гравиметријских или
сличних мјерења. Умјесто тога, модел се искључиво ослања на директно моделовање
утицаја маса тијела Земље. Масе су подијељене на три дијела, масу нормалне Земље,
топографске масе и масе између геоида и елипсоида. Утицај масе нормалне Земље
срачунат је на основу нормалног поља и других извода нормалног потенцијала теже,
док су друга два сегмента моделована њиховом дискретизацијом и апроксимацијом
помоћу призми као правилних геометријских тијела. У ту сврху коришћени су
дигитални модели терена и званични модел квазигеоида, као и глобални
геопотенцијални модели.
Практично истраживање спроведено је за територију Србије. У директној провјери
модела, срачунати градијенти су упоређени са резултатима мјерења торзионом вагом
у полигону код Новог Сада. За стандардно одступање градијената добијене су
вриједности од 15 E – 20 E, односно
1.5 Gal/m - 2 Gal/m
. Вертикални градијенти су
тестирани на основу мјерења широм Србије, те је утврђено стандардно одступање од
око 230 E. За све градијенте срачунате су и вриједности из глобалног геопотенцијалног
модела, те је утврђено да на изразито равничарском терену имају исту или бољу
сагласност са мјерењима у односу на вриједности из модела.
Модел је тестиран и посредно, у оквиру гравиметријког полигона у Бору, рачунањем
компоненти одступања вертикала из моделованих градијената. Ове вриједности
упоређене су са компонентама оцијењеним из званичног модела квазигеоида.
Установљена је врло добра сагласност оцијењених компоненти са познатим, уз
стандардно одступање мање од једне лучне секунде по компоненти. На основу ових
резултата извшена је оцјена тачности градијената, те су за њихова стандардна
одступања добијене вриједности од 30 E – 40 E.
Добијени резултати су показали да је примјеном предложеног концепта могуће
остварити тачност моделовања градијената на нивоу тачности мјерења, или за један
ред величине мању. На крају су дата додатна запажања о оствареној тачности и
потенцијалним изворима грешака, као и препоруке за даља истраживања и
унапређење модела.The subject of this thesis is research into the possibility of modeling Earth’s gravity gradients, the elements of the so-called of the Eöetvös tensor. The analyzed concept implies modeling that is performed without using any results of gravimetric or similar measurements. Instead, the model relies exclusively on forward modeling of the effects of the Earth's masses. The masses are divided into three parts, the mass of the normal Earth, the topographic masses and the masses between the geoid and the ellipsoid. The influence of the mass of the normal Earth was calculated on the basis of the normal gravity field and second derivatives of the normal gravity potential, while the other two segments were modeled by their discretization and approximation using prisms as regular geometric bodies. For this purpose, digital terrain models and the official quasigeoid model, as well as global geopotential models, were used.
Practical research was conducted for the territory of Serbia. In the direct verification of the model, the calculated gradients were compared with the results of torsion balance measurements in the polygon near Novi Sad. For the standard deviation of the gradients, values of 15 E - 20 E were obtained, that is, . Vertical gravity gradients were tested based on measurements across Serbia, and a standard deviation of about 230 E was determined. For all gradients, values from the global geopotential model were also calculated, and it was determined that on extremely flat terrain they have the same or better agreement with measurements compared to modeled values.
The model was also tested indirectly, within the gravimetric polygon in Bor, by calculating the vertical deflections components based on modeled gradients. These values were compared with the components estimated from the official quasigeoid model. A very good agreement of the evaluated components with the known ones was established, with a standard deviation of less than one arcsecond per component. Based on these results, the accuracy of the gradients was evaluated, and values of 30 E - 40 E were obtained for their standard deviations.
The obtained results showed that by applying the proposed concept, it is possible to achieve the accuracy of modeling gradients at the level of measurement accuracy, or one order of magnitude lower. At the end, additional observations are given about the achieved accuracy and potential sources of errors, as well as recommendations for further research and improvement of the model
Properties of Green Self-Compacting Concrete Designed by Particle Packing Density Method
Get PDFSince depletion of natural resources and the amount of construction and demolition waste have overcome the socially and environmentally acceptable level, the construction industry must address this issue and reduce its impact on the environment. A step towards sustainability in the construction industry is the application of recycled aggregates and supplementary cementitious materials as integral components of concretes, which provides conserving natural aggregates and waste reduction. This study adopts a holistic approach to producing green self-compacting concrete with the highest portion of recycled aggregate as a replacement for natural aggregate and fly ash as filler. Based on the particle packing density method, four series of self-compacting concrete were prepared: the first series was made with natural fine and coarse aggregate, the second series was made with fine natural aggregate and recycled coarse aggregate, the third with 50 % (by mass) of fine natural aggregate replaced by recycled fine aggregate and recycled coarse aggregate, and the fourth series completely with recycled fine and coarse aggregate. The content of fly ash remained constant. Regardless of the expected decrease of workability in a fresh state with the increase of the recycled aggregate content, all series exceeded the requirements set for the hardened structural concrete
Development of the Apparatus for In Situ Testing of Solar Panel Racking Anchors
Get PDFIn certain cases, solar panels are placed on suitable structures that are supported on the ground,
and this includes the appropriate dimensioning of anchor supports, i.e. suppor elements, within the
framework of the concrete construction project. Bearing in mind the great variations in soil qualiy
and different ambient conditions that depend on the location, different ways of dimensioning have
been developed, from experiential, through those defined based on soil conditions and theoretical
models, and to numerical ones characterized by the appropriate degree of accuracy. The paper
presents the principle of in situ testing of the load capacity of trial anchors using specially
developed apparatus, in order to check the designed conditions and possible correction of this part
of the construction project
A landslide data base model for ClirTheRoads project in Serbia
Get PDFWithin the project Mainstreaming Climate Resilience in the Road Transportation Management in Serbia (CliRtheRoads), a complex software solution was developed to support Public Enterprise Roads of Serbia in climate change adaptation planning and management. The software solution comprises 1) web portal for data entry and management for authorised users 2) publicly available web GIS part 3) mobile GIS application and 4) back-end database (Figure 1). In order to store and process the data collected during field visits and surveys, the data base developed in project first phase (Valjevo test area), was modified to include new datasets and to store new datatypes (as floods), and new modules (as activity cost) for Kraljevo test area. Both test areas have been chosen due theirs diversified characteristics, many climate related hazards, and the fact they suffered greatly from disasters recently (Abolmasov et al. 2017, Abolmasov et al. 2021). The database was upgraded to new model aimed for maintaining legacy data from both test areas, but also for future infrastructure resilience projects based on same approach, to enable
that all data will be stored and mapped in a unified manner. The data model include 1) main concepts (entity types) for the instabilities, with detailed data comprising common and specific attributes, 2) storage of multimedia (mainly photo from field work, but possible video as well), 3) knowledge base with cost of activities, including catalogue per each entity type with job type and description, unit and total price, maintenance type (regular maintenance, rehabilitation, urgent maintenance), including recommending activities (system allow user to add specific activities, description and cost that is further calculated and aggregated with other data); 4) secondary data from other sources (other projects, legacy data and external resources), or from interpreted data. The data was stored in the PostgreSQL Database, a web application was developed (using PHP) to facilitate data input, maintain knowledge database and calculate cost of recommended activities. There is a total of 461 records with fully described instabilities (slides, falls, topples, flows), documented by large number of photographs from the field. Additionally, every record is supplemented by engineering solution to support field engineers or decision makers for better road management in climate changing conditions
A note on r-circulant matrices involving generalized Narayana numbers
Get PDFIn order to further connect structured matrices and integer sequences, r-circulant matrices involving the generalized Narayana numbers are considered. Estimates for spectral norms bounds of such matrices are presented and their eigenvalues are determined. Moreover, the conditions under which the circulant matrix and the skew circulant matrix involving generalized Narayana numbers are invertible are given. In particular, it is shown that every circulant matrix with Narayana numbers is necessarily invertible
Experimental and numerical study of structural damping in a beam with bolted splice connection
Get PDFThe objective of this research is to develop a numerical model of one widely used bolted beam splice connection
that dissipates energy through structural damping. The reference experimental setup is carefully designed to
obtain the highly nonlinear dynamic response due to the suddenly released load. The fact that the monolithic
beam with welded connection has a linear response is utilized for the initial calibration of the numerical and
experimental models. Then, the numerical model of bolted beam splice connection is verified and adopted
through an iterative process. The influences of time and spatial integration, bolt load application, element
type, contact formulation, bulk viscosity, and mass scaling are discussed. A special attention is given to the
load application and load release functions. After the verification, the Abaqus/Explicit numerical model is
validated through the comparison with experimental data, where an appropriate friction coefficient is adopted.
It is demonstrated that the nonlinear structural damping occurs due to the complex micro slip behavior at the
contact interface
Concrete modeling in finite element push-out test simulations
Get PDFPush-out tests are commonly used to investigate the shear performance of mechanical connectors
applicable in steel-concrete composite beams. These tests can be complemented by numerical finite element simulations to reduce the need for extensive experimental testing. After validation against experimental results, numerical models could be used for additional analysis and parametric studies. The development of finite element models of push-out tests requires special attention to be put on modelling concrete behaviour, especially if concrete failure is the dominant failure mode. The concrete damage plasticity (CDP) models, combining plasticity and damage mechanics to represent the nonlinear behaviour of concrete, are commonly applied. This paper summarises and presents four different CDP models that have been successfully used by researchers in finite element simulations of push-out tests. The applicability of different models has been discussed in the specific case of shear connection with headed studs in profiled steel sheeting with a varied angle between profiled sheeting ribs and the beam. Results of comparative analysis are presented, indicating a significant influence of the applied CDP model on the response of push-out specimen. The best match between experimental and numerical results is accomplished by implementing the material model proposed by Pavlović with calibrated input parameters. Nevertheless, the applicability of each CDP model depends on the specific problem that is being analysed and therefore should be carefully approached
Hardened properties of 3D printed concrete - experimental investigation
Get PDFAt the end of the last century, 3D printing of concrete became an innovative method for producing
concrete structures. The beginning of the application of 3D printing in the concrete construction industry is referred to the Contour Crafting printing method. In addition to Contour Crafting, other methods such as Fused Deposition Modeling, Shotcrete 3D Printing, and ink printing method, developed and utilized
by D-Shape, have been applied in this field. Through the use of these technologies, numerous structures
have been successfully created, including one-story and multi-story houses, residential buildings,
pedestrian bridges, as well as individual elements like columns, walls, facade panels and outdoor
furniture. However, the wider implementation of this technology has revealed various challenges, such
as the lack of regulations and standards for the production and testing of these concrete materials as well
as the structural analysis of 3D printed structures.
The topic of this research is the investigation of the hardened properties of 3D printed concrete. The
focus is on the physical and mechanical properties such as the bulk density of concrete, compressive
strength, flexural strength and interlayer bond strength. This paper gives an overview of previous
research on these properties, while the experimental part gives insight into the results of own research.
Two types of specimen processing were used: full-notch removal (series 1) and printed samples (series
2). Additionally, samples with four or six layers were analyzed.
The obtained values for bulk density were 1964.46 kg/m³ for full-notch removal samples and 1859.62
kg/m³ for printed samples. The compressive strength was 25 MPa for perpendicular and lateral
directions, while the bending strength was 5.57 MPa. A significant influence of layering on fracture
patterns and results was observed during the bond strength testing. The obtained values ranged from
1.59 to 2.91 MPa, the lowest value was obtained in the axial tension test, while the highest value was
achieved in the shear test. The highest uniformity of results was achieved for series 1 samples tested in
axial tension and splitting tests