Scientific papers

The analysis of footbridge vibrations induced by pedestrian traffic

Authors: M.Sc.C.E. Sara PircFaculty of Civil Engineering University of Zagreb

                 B.Sc.C.E. Petra Mužic, Faculty of Civil Engineering University of Zagreb 

This paper analyses the impact of pedestrian traffic models on the dynamic behavior of
pedestrian bridges. Experimental dynamic tests were conducted on the truss bridge at the Faculty of
Civil Engineering in Zagreb.
After the dynamic characteristics of the bridge were acquired, a numerical model that defined a
time function of pedestrian movement was made. By comparing results of this test with the numerical
model ones, it was confirmed that the applied “Time history” method used for calculations, as well as
numerical model, were valid. Load model entails an activity that varies in time and space, which
means that it changes its position according to a certain function of time.
In further analysis, the confirmed models of pedestrian load and calculations of dynamic behavior
were applied with the “Time history” method on two common static systems used in the construction
of bridges - beam and suspension systems. By setting different variants of construction elements and
changing the conditions of support, it was established that there was a difference in accelerations on
the vibrating bridge structure.
The comparison of dynamic response values led to a conclusion that a particular construction
solution would be suitable to decrease vibrations.

ASSESMENT OF APPROACH STRUCTURE AND PIERS OF ST. ANDREA'S BRIDGE IN NOVI SAD

Authors: Bukvić, O., Milošević, O., Božulić, I., Arsić, D., Pijanić, I. 

                  Faculty of Technical Sciences University of Novi Sad

The paper presents the assessment of approach structure and piers of St. Andrea’s bridge in Novi Sad, conducted in order to determine the degree of capacity, stability, durability and serviceability of the bridge structure, as a very significant part of the transport infrastructure. St. Andrea’s bridge is a road bridge on the Danube-Tisa-Danube canal. It was built in 1964, and made of prestressed and reinforced concrete, according to valid regulations from that period (Temporary technical regulations for concrete and reinforced concrete). Detailed visual inspection showed characteristic defects and damage of the available part of the structure (the approach structure and bridge piers), as well as the causes of their occurrence. The analysis of the collected data is shown, as well as the results of non-destructive testings of the built in materials, which indicates that it is necessary to perform structural repair of the object.

T Stub Macro Components of Beam to Column Connections Following the Loss of a Column

Author: Ivana Tadić, Faculty of Civil Engineering University of Belgrade

Accidental loadings such as fire, explosions, impacts or consequence of human error, may
easily cause failure of the elements exposed or located in the vicinity of the hazard; therefore,
assessment of the structural over strength is critical for structural engineers to ensure a certain
level of security and validate alternative loading paths. The need is to prevent
disproportionate or progressive collapse which is defined as a phenomenon causing entire
structure or large part of it to collapse due to the local failure of a structure. First studies and
research works dedicated to mentioned structural problems started after the collapse of Ronan
Point apartment in 1968 leading to the development of concept of robust design of structures.
Robustness is described as an ability of a structure to withstand disproportionate collapse
because of accidental loadings. In order to achieve endurance of the structures under extreme
loadings primary importance is in structural elements, continuity between elements as well as
ductility of elements and their connections [7]. Several structural collapse incidents indicate
that failure usually started from beam to column joints when exposed to abnormal loads.
Beam to column connections represent one of the essential parts required to be investigated
and evaluated in order to control the robust resistance and provide enough strength, stiffness
and ductility. If bolted connections are not design for these special loading conditions it is
most probably to happen the failure without allowing any redistribution of loads [2]. The
thesis work focuses on examination and evaluation of macro components of T-Stub elements
in bolted beam to column connections, their ultimate capacity and ductility under monotonic
loads through large deformation demands. However, connection ductility capacity
characterisation often remains problematic, usually requiring the development of challenging
finite-element models [2]. Extensive experimental studies were used to identify ultimate
strength and deformation capacity and the data was used to validate numerical models and
employed in a parametric study on two main parameters, distance between the bolts and endplate thickness. The goal is to give conclusions in beam to column connections behaviour in
order to contribute designing higher resistance joints and global integrity of structures.

COMPARATIVE ANALYSIS OF DIFFERENT OUTRIGGER STRUCTURAL SYSTEM VARIANTS IN A HIGH RISE BUILDING

Author: M. Sc. Ivan Hafner, Faculty of Civil Engineering University of Zagreb

The research topic for this thesis is the comparative analysis of different variants in placing
the outrigger trusses throughout the height of the building and how this placement and their
number effect the behaviour of the building itself. The main purpose of the outriggers is the
reduction of the overturning moment in the core of the building, so that will be the main
parameter used in the comparison of different building variants. Besides the overturning
moment, the most important parameters are the horizontal displacement at the top of the
building and the interstorey drift due to the same load combination. The last factor to take in
consideration is the steel consumption in outrigger construction. Based on the analysis of
eight different models using the SciaEngineer 2011 software, a conclusion was reached that
the placement of outrigger trusses on multiple locations throughout the height of the building
is a more efficient solution then the usage of more outrigger trusses on less locations. On
the other hand, the complexity of the outrigger construction in multiple locations must be
taken in consideration. In the upcoming sections these results will be explained in detail.

Structural design of a diagrid structural system high rise building in Zagreb

Author: M. Sc. Karlo Ožić, Faculty of Civil Engineering University of Zagreb

The idea behind choosing design of a diagrid structural system in a high rise building as the thesis is the effectivness and uniqueness, despite its complexity. It is a system that combines high structural efficiency and great aesthetic value. Diagrid system forms a grid of diagonal elements on the outside perimeter of the building. Diagonalized applications of structural steel members for providing efficient solutions both in terms of strength and stiffness are not new, but applications in a system without vertical column is something not commonly used. In diagrid tall buildings with no vertical columns, the diagonals carry not only shear and moment caused by lateral loads but also vertical gravity loads, utlizing mainly axial rigidity of members. Diagrid structures can be configured with any angle(s) to meet both architectural and structural requirements. The basic unit in diagrid is the triangle diagrid module which is defined by the angle of diagonal elements, height of the floor and number of floors that are included in one diagrid module. The second reason behind choosing this system is to bring it closer to our regional practice because it is already well known to the rest of the world. Diagrid constructions are impressive and attractive from both architectural and structural point of view and can emphasize nations prosperity and competence of its engineers. In this work, through the construction modelling in SCIA Engineer, utilizing 2nd order theory excellent results in terms of horizontal displacements and interstory drift are shown, as well as economical benefits for this structural system.

DESIGN OF FREE CANTILEVER BOX GIRDER BRIDGE ACROSS ČIKOLA RIVER

Author: M.Sc.C.E. Matija Adaković, Faculty of Civil Engineering University of Zagreb

 The role of this bridge is for crossing Čikola river and canyon. According to its span, this bridge belongs to the medium span bridges category, but according to the method of building it is considered as a serious engineering task because of the length of cantilever. Model and static design were made in software "SOFiSTiK". Because of the free cantilever method, it is required to design and fullfill ultimate limit states and service limit states during all of the construction stages and bridge service. Box girder section is prestressed in two phases, during construction and before traffic opening. Based on the design results, technical drawings, formwork assemblage plan and disposition of tendons for both phases of prestressing were made.

Fractals and their biomimetic application in structural engineering

Author: B.Sc. Dušan Arsić, Faculty of Technical Sciences University of Novi Sad

This paper is concerned with fractals and their implementation in structural engineering. In the paper, we first deal with the term fractals and their short historical development. Fractals in nature and their use in technology are then shown. The second part of the paper is based on the analysis of fractal wood. The term is explained and the basic parameters are defined. The analyzes were approached in two ways: analytical and numerical. In the analytical part, the directions of the main stiffness of each point and this stiffness are obtained. Also, the ellipse of the displacement of each point is obtained and the formula for the position of the center of mass is given. In the numerical part, we dealt with modal frequencies of fractal structures, the oscillation localization was noticed, and the previous assumption about the relations of modal frequencies was verified.