Davor Grandić

Evaluation of torsional stiffness in beam and slab bridge decks based on load testing

In this paper, evaluation of torsional stiffness in beam and slab bridge deck elements is presented. A beam and slab bridge decks structurally behave as a grillage. A grillage has an efficient transverse load distribution due to transverse asymmetric load. In the case of bridge deck without transverse beams in the span, transverse load distribution depends on the torsional stiffness of longitudinal beams, transverse beams over the. supports and deck slab. The results of load testing conducted on series of bridges in Croatia is compared with results obtained on different numerical grillage models in which torsional stiffness of main structural elements was varied. Five different numerical models for each tested bridge is used. To evaluate torsional stiffness of main structural elements of the bridge the transverse distribution coefficients are introduced. The design value of the coefficients of torsional stiffness reduction for verification of the serviceability limit state (SLS), with assumption of normal probability distribution is determined. The same coefficient is calculated using recommendation for torsional stiffness reduction in concrete elements defined by Model code CEB-FIB 1990 (MC 90). According to conducted analyses the design value of the coefficient of torsional stiffness reduction for verification of the serviceability limit state of main structural elements of beam and slab bridge deck is proposed.

The Guidelines for Modelling the Preloading Bolts in the Structural Connection Using Finite Element Methods

The aim of this paper is the development of the two different numerical techniques for the preloading of bolts by the finite element method using the software Abaqus Standard. Furthermore, this paper gave detailed guidelines for modelling contact, method for solving the numerical error problems such as numerical singularity error and negative eigenvalues due to rigid body motion or the problem of the extensive elongation of bolts after pretension which is occurring during the analysis. The behaviour of bolted joints depending on the two different approaches of pretension was shown on the example of an extended end-plate bolted beam-to-column connection under the monotonic loading. The behaviour of beam-to-column connection was shown in the form and moment-rotation ( - ) curves and validated by experimental test. Advantages and disadvantages of pretension techniques, as well as the speed of numerical models, were also presented in this paper.

Experimental and Numerical Study of Mild Steel Behaviour under Cyclic Loading with Variable Strain Ranges

To simulate the effect of variable strains on steel grades S275 and S355, an experimental displacement control test of plate specimens was performed. Specimens were tested under monotonic and cyclic loading according to the standard loading protocol of SAC 2000. During experimental testing, strain values were measured with an extensometer at the tapered part of the specimen. Strains obtained by the experimental tests are disproportional to the applied displacements at the ends of the specimens. This phenomenon occurs due to the imperfections of the specimen, hardening of the material, and the buckling behaviour that appears in real structures due to the high deformation experienced during earthquakes. Due to the relative simplicity and wide applicability of the Chaboche hardening model of steel, the calibration of hardening parameters based on experimental test results was conducted. For the first time, calibration of steel hardening parameters was performed following the Chaboche procedure to define the cyclic behaviour with variable strain ranges. The accuracy of the hardening model with variable strain ranges, which were simulated using ABAQUS software, was verified using the experimental results.

ODREĐIVANJE DINAMIČKOG KOEFICIJENTA NA MOSTOVIMA

U radu je, sa svrhom određivanja globalnog dinamickog koeficijenta mosta, koristen programski paket DARK kojim se može provesti dinamicki proracun ravninskih stapnih konstrukcija pod djelovanjem pokretnog opterecenja. Programom DARK mogu se, uz osnovne dinamicke karakteristike, izracunati dinamicki progibi, brzine i ubrzanja konstrukcije izložene djelovanju opterecenja koje se krece konstrukcijom. Primjena programa za određivanje globalnog dinamickog koeficijenta prikazana je na modelu mosta Drave u Osijeku. Uporabom navedenog programa određeni su dinamicki progibi mosta zbog prometovanja razlicitih kamiona razlicitim brzinama po mostu i uspoređeni sa statickim progibima od istih opterecenja, tj. određeni su dinamicki koeficijenti. Ovako određeni dinamicki koeficijenti uspoređeni su s normama i pravilnicima predviđenim koeficijentima.

Simplified procedure for maximum acceleration determination on simple bridge structures

A verification of the comfort criteria for serviceability limit state due to pedestrians should be done if the fundamental frequencies of the bridge deck are below values determined in bridge design codes. Nowadays, the comfort criteria is usually defined as maximum acceptable acceleration of any part of the bridge deck. Dynamic load models of single pedestrian and group of pedestrians are determined as single pulsating force moving along the bridge. Though the model of moving pulsating force is similar to real character of pedestrian loading (walking along the bridge) acceleration assessment is not simple because the lack of easily available software able to conduct dynamic analysis due to moving loads. The process of bridge designing can be significantly accelerated if a simplified procedure for maximum acceleration determination is established. In this paper an improved simplified procedure based on response of single degree of freedom oscillator i.e. response of a structure due to pulsating stationary force of unlimited duration is proposed.

Shear resistance of reinforced concrete beams in dependence on concrete strength in compressive struts

In the current European Code EN 1992-1-1 a truss model with variable inclination angle of concrete compressive struts with a quite wide range of inclination angle, from 21, 8 degrees to 45degrees, is intended for use for shear design of reinforced concrete beams. However, some researches and recommendations indicate special attention when choosing the lower bound of inclination angle of the concrete compressive struts, due to the reduced compressive strength of cracked concrete. This work reviews theoretical background and shear design methods of reinforced concrete beams. Relation of the shear resistance to crushing of the compressive struts as a function of their inclination angle has been investigated through a parametric study, where three different approaches have been used in order to limit stresses in the compressive struts. Based on the comparison of results from the analysis a recommendation for shear resistance calculation of reinforced concrete beams in dependence on concrete strength in compressive struts of the truss model is given.

Estimation of damage severity using sparse static measurement

AbstractA new structural damage estimation procedure using grey relation coefficient and curvature of displacement influence line in beams using sparse measurement is proposed in this paper. The method is based on static structural response which can be obtained using single sensor. determination of damage location as well as determination of corresponding damage severity can be easily calculated with simple arithmetic operations, which is the main advantage of the proposed method. Conducted numerical simulation for different damage scenarios and various measurement sparseness and experimental validation confirm the effectiveness of proposed damage severity estimation procedure.

ODREĐIVANJE PRORAČUNSKE ŠIRINE T-PRESJEKA POPREČNOG NOSAČA

In this paper an effective width of a T-beam cross section of transversal girder of underpass Vrata 1 is analyzed and valorized on the basis of field testing results and results of conducted calculations. The most common method used in ribbed bridge decks analysis is grillage analogy. Longitudinal and transversal girders, together with an effective part of a deck slab acts as T-shaped beams. Stiffness of longitudinal and transversal structural elements depends on effective width of the T-beams. The effective width of T-beams depends on several factors, among others it depends on the load applied on the bridge, which can vary in intensity and position. In this paper the effective widths of the T-beam of the transversal girder in the span are determined by using numerical calculation on finite element model for different load testing schemes. The effective widths of T-beam determined in this way are used for the calculation of deflection on a simple grillage models. Calculated deflections are compared with the corresponding measured deflection on underpass under test loading and deflections calculated on a simple grillage model in which the effective width of T-beam cross-section in the span is determined according to HRN ENV 19921-1.

Reinforcement Corrosion Rate in Cracked Areas of RC-Members Subjected to Sustained Load

The results of measuring the reinforcement corrosion rate of reinforced concrete beam and slab specimens subjected to sustained load are presented in this paper. Beam and slab specimens were subjected to corrosion of reinforcement under controlled conditions in an environmental chamber, where corrosion was initiated and accelerated in cycles of spraying with sodium chloride solution and drying the specimens. Cracks in concrete were caused by sustained load. During the experiment reinforced concrete samples were cracked, except near the supports, in area with small bending moments. A significant effect of increasing of corrosion rate due to presents of cracks was observed. The corrosion rates in uncracked areas of specimens were significantly smaller than in the cracked areas of the same specimens. The corrosion rate was measured by using galvanostatic impulse method. The measuring points were distributed along the beam and slab specimens. In this paper the influence of cracks on the time of initiation of corrosion and corrosion rate is analysed. Also, the relation between the measured values of the half-cell potential and corrosion rate is investigated. The results presented in the paper are part of the comprehensive experimental research.