Jure Radnić

Selection of the Method for Rehabilitation of Historic Bridges—A Decision Support Concept for the Planning of Rehabilitation Projects

ABSTRACT This article presents a decision support concept for management of rehabilitation projects. The focus of the research is on the application of multicriteria methods of decision-making in planning a historic bridge rehabilitation project. The problem addressed in this research is a major one from many different perspectives, such as civil engineering, economics, etc., which indicates a need for the evaluation of different rehabilitation methods using several different criteria. Therefore, a decision support concept for a historic bridge rehabilitation method based on the PROMETHEE method has been designed. Three groups of stakeholders have been included (civil engineering experts, economic experts, and government experts) to define appropriate criteria, their weights, and preference functions. For determination of criteria weights, the AHP method has been used. The model has been tested on the problem of choosing the rehabilitation method for the Pavića Bridge in Croatia.

Nonlinear Time-Dependent Analysis of Prestressed Concrete Shells

The numerical model for analysis of prestressed concrete plates and shells under short term and long-term static load are briefly presented. The model simulates the dominant nonlinear effects of concrete: the creep, shrinkage and aging, the development of cracks in tension and yielding in compression, and the changes in the tensile and shear stiffness in cracking zones. Reinforcing steel is modelled as a separate layer with anisotropic material properties i.e. with a possibility to transfer the stresses in the reinforcement bars direction only. Prestressing steel is simulated by 1-D curved element embedded in the shell finite element. A description of the tendon geometry, transfer of the prestressing effects from the tendon to the concrete, numerical modelling of the prestressing losses and the numerical procedure for analysis of the prestressing structures are briefly presented. The model is verified by comparison of the numerical results with the results of performed experimental test of prestressed concrete shell.

WYD method for an eigen solution of coupled problems

Designing efficient and stable algorithm for finding the eigenvalues andeigenvectors is very important from the static as well as the dynamic aspectin coupled problems. Modal analysis requires first few significant eigenvectorsand eigenvalues while direct integration requires the highest value toascertain the length of the time step that satisfies the stability condition.The paper first presents the modification of the well known WYDmethod for a solution of single field problems: an efficient and numericallystable algorithm for computing eigenvalues and the correspondingeigenvectors. The modification is based on the special choice of thestarting vector. The starting vector is the static solution of displacements forthe applied load, defined as the product of the mass matrix and the unitdisplacement vector. The starting vector is very close to the theoreticalsolution, which is important in cases of small subspaces.Additionally, the paper briefly presents the adopted formulation for solvingthe fluid-structure coupled systems problems which is based on a separatesolution for each field. Individual fields (fluid and structure) are solvedindependently, taking in consideration the interaction information transferbetween them at every stage of the iterative solution process. The assessmentof eigenvalues and eigenvectors for multiple fields is also presented. This eigenproblem is more complicated than the one for the ordinary structural analysis,as the formulation produces non-symmetrical matrices.Finally, a numerical example for the eigen solution coupled fluidstructureproblem is presented to show the efficiency and the accuracy ofthe developed algorithm.

Effect of the joint type on the bearing capacity of a multi–drum column under static load

ABSTRACT The results of an experimental study on the effect of the joints between the blocks on the ultimate bearing capacity of a multi-drum column loaded to centric vertical force and horizontal force in the middle of its height are shown. The column is approximately 2.5 m high, with one hinge at the top and another hinge at the bottom. Four types of joints between the blocks were considered: a dry joint (column C-DJ) and joints with stone powder (column C-SPJ), lead (column C-PBJ), and epoxy (column C-EPJ). The applied vertical and horizontal forces, horizontal displacement, vertical strains, and horizontal circumferential strains in the middle of the column height, as well as shortening of the column, were measured. Under axial compression, ratios between the ultimate load bearing capacities of tested columns were C-EPJ: C-DJ: C-SPJ: C-PBJ = 1: 0.68: 0.59: 0.51. The bearing capacity of the tested columns with regard to the horizontal force depended on the level of the applied centric compression force. Columns with soft joints (C-PBJ, C-SPJ) had the largest shortening and the largest horizontal displacements for the equal forces.

Numerical Model for Static and Dynamic Analysis of Masonry Structures

Firstly, the main problems of numerical analysis of masonry structures are briefly discussed. After that, a numerical model for static and dynamic analyses of different types of masonry structures (unreinforced, reinforced and confined) is described. The main nonlinear effects of their behaviour are modelled, including various aspects of material nonlinearity, the problems of contact and geometric nonlinearity. It is possible to simulate the soil-structure interaction in a dynamic analysis. The macro and micro models of masonry are considered. The equilibrium equation, discretizations, material models and solution algorithm are presented. Three solved examples illustrate some possibilities of the presented model and the developed software for static and dynamic analyses of different types of masonry structures.

Behavior of fiber reinforced mortar composites under impact load

This paper presents results of the experimental study on the behavior of plain and fiber reinforced cement mortars with different fibers under static and impact compressive load. Glass, polypropylene and carbon fibers were used in equal dosage by mass. The impact test was conducted using an impact tower with drop hammer, which represented the modification of the split-Hopkinson pressure bar system, with strain rates ranging from approximately 35 to 60 s-1. The results of the static test and impact test with two different drop heights were compared and discussed. Among other, it has been concluded that the tested fiber reinforced mortars had no greater static and impact strength compared to the plain mortar. Only their ductility was increased at both static and impact failure. Strengths and ductility of all composite specimens were similar, i.e. without the effect of fiber type. With the increase of strain rate, compressive strength is increased and ductility is decreased for all tested specimens.

Comparison of Developed Numerical Macro and Micro Masonry Models for Static and Dynamic Analysis of Masonry-infilled Steel Frames

First, the basic characteristics of macro and micro masonry models in numerical analyses of masonry structures are discussed. Afterwards, developed numerical macro and micro masonry models, intended for the nonlinear static and dynamic analysis of unreinforced and confined masonry walls, as well as of masonry-infilled frames, are briefly presented. The models are tested on previously performed experimental tests of masonry-infilled steel frame under horizontal static force and masonry-infilled steel frame on a shake-table. The precision of both models is compared. It is concluded that both numerical models can provide reliable results. However, the macro model has more advantages for wide practical application.

Numerical model for analysis of stress-ribbon bridges

U radu je prikazan razvijeni numericki model za analizu prednapetih provjesenih mostova opterecenih kratkotrajnim statickim, dinamickim i dugotrajnim opterecenjenjima i djelovanjima. Model simulira najvažnije nelinearne efekte ponasanja takvih konstrukcija, ukljucujuci nelinearno ponasanje gradiva, promjene geometrije konstrukcije, nastajanje konstrukcije u fazama, prednapinjanje i sl. Prikazana su osnovna rjesenja provjesenog mosta preko rijeke Cetine kod Zadvarja, te neki rezultati njegovog proracuna s pomocu razvijenog numerickog modela.

Stirrup effects on compressive strength and ductility of confined concrete columns

The results of experimental testing of stirrup effects on compressive strength and ductility of axially loaded confined reinforced concrete columns of rectangular cross-section are presented. Effects of different concrete strengths, different stirrup bar diameters and different stirrup spacing on columns bearing capacity and ductility have been researched.

Effect of the Shear Force on the Failure of Spatial Concrete Framework Structures

Firstly, the previously developed numerical model for static analysis of spatial concrete frame structures is briefly described. In this model, cross-sections of structural elements can be of arbitrary shape and formed by various materials, with arbitrary normal stress normal strain relations. This model only includes the effect of normal stresses on the structure failure. Here, it was improved by including the effect of shear forces on the failure of reinforced concrete beam elements. Shear bearing capacity of reinforced concrete section includes the concrete capacity, as well as the shear bearing capacity of longitudinal, transversal and inclined reinforcement bars. The developed numerical model and appropriate software were verified on experimental shear test of a concrete beams. Good agreement was obtained between the experimental and the numerical results. However, further verifications of the presented numerical model are needed.