STRENGTHENING OF REINFORCED CONCRETE BEAM ELEMENTS USING ROD-FORM COMPOSITE MATERIALS

The paper emphasizes the advantages of using FRP (fiber reinforced polymer) materials for strengthening reinforced concrete structures. The results of experimental research on the effects of strengthened reinforced concrete beam elements exposed mainly to bending using FRP rod-shaped elements are presented. The load disposition (experimental setup) was in accordance with the "four point load" scheme, and the measurements were made using modern measuring techniques. The results regarding the increase in the bearing capacity of strengthened beams using the NSM (near surface mounting) and EB (externally bounding) methods were compared. In particular, the load-deflection ratio until failure was analyzed, as well as the change in stiffness depending on the load level. It has been shown that the load capacity of beams strengthened with carbon fiber rods (NSM CFRP) increases by 89%, and the load capacity of beams strengthened with glass fiber rods (NSM GFRP) by 73%. The bearing capacity of beams strengthened with EB CFRP laminates increases by 51%. The ductility of strengthened beams was analyzed and it was shown that it is higher when using GFRP rod-shaped elements (DI=6.5) compared to CFRP rods (DI=5.3). The ductility of the beams strengthened by the EB CFRP method was not satisfactory (DI=2.6)

Unique function for describing stress and strain behaviour of fire-affected concrete

U radu je predložena jedinstvena analitička funkcija za aproksimaciju EC2 krivulja koje opisuju ovisnost naprezanja i deformacije betona na temperaturama u požaru. Na osnovu predložene funkcije dobivena je familija krivulja koje se razlikuju samo po vrijednosti jednog parametra - maksimalne temperature pri požaru. Prikazani su numerički eksperimenti kojima je dokazano da se jednom funkcijom može opisati ponašanje betona u požaru i predloženi su smjerovi daljnjih istraživanja.A unique analytic function for the approximation of EC2 curves describing dependence of stress and strain of concrete at fire-generated temperatures is presented n the paper. The proposed function enables generation of a family of curves differing only in the value of a single parameter - maximum temperature during fire. Numerical experiments demonstrating that fire behaviour of concrete can be described with a single function are presented, and directions for further study are proposed

Comparative analysis of limit bearing capacity of a continuous beam applying the limit and shakedown analysis depending on the character of the load

Primjenom poučaka analize granične nosivosti moguće je odrediti granično opterećenje linearnih sustava izloženih opterećenju koje se proporcionalno povećava dok ne dođe do loma. U slučaju kada su nosivi sustavi izloženi ponovljenom opterećenju, postavke granične analize ne daju odgovarajuća rješenja. Zbog toga su simultano razvijeni adaptacijski poučci koji su omogućili sigurno određivanje graničnog opterećenja. U ovom je radu određeno opterećenje loma kontinuiranog nosača s dva polja, primjenom statičkog i kinematičkog poučka granične analize i metode adaptacije. Pokazana je također razlika između vrijednosti sila loma ovisno o karakteru opterećenja i vrijednosti raspona nosača da bi se procijenila opravdanost primjene metode adaptacije u analizi granične nosivosti nosača.Applying the theorems of structural limit analysis it is possible to determine the limit load of linear systems exposed to load which increases proportionally until the formation of failure mechanism. In the case when beam systems are exposed to repeated load, the limit theorems do not yield the adequate solutions, thus the adaptation theorems which made safe limit load determination possible were developed simultaneously. In this paper, applying the static and kinematic theorem of limit and shakedown analysis, the failure load of continuous beam with two spans has been determined. Also displayed is the difference between the values of failure forces depending on the character of load and the beam span value in order to assess justification for application of the shakedown method in the analysis of the limit bearing capacity of the beams

A NEURAL NETWORK APPROACH FOR THE ANALYSIS OF LIMIT BEARING CAPACITY OF CONTINUOUS BEAMS DEPENDING ON THE CHARACTER OF THE LOAD

Being a part of civil engineering, limit state analysis represents a structural analysis with a goal of developing efficient methods to directly estimate collapse load for a particular structural model. As a theoretical foundation, limit state analysis uses a set of bound (limit) theorems. Limit theorems are based on the law of conservation of energy and are used for a direct definition of the limit state function for failure by plastic collapse or by inadaptation. This study proposes an artificial neural network (ANN) model in order to approximate the residual bending moment, limit and the incremental failure force of continuous beams. The neural network structure applied here is a radial-Gaussian network architecture (RGIN) and complementary training procedure. This structure is intended to be used for civil engineering purposes and it is demonstrated on the example of the two-span continuous beam loaded in the middle of the span that the limit and the incremental failure force can be obtained using neural network approach with sufficient precision and is especially suitable in analysis when some of the model parameters are variable

Knowledge and Perception of Secondary School Students in Belgrade about Earthquakes as Natural Disasters

The aim of this quantitative research is to determine the perception and actual knowledge of secondary school students in the Belgrade region with respect to earthquakes as a natural disaster and security threat, and to identify the factors that influence their knowledge and perceptions. The authors used a method of surveying students to identify and describe the factors that influence student knowledge and perceptions about earthquakes. For the purpose of this research, a sample of 3,063 students was drawn from the total population of secondary school students in Belgrade (65,561 students), which equates to 4.67% of the population. The results show that the sources of information on natural disasters and their threatening consequences influence the perceptions of secondary school students. In view of the evident lack of education about natural disasters in Serbia, the results of this study can be used when creating a strategy for educational programs. This research is the first step in developing and realizing a future strategy for natural disaster management by informing and including public (school population), scientific, and administrative communities in the process

A novel approach for vibration analysis of fractional viscoelastic beams with attached masses and base excitation

The Galerkin method is widely applied for finding approximate solutions to vibration problems of beam and plate structures and for estimating their dynamic behavior. Most studies employ the Galerkin method in the analysis of the undamped systems, or for simple structure models with viscous damping. In this paper, a novel approach of using the Galerkin method and Fourier transform to find the solution to the problem of vibration of fractionally damped beams with an arbitrary number of attached concentrated masses and base excitation is presented. The considered approach is novel and it lends itself to determination of the impulse response of the beam and leads to the solution of the system of coupled fractional order differential equations. The proposed approximate solution is validated against the exact solution for a special case with only one tip mass attached, as well as against the Finite Element Method Solution for a special case with classical viscous damping model. Numerical analysis is also given, including the examples of vibration analysis of viscoelastic beams with different fractional derivative orders, retardation times, and the number, weight and position of the attached masses

DOI: 10.2298/FUACE0801075M LIMIT ANALYSIS OF BEAMS UNDER COMBINED STRESSES UDC 624.072.2:624.04201(045)=111

Abstract. The problem of the determination of limit bearing capacity of beam cross section under pure bending, eccentric tension, pure shear, as well as combined stress is considered in this paper. The influence functions of the bending moment and axial force, as well as the bending moment, axial and shear force on the cross section limit bearing capacity in case of rectangular and I beam cross section are derived

Otkrivanje oštećenja određivanjem dinamičkih karakteristika

The change of dynamic parameters (stiffness, damping), as a consequence of structural history (erosion, friction, fatigue, internal damages and cracks), has an impact on decrease of reliability and serviceability of a structure or, drastically, causes its collapse. Having in mind that structural damage is small or embedded in the system, hence the detection cannot be done visually, one useful non-destructive procedure for damage determination by dynamic parameters evaluation - vibration monitoring of the structure.Promene dinamičkih karakteristika (krutosti, prigušenja) kao posledice istorije konstrukcije (erozija, trenje, zamor, unutrašnja oštećenja i prsline) utiču na smanjenje pouzdanosti konstrukcije kao i na njenu upotrebljivost ili, u najgorem slučaju, mogu dovesti do njenog kolapsa. Imajući u vidu da je oštećenje konstrukcije malo ili unutar sistema, stoga ne može biti detektovano vizualno, u radu je predložen koristan ne-destruktivan postupak za određivanje oštećenja preko dinamičkih parametara - monitoring vibracija konstrukcije

Otkrivanje oštećenja određivanjem dinamičkih karakteristika

The change of dynamic parameters (stiffness, damping), as a consequence of structural history (erosion, friction, fatigue, internal damages and cracks), has an impact on decrease of reliability and serviceability of a structure or, drastically, causes its collapse. Having in mind that structural damage is small or embedded in the system, hence the detection cannot be done visually, one useful non-destructive procedure for damage determination by dynamic parameters evaluation - vibration monitoring of the structure.Promene dinamičkih karakteristika (krutosti, prigušenja) kao posledice istorije konstrukcije (erozija, trenje, zamor, unutrašnja oštećenja i prsline) utiču na smanjenje pouzdanosti konstrukcije kao i na njenu upotrebljivost ili, u najgorem slučaju, mogu dovesti do njenog kolapsa. Imajući u vidu da je oštećenje konstrukcije malo ili unutar sistema, stoga ne može biti detektovano vizualno, u radu je predložen koristan ne-destruktivan postupak za određivanje oštećenja preko dinamičkih parametara - monitoring vibracija konstrukcije