CASE STUDY OF STRUCTURAL RELIABILITY OF EXISTING BUILDING

– Structural reliability of buildings has become an important issue after the collapse of a shopping centre in Riga 21.11.2013, caused the death of 54 people. The reliability of a building is the practice of designing, constructing, operating, maintaining and removing buildings in ways that ensure maintained health, ward suffered injuries or death due to use of the building. Evaluation and improvement of existing buildings is becoming more and more important. For a large part of existing buildings, the design life has been reached or will be reached in the near future. The structures of these buildings need to be reassessed in order to find out whether the safety requirements are met. The safety requirements provided by the Eurocodes are a starting point for the assessment of safety. However, it would be uneconomical to require all existing buildings and structures to comply fully with these new codes and corresponding safety levels, therefore the assessment of existing buildings differs with each design situation. This case study describes the simple and practical procedure of determination of minimal reliability index β of existing steel structures designed by different codes than Eurocodes and allows to reassess the actual safety level of different structural elements of existing buildings under design load

EXPERIMENTAL METHOD ON INVESTIGATION OF FIBRE REINFORCED CONCRETE AT ELEVATED TEMPERATURES

Generally speaking, adding a certain amount of steel fibres to a concrete mixture improves its mechanical properties. Currently, a lack of information considering tensile and post cracking behaviour of FRC at elevated temperatures is an issue to be faced. An experimental study of steel fibre reinforced concrete, also containing polymer fibres (FRC), subjected to high temperature is presented herein. Compressive strength, split tensile strength and ultimate bending strength were evaluated. Specimens were heated by the use of ceramic heaters and repacked for testing consequently. A finite-element based model was developed to predict the temperature distribution inside a specimen during both the heating and the cooling process

TO TESTING OF STEEL FIBRE REINFORCED CONCRETE AT ELEVATED TEMPERATURE

Addition of steel fibres improves properties of concrete. The lack of information considering tensile and post cracking behaviour of SFRC at elevated temperatures is an obstacle on the wide use of this composite material. This work presents an experimental study of steel fibre reinforced concrete subjected to high temperature. Compressive strength, split tensile strength and ultimate bending strength were evaluated. The specimens were heated by ceramic heaters and then repacked for testing

Decreasing displacements of prestressed suspension bridge

A suspension bridge is the most suitable type for a long-span bridge due to rational use of structural materials. Increased deformability, which is conditioned by the appearance of the elastic and kinematic displacements, is the major disadvantage of suspension bridges. The problem of increased kinematic displacements under the action of symmetrical and non-symmetrical load can be solved by the prestressing. A prestressed suspension bridge with span of 200 m was considered as an object of investigations. The cable truss with the cross web was considered as the main load carrying structure of prestressed suspension bridges and was compared with the single cable. The considered prestressed suspension bridge was investigated by the FEM program ANSYS 12 and by the small scale physical model. Rational, from the point of view of minimal vertical kinematic displacements, main load-carrying structure of prestressed suspension bridge was developed. The obtained results shows, that usage of cable truss with the cross web as the main load carrying structures of prestressed suspension bridge in comparison with the single cable, reduces vertical displacements upwards by 63.1%, downwards by 1.8% and total displacements by 29.6% under the action of worth situated load

Optimal design of rational fiber orientation for variable stiffness plywood-plastic plate – numerical and experimental investigations

The new optimization method of outer layer fiber directions and concentrations of plywood plate with glass fiber-vinyl ester resin outer layers are proposed. The method minimizes structural compliance. It consists of two phases. The fiber directions are optimized in the first phase and concentrations in the second phase. The increase of stiffness is about 30% of plate with optimized fiber direction and concentration comparing to similar non-optimized plate

Evaluation of rational parameters of combined stayed roof

Combined stayed roof with the span equal to 60 m is considered in the paper. The framework of the roof is formed by two groups of structural members, which are placed in longitudinal and transversal directions. The main girder and pylons, which form the main frame, just as suspenders are the members, placed in the longitudinal direction. Transversal frames, which are formed by the trusses and columns, are the members, placed in transversal direction. Structural steel S355 is considered as a materials of all rigid members – pylons, columns and girders. Three variants of materials for suspenders were considered. Steel cables with modulus of elasticity of 1.70٠105 MPa and tensile strength of steel wire of 1960 MPa were the first variant. Carbon fiber reinforced plastic (CFRP) with the modulus of elasticity of 1.65٠105 MPa, tensile strength of 2800 MPa and ultimate strain in tension of 1.8 % was the second variant. Hybrid composite element, consisting from steel, CFRP and Kevlar components with the volume fractions of 0.6, 0.2 and 0.2, correspondingly, was the last variant of suspenders. The dependences of material consumption and main geometrical parameters of combined stayed roof were obtained for three above mentioned variants of suspender materials. They were obtained on the basis of numerical experiment, which was carried out using the software LYRA 9.4. It was stated that the rational values of the number of suspenders, transversal frame bay and height of pylon are equal to 8, 6 m and 18 m, correspondingly

Analytical model of composite floors with steel fibre reinforced concrete slab subjected to fire

Under fire, membrane action plays an important role in the performance of slabs subjected to large deflections. In this paper, a new model is proposed based on a proper approximation of horizontal displacements for a simply sup­ported composite slab. The novelty of the proposed approach consists in a special treatment of the system of shape func­tions for the “in-plane” displacements. Moreover, a load applied to the slab is divided into two components, so that one component is balanced by the membrane forces, while the second one is transmitted by the bending forces (including transfer of shear and moment). The deflection due to thermal elongations is replaced by the identical deflection caused by a fictitious load. Unknown parameters are calculated using the principle of virtual displacements. The effectiveness of the model is validated by the results obtained from experiments. First published online: 25 Nov 201

Analysis of perforated web girder load bearing capacity

A steel beam with perforated steel web is a type of flexural members, which is characterized by the decreased materials consumption. Existence of holes in the web enables to simplify placement of communications on the other hand. The using of beams with perforated web with hot-rolled double-T cross-section as a girder of transversal frame of trees hothouse is analysed in the paper. The beams are considered under the action of design vertical load, consisting from dead weight of the roof and snow load. The value of design vertical load is equal to 28kN/m. The grade of steel was S235. The dependence between diameters of holes, distances between holes, height of the beams cross-sections and materials consumption was obtained on the basis of numerical experiment. The numerical experiment was conducted for the simple beam with the span equal to 12 m. The obtained dependence allows determining rational from the point of view of materials consumption diameters of holes, distances between holes and height of the beam, which were equal to 0.25 m, 1.03 m and 0.55m, correspondingly. The methodology for determination of coefficients of stress concentration was considered in the paper. The stress concentration factors were obtained by the FEM with the using of computer program ANSYS v14, the obtained results were also compared. It was stated that the difference does not exceed 2.34%

Hybrid composite cable for prestressed suspension structure

A prestressed suspension structure is a type of structures that allows covering long spans due to rational use of structural materials. Prestressing of a suspension structure allows minimizing cinematic displacements. The prestressed suspension structure with the main span equal to 200 m was considered as an object of investigation. Replacement of a single steel main cable of the prestressed suspension structure by the hybrid composite cable with CFRP (Carbon Fibre Reinforced Polymer) middle layer and external steel layers with cross-section variable by the cable length considerably decreases dead weight of the cable. Hybrid composite cable ensures functioning of the structure in case of destruction of the middle CFRP layer. The considered prestressed suspension structure was investigated by the FEM software ANSYS. Rational steel distribution by the cable length was determined by optimization. Behaviour of the hybrid composite main cable in the case of destruction of the middle CFRP layer was experimentally tested using the physical model. The dynamic coefficient was obtained