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abstract. Currently, the bending resistance of composite steel and concrete circular beams and beam-columns may be analysed assuming the interaction between the steel shell and concrete core but ignoring the behaviour of the part of the concrete core in tension. Some natural and numerical experiments show that an influence of this part of the concrete core on the total value of bending resistance of a composite member may be rather important. Therefore, this paper presents the method developed for the design of hollow and solid concrete-filled steel tubular beams based on the test data. It takes into account an effect of the part of the concrete core in tension and gives a better agreement with test results than EC4 (EN 1994-1-1 2004). Also, the paper presents the results of carried out analytical, experimental and numerical investigations of the hollow centrifuged and solid concrete-filled steel tubular beams.

Article presents a priority determination and utility analysis of energy generation technologies; it was done with the help of AHP and COPRAS, mathematical multi-criteria methods, and the EGT-SELECT-DS, a decision support system based on these methods. The research results suggest that the assessment and choice of energy generation technologies using multi-criteria methods and DSS is a good way to combine the performance criteria, cost-effectiveness, and ecological integrity with the criteria of technological innovativeness, socially responsible operation and sustainable development. The main objective and novelty of the paper is developed MCDM DSS in which are aggregated two different methods.

The paper investigates the general buckling of an axially loaded column using the finite element method with different slenderness ratios of axes x-x and z-z. The paper deals with three different modes of buckling. The conducted numerical experiments have suggested correction factors and appropriate buckling modes of the built-up columns. The obtained modelling results were compared with data on analytical calculations made according to Lithuanian national codes STR and Eurocode 3. The FEM analysis of the builtup column has showed that both codes (STR and EC3) are giving safe enough results for a considered type of conditions for column support.