The use of lightweight concrete in timber-concrete composite structures for the purposes of reconstruction, upgrading, and strengthening has increasing application potential. The correct combination of mechanical properties of both materials can preserve the beneficial aspects of timber in tension and concrete in compression, while reducing the weight of the structure. This paper experimentally evaluated the slip modulus of screw connectors as one of the key issues in the structural design of these types of composite structures. The results of four groups of push-out tests, which were performed on composite samples, are presented. All of the samples had identical cross sections, but each group was made with a different lightweight concrete density class according to Eurocode 2. The obtained results were compared with the values recommended by Eurocode 5. The analysis showed that the code recommendations yielded slip modulus values that were considerably higher than the ones obtained experimentally, which could lead to unsafe timber and lightweight concrete structures.

This paper presents an original contribution with assessment of the current state in exploitation safety and usability of thin concrete domes of the beauteous Subotica Synagogue, built in 1902. The authors are analyzing the condition of the materials used in the Subotica Synagogue, on extracted samples of concrete and steel reinforcement with a binder which was used instead of cement, a gypsum -CaSO4×0,5H2O. The source of the problem, according to the author, is the lack of limeCa(OH)2 from the mixture of gypsum and pozzolanic aggregates made of baked clay. This is the main reason for poor concrete strength of only 7.6 MPa and the present significant corrosion processes in the steel reinforcement of that concrete, which far from the recommended values of pH ≥ 12, have a measured value of only pH = 7.55. These results advise a need for repair of the part of the building that has not been analyzed or investigated yet, partially due to difficult access and also apparently good condition, since cracks, larger deformation or collapse have not appeared yet. The condensation on the domes is damaging the painted decorations with gilding which is falling and reduces the exploitation safety and the mood of the visitors and believers, who came to the synagogue. The authors are proposing a method for rehabilitation of the vaults and ribs of the beautiful Subotica Synagogue domes by simultaneously satisfying the exploitation safety and avoiding the occurrence of condensation and damaging of the painted and gilded ceilings. We believe that the article will inspire and have a positive effect in the professional and scientific society so in other synagogues in Europe and around the world the exploitation usability of vaults will be inspected and if necessary, possible repairs can be made in the same or any similar way as proposed in this scientific work.

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Today's procedures of design mix of fresh concrete mixtures do not allow for water mass (mw) to be calculated exactly but through approximation methods which include calculating the type of aggregate, demanded consistency (slump concrete) and the largest aggregate grain (Dmax). The other way demands that the water mass (mw) be read from a table which is based on the largest aggregate grain, aggregate origin and the demanded concrete of concrete subsidence. Hence, cement mass (mc) which is calculated based upon the aforementioned water mass (mw) is also approximate and, ultimately, the whole process is conducted in an approximate and not precise manner. According to the new method the authors are proposing, water mass is calculated precisely and in an exact manner in regard to the cement mass (mc) and the mass of all of the aggregate fractions (ma) in accordance with the projected or set granulometry. According to the new procedure, cement mass (mc), water mass (mw) and aggregate mass (ma) are calculated simultaneously in regard to the projected or set concrete class (C fck, cyl/fco, cube) and required concrete strength fk,28 through a set of three equations with cement mass (mc), water mass (mw) and aggregate mass (ma) being the unknowns in these equations. This precise procedure is a necessity in a chase for better structures that could be seen standing in all their glory 1000 or 2000 years from now, as we are seeing Egyptian, Roman and Chinese and structures standing today.

In this paper, a 1D dynamical model with substrate resistance was imposed with three frequencies of displacement amplitudes with two amplitudes with frequencies in the resonant region. If the external excitation is treated as a continuous periodic real function with two variables (the basic oscillation period-the first and the ratio of the frequency of the external excitation and the response of the model-the second) then we can present the final solution of the motion of the 1D model in conjugated complex form. Applying FFT algorithms with MathCAD, the treated displacement amplitudes in the frequency and time domains respect the mapping suggested by the transfer function (I.M.Miličić, 2015) and with a smaller number of order members. Computer simulations confirmed that the harmonic response of a 1D dynamic model system can be successfully modeled based on the equivalent solution which shown here.