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The paper presents fire design of composite steel-concrete slabs and a description of the use of the advantages o such a structure. Following the review of scientific literature on composite steel-concrete slabs, behaviour under fire temperature may confirm that this solution has no negative consequences for the construction of the building in fire. Profiled steel sheet is a very important building component, because it helps ensuring integrity and insulation properties. Such sheeting serves as a restraint preventing the spread of fire and hot gases, as well as protects the concrete from direct heat action not allowing its chipping off. Fire tests show that the construction of composite steel-concrete slabs without a protective coating under influence of fire is an important bracing frame provided by these conditions. In addition, it may be too conservative to establish the fire resistance coefficient for each element. Maybe it is not necessary to protect all load bearing steal elements in a building from fire, especially when they are in one setup with composite steel-concrete slabs. Fire protection methods make it possible for composite steel-concrete slabs to behave under a plastic bending moment allowing increased temperatures and distributing evenly in an element. The paper provides a brief description of methods for fire design. It analyzes the fire design method according to EN 1994-1-2:2005 regarding unprotected composite steel-concrete slabs exposed to fire from the bottom according to the standard temporary temperature curve. The paper provides an example of the calculation of composite steel-concrete slab according to described method without longitudinal reinforcement and the composite slab with longitudinal reinforcement. Results of calculations let to designate fire resistance of composite slab to heat isolation (I parameter) and the resistance value of the bending moment. Solutions for extra fire protection or increasing bending moment value depend on estimated results. [ABSTRACT FROM AUTHOR]

The article analyzes the optimization of grillage-type foundations seeking for the least possible reactive forces in the poles for a given number of poles and for the least possible bending moments of absolute values in the connecting beams of the grillage. Therefore, we suggest using a compromise objective function (to be minimized) that consists of the maximum reactive force arising in all poles and the maximum bending moment of the absolute value in connecting beams; both components include the given weights. The variables of task design are pole positions under connecting beams. The optimization task is solved applying the algorithm containing all the initial data of the problem. Reactive forces and bending moments are calculated using an original program (finite element method is applied). This program is integrated into the optimization algorithm using the "black-box" principle. The "black-box" finite element program sends back the corresponding value of the objective function. Numerical experiments revealed the optimal quantity of points to compute bending moments. The obtained results show a certain ratio of weights in the objective function where the contribution of reactive forces and bending moments to the objective function are equivalent. This solution can serve as a pilot project for more detailed design. [ABSTRACT FROM AUTHOR]

The article accurately describes the influence of water repellent and silane based concrete admixtures on the technological, physical, mechanical and porosity properties of fine - concrete specimens. To obtain the expected results by changing the amount and type of the silane based chemical admixture, six compositions of concrete slurries were designed using six cube shaped (70,7 x 70,7 x 70,7 mm) and six plate shaped (250 x 250 x 30 mm) specimens. In order to get technological, physical and mechanical properties of concrete (concrete slurry), tests on the rigidity of concrete slurries, compression, bending and splitting strength were performed. In addition, experiments on porosity, frost resistance and water penetration were conducted. On the basis of the obtained results and using different amounts and types of silane based chemical admixtures, the rigidity of concrete (Vebe test) decreased up to 1.78 times in respect to the control specimen. On the other hand, when applying the above introduced silane based chemical admixtures, the results show that the density of concrete specimens (70,7 x 70,7 x 70,7 mm and 250 x 250 x 30 mm) varies accordingly (in respect to control specimen) from -1.69% (using WACKER BS 1001 0.1% in respect to the amount of cement used) to 0.84% (using SILRES BS 290 0.2%) and from -2.03% (using WACKER BS 1001 0.1%) to 0.71% (using SILRES BS 290 0.2%). Bending strength (testing plate shaped specimens) has decreased by 27.4% (using SILRES BS 209 0.2%), compression strength (testing cube shaped specimens) - by 34.6% (using WACKER BS 1701 0.2%) and finally, splitting strength - by 34.7% (by using SILRES BS 290 0.2%) in respect to the control specimen. Water absorption of concrete specimens (cube and plate shaped) without chemical silane based admixtures makes accordingly 2.61% and 4.09%. On the other hand, water absorption of concrete specimens (cube and plate shaped) with chemical silane based admixtures varies from 1.49% (using WACKER BS SMK 2101 0.1%) to 3.71% (using WACKER BS 1001 0.1%) and from 2.03% (using SILRES BS 3003 0.4%) to 4.14% (using WACKER BS 1001 0.1%) in respect to control specimens. The results achieved when conducting the water penetration test show that only the specimens without chemical silane based admixtures have failed the experiment. The results obtained following 100 cycles of freezing-thaw show that all specimens have passed the test and heir surfaces do not contain any cracks. [ABSTRACT FROM AUTHOR]

The paper presents the analysis of built-up laced axially loaded steel columns in light of Eurocode 3 and Lithuanian design code STR 2.05.08:2005. The theoretical part analyzes two design methods. Some cases indicate principal differences. According to STR, axial forces are equally divided into two parts for both chords. However, in Eurocode 3, axial force (formula 8) for one chord increases due to the additional bending moment (Formula 6) that depends on the shear stiffness of lacings (Formula 5). For very slender columns, the axial force of one chord, considering Eurocode 3, is 2.7 times bigger than that taking into account the STR method. Another big difference between the methods is that according to Eurocode 3 it is not necessary to check the overall stability of the built-up member round the z-z axis (only checking the stability of one chord round the z1-z1 axis is obligatory). Both methods require checking the stability of one chord round the y-y axis. In two cases, calculations referred to the same initial data (Table 1, 2) applying different design codes. The obtained results are presented in the diagrams. The first case shows that column slenderness in both planes equals λy = λz. The axially loaded column calculated with reference to the STR method has bigger bearing capacity reserve than that calculated considering the Eurocode 3 method. In this case, the stability of one chord round the y-y axis (Fig. 3) is the most dangerous. This example illustrates that the stability condition of the axially loaded column according to Eurocode 3 is not satisfied; thus, a necessity of increasing the column cross-section arises. The main reason for the latter situation is a different method used for calculating the axial force of one chord. This difference is greater for more slender columns. In the second case -- column slenderness makes λy = λz/2. When slenderness is λz ≤ 100, the axially loaded column calculated according to the STR method has similar results compared to the Eurocode 3 method (Fig. 10). The most dangerous according to STR is the stability of the entire column round the z-z axis (Fig. 8), whereas in accordance with Eurocode 3 it appears to be the stability of one chord round the y-y axis (Fig. 9). In such a case, the stability condition of the axially loaded column according to Eurocode 3 has more reserve only when slenderness is λz > 100 (Fig. 10). Therefore, calculation according to Eurocode 3 is less safe if compared to the STR method. The main reason is that Eurocode 3 does not require checking the entire column stability round the z-z axis. Hence, for calculating slender columns according to Eurocode 3, some cases (λz > 100) are not very safe, which was also noticed in the numerical investigations provided by other authors Kalochairetis (2011). In some cases, results are controversial, and therefore it is necessary to perform additional analysis or experimental investigation. [ABSTRACT FROM AUTHOR]

The aim of the article is to report a technology for the optimization of grillage-type foundations seeking for the least possible reactive forces in the piles for a given number of piles and in the absolute value of the bending moments when connecting beams of the grillage. Mathematically, this seems to be the global optimization problem possessing a large number of local minima points. Both goals can be achieved choosing appropriate pile positions under connecting beams; however, these two problems contradict to each other and lead to different schemes for pile placement. Therefore, we suggest using a compromise objective function (to be minimized) that consists of the largest reactive force arising in all piles and that occurring in the absolute value of the bending moment when connecting beams, both with the given weights. Bending moments are calculated at three points of each beam. The design parameters of the problem are positions of the piles. The feasible space of design parameters is determined by two constraints. First, during the optimization process, piles can move only along connecting beams. Therefore, the two-dimensional grillage is "unfolded" to the one-dimensional construct, and supports are allowed to range through this space freely. Second, the minimum allowable distance between two adjacent piles is introduced due to the specific capacities of a pile driver. Also, due to some considerations into the scheme of pile placement, the designer sometimes may introduce immovable supports (usually at the corners of the grillage) that do not participate in the optimization process and always retain their positions. However, such supports hinder to achieve a global solution to a problem and are not treated in this paper. The initial data for the problem are as follows: a geometrical scheme of the grillage, the given number of piles, a cross-section and material data on connecting beams, the minimum possible distance between adjacent supports and loading data given in the form of concentrated loads or trapezoidal distributed loadings. The results of the solution are the required positions of piles. This solution can serve as a pilot project for more detailed design. The entire optimization problem is solved in two steps. First, the grillage is transformed into the one-dimensional construct and the optimizer decides about a routine solution (i.e. the positions of piles in this construct). Second, backward transformation returns pile positions into the two-dimensional grillage and the "black-box" finite element program returns the corresponding objective function value. On the basis of this value, the optimizer predicts new positions of piles etc. The finite element program idealizes connecting beams as beam elements and piles - as mesh nodes of the finite element with a given boundary conditions in the form of vertical and rotational stiffness. Since the problem may have several tens of design parameters, the only choice for optimization algorithms is using stochastic optimization algorithms. In our case, we use the original elitist real-number genetic algorithm and launch the program sufficient number of times in order to exclude large scattering of results. Three numerical examples are presented for the optimization of 10-pile grillage: when optimizing purely the largest reactive force, purely the largest in the absolute value of the bending moment and both parameters with equal weights. [ABSTRACT FROM AUTHOR]

This article presents the investigation of a new structure of the guyed mast with combined guys. Technical and economical effectiveness based on material saving criteria of this structure is analysed. Formulas and recommendations are given for determining the rational bending moments distribution in the mast and the coordinates of the guy attachment points. Numerical simulation shows that the new guy cable system allows reducing the quantity of materials for steel masts. [ABSTRACT FROM AUTHOR]