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It is a well-known fact that the size of the sample influences values of mechanical properties of concrete measured during the tests. However, the comparison of results of various researchers clearly shows that the importance of this effect varies for different types of concrete. The paper presents outcomes of extensive experimental study focused on determination of relations between the size of the specimen and results of mechanical tests of high-strength fibre-reinforced concrete (HSFRC) with coarse aggregate (maximum aggregate size 16 mm). The main observed parameter was compressive strength. Six different HSFRC mixes having the expected compressive strength between 100 and 175 MPa were investigated. Cube samples of four sizes – 40, 100, 150 and 200 mm – were examined. The results proved that the size dependence of compressive strength diminishes with increasing strength of concrete. For very high strength materials (more than 130 MPa), the results were almost size independent. Additionally, flexural strength of two high-strength concrete mixes was measured on prismatic specimens of two different sizes. The results indicated that flexural strength of HSFRC with coarse aggregate is size dependent without regard to expected compressive strength. Conversion factors for the tested type of material were proposed for both compressive and flexural strength measurements. [ABSTRACT FROM AUTHOR]

Three dimensional FEM model is used to estimate the effect of steel liner on the ultimate bearing capacity of a prestressed concrete containment. The model is subjected to internal pressure exceeding LOCA pressure that is increased up to the failure of the structure. By comparison with the experiment described in the literature and with the similar model without steel liner, it is concluded that the liner can increase the bearing capacity of the containment by up to 40%. The 3D model is also exploited for verification of plausibility of previously created set of partial models of the same containment, leading to confirmation of the hypothesis that it is possible to model the behavior of the containment with relatively high precision and low time consumption by a set of simplified models with properly set boundary conditions. [ABSTRACT FROM AUTHOR]

The latest modern nuclear energy systems currently researched and developed are the Generation IV (Gen IV) nuclear reactors, and one of the more promising Gen IV designs is the Gas-cooled fast reactor (GFR). Among the number of challenging problems of the design of GFR, the development of passive safety systems ensuring passive decay heat removal (DHR) during loss-of-coolant-accidents (LOCA) is of the highest importance. The currently proposed DHR strategy relies on intentionally increasing pressure inside a gas-tight guard vessel containing the reactor to approximately 4 bar. This, however, presents a significant engineering challenge as the vessel must be capable of withstanding high pressure of up to 10 bar, due to pressure spikes and safety coefficients, while also withstanding increased temperatures during the LOCA. As no GFR guard vessel has ever been designed, this paper presents a feasibility study establishing whether such vessel can be designed. The feasibility study is aimed at the assessment of a preconceptual design of a prestressed concrete vessel previously created by the authors. In the study, stresses in the structure induced by normal-operation loads and LOCA loads are calculated for three types of extreme constraint conditions covering all possible real constraints of the structure. The calculations are based on heat transfer equations, Euler–Bernoulli theory, and Lamé equation implemented in a in-house Python code. In the results, stresses in the vessel are presented and compared to design criteria. The main conclusion of the paper is that the vessel can be designed; however, certain adverse phenomena which complicate the design process, such as non-linear creep of concrete and occurrence of tensile stress up to 1 MPa, will have to be addressed and considered during future detailed design. Following on from this affirmative conclusion, the authors will create the detailed design using advanced three-dimensional modelling in their future work. • The novel GFR reactor ALLEGRO requires an especially resistant containment vessel. • A prestressed-concrete containment vessel can withstand gas pressure of up to 10 bar. • The high pressure needed for the safety systems proposed for ALLEGRO can be maintained. • Non-linear creep of concrete may occur and must be considered in a detailed design. [ABSTRACT FROM AUTHOR]

Safety is always the main consideration in the design of containment of nuclear power plant. However, efficiency of the design process should be also taken into consideration. Despite the advances in computational abilities in recent years, simplified analyses may be found useful for preliminary scoping or trade studies. In the paper, a study on sensitivity of finite element model of prestressed concrete containment to changes in geometry, loads and other factors is presented. Importance of steel liner, reinforcement, prestressing process, temperature changes, nonlinearity of materials as well as density of finite elements mesh is assessed in the main stages of life cycle of the containment. Although the modeling adjustments have not produced any significant changes in computation time, it was found that in some cases simplified modeling process can lead to significant reduction of work time without degradation of the results. [ABSTRACT FROM AUTHOR]

• Time-dependent strain of mass concrete structures at elevated temperature studied. • Comprehensive database of parameters of prestressed concrete containments created. • Data about 16 containment types or 40 particular structures included. • Verification of analytical model for prediction of time-dependent strains. • Model proved suitable for preconceptual design of prestressed concrete containments. Nowadays, for the containment of nuclear reactors, the prestressed concrete containments (PCCs) are most often used for their high resistance to both design and accidental loads. When designing a safe and effective PCC, an accurate prediction of prestress losses is of vital importance. One of the most considerable prestress losses is caused by the time-dependent strain due to creep and shrinkage of concrete. Thus, in the preconceptual design phase, a tool for making relatively simple but safe prediction is required. When designing a PCC in particular, the situation is complicated by the fact that the PCC is a mass concrete structure exposed to increased operation temperature which affects the creep and shrinkage of concrete greatly. Bažant́s widely accepted creep and shrinkage model B3 with the extension for elevated temperature (called B3T) allows to take into account increased operation temperatures for thick concrete elements. However, this model is not primarily aimed at mass structures at elevated temperatures, and its usability for prediction of creep and shrinkage of concrete in these structures should be verified. In this paper, the authors analyse the usability of this model for the PCCs by comparing real-world measurements gathered from publicly available sources for 13 types of containments (31 structures in total) with B3T model predictions. The analysis shows that the B3T model provides a safe estimation of creep and shrinkage in 28 out of the 31 structures. In the remaining three cases, an unsafe result was obtained, probably due to a nonstandard course of the construction schedule; however, the inaccuracy of B3T model predictions was below 15 % in these cases. Moreover, the unique database of containment parameters presented in this paper may provide useful for future researchers or designers dealing with the preconceptual design of PCCs. [ABSTRACT FROM AUTHOR]

The following paper deals with the comparison of adhesion of specimens made of fired clay and selected adhesives. The adhesion was tested on specimens at the age of one, two and three days in order to determine the parameters of young masonry. Nine different adhesives (adhesives intended for masonry and adhesives for others material) were tested in total. The above mentioned test is not standardized. The obtained results from the adhesion test determine the tensile strength between the adhesive and the fired clay and the adhesion of selected adhesive to the fired clay. The small specimens were made of two ceramic plates and an adhesive. Selected adhesives were applied to ceramic plates according to the usual standards. Eighty-one small specimens were produced in total - twenty-seven specimens for the adhesion test at each defined age of the specimens (one day, two days, three days). The produced specimens were cured in the climatic chamber with set laboratory conditions until the time of the test. The specimens were tested in the laboratory of the Heluz brick plant in Dolní Bukovsko. This paper deals with the procedure of preparation of the specimens, the course of the test and the comparison of gained results. [ABSTRACT FROM AUTHOR]

Focuses on the issue of poor funding of the Prague Transport Authority on public utilities in Czech Republic. Analogy on the back page photo of the person standing in the right side of the escalator; Sights of the worn switched escalator belts; Views of the Czech state institution on the suggestions from the general public.

Comments on the attendance Miraslov Ransdorf, Deputy-Chairman of the Czech Communist Party in a cultural event celebrated by Czech and Slovak immigrants in New York City. Efforts of the audience for Ransdorf to leave the cultural center; Contention over the failure of the Communist Party to renounce its misdeeds; Explanation on the arrogance of Ransdorf.