Key Engineering Materials Vol. 976

Abstract: Glassfibre reinforced concrete (GRC) is a close-grained concrete material reinforced with glass fibres that allows architects complete freedom in designing rear-ventilated façades. It can be shaped, coloured, surface-treated or otherwise tailored to the specific needs of their projects without significant limitations. The main properties of GRC material include its long life-time and sustainability. The results are visually appealing façade panels that can withstand adverse weather conditions for decades. The characteristic high strength and durability is achieved by dispersing glass fibres within the base mixture of Portland cement, sand, water and further refining additives. Fine-grained particles in the composite structure ensure low water absorbency and high frost resistance. This article is an overview of the technical solution and process of GRC façade design. It deals with the design possibilities for anchoring large-format and 3D shaped façade panels. The article further presents all of the above-mentioned characteristics and process details as they are used on three specific structures. The first presented project is the ČSOB Central Office in Hradec Králové, with its typical distinct ledges combined with glazed surfaces. The cascading entrance portal is a significant element of its façade. The next implementation chosen is the renovation of the C&A department store building in Zürich, Switzerland. This building’s façade is comprised of structured large-area panels with distinctive frames. The article concludes with the creatively implemented renovation of the Illuster shopping centre in Switzerland, with its kaleidoscopic façade made up of glassfibre reinforced concrete panels.

Abstract: The paper deals with the problem of stress in the connection detail of vertical supporting structures with a flat slab and possible methods for its analysis. It mainly focuses on the problem of non-axial connection of columns and walls, which is typical for today's architectural designs. The parametric study compares the effect of the distance of the connected vertical support structures on reinforcement in the discontinuity region. Three different computational methods are used to stress analysis of this region - linear Finite Elements Method in SCIA Engineer software, 2D Strut-and-Tie Model and 2D non-linear Finite Elements Method in IDEA StatiCa software. The conclusion of the study is a comparison of the accuracy of different calculation methods and also a comparison of the solved design variants in terms of shear and bending stress and specific form of reinforcement.

Abstract: The paper deals with the methods of software optimization of the concrete structure in terms of environmental issues, durability, and cost. It links to previously developed software tool that enables multi-criteria optimization of a 1 m² one-way slab. A feasibility study focused on the optimization of larger structural units, and it analyses and compares methods of concrete structures optimization in terms of environmental impacts, durability, and life-cycle cost.

Abstract: When analyzing slender columns, the second-generation Eurocode FprEN [2] recommends the calculation of the bending moment envelope, which consists of both first-order and second-order moments. This paper presents the aforementioned calculation method for both braced and bracing columns, utilizing a comprehensive “general” nonlinear approach.

Abstract: One of the most effective and common ways of an increasing the punching shear capacity of the flat slabs is using of shear reinforcement. An important limit during the design is the determination of the maximum punching shear resistance. The fact that the calculation of such an important value is still clearly empirical has met with criticism from many experts in recent years. Consequently, a new design model for the calculation of the maximum punching shear resistance, based on the critical shear crack theory was developed. The second generation of the Eurocode 2 (prEC2) introduces a more accurate and sophisticated design model for the determination of the upper limit of the punching shear capacity and considers several parameters. The main aim of this paper is to describe the new methodology of calculation of the maximum punching shear strength and the parameters that could influence it. The paper deals also with an assessment of the suitability of new model by comparing it with experimental results, that have been selected from a database of specimens that failed by punching at the level of V_R,max.

Abstract: Massive concrete structures are exposed to the risk of high temperatures due to cement hydration. In accordance with requirements for sustainable development, the clinker content in commonly produced cements is reduced and mixed cements are developed and gradually introduced into production. The development of temperatures in massive foundation structures made of concrete containing modern mixed cements is the subject of an experimental program. Its results are evaluated from the point of view of the final properties of the concrete, but also from the point of view of the possibilities of concrete production and implementation technologies. In conclusions, general recommendations are formulated for the design of concrete mixtures for application in massive structures.

Abstract: Blast performance of concrete and ultra-high performance fiber concrete (UHPFRC) has been subject to numerous publications in the past decades. The enhanced force-deflection diagram of fiber concrete and ultra-high performance fiber concrete provide massive increase on the protective function of these materials compared to regular concrete. Nevertheless, concrete spalling cannot be fully avoided even when using UHPFRC. The next step for harmful debris ejection prevention can be supplementing the concrete specimens with steel slabs. The steel slab will not just hold the debris, but can, if properly bonded with concrete, contribute to the load bearing capacity as steel-concrete composite structure. This paper presents an overview of recent experiments on blast resistance of steel-concrete composite slabs. In total 6 pairs of specimens (dimension 1.000/1.000/150mm) were prepared, 6 specimens using regular concrete and 6 specimens using UHPFRC. One pair of specimens was reinforced by a steel mesh at 30mm cover from the soffit, one pair was supplemented by a steel plate bonded with 4 studs in the corners, at the complementary specimen pair, the concrete was also covered with a steel plate at the side subjected to blast loading, in the case of the further pair of specimens, the steel plates were connected by steel bars arranged in a mesh 150/150mm. The final 2 pairs represented steel-concrete composite slabs, in the first case, the shear studs were supplemented with a steel mesh (according to provisions of the European standard for steel-concrete composite structures), in the last case, the shear studs were replaced by a shear plate. All specimens were subjected to the same contact blast loading. The paper presents the experimental arrangement, the achieved results and a brief discussion on the structural behavior.

Abstract: This paper deals with failure modes of a steel-concrete-steel sandwich loaded by pure in-plane shear. Current research together with the developed models imply that increase of reinforcement ratio leads to decrease of ductility and possibly to change a failure mode from yielding of steel in tension to crushing of concrete in compression which results in brittle failure. In order to give a reader basic information about in-plane shear behavior of a steel-concrete-steel sandwich, an analytical model is introduced. Japanese experimental program that researched a behavior of SCS panels with reinforcement ratio 2.3%, 3.2% and 4.5% is also shown. In addition to the effect of changing the reinforcement ratio, the experimental program also investigated the effect of the transverse steel plate on the ductility of test panels with a degree of reinforcement of 3.2%. The next chapter describes the methodology used by the author to model the individual parts of the model, the loads, and especially the method of supporting the model. This is followed by the presentation of the results of the analysis on the calibration and extrapolation models. Finally, a discussion is conducted on the agreement of the analysis results on the calibration models with the Japanese experimental results, followed by an evaluation of the analysis results on the extrapolation models. According to the results on the extrapolation models the critical degree of reinforcement at which a change in the failure mode of the structure occurs under in-plane shear loading is around 13%.

Abstract: This paper describes an experimental investigation of the behaviour of anchors precast in Ultra High-Performance Fiber-Reinforced Concrete (UHPFRC) under static loading. Initially, the current state of the art and related experimental studies are briefly mentioned. The next part of the paper is devoted to an experimental program aimed at describing the anchorage in cement composite UHPFRC in more detail. A total of 45 pull-out tests were performed. The tests investigated the effect of the fiber quantity in volume in the UHPFRC matrix (v_f), the effective embedment depth of the anchor (h_ef) and the position of the anchor in the mould during concreting. Finally, the results are documented, the failure mode and the shape of the concrete cone, load-displacement curves and summary tables are presented. The paper concludes with a discussion of the results and further directions for solving the problem.