No abstract

In this study, structural thin-layer sandwich walls (SWs) made of steel-fibre-reinforced concrete (SFRC) without conventional reinforcements were investigated. Other researchers have shown that SWs with thin wythes can be used as load bearing structures in low-rise buildings, thereby reducing the amount of concrete by 2–5 times if compared to conventional reinforced-concrete SWs. In most studies, relatively warm climatic regions are the focus, and thin-layer SWs with shear connectors to obtain a certain level of composite action are investigated. In almost no studies has sound insulation been evaluated. In this study, a numerical investigation of structural, thermal and sound insulation performances was carried out. The load-bearing capacities of composite and non-composite SWs are compared. Regions with the lowest five-day mean air temperature of −20 ∘C were considered. The characteristics of the SW are compared to the requirements given in relevant European and Latvian standards. The minimum thermal insulation for family houses varies from 120 mm to 200 mm, depending on the material. To ensure sufficient sound insulation, the average thickness of the concrete wythes should be around 60 mm, preferably with a 15 mm difference between them. Structural analysis of the proposed wall panel was performed using non-linear finite element analysis software ATENA Science. The obtained load-bearing capacity exceeded the design loads of a single-story family house by around 100 times, regardless of the degree of composite action.

By adding fibres to concrete mix the objective is to bridge discrete cracks providing for some control to the fracture process and increase the fracture energy. Fibres become active mainly when cracking starts and deformation of the fibre occurs. Pullout tests with four types of fibres with different orientation, embedment lengths, and concrete strengths are performed to simulate the bridging process. Fibre pullout behaviour is analysed for relatively small slippage displacement to keep it close to real designing situations. The test results show significant effect of fibre type on pullout behaviour, nevertheless the effect is intangible on fibres inclined at 30 degrees or more. An effective displacement is introduced, derived from experimental force-slip curves, when fibre becomes involved in bridging. Based on the efFective displacement and simplified average force-slip curves a numerical model is proposed to analyse the tensile stresses transferred by fibres crossing a crack.

Precast concrete slabs and their supporting walls are connected using dowel pins, anchoring loop bars, and cast-in-situ concrete. The design resistance of such connections can be calculated using multiple different methods. The design load bearing capacity can vary depending on the method used and assumptions made during calculation, making it difficult to determine, which methods are reliable and should be preferred. The study ordered by construction company JSC “UPB” discusses two design methods proposed by Eurocode 2 and fib Bulletin 43. A semi full-scale loading tests of concrete walls and slab specimens are carried out. The results show that the design methods considering only the contribution of steel dowel pins, underestimates the actual capacity of the connection by 2 to 4 times. On the other hand, the methods, considering both the contribution of the dowels and the friction between concrete interfaces, correspond well with the experimental results.

The positive effect of fiber‐reinforced concrete (FRC) on shear capacity of reinforced concrete beams is well presented in many experimental studies since 1970s. However, as the main effect of fibers is in the cracking stage, it increases the complexity to analyze such structures numerically. With the increased availability of nonlinear finite element analysis software, structural designers are encouraged to use them to solve complex structural problems. In such cases, understanding and correct definition of material laws in cracked stage of FRC structures are crucial. A blind competition was organized by fib WG 2.4.2 to address this issue. It revealed that the numerical predictions of almost all of the participants overestimated the shear capacity of a T‐beam subjected to bending. The aim of the current study is to demonstrate critical aspects in the definition of input parameters of FRC analysis. A comprehensive parametric analysis is performed considering tensile softening law, shear stiffness, and shear strength definition in cracked stage as well as shrinkage effects. The results suggest that most important aspect is the correct definition of tensile softening law, which should correspond to the lower bound of residual strength obtained by standard notched prisms tests according to EN 14651 or even smaller.