# Concrete Structures: Latest Advances and Prospects for a Sustainable Future
## 2 An Overview of Published Articles
The success of cement-based composites in civil structures is mainly due to their versatility, durability, and cost, even if they require rigorous design procedures to overcome their weak tensile strength and low ductility. In view of improving the mechanical behaviour of these materials, fibre-reinforced cement mortar (FRCM) has been developed by adding chopped fibres in cement composites. In detail, two kinds of FRCMs are available: mono fibre-reinforced cement mortar (MFRCM), which is characterised by the use of only one type of fibre, and hybrid fibre-reinforced cement mortar (HyFRCM), which is obtained by adopting two or more different fibres. These materials are commonly used in during reparations. Consequently, a deep knowledge of their mechanical behaviour represents an important objective in the management of r.c. structures. In contribution 4, the authors study the flexural performance, compressive strength, and impact resistance of both MFRCMs, containing only steel fibre (SF) or carbon fibre (CF), and hybrid fibre-reinforced cement mortar (HyFRCM) containing different combinations of SF and CF. The main aim of the study was to select the optimal fibre combination able to guarantee the required mechanical performance compared with plain mortar. The authors highlighted that the use of MFRCM or HyFRCM improves flexural performance in comparison to plain mortar. Moreover, they estimated how to choose the percentages of SF and CF to acquire higher values of impact resistance or flexural toughness, showing that the adoption of HyFRCM can improve the energy absorption capacity compared with MFRCM. In recent decades, several multi-storey reinforced concrete buildings have been built with pillars on the ground floor for parking purposes, while the upper floors were reserved for residential use and were realised by inserting unreinforced masonry infills. However, earthquake events highlighted that this configuration is responsible for a different distribution of stiffness along the height of the structure, which is characterised by high stiffness on the upper floors and a \"soft-storey\" on the ground level. Therefore, during earthquakes, the ground floor columns and/or shear walls are subjected to an increased earthquake demand. However, usually, these structural elements are not designed to withstand such forces; thus, plastic hinges become damaged and in these scenarios, which can lead to a partial or total collapse of the building. This behaviour can also be observed when there is an irregular distribution of infills in plan, which can be responsible for torsional responses and an increase in vulnerability. In contribution 5, the authors investigate a retrofitting intervention aimed to increase the stiffness, shear capacity, and ductility of ground floors in irregular buildings. The intervention involves the realisation of reinforced concrete infills within existing r.c. frames located on the ground level after the execution of r.c. jacketing of the chosen frames. The retrofitting intervention is investigated by performing experimental tests on six 1/3-scaled single-story one-bay r.c. frames subjected to cyclic horizontal forces. The study highlights the key role played by the connections between the r.c. infill and the surrounding jacketed frame realised by means of steel ties. The paper also discusses a numerical procedure for the estimation of the behaviour of retrofitted frames, considering the nonlinearities related to the RC infill, RC frame, steel ties, and mechanisms at the interface. The numerical procedure is also validated by means of the experimental results and may be utilized for design purposes. In the design of r.c. structures in seismic prone zones, building codes [12; 13; 14] introduce a factor whose symbol and name vary for each code but whose introduction is aimed to reduce the full elastic demand in a structure to bring the structure closer to the inelastic range.