International Concrete Abstracts Portal

Radon is a radioactive invisible, odorless, tasteless gas that seeps up through the ground and diffuses into the air. Radon gas naturally moves into the permeable soil and gravel bed surrounding foundations and then, inside the buildings through openings, cracks, and pores of the concrete. The type of constructions more exposed to the radon risk emanated from the ground are industrial buildings, supermarkets, shops, restaurants, and all the residential buildings where people work or live on the ground floors. In the present paper, the rehabilitation of building polluted by radon gas has been studied. Two techniques can be adopted to reduce the radon concentration in the building environments: A) change of the environmental air opening doors and windows of the building; B) if the change of air is incompatible with the industrial activity carried out in the building the radon entry can be blocked using the application on the existing concrete surface of a specific cap sheet membrane; in particular a bitumen-based radon gas barrier has been examined already studied and acting as an effective radon gas barrier. In the end, the radon barrier can be covered by a concrete layer. According to the Italian Legislative Decree No. 101/2020 presently the radioactivity caused by the radon gas in the houses and industrial buildings must be lower than 300 Bq/m³, whereas for the building erected after December 31, 2024, should be lower than 200 Bq/m³.

The present paper describes the building of the Fourth Bridge on the Grand Canal in Venice, designed by the Architect Santiago Calatrava. In particular, this paper is devoted to the laboratory and field tests to develop the composition of a self-compacting concrete (SCC) to be placed in the congested reinforced foundations of the Calatrava Bridge. To ensure a durable service life of at least 100 years, a water-cement ratio as low as 0.45 was adopted due to the contact of the reinforced foundations with the seawater. The placement of the SCC was carried out in only a few hours of a night to reduce the interruption of the ferry traffic in the Grand Canal. The concrete was pumped from truck mixers, all located on the Rome Square side of the bank of the Grand Canal, and feeding the fresh mixture in both the reinforced spaces devoted to the foundations. The reinforced foundations are exposed to a significant load due to the heavy weight of the bridge manufactured of steel and glass, as well as to the shear stress caused by the peculiar shape of the bridge characterized by a segmental arch. Due to these factors, some cracks were observed every year on the top of the foundations. This means that in the next future some measures should be taken to block the formation of new cracks. Meanwhile, the already formed cracks have been sealed and protected by an upper coating stone in order to inhibit the ingress of the airborne swept by the wind from the close sea water causing the corrosion of the metallic reinforcements promoted by the presence of chloride ions.

This paper presents a case study involving the structural analysis and design of an elevated foundation plinth to support multiple pieces of rotating machines with different operating weights and speeds. The equipment is used to operate a high-speed balancing testing facility for turbines and rotors that are located within an adjacent testing chamber. This project comprised of several layout and design challenges, including vibration and resonance concerns, effects of multiple operating frequencies, plinth shape, and pile foundation effects. Major concern was to maintain the high precision and strict tolerance limitations required by the high-speed balancing operations. Elevated machine foundations integral with other structures possess many natural frequencies, both locally and globally. The traditional design rules-of-thumb are not adequate for analyzing and designing elevated machine foundations. A computer-based finite element analysis method is required to identify the multiple natural frequencies of a complicated foundation structure. The strength design of a machine foundation can become very challenging when trying to implement code requirements that are mostly applicable to building elements and not to massive concrete foundations. This study recognizes the need for the development of a design standard to include special design requirements for mass concrete machine foundations.

The first international FRC workshop supported by RILEM and ACI was held in Bergamo (Italy) in 2004. At that time, a lack of specific building codes and standards was identified as the main inhibitor to the application of this technology in engineering practice. The workshop aim was placed on the identification of applications, guidelines, and research needs in order for this advanced technology to be transferred to professional practice. The second international FRC workshop, held in Montreal (Canada) in 2014, was the first ACI-fib joint technical event. Many of the objectives identified in 2004 had been achieved by various groups of researchers who shared a common interest in extending the application of FRC materials into the realm of structural engineering and design. The aim of the workshop was to provide the State-of-the-Art on the recent progress that had been made in term of specifications and actual applications for buildings, underground structures, and bridge projects worldwide. The rapid development of codes, the introduction of new materials and the growing interest of the construction industry suggested presenting this forum at closer intervals. In this context, the third international FRC workshop was held in Desenzano (Italy), four years after Montreal. In this first ACI-fib-RILEM joint technical event, the maturity gained through the recent technological developments and large-scale applications were used to show the acceptability of the concrete design using various fibre compositions. The growing interests of civil infrastructure owners in ultra-high-performance fibre-reinforced concrete (UHPFRC) and synthetic fibres in structural applications bring new challenges in terms of concrete technology and design recommendations. In such a short period of time, we have witnessed the proliferation of the use of fibres as structural reinforcement in various applications such as industrial floors, elevated slabs, precast tunnel lining sections, foundations, as well as bridge decks. We are now moving towards addressing many durability-based design requirements by the use of fibres, as well as the general serviceability-based design. However, the possibility of having a residual tensile strength after cracking of the concrete matrix requires a new conceptual approach for a proper design of FRC structural elements. With such a perspective in mind, the aim of FRC2018 workshop was to provide the State-of-the-Art on the recent progress in terms of specifications development, actual applications, and to expose users and researchers to the challenges in the design and construction of a wide variety of structural applications. Considering that at the time of the first workshop, in 2004, no structural codes were available on FRC, we have to recognize the enormous work done by researchers all over the world, who have presented at many FRC events, and convinced code bodies to include FRC among the reliable alternatives for structural applications. This will allow engineers to increasingly utilize FRC with confidence for designing safe and durable structures. Many presentations also clearly showed that FRC is a promising material for efficient rehabilitation of existing infrastructure in a broad spectrum of repair applications. These cases range from sustained gravity loads to harsh environmental conditions and seismic applications, which are some of the broadest ranges of applications in Civil Engineering. The workshop was attended by researchers, designers, owner and government representatives as well as participants from the construction and fibre industries. The presence of people with different expertise provided a unique opportunity to share knowledge and promote collaborative efforts. These interactions are essential for the common goal of making better and sustainable constructions in the near future. The workshop was attended by about 150 participants coming from 30 countries. Researchers from all the continents participated in the workshop, including 24 Ph.D. students, who brought their enthusiasm in FRC structural applications. For this reason, the workshop Co-chairs sincerely thank all the enterprises that sponsored this event. They also extend their appreciation for the support provided by the industry over the last 30 years which allowed research centers to study FRC materials and their properties, and develop applications to making its use more routine and accepted throughout the world. Their important contribution has been essential for moving the knowledge base forward. Finally, we appreciate the enormous support received from all three sponsoring organizations of ACI, fib and Rilem and look forward to paving the path for future collaborations in various areas of common interest so that the developmental work and implementation of new specifications and design procedures can be expedited internationally. June 2018 Bruno Massicotte, Fausto Minelli, Barzin Mobasher, Giovanni Plizzari

Performance based seismic design (PBSD) has created new opportunities for enhanced performance, improved cost efficiencies, and increased reliability of tall buildings. More specifically, flexibility with initial design methods and the utilization of response history results for design, not just verification, have emerged. This paper explores four refined design methods made available by the employment PBSD to influence seismic performance and identify areas of importance. First is the initial proportioning of reinforcement to encourage plastic hinge behavior at specific locations. Second is the initial proportioning of wall thicknesses and reinforcements to encourage a capacity-based design approach for force-controlled actions. Third is the mapping of observed strain demands in shear walls to specific detailing types such as ordinary and special boundary zones. Fourth is an efficient envelope method for the design of foundations. Through these design methods, initial proportioning can be conducted in a more refined way and targeted detailing can result in cost savings. A case study of a recently designed high-rise residential building demonstrates that cost savings can be achieved with these methods.