International Concrete Abstracts Portal

Columns supporting reinforced concrete two-way slabs often have non-circular or non-square cross-sections. The punching shear design of alternative column geometries is addressed in ACI 318-19, although the basis for these provisions is unclear as experimental tests of irregular column geometries are limited. In particular, the punching shear behaviour of special-shaped slab-column connections, such as L-shaped connections, has received limited interest. In this paper, nonlinear finite element analysis (FEA) is used to study the influence of column geometry, column location with respect to the slab centroid and the presence of slab openings on the punching shear behaviour of interior L-shaped slab-column connections subjected to gravity loading. The FEA suggests that the diagonal portion of the critical perimeter between the column flanges assumed in ACI 318-19 is ineffective in transferring load between the slab and the column. The FEA also suggests that ideally slab openings around interior L-shaped slab-column connections should be located between the two column flanges of each connection. Locating the openings in this area minimizes their negative impact on punching capacity and is beneficial from an architectural perspective, as the openings and services can be hidden from view. The punching capacities predicted by the FEA, the ACI 318-19 concentric punching shear provisions and the eccentric shear stress model outlined in ACI 421.1R-20 are also compared.

The new San Giorgio bridge replaced the Polcevera viaduct, built between 1963 and 1967 and collapsed during a storm in summer 2018. The new bridge was designed by Renzo Piano and is made by 19 steel spans supported by 18 concrete pillars. Beside the architectural aspects, special attention was devoted to the mix-design of the pillars, to ensure the production of durable concrete in the marine environment. The use of slag cement combined with limestone filler and polycarboxylate superplasticizers allowed to cast flowable concrete associated with low water to cement ratio and high final compressive strength. A new generation accelerating admixtures, working on the homogeneous nucleation technology, was used to accelerate the cement hydration and gain early compressive strength to speed-up the elevation of the pillars. In the present paper, the advantage of using the new admixture is discussed both in terms of early strength development and microstructure of the cement paste. Beside the improvement of the early strength development, the new admixture reduced the water permeability and the chloride diffusion and improved the resistance to carbonation of the concrete used for the pillars, with further advantages for the durability of this structure.

After World War II the research about the double curvature structures in reinforced concrete was a frontier in the field of typological, spatial and expressive innovation. Among the principal leading figures was the swiss engineer Heinz Isler with his methods called “form finding” based on the use of physical modeling to determine the form and subsequently investigate its stability. When a concrete shell is shaped using a hanging-membrane model, it assumes an ideal form using a minimum of materials, with minimal deformations and in compression only. This is only the first step in the process of finding the form. Then one has to do the exact structural analysis, the layout of the reinforcement and prestressing elements, and the detailing, to deal with construction problems, and finally to carefully observe the structure in use.

The need to protect the works of Heinz Isler has slowly been bearing fruit in recent years. This highlights in a very special way the crucial point of the debate on the protection of modern and contemporary architecture: the recognition of their architectural and cultural values, and consequently the difficulties of the institutions responsible for undertaking their preservation.

The paper intends to investigate the case of the Deitingen service station built in 1968-1969 which represents a fortunate phase in this process and shows how the factors linked to the durability of structures play a small role in the decision-making processes regarding the future of these works. The key role is played by the significance and values that acquires (or loses) over time.

Textile reinforced concrete (TRC) is a high-performance composite material made of impregnated filaments and a concrete matrix with a longer service life compared to steel reinforced concrete. Due to the non-corrosive reinforcement it is possible to reduce the concrete cover and realize slender and architectural attractive concrete structures. In addition, resources and CO₂-emissions can be saved.

Despite the non-corrosive reinforcement, a loss of strength occurs over the service life due to environmental impacts. Therefore, a testing concept is required to determine a reduction factor that takes the loss of strength during the service life into account. This enables a safe design of textile reinforced concrete structures.

A testing concept for TRC is derived from existing concepts for fiber reinforced polymers (FRP). Available concepts (e.g. ACI 440.3R-12, ASTM 7337, CSA S806-12, ISO 10406-1) differentiate between creep rupture and alkaline resistance. Therefore, a test setup was derived which combines the existing concepts and enables the determination of the long-term durability of non-metallically reinforced concrete structures. The long-term durability is defined as a constant stress on a reinforcement that can be applied during the service life without a failure of the reinforcement.

Sustainability of cement-based construction components is becoming a key point of the structural design process, since the implementation of green strategies favors an overall reduction of economic and environmental impacts. In the framework of a regionally funded research project, an innovative multi-layered roof element for the retrofitting of existing industrial buildings was developed at Politecnico di Milano. The development followed a holistic approach focusing on two main levels: 1) the optimization of the transverse section, aimed at minimizing the employment of cementitious composites such as High Performances Fiber Reinforced Concrete (HPFRC) and Textile Reinforced Concrete (TRC) and 2) the improvement of the energy performances, through the selection of adequate insulating materials (polystyrene and glass foam were considered) and the design of Building-Integrated PhotoVoltaics (BIPV). In this paper, preliminary considerations pertaining to the sectional and structural behavior of a 2.5 × 5 m [8.2 × 16.4 ft.] secondary panel are followed by the numerical/experimental evaluation of the thermal transmittance U and the BIPV performances. In this regard, a small demo roofing system housing three full scale panels was monitored throughout two Summer weeks, leading to the assessment of photovoltaics Performance Ratios (PR) and effectiveness of the architectural integration.