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Precast concrete floors
Published in Kim S. Elliott, Precast Concrete Structures, 2019
Hollow core units were developed in the 1950s when the dual techniques of long-line prestressing and concrete production through machines were being developed by companies such as Spiroll in the United States and Roth in Europe. Precast concrete engineers continued to optimise the cross section of the units leading to the so-called double-tee unit, shown in Figure 4.8, achieving even greater spans and reduced mass compared with hollow core units. Although the finer points of detail of double-tees vary in many different countries, the unit comprises two deep webs, reinforced for strength, joined together by a relatively thin flange, for stability. Two major drawbacks with double-tees are Not being able to provide sufficient pretensioning force to satisfy the available section as strands can only be placed in pairs at the bottom of the webs, forcing more strands to be positioned higher in the web-reducing eccentricity.
Precast concrete floors
Published in Kim S. Elliott, Precast Concrete Structures, 2016
Hollow core units were developed in the 1950s when the dual techniques of long-line prestressing and concrete production through machines were being developed by companies such as Spiroll in the United States and Roth in Europe. Precast concrete engineers continued to optimise the cross section of the units leading to the so-called double-tee unit, shown in Figure 4.8, achieving even greater spans and reduced mass compared with hollow core units. Although the finer points of detail of double-tees vary in many different countries, the unit comprises two deep webs, reinforced for strength, joined together by a relatively thin flange, for stability. Two major drawbacks with double-tees are Not being able to provide sufficient pretensioning force to satisfy the available section as strands can only be placed in pairs at the bottom of the webs, forcing more strands to be positioned higher in the web-reducing eccentricity.The centroidal axis is high in the section, typically yb = 0.7h × depth from the bottom, resulting in a low value of the section modulus at the bottom Zb relative to the cross-sectional area, for example Zb/Ac h ≈ 0.12 compared with 0.24 for hollow core units. This offers the potential for composite action with a structural topping.
Influence of Closure External Panels Modelling on the Seismic Response of Non-Residential Precast Buildings
Published in Journal of Earthquake Engineering, 2023
Davide Bellotti, Francesco Cavalieri, Roberto Nascimbene
The first case study is a single-storey precast structure representative of the Italian construction period of the ‘70s, located in Naples and designed on the base of gravity loads only (Fig. 3). The geometry consists of a single span with total plan size of 20 × 54 m2. The columns, with a 0.35 × 0.35 m2 cross-sectional area and a 6 m height, are installed into socket foundations filled with concrete. The prestressed main beams in the transverse (x) direction feature a span length of 20 m and a double slope of 10% inclination; their I-section has variable height (max 1.82 m at midpoint) and thickness (min 0.08 m at midpoint). The secondary beams (or girders) in the longitudinal (y) direction are 6 m long with a tee cross-section. The connections of the main beams to the columns only rely on friction and are characterised by the presence of neoprene pads on the column top allowing for beam seating. On the other hand, the girders are fastened by steel dowels protruding from the top of the columns. The roof is composed of double-tee prestressed elements, rigidly fastened to the main beams by reinforcement stirrups protruding from the beams, additional steel bars between the elements and a finishing concrete casting. The external closure is present on all sides of the building and is constituted of masonry infill panels creating ribbon windows of a 1.5 m height.
Modelling and Seismic Response Analysis of Non-residential Single-storey Existing Precast Buildings in Italy
Published in Journal of Earthquake Engineering, 2023
Marco Bosio, Chiara Di Salvatore, Davide Bellotti, Luca Capacci, Andrea Belleri, Valeria Piccolo, Francesco Cavalieri, Bruno Dal Lago, Paolo Riva, Gennaro Magliulo, Roberto Nascimbene, Fabio Biondini
The first structural system (EE1) refers to a single-storey precast structure built in 1972 and designed based on static analysis (Fig. 1). The geometry of the investigated structure was regularized, analysing a single 20 m span of the original building: this structural configuration substantially corresponds to the lateral span of the real building with total plan size 20 × 54 m2. The columns are precast elements with 0.35 × 0.35 m2 cross-section and 6 m height. The main beams in the transverse (Y) direction have a span of 20 m and a double slope (10% inclination) with an I-section variable in both height and thickness. The secondary beams in the longitudinal (X) direction are 6 m long with an inverted double-tee cross-section. The assumption of rigid diaphragm was adopted for the roof, given the presence of cast-in-place concrete topping with continuous steel reinforcement between the inverted double-tee roof elements. For such reason, the connection between the roof element and the supporting beam is considered fixed in the analyses. The masonry infill panels, 4.5 m high, do not cover the total column height, creating a ribbon window; such infill elements were assumed to be present on all sides of the building.
Parametric analysis of the dynamic response of railway bridges due to vibrations induced by heavy-haul trains
Published in Structure and Infrastructure Engineering, 2022
Emrah Erduran, Semih Gonen, Aya Alkanany
Norddals bridge, a prestressed concrete, single-span bridge with a span length of 50 m, was used as the benchmark bridge in the study. The bridge deck has a double-tee cross-section with a total depth of 2.85 m. It is 6.6 m wide and houses a single, ballasted track. The area and the moment of inertia of its cross-section are 6.81 m2 and 16.89 m4, respectively. The longitudinal axis of the bridge is straight with no curvature.