Evaluation of the resistance of trussed slabs with steel formwork in cold formed U profile

Abstract

In the last decades, the modernization in structural engineering has increased the use of steel-concrete composite and hybrid systems for slabs, when the adherence in the interface of the materials is present or not, respectively. In addition to the traditional steel deck, a similar solution for precast trussed slabs has been used for small constructions, in which a cold formed U profile acts as steel formwork before the concrete curing, resisting to self-weight of the concrete and to the construction overload. After this period, the steel profile gets incorporated to the concrete element, allowing the composite behavior of the structure, system that usually goes without additional reinforcements. This slab includes, besides concrete, a light filling material between ribs, cold formed profiles and the trussed reinforcement. Once this technology has just arrived to the construction market, there is a gap of knowledge related to its design procedure. In this context, this study aims to present a methodology to analyze the limit-states that govern the design of these slabs. A computational tool was developed to evaluate the resistance through data entry related to geometry, service loads and materials, which grants to conduct a parametric study with pre-defined geometries to obtain, as result, spans and loads. Conclusions about the maximum span without shoring and general data are also discussed. Keywords Steel-concrete composite slabs, trussed slabs, cold formed U profile, design procedure. Evaluation of the resistance of trussed slabs with steel formwork in cold formed U profile Lucas Fadini Favarato et al. Latin American Journal of Solids and Structures, 2019, 16(7 Thematic Section), e178 2/18 (2015) also states that the major advantage in the use of this structural technology is related to the fabrication process: thin plates, with small resistance in its original shape, are stiffened where buckling can occur. Hence, the folding procedure changes steel original mechanical properties, leading to highest yield and ultimate strengths. Otherwise, residual stresses may come up, reducing the ductility of the material. Whereas rolled and welded steel profiles are more suitable for medium and large constructions, cold-formed ones are commonly used in small and medium constructions to compose roof structures, composite slabs and beams, mezzanines, popular houses, small warehouses and up-to-four-storey buildings. In addition, many cross sections are available for design, as C, Z, L and hat, doubled or not, stiffened or not (Silva et al., 2014). One important application of cold formed steel profiles in structural engineering, as presented previously, is in composite slabs. It gets incorporated to concrete after curing, allowing the composite behavior, and works as reinforcement, usually sparing additional ones. Besides, it's necessary to verify the structural safety before concrete curing, in which the steel formwork acts as a single steel beam and must resist to all ultimate limit states that can occur in construction st...

Proposition of a simplified analytical design procedure for lattice girder slabs with shuttering in cold-formed steel lipped channel section

“…The simplified analytical design procedure proposed for Trelifácil® slabs is detailed in this topic. Whereas no previous researches are found in the literature for this exact floor system, Favarato et al [33] suggested an alternative to assess the resistance of Trelifácil® for unpropped construction. Based on numerical buckling analyses, the author evaluates the maximum allowed unpropped span as well as maximum live load capacity.…”

“…Based on numerical buckling analyses, the author evaluates the maximum allowed unpropped span as well as maximum live load capacity. Nevertheless, on account of the high slenderness and low stiffness of the steel cross section, the unpropped spans can reach up to 1.40 m depending on section geometry [33]. Here, a computational tool is developed to estimate the number of props and maximum force applied on propping devices.…”

“…Additionally, the serviceability limit state of excessive deflection is also verified, accounting for the influence of creep and crack width of the concrete. Based on the span length L and using the appropriate load combination, one can define the live load bearing capacity, in kg/m 2 , that causes the predominant limit state [33].…”

“…Thus, stiffness and resistance to combined bending and shear during construction, are estimated considering minor axis bending of the lipped channel profile exclusively. d) Each concrete rib is assumed to behave as a simply supported T-shaped beam, and dimensions depend on filling element and steel profile geometry [33], in accordance with…”

“…The design procedure for T-shaped concrete beams was previously detailed by Favarato et al [33]. Here, only the key equations will be presented.…”