Analysis of the assembling phase of lattice slabs

Abstract

Lattice slabs are usual in Brazil. They are formed by precast joists with latticed bars on a base of concrete, and a cover of concrete placed at the jobsite. The assembly of the joists and the filling elements is simple and do not require manpower with great skill, presenting low cost-benefit ratio. However, it is precisely in assembling phase that arise questions related to the scaffold support distance. A mistake in the proper positioning can lead to two undesirable situations. In one of them, a small space between the support lines increases the cost of scaffold, and in other an excessive space can generate exaggerated displacements, and even the collapse of the slab in the stage of concreting. The objective of this work is to analyze the bearing capacity of lattice joists in assembling phase, looking for information that is useful in defining the scaffold support distance. Several joists were tested to define the failure modes and their load bearing capacities. The results allowed to determine equations for calculating the appropriate distance between the support lines of the joists.

Self-supporting tests in lattice joists subject to negative bending

“…When a joist, mini panel or panel is loaded and positioned over the supports, bending moments and shear loads will develop. For cases of sagging moments acting on the structure, the adequate equation can be found in Sartorti et al [3]. For cases of hogging moments acting on the structure in regions where a concrete opening exists, the present article defines equations for calculating the resisting hogging moment and shear forces.…”

“…The code ABNT NBR 14859-1 [2] regulates the precast lattice joists fabrication (VT) with a base of concrete. The lattice girder partially embedded in the concrete base provides a light element easy to handle, requiring fewer shuttering components according to its selfsupporting capacity (SARTORI [3]). The joists can be reinforced or not, depending on its structural demand.…”

“…Terni et al [11] developed researches using computer programs in order to analyze this behavior in the upper flanges. Sartorti et al [3] developed experimental studies with positive bending and shear in lattice joists subject to sagging moments, aiming to provide data about the calculation of spacing between prop lines. It also aimed to obtain a more economic construction process, eliminating issues during the construction phase and ensuring security.…”

Theoretical and experimental analysis of precast slabs composed of pre-stressed joists

“…Implementing these types of floors leads to slabs with high thicknesses, often making the structure uneconomic since part of the structural capacity of this system is used to bear the demands arising from its own weight [1][2][3]. To solve this problem, joist slabs have been used in place of solid slabs which allows the construction of slabs with greater spans and less weight in the construction system [4]. Joist slabs also simplify design execution, reduce losses, and increase productivity [5,6].…”