1,721,056 research outputs found
Effect of Endogenous Deformations in Composite Bridge Beams
No full textEarly age endogenous deformations due to concrete hydration heat, shrinkage and creep can represent a real cracking risk for composite bridge beams. The phenomenon is difficult to take into account during design of composite bridges, as it takes place just after slab casting, when material properties of concrete are quickly changing with time.
Recommendations on this topic in design codes and literature are generally poor and sometimes ambiguous. For instance, EN 1994-2 (CEN, 2005) states that short term elastic modulus and 20 K temperature difference between concrete slab and steel beam should be used. SETRA Guidance book Eurocodes 3 and 4 (Davaine et al., 2007) reduces the temperature difference to 10 K, but it gives no precise indication on the elastic modulus to be used.
The aim of this work is to perform a set of non-linear thermo-mechanical analyses in order to evaluate the cracking sensitivity of a simply supported composite bridge and to understand if early age endogenous deformations can be modelled in elastic analysis by an equivalent temperature difference between concrete and steel with an appropriate elastic modulus for young concrete
Autogenous deformations in massive concrete structures
No full textThe design of concrete structures exposed to environmental attack requires serious attention for concrete durability. Early age cracking due to autogenous deformations should be avoided.
In the proposed work the study of the structural effects of hydration heat and rheological properties of concrete on structures realized by means of massive concrete castings is presented. The object of the study are a skyscraper foundation slab and the Venice Barriers (M.O.S.E.) foundations. Aim of this work is the numerical simulation of what occurs to the structure from the first hours after the casting, in order to design the structure avoiding unforeseen autogenous cracking.
Non-linear finite element coupled thermal and mechanical analyses have been performed taking into account: hydration heat, dimension of the casting, evolution of concrete mechanical properties in time during the hardening reaction, creep and differential shrinkag
A Finite Element formulation for concrete structures in plane stress
No full textA comprehensive, very compact non-linear finite element is proposed, which is able to describe the behaviour of two-dimensional concrete structures from serviceability conditions up to collapse. The formulation of this finite element takes into account all the material non-linearities typical of concrete structures such as cracking, non-linear behaviour in compression, tension and compression softening and shear transmission along cracks. The robustness of the finite element derives from its compactness and from the reduction of the number of input parameters that control the structural response, but whose values very often cannot be properly introduced. The proposed finite element is calibrated by reproducing a wide range of well-known experimental tests, carried out both on simple panels and complex two-dimensional structures; it is then tested with reference to three additional cases, where it shows a satisfactory capability to predict reinforced concrete two-dimensional structural behaviour
A hybrid genetic algorithm for skew reinforcement minimization in concrete shell finite elements
No full textIn structural design, structures are often modeled using the finite elements method (FEM). One of the most common element type is the shell, which is used to model surfaces in three dimensional space as far as the surface thickness is smaller than the other two dimensions. Designers are generally interested in providing a solution that respects all the problem constraints and guarantees structural safety [1], without trying to further improve it as optimization is not trivial even if it could yield a huge benefit both from the economic and the construction point of view. Additionally, saving materials is one of the fundamental criteria for the sustainable approach to the design. In this paper we address the Skew Reinforcement Design in Reinforced Concrete Two Dimensional Elements (SRD2D) under multiple loading conditions. It consists of determining the minimum reinforcement required to respect all the constraints given by the geometric properties and the internal actions working on it, for all the loading conditions that may occur, i.e. for different combinations of internal actions acting on the element. We present a heuristic framework that guides a Genetic Algorithm. Computational results show the efficacy and the effectiveness of the method
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