Prefabricated timber-concrete composite floors
The presented investigation concerns the study of novel types of timber-concrete composite floors, manufactured with “dry connections” (Crocetti et al. In: 11th WCTE, Riva del Garda: international conference proceeding of 11th WCTE, Riva del Garda, 2010; In: RILEM 2013: Materials and Joints in Timber Structures—Recent Advancement of Technology Stuttgart, Germany, 2013: RILEM 2013, Stuttgart, 2013; Sartori et al. In: Enhance mechanical properties of timber, engineered wood products and timber structures. University of Bath, COST FP1004, Zagreb, 19 April 2012, 2012). Three full-scale nominally identical floor elements were investigated. The shear connector system used in the investigation was realized by means of self-tapping screws driven at an angle of 45° into the wood. First, the screws were inserted on the top of the glulam beams. Then, the beams were twisted upside-down and placed on concrete formwork (Fragiacomo In: Struct Eng Mech 20(2):173–189, 2005). Then fibre reinforced concrete (FRC) was cast in the formwork. Quasi-static bending tests and long-term bending test were performed. It was found that the proposed connection systems performed more than satisfactory in the short term, showing a very high degree of composite action even at load levels close to the failure load. However, long-term loading (Fragiacomo and Ceccotti In: J Struct Eng 132(1):13–22, 2006) induces increased deformation, which should be taken into account in SLS design.
Long-Term Behavior of Timber–Concrete Composite Beams. I: Finite Element Modeling and Validation
This first part of two companion papers deals with the numerical modeling of timber–concrete composite beams (TCCs) under long-term loading. All phenomena affecting the long-term behavior of timber, concrete, and the connection system, such as creep, mechanosorptive creep, shrinkage/swelling, and temperature variations, are fully considered. The structural problem is solved through a uniaxial finite element model with flexible connection and a step-by-step numerical procedure over time. The important role played by the environmental thermohygrometric variations on TCCs is highlighted through some analyses. The proposed numerical procedure is validated on two long-term experimental tests in outdoor conditions. Despite some uncertainties in environmental conditions and material properties, a good fit between experimental and numerical results is obtained. A parametric analysis is performed in the second part, showing the contribution of different rheological phenomena and thermohygrometric variations on beam deflection and connection slip. Based on results carried out, a simplified approach for long-term evaluation of TCCs is then proposed.
Nonlinear Analysis of Composite Beams with Deformable Shear Connectors
Composite floor systems, consisting of reinforced concrete slabs and steel girders, are common in buildings and bridges. Partial restraints at the interface of the concrete slab and the steel girder have significant effects on the response of the composite beam. A few analytical models capable of accounting for these effects are available; however, none can be efficiently used for the nonlinear analysis of composite beams. In this paper, the basic governing equations are presented for a composite beam with deformable shear connectors under small displacements. Based on these equations, a new composite beam element is developed using the force method of analysis. The performance of this new element is compared with that of a previously developed displacement-based composite beam element. Both elements consist of two beam components connected through a deformable interface. A distributed spring model is used to account for the shear deformation at the interface. Two numerical examples on the nonlinear behavior of composite beams are solved using both displacement- and force-based elements. Comparison of the numerical results shows the superior performance of the newly developed force-based element over the displacement-based element.