VILNIUS TECH Library invites you to follow the published new dissertations. The dissertation „Flexural stiffness model for layered concrete elements with partial shear connection“ prepared at VILNIUS TECH by Juozas Masėnas. The dissertation was prepared in 2021–2026. Scientific consultant – Prof. Dr Juozas Valivonis.
The dissertation was defended at the public meeting of the Dissertation Defence Council of Civil Engineering in the Aula Doctoralis Meeting Hall of Vilnius Gediminas Technical University at 10 a.m. on 14 May 2026.
Layered concrete structural elements consist of two or more concrete layers cast at different times and often with varying material properties. These elements can offer significant structural, architectural, and environmental advantages, provided that composite behaviour between the layers is maintained. The key factor governing this composite action is the performance of the interface between the concrete layers. In practice, the interface may exhibit reduced initial stiffness and will inevitably experience stiffness degradation as cracking develops. As the interface loses stiffness, the individual layers begin to perform more independently, leading to a reduction in the overall flexural stiffness of the layered element. Despite this, most current design codes lack an analytical approach for calculating deflections that account for interface partial shear connection, and such methods remain limited in scientific literature. In practice, standard reinforced concrete flexural analysis is typically suggested. This dissertation proposes an analytical approach to determine the flexural stiffness (deflection) of layered concrete elements, accounting for the varying interface stiffness as the element deforms. The approach begins with an interface behaviour model, which describes the relationship between interface shear stress and layer slip. This model is characterised by four distinct stages of interface behaviour, each governed by different shear mechanisms, interface material properties, and a differential shrinkage effect. It remains applicable from the onset of interface loading through to significant interface deformations. From the shear stress-slip relationship, the variable interface shear stiffness modulus is derived. This modulus is then used in the second stage of the analytical approach: the built-up layers deflection estimation model. This model allows for the calculation of deflection in layered elements while accounting for the stiffness of individual layers, the composite stiffness of the entire element, evolving geometries due to cracking, and the changing interface shear stiffness. Experimental and numerical analyses were conducted on concrete interfaces and layered concrete elements subjected to bending. The interface analysis provided insights into the effects of concrete strength, connector geometry and strength, differential shrinkage, interface roughness, and its overall geometry on interface strength, stiffness, and the intensity of different shear mechanisms. The analysis of layered beams and slabs clarified the cracking behaviour of individual concrete layers, the distribution of shear stress along the interface, the influence of connector inclination, and layer depth on flexural capacity and cracking patterns. Experimental results were used to validate the proposed analytical approach, showing strong agreement and confirming its effectiveness for analysing layered concrete elements.
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