Testing and Analysis of Multi-Joist Transversely-Indeterminate Timber-Concrete Composite Floors

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

This thesis presents experimental and numerical research into multi-joist transversely-indeterminate timber-concrete composite (TCC) floors. Two three-joist specimens were designed and tested, and provided a significant new body of work to the field of TCCs, and the comprehensive instrumentation on these specimens allowed for a detailed and in-depth understanding of their load response from zero load to failure. Complementary shear connection tests allowed for the determining of characteristic properties of the chosen expanded steel mesh shear connector, which was utilised throughout the thesis and enabled in-depth analysis of the experimental data, and creation of accurate finite element (FE) models.
Significantly more is now known about the bending moment distributions in TCC
specimens and crucially that they are more favourable compared to support reaction distributions. This work has also highlighted the potentially significant influence of an altered connection layout on the load response of TCCs, where a reduced connection distribution lowered the strength of the specimen whilst at the same time significantly extending the ductility range and maximum deflection. Dynamic impact testing showed that a lower connection density and lower concrete strength led to a 10% drop in the first natural frequency,
and that values of damping ratio prescribed by the design codes may be overly
conservative for TCC floors, and require special consideration. A simplified model was able to better predict the first mode than recommended equations, however a more in-depth model was required to accurately match mode shapes and higher mode frequencies.
A full 3D model created using the Abaqus software package utilised best practice modelling from previous studies to effectively and accurately model the behaviour of complex indeterminate TCC structures up to significant applied loads. Parametric studies also provided insight into the effect that further changes to material and geometric properties would have on the specimens, highlighting that a lower longitudinal specimen stiffness may increase the ability of the specimen to distribute loads transversely.
A simplified model was validated for a new three-joist specimen layout and geometry - which itself was designed using feedback from industry - against the full 3D model. Under low loads the simplified linear model matched excellently with the complex model, highlighting that these techniques may be used by the design engineer to quickly and efficiently analyse the response of multi-joist TCC structures to applied concentrated loads, and further their use in practice.
Date of Award26 Nov 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJames A P Norman (Supervisor) & Ian P Bond (Supervisor)

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