Development of Empirical Model of Shear Force Capacity and Stiffness of the Screw Connections in Timber – Concrete Composite Structures

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

The stiffness and shear force capacity of Timber Concrete Composite (TCC) structures in flexure depend significantly on the connection between the two materials. This work was carried out due to some limitations found in Eurocode 5 (EC5) and existing predictive strength and slip modulus models of screw connections. One deficiency seen in these models is the neglect of consideration of the local characteristics of the screw embedded within the concrete on the behaviour of the connection between the timber and concrete. In addition, while Eurocode 5 currently gives guidance for evaluation of the shear force capacity of timber-timber connections, no guidance is available for timber-concrete connections in the code. Reviews have been made on the existing model of shear force capacity and stiffness. It was found that there was no research done on developing the shear force capacity and stiffness model based on the X-formation screw and considering variety in screw angle between 0° to 90°.Therefore a set of experimental tests on Timber-Concrete Composite structures was performed to investigate the effect of the screw angle on the effective length of the screw which also influences the embedment strength of the screw embedded within the concrete. In the experimental tests, strains were measured along the screw length embedded within the concrete for a number of double shear test specimens. The strain data obtained from the double shear tests were used to develop local bending moment curves along the screw embedded within the concrete. A strip analysis method was used across the screw diameter to determine the internal forces in every strip. The summation of internal moment across the screw diameter produced the local bending moment at point the strain gauges were located. Then the distribution of bending moments along the screw was produced by interpolating the moments at the gauged locations. From the plot of bending moment along the screw embedded within the concrete, the load distribution was obtained by double differentiating the moment curves. Displacement profiles were also produced by double integrating the moment curves. The plot of bending moment and displacement generated from strain gauges method then compared with scans of the actual screw shapes at the end of the tests. The screws were taking out of the tested specimen as careful as possible to avoid changing the screw shape. A scanner recorded the coordinates of the screw and translated them into a 2D data set. By analysing the 2D data from the screw scans it was possible to determine the screw curvature. From the curvature the local bending moment was calculated then the distribution of moment along the screw embedded within the concrete at the end of the test was produced. Comparison was made between the bending moment distribution and displacement generated by the strain gauges and the scanning, and the two methods showed very good agreement. The very useful parameter obtained from bending moment distribution from both methods was the distance of hinge from the interface between timber and concrete. This parameter was used in analysis of multiple linear regression to develop shear force capacity and stiffness model. After new model of shear force capacity and stiffness successfully developed, comparison was made with the suggested formulae from published model.
Date of Award30 Jul 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorPaul J Vardanega (Supervisor) & Adam J Crewe (Supervisor)

Keywords

  • timber concrete structures
  • timber hybrid structure

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