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Timber Concrete Composite Floors with Cross Laminated Timber - Structural Behavior & Design

https://research.thinkwood.com/en/permalink/catalogue2723
Year of Publication
2020
Topic
Design and Systems
Material
CLT (Cross-Laminated Timber)
Application
Floors
Author
Forsberg, Albin
Farbäck, Filip
Publisher
Lund University
Year of Publication
2020
Country of Publication
Sweden
Format
Thesis
Material
CLT (Cross-Laminated Timber)
Application
Floors
Topic
Design and Systems
Keywords
TCC
Timber Composites
Structural Behavior
Design Methods
Gamma Method
Equivalent Gamma Method
Extended Gamma Method
RFEM
First Natural Frequency
Serviceability Limit State
Ultimate Limit State
Language
English
Research Status
Complete
Summary
Due to the increasing environmental awareness, the transition pace to renewable materials has increased, and the use of timber in construction is no exception. However, using timber in high rise building applications comes with structural challenges, e.g dynamic issues originating from timber being lightweight compared to conventional building materials. Some of the structural challenges with timber can be resolved by the implementation of Timber Concrete Composites (TCC), which increases the effective bending stiffness by adding a concrete layer connected to the underlying timber floor. Furthermore, the higher self-weight of concrete contributes to improved dynamic performance. Despite the fact that the TCC floor is a versatile and quite common structural design solution in Europe, the TCC knowledge in the Swedish construction industry is limited. The main scope of the thesis is to raise this knowledge of TCC by studying the structural behavior and develop applicable design methods. Both analytical design methods and FE-modelling are addressed. The content is limited to TCC floors with a 5-layer Cross-Laminated Timber (CLT) section, with use of notches or screws as shear connectors. In CLT design, the Gamma method is commonly used and applicable to a CLT layup up to 5 layers. This method can, by a slight modification, be applicable for TCC sections with a 5-layer CLT as well. The concrete layer on top is regarded as an additional longitudinal layer, flexibly connected to the CLT section. The Equivalent gamma method and the Extended gamma method are two modified versions of the conventional Gamma method, valid for TCC floors with 5-layer CLT sections. Each method determines the effective bending stiffness accurately, compared to FE-modelling and laboratory test results. The Extended gamma method has a more solid theoretical base compared to the Equivalent gamma method, and is considered the recommended design method. The simplified methodology of the Equivalent gamma method is theoretically questionable, hence its recommended use is for preliminary calculations only. The following concluding remarks can be drawn from the analysis of the structural behavior of TCC floors: - The shear connectors should be concentrated to areas of high shear flow, i.e. close to support, for optimal structural performance. - An increased ratio of timber in the longitudinal, load-bearing direction of the CLT section increases the effective bending stiffness of the TCC. - The concrete layer increases the effective bending stiffness due to the high Young's modulus. However, the high density of concrete entails a thin concrete layer thickness to achieve a light-weight and structural efficient TCC system, and the decisive optimisation factor is the ratio of mass-to-effective bending stiffness, m/EI.
Online Access
Free
Resource Link
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