Within several research projects and with the aim to optimize energy efficiency and ecological characteristics of structural building components the Department of Structural Design and Timber Engineering (ITI) at the Vienna University of Technology (VUT) developed several wood-based composite systems, which combine timber products with other conventional building materials and components. As a representative example for these developments, the application of wood lightweight concrete composites illustrates the extent of interrelationships in the development of complex system solutions when focusing on the increase of resource efficiency. The environmental assessment shows the ecological advantages of the developed concept compared to conventional concrete elements and underlines the potential for further developments. Assessment of structural wood-based wood lightweight concrete composites are illustrated in this paper.
The application of cross-laminated timber (CLT) as floor panels is limited by excessive deflection and vibration. A composite system combining CLT and ultra high-performance fibre-reinforced concrete (UHPFRC) was developed to extend span limits. Push-off tests were conducted on different connectors, and a glued-in rod connector was chosen and further refined for the proposed system. Static bending tests and free vibration tests were conducted on bare CLT panels and two composite specimens. By comparing the results, it is concluded that the proposed system considerably extend the span limits of CLT panels.
Project contact is Luca Sorelli at Université Laval
This project aims to develop a new precast wood / concrete floor system that can push the span limits in multi-storey wood buildings. The multidisciplinary methodology includes a finite element analysis technique using the “DDuctileTCS” software developed at CIRCERB, shear tests on connections, bending tests of the composite beam and an extension of technical standards for the design of composite structures. This project will develop solutions to optimize the composite action and vibration of long-span precast and mixed floors. The methodology consists of: (i) analysis of systems and optimization of shapes by numerical finite element techniques; (ii) connection shear tests; (iii) proof of concept on a prototype beam in the laboratory.
This paper examines a new and very promising concept for prefabricated timber-concrete-composite floors (TCC-floors), were the heavy normal weight concrete is replaced by a lightweight concrete (LC) with a density of about 17 kN/m³. Investigations into the connections between lightweight concrete and timber indicate that the...
Nail-laminated timber-concrete composite (TCC) is a system composed of a nail-laminated timber (NLT) panel connected to a concrete slab through shear connections. When used as flexural elements such as floors, the concrete and NLT are located in the compression and tension zones, respectively...
International Structural Engineering and Construction Conference
Proceedings of International Structural Engineering and Construction
The main objective of this paper is to study the structural performance of a high-rise
structure when alternative lightweight material known as cross-laminated timber was
used as a slab in floor system in lieu of conventional reinforced concrete slab. A
numerical case study was conducted using a highly irregular RC frame building with its
two 60-story towers joined at the top. Three major analyses were considered. First,
modeling and analyzing the building with an RC slab was conducted to determine the
design reference. Second, substituting the RC slab with the CLT slab was performed
using the same building skeleton. Third, redesigning and optimizing the building
skeleton with that CLT to observe skeleton material saving obtained using the same
structural performance criteria. Major lateral loads applicable in the Eastern Province
of Saudi Arabia were inputted. Strengths and serviceability requirements for floor
diaphragm and lateral load resisting system were checked first before performing a
comparative analysis between traditional RC and CLT slabs as floor diaphragm. The
structural performance criteria to be used for comparative study between RC and CLT
slabs included total drift, inter-story drift due to lateral loads, and base reactions.
Structural periods and acceleration responses for each floor were investigated and
contrasted with the existing building code. The foundation demand was also
investigated based on the structural weight and reactions generated from the RC and
CLT floor systems.
Project contact is Luca Sorelli at Université Laval
This project aims to develop a new prefabricated wood / concrete floor system that is innovative and competitive in multi-storey wood buildings. The design of the floor will be carried out through a multidisciplinary approach that considers the composite action of the precast floor, the integration of sound insulation, vibrations, the weight of the structure, construction time and environmental impact. Among other things, the construction method and the use of ultra high performance green composite concretes with CLT slabs or GLULAM beams will be considered. The methodology includes digital analysis tools and a new method for the design of mixed structures as well as the life cycle tool. The laboratory proof of concept will assess the performance of the optimized floor system and compare it to existing floors.
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.
Project contact is Sylvain Ménard at Université Laval
Designers of large buildings generally want floor systems with large spans (9 m). These floors are often sized by the requirement of vibratory performance and, correlatively, deflection. The composite wood-concrete floors allow large spans with reduced static height. They are a promising alternative to simple concrete slabs. Objective 1 - Determine the evolution of the natural frequency of the CLT-concrete composite floor as a function of the stiffness of the connector, and correlate the experimental results with the model by the finite element method. Objective 2 - Parametric study of the vibration performance of the CLT-concrete composite floor. The impact of several parameters on the dynamic performance of the floor will be determined, especially the characteristics of the constituent materials, connector and the creep of the floor. Objective 3 - Build the metamodels for the study of multi-objective optimization optimization of a wood-concrete composite floor solution in relation to a regional problem in Aquitaine.
Wood-concrete composite slab floors provide a promising solution for achieving long spans and shallow wood-based floor systems for large and tall wood buildings. In comparison with conventional wood floor systems, such long span and heavy floors have a lower fundamental natural frequency, which challenges the floor vibration controlled design. A laboratory study, including subjective evaluation and measurement of the natural frequencies and one-kN static deflections, was conducted on wood-concrete composite floors. Method of calculation of the composite bending stiffness of the wood-concrete composite floor is proposed. The design criterion for human comfort was derived from the subjective evaluation results using the calculated fundamental natural frequency and 1 kN static deflection of one meter wide strip of the composite floor. The equation to directly determine the vibration controlled spans from the stiffness and mass was derived. Limited verification was performed. Further verification is needed when more field wood-concrete composite floors become available.