ICSI 2021 The 4th International Conference on Structural Integrity
Research Status
Complete
Series
Procedia Structural Integrity
Summary
Rigid timber to concrete connection is the most effective solution for timber-concrete composite members subjected to the flexure which provides full composite action and better structural behaviour. One of the most used technologies to produce glued connection of the timber-concrete composite is “dry” method, which includes gluing together of timber and precast concrete slab. This technique has high risk of forming a poor-quality rigid connection in timber-concrete composite, and there are difficulties in controlling the quality of the glued connection. The effect of the non-glued areas in connection between composite layers on the shear stresses and energy absorption were investigated by finite element method and laboratorian experiment. Three timber-concrete composite panels in combination with carbon fibre reinforced plastic composite tapes in the tension zone with the span 1.8 m were statically loaded till the failure by the scheme of three-point bending. Mid-span displacements were measured in the bending test. One specimen was produced by dry method, by gluing together cross-laminated timber panel and prefabricated concrete panel. Timber-concrete qualitative connection of the other two specimens was provided by the granite chips, which were glued on the surface of the cross-laminated timber by epoxy, and then wet concrete was placed. Dimensions of the crushed granite pieces changes within the limits from 16 to 25 mm. The investigated panel with different amount and sizes of non-glued areas in the timber to concrete connection was numerically modelled. Obtained results shown, that the increase of shear stresses is influenced not so much by a total amount of non-glued areas, but by the size of the individual defective areas. Moreover, large non-glued areas significantly reduce the energy absorption of elements subjected to the flexure, which was observed experimentally for defective panel produced by the classical dry method with almost 4 times larger mid-span displacements than for panel with full composite action provided by the proposed production technology of the timber to concrete rigid connection. So, the proposed technology based on the use of granite chips, provides a high-quality connection between timber and concrete layers, with insignificant ration between possible defect and total connection surface area, which is equal to the area of one granite chips edge.
The Mass Timber Panel-Concrete (MTPC) composite floor system considered in this paper consists of a Mass Timber Panel (MTP) connected to reinforced concrete slab with Self-Tapping Screw (STS) connector and a sound insulation layer in between. This type of composite floor system is intended for mid- to high-rise building applications. Two types of MTPs with normal weight concrete, two insulation thicknesses, two screw embedment lengths and two screw angles were investigated through connection tests to characterize connection stiffness and strength. The main goal of this connection test program was to provide preliminary test data to assist in the development of a model to predict connections lateral stiffness and strength under consideration of insulation thickness, screw angle, withdrawal and embedment properties of screws in MTP. Connection test results show that screws at an insertion angle of 30° have a higher stiffness and strength along with a larger embedment length compared to the screws at a 45° angle and smaller embedment length. Stiffness seemed to be more susceptible to the influence of presence of insulation compared to strength with 40-65% reduction of stiffness and 10-20% reduction of strength were noticed for an insulation thickness of 5 mm. Screws in CLT showed higher strength while screws in CLP showed higher stiffness but the difference is insignificant.
Bending strength tests were conducted of cross-laminated timber (CLT)-concrete composite slabs according to the shear connection method and carbon fiber reinforced plastic (CFRP) reinforcement. The bending strength of the composite slab that was shear-connected with an epoxy adhesive was 17% higher than that of a composite slab that was shear-connected with a self-tapping screw. In addition, the CLT-concrete slip of the former composite slab was also measured as 20% lower than the latter under the same load, showing a behavior close to that of a full composite. Both shear connection methods generated a failure in a low load-deformation section when there was a defect in the outermost tensile laminae of the CLT. In contrast, the CFRP reinforcement in the tension part of the composite slab suppressed the failure at the defect in the outermost tensile laminae. This reinforcement effect increased the reliability of the bending performance of the composite slab by preventing the failure of the composite slab while in a constant failure mode. Furthermore, the slip of the composite slab decreased 49% after its reinforcement with CFRP, showing a behavior close to that of a full composite.
Design for disassembly using deconstructable connections facilitates recycling and reusing of building materials and, therefore, reduces waste management problems at the end of service life. In this regard, a deconstructable timber-concrete composite connector using self-tapping screws has been developed at Aalto University. In the presented research, an experimental investigation was performed to further evaluate the effectiveness of this connector in fabricating deconstructable cross-laminated timber (CLT)-concrete composite floors. For this purpose, several CLT-concrete composite beams were fabricated using 5-layer CLT and low-shrinkage concrete. Each beam contained one row of connectors to represent a strip of a full-scale floor. The vibration performance, bending properties, interface slip, failure modes, and ease of disassembly of the beams were investigated. The results were compared with the ones from a reference group of beams fabricated with regular screws. Overall, the deconstructable beams performed exceptionally well by attaining 98.5% of the average bending stiffness of the regular beams. The load-carrying capacity was also similar but governed by the CLT plate. The vibration characteristics were comparable in both groups. After the bending test, the deconstructable beams were disassembled. Although the beams had been exposed to unproportionally large deformations under the bending load, the disassembly process was performed successfully.
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 performances of the existing connection types are unsatisfactory if combined with lightweight concrete. Therefore, a new connection method is proposed, adhesively bonding the lightweight concrete with the timber by means of a filled epoxy resin. Different ways of manufacturing the bonded timber-lightweight concrete-composite beams (TLCC-beams) are investigated in a research project at the Technische Universität Berlin, to examine the differences in their structural performances. Most promising are the test results for TLLC-beams, fabricated with a wet-in-wet bonding method.
Calculative Cost and Process Analysis of Timber-Concrete-Composite Ceilings with Focus on Effort and Performance Values for Cost Calculations of Multi-Storey Timber Buildings
Composite structures use the advantages of two materials – timber and concrete – and improve the efficiency of a material application. Especially the concept of timber-concrete-composite ceilings has synergetic effects to achieve an effective ratio of thickness to span with high cost effectiveness simultaneously. Following the systematic...
In the presented paper, results of theoretical and experimental investigation of timber-concrete composite members with adhesive connection are described. For the timber part of composite beams Cross Laminated Timber and for concrete part lightweight concrete was used. For the composite connection special adhesive to bounding wet concrete and timber was applied. For experimental investigation two types of composite beams with different dimensions was used. Due to the shrinkage of lightweight concrete small precamber of timber beams during concrete hardening was applied. CLT panels combined with concrete slab dispose of higher load-carrying capacity, lower deformation and vibration. In case of theoretical analysis, simplified analytical -method was used to consider shear flexibility of the CLT cross layer. Results of presented experimental and theoretical analysis provide wider scope for further research and application of adhesively bonded CLT-concrete composite members.
Proceedings of the Institution of Civil Engineers - Construction Materials
Notes
DOI link: https://doi.org/10.1680/jstbu.171.9.661
Summary
As the only renewable construction material, and owing to the superior specific stiffnesses and strengths of the different species, timber has been used in major load bearing applications for thousands of years. The advent of waterproof adhesives during World War II and recent advances in manufacturing have combined to exploit the ease of forming and machining this material, leading to various forms of engineered timber including glulam, laminated veneer lumber (LVL) and cross-laminated timber (CLT). Manufactured in lightweight modules that are easily transported, then quickly craned into position and connected to produce eye-catching structures, engineered timber provides cost-effective alternatives (with minimal numbers and complexity of connections) to conventional materials for rapid construction of affordable residential and office spaces in busy city centres.
Comparing the environmental impacts of building materials at the building level can be biased because a building design is optimized for a primary structural material. To achieve objective comparisons, this study compares the environmental impact of reinforced concrete (RC), cross-laminated timber (CLT), and timber-concrete composite (TCC) at the component level with equivalent structural performance. A slab was selected as the target structure member because its design does not consider lateral forces. Equivalent structural performance was defined as the minimum quantity of slab materials for comparable span and live load conditions. The functional unit for this study was defined as a 1 m2 slab. The system boundary covered the cradle-to-gate perspective, including raw material extraction, transportation, and manufacturing. The structural design method and material design values followed the Korean building code and standards. Environmental product declaration data developed in Korea were used to evaluate the carbon footprint. The CLT emitted 75 % less carbon dioxide, the primary greenhouse gases responsible for anthropogenic climate change, compared with RC regardless of conditions, while the TCC emitted 65 % less CO2, and its environmental impact improved as the span lengthened. The results also indicated that timber slabs are thinner than concrete slabs and can be structurally rational.
A Comparative Life Cycle Assessment Approach of Two Innovative Long Span Timber floors with its Reinforced Concrete Equivalent in an Australian Context
International Conference on Performance-based and Life-cycle Structural Engineering
Research Status
Complete
Summary
The building sector contributes 24% of the total greenhouse gas emissions in Australia. This is expected to rise by 110% by 2050. Consequently, there has been an increased demand for more sustainable building materials which can play a significant role in reducing carbon emissions. Engineered timber wall and floor panels are being seen as a viable alternative for multi-storey buildings for both strength and environmental purposes and are gaining popularity in Europe, North America and New Zealand. A number of previous Life Cycle Assessments (LCA) comparing timber and concrete mid-rise buildings have highlighted the environmental benefits of using timber, particularly during material production and on-site construction stages. Furthermore, the choice of endof-life scenario had a significant effect on the LCA outcome. The objective of this paper is to compare the environmental impacts associated with alternative designs for a long span floor in a multi-storey building in Australia. The comparison, using an LCA approach, is based on a recently built long span Timber Concrete Composite (TCC) floor in a University building in Sydney. Three design options are considered: the original design of TCC, a Cross Laminated Timber (CLT) panel, and a traditional in-situ reinforced concrete (RC) slab. The CLT and RC designs were conceived with reference to the floor plans and structural loads obtained from issued-for-construction drawings. With this evaluation, recommendations for increasing the competitiveness of CLT and TCC within the Australian market are made.
