This paper presents the results of long-term experiments performed on three timber-concrete composite (TCC) beams. An innovative fabricated steel plate connection system, which consists of screws and steel plates embedded in concrete slabs, was adopted in the TCC beam specimens. The adopted shear connection can provide dry-type connection for TCC beams. Steel plates were embedded in concrete slabs while the concrete slab was constructed in factories. The timber beam and concrete slab can be assembled together using screws at the construction site. In this experimental programme, the beam specimens were subjected to constant loading for 613 days in indoor uncontrolled environments. The influence of long-term loading levels and the number of shear connections on the long-term performance of TCC beams was investigated and discussed. The mid-span deflection, timber strain, and interface relative slip at the positions of both connections and beam-ends were recorded throughout the long-term tests. It was found the long-term deflection of the TCC beam increased by approximately 60% while the long-term loads were doubled. Under the influence of the variable temperature and humidity, the TCC specimens with 8 shear connections showed slighter fluctuations compared with the TCC beam with 6 shear connections. In the 613-day observation period, the maximum deflection increment recorded was 6.56 mm for the specimen with eight shear connections and 20% loading level. A rheological model consisting of two Kelvin bodies was employed to fit the curves of creep coefficients. The final deflections predicted of all specimens at the end of 50-year service life were 2.1~2.7 times the initial deflections caused by the applied loads. All beam specimens showed relative small increments in mid-span deflection, strain and relative slip over time without any degradations, demonstrating the excellent long-term performance of TCC beams using the innovative steel plate connection system, which is also easily fabricated.
Moisture may significantly influence the dimensions and behavior of wooden elements and, thus, it is important to consider within both serviceability as well as ultimate limit state designs. Dimensional changes, also called swelling (during wetting) and shrinkage (during drying), are non-uniform due to the direction-dependent expansion coefficients of wood and usually lead to eigenstresses. If these exceed certain strength values, cracking may occur, which reduces the resistance to external loads, especially to shear stresses. The current standard Eurocode 5 takes these circumstances very simplified into account, by so-called service classes, defined based on the surrounding climate and average moisture levels over the course of a year. Accordingly, reduction factors for strength values and cross section widths are assigned.
For a better understanding of the climate-induced changes in wooden beams, we exposed 18 different beams with varying cross sections to a representative climate of Linz, Austria, within the framework of a finite element simulation and investigated the resulting moisture fields and crack patterns. For this purpose, expansions and linear-elastic stresses were simulated by using the thermal and moisture fields obtained in the first simulation step and expansion coefficients. Using a multisurface failure criterion, two critical points in time were determined for each cross section, at which advanced crack simulations were carried out using the extended finite element method. The resulting crack lengths showed that the Eurocode 5 assumption of a linear relationship between crack-free and total width could be verified for both drying and wetting cases.
In future, the obtained crack patterns might also be used to investigate the actual reduction of load-bearing capacities of such cross sections, since the position of a crack and, for example, the maximum shear stress may not coincide. For the first time in this work, a consistent concept is presented to estimate the resulting crack formation in a wooden element from any moisture load based on a mechanical well-founded simulation concept. For this reason, this work is intended to lay a basis for a more accurate consideration of climate-related loads on wooden elements up to timber constructions.
The development of this primer commenced shortly after the 2018 launch of the Mass Timber Institute (MTI) centered at the University of Toronto. Funding for this publication was generously provided by the Ontario Ministry of Natural Resources and Forestry. Although numerous jurisdictions have established design guides for tall mass timber buildings, architects and engineers often do not have access to the specialized building science knowledge required to deliver well performing mass timber buildings. MTI worked collaboratively with industry, design professionals, academia, researchers and code experts to develop the scope and content of this mass timber building science primer. Although provincially funded, the broader Canadian context underlying this publication was viewed as the most appropriate means of advancing Ontario’s nascent mass timber building industry. This publication also extends beyond Canada and is based on universally applicable principles of building science and how these principles may be used anywhere in all aspects of mass timber building technology. Specifically, these guidelines were developed to guide stakeholders in selecting and implementing appropriate building science practices and protocols to ensure the acceptable life cycle performance of mass timber buildings. It is essential that each representative stakeholder, developer/owner, architect/engineer, supplier, constructor, wood erector, building official, insurer, and facility manager, understand these principles and how to apply them during the design, procurement, construction and in-service phases before embarking on a mass timber building project.
When mass timber building technology has enjoyed the same degree of penetration as steel and concrete, this primer will be long outdated and its constituent concepts will have been baked into the training and education of design professionals and all those who fabricate, construct, maintain and manage mass timber buildings.
One of the most important reasons this publication was developed was to identify gaps in building science knowledge related to mass timber buildings and hopefully to address these gaps with appropriate research, development and demonstration programs. The mass timber building industry in Canada is still a collection of seedlings that continue to grow and as such they deserve the stewardship of the best available building science knowledge to sustain them until such time as they become a forest that can fend for itself.
The use of timber–concrete composite (TCC) bridges in the United States dates back to approximately 1924 when the first bridge was constructed. Since then a large number of bridges have been built, of which more than 1,400 remain in service. The oldest bridges still in service are now more than 84 years old and predominately consist of two different TCC systems. The first system is a slab-type system that includes a longitudinal nail-laminated deck composite with a concrete deck top layer. The second system is a stringer system that includes either sawn timber or glulam stringers supporting a concrete deck top layer. The records indicate that most of the TCC highway bridges were constructed during the period of 1930–1960. The study presented in this paper discusses the experience and per-formance of these bridge systems in the US. The analysis is based on a review of the relevant literature and databases complemented with field inspections conducted within various research projects. Along with this review, a historical overview of the codes and guidelines available for the design of TCC bridges in the US is also included. The analysis undertaken showed that TCC bridges are an effective and durable design alternative for highway bridges once they have shown a high performance level, in some situations after more than 80 years in service with a low maintenance level.
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.
The aim of this study was to assess the durability of commercially available coatings on cross- laminated timber (CLT) during natural and artificial weathering and against wood decay fungus. The CLT samples coated with twelve coatings were tested based on their moisture exclusion, water repellency, volumetric swelling and anti-swelling efficiency. Among all the tested coatings, only five (A, C, F, I and J) were able to promote water repellency and limiting dimensional changes. The top five coatings were then tested on CLT blocks exposed to natural (Starkville-MS and Madison-WI) and artificial weathering conditions and brown-rot fungi (G. trabeum). Variables such as visual ratings, water uptake, color and gloss change were determined during both weathering procedures. Damage caused by Gloeophyllum trabeum on uncoated and coated CLT was analyzed based on visual appearance and weight loss. For the coatings C and F, the visual rakings and color change results indicated high consistency during outdoor exposure. The artificial weathering showed that coating C and F were the most resistant to chalking, lightness, color and gloss change. In the soil block test, coating C obtained satisfactory performance against G. trabeum with weight loss of 1.33%. Coatings F and J did not offer any protection to water penetration, which eventually contributed to fungal development. For future, new coatings specifically designed for the protection of high percentages of end-grain in CLT panels should be a target of research and development.
International Journal of Design & Nature and Ecodynamics
Technological developments and social trends can create demand for new building functionalities, necessitating the adaptation of existing buildings. This paper presents the development of a modular building structural system that provides for the harmonization between the structural and functional lifespans of a building in order to achieve greater sustainability. The limitations of the existing prefabricated urban buildings with respect to their adaptability are contrasted with the proposed solution. The use of prefabricated engineered materials, such as cross laminated timber (CLT) and CLT-concrete composites, in conjunction with a modular system, reduces any climatic effects. The inherent advantages of incorporating detachable connections allows for the necessary structural adaptability, subsequently harmonizing and elongating the structural and functional lifespans. The resulting sustainable concept, when applied to residential buildings, could serve as a solution to address projections of future urban growth.
his thesis discusses the possibilities of using glued laminated timber as load bearing structural elements in structures in close vicinity of saltwater. Glued laminated timber, also referred to as glulam, is a refined timber product constructed of timber lamellae that are glued together. The thesis contains a literature study and a case study that covers glulam beams in a pedestrian jetty located on the Swedish west coast. The literature study addresses wood in relation to moisture, the effects that salt may have on wood in a marine environment, wood decaying mechanisms and suitable wood preservatives to prevent decay. The literature study also covers glulam as a material and the possibilities of wood pressure impregnation. A method of estimating the service life of timber elements is also discussed.
The results of the literature study were applied in a case study of a specific case, to explore the possibility of replacing the current steel beams of the structure with glulam beams. From the case study, the strength and deflection of the prospective glulam beams were calculated. Service life of the prospective glulam beams was estimated based on the environment they would be exposed to. An analysis of the market for glulam products in Sweden was also performed to find out what dimensions and wood impregnation classes are available.
The results of the literature study show that glulam can be used as main load bearing elements in a marine environment, given that the structure is placed above sea level. Salt water does not affect the wood, rather it works as a wood preservative and gives some protection against rot. However, the structure is subjected to high moisture content and pressure impregnation is necessary. The high moisture content also affects the mechanical properties of the wood as the strength and stiffness of glulam decrease with increasing moisture content. Creep of the material is also affected as it increases with increased moisture content.
Regarding strength and deflection, the results of the case study show that glulam beams available on the Swedish market are of sufficient dimensions to be used. Regarding service life, the case study showed that the estimated service life of the glulam beams is only 19 years, but the service life required is 50 years. The current structure design with prospective glulam beams does not meet the requirements for durability of the material. However, suitable design changes regarding wood moisture protection could increase service life of the glulam beams.
Biological durability issues in cross-laminated timber (CLT) have been majorly ignored in North America because of the European origin of the material and careful construction practices in Europe. However, the risks of fungal and insect attacks are increased by the North American climatic conditions and lack of job-site measures to keep the material dry. The methods to evaluate durability in solid timber are inadequate for use in mass timber (MT) for a number of reasons, such as moisture variation and size being critical issues. This study therefore proposes a method, which is suitable to evaluate the strength of MT assemblies that are exposed to fungal degradation. The objective of the study was to explore a controlled method for assessing the effects of wetting and subsequent fungal attack on the behavior of CLT connections. Two different methods were used to create fungal attack on CLT assemblies. Although they were both successful, one was cumbersome, left room for many errors, and was not as efficient as the other. In addition, a standardized method to evaluate and characterize key performance metric for the connections is presented.