Construction of eco-friendly high-rise buildings using cross-laminated timber (CLT)-concrete composite (CCC) slabs is increasing. CLT and concrete, which are major component materials of the CCC slab, are significantly affected by moisture. In particular, the moisture content of concrete in the production process affects the quality of both materials. In this study, the effects of the wet construction method on CLT and concrete component materials are examined by monitoring the behavior of the CCC slab during curing time (28 d) and by evaluating the quality of the concrete and CLT after curing. When manufacturing the CCC using the wet construction method, moisture penetration from the concrete into the CLT during the curing time is suppressed by the shear bonding between the concrete and the CLT when an adhesive is used. This minimizes the effect of the moisture on both component materials, consequently yielding uniform compressive strength to the concrete after curing and preventing the deterioration of the CLT’s delamination performance. Therefore, the shear bonding method using an adhesive is expected to minimize the quality deterioration observed in concrete and CLT after curing.
Cross-Laminated Timber (CLT) is an engineered mass timber product manufactured by laminating dimension lumber in layers with alternating orientation using structural adhesives. It is intended for use under dry service conditions and is commonly used to build floors, roofs, and walls. Because prolonged wetting of wood may cause staining, mould, excessive dimensional change (sometimes enough to fail connectors), and even result in decay and loss of strength, construction moisture is an important consideration when building with CLT. This document aims to provide technical information to help architects, engineers, and builders assess the potential for wetting of CLT during building construction and identify appropriate actions to mitigate the risk.
Le bois lamellé-croisé (CLT) est un produit massif de bois d’ingénierie qui est fabriqué à partir de multiples pièces de bois de dimension assemblées en couches orthogonales avec des adhésifs structuraux. Ce produit est conçu pour des conditions de service sèches et est couramment utilisé pour construire des planchers, des toits et des murs. Comme l’humidification prolongée du bois peut causer des taches, de la moisissure, des variations dimensionnelles excessives (parfois suffisantes pour provoquer la défaillance des attaches), et même la pourriture et la perte de résistance, l’humidité est un facteur important dans la
construction avec le CLT. Le présent document a pour but de fournir de l’information technique pouvant aider les architectes, les ingénieurs et les constructeurs à évaluer les risques d’humidification du CLT pendant la construction de bâtiments et à prendre les mesures appropriées pour atténuer ces risques.
Cross-laminated timber (CLT) is revolutionizing the use of wood in the construction sector of North America as a solution for walls and diaphragms in mid-rise or even high-rise timber structures on account of its environmental advantages, high strength-to- weight ratio, fire-safety performance, and propensity for prefabrication. However, considering the hygroscopic nature of wood, moisture intrusion can affect material properties and, moreover, moisture increases the possibility of biological degradation, which can directly affect the durability of CLT structural members and their connections. The favorable seismic performance of connections in the CLT structural systems has been well researched in numerous studies. In addition, even though several research efforts have been conducted to understand the hygrothermal performance of CLT panels, knowledge of the CLT connections when subjected to moisture cycling is minimal. In this study, a CLT shear wall-to-diaphragm L-bracket connection is exposed to two high moisture exposure conditions - flood and simulated rain with increased humidity as well as different exposure durations to investigate the connection performance under the effects of moisture intrusion. Currently, there are four major species that are used for CLT, namely, Douglas-fir, Southern yellow pine, Norway spruce, and Spruce Pine Fir. All four species were incorporated into the study. A total of 264 cyclic tests were performed on wall-to-diaphragm L-bracket connection specimens to evaluate the connection performance in terms of strength, stiffness, and energy dissipation along with the development of two force-displacement engineering models. Results from both exposure studies suggest no significant degradation in connection performance after a moisture cycle of wetting and drying apart from a significant decrease in energy dissipation in flood exposure. However, the effects of multiple moisture cycling merit further study.
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.
The Tallwood House project was intended to advance the design and
manufacture of mass timber products in Canada and demonstrate
that mass timber is a viable structural option for mid-rise and
high-rise buildings. The use of mass timber and engineered wood
products in high-rise construction is becoming more common
around the world leading to a growing interest in the performance of
mass timber over time.
This report describes the performance of the mass timber structure
in Tallwood House, between September 2017 and August 2019,
based on measurements of the moisture content in the prefabricated
CLT floor panels and the displacement of the vertical structural
system. It is intended to initiate discussions on the performance of
mass timber structure elements during building occupancy and lead
to further research that can explore the influential factors.
"As an alternative option to conventional sprinkler system, water mist systems are considered for the protection of timber buildings because they use much less amounts of water compared to sprinkler systems. The effectiveness of high pressure water mist (HPWM) and low pressure water mist (LPWM) systems was investigated in comparison to sprinkler systems for a residential fire scenario involving mass timber structures. The most distinct characteristic of the HPWM and LPWM systems was fine water droplets generated from the nozzles, which demonstrated effective smoke cooling in the room. Although the water spray rate of the HPWM was four times lower than that of the sprinkler system, the water mist systems effectively control the fire and maintained the room tenable. Most systems (HPWM, LPWM and sprinklers) tested in this study did not prevent fire damage on the CLT walls, but the HPWM system with a wide spray angle demonstrated rapid fire suppression and protection of the CLT walls. In all tests, a large water pool formed on the floor, which appeared proportional to the total water spray discharge in each test, and the moisture contents measured on the surface and bottom edges of the CLT panels indicated that water can penetrate into the interface between the floor and the wall in a typical CLT assembly"--Executive summary, page 1.
Cross-laminated timber (CLT) construction systems have been used commercially for over 20 years, mainly in Western Europe and North America. However, there has not been a report on the current status of CLT buildings. Deterioration of wooden buildings could result from a variety of causes and the life of the structures could be extended if periodic inspections were conducted. This research introduces a visual inspection methodology for assessing deterioration of CLT structures. The inspection methodology was tested in six CLT buildings in Austria. The methodology was proven to be effective in determining the current internal and external condition of the examined CLT structures. The oldest CLT structure inspected dates from 2004. The newest structure inspected was still under construction. The results of the application of the visual inspecting tool show that there was very little damage to the CLT structures. The main causes of damage came from exposure to water on the exterior of the buildings and poor control of humidity and temperature in indoor conditions. Architects who designed the inspected buildings were interviewed to cross validate the results of the visual inspection methodology. In addition, the interviews provided important insights related to the design, construction, and current conditions of the buildings. Furthermore, the architects also provided information regarding the main barriers and drivers that affect CLT construction in Austria.
Cross-laminated timber (CLT) panels are increasingly used in mid-rise buildings or even taller structures in North America. However, prolonged exposure to moisture during construction and in service is a durability concern for most wood products including CLT. To investigate practical solutions for reducing on-site wetting of mass timber construction, CLT specimens with a range of moisture protection measures, in six groups were tested in the backyard of FPInnovations’ Vancouver laboratory from Oct. 2017 to Jan. 2018. This study investigates the wetting and drying behaviours of the tested CLT specimens through 2-D hygrothermal simulations. The simulations are performed for base specimens (no protection measures) of group 1 (without joint or plywood spline) and group 2 (with a butt joint and plywood spline). For group 1, three data sources of material properties are used to create the models, and the data that led to the best agreement between simulations and measurement are used for creating the models of group 2. For group 2, two types of hygrothermal models are created with or without considering the differences in water absorption between the transverse and the longitudinal grain orientations. In addition, rain penetration is taken into account for the joint area. It is found that the model with considering the differences between transverse and longitudinal grain orientations shows a better agreement than that without considering such differences.
The use of CLT has been increasing the last decade, and a subsequently focus on documentation of the accompanying indoor climate and exposed wooden surfaces on human well-being. This study presents the results of a measurement campaign conducted over one year of a CLT apartment building in Grimstad, Norway. The apartment building consists of three floors with 35 apartments and comply with the Norwegian passive house standard and energy grade A. Measurements of the relative humidity (RH), indoor air temperature and wood moisture content (MC) were performed in the exposed CLT spruce panels in three apartments in two different floors. The results from the three apartments show a relatively small variation in the MC values regardless the residents behavior measured as RH variation through a complete year. Selected periods from a cold period (winter) and a warm period (summer) show the variation in relative humidity (RH) and moisture content in the CLT element. However, results from control measurements showed higher MC values. The gap between the measurements and methods are discussed.
Cross-laminated timber (CLT) is a type of mass timber panel used in floor, wall, and roof assemblies. An important consideration in design and construction of timber buildings is moisture durability. This study characterized the hygrothermal performance of CLT panels with laboratory measurements at multiple scales, field measurements, and modeling. The CLT panels consisted of five layers, four with spruce-pine-fir lumber and one with Douglas-fir lumber. Laboratory characterization involved measurements on small specimens that included material from only one or two layers and large specimens that included all five layers of the CLT panel. Water absorption was measured with panel specimens partially immersed in water, and a new method was developed where panels were exposed to ponded water on the top surface. This configuration gave a higher rate of water uptake than the partial immersion test. The rate of drying was much slower when the wetted surface was covered with an impermeable membrane. Measured hygrothermal properties were implemented in a one-dimensional transient hygrothermal model. Simulation of water uptake indicated that vapor diffusion had a significant contribution in parallel with liquid transport. A simple approximation for liquid transport coefficients, with identical coefficients for suction and redistribution, was adequate for simulating panel-scale wetting and drying. Finally, hygrothermal simulation of a CLT roof assembly that had been monitored in a companion field study showed agreement in most cases within the sensor uncertainty. Although the hygrothermal properties are particular to the wood species and CLT panels investigated here, the modeling approach is broadly applicable.
Nationwide, bridges are deteriorating at a rate faster than they can be rehabilitated and maintained. This has resulted in a search for new methods to rehabilitate, repair, manage, and construct bridges. As a result, structural health monitoring and smart structure concepts have emerged to help improve bridge management. In the case of timber bridges, however, a limited amount of research as been conducted on long-term structural health monitoring solutions, and this is especially true in regards to historic covered timber bridges. To date, evaluation efforts of timber bridges have focused primarily on visual inspection data to determine the structural integrity of timber structures. To fill this research need and help improve timber bridge inspection and management strategies, a 5-year research plan to develop a smart timber bridge structure was undertaken. The overall goal of the 5-year plan was to develop a turnkey system to analyze, monitor, and report on the performance and condition of timber bridges. This report outlines one phase of the 5-year research plan and focuses on developing and attaching moisture sensors onto timber bridge components. The goal was to investigate the potential for sensor technologies to reliably monitor the in situ moisture content of the timber members in historic covered bridges, especially those recently rehabilitated with glulam materials. The timber-specific moisture sensors detailed in this report and the data collected from them will assist in advancing the smart timber bridge.
The intent of this project is to research evaluation and rehabilitation methods that are applicable to mass timber structures following a fire. This includes addressing both fire damage and water damage from sprinkler activation and/or the use of firefighting hoses. This report provides an overview of the type of damage that might be expected following a fire and methods that might reduce potential damage (including design elements and firefighting tactics). Current and existing rehabilitation methods for wood construction will be reviewed and their applicability to mass timber structures will be discussed. This includes the ability to conduct condition assessments and repairs on building elements that can be done in place. The overall objective is to reduce uncertainty related to mass timber construction, which ultimately would allow for more accurate risk evaluation by insurance companies.