Timber Floor Research Articles

Composite connections between CFS beams and plywood panels for flooring systems: Testing and analysis

A composite floor consisting of cold-formed steel (CFS) beams connected to structural plywood panels is a sustainable and economical alternative to concrete only floors or the traditional floor systems supported by solid lumber joists. The structural performance of the composite CFS-plywood floor depends on the strength and stiffness properties of the shear connection. This study presents an experimental investigation into the load-slip behaviour of connections between CFS and plywood panels constructed with self-drilling screws, coach screws, and nut and bolt. The influence of structural adhesives at the shear interface alongside fasteners was also investigated. The stiffness, ductility and load-carrying capacity of the eight different types of connections were evaluated through a series of push-out tests. Nut and bolt connections were demonstrated to be the best choice amongst the shear connectors, followed by self-drilling screws; however, the size of the nuts and bolts should be determined based on the crushing strength of the timber itself. Connection with coach screws was less stiff and relatively less ductile than other tested shear connections. Composite connections with fasteners along with adhesives demonstrated higher stiffness and load-capacity than the fastener alone. Furthermore, a simple analytical expression for the load-slip response of the connections is proposed based on the Foschi formula, which showed a good correlation with test results. Based on the observations in this study, self-drilling screws and M8 nuts and bolts are recommended as shear connectors for lightweight cold-formed steel and timber flooring systems.

Separating function of timber floor and wall assemblies

Abstract The basic concern on the fire compartmentation is focused on to limit the spread of the fire and smoke outside of the room of the fire origin. Where the fire compartmentation is required, the elements forming the boundaries of the fire compartment should be designed and constructed in such a way that they maintain their separating function during the relevant fire exposure [1]. The general accepted method for assessing the fire resistance of a structural or non-structural member is the full-scale testing of the fire performance, however, several calculation methods for verification of the separation function of timber assemblies can also be used in order to prove compliance with the code regulations [2].

Cross-Laminated Timber Floor: Analysis of the Acoustic Properties and Radiation Efficiency

Cross-Laminated Timber (CLT) is a building technology that is becoming increasingly popular due to its sustainable and eco-friendly nature, as well as its availability. Nevertheless, CLT presents some challenges, especially in terms of impact noise and airborne sound insulation. For this reason, many studies focus on the vibro-acoustic behavior of CLT building elements, to understand their performance, advantages and limitations. In this paper, a 200 mm CLT floor has been characterized in the laboratory, according to ISO standards, by three noise sources: dodecahedron, standard tapping machine and rubber ball. In order to understand the vibro-acoustic behavior of the CLT floor, measurements through the analysis of sound pressure levels and velocity levels, measured by dedicated sensors, were performed. Analysis was carried out in order to understand what is prescribed by the prediction methods available in the literature and by the simulation software. Then, a specific prediction law for the CLT floor under investigation was derived. Finally, an analysis on sound radiation index is provided to complete the vibro-acoustic study.

Experimental and numerical investigations of two-way LVL–concrete composite plates with various support conditions

Design of modern timber floors is often governed by the vibration serviceability requirements. One way to improve vibration serviceability is through the design of two-way floor systems. In this paper, the behaviour of two-way LVL–concrete composite plates and a plate strip is investigated experimentally, with an emphasis on the performance of proposed dovetail joint for connecting the adjacent LVL panels. The investigations consist of the experimental modal analysis and static load deformation tests, performed under multiple support conditions. The results show a significant two-way action, indicated by about 45% higher fundamental natural frequency when four edges are supported instead of two. The point load deflection in the centre of the plate was reduced of about 9%. Furthermore, a numerical model for two-way TCC plates was developed and results show a wide agreement with the experimental behaviour, except for discrepancies related to deflections on the plate edge. The results from the experimental and numerical investigations indicate that the dovetail joint can produce a stiff connection, such that the LVL layer could be regarded as continuous in the connected direction.

Life Cycle Regional Economic Impacts of Bridge Repair Using Cross-Laminated Timber Floor Slabs: A Case Study in Akita Prefecture, Japan

Recently, cross-laminated timber (CLT) has attracted attention as a civil engineering material in Japan. In particular, the use of CLT floor slabs for bridge repair is expected to have regional economic impacts throughout their life cycle, but their economic impacts have not been evaluated. In this study, the life cycle regional economic impacts of using non-waterproofed CLT, waterproofed CLT, and reinforced concrete (RC) floor slabs for bridge repair in Akita Prefecture, Japan, were compared. Using past-to-present input–output tables, we quantitatively evaluated the economic impacts over the life cycle of floor slabs by estimating the future input–output tables for construction, maintenance, and disposal. The results showed that the construction and maintenance costs (final demand increase) of CLT floor slabs are higher than those of RC slabs, but the regional economic impact is larger. In addition, the non-waterproofed CLT must be renewed every time it is maintained. Therefore, the demand for CLT production in the prefecture will increase, and the economic impact will be larger than that of the other two floor slabs. This demand for CLT production will not only redound to the benefit of the forestry and wood industry but also the revitalization of regional economies.

Status of vibration serviceability design methods for lightweight timber floors

Since the 1970s occupant complaints about vibration serviceability performances of lightweight timber floors have risen in many countries. Initially concerns commonly centered on behaviours of joisted floors in non-commercial buildings. Empirical design methods were developed, but those methods sidestepped generalize understanding of the issues. Subsequent evolution of building construction techniques and material options often exacerbated inadequacies of empirical design methods. Consequently, interest in understanding why vibration serviceability problems occur and how to avoid them has reemerged as a priority research topic. This paper discusses technical issues associated with predicting vibration serviceability performances of lightweight timber floors, and identifies best current analysis and design practices. Emphasis is on ability to handle the full range of variables associated with 21st century lightweight construction methods. This includes capability to address effects of architectural and construction design choices, and effects types of building occupancies have on dynamic loads and motion responses of floor systems. Need to utilize capabilities of modern numerical engineering analysis tools is also emphasized. Ongoing R&D activities are mentioned, including need to address Human-Structure Interaction effects commonly important to proper design of lightweight building superstructures.

A comprehensive vibroacoustic investigation of a cross laminated timber floor

In recent years, the use of sustainable construction materials has increased significantly. It is of paramount importance to increase the general knowledge of acoustic behaviour of these materials. This research presents the results of a comprehensive acoustic investigation of a 200 mm timber slab. Excitations using different acoustic sources are performed. The results to this investigation are reported in this paper, focusing on the sound reduction index, impact noise reduction, static and frequency-dependant Young’s modulus, vibration and modal mapping and radiation efficiency. Finally, a correlation between impact noise levels caused by the tapping machine and the rubber ball is provided.

Parametric approach to the reconstruction of timber structures in Campanian Roman houses

The virtual reconstruction of ancient architecture aims at describing the ‘original’ elevation and volume of a disappeared building. The feeble archaeological traces, often limited to their foundations, left by houses impair the reinstating of their image, in contrast to that which is made possible by the massive structures of public buildings. A twofold problem arises when dealing with timber structures during a reconstruction procedure: at the local scale of the individual beam (e.g. joists or rafters), one must define a beam’s cross-section given its span; at the overall scale, the shape of a building results from that which its structures allowed it to have been. Therefore, this work proposes a procedure to deal with the ‘local’ problem, i.e. the definition of a beam’s cross-section from its span. To that end, a simplified, parametric structural model is required. The available bits of information are organized into inputs, parameters and outputs of the analytical problem by matching each information with a structural quantity (load, cross-section, spacing, etc.). Two mathematical relationships among them are proposed, which express two equally possible dimensioning criteria, based either on joists’ strength or deformability. It seems that the joist’s strength was the option for lightly loaded joists, as in roofs or tightly spaced floor frames; conversely, heavily loaded joists conformed to the deformability criterion. Both dimensioning procedures are translated into a visual algorithm in Grasshopper, a plugin for Rhinoceros modelling software, which enables the parametric definition of objects. Finally, the proposed procedure is tentatively applied to automatically reconstruct the floor and roof frames that belonged to the domus on top of the Sarno Baths in Pompeii. The algorithm automatically picked the dimensioning criterion in relation to each frame’s span and hypothesized loads and determined joists’ orientation and minimum cross-sections. The obtained floor frames, whose structural conditions are considered as sensible, will be adopted in the overall virtual reconstruction proposal of the ruins, also based on the analytical evaluation of masonry structures.Highlights:- Proposal of a structural model for the dimensioning of timber floor beams in domestic spaces based on archaeological and literature information.- Parametrical interpretation of the model in Grasshopper for Rhinoceros software and optimization analysis of the structural parameters involved.- Application of the model to the reconstruction of floor frames in a house in the Sarno Baths complex, Pompeii.

Experimental research on temperature distribution and charring rate of typical components of wood structure building

This study presents the fire performance of typical components of wood structure buildings. The wooden beams and floor slabs, quite common in wood structure buildings, were burned with different fire exposure times by a pool fire source. Then, the surface temperature evolution and the charring rate were recorded and analyzed. The results show that the flashover and re-ignition phenomenon occurred in all wood materials under the burning pool fires. The glulam beam cross-section was U-shaped, and the maximum charring rates of glulam beam, cross-laminated timber floor, and cross-laminated timber partition board were 0.833 mm/min, 1.538 mm/min, and 0.435 mm/min, respectively. It can be seen that the combustion behavior time of specimens with different cross-section thicknesses is different. If the thickness of the specimens is appropriately increased, their combustion behavior time can be significantly improved.

Finite element modelling of the progressive collapse of post-and-beam mass timber building substructures under edge and corner column removal scenarios

The structural behaviour of mass timber buildings under a load bearing element removal scenario is complex. To well understand this phenomenon and ultimately develop scientifically based design guidelines against progressive collapse for this type of buildings, there is a need to develop a Finite Element model which accurately captures the non-linear response, load redistribution mechanisms (alternative load paths) and failure modes of such buildings. As such, this paper presents for the first time how mass timber post-and-beam systems can be accurately modelled using Finite Element under edge and corner column removal scenarios. The model was validated against published 2D and 3D experimental tests performed on scaled-down substructures. The non-linear structural responses of the main structural connections were experimentally quantified and inputted into the model using the component method. Results show that the model accurately replicated load redistribution mechanisms, ultimate loads, failure modes, and strain developments. The use of the model was then illustrated by running parametric studies to quantify (i) the influence of the Cross Laminated Timber (CLT) floor panels layout and (ii) one alternative load path, typically ignored in design, on the progressive collapse resistance capacity.

The Effect of the Environment on the Serviceability of the Cross‐Laminated Timber (CLT) Floor: Virtual Reality as a Research Tool

The environment is one of the factors that may influence occupants’ perception of floor vibration and the assessment of floor serviceability. In this study, laboratory tests were conducted on a 3‐ply CLT floor. Occupants’ assessment of the floor serviceability under human‐induced vibration was investigated. Virtual reality (VR) technique was used as a research method, simulating two common environments in life. First, the correlation between the occupants’ annoyance rating and serviceability indicators (response factor and vibration dose value (VDV)) was compared with existing standards. The results show that the response factor method in ISO 10137:2007 is conservative for timber floors in both bedroom and gym environments. The VDV method in BS 6472‐1:2008 can generally reflect the vibration acceptability of timber floor vibration. Then, the effect of acceleration and environment on the floor serviceability assessment was investigated through statistical methods, respectively. A weak positive correlation between the annoyance rating and the acceleration was found. The effect of the environment on floor vibration assessment was found to be significant.

Design of nailed timber-concrete composite joint according to Eurocode and FEA

During rehabilitation of residential buildings built in the first half of the 20th century, it is necessary to strengthen timber floors so they can fulfill the requirements of strength and serviceability according to contemporary regulations. Floors made of monolithic timber girders can be most easily strengthened by forming a composite structure with a reinforced concrete slab supported on a trapezoidal steel sheeting, with appropriate connections between different materials. In the paper, the procedure of calculation of nails used as shear connectors for composite action of timber and concrete is presented. The procedure is based on equations given in Eurocode 5, and besides that, a calculation applying FEM has been conducted, and a comparison of results is presented.

Mortise-and-tenon joinery for modern timber construction: Quantifying the embodied carbon of an alternative structural connection

The mass timber industry offers a compelling pathway for low-carbon structural systems in buildings, replacing carbon-intensive materials like concrete and steel with sustainably forested wood. However, conventional structural connections in mass timber construction are largely made of metallic materials, such as screws, nails, and plates. In contrast, joinery, or geometrically interlocking all-timber connections, is globally prevalent in historic timber construction. This paper investigates the potential of applying joinery, specifically the “Nuki” mortise-and-tenon joinery connection, to contemporary mass timber construction from perspectives of structural behavior and carbon savings. Considering single spans supporting one-way cross-laminated timber (CLT) floor systems at the mid-rise residential scale, carbon savings ranging from 7 to 40% are possible at the beam-joint scale by using Nuki joints instead of steel concealed beam hangers, a more conventional mass timber connection. While these savings are smaller at the building scale, the paper nevertheless demonstrates a methodology and results for quantitatively comparing the scale of savings achieved by implementing this historic but contemporarily alternative connection type.

Optimizing Seismic Capacity of Existing Masonry Buildings by Retrofitting Timber Floors: Wood-Based Solutions as a Dissipative Alternative to Rigid Concrete Diaphragms

The inadequate seismic performance of existing masonry buildings is often linked to the excessively low in-plane stiffness of timber diaphragms and the poor quality of their connections to the walls. However, relevant past studies and seismic events have also shown that rigid diaphragms could be detrimental for existing buildings and do not necessarily lead to an increase in their seismic performance. Therefore, this work explores the opportunity of optimizing the retrofitting of existing timber floors by means of a dissipative strengthening option, consisting of a plywood panel overlay. On the basis of past experimental tests and previously formulated analytical and numerical models for simulating the in-plane response of these retrofitted diaphragms, in this work nonlinear incremental dynamic analyses were performed on three case–study buildings. For each structure three configurations were analyzed: an as-built one, one having floors retrofitted with concrete slabs and one having dissipative diaphragms strengthened with plywood panels. The results showed that the additional beneficial hysteretic energy dissipation of the optimized diaphragms is relevant and can largely increase the seismic performance of the analyzed buildings, while rigid floors only localize the dissipation in the walls. These outcomes can contribute to an efficient seismic retrofitting of existing masonry buildings, demonstrating once more the great potential of wood-based techniques in comparison to the use of reinforced concrete for creating rigid diaphragms.

Dynamic Characterization of Timber Floor Subassemblies: Sensitivity Analysis and Modeling Issues

AbstractTimber floors are prone to exhibit vibration levels, which can cause discomfort to the occupants. In the last 20 years, ambient vibration tests have become very popular due to the many adv...

Optimization framework for cost and carbon emission of timber floor elements

Long-span timber floor elements increase the adaptability of a building and they exhibit a significant market potential. High cost of the floor elements is a challenge, and the timber sector is under substantial pressure to find more economical solutions without weakening otherwise favourable environmental performance. The range of technical timber-based materials and components, structural typologies, overlays and ceiling systems represent an immense solution space when searching for a competitive design for a specific building application. Finding the optimum solution requires a computational procedure. In this study a recent development for the accounting of manufacturing resources for timber elements is utilized to build an optimization framework for cost and ECO2 minimisation of timber floor elements finalized at the factory gate. The design of the element is formulated as a discrete optimization problem which is solved by a mixed-integer sequential linearization procedure. Various material combinations and constraint combinations are treated. The optimization framework provides a tool for rapid design exploration that can be used in timber floor design situations. The results of the calculations carried out in this study provide insight on the general trends of optimum floor elements. The optimization model is used to analyse the characteristics of the optimum designs, and a comparison between the current and the proposed method for the second generation of Eurocode 5 is chosen as a vehicle for demonstrating achievable implications.

Finite Element Analysis of Dynamic Characteristics and Bending Stiffness for Cross Laminated Timber Floor Panels with and without Openings

The aim of this paper is to present numerical investigations of dynamic characteristics and bending stiffness for cross laminated timber floor panels with and without service openings. Five-layer panels with the outer layers oriented in the longitudinal direction of the panel have been analyzed. In order to explore the full potential of this floor system using a limited number of measurements and structural tests, models based on the finite element method have been proposed, validated against experimental results and then used to investigate the effect of opening position in the floor on main structural performance parameters. The results showed that, when the need for additional service opening appears, a slight decrease of the main structural characteristics of the cross laminated timber floor panels is achievable with an adequate geometrical position of the opening in the floor.

A comprehensive vibroacoustic investigation of a cross laminated timber floor

A comprehensive vibroacoustic investigation of a cross laminated timber floor

Evaluation of the Seismic Response of an Innovative Hybrid Steel‐Timber Structure

AbstractThis study evaluates the seismic response of an advanced hybrid steel‐timber structure using a nonlinear static and dynamic analyses. A three‐story prototype building located in Vancouver, BC, Canada was designed first. The gravity load resisting system (GLRS) consists of cross‐laminated timber (CLT) floor slabs, glulam beams, and glulam columns. The lateral load resisting system (LLRS) includes a chevron‐type steel Concentrically Braced Frame. The numerical model of the structure was then developed in the OpenSees program. Nonlinear hysteresis response of steel braces and timber joints were explicitly simulated. The results of the analysis revealed that the hybrid structure possess an acceptable lateral stiffness while providing sufficient ductility to dissipate seismic energy. No unsatisfactory response was observed in the timber system.

In situ assessment of the timber structure of an 18th century building in Madrid, Spain

The timber structural members of a seven-story building from the end of the 18th century were evaluated following a procedure based on previous research works. The structure consisted of timber-framed brick walls and heavy timber floors with mortar filling. Non-destructive measurements were taken in 13 sampling areas of the floors and framed walls. Detailed measurements of at least 3 pieces in each sample were taken (stress wave Time-of-Flight and probing tests). Mean density and modulus of elasticity values and characteristic values of bending and compression strength were estimated. On-site load tests were carried out on three floor slabs to deduce their actual bending stiffness and compare it with estimation by NDT. They behaved more rigidly than expected, which is explained by floor screed stiffness, the transverse stiffness effect and possible semi-rigid connection behaviour at the supports. Structural verification determined the required strength of the critical members to compare this with the estimated strengths, showing a correct safety level.