The paper describes experimental and numerical analyses on a completely new connection system developed for CLT (Cross Laminated Timber) constructions. The innovative solution herein proposed, named X-RAD, consists of a point-to-point mechanical connection system, fixed to the corners of the CLT panels. This connection, that is designed to be prefabricated, is made of a metal wrapping and an inner hard wood element which are fastened to the panel by means of allthreaded self-tapping screws. Such system permits to reduce significantly the number of bolts/fasteners required to assemble two or more panels together or to connect them to the foundation. This results in the enhancement of the installation process in terms of speed, quality and safety. One of the reasons that fuelled the development of the presented system, is the desire of offering a solution to those issues (e.g. to satisfy ductility and energetic dissipation requirements) commonly related to the seismic safety of timber structures. In other words there was the will of defining a system able to guarantee an adequate level of ductility and energetic dissipation.
The widely available automated prefabrication in timber construction companies, as well as modern CAD software with application programing interfaces, allow for the design and production of increasingly geometrically complex building components. This development also enables and demands at the same time advanced joinery techniques. Analog to the developments in timber framing, this article presents the adaptation of a traditional wood-wood joinery technique from cabinetmaking, on the casestudy of a shell structure built from curved cross-laminated timber (CLT) panels. The dovetail-joints allow for a load-bearing glued joint between the CLT panels. They provide an aesthetic, visible connection and simplify the assembly through their integrated locator features.
The present work aims to define horizontal joint dimension tolerances for newly proposed prefabricated façade systems for applications in tall cross laminated timber (CLT) buildings based on the compression perpendicular to grain characteristics of the component. This requires a thorough understanding of structural settlement under vertical loads which can vary at each floor height. An experimental program has been carried out with reference to the case of a platform frame building construction, where major perpendicular to grain compression of the floor can occur under high loads. Five-layer CLT specimens have been tested under compression via the application of a line load with steel plate as well as actual CLT wall specimens. Strengthening contribution using full threaded self-tapping wood screws has also been investigated. Results of deformation characteristics have been validated through a non-linear finite element analysis and further elaborated in order to outline implications in the design of a prefabricated façade.
Project contact is Cristiano Loss at the University of British Columbia
This research aims at developing novel multi-material deconstructable hybrid connections for mass timber prefabricated buildings. Connections will be conceived in order to (i) meet multi-objective structural performance, (ii) favour modular construction, (iii) favour quick erection of buildings, (iv) quick disassemble and possible reuse of the timber members, and (v) provide seismic-resistant structural assemblies.
Timber has been used for building construction for centuries, until the industrial revolution, when it was often replaced by steel and concrete or confined to low-rise housings. In the last thirty years however, thanks to the development of mass timber products and new global interest in sustainability, timber has begun to make a resurgence in the building industry. As building codes and public perception continues to change, the demand for taller and higher-performance timber buildings will only grow. Thus, a need exists for new construction technology appropriate for taller mass timber construction, as well as for fabrication and deconstruction practices that respect wood’s inherent sustainable nature. With this in mind, this research program aims to develop a new hybrid shear connection for mass timber buildings that allows for easy construction, deconstruction, and reuse of the structural elements.
This report includes results of Phase 1, which focused on connections consisting of partially threaded 20M and 24M steel rods bonded into pockets formed in CLT and surrounded by thick crowns of high-strength three-component epoxy-based grout. A total of 168 specimens were designed and fabricated, and push-out shear tests carried out with a displacement-controlled monotonic loading protocol. Strength and stiffness values were assessed and effective failure modes in specimens identified. These latter, along with the recorded load-deformation curves, indicate that it is possible to develop mechanics-based design models and design formulas akin to those already used for typical dowel-type fastener timber connections. Additionally, the specimens were easily fabricated in the lab and quickly fastened to the test jig by means of nuts and washers, suggested such connections have a strong potential for prefabrication, disassembly, and reuse.
Project contact is Y.H. Chui at the University of Alberta
The objective of this research is to develop efficient panel-to-panel connection details, and optimum floor configuration, including rigging details, for handling in the factory and at the construction site. Computer modelling will be conducted to develop preliminary recommendations on panel-to-panel connection details and optimum floor panel configuration. These recommendations will then be validated by a testing program in the laboratory.
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.
An innovative steel-timber composite floor for use in multi-storey residential buildings is presented. The research demonstrates the potential of these steel-timber composite systems in terms of bearing capacity, stiffness and method of construction. Such engineered solutions should prove to be sustainable since they combine recyclable materials in the most effective way. The floors consist of prefabricated ultralight modular components, with a Cross-Laminated Timber (CLT) slab, joined together and to the main structural system using only bolts and screws. Two novel floor solutions are presented, along with the results of experimental tests on the flexural behaviour of their modular components. Bending tests have been performed considering two different methods of loading and constraints. Each prefabricated modular component uses a special arrangement of steel-timber connections to join a CLT panel to two customized cold-formed steel beams. Specifically, the first proposed composite system is assembled using mechanical connectors whereas the second involves the use of epoxy-based resin. In the paper, a FEM model is provided in order to extend this study to other steel-timber composite floor solutions. In addition, the paper contains the design model to be used in dimensioning the developed systems according to the state of the art of composite structures.
The wood construction industries are becoming more focused on climate change and resource depletion, and individual and industrial consumption must reflect a greater degree of concern for the climate and environmental wellbeing. This paper presents a new concept for timber engineering, the purpose being to acquire information about the failure modes and the tensile and compressive strengths of two types of joint, the Simple Gooseneck and Thick Gooseneck, that can be used in a new concept for joining members in timber structures. This Makerjoint concept uses laminated veneer lumber (LVL) as nodes in regions with a pronounced non-uniform stress distribution and sawn timber in regions with a more uniform stress distribution. No metal fasteners or adhesives are used in the joint between timber and LVL. The concept is intended for joints using 3-axis CNC machinery and to be a system for on-site- and pre-fabrication of e.g. small houses, emergency shelters and exhibition stands. The joints have a higher compressive than tensile strength. The joints exhibited brittle failure in tension (beam and/or node failure) and buckling occurred in compression around the thinnest cross section of the beams. Suggestions are made for how the mechanical properties of the joints can be improved.
The technique proposed herein, aims to solve the construction site issues related to both the handling and the assembly of cross laminated timber walls (CLT), through an innovative preassembled connection system. This system, which thanks to its being prefabricated permits to save time during the installation process, provides also a high strength and a high stiffness to the panel joints. As a result, an improvement of the building safety is attained for both static and seismic conditions. The main purpose of the original solution is the enhancement of the production, the handling and the onsite assembly processes of CLT panels, by means of an higher degree of prefabrication which implies higher safety, precision and speed of assembly as well as an advantage in terms of costs and time schedule planning.