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.
Compared to light-frame wood shear walls, it is relatively difficult for panelized CLT shear walls to achieve similar levels of lateral deflection without paying special attention to design details, i.e., connections. A design lacking ductility or energy dissipating mechanism will result in high acceleration amplifications and excessive global overturning demands for multistory buildings, and even more so for tall wood buildings. Although a number of studies have been conducted on CLT shear walls and building assemblies since the 1990s, the wood design community’s understanding of the seismic behavior of panelized CLT systems is still in the learning phase, hence the impetus for this article and the tall CLT building workshop, which will be introduced herein. For example, there has been a recent trend in engineering to improve resiliency, which seeks to design a building system such that it can be restored to normal functionality sooner after an earthquake than previously possible, i.e., it is a resilient system. While various resilient lateral system concepts have been explored for concrete and steel construction, this concept has not yet been realized for multistory CLT systems. This forum article presents a review of past research developments on CLT as a lateral force-resisting system, the current trend toward design and construction of tall buildings with CLT worldwide, and attempts to summarize the societal needs and challenges in developing resilient CLT construction in regions of high seismicity in the United States.
The design-build of a Wooden Adaptive Architectural System is part of a larger research-creation project on Adaptive Architecture (AA)  exploring the entire design process leading to a fully adaptable three story high 1:3/4 wooden structure. This system allows the easy manoeuvrability by the occupants of walls and floors in x, y and z directions in order to adapt the space to their environmental and functional needs. The omnidirectional mobility criteria challenged conventional building techniques and led to an innovative all-wood rigid node. Extensive prototyping using digital fabrication allowed the team to optimize the node assemblage and precision through parametric experimentation before proper production. The Wooden Adaptive Architectural System, made of 2000 prefabricated sticks measuring as little as 1 ¾” x 1 ¾” x 24” provides fully adaptive space configurations and be easily deconstructed, transported, and reassembled in totally new building shapes.
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.