Case-Study on the Creep Behavior of Interconnected Timber Elements using Wood-Wood Connections

With the increasing use of automation and computer-aided manufacturing in timber construction, a standardized timber construction system using digitally produced wood-wood connections has recently been developed for basic building components. Its structural performance has already been characterized with static bending tests in a previous case-study. Based on this work, the creep behavior of such a construction system is investigated in this paper. An experimental test was conducted in outdoor conditions to perform a simple quantitative and comparative study with the creep-reduction factor k de f for wood-wood connections described in the Eurocode 5 standard. A large-scale specimen was placed on two supports under a ventilated shelter and exposed to natural variations of humidity and temperature over a total period of approximately 400 days. The results were reassuring for the long-term performance of this type of construction system. Creep due to the connections accounted for 25% of the final displacement. In addition, the existing guidelines concerning the factor k de f for wood-wood connections were conservative for this specific configuration and could be optimized with future investigations on this topic.

Fire endurance of multicellular panels in an FRP building system

Craig Tracy

Fiber-reinforced synthetic polymers (FRP) are the building materials that may permit both the improvement of long-term building performance and the simplification of the construction process. Thanks to their high specific strength, low thermal conductivity, good environmental resistance, and their ability to be formed into complex shapes, FRP materials are well-suited to fulfilling many building functions. By integrating traditionally separate building systems and layers into single function-integrated components and industrially fabricating those components, the amount of on-site labor can be greatly reduced and overall quality can be improved. In order to profit from the advantageous qualities of FRP, however, it is essential to address the unique weaknesses and disadvantages of the material. Most notably, the problems of poor fire safety and high material costs must be overcome. In response to these challenges, a new multiple-story building system employing FRP materials is proposed. Within this system, fire safety is ensured through the use of an internal liquid cooling system, which circulates a cooling medium through the load-bearing FRP elements to maintain their temperature within a safe operating range. This system is made cost-effective through the integration of the building's heating and cooling system. By controlling the temperature of the circulating liquid, the building's structural elements can serve as heating or cooling emitters (radiators). Further, the addition of the liquid within the cells of the FRP elements helps maintain a more constant interior climate through the "thermal flywheel" effect, which improves energy efficiency and comfort. Experimental investigations were performed to explore the fire safety aspects of the proposed system. An existing FRP cellular bridge deck material was adapted to incorporate an internal liquid cooling system. After several preliminary investigations, large-scale experiments involving structural and fire loading were conducted on both liquid-cooled and non-liquid cooled specimens. The experiments demonstrated the efficacy of the system in protecting load-bearing FRP elements from the weakening effects of high temperatures, especially those that are stressed in compression. Structural fire endurance times were improved from less than one hour to more than two hours (EC1 Part 1.2) through the implementation of the liquid cooling system. Alongside the experimental program, a series of mathematical models were developed. Numerical thermochemical and thermomechanical models simulate the response of loaded liquid-cooled FRP panels in fire, while analytical models predict the post-fire mechanical behavior of fire-damaged sections. All models provide predictions that are within 10% of experimentally measured values.

EPFL2005

Experimental and numerical study on structural behavior of a single timber textile module

Markus Hudert, Laurent Humbert, Meisam Sistaninia, Yves Weinand

The present work investigates an innovative class of timber structure with potential applications in roofing, facade and bridge construction, called Timberfabric. The development of Timberfabric structures originates from the approach of harnessing the structural, modular and qualities of textiles in timber construction (Weinand and Hudert, 2010) [9]. Timberfabric structures are comprised of repetitive arrangements of one or more structural unit cells called Textile Modules. When properly designed, one obtains a modular and lightweight structure with interesting and unusual geometrical and structural qualities.This paper focuses on the single timber Textile Module. Based on the finite element (FE) method, a reliable procedure is proposed for modeling the overall assembly process of the Textile Module. For comparison, Textile Module prototypes are constructed at two different scales (large and intermediate scales) with different assembly conditions. The proposed geometrically nonlinear FE model allows evaluation of the stresses that are induced during the construction process and which may affect the structural integrity of the module. In particular, the risk of failure during assembly is identified using the anisotropic Tsai-Hill criterion. The structural behavior of the timber Textile Module is then investigated through bending tests using the constructed prototypes. During the loading procedure, the vertical deflections are measured at different locations on the prototype surface by means of external displacement transducers. Using the FE model, the corresponding deformed shapes are simulated by applying the bending loads on the prestressed Textile Module. Experimental displacements and FE predictions are thus compared and found to be in good agreement.

Elsevier2013

Integrally attached timber folded surface structures

Andrea Stitic

In structural engineering, folded surface structures present one of the concepts for construction of self supporting column free systems. They utilize structural benefits of folding to achieve material saving and improve structural efficiency. The folding principle can be simply described as stiffening a thin surface by placing its material further away from the axis of flexure. The application of folded surface structures in timber engineering is motivated by multiple advantages of relatively recently developed, high-performance engineered wood panel products. When used in folded systems, such panels can provide for a sustainable and lightweight solution with high load-bearing potential and high prefabrication possibilities. However, same as all timber products, these panels have limitations concerning the dimensions of the prefabricated units. These limitations are dictated by demands of transportation, assembly and, more stringently, by available manufacturing techniques. These factors influence the selection of timber structuresâ potential folded form, by constraining the dimensions of their discrete elements. Accordingly, structural forms with multiple elements along the span are needed for facilitating large spanning timber folded surface systems. Consisting of a large number of discrete plane elements, their realization requires proper edgewise connection details for ensuring an efficient load bearing system. For structures made of thin timber panels, this presents a great challenge when using the conventional joining techniques. For this reason, the use of timber folded structures for civil engineering applications has been very limited. However, recently, the re-discovery of integral mechanical attachments resulted in a new technical solution for edgewise joining of thin timber panels, which utilize digital prefabrication to integrate connectors through plate geometry. This thesis aims to facilitate the realization of large span timber folded surface structures which use one-degree-of-freedom multiple tab-and-slot joint integral mechanical attachment technique. Regarding the material, the presented work concentrates on certified Kerto-Q laminated veneer lumber panels. Taking into consideration the constraints of material, fabrication and chosen connection detail, various folded form topologies were examined for the considered application. Moreover, a relation was established between the structural form and the mentioned constraints, allowing for their implementation into the folded form design from the very start. The structural behaviour of folded systems was studied by performing extensive experimental tests. The innovative test setup developed for this purpose is presented. The results of this in-depth experimental analysis provide new insights regarding the substantial influence of the semi-rigid connection details on the global behaviour of timber folded surface structures. In addition, for analysing their feasibility, the tested structures are reviewed in terms of fabrication time, assembly and on-site construction. Furthermore, based on the experimental test results, a pertinent numerical model for predicting the load bearing behaviour of the regarded structures is provided. Using finite element method the semi-rigid structural behaviour of multiple tab-and-slot joints, as well as the entire timber folded system, was modelled with sufficient accuracy. Using the developed numerical models, a correlation is established...