This paper presents energy and environmental performance analyses, a study of summer indoor temperatures and occupant behavior for an eight story apartment building, with the goal to combine high energy efficiency with low environmental impact, at a reasonable cost. Southern Portvakten building is built with prefabricated timber elements using passive house principles in the North European climate. Energy performance was analyzed through parametric studies, as well as monitored energy data, and complemented with analysis of occupant behavior during one year. Results show that airtight, low-energy apartment buildings can be successfully built with prefabricated timber elements in a cold climate. The monitored total energy use was 47.6 kWh/m2, excluding household electricity (revised to a normal year), which is considerably lower than of a standard building built today in Sweden—90 kWh/m2. However, the occupancy level was low during the analyzed year, which affects the energy use compared to if the building had been fully occupied. Environmental analysis shows that the future challenges lie in lowering the household and common electricity use, as well as in improving the choices of materials. More focus should also lie on improving occupant behavior and finding smart solar shading solutions for apartment buildings.
This study explores the use of Cross Laminated Timber (CLT) in a 10-story residential building as an alternative building method to concrete and steel construction. The study is not meant to be exhaustive, rather a preliminary investigation to test the economic viability of utilizing this new material to increase density, walkability and sustainable responsiveness in our built environment.
Based on international precedent, CLT is an applicable material for low-rise, as well as mid-rise to high-rise construction and has a lighter environmental footprint than traditional concrete and steel construction systems. Cross-laminated timber is a large format solid wood panel building system originating from central Europe. As a construction system it is similar to precast concrete in which large prefabricated panels are lifted by crane and installed using either a balloon frame or platform frame system. The advantages to using CLT are many, but the main benefits include: shorter construction times, fewer skilled laborers, better tolerances and quality, safer work environment, utilization of regional, sustainable materials, and reduction of carbon footprint of buildings. As a new, unproven material in the Pacific Northwest, this study investigates the cost competitiveness of CLT versus traditional materials for “low high-rise” buildings.
Hybrid construction systems proved to be valid structural solutions for the implementation of multi-storey buildings, especially if they require only the assembly of prefabricated and modular building elements. The structures here considered are designed to make different materials - firstly steel and timber - structurally collaborate, in order to develop a construction system with marked performance and architectonic flexibility features. Such systems can make the most of the heavily industrialized construction technology typical of steel systems, as well as of the advantages offered by CLT panels -lightness and structural stability- in which the timber element is recognized as an eco-friendly and eco-compatible material. Furthermore, in a sustainable urban development prospective, the use of cross-laminated timber panels, in short CLT, is recommended because wood is one of the fewest materials which has the capacity to isolate and store CO2 for a long period of time.
This paper presents a design method for multi-story timber building with consideration of regulatory constraints. The objective is to optimize in the same time thermal, structural and environmental objectives taking into account the industrial feasibility. To set up this method and the appropriate tool a study case is developed and will be implemented.
April 3-5, 2014, Boston, Massachusetts, United States
Summary
Cross-laminated timber (CLT) is widely perceived as the most promising option for building high-rise wood structures due to its structural robustness and good fire resistance. While gravity load design of a tall CLT building is relatively easy to address because all CLT walls can be utilized as bearing walls, design for significant lateral loads (earthquake and wind) can be challenging due to the lack of ductility in current CLT construction methods that utilize wall panels with low aspect ratios (height to length). Keeping the wall panels at high aspect ratios can provide a more ductile response, but it will inevitably increase the material and labor costs associated with the structure. In this study, a solution to this dilemma is proposed by introducing damping and elastic restoring devices in a multi-story CLT building to achieve ductile response, while keeping the integrity of low aspect ratio walls to reduce the cost of construction and improve fire resistance. The design methodology for incorporating the response modification devices is proposed and the performance of the as-designed structure under seismic is evaluated.
This paper presents a numerical study conducted on a seven-story timber building made of cross-laminated (X-lam) panels, equipped with a linear translational tuned mass damper (TMD). The TMD is placed on the top of the building as a technique for reducing the notoriously high drifts and seismic accelerations of these types of structures. TMD parameters (mass, stiffness, and damping) were designed using a genetic algorithm (GA) technique by optimizing the structural response under seven recorded earthquake ground motions compatible, on average, with a predefined elastic spectrum. Time-history dynamic analyses were carried out on a simplified two-degree-offreedom system equivalent to the multistory building, while a detailed model of the entire building using two-dimensional elastic shell elements and elastic springs for modeling connections was used as a verification of the evaluated solution. Several comparisons between the response of the structure with and without TMD subjected to medium- and high-intensity recorded earthquake ground motions are presented, and the effectiveness and limits of these devices for improving the seismic performance of X-lam buildings are critically evaluated.
Seismic Analysis of Cross-Laminated Multistory Timber Buildings Using Code-Prescribed Methods: Influence of Panel Size, Connection Ductility, and Schematization
This paper presents the results of an experimental study whose objective was to investigate the behavior of a hybrid wood shear-wall system defined herein as a combination of traditional light-frame wood shear walls with post-tensioned rocking Cross-Laminated Timber (CLT) panels. The post-tensioned CLT panels in the hybrid system offer both vertical and lateral load resistance and self-centering capacities. The traditional Light-Frame Wood Systems (LiFS) provide additional lateral load resistance along with a large amount of energy dissipation through the friction of nail connections. Thus, a combination of these two types of structures, in which traditional light-frame wood shearwalls are utilized as structural partition walls, may provide an excellent structural solution for mid-rise to tall wood buildings for apartments/condos, where there is a need for resisting large lateral and vertical loads as well as structural stability. In this study, a real-time hybrid testing algorithm using a combination of time-delay updating and Newmark-Beta feed forward to reduce the undesirable effects of time delay was introduced. The top two-stories of a three-story building were modeled as a numerical substructure with the first story as the experimental CLT-LiFS substructure. The experimental results of the hybrid wall are presented and discussed in this paper.
This paper investigates the seismic analysis of multi-story cross laminated timber (XLAM) buildings. The influence of different parameters such as wall geometry, vertical load level, friction and, most importantly, connection stiffness, strength and ductility is assessed. Linear and nonlinear finite element (FE) analyses are carried out on a hypothetic four-story case study building. The XLAM building behaviour factors are derived for different cases using a simplified method. Values in the range of 2 to 3 have been obtained depending on whether monolithic or segmental walls are used. Further nonlinear dynamic analyses carried out on a part of the case study building show that friction may have a beneficial effect on the seismic resistance of XLAM buildings. However it is advised that its influence is conservatively neglected until further investigations are performed. Obtained results provide an important insight for both academics and practicing engineers into the FE modelling and design of XLAM buildings using different code-based approaches. This data is also crucial for the preparation of new seismic design codes on XLAM timber buildings.
Glued glass front constructions have long been in use and are generally considered the state of the art. However, with these solutions the glass serves no stiffening or bearing function, but merely functions as an outer cover. The objective of several research projects was to investigate alternative constructions of stiffening glass fronts, which replace St. Andrew’s cross wind bracings and costly frameworks. To this end, the Department of Structural Design and Timber Engineering (ITI) studied and optimized the load-bearing capacity of these existing construction components and subsequently developed simple calculation and sizing concepts. Based on the results of the research project „Timberglass composites: calculation and sizing concept (HGV III)“ the ITI coordinated the follow-up international research project “Load bearing timber-glass composites (LBTGC)” within the framework WoodWisdom-Net. In consideration of its long-term behavior and practical application, the objective of the research project LBTGC was to develop “stiffening timber-glass composite (TGC) structures”. With the purpose to meet the highest standards of cost effectiveness, alternative stiffening TGC constructions for multi-story buildings were investigated. This paper illustrates these developments.
Up to now, structural sealant glazing façades have been extensively applied. They are at the cutting edge of technology and meet the highest standards. The objective of several research projects was to develop stiffening glass fronts, which replace expensive frameworks or wind bracings behind the large glass windows. Thus, potential applications of timber-glass composites (TGC) as alternative stiffening constructions for multi-story façades were investigated. Based on the results of those previous research projects the Department of Structural Design and Timber Engineering (ITI) coordinated the follow-up international research project “Load bearing timber-glass composites (LBTGC)” within the framework WoodWisdom-Net. In consideration of long-term behavior and practical application, the objective of the joint research project LBTGC was to develop load-bearing and stiffening TGC structures. With the purpose to meet the highest standards of cost effectiveness and environmental compatibility, alternative stiffening TGC constructions for multi-story facades were investigated. This paper illustrates these developments and application of TGC multi-story façades.
