Projects / Programmes
SAFETY OF PASSIVE HOUSES SUBJECTED TO EARTHQUAKE
| Code |
Science |
Field |
Subfield |
| 5.12.01 |
Social sciences |
Architecture and Design |
Architecture |
| Code |
Science |
Field |
| T240 |
Technological sciences |
Architecture, interior design |
| Code |
Science |
Field |
| 5.09 |
Social Sciences |
Other social sciences |
passive house, thermal insulation, earthquake safety
Researchers (15)
Organisations (3)
Abstract
In recent years the building of passive houses has widely spread across Slovenia, mainly in order to protect environment and save the energy. The thermal bridges have to be avoided and the isolation should run without interruptions around the building – even under the building or its foundations. The technology of passive houses used in Slovenia has been mainly transferred from West Europe or Scandinavia, where there is no seismic risk. The structural systems have been adopted to sustain vertical or wind loading and there is no guarantee that they can perform well also under cyclic earthquake loading. It should be pointed out that by inserting the flexible layers of thermal isolation under the building we prolong the fundamental period of the structure, because the building on isolation layer oscillates slower as on a firm ground. Most of passive houses are low rise buildings with short fundamental periods, witch could be elongated by insertion of isolation and thus moved into resonance part of the design response spectrum (into the period of constant accelerations). In some cases of stiffer building on softer soil the expected forces on the object can be raised up to two or three times as for the fixed base one. Such increase can not be completely ignored and before wide use of such objects in earthquake prone areas their seismic resistance should be examined in detail.
Additionally, a so called isolation pedestals are frequently used in passive houses in order to prevent thermal bridges. Usually they are inserted between the superstructure and foundations or unheated basement. Such elements – designed for vertical loading only – can decrease the shear resistance of walls and columns, which is very important for the structure to behave safely and controllably during a strong earthquake.
It can be therefore concluded that the uncontrolled transfer of technology from earthquake non prone regions to the earthquake prone ones can be dangerous, especially for heavier and bigger object in areas with higher seismicity. This topic has not been scientifically addressed yet, mainly due to the fact that passive houses are used in colder climate areas which are usually less exposed to seismic risk. From this point of view Slovenia presents an exception and such a research project a necessity what has been recently realized also by some investors and producers of passive houses, which decided to support the project as its beneficiaries.
The project researches in which cases and until which extent the use of passive house can be dangerous in earthquake prone areas and how the seismic risk can be avoided by correct architectural design and by implementing additional measures to increase seismic resistance. The design of such seismic resistant structural details will be examined within the project. The applicative part of the project includes: a) study of the most used systems of passive houses thru the prism of earthquake resistance, b) Analysis of all structural details which are important for seismic resistance, c) Proposals for their construction and proportioning and d) the guidelines for design of earthquake resistant European passive house.
The behaviour of structures founded on thermal insulation is very similar to the behaviour of seismically isolated structures. The seismic isolation is the field where we have been successfully conducted research in the past years. We have published a series of research papers on this topic, some of them also in high ranked international journals. The gathered knowledge will be used also in this project and it is a warranty for successful accomplishment of the research proposed herein. The project is divided into 10 Working Packages and handeled by three research organizations.
Significance for science
The main scientific contributions arising from the results obtained within the research project are as follows: i) Actuality of the research topic in the frame of the European Union (EU) energy efficiency directive. The EU directive, which was proposed in 2010, has set new requirements for energy efficiency in buildings. For all the EU member countries, a demand in the directive for increasing the number of nearly zero-energy buildings should ensure that by 2021 all new buildings will be nearly zero-energy. One of the basic principles for improving the energy efficiency in buildings is a continuous thermal insulation (TI) layer, which is provided also under the ground floor slab. In this case the TI has to be considered as one of the structural elements with a suitable compressive strength to withstand the vertical loads. ii) Recognizing the differences in the seismic response of buildings founded on a TI layer compared to the buildings founded on a regular soil site. The TI layer under the foundation slab causes an increase in the vertical and shear deformability of the ground floor if compared to a regular soil. During the seismic shaking of such buildings, the phenomenon of rocking can cause an uplift of the foundation slab, which is dependent on the intensity and frequency of the seismic excitation. Strong seismic excitation can also cause inelastic vertical compressive deformations of the TI layer (on the compressed side). To ensure a more controlled and safer behaviour of passive houses founded on a TI layer, the exceedance of the limit vertical compressive and horizontal shear deformations has to be prevented. The exceedance of the maximum allowable deformations could in extreme cases lead to irreversible deformation of the TI layer, which could result in the permanent leaning of the building. In addition to the increased deformations of the TI layer, the seismic forces on the superstructure could also be significantly increased. The latter is more significant for stiff and heavy buildings, with a narrow floor plan ratio, where the amplifications of seismic forces can increase the level of damage of the superstructure. iii) An extensive parametric study of the seismic response of buildings founded on a TI layer. A nonlinear time history analysis was used to analyse different models differing in the building’s height, floor plan, mass, ductility capacity, stiffness, inelastic behaviour and the TI layer strength and thickness. The engineering design parameters considered in the parametric study were the following: the building’s top displacement, the ductility demand of the superstructure, the vertical deformability of the TI layer, the percent of the foundation in contact with the TI layer, and the friction coefficient demand. Furthermore, a detailed case study of a reinforced concrete structure founded on a TI layer was performed. In this study the soil structure interaction and the influence of the stiffness of the foundation slab, which proved to be significant, were also considered. iv) The performed experimental tests of the extruded polystyrene (XPS) boards. The XPS characteristics obtained with static monotonic or cyclic shear and compressive tests were necessary to perform numerical simulations of buildings founded on a XPS layer. The research of the material static and cyclic characteristics of the XPS was unknown in the relevant scientific literature until now. In addition, the shear response of the 9 most commonly used composed foundation sets was also obtained. For each of the foundation sets tested at different pre-compression levels the friction coefficients calculated. v) Patent applications for improving the seismic response of buildings founded on a layer of thermal insulation. The co-financer Fibran Nord has already applied a patent at The Slovenian Intellectual Property Office. Another patent application for a technically more improved solution will be proposed in May 2014.
Significance for the country
The topic researched within the project stemmed from two otherwise quite unrelated fields, i.e. seismic safety and energy efficiency that in European countries do not frequently appear together. Just in Slovenia these two fields join each other, so identifying the problem and establishment of research right in Slovenia represents uniqueness and specificity. The majority of Slovenia is situated in area of moderate seismic risk. In order to ensure adequate mechanical resistance and stability of structures constructed in such area, the consideration of seismic effects is required by law. In Slovenia the number of passive houses and energy-efficient buildings increases rapidly. However, for the time being the structural solutions that have been developed and broadly applied mainly in the areas with low seismicity are used. Within the framework of the project, the seismic response of buildings with thermal-insulating (TI) layer beneath the foundations has been investigated. Thermal insulation under the building foundations prevents the thermal bridge on the contact between the building and supporting terrain and reduces the energy consumption in modern energy efficient houses. In Slovenia such applications of TI is more and more frequent, what follows the recommendations of the European Union (EU) energy efficiency directive. For Slovenia as a country with (moderate) seismic risk the problem of seismic safety of energy efficient buildings is crucial in terms of providing adequate mechanical resistance and stability. Therefore, the awareness and education of the professional public, which took place within the project presents an important contribution to the development of the profession in Slovenia. Additionally, based on the results obtained, the guidelines for designers of building structures lying on soft TI layers have been developed. In the framework of research project several young Slovenian researchers have been involved, which represents the development potential of highly educated staff. Related research in this field is being successfully continued by young researcher Boris Azinović. As an important contribution of the project also the constructive cooperation with manufacturers of thermal insulation products (co-financier of the project FIBRAN NORD) should be mentioned. A big part of the results obtained in the framework of the project were used for their technical solutions and products. The main results of performed numerical simulations are also included in their technical material.
Most important scientific results
Annual report
2011,
2012,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2011,
2012,
final report,
complete report on dLib.si
