In recent years the building of passive houses has widely spread across Slovenia, mainly in order to protect the environment and save 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 the isolation layer oscillates slower as on the firm ground. Most of the passive houses are low-rise buildings with short fundamental periods, which could be elongated by insertion of isolation and thus moved into the 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 to two or three times as for the fixed-base one. Such increase can not be completely ignored and before the wide use of such objects in earthquake-prone areas their seismic resistance should be examined in detail.
Additionally, a so-called isolation pedestal is frequently used in passive houses to prevent thermal bridges. Usually, they are inserted between the superstructure and foundations or an 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.
Therefore, it can be concluded that the uncontrolled transfer of technology from earthquake non-prone regions to earthquake-prone ones can be dangerous, especially for heavier and bigger objects in areas with higher seismicity. This topic has not been scientifically addressed yet, mainly since 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 recently realized by some investors and producers of passive houses, which decided to support the project as its beneficiaries.
Gradnja pasivnih hiš se je v zadnjih letih ob povečani skrbi za varovanje okolja in varčevanja z energijo močno razširila tudi pri nas. Toplotni mostovi morajo biti preprečeni in toplotni ovoj mora potekati neprekinjeno okrog in okrog stavbe – tudi pod stavbo ali njenimi temelji. Praviloma se pri nas uporabljajo prenešene tehnologije gradnje pasivnih hiš in izvedbenih detajlov, ki so bili razviti v zahodni Evropi ali v skandinavskih deželah, v katerih nevarnosti močnejše potresne obtežbe ni. Konstrukcijski sistemi pasivnih hiš so bili izdelani za prevzem vertikalne obtežbe in obtežbe z vetrom, nobene garancije pa ni, da se bodo dobro in duktilno obnašali tudi pri ciklični potresni obtežbi. Zavedati se je treba tudi, da z vstavljanjem mehkejših slojev izolacije z izboljšano vertikalno nosilnostjo konstrukciji podaljšamo nihajni čas, saj konstrukcija na sloju toplotne izolacije niha počasneje kot pa na trdnih tleh. Večina tovrstnih stavb je nizkih in imajo sicer zelo kratke nihajne čase, s podaljšanjem nihajnega časa pa jih lahko premaknemo v resonančni plato spektra (območje konstantnih pospeškov), tako da lahko v nekaterih primerih bolj togih stavb na slabših tleh pričakujemo od 2 do 3,5 krat večje sile na objekt. To že ni več zanemarljivo povečanje sil in pred široko uporabo je treba varnost takšnih objektov posebej preveriti.
Dodatno se v pasivnih hišah pogosto uporablja tudi tako imenovane izolacijske podstavke, ki se jih zaradi preprečevanja toplotnih mostov vstavi med zgornjo konstrukcijo in temelje ali neogrevano klet. Pri potresu je zelo pomembna tudi strižna nosilnost sten in stebrov, ki jo lahko z vstavljanjem tovrstnih vmesnih izolacijskih nosilnih elementov, načrtovanih le za prevzem vertikalne obtežbe, zmanjšamo do te mere, da konstrukcija ni več potresno varna.
Pri raziskovalnem in strokovnem delu na FA sicer spodbujamo izgradnjo pasivnih hiš, vendar pa ugotavljamo, da je tovrsten prenos tehnologije lahko nevaren, še posebej pri večjih in težjih večetažnih objektih na področju močnejše potresne ogroženosti. Ta problem v znanstveni literaturi še ni bil obdelan, predvsem zato ker se pasivne hiše uporabljajo v hladnejših klimatskih področjih, kjer potresov praviloma ni. V tem pogledu je Slovenija in njej klimatsko in potresno ogrožene podobne dežele izjema, taka raziskovalna študija pa nujnost, ki se je zavedajo tudi nekateri investitorji in proizvajalci pasivnih hiš pri nas.
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