Seismic Aspects of the Application of Thermal Insulation Boards Beneath the Foundations of Buildings

Abstract

In recent years, there has been a significant increase in the construction of energyefficient buildings. These buildings are mainly characterized by their thermal envelope, which needs to follow the complete outer perimeter of the building without any interruptions, to avoid thermal bridges. It has been observed, however, that the specific new details which prevent the occurrence of thermal bridges can, in many cases, substantially affect the structural integrity of such buildings during earthquakes. This chapter deals with the seismic aspects of the application of thermal insulation (TI) boards beneath the foundations of buildings. For this purpose, the mechanical characteristics of the most commonly used material in practice (i.e., extruded polystyrene-XPS) were experimentally determined. Additionally, the shear behaviour of differently composed TI foundation sets was investigated and their friction capacity estimated. The authors have proposed a new solution for the foundation detail, which is based on controlling the sliding mechanism between the individual layers of TI boards in order to reduce the seismic forces induced on the superstructure. The proposed detail with a specially designed sliding layer surface is made of commonly used TI materials for modern passive houses, thus reducing the potential additional costs. The solution was verified by means of nonlinear dynamic analysis of several realistic building models and various friction coefficients between XPS boards. The selected results are presented in terms of fragility curves for the occurrence of sliding between the layers of XPS boards. Based on these curves, the desired seismic response scenario and level of protection of a building structure could be selected.

Impact of Energy Efficient Construction Details on Seismic Resistance of Passive Buildings

“…Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved. ISBN: 978-1-63248-088-0 doi: 10.15224/ 978-1-63248-088-0-24 house buildings [5,7]. The effect of different friction coefficients was analysed, as well as their influence on the structural behaviour.…”

“…In such cases the expected top accelerations of the structure could increase by a factor of two or three in comparison with a structure on a fixed base. Such an increase could lead to damage to the superstructure or its content, which should not be ignored [1][2][3][4][5][6][7]. However, if the fundamental period of the superstructure is already on the plateau of constant accelerations, the insertion of TI under the foundation slab might prolong the structural period into the descending Proc.…”

“…In the first stage of the research, the cyclic material characteristics of the XPS foam, which is one of the most frequently used material for TI under foundations, have been tested for the first time. The cyclic compressive and shear stress-strain behaviour of XPS foam obtained by experiments can be found in [4,7,15,16]. In the same reference the sliding resistance of the individual surfaces located between the layers of the thermally insulated construction sets was also studied.…”

“…On the other hand, in the case of more flexible structures a positive effect due to a reduction in the superstructure ductility demand was detected. Recently, the seismic response of an actual multistoreyed RC frame (wall) building founded on an RC foundation slab has been analysed [7]. In this reference the superstructure was modelled by a complete 2D Multiple-Degree-of-Freedom (MDOF) lumped plasticity frame model (with rigid links) that enables to track the development of damage induced by insertion of a soft TI layer beneath the foundation slab.…”

“…These response amplifications could be substantial and might result in the exceedance of the structural or TI layer capacity values. For this reason, a new technological solution for reducing the seismic response of passive houses founded on layers of TI boards has been recently proposed by the authors [5,7]. The reduction of the seismic forces which are induced on the superstructure was achieved by allowing controlled lateral sliding to occur along the horizontal surface between the individual layers of the TI boards, as a kind of seismic fuse.…”