David Koren

Principles of Energy Efficient Construction and their Influence on the Seismic Resistance of Light-weight Buildings

Recently, an increasing trend of passive and low-energy buildings transferring from non earthquake-prone to earthquake-prone regions has thrown out the question about the seismic safety of such buildings. The paper describes the most commonly used details of energy efficient construction, which could be critical from the point of view of earthquake resistance. The paper focuses on the prevention of ground floor slab thermal bridge and presents a case study on the seismic response of multi-storey wooden buildings founded on the RC foundation slab lying on a thermal insulation (TI) layer made of extruded polystyrene (XPS). The structural response is investigated with reference to the following performance parameters: the buildings lateral top displacement, the ductility demand of the superstructure, the friction coefficient demand, the maximum compressive stress in the TI layer and the percentage of the uplifted foundation. A comparison between the response of models founded on a fixed base and models founded on a layer of TI with the same wooden crosslam structure differing in the number of storeys, strength capacity and subjected to earthquakes with different levels of seismic intensity is done. Regarding the buildings top displacements, the maximum compressive deformation in the TI layer, and the percentage of the uplifted foundation, the results have shown that the potentially negative influences of inserting the TI under the foundation slab could be expected only for high-rise buildings subjected to severe earthquakes. Oppositely, for the superstructures ductility demand and for the friction coefficient demand it was demonstrated that the largest demands could be expected in the case of low-rise buildings. The control of friction coefficient demand, which was recognized as critical parameter for analyzed wooden buildings, has shown that the capacity value could be exceeded yet in the case of moderate earthquake occurrence.

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

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.

Proposal for Holistic Assessment of Urban System Resilience to Natural Disasters

Urban system is a complex mix of interdependent components and dynamic interactions between them that enable it to function effectively. Resilience of urban system indicates the ability of a system to resist, absorb, accommodate to and recover from the effects of a hazard in a timely and efficient manner. In the relevant literature, most studies consider individual components separately. On the other hand, the purpose of this paper is to assess the urban system as a whole, considering all relevant components and their interactions. The goal is a study of possibilities for holistic evaluation of urban system resilience to natural disasters. Findings from the preliminary study are presented: (i) the definition of urban system and categorization of its components, (ii) a set of attributes of individual components with impact on disaster resilience of the entire system and (iii) review of different methods and approaches for resilience assessment. Based on literature review and extensive preliminary studies a new conceptual framework for urban resilience assessment is proposed. In the presented paper, a conceptual model of urban system by abstraction of its components as nodes (buildings), patches - specific nodes with spatial properties (open space), links (infrastructures) and base layer (community) is created. In the suggested model, each component is defined by its own quantitative attributes, which have been identified to have an important impact on the urban system resilience to natural disasters. System is presented as a mathematical graph model. Natural disaster is considered an external factor that affects the existing system and leads to some system distortion. In further analyses, mathematical simulation of various natural disasters scenarios is going to be carried out, followed by comparison of the system functionality before and after the accident. Various properties of the system (accessibility, transition, complexity etc.) are going to be analysed with graph theory. The final result is going to be an identification of critical points and system bottlenecks as basis for further actions of risk mitigation.