EN 1998: EUROCODE 8 DESIGN OF STRUCTURES FOR EA...

Abstract:Since 2015 the transition from the traditional seismic design regulation to the newly developed code of practice has been initiated in Kazakhstan. The introduced regulatory system involves the application of the European approach for the seismic design of buildings and structures on the territory of Kazakhstan. This study aims to present a comparative analysis of seismic design codes applied in Kazakhstan (i.e., SP RK 5.01-102-2013* Foundations of Buildings and Structures and SP RK 2.03-30-2017* Construction in Seismic Regions) and SP RK EN 1998-5:2004/2012 Design of Structures for Earthquake Resistance, identical to Eurocode 8 (EC8). One of the critical aspects of the research investigates the difficulties of integrating European design standards into the local regulatory system. The necessity of applying the European approach considering the geotechnical features of the country provided in the National Annex (NA) is defined and proved. The designed codes of practice are also compared in terms of conservativeness, when considering a design problem verifying the seismic bearing capacity of a shallow foundation in Almaty city.Keywords: Eurocode; SNiP; seismic design; earthquake design; seismic bearing capacity

EN 1998: EUROCODE 8 DESIGN OF STRUCTURES FOR EA...

Practicing engineers typically follow linear methods for seismic design and assessment, confining their approach to the requirements of SANS 10160-4 (SANS 2017). This generally leads to a conservative design, leaving little space to apply additional tools for design refinement. Soil-structure interaction has beneficial effects for most building structures under seismic action. However, incorporating soil-structure interaction in the analysis influences the fundamental period, damping and ductility, and will therefore influence the behaviour factor prescribed by design codes. The behaviour factor is necessary for linear methods (force-based methods) to predict the nonlinear behaviour of the structure. This investigation assessed the current behaviour factor for reinforced concrete walls in low- to medium-rise buildings, as prescribed by SANS 10160-4 (SANS 2017), when soil-structure interaction is incorporated in the analysis. The buildings were initially designed and detailed using linear methods, with the prescribed behaviour factor, and then tested using nonlinear methods that do not require the use of a behaviour factor.

SANS 10160-4 (SANS 2017) does not explicitly set out specifications for soil-structure interaction. Eurocode 8 part 5 (EN 2004c) lists the types of structures that require SSI analysis. These are structures where the interaction between the soil and the foundation could have a negative effect on the seismic response, therefore a "fixed base" analysis is likely to be unconservative. Annex D of Eurocode 8 part 5 (EN 2004c) states: "For the majority of common building structures, the effects of SSI tend to be beneficial, since they reduce the bending moment and shear forces in the various members of the superstructure." Eurocode 8 does not, however, provide more specific guidelines on the design and modelling aspects.

SANS 10160-4 (SANS 2017) prescribes a peak ground acceleration (PGA) of 0.1 g for all regions experiencing natural seismic activity in South Africa (Zone I regions), despite indicating higher nominal peak ground accelerations with a 10% probability of exceedance in 50 years in Figure A.1 of SANS 10160-4 (SANS 2017). The code committee deemed it inappropriate to increase the PGA magnitude, as one of the main motivations for revising the seismic loading code was due to the perception from engineers that the PGA was too conservative. To overcome this concern, the lower limit of the redundancy factor borrowed from Uniform Building Code:1997 (UBC) was rather adjusted to effectively increase the PGA from 0.1 g to between 0.12 g and 0.15 g (Retief & Dunaiski 2009 pp 173-174). Remaining consistent with SANS 10160-4 (SANS 2017), a PGA of 0.1 g, together with the redundancy factor, was used for design; however, a PGA of 0.15 g was used for the nonlinear assessment of the structures. A PGA of 0.15 g reflects a more accurate value for the southwestern region of the Western Cape Province.

Wall elements consist of confined concrete elements to represent the wall boundary elements, and unconfined concrete for the web section of the wall. Slab elements are fixed to the wall with rigid links along the length of the wall. The slab elements are beam elements with the width equal to the panel width of the bay. All slab elements are modelled as unconfined concrete elements and are connected to the columns with pinned connections, therefore not transferring moments to the columns. Column elements are designed to remain elastic, therefore limiting the column contribution to the ductility of the lateral resisting system. Base elements are fixed to the wall elements and are modelled as rigid beams over a set of zero-tension, zero-length spring elements. As this study assesses the relative change in ductility, it was deemed unnecessary to introduce the additional parameter of base stiffness to the investigation. The stiffness of the base was therefore assumed to be rigid for all structures considered. Modelling a rigid foundation is an accepted method for inclusion of SSI in the analysis. The reader is referred to the design standards of ASCE/SEI 41-17 (ASCE 2017) for the recommended methods of analyses. 041b061a72