Abstract
Full base shear seismic demand analyses with calculated examples for heavy stone masonry buildings are not present in the literature. To address this shortcoming, analyses and calculations are performed on nominally reinforced rubble stone masonry house and school designs, as typically built in Nepal. The seismic codes are literally applied for countries where the technique is still allowed (Nepal, India, China, Tajikistan, Iran, Croatia), or should be reintroduced based on current practices (Pakistan, Afghanistan, Turkey). First, this paper compares the base shear formulas and the inertia forces distributions of these codes, as well as material densities, seismic weights, seismic zoning, natural periods of vibration, response spectra, importance factors and seismic load combinations. Large differences between approaches and coefficients are observed. Then, by following Equivalent Lateral Force-principles for Ultimate Limit State verifications (10%PE50y), the base shear and story shears are calculated for a design peak ground acceleration of 0.20 g, as well as the effects of critical load combinations on the forces and moments acting on the lateral-resisting elements. It is concluded that Pakistan has the most tolerant code, Nepal represents an average value, whereas India and China are most conservative toward the case study buildings. Overall, it is observed that heavy-masonry-light-floor systems with negligible diaphragm action behave different under seismic motion than most other building typologies. Given the observations in this paper, the applicability of conventional ELF, S-ELF and S-Modal methods for heavy masonry buildings is questionable. The codes however do not introduce modified approaches that address these differences. Possible implications of the exclusion of plinth masonry and large portions of seismic weight need further assessment and validation, for which different (possibly more sophisticated) concepts must be considered, such as the equivalent frame method or distributed mass system. Since Nepal allows stone masonry in areas with higher seismic hazard levels >0.40 g (opposed to India <0.12 and China <0.15 g), their code is taken as the reference and starting point for follow-up research, which aims to verify the seismic demand by performing seismic capacity checks of the masonry piers and spandrels. The paper ends with an appeal for global collaboration under the research project SMARTnet.
Highlights
Between 2007 and 2012 the Dutch NGO Smart Shelter Foundation (SSF) built earthquake-resistant schools in rubble stone masonry in Nepal, which have survived the 2015 Gorkha earthquakes without any significant damage
The floor inertia forces are distributed to the lateral-resisting elements by tributary wall masses
- Since generation of inertia forces is proportional to mass, it is important to determine the correct stone typology, as large differences exist between densities for sandstone and granite
Summary
Between 2007 and 2012 the Dutch NGO Smart Shelter Foundation (SSF) built earthquake-resistant schools in rubble stone masonry in Nepal, which have survived the 2015 Gorkha earthquakes without any significant damage. The empirical knowledge is based on a few publications from the 1980s which have not been updated since, as concluded by Schildkamp and Araki (2019a) It was already noted in 1977 that “a review of the earthquake codes of various countries shows that much of the information is empirically based and not theoretically derived. For “nonengineered” structures this has not been undertaken to date, and the authors of this paper have started a longterm research program with the aim of upgrading the knowledge and improving the seismic resilience of rubble stone masonry buildings, to be published in a series of papers that already includes a literature review of practical manuals, a detailed cost analysis (Schildkamp and Araki, 2019a; 2019b) and an overview of design specifications in national seismic and masonry codes worldwide (Schildkamp et al, 2020) Bertero and Bertero (2002) state that “codes and standards should be simple enough so that they can be applied effectively according to the education (knowledge) of the professionals involved (designers, builders, governmental bodies) as well as the owners, but without compromising the reliability of the structure. (. . .) Codes should reflect the most reliable procedures that can be developed according to the state-ofthe-art in seismic engineering.” Effectively, for “nonengineered” structures this has not been undertaken to date, and the authors of this paper have started a longterm research program with the aim of upgrading the knowledge and improving the seismic resilience of rubble stone masonry buildings, to be published in a series of papers that already includes a literature review of practical manuals, a detailed cost analysis (Schildkamp and Araki, 2019a; 2019b) and an overview of design specifications in national seismic and masonry codes worldwide (Schildkamp et al, 2020)
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