Cost Analysis of Mountain Schools in Nepal: Comparison of Earthquake Resistant Features in Rubble Stone Masonry vs. Concrete Block Masonry

This literature review examines the state of the art concerning non-engineered rubble stone masonry construction, specifically for school buildings, in seismic areas. The research focuses on structures built with loadbearing walls of rubble stone masonry in cement mortar, reinforced with horizontal elements. A total of 47 relevant field manuals published between 1972 and 2017 were analyzed, alongside 109 national building codes. The objective was to identify similarities, contradictions, gaps, and discrepancies among these publications. Given that most practical manuals target the Himalayan context, Indian and Nepali seismic and building codes were particularly relevant for comparison. A significant finding is that only nine manuals provide design and construction processes for schools, despite these often conflicting with codes that explicitly prohibit stone masonry for buildings with an importance factor of 1.5 or higher (which includes schools). It was observed that seven of these nine manuals were either written or co-written by the same author, Martijn Schildkamp, and that much of the available knowledge, largely empirical, stems from a limited number of primary sources. However, consistency and consensus were lacking across almost all critical topics, such as main dimensions, opening parameters, and reinforcing elements. Furthermore, the persistent copying of identical illustrations and tables, including those with apparent conflicts, suggests that knowledge in this domain has not significantly advanced since the 1980s, an observation reinforced by the fact that Indian and Nepali seismic codes have not been substantially updated since 1994. The review highlights that existing information contains numerous contradictions and has become ambiguous, raising concerns about its correctness, reliability, and practical value. For instance, while Indian codes prohibit low-strength masonry for important buildings (like schools) in high seismic zones, the Nepali government has approved school designs in rubble stone masonry, directly contradicting its own regulations. The authors propose that the current body of knowledge requires comprehensive assessment, validation, optimization, and supplementation through modern computational, testing, and modeling techniques. To address this, the authors have launched the SMARTnet initiative (Seismic Methodologies for Applied Research and Testing of non-engineered Techniques), which aims to update and disseminate knowledge about traditional building techniques, starting with rubble stone schools in Nepal as a case study. This initiative calls for global collaboration from experts and academics. The paper details the specific design parameters of schools built by the Smart Shelter Foundation in Nepal, which largely withstood the 2015 Gorkha earthquakes. These designs feature maximum classroom dimensions of 4.8 x 4.8 meters, 350mm thick random rubble stone masonry walls with cement-sand mortar, buttresses at wall ends, and horizontal reinforced concrete bands at five levels. The decision not to include vertical reinforcements in critical wall connections, based on expert advice regarding potential weakening, remains a debated topic. The type of stone masonry and mortar is also discussed, categorizing stone types (rubble vs. ashlar) and mortar compositions (mud, cement, lime-sand) in relation to seismic safety. Rubble stone masonry with cement mortar is classified as the second safety level according to Arya (2003). Additionally, the paper distinguishes between reinforced, confined, and unreinforced masonry systems, noting the ambiguity in classifying structures with minimal reinforcement. It discusses the concept of "non-engineered" construction and the historical development of guidelines for such buildings, highlighting the need for separate code specifications for engineered and non-engineered structures. The article also examines how building categories are determined, referencing seismic zonation, ground conditions, and building importance, and critically assesses the "one-size-fits-all" approach in some publications. The eligibility of national seismic codes is narrowed down to the Himalayan region due to global restrictions on rubble stone masonry in high seismic zones and linguistic challenges. For practical manuals, a completeness analysis revealed that only one manual fully aligned with the specific search criteria, emphasizing the scarcity of precise and comprehensive guidance for this construction type. #RubbleStoneMasonry #SeismicCodes #NonEngineeredConstruction #SchoolBuildings #EarthquakeEngineering #BuildingManuals #HimalayanRegion #ConstructionSafety #StructuralIntegrity

This study addresses the lack of comprehensive analyses and calculated examples for base shear seismic demand in heavy stone masonry buildings by examining nominally reinforced rubble stone masonry house and school designs commonly found in Nepal. The research applies seismic codes from countries where this construction technique is permitted (Nepal, India, China, Tajikistan, Iran, Croatia) or could be reintroduced (Pakistan, Afghanistan, Turkey). The initial phase of the study compares base shear formulas, inertia force distributions, material densities, seismic weights, seismic zoning, natural periods of vibration, response spectra, importance factors, and seismic load combinations across these codes, revealing significant discrepancies in approaches and coefficients. The research then calculates base shear and story shears for a design peak ground acceleration of 0.20g, along with the effects of critical load combinations on lateral-resisting elements, adhering to Equivalent Lateral Force (ELF) principles for Ultimate Limit State (ULS) verifications (10%PE50y). Pakistan's code is identified as the most lenient, Nepal's as an average, and India's and China's as the most conservative for the case study buildings. A key observation is that heavy-masonry-light-floor systems with negligible diaphragm action behave distinctly under seismic motion compared to other building typologies. The applicability of conventional ELF, S-ELF, and S-Modal methods for such heavy masonry buildings is questioned, as current codes do not offer modified approaches for these differences. Further assessment and validation are required for implications such as the exclusion of plinth masonry and large portions of seismic weight, necessitating potentially more sophisticated concepts like the equivalent frame method or distributed mass system. Considering Nepal's allowance of stone masonry in higher seismic hazard areas (>0.40g), in contrast to India (<0.12g) and China (<0.15g), Nepal's code serves as the reference for subsequent research aimed at verifying seismic demand through capacity checks of masonry piers and spandrels. The article highlights that these buildings, with heavy stiff walls and light flexible diaphragms, derive almost all their lateral-force-generating mass from the walls (approximately 97.5% versus 2.5% for diaphragms, including live loads). The choice of stone type significantly influences inertia forces, and current codes may underestimate base shear by excluding lower wall sections and lumping seismic weights at floor levels. Empirical formulas for the fundamental period (T1) can also lead to overestimation of maximum base shear in short-period buildings. The structural behavior factor, typically 2.0 for nominally reinforced stone masonry with cement mortar, is crucial, with values like Pakistan's R=4.5 potentially leading to underestimation. While many countries accept simplified analytical methods for regular structures, India's requirement for dynamic analysis at lower seismic levels seems inconsistent with non-engineered seismic design principles. Significant variations in seismic hazard levels and PGA values exist across the selected countries, with India and Tajikistan showing relatively low design accelerations not based on probabilistic approaches. Despite variations in coefficients, the resulting base shear for houses is similar across Nepal, India, Afghanistan (ELF), Iran, Turkey, and Croatia, with Nepal representing the average. Pakistan is the most tolerant, and China the most conservative in terms of base shear. When load combinations are applied, India's seismic demands become comparable to China's due to a high load combination factor. The study emphasizes the need for modified design approaches and rigorous validation of parameters specific to nominally reinforced stone masonry, advocating for global collaboration through initiatives like SMARTnet to improve seismic resilience in such structures globally. #RubbleStoneMasonry #SeismicDemand #SeismicCodes #BaseShear #LoadCombinations #EarthquakeEngineering #StructuralBehavior #BuildingDesign #HimalayanRegion

The Himalayan region of Nepal, characterized by ongoing neo-tectonic activities, is highly vulnerable to seismic events. Stone masonry, often constructed with or without mud mortar, has been the primary building material for centuries. A significant structural survey of approximately 223 buildings in three remote rural villages revealed prevalent structural irregularities, such as variations in wall thickness between floors leading to mass irregularities, asymmetrical vertical openings causing in-plane discontinuity, and out-of-plane offset irregularities due to cross walls on the ground floor. These constructions were typically built without seismic considerations, making them highly susceptible to earthquake damage, as evidenced by the 2015 Gorkha earthquake. This study examines a typical building, incorporating construction information gathered post-2015 Gorkha earthquake, to enhance seismic design based on local construction practices. The use of mud/cement mortar was minimal in these traditional structures. Timber bands at various wall heights and appropriate roof-to-wall connections were also largely absent. Following the 2015 earthquake, communities implemented several improvements, including replacing gable walls with metal sheets, reducing individual stone masonry homes to a single story, and using lighter construction for the upper stories of hotel buildings. The study emphasizes the potential for seismically resilient building forms by meticulously detailing the construction of these structures using mud/cement mortar and other regional materials. Non-linear finite models were simulated for both typical and enhanced buildings, based on regional building techniques. The inherent irregularities of stone units, construction variability, and constrained linear behavior present challenges for detailed numerical analysis of stone masonry with and without mud mortar. Traditional Sherpa homes, characterized by their elongated shape and strategic placement parallel to hill slopes, often feature thick outer protective walls of locally available stone, reaching up to 1 meter in thickness. These are usually unshaped rubble plastered with yak dung and mud mixture. An internal timber frame supports a wooden ceiling. Older, simpler rubble-built houses often lack horizontal timber beams integrated into the outer stone walls, a feature that would enhance earthquake resistance. Foundations and floors are typically stone, with houses being single or two stories. Two-story homes historically used the ground floor for livestock and storage, with living areas upstairs. The 2015 Gorkha earthquake severely damaged 93% of traditional houses and tourist structures in the Thame Valley, with 66% completely damaged. Observed damage patterns included 'X cracking' of external walls, stones toppling from wall tops and roof triangles, and subvertical cracks. Out-of-plane failure of long, thick stone masonry walls was common due to the absence of cross walls and seismic bands, indicating a lack of lateral load resistance and proper roof-to-wall connections. The construction of dry stone stacks with external pointing and plastering contributed to individual masonry unit failure rather than cohesive wall strength. Post-earthquake reconstruction, often carried out by the community with some government support, did not always incorporate seismic-resistant designs due to the urgency. A rapid visual screening (RVS) in August 2022 confirmed that 92% of buildings were stone masonry, with 43% being uncoursed random rubble. Only 2% of buildings used cement mortar, primarily schools and monasteries, while less than 1% used mud mortar. About 88% of buildings now have CGI metal sheet roofing, replacing heavier slate roofs. While corner tie stones are still common (68%), less than 5% and 2% of buildings had timber and reinforced concrete bands, respectively. A significant change was the replacement of stone masonry gable walls with lightweight metal CGI sheets in 43% of buildings. The majority (72%) of reconstructed individual homes are now single-story, with separate structures for animals and storage, reflecting community-learned adjustments. The study concludes that while the introduction of timber bands and wall buttresses (Enhanced-Irregular Stone Masonry Building, E-ISMB) significantly improved building performance under lateral loading, a more comprehensive approach to incorporating additional enhancement techniques is required. Numerical analysis showed that E-ISMB had a fundamental time period reduced by 28.2% and lateral strength increased by 73.5% compared to Current-Irregular Stone Masonry Building (C-ISMB), indicating enhanced rigidity and capacity. Cross walls, buttress walls, and timber bands, in conjunction with mud mortar, can effectively reduce out-of-plane deformation and distribute stresses more uniformly, thus delaying collapse and improving overall seismic performance. Further numerical and experimental studies are needed to fully understand the local failure modes and optimize additional recommended enhancement techniques. #HimalayanBuildings #SeismicDesign #StoneMasonry #EarthquakeResistance #NepalArchitecture #StructuralIrregularities #PostEarthquakeReconstruction #ResilientDesign

The widespread use of rubble stone masonry, particularly with cement mortar and wooden diaphragms, in seismic regions globally necessitates a comprehensive review of existing design specifications and construction requirements outlined in national seismic and masonry codes. This analysis covers nearly 325 codes from countries where this building technique is, or has been, common. The review focuses on identifying the allowances, restrictions, and specific details related to newly constructed houses and schools using "nominally reinforced rubble stone masonry (NRM) with cement mortar and wooden diaphragms in seismic areas." This particular type of construction is specifically detailed and permitted in the codes of only seven countries: Nepal, India, China, Tajikistan, Georgia, Iran, and Croatia. Significant inconsistencies are observed among these national codes regarding design specifications. Parameters such as maximum building dimensions (length, width, and height), minimum and maximum wall and opening dimensions, and specifications for horizontal and vertical reinforcements vary considerably. For instance, maximum building lengths between seismic gaps range from 25m in Iran to 80m in Georgia, and the number of allowed stories ranges from one to five, even for similar design accelerations. Reinforcement requirements also differ widely, with some codes mandating multiple horizontal and vertical reinforcements, while others require only a few horizontal tie-beams. The discrepancy extends to maximum allowed design accelerations, which range from 0.08g in Indian zone III to 0.52g in Georgia. Such wide variations raise concerns about the completeness, correctness, and reliability of the current knowledge base in this field. Another critical observation is the lack of clear descriptions regarding the types of stone masonry and stone properties addressed in many codes. Often, codes fail to distinguish between random rubble and cut, dimensioned stones, leading to ambiguity and potential misinterpretation. This is particularly prevalent in former Soviet countries whose codes are based on outdated clauses for dimensioned tuff stones, despite rubble stone being the prevalent local material. Furthermore, many codes use vague language, such as "should preferably be avoided," which weakens mandatory compliance. To address these issues, the introduction of "Nominally Reinforced Masonry" (NRM) as a distinct, fourth category of masonry, alongside Unreinforced Masonry (URM), Confined Masonry (CM), and Reinforced Masonry (RM), is proposed to provide clearer terminology and avoid confusion. It is also recommended that codes explicitly state whether rubble stone masonry is permitted, specifying the types of buildings and structures to which it applies. Moreover, the study highlights that many countries where stone masonry is still a widely practiced technique, such as Afghanistan, Pakistan, Bhutan, Azerbaijan, Kyrgyzstan, Morocco, Tunisia, Turkey, Yemen, and Albania, either prohibit it in their codes or lack relevant regulations entirely. This disparity between traditional construction practices and formal building codes creates a significant challenge for local builders and communities. The paper advocates for the development of a stand-alone code specifically for NRM rubble stone buildings with cement mortar, consolidating all necessary design and execution information into a single, accessible document. Such a code would prevent the interchanging of incompatible specifications meant for other masonry types. This comprehensive review forms the basis for future research within the "SMARTnet" initiative (Seismic Methodologies for Applied Research and Testing of Non-Engineered Techniques). This initiative aims to assess, validate, optimize, and complement existing knowledge through modern calculation, testing, and modeling methods. The goal is to develop a structured research approach, termed "Non-Engineered 2.0," focused on vernacular and traditional construction techniques to improve the seismic resilience of rubble stone masonry buildings globally. This effort is crucial for providing clear, reliable, and up-to-date information to millions of people who reside in stone houses worldwide, ultimately strengthening confidence in this traditional building method and potentially reintroducing it where it is currently prohibited. #RubbleStoneMasonry #SeismicCodes #MasonryDesign #EarthquakeEngineering #BuildingCodesWorldwide #NominallyReinforcedMasonry #TraditionalConstruction #SustainableDesign #BuildingResilience