School Buildings in Rubble Stone Masonry With Cement Mortar in Seismic Areas: Literature Review of Seismic Codes, Technical Norms and Practical Manuals

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 This is particularly prevalent in former Soviet countries whose codes are based on outdated clauses for dimensioned tuff stones, despite rubble stone being the prevalent local material.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

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

This paper presents a detailed cost analysis of earthquake-resistant school buildings in the Kaski District of Nepal, specifically those constructed by the Smart Shelter Foundation (SSF) between 2007 and 2017. The study compares three primary designs: rubble stone masonry with a wooden roof, and concrete block masonry with either a wooden or a steel trussed roof. The analysis is based on a unique dataset of local building prices collected from 19 different villages, alongside general District Rates, spanning a decade. The cost breakdown is meticulously segmented into five main construction phases—foundation, walls, roof, floor, and finishing—and further categorized into materials, labor, and transportation costs. The research addresses several key questions, including the impact of materials and construction phases on overall costs, the economic viability of rubble stone versus concrete block masonry, cost implications of alternative foundation, wall, and roofing solutions, the effect of the 2015 Gorkha Earthquakes on construction costs, and the cost difference between traditional unreinforced school buildings and fully reinforced seismic designs. Master designs with consistent dimensions were prepared for fair comparisons, and master estimates were developed considering local contextual factors such as material prices and labor wages. These local rates were then contrasted with the official District Rates to identify discrepancies and general cost distribution patterns. The study reveals significant fluctuations in market prices, particularly for locally sourced materials, which complicate the detection of consistent patterns for future predictions. No clear similarities were found between local village rates and general District Rates, indicating that official rates often fail to capture micro-level variations like material availability, site accessibility, and local preferences. To aid future estimations, the paper introduces a tool for rapid cost estimation of different school designs. The cost distribution across main construction phases varied significantly over the 10-year period, with the proportion for labor increasing and transportation costs decreasing, possibly due to improved road networks. In 2017, steel roofs emerged as the most economical option across all three construction groups, contrasting with earlier periods where wooden roofs were often cheaper in certain areas. A specific analysis of seismic features indicates that while improving masonry with cement mortar has the most substantial cost impact, incorporating essential seismic elements such as horizontal bands, buttresses, and steel bars is not prohibitively expensive. The cost of adding two continuous horizontal beams, for instance, is a minimal increase, suggesting that financial constraints are not a major barrier to implementing these safety measures in new constructions. The paper also simulates the transformation of a traditional unreinforced building into a fully reinforced school, demonstrating that seismic improvements contribute significantly to the total cost, but non-structural elements like flooring and finishing can be even more costly, primarily due to labor intensity. The findings suggest that despite some expectations of dramatic price surges after the 2015 Gorkha Earthquakes, the actual increases in Kaski and Gorkha Districts were more moderate, particularly when compared to previous claims of doubling or tripling prices. The paper concludes by providing Bills of Quantity (BoQ) for various school types, offering a practical framework for villagers to compare construction costs based on local prices. It emphasizes that while cost is a major factor, local customs, material availability, and accessibility also play crucial roles in construction choices. The authors advocate for further interdisciplinary research and collaboration to validate and optimize traditional building techniques for seismic resilience, an initiative launched under the name SMARTnet. #EarthquakeEngineering #CostAnalysis #RubbleStoneMasonry #ConcreteBlockMasonry #SeismicResilience #NepalConstruction #BuildingMaterials #ConstructionManagement #SustainableDesign

In regions characterized by low to moderate seismic activity, such as Switzerland, structures that combine reinforced concrete (RC) and unreinforced masonry (URM) walls are prevalent. Despite their commonality, a comprehensive understanding of their seismic performance remains elusive. The structural integrity of these mixed RC-URM buildings is significantly influenced by both types of walls, given that their stiffness and strength are often comparable. This research project aims to deepen the understanding of the seismic behavior of buildings incorporating both RC and URM walls. A key objective is to formulate performance-based seismic design guidelines specifically tailored for these structures. This includes establishing clear definitions for various performance limit states that these buildings should meet under seismic loading. Additionally, the project focuses on the out-of-plane response of URM walls within these composite structures, investigating how boundary conditions provided by slabs and adjacent walls affect their behavior. The research methodology involves two extensive large-scale testing programs. The first program entails quasi-static cyclic tests conducted on systems comprising one RC wall and one URM wall. These tests are designed to simulate the cyclic loading experienced during an earthquake and to observe the structural response. The second program, known as the CoMa-WallS Project, involves shake table tests on a four-story building constructed at half-scale, integrating both RC and URM walls. This larger-scale test allows for a more realistic assessment of the overall structural performance under dynamic seismic excitation. The project has already yielded significant insights, including the publication of an article on quasi-static cyclic tests of two mixed reinforced concrete–unreinforced masonry wall structures. A dataset associated with this research is also publicly available. The project has received funding from several sources, including the Federal Office for the Environment, the FP7 program for access to the TREES laboratory of EUCENTRE under a specific grant agreement, and in-kind contributions from Morandi Frères SA. Ultimately, the findings from this research are intended to improve the seismic resilience of mixed RC-URM structures. By providing a better understanding of their behavior and developing robust design guidelines, the project contributes to enhancing the safety and performance of these common building types in earthquake-prone areas, ensuring they can withstand seismic events effectively and minimize damage and risk to occupants. #SeismicBehavior #ReinforcedConcrete #UnreinforcedMasonry #StructuralEngineering #EarthquakeResilience #PerformanceBasedDesign #ShakeTableTests #BuildingStructures

This study investigates the seismic performance of mid-rise and high-rise reinforced concrete (RC) buildings with unreinforced masonry (URM) infill walls containing various percentages of openings, considering the critical effects of soil–structure interaction (SSI). The research employs a soil–foundation–structure (SFS) modeling approach using the finite element software PLAXIS 3D, analyzing both a six-storey mid-rise and an eleven-storey high-rise RC building. The infill walls are modeled with opening percentages of 0% (fully infilled), 20%, 30%, and 40% to represent realistic door and window configurations, while also including a bare frame model for comparison. These building models are subjected to non-linear time–history analysis under bidirectional loading, simulating severe earthquake conditions from the 1995 Kobe earthquake, spectrally matched to Indian standards for seismic zone V. The analysis considers two distinct soil conditions: stiff (Type-B/medium) and soft (Type C) soils. The performance assessment parameters include maximum roof displacement, inter-storey drift ratio (ISDR), mode shapes, and damage state levels, determined using the HAZUS methodology. A key finding is that the inter-storey drift ratio significantly increases for all models under soft soil conditions, particularly for structures with 40% infill opening. The HAZUS damage assessment reveals that mid-rise buildings generally reach a moderate damage state, while high-rise buildings exhibit moderate-to-extensive damage with a 30% infill opening under both soft and stiff soil conditions. Notably, the study consistently shows that assuming fixed-base conditions significantly underestimates the actual storey damage state levels, highlighting the importance of incorporating SSI in seismic assessments. Mode shape analysis demonstrates that SSI considerably alters the lateral responses, increasing the dynamic time periods of the buildings. Buildings without infills (bare frames) are found to be highly vulnerable to SSI effects, experiencing large deformations. Conversely, fully infilled structures (0% opening) exhibit negligible lateral displacement, indicating that infill stiffness effectively resists deformation even with SSI. Structures on soft soil generally show enhanced deflection compared to those on stiff soil, further emphasizing the impact of soil flexibility. Regarding lateral displacement, both absolute maximum roof displacement and relative displacement are higher in soft soil conditions than in stiff soil. For instance, mid-rise structures on soft soil show relative displacement amplifications of up to 25.6% for certain infill configurations compared to stiff soil. Similarly, high-rise structures on soft soil show substantial amplifications, with the M4H model on stiff soil displaying 31.3% higher lateral displacement than a fixed-base counterpart. The varying infill opening percentages also influence these displacements, with larger openings generally leading to increased structural movements. Analysis of shear force and bending moments indicates that infill walls with openings, particularly those with 40% opening, experience higher concentrations of these forces near edges and openings. These concentrations suggest potential vulnerabilities to diagonal cracks or shear failure. The presence of openings modifies load paths, making structures more susceptible to localized damage, while soft soil conditions further amplify structural movements and twisting, increasing the likelihood of shear and bending failures in infills. Torsional moments are also significantly observed in models with openings, especially along the corners, and are more pronounced in soft soil due to increased flexibility. The study concludes that optimal infill opening percentages are highly dependent on soil type and building height. Under stiff soil conditions, optimal opening percentages are estimated to be 40% for mid-rise buildings and 30% for high-rise buildings. However, these optimal percentages are significantly reduced to 30% and 20%, respectively, under soft soil conditions. The findings underscore the critical need for SFS modeling in seismic assessments, particularly for URM-infilled buildings in seismically active regions, to accurately predict structural behavior and optimize infill opening designs. The performance assessment parameters utilized in this research are deemed satisfactory for achieving this optimization. #SeismicPerformance #ReinforcedConcreteBuildings #UnreinforcedMasonryInfill #InfillOpenings #SoilStructureInteraction #PLAXIS3D #NonLinearTimeHistoryAnalysis #DamageAssessment #InterStoreyDriftRatio

The article discusses the evolving landscape of structural flooring solutions in New Zealand following the Canterbury earthquakes, which prompted a re-evaluation of design standards for both new and existing buildings. Previously, concrete held over 90% of the market share for structural flooring due to its cost-effectiveness. However, the earthquakes led to a noticeable shift towards timber-based solutions, partly fueled by the perception of concrete's failure and further accentuated by the Labour Party's 'pro-wood' policy, which proposes mandating timber design options for new low-rise government-funded buildings. The Cement and Concrete Association New Zealand (CCANZ) chief executive, Rob Gaimster, acknowledged concrete's dominant market position but also noted the market pressure created by the earthquake damage. Rob Fulford, executive director of PreCast New Zealand and a member of the Standards Committee for structural concrete design, explained that the committee is incorporating recommendations from the Canterbury Earthquakes Royal Commission and forensic engineers. A key issue identified was the inability of concrete floors to perform effectively as a diaphragm, which is crucial for transferring horizontal forces from wind and earthquakes to the building's resistant elements. This failure was often linked to the breaking of non-ductile reinforcing mesh in the concrete topping, a material not permitted in the 2006 design code. Although the loss of seating of floors did not cause collapses, new design standards will require these effects to be accounted for in future building designs. Conversely, some industry experts, such as Gavin Robertson, director of Potius Building Systems, believe the construction market has been overly reliant on concrete floors. He has observed a significant increase in the adoption of engineered timber flooring solutions post-quake, attributing this to timber's performance and flexibility during seismic events. Robertson highlighted that timber floors impose substantially less weight on a building's structure, enhancing its seismic resilience. While he acknowledges the benefit of the 'pro-wood' policy for his business, he also shares the widespread sentiment that government intervention to control the market is unfair, a view echoed by CCANZ's Rob Gaimster, who warns of potential job losses in the concrete sector. Amidst this industry debate, a novel hybrid flooring system called 3PT has emerged from the University of Canterbury, developed by Dr. Alessandro Palermo and Professor Stefano Pampanin. This innovative system combines engineered timber, concrete anchorage, and high-strength pre-stressed or post-tensioned reinforcement. The pre-stressing feature creates a pre-camber that balances self-weight and a portion of the live load, while the concrete anchorage ensures movement continuity at mid-supports. This system allows for longer floor spans compared to traditional timber methods and offers a reduced weight, making it a promising solution for Christchurch's rebuild, where lightweight flooring systems are highly sought after. The 3PT system is slated for its first installation in a mixed-use timber building in Nelson, potentially offering a sophisticated answer to contemporary structural flooring challenges. #StructuralFlooring #ConcreteConstruction #TimberConstruction #EarthquakeResilience #BuildingStandards #HybridFlooring #NewZealandArchitecture #SeismicDesign #ConstructionMaterials

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

Mass-timber construction, encompassing elements like glued-laminated timber (glulam), cross-laminated timber (CLT), and nail-laminated timber (NLT), is gaining traction in the United States. These timber components offer inherent fire resistance through charring and possess high load-carrying capacities, making them suitable for high-rise buildings. Skidmore, Owings & Merrill LLP (SOM) has been researching the application of mass-timber in tall buildings since 2013. Their initial report, the Timber Tower Research Project, identified timber-concrete composites as an efficient solution for high-rise structures, capable of reducing embodied carbon. Following this, SOM released three additional reports specifically addressing the floor systems in high-rise, mass-timber buildings. Floor systems typically constitute the largest portion of a structure's cost and carbon footprint. While often governed by non-structural factors, floor systems significantly influence the design of supporting structural elements. They commonly incorporate concrete for acoustic control, fire resistance, and to conceal utilities. In conventional reinforced concrete and structural steel buildings, floor weight typically accounts for 60 to 80 percent of the total structural frame weight. Mass-timber floor systems, with their natural insulation and lower density (20 to 25 percent of concrete), offer an alternative. CLT floor planks, usually comprising three to five plies of wood for cost-effectiveness, range from 105 to 175 mm (4 1/8 to 6 7/8 in.) in thickness. These planks have a sound transmission class (STC) of 30 to 40, which falls below the International Building Code (IBC) requirement of 50 for dwelling units, thus necessitating acoustic treatment. A common method to enhance acoustic performance, as well as fire resistance and utility concealment, involves adding a 50 to 75 mm (2 to 3 in.) thin concrete topping slab over the timber. European mass-timber construction has already adopted this approach, developing connector systems to create structurally composite CLT and concrete topping slabs. These timber-concrete composite floor systems can achieve longer spans than conventional timber floors, thereby reducing the need for columns and bearing walls, which increases their market competitiveness. SOM's two recent reports further explore timber-concrete composite floors. The first details a physical testing program of these systems at Oregon State University (OSU), funded by the Softwood Lumber Board. The second, conducted with the American Institute of Steel Construction (AISC), investigates combining timber-concrete composite floors with structural steel frames for multifamily construction. Both reports are accessible on SOM's research website. The OSU testing program, completed in 2016, involved 20 individual tests across 14 full-scale specimens. These tests focused on structural behaviors crucial for design, such as composite connector effectiveness, two-way bending stiffness, long-term creep deflections, and a full-scale mockup test. The results indicated superior performance from epoxied connectors compared to mechanical ones, and that connector tests aligned with predictions. Two-way bending stiffness varied as anticipated across different axes and bending types. Long-term creep deflection increases were consistent with recommendations from the American Concrete Institute (ACI) and the US CLT Handbook. The full-scale mockup test demonstrated the floor system's capacity to support approximately eight times the code-required design load. While not necessary for design (which is governed by deflections and vibrations), this excess strength is advantageous for fire resistance, allowing for significant charring before load-carrying capacity is compromised. Future research at SOM will concentrate on fire testing of the system. The joint research project between SOM and AISC, concluded in 2017, explored timber-concrete composite floor systems with structural steel framing for high-rise residential buildings. The research aimed to develop a lightweight, prefabricated steel and timber system for buildings typically constructed with reinforced concrete. An 11-story reinforced concrete building designed by SOM, featuring a 200-mm (8-in.) thick post-tensioned flat plate floor, served as the benchmark. The proposed SOM and AISC solution involved timber-concrete composite floor planks supported by asymmetric steel beams. These beams had wider bottom flanges to support CLT plank ends, and their depth was designed to be integrated within the composite timber floor planks, creating a floor structure similar to a concrete flat plate without downward-projecting beams. Careful design of the steel beams and their column connections was essential to control deflections and vibrations. Material quantity estimates revealed the proposed system could achieve marketable column bays and a structural slab thickness comparable to concrete-framed buildings. Although further verification is needed, initial findings are promising, suggesting the system's market competitiveness. Timber-concrete composite floor systems represent an emerging technology in the United States, offering a unique combination of low weight, extensive spanning capabilities, and sustainability. They can be integrated with various framing systems to optimize overall performance. Further testing and precedent projects are necessary to establish a foundation for future code provisions governing the design of these innovative floor systems. #MassTimber #CompositeFlooring #TimberConcrete #TallBuildings #SustainableConstruction #StructuralEngineering #BuildingCodes #FireResistance #AcousticPerformance

This article presents an interview with Kyle Tourjé, Executive Vice President of Alpha Structural Inc., focusing on the critical aspects of concrete foundation repair and seismic retrofitting, particularly in earthquake-prone regions like Southern California. Alpha Structural Inc., a second-generation company, offers comprehensive civil and structural engineering services, alongside licensed general engineering and concrete specialty contracting. Their expertise spans structural concrete, geohazard repair, and various seismic retrofits, including coastal and hillside repairs, structural steel and concrete repairs, foundation replacement, landslide remediation, slope stabilization, deep foundation systems, and retaining walls. The company integrates both engineering and construction disciplines to ensure a seamless project execution from design to completion. Tourjé highlights geology-related issues as the most common causes of concrete foundation problems, where substandard bearing materials often lead to settlement and instability. Corrosion-related damage is another significant factor, causing deterioration in concrete structures, along with poor drainage which accelerates the overall degradation of foundations over time. He emphasizes the importance of collaboration between structural engineers and concrete contractors, advocating for contractor input during the engineering design phase to enhance constructibility and prevent project delays, performance issues, or disagreements. This integrated approach ensures that practical construction considerations are factored into the theoretical design. In Southern California, specific construction practices are implemented to resist seismic forces, which are often not mandated in other states. These practices include the precise placement of reinforcing steel, the use of high-strength concrete mixes, and meticulous rebar installation to prevent corrosion and ensure long-term foundation resilience. Key details such as maintaining adequate clearance between reinforcing steel and the concrete surface are critical, underscoring that cutting corners on these installation steps can compromise structural integrity. Contractors in other regions can learn from these practices, particularly focusing on preventing corrosion by ensuring correct concrete slump and proper rebar placement. Recent updates in ACI documents and committees relevant to concrete foundation placement in seismic areas include clarifications to seismic design criteria, new maximum stirrup spacing for closed stirrups under seismic demand, and updated seismic design requirements for deep foundations across all categories. These changes are crucial for adhering to the latest safety and durability standards in earthquake-prone zones. Emerging technologies and trends in concrete construction include pressure-injected concrete, advanced mix designs for improved corrosion resistance and strength, and the application of fiber-reinforced polymer (FRP) as an alternative to traditional steel rebar. These innovations contribute to building stronger and more durable foundations. Tourjé advises concrete contractors to remain committed to quality, especially during challenging project phases, and to strive for perfection in every pour to deliver work that meets the highest standards. #ConcreteConstruction #SeismicRetrofitting #FoundationRepair #StructuralEngineering #ConstructionTechnology #EarthquakeResilience #CorrosionPrevention #ConstructionBestPractices #SouthernCalifornia

The demand for enhanced floor/ceiling acoustics in multifamily construction has increased significantly due to consumer preferences, updated guidelines from code bodies, and stricter enforcement of existing regulations. Design professionals face the challenge of adapting traditional sound control methods to these evolving requirements. This article examines crucial new guidelines for architects and specifiers and explores how construction manufacturers are developing innovative products and improving existing ones to achieve superior acoustical performance. Two primary measurement standards for acoustics in multifamily construction are the sound transmission class (STC) and the impact insulation class (IIC). STC quantifies the amount of airborne sound a building element, such as walls or floor/ceilings, can contain. IIC measures impact noise, like footsteps or dropped objects, transmitted through a floor/ceiling system. These single-number ratings apply to the entire assembly of materials separating tenants. For over 50 years, these metrics have guided architectural design teams in quantifying acoustic levels. Early documents like HUD's 1967 guide and the Uniform Building Code (UBC) emphasized sound control, with UBC requiring a minimum STC and IIC rating of 50 (or 45 if field-tested). Higher ratings indicate better performance. The adoption of the International Building Code (IBC) in 1997 raised awareness of acoustical ratings, though minimum requirements remained consistent with UBC. Despite growing competition in the multifamily industry leading to upgrades in flooring and lighting as amenities, acoustical performance often received little attention. This oversight is problematic given that acoustics significantly influence vacancy rates and are a common source of litigation. Furthermore, popular amenity upgrades, such as hard-surfaced floors and canister lighting, can negatively affect a floor/ceiling assembly's acoustical performance. To address the need for updated acoustical guidance, the International Code Council (ICC), in collaboration with acoustical experts, developed ICC G2-2010, "Guideline for Acoustics." This guideline acknowledges that current code requirements are insufficient for occupant needs and introduces two performance levels: 'acceptable' and 'preferred,' both surpassing minimum code requirements. These levels offer clearer targets for desired acoustical performance based on building type. For example, a luxury building or one with noise-sensitive occupants would aim for the 'preferred' level. A common design for multifamily projects, recommended by acoustical consultants, includes hard-surfaced flooring, at least 25 mm (1 in.) of gypsum concrete, a 6.4-mm (¼-in.) entangled mesh sound mat, a wood subfloor, wood floor trusses or joists, insulation, resilient channel, and a single layer of gypsum board. This assembly typically achieves an IIC of 51 to 55 and an STC of 56 to 60, depending on the floorcovering. While these ratings exceed code minimums and often meet the 'acceptable' STC requirement, they only marginally satisfy 'acceptable' IIC levels for nuisance impact noises. Achieving these ratings relies on proper selection and installation of all components, such as using high-quality resilient channels. To further improve IIC ratings, upgrades to the sound mat or resilient ceiling system are necessary. Advancements in sound mat technology include traditional entangled mesh mats manufactured with an additional acoustical fabric laminated to the underside, creating an extra vibration break and absorptive layer. This innovation improves IIC performance by two to five points without increasing the floor system's thickness. Another option involves using the standard 6.4-mm entangled mesh sound mat with a secondary topical mat placed between the gypsum concrete and the finished floor, provided the secondary mat is high-quality and tested for sound ratings specific to the assembly. Properly installed, high-quality resilient channels enhance IIC ratings, but faulty installation can undermine their effectiveness. New resilient clips have emerged that are less prone to improper installation and can deliver comparable performance. Hanging systems that incorporate springs and minimize contact between the resilient channel and the joist offer even better performance. Combining these products, such as ceiling wave hangers or spring isolators with a 6.4-mm entangled mesh sound mat, can enable systems to exceed 'acceptable' and approach 'preferred' IIC levels for hard-surfaced floorcoverings. Specifiers and architects must determine the desired level of acoustic performance for each project, moving beyond mere code compliance. Key considerations include the importance of acoustical privacy for tenants, the project's long-term use (e.g., apartments versus condominiums), and the potential for future changes in flooring. For instance, projects that may convert to condominiums should be designed from the outset with high-performance sound control throughout, as future owners might replace carpets with hard-surfaced flooring, necessitating stringent acoustical criteria. The wood-frame multifamily industry is increasingly prioritizing floor/ceiling acoustics, requiring specifiers to stay informed about new products and adapt specifications to meet specific sound control levels that contribute to end-user satisfaction. #MultifamilyConstruction #SoundControl #AcousticalPerformance #FloorCeilingAssembly #STC #IIC #BuildingCodes #GypsumConcrete #SoundMats #ResilientChannels #ArchitecturalDesign #ConstructionTechnology

Purlin roof structure houses are common in rural China, valued for their accessible materials and simple construction. However, these structures are highly vulnerable to seismic damage, often experiencing purlin detachment and wall cracking during earthquakes. To address these deficiencies, a new damping-limit device has been developed and investigated. This device is installed at the connection point between the gable and the wooden purlin, aiming to improve the structure's seismic performance. Traditional rural houses in southern China, particularly in provinces like Jiangxi, Anhui, Hunan, and Hubei, frequently feature brick-wood structures with purlin roofs. These buildings, many predating the 1980s, often lack adequate seismic measures, making them susceptible to damage. Earthquakes can cause excessive displacement of purlins, leading to their dislodgement and stress concentration at the gable peak, which can result in wall collapse. Existing strengthening methods, such as adding cement mortar surfaces with steel mesh or ring beams, primarily target load-bearing walls and have not adequately addressed the vulnerabilities of gable peaks and roof truss systems. Furthermore, these traditional methods can be costly, time-consuming, and prone to poor construction quality due to reliance on unskilled labor. This study utilized numerical simulations with ADINA finite element analysis software to evaluate the seismic performance of an unreinforced original structure, a structure reinforced with traditional methods, and a structure enhanced with the novel damping-limit device. An example of a two-story brick-wood house in Jiangxi Province, built in the 1980s, served as the case study. The house features 240mm thick walls made of mixed clay bricks and adobe masonry, lacking ground beams, ring beams, or constructional columns, which compromises its structural integrity. The roof system consists of wooden purlins (200mm diameter, over 4m long) supported by gable walls, overlaid with slats and tiles. The proposed damping-limit device consists of a rubber partition layer sandwiched between two identical steel gaskets, installed at the purlin-gable overlap joint. The wooden purlin is bolted through these layers, ensuring that the purlin, rubber, and steel plate act as a single unit. The rubber layer is designed to dissipate seismic wave energy, thereby reducing acceleration in the purlins and the overlying structure. This mechanism alleviates compression and impact on the wall, significantly mitigating stress concentration and cracking at the joint. The material properties for masonry, wooden purlins, and rubber were defined for the numerical model, with rubber modeled using the Ogden constitutive model to account for its hyperelastic behavior. Seismic waves (EL-Centro, Taft, and Tianjin) with a peak amplitude of 2.2 m/s² (corresponding to a rare 7-degree earthquake) were applied in time history analyses. Modal analysis revealed that the original structure was prone to X-direction vibration due to fewer longitudinal walls and weak gable constraints. The traditional strengthening method improved X and Y-direction constraints, shifting vibration towards the Z-direction. The novel device improved X-direction stiffness. Displacement response analysis showed that the damping-limit device significantly reduced gable peak displacement and overall structural displacement compared to the original structure, though traditional reinforcement showed slightly better overall displacement control. The inter-story drift angle of the reinforced structures indicated good condition, while the original structure was near a moderately damaged state. Principal tensile stress analysis demonstrated that the original structure experienced significant stress concentration at wall junctions and the purlin-wall overlap, leading to potential failure. Both strengthening methods reduced principal tensile stress at the gable peak, with the traditional method achieving a 60% reduction and the novel device a 40% reduction. Shear stress analysis showed that the original structure had severe shear stress concentrations, particularly at the bottom of walls and gable peaks. Traditional reinforcement significantly reduced shear stress (around 70% at the wall bottom), while the novel device had a limited effect on the lower wall's shear stress. Acceleration response analysis indicated that the novel device remarkably reduced X-direction acceleration by approximately 50% compared to the amplitude-modulated seismic wave, demonstrating its effective shock absorption capacity. In contrast, traditional reinforcement did not significantly reduce acceleration response in the X-direction. In conclusion, the novel damping-limit device effectively addresses the seismic vulnerabilities of purlin roof structures by limiting purlin displacement, alleviating stress concentration at purlin-wall connections, and significantly reducing seismic response and acceleration. While traditional methods offer broader improvements in structural stiffness and stress reduction across the entire structure, the damping-limit device provides a simpler, easier-to-install, and quality-controlled solution, making it suitable for rural housing reinforcement. Combining this device with local wall strengthening could further enhance overall seismic performance. Future considerations include exploring alternative materials like nylon plates to reduce costs and enhance applicability. #PurlinRoofStructure #SeismicPerformance #DampingLimitDevice #StructuralStrengthening #NumericalSimulation #RuralHousing #EarthquakeResistance #BrickWoodStructure #MaterialScience

The 6.9 magnitude earthquake that struck Morocco on September 8 claimed nearly 3,000 lives and injured 5,530, with the epicenter located in the Atlas Mountains, flattening entire villages and severely damaging neighborhoods in Marrakech's Old City. Media coverage has largely attributed the extensive destruction to the region’s traditional earthen architecture, with some experts suggesting these structures are inherently weak and ill-suited for earthquake-prone areas. For instance, Antonio Nogales, head of Spain’s United Firefighters Without Borders NGO, stated that traditional building materials, when collapsing, do not create air pockets for survival as steel-and-concrete buildings might. Similarly, US earthquake geologist Wendy Bohon commented that these buildings were not designed to withstand strong seismic shaking. This perspective, however, overlooks the inherent resilience of traditional earthen architecture when properly maintained and understood. Historically, earth has been a fundamental building material for at least 12,000 years, adapted to diverse local geographies, geologies, and climates globally. Examples range from adobe structures in the American Southwest and mudbrick in Mali’s Grand Mosque in Djenne to rammed earth in Yemen’s tower houses and cob construction in China’s Great Wall and 16th-century English homes. These diverse building cultures integrate features like horizontal timbers, fibers, or netting in seismic regions to resist displacement and lateral movement, minimizing damage. In Morocco, traditional mudbrick, rammed earth, stone, and timber houses are designed to be thermally efficient, staying cool in summer. The notion that earthen buildings are primitive and inherently prone to destruction is a historical mischaracterization often rooted in colonial narratives used to discredit indigenous cultures and promote colonial building practices and materials. This perception has led to earth buildings being classified as 'unsafe' or lacking adequate building codes, despite their proven durability. Such classifications can inadvertently push communities away from traditional, sustainable building methods towards commercial materials like concrete and cement, which may not be compatible with existing structures and can reduce seismic resilience if not properly integrated. The introduction of new, incompatible materials, or inadequate maintenance and alterations due to the loss of traditional knowledge, can weaken these structures. Disruptions in traditional knowledge transfer, vital for the repair and maintenance of these unique buildings, contribute significantly to their vulnerability during seismic events. When the skills required for traditional construction and repair are lost, structures become susceptible to damage, creating a cycle where inadequate repairs lead to increased vulnerability in subsequent earthquakes. The article highlights that media coverage should be sensitive to local building cultures, as pressuring communities to abandon traditional methods for poorly constructed modern alternatives can exacerbate the problem. Following the 2023 Turkey-Syria earthquake, damage was attributed to modern concrete, steel, and brick constructions that disregarded building codes, not traditional methods. Similarly, after the 2003 Bam earthquake in Iran, subsequent studies revealed that traditional earth buildings performed better than modern constructions and poorly executed restoration work. Thus, a lack of understanding regarding the resilience of traditional building cultures can further endanger communities already traumatized by seismic events. #MoroccoEarthquake #EarthenArchitecture #BuildingResilience #SeismicDesign #TraditionalKnowledge #CulturalHeritage #DisasterPreparedness #BuildingMaterials #VernacularArchitecture

Floating walls are a crucial structural solution in construction, particularly in areas with challenging soil conditions. These walls address the problem of soil expansion and contraction, which can significantly impact concrete foundations. When heavy rains or freezing ground cause the soil beneath a basement to swell, it can lead to ground heave, exerting immense pressure on a building's structure. In regions characterized by heavy clay soils, framing floating walls creates a necessary gap that relieves this pressure, preventing damage to the home's joists and other structural components. This method is essential for maintaining structural integrity and avoiding issues such as cracked tiles and buckled wood flooring. Carmine Argano, owner of Creative Design Ceramic Tile & Bath, highlights that floating walls are specifically designed to accommodate movement in a concrete slab. This movement can arise from expansive soil, seismic activity, or frost heave. A rigid wall frame in such conditions would transfer any slab lift directly into the floor system above, leading to extensive damage. The typical approach to building a floating wall involves leaving a 3-inch gap between the base of the wall frame and the bottom of the framed wall. This gap allows the bottom plate to slide slightly on the nails if the slab shifts upward, preventing the pressure from being transferred to the rest of the structure. While this system provides crucial movement tolerance, Argano notes that it does result in a slight loss of rigidity compared to a fully secured wall. The necessity of floating walls is determined by site-specific conditions and local building codes, rather than personal preference. These walls are commonly found in basements located in areas like Colorado, Utah, and California, or any region with unstable or shifting ground. Without this space between the plates, upward movement of the concrete can force joists up, causing floors to buckle or tiles to break. Although DIY basement framing is possible, it is imperative to consult local building codes to ascertain whether floating walls are required in a particular area. The framing process itself is relatively straightforward and can be completed in a few hours, representing a small upfront investment that can prevent significant and costly problems in the future. Constructing a floating wall begins with selecting pressure-treated wood for the bottom plate, as it will be in direct contact with the concrete slab. This bottom plate is then secured to the concrete floor using concrete anchors, ensuring it is level and square to existing walls. Temporary 2-inch by 4-inch blocks are used to create the necessary clearance, typically matching building code requirements. Another 2-inch by 4-inch beam, serving as the floating plate, is placed on top of these blocks and secured to the pressure-treated plate with 6-inch nails after drilling pilot holes. Once the temporary blocks are removed, a top plate is installed by drawing plumb lines up to the ceiling joists on both sides and securing a 2-inch by 4-inch beam, ensuring it is perfectly plumb with the bottom plates. Finally, vertical studs are fitted snugly between the top and bottom plates, completing the floating wall structure. #FloatingWalls #HomeImprovement #StructuralStability #SoilMovement #BasementFraming #ConstructionTechniques #BuildingCodes #ConcreteFoundations