Performance-Based Design of Tall Timber Buildings Under Earthquake and Wind Multi-Hazard Loads: Past, Present, and Future

Light-frame wood construction constitutes a significant portion, approximately 90%, of the housing industry in Canada and the United States. Within this construction method, roofs are typically built either using prefabricated trusses or through stick-framing, where the roof structure is assembled on-site. Current building codes for stick-framing are largely based on historical practices and provide limited consideration for high-speed wind events, rendering these roof structures vulnerable to failure during tornadoes. This research addresses this vulnerability by proposing enhanced stick-framing guidelines designed to withstand EF-2 tornadoes. The study employs non-linear finite element analysis to model a stick-framed roof, initially designed according to the National Building Code of Canada. Connections between structural members are represented using non-linear links, while frame elements model the members themselves. An iterative performance-based design approach is applied: increasing wind loads are simulated, and upon identifying the first points of failure, the corresponding elements are improved. This process is repeated until the roof structure meets the performance target of resisting EF-2 tornadoes. Key issues identified and addressed during this process include the failure of roof-to-wall connections (RTWCs) and an insufficient number of members in the initial framing. The observed failure modes in the model are validated against damage survey photos from actual tornado events, revealing consistent patterns of structural failure. To improve the roof's resilience, several recommendations are put forth. A notable improvement involves an enhanced gable end frame, which increases the number of RTWCs and provides a more robust frame in areas subjected to the highest loads. Other suggested additions include the incorporation of struts, the use of hurricane ties at all RTWC locations, and an increased number of nails in various connections within the repeating inner frames. Minimum member sizes and material qualities for each roof structural component are also specified. The research highlights that the initial NBCC-compliant design fails at a mere 14% of the target EF-2 load, primarily due to RTWC weaknesses. This significant finding underscores the inadequacy of existing guidelines for tornado loads and emphasizes the need for the proposed improvements. The iterative design process reveals that the majority of structural elements experience their highest demand-capacity (D/C) ratios at the gable end frame, necessitating its strengthening. The implementation of specific gable end framing, including bracing and hurricane ties, significantly enhances the structure's capacity. Additionally, adding struts one-third of the way up the rafters, connecting them to the ceiling joists, effectively reduces moments in the members. Snow load cases also influence the design, particularly affecting rafter members and their connections to collar ties and ceiling joists. The final design incorporates these improvements, ensuring the roof can withstand both EF-2 tornado wind loads and significant snow loads. Comparison of the model's failure points with real-world tornado damage photos confirms the efficacy of the identified weak points. The failure of RTWCs, especially rafter RTWCs, and connections between rafters and ceiling joists, are common in both the model and actual tornado events. The proposed guidelines aim to provide easily implementable solutions for builders, promoting resilience in light-frame wood roof structures against tornado forces. The recommendations cover repeated inner framing connections, gable end frame specifications, and outrigger framing, alongside detailed specifications for nails, spacing, and bracing. These findings bridge a critical knowledge gap in stick-framing construction for tornado-prone regions, suggesting a feasible design approach for EF-2 level tornado resistance, with potential for adaptation to other roof types and sizes. #LightFrameConstruction #WoodRoofs #TornadoWindLoads #EF2Tornado #StickFraming #NonLinearFiniteElementAnalysis #BuildingCodes #PerformanceBasedDesign #RoofToWallConnections #StructuralResilience #GableRoofDesign #HurricaneTies #ConstructionGuidelines

The devastating impact of severe tropical cyclones in Australia during the 1970s, particularly Cyclones Althea and Tracy, underscored the critical need for integrating research-based structural engineering principles into residential building design and construction. Historically, house construction relied on traditional methods that evolved slowly, rendering them vulnerable to extreme weather events compared to engineered structures. The inherent structural redundancies and complex load paths within houses complicated their analysis, prompting the Cyclone Testing Station (CTS) to initiate full-scale house testing in the early 1980s. These initial tests involved static multipoint loading of an older house slated for demolition, followed by comprehensive testing of nine full-scale houses under both static and cyclic loading. This extensive testing program aimed to understand load paths in various house types, incorporating different building practices and materials, and its findings were instrumental in amending Australian house construction codes, standards, and manuals. Over time, advancements in computer modeling and instrumentation have enabled more sophisticated full-scale studies. Current research benefits from real-world data on houses under construction, allowing for analytical models that account for the variability in connection strengths, an aspect difficult to capture in single tests. This approach facilitates the study of progressive failure in timber-framed housing systems, distinguishing between structures that sustain significant damage and those with limited damage during the same wind event. These studies integrate wind tunnel investigations to map temporal pressure distributions, full-scale multiple tests on connections (including those with construction defects) to establish statistical distributions of strength and load/deflection relationships, and full-scale tests on complete houses or sections thereof to determine load-sharing mechanisms among parallel structural and non-structural elements. The test program results serve to calibrate analytical models, which are subsequently used for reliability studies. Early full-scale tests by CTS involved applying simulated wind loads to various house types, including a high-set house, a single-story house with a concrete floor, a Tongan hurricane house, brick veneer houses for both cyclonic and non-cyclonic regions, a light-gauge steel-framed panelized building, and a split-level brick veneer house. These tests provided crucial insights into vulnerable elements and load paths. For instance, initial tests consistently revealed that at least one element or connection failed below the design load, often due to low-cycle fatigue. However, after minor design modifications, the houses could resist significantly higher loads. The tests also demonstrated that non-structural elements, such as cornices, played a crucial role in transferring wind loads, creating stiff and direct load paths. Furthermore, the studies highlighted the importance of structural redundancy, where parallel elements could share loads, mitigating the risk of significant damage from the failure of a single weaker element. Limitations of these early tests included the challenge of replicating construction variations and the generalized nature of simulated wind loading compared to actual spatial and temporal wind pressure fluctuations. Recent research has expanded full-scale testing to focus on house roofs, examining structural response and load sharing. Unlike studies in North America and Canada, Australian research addresses the unique construction types prevalent in the region. This involves combining full-scale tests on house sections with numerical models, characterizing component variability, and utilizing detailed wind tunnel loading data. Investigations into contemporary house construction practices, informed by surveys, revealed deficiencies in design and installation, such as incorrect site classifications and faulty connections. These deficiencies are now being incorporated into full-scale tests to understand their role in progressive failure and the effectiveness of redundancies. For example, testing of truss-to-wall connections, both ideal and defective, demonstrated how wall linings and cornices contribute to load sharing around weak connections. Finite element models, validated against experimental data, further explore load sharing and structural responses under various defect scenarios. Another area of recent focus is the progressive failure and load redistribution of batten-to-truss connections. Laboratory tests on both new and aged connections, subjected to static and dynamic wind loads, showed significant variability in strength and highlighted the impact of nail slip on connection performance. Wind tunnel studies provided time-history data of loadings on roof elements, revealing correlations between peak loads on adjacent connections, which is critical for understanding the initiation of progressive failures. Non-linear finite element analysis simulated load redistribution as connections fail, showing how loads are shared among neighboring connections based on the stiffness of battens and cladding. The analysis indicated that connection failures can cascade rapidly, emphasizing that while some elements provide redundancy, critical connections near the cladding have limited load-sharing capacity, making it essential for each connection to meet its design load. This ongoing research continues to quantify the varying resilience of connections within houses, contributing to more robust and wind-resistant building practices. #WindLoads #StructuralTesting #HouseConstruction #BuildingCodes #CycloneResistance #TimberFramedHouses #ProgressiveFailure #LoadPaths #FiniteElementModeling

Residential roof failures are a prevalent and costly issue during extreme wind events, with hip roofs generally considered more resilient than gable roofs. However, recent damage survey data from tornadoes reveal an understudied failure mode: partial framing failures in hip roofs. This study investigates these failures, reviews common roof design and construction practices, and utilizes two-dimensional finite element models to estimate element-level load effects on hip roof trusses and stick-frame components. The likelihood of failure for each member is assessed based on demand-to-capacity (D/C) ratios, comparing trussed and stick-frame structures to evaluate their relative performance. The research begins by reviewing existing literature on residential wind damage, noting that most previous work focuses on roof-to-wall connection (RTWC) failures and sheathing loss. While the Enhanced Fujita (EF) Scale for tornadoes categorizes damage (DOD-4 for sheathing loss, DOD-6 for major roof failures), the current understanding of DOD-6 is often limited to RTWC failures. Damage survey data from the 2013 Moore, Oklahoma (EF5) and 2011 Tuscaloosa, Alabama (EF4) and Joplin, Missouri (EF5) tornadoes were analyzed. This analysis revealed numerous instances of partial hip roof framing failures, where parts of the roof frame, in addition to sheathing, were removed while RTWCs appeared intact. In some areas, these framing failures constituted a significant portion of observed roof damage, particularly in newer, steep-sloping, stick-frame hip roofs. Statistical analysis of damage in two neighborhoods in Joplin, Missouri, following the 2011 tornado showed that in Region 1, 56% of houses with relevant damage experienced partial framing failure, compared to 35% with RTWC failure. In Region 2, these numbers were 33% and 37%, respectively, indicating that framing failures are a common occurrence. The varying distribution of failure types between regions suggests that factors like construction age, roof slope, and potential debris impact may influence failure modes. A numerical modeling method was developed using SAP2000 to analyze internal load effects and strength behavior of wood-frame roof components under wind uplift. The method identifies vulnerable elements by comparing maximum demand on framing members and connections to their minimum capacities. The analysis confirmed that toenailed RTWCs are highly vulnerable in both trussed and stick-frame hip roofs, often being the first element to fail. However, the study highlights that if hurricane straps are used to reinforce RTWCs, the point of failure can shift to other framing members and joints within the roof structure. For instance, in a truss with hurricane straps, the top chord members and joints show higher D/C ratios than the RTWC, indicating their increased vulnerability. For stick-frame roofs, the analysis of a representative jack rafter also indicated the toenailed RTWC as the most vulnerable point, followed by the connection at the ridge. The D/C ratios suggest that stick-frame roofs, especially older ones potentially built to outdated standards or with construction errors, may contain more highly vulnerable elements. The study acknowledges limitations in its two-dimensional modeling, emphasizing the need for three-dimensional models to account for load sharing and sheathing effects. It concludes that framing failures are a possible and common mode of failure in hip roofs, potentially occurring at lower wind speeds than previously assumed for major roof damage, and suggests the need for further investigation to refine building codes and the EF-Scale for different residential design methods. #WoodFrameStructures #TornadoDamage #EnhancedFujitaScale #HipRoofs #FiniteElementModeling #DegreesOfDamage #ResidentialStructures #WindLoad #StructuralEngineering

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

This article explores the rapidly evolving field of mass timber construction, an ancient material reimagined for modern architectural challenges. It details how mass timber, incorporating products like glulam, CLT, NLT, and DLT, offers structural and fire-resistance qualities that open new possibilities for building design, particularly in commercial contexts. Unlike traditional concrete and steel construction, which often relies on standardized templates, mass timber projects frequently feature unique structural systems, allowing for innovative design approaches beyond mere pragmatism. The fundamental differences between mass timber and conventional construction materials are highlighted. Mass timber systems follow distinct rules; for instance, square bays, efficient for materials with uniform strength and stiffness in all directions, are less so for wood, which is inherently "stick built" with "one-way" elements. Consequently, mass timber systems, relying on deeper beams, often necessitate greater floor-to-floor heights. The article also addresses the aesthetic appeal of exposed wood structures, a common design goal that presents challenges in fire protection and weatherproofing during construction, adding to overall costs. Economically, mass timber construction is characterized by the material cost, particularly fiber, accounting for approximately two-thirds of the structural expense. The prefabrication of large mass timber elements off-site, often utilizing CNC milling, significantly reduces on-site and factory labor costs. This economic model suggests that systems minimizing material use can be economical even if they introduce complexity. The article anticipates that increased adoption of mass timber will lead to greater affordability. It also positions wood as a renewable resource that sequesters carbon, aligning with the shift towards a carbon-based economy and offering a sustainable solution to climate change. The article then delves into various mass timber structural systems, each with distinct advantages and applications. The "Long Beam Short Deck" system is presented as a common configuration where beams are oriented in the long direction and the deck in the short, minimizing deck cost by reducing its span, though potentially leading to deeper floor systems. Conversely, the "Short Beam Long Deck" system prioritizes shallower floor heights by orienting beams in the short direction. The "Beams and Girders" system aims for minimal cost by using the thinnest possible deck, supported by girders that transfer loads to columns, though it can limit flexibility in service distribution. More complex systems are also examined. "Two-Way Beams" are suitable for equal bay sizes, distributing loads evenly by alternating deck orientation. The "Reciprocal Frame" is a self-supporting network of mutually reinforcing beams, offering structural efficiency and vibration mitigation, though requiring temporary support during erection. "Point Supported CLT" eliminates beams entirely by leveraging CLT's two-way bending strength, creating thin floor systems, but is constrained by CLT's directional weakness and fire protection requirements. "Wide Flat Beams," whether placed on the bottom, top, or flush, aim for long spans with minimal structural depth, though they can be less efficient or present unique stability challenges. The "Staggered Deck" system, using two offset layers of deck fastened with diagonal screws, achieves long spans with minimal material. "Cassette" systems involve prefabricated assemblies of beams and decks, optimized for crane capacity and faster construction, such as timber box beams that remove less effective material near the neutral axis. The "Stressed Skin Lattice" extends this concept to two-way systems, using CLT panels in opposing orientations to achieve flexural strength. Drawing inspiration from Pier Luigi Nervi, the article also considers optimizing material use in mass timber, adapting his concrete strategies to create radial beam systems. Proprietary systems like "VCTC Voided Concrete Timber Composite," which combines timber with a thick, voided concrete topping to eliminate beams and achieve long spans, and "DELTABEAM®," a flush steel beam system adapted for mass timber, are also discussed. The "Cree by Rhomberg" system offers modular mass timber beams with composite concrete decks. The "Zollinger Lamella" uses a rhomboid pattern of standard timber segments for efficient roof structures, adaptable to flat applications for strong diaphragms. Finally, the "Triple Beam" system, an all-wood shallow beam approach, allows columns to pass through, mitigating crushing and shrinkage issues while offering fire protection benefits, particularly for taller timber buildings. This comprehensive overview underscores the versatility and potential of mass timber in contemporary architecture. #MassTimberConstruction #WoodArchitecture #StructuralEngineering #SustainableBuilding #ConstructionTechniques #BuildingMaterials #TimberDesign #ArchitecturalInnovation #Prefabrication

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

The article addresses the ongoing challenge in high-performance building design: balancing the need for natural daylight and views with energy efficiency and occupant comfort. Traditional building codes and sustainable standards like ASHRAE 189.1, IgCC, and LEED emphasize daylight and views, but these often conflict with goals to reduce building energy consumption and can lead to thermal and visual discomfort. This conflict often results in arguments for reducing allowable window areas, despite growing evidence of the positive impact of daylight on human health, well-being, and productivity, including its role in regulating circadian rhythms and reducing risks of obesity, cancer, heart disease, and depression. Electronically tintable glass, or electrochromic (EC) glass, is presented as an elegant solution to this dilemma. EC glass can dynamically modulate its solar heat gain coefficient (SHGC) and visible light transmission, offering a range of settings from 60% to 1% visible light transmission and 0.41 to 0.09 SHGC. This capability allows for maximum daylight harvesting, reduced cooling loads, and passive solar gains during heating seasons, thereby saving energy in all climate zones. Crucially, EC glass can control glare effectively without the need for blinds, thus preserving views and connection to the outdoors, which static solutions often obstruct. Recent advancements in EC glass technology have significantly enhanced its design flexibility and performance. These improvements include increased size availability (up to 5’x10’), higher manufacturing volumes, a wider range of exterior aesthetic colors, and the innovative ability to control up to three different segments within a single pane. This in-pane zoning is particularly beneficial for floor-to-ceiling glass installations, enabling co-optimization of glare control, light color quality, daylight admission, and energy performance. By allowing different sections of a pane to be in various tint states, architects can maintain excellent color rendering and provide sufficient daylight even when most of the glass is tinted for solar control, without compromising the overall aesthetic or the number of mullions. Case studies illustrate the practical applications and benefits of EC glass. In a “green” glass cube design at Colorado State University’s Morgan Library, EC glazing tamed intense western sun while preserving the building's transparency and achieving LEED® Silver certification. Similarly, a glass cube for TD Bank in Miami used EC glass to manage heat and light from south and west-facing walls in a challenging climate, ensuring occupant comfort and energy efficiency. In healthcare, at Butler County Medical Center in Nebraska, EC glass provided expansive views and comfortable daylighting for a wellness center, eliminating blinds that could harbor bacteria, thus supporting infection control. For historic preservation, the St. Johnsbury Athenaeum in Vermont used triple-pane EC glass in skylight renovations to protect its art collection from fading and sun damage, while maintaining the building's original appearance and achieving superior thermal performance, significantly reducing energy consumption. Moreover, EC glass proves valuable in retrofit applications, as demonstrated by the Kimmel Center for the Performing Arts in Philadelphia. Here, EC glass in the roof of the Dorrance H. Hamilton rooftop garden transformed an almost uninhabitable space into a comfortable, rentable venue year-round, preserving panoramic city views. These examples underscore how dynamic glazing relieves constraints imposed by static building envelopes, allowing architects to embrace highly glazed designs that deliver both high energy performance and superior occupant comfort, without sacrificing aesthetic vision or connection to the natural environment. The technology offers an invaluable tool for meeting rising energy efficiency targets and creating people-friendly workspaces. #DynamicFacades #ElectrochromicGlass #HighPerformanceBuilding #SustainableDesign #Daylighting #EnergyEfficiency #OccupantComfort #GreenBuildingCodes #ArchitecturalDesign #GlassFacades

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 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

In areas increasingly prone to wildfires, such as Austin, Texas, building fire-resistant homes is crucial for protecting lives, structures, and wildlands. The International Wildland-Urban Interface Code (IWUIC) provides guidelines for constructing structures in Wildland-Urban Interface (WUI) zones to mitigate fire risks. This code is regularly updated and applies to new builds, additions, relocations, and repairs. The article focuses on wood-framed homes and highlights key aspects of the 2024 IWUIC, acknowledging that local building departments have the final say on acceptable fire-resistant designs. The IWUIC categorizes fire-hazard severity into extreme, high, and moderate, based on factors like fuel type, terrain slope, critical fire weather days, water supply for firefighting, and the quality of defensible space. Defensible space, which can be natural or designed, aims to slow wildfire progression and create areas for fire suppression. The code also assigns levels of ignition-resistant construction (Class 1 IR, Class 2 IR, Class 3 IR), with Class 1 IR offering the highest protection. For example, homes in extreme fire-hazard zones with conforming water supplies must meet Class 1 IR requirements, while those in moderate zones with conforming water supplies may follow Class 2 or Class 3 IR provisions depending on defensible space. A critical component of fire-resistant design is the roof and its assembly. Class A-rated roof assemblies, which perform well under severe fire exposure, are mandatory for Class 1 IR structures. Class 2 IR zones require Class A assemblies or approved noncombustible roof coverings, while Class 3 IR zones allow Class B assemblies or noncombustible coverings. Examples of Class A-rated coverings include asphalt shingles, composite shakes, and TPO membranes. Metal roofing, though noncombustible, needs ignition-resistant underlayments to achieve a Class A rating. Underlayments like Owens Corning's Titanium FR and GAF's VersaShield are commonly used. Noncombustible materials like clay, concrete, and slate roofs offer superior protection but require meticulous installation to prevent ember intrusion, especially at eaves, ridges, and valleys. For roofs with gaps where embers can lodge, the roof deck must be protected, often with a 72-lb. mineral-surfaced cap sheet or Class A-rated deck protection products like Type X gypsum sheathing. Eaves, vents, and gutters also require specific fire-resistant treatments. In Class 1 IR and Class 2 IR zones, the underside of eaves must be protected by ignition-resistant materials, fire-resistant treated wood, or materials with a 1-hour fire resistance rating. Open rafter tails are generally prohibited, or only allowed if constructed of heavy timber. Attic vents, gable-end vents, and dormer vents in Class 1 IR and 2 IR zones must be strategically located, covered with noncombustible, corrosion-resistant mesh with small openings (not exceeding 1/8 inch), and designed to prevent flame or ember penetration. Gutters and downspouts must be noncombustible and designed to prevent debris accumulation. For walls and wall assemblies, noncombustible cladding such as brick, stone, stucco, ceramic tile, metal, and fiber-cement provides superior protection. Certain dense tropical hardwoods and fire-retardant-treated wood (FRTW) sidings are also ignition-resistant options. In some cases, a 1-hour fire-rated wall assembly is required, often incorporating 5/8-inch-thick Type X exterior gypsum board or specialized sheathing like Georgia-Pacific’s DensGlass. In extreme fire-hazard zones, the bottom 6 inches of a Class 1 IR wall must be noncombustible or protected with metal flashing where it meets the ground, a deck, or a roof. The article also advises careful consideration for rainscreens and open-joint cladding to prevent ember entry. Windows and doors in Class 1 IR and Class 2 IR constructions must use specific glazing types, including tempered glass, multilayered glazed panels, glass block, or glass with a minimum 20-minute fire rating. While window-frame material is not restricted, many jurisdictions require at least one tempered glass layer. Exterior doors must be noncombustible (e.g., hollow-core steel, fiberglass) or solid-core wood with a minimum thickness of 1 3/4 inches, with glazing requirements mirroring those for windows. Vehicular access doors like garage doors are exempt from IWUIC but may have local sealing stipulations. Porch ceilings and underfloor areas also have specific requirements. If a porch has living space above, its underside and supporting elements must be made of heavy timber, FRTW, or 1-hour fire-resistant construction. Crawlspaces and overhanging projections like balconies must also comply with these "underfloor enclosure" provisions. Deck surfaces in Class 1 IR and Class 2 IR areas must be noncombustible or ignition-resistant, including materials like flagstone, concrete, and Class A-rated composite or hardwood decking. Deck framing in these zones must be noncombustible, ignition-resistant, heavy timber, or FRTW. Undersides of decks over steep descending slopes require enclosure with walls meeting house exterior wall standards. Detached accessory structures within 50 feet of a habitable building in Class 1 IR and Class 2 IR zones must have ignition-resistant exterior walls or be constructed with 1-hour fire-rated materials. Automatic sprinkler systems are required in Class 1 IR areas to contain internal fires. The article emphasizes the importance of consulting local building officials due to the complexity and potential for interpretation in building codes, concluding that despite restrictions, resources are available to design and build attractive and safe homes in wildfire-prone regions. #WildfireResilience #FireResistantDesign #WildlandUrbanInterface #BuildingCodes #ConstructionMaterials #HomeSafety #ArchitecturalDesign #SustainableBuilding

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

The article addresses the growing demand for large, straight, and durable lumber for modern home construction, particularly for ceilings and roofs, given the increasing median size of new single-family homes. Traditional solid-sawn lumber often presents challenges due to limited availability in lengths greater than 20 feet and its propensity to warp or sag, which can lead to unsightly issues like wavy drywall. Engineered lumber products, such as laminated veneer lumber (LVL) and laminated strand lumber (LSL), are presented as a solution to these challenges. These engineered wood products offer superior dimensional stability, consistency, and are available in significantly longer lengths and deeper dimensions compared to conventional lumber. The discussion highlights specific applications where engineered lumber proves particularly beneficial. For flat roofs, which are gaining popularity in modern residential architecture for their sleek aesthetic, the inherent straightness and stiffness of engineered lumber are crucial to prevent sagging over time. This ensures the structural integrity and aesthetic appeal of the roof. TimberStrand LSL and TJI Joists are mentioned as examples, offering depths up to 16 and 24 inches, respectively, to accommodate longer spans and higher loads. Cathedral roofs and ceilings, often central focal points in great rooms or over staircases, also greatly benefit from engineered lumber. The demand for a perfectly flat and straight surface for sheetrock in these applications makes traditional lumber less ideal due to its tendency to warp. Engineered products like TimberStrand LSL and Microllam LVL ridge beams are recommended for their ability to maintain straight lines, preventing the visual imperfections that can arise from crooked framing materials. This ensures the dramatic architectural features remain visually striking and structurally sound. Another significant application discussed is the creation of bonus rooms, often converted attics or spaces above garages, which are becoming increasingly common for adding livable square footage. In these scenarios, the framing material for floor joists must support both floor loads and, in some cases, roof loads. TJI Joists are specifically highlighted for their performance in these spaces, effectively mitigating issues like twisting, warping, and shrinking that are common with solid-sawn lumber. This ensures a stable and reliable floor system for these converted living areas. The article emphasizes that engineered wood products offer consistent mechanical properties, which translate to predictable performance and fewer installation problems, ultimately reducing costly callbacks for builders. Weyerhaeuser's TimberStrand LSL, Microllam LVL, and TJI Joists are presented as key examples of engineered lumber that address the modern construction needs for large, straight, and robust framing components in various roof and ceiling designs. #HomeConstruction #RoofingMaterials #CeilingDesign #EngineeredLumber #FramingSolutions #WeyerhaeuserProducts #StructuralIntegrity #ModernArchitecture