بررسی فناوری های حفاظت لرزه ای در ساختارهای چوبی تاریخی (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
این پژوهش با مرور و مطالعه بر ساختمان های تاریخی که در ساختار بنایی خود با هدف مقاوم سازی در برابر زلزله از عنصر چوب در پی، جرز و پوشش ها بهره جستند، در پی یافتن پاسخ به پرسش های زیر است: 1. ساختمان های تاریخی نمونه از چه فناوری حفاظتی استفاده کرده و چه تمهیداتی در برابر زلزله دارند؟ 2. سیستم های این فناوری چیست، چه ویژگی هایی دارد و آیا کاربردی صرفاً مقاوم سازی داشته اند؟ 3. نمونه های ایران از چه نوع فناوری هستند و تا چه میزان در کاهش خسارات زلزله موفق بوده اند و آیا امروزه نیز از این سیستم ها در معماری بومی استفاده می شود؟ تا بدین طریق بتواند در پژوهش های آتی با محوریت حفظ و توسعه این سیستم ها در آینده به حفاظت لرزه ای ساختمان ها کمک کند. پژوهش حاضر با مطالعه کتابخانه ای به شناسایی این سیستم ها پرداخته و جامعه آماری پژوهش بر سیستم های شناخته شده جهانی و به طور ویژه معماری بومی ایران تمرکز دارد و نوع تحقیق آن توصیفی است. چهار فناوری شناسایی شده مقاوم لرزه ای شامل جداسازی پایه، کلاف های افقی و عمودی و قاب چوبی هستند. چوب در این سیستم ها منحصراً کارایی مقاوم سازی نداشته و عوامل دیگری در انتخاب آن اثرگذار بوده اند. در ایران نیز سیستم های منحصر به فردی از فناوری های مذکور وجود دارد که در مقایسه با ساختمان های اطرافشان که فاقد این فناوری بوده اند، در برابر زلزله نمونه های موفقی محسوب می شوند؛ اما امروزه ناشناخته مانده و روبه فراموشی هستند. این مطالعه می تواند با جمع آوری دانش بومی و ایجاد یک پایگاه اطلاعاتی از سیستم های شناخته شده تاریخی ایران در ایجاد حساسیت جوامع نسبت به حفاظت این سیستم ها مؤثر واقع شود و در پژوهش های آتی بینش های ارزشمندی را درمورد این نوآوری های محلی ارائه دهد. شناسایی و طبقه بندی این نمونه ها به درک سیستم های سنتی ساخت و ساز چوبی و پتانسیل آن ها برای کاربردهای مدرن کمک می کند و بر اهمیت ادغام دانش تاریخی با شیوه های معماری امروزی، بر پایداری آن ها در برابر زمین لرزه تأکید دارد.Study of Seismic Protection Technologies in Historical Wooden Structures
This research, by reviewing historical buildings that use wood elements in their masonry structure with the aim of earthquake resistance, tries to find answers to the following questions:1-What kind of protection technology do the studied historical buildings use and what are their solutions against earthquakes?2-What are the systems of this technology, what are their characteristics and have they been used only for seismic retrofitting?3-What kind of technology are the examples of Iran and To what extent have they been successful in reducing earthquake damage and Are these systems still used in local architecture today? In this way, in the future research, focusing on the maintenance and development of these systems, it will help to protect the buildings in the future. The research identified and analyzed these systems with a library study, and the statistical population of this research focuses on the world-known systems and especially the local architecture of Iran, and the type of research is descriptive. Four identified earthquake-resistant technologies include foundation isolation, tie beam and timber bracing, and wooden framing. In these systems, wood is not exclusively used for seismic strengthening, and other factors have been effective in its selection.In Iran, there are also unique systems of the mentioned technologies that are considered successful examples against earthquakes, but today they forgotten. This study can be effective in creating the sensitivity of communities towards the protection of these systems by collecting local knowledge and creating a database of known historical systems of Iran and provide valuable insights about these local innovations in future research. Identifying and classifying these examples helps to understand traditional wooden construction systems and their potential for modern applications and it emphasizes the importance of integrating historical knowledge with modern architectural methods and their stability against earthquakes.
Keywords: Seismic Protection Technologie, Foundation Isolation, Timber Bracing, Wooden Framing, Tie Beam, Historical Building.
Introduction
This research explores the use of wood in historical masonry buildings for seismic resistance. The objectives of this study are to identify various protection technologies used in historical wooden structures and assess their effectiveness in mitigating earthquake damage. The necessity of this research arises from the increasing frequency of seismic events and the potential loss of cultural heritage associated with the destruction of these structures.By examining unique systems developed, this study seeks to uncover forgotten technologies that have proven successful in the past. The study aims to create a comprehensive database of historical systems, fostering greater awareness and appreciation for the role of historical wooden structures in contemporary architecture.This research is not only significant for preserving cultural heritage but also for informing modern architectural practices that prioritize sustainability and resilience.
Materials and Methods: The research employs a descriptive methodology, utilizing a library study reviews literature from the past 25 years on traditional, earthquake-resistant buildings using wood. The statistical population includes historical buildings that incorporate wooden elements in their foundations, walls, and roofs, which are essential for earthquake resistance. This studyIt focuses on analyzing 42 case studies of wooden systems with seismic protection technology in earthquake-prone areas worldwide and ,particularly those found in Iran.
Data: Wood has been one of the earliest and most abundant natural materials used in construction worldwide.Archaeological evidence shows wooden houses dating back to 4200BCE in Iran(zomorshidi,1381) and ancient wooden structural elements in places like Knossos and Herculaneum, including rare multi-story wooden frame buildings(Dutu et.al.,2012).Medieval wooden structures discovered in Pertikara reveal sophisticated geometric designs and represent an important stage in the evolution of timber construction knowledge(Ruggieri et.al.,2013).Timber framing with brick infill first appeared in 8th-century Turkey and remains common in earthquake-prone and culturally significant regions, including parts of Europe(Dutu et.al.,2012).
During earthquakes, buildings experience vertical, horizontal, and torsional forces.Horizontal forces mainly cause shaking and damage, while vertical forces affect heavy structural parts(Carazas,Rivero,2010). Key qualities for earthquake resistance include flexibility, deformability, and strength-allowing buildings to withstand large deformations without collapse(Szakats,2007).
Building geometry is critical for seismic stability; simple, symmetrical plans with minimal projections perform better. Structural elements must be well-connected to act integrally during shaking. Quality construction and the use of lightweight materials like wood and bamboo significantly enhance resilience.
Wood’s high tensile strength along fibers and light weight make it valuable for seismic resistance, especially in elevated parts, connections, and roofs. However, wood alone is vulnerable to seismic loads and is often combined with masonry and used in framed connections and wooden ties, which remain key in strengthening historic buildings against earthquakes(tabeshpor,farhangfar,2005).
Wooden structures are effective in earthquake resistance due to their high tensile strength, light weight, and flexibility. However, wood alone is vulnerable to seismic loads(Olivier Moles,2006). Common seismic solutions include wooden base isolation (which reduces seismic demand by decoupling the structure from ground motion, lowering energy transfer and keeping buildings mostly elastic during quakes), vertical and horizontal wooden ties, and light wooden frames, which improve structural integrity and distribute seismic forces, enhancing the resilience of masonry buildings.
Discussion
The seismic protection technologies can be categorized into four main types:1)foundation isolation,2) wooden framing,3) Tie beam, and 4Timber bracing. wooden frames, both regular and irregular, use various bracing shapes and are constructed with different infill materials such as stone, brick, adobe, plaster, wood, or bamboo, sometimes as single or double layers. Some frames are even without infill(open porches)or feature intricate decorations like stained glass and latticework(Figure11,12)
These systems are found in different structural locations:throughout the entire building(e.g., Quchan shelters,Darvarchin system),foundations(e.g.,Eskati,Shikili),exterior walls(most examples),sometimes interior walls(Pombalinos),around openings(Tak system),and roofs (Romanian,TaleBast).The critical factor is the system’s integration from foundation to roof, ensuring structural unity(Figure13).
Wood connections are mainly done by palate and tongue joints, natural fibers and ropes, or nailing. These systems were not developed solely for seismic resistance but also due to material availability, functional needs, aesthetics, construction speed, lateral force control during construction, compression force management, ventilation, and comfort. Overall, their effectiveness can be grouped into structural, decorative, functional, and other categories) Table 5(.
In Iran, all four historical seismic protection technologies have been used. For example, wooden base isolation in Shikili foundations is a notable historic example recognized globally. Except for pigeon towers and lattice windows(orosi or sash),these systems were directly aimed at earthquake resistance and were primarily built in highly seismic cities like Rudbar,Quchan, and Tabriz.They showed minimal damage compared to adjacent buildings without such technologies.
Today, except for some tie beam and occasionally wooden foundations,other seismic protection technologies like wooden frames and Darvarchin walls are fading in Iranian vernacular architecture(Figure14,15).
Conclusion
Masonry buildings have low earthquake resistance due to their poor tensile strength, limited ductility, weak connections between components, and heavy mass. Earthquake damage to these structures can manifest as bending, twisting, cracking, sagging, and in the worst cases, collapse and destruction. The mentioned structural systems, when incorporating wood within their framework, demonstrate adaptability and flexibility. This integration of wood not only reduces the building’s weight but also enhances its strength, depending on the type of wood used and the connection details.
Historical examples show that these systems have effectively provided seismic resistance over long periods. Key factors influencing the earthquake resilience of wooden systems include the choice of wood species, its age and condition (avoiding decay), the quality of wood connections and integration with infill materials, climate and environmental conditions (such as moisture protection), proper construction methods, and structural dimensions like height and cross-sectional area.
The four technologies discussed have been implemented worldwide in different regions using varied methods but share common fundamental principles. Iran, being an earthquake-prone country, has historically utilized these technologies in its traditional and vernacular architecture, with successful seismic performance. Studying these systems offers valuable insights into local innovations and their potential application in contemporary society.
This is especially important since global studies aimed at reviving these systems for modern architecture have produced positive seismic results. However, in Iran, these wooden technologies remain largely unknown or have not been modernized for current use. Future research could focus on testing these wooden systems in Iran, providing quantitative data to validate their effectiveness. Additionally, it could promote designs based on indigenous wooden systems while adhering to conservation principles and regulations.
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