Modal parameter identification and damping ratio estimation from the full-scale measurements of a typical Tibetan wooden structure

Tibetan heritage buildings have a high historical and cultural value. They have endured adverse environmental loadings over hundreds of years without significant damage. However, there are few reports on their structural characteristics under normal environmental loadings and their behavior under dynamic loadings. In this research, a typical Tibetan wooden wall-frame building is selected to study its dynamic characteristics. Field measurements of the structure were conducted under environmental excitation to collect acceleration responses. The stochastic subspace identification （SSI） method was adopted to calculate the structural modal parameters and obtain the out-of-plane vibration characteristics of the slab and frames. The results indicated that the wall-frame structure had a lower out-of-plane stiffness and greater in-plane stiffness due to the presence of stone walls. Due to poor identified damping ratio estimates from the SSI method, a method based on the variance upper bound was proposed to complement the existing variance lower bound method for estimating the modal damping ratio to address the significant damping variability obtained from different points and measurements. The feasibility of the proposed method was illustrated with the measured data from the floor slab of the structure. The variance lower and upper bound methods both provided consistent results compared to those from the traditional SSI method.

A feasibility study of using two-component polyurethane adhesive in constructing wooden structures

This investigation was conducted to determine the feasibility of using a two-component polyurethane （PUR） adhesive, with special waterproof properties, in constructing wooden structures. We designed and conducted tests to compare the shear strength and adhesion performance of PUR with polyvinyl acetate （PVAc） adhesive on block-shear specimens constructed of oriental beech （Fagus orientalis L.）, fir （Abies alba Mill.）, poplar （Populus deltoides Bartr.）, white oak （Quercus alba L.）, sycamore （Platanus orientalis L.） and white walnut （Juglans cinerea L.）. The values of the percentage of wood failure were also determined in specimens constructed with each adhesive. The highest shear strength values of both adhesives were obtained in specimens constructed of beech, while the lowest shear strength values were obtained in fir and poplar specimens. Average shear strength of the PUR adhesive was 16.5% higher than that of the PVAc adhesive. Specimens constructed of fir, poplar and sycamore were characterised by the highest percentages of wood failure, whereas the lowest average percentages of wood failure were obtained in beech and oak specimens. With the exception of oak specimens, there was no statistically significant difference between percentage of wood failure among the PUR and PVAc adhesives. Generally, the PUR adhesive showed an acceptable adhesion performance on wood materials used in our study.

Wooden Structures within the Context of Parametric Design: Pavilions and Seatings in Urban Landscape

Today,on the one hand,while the traditional design process continues,on the other hand,digital design systems along with advances in computer technologies continue to present designers with new and effective ideas.Parametric design is preferred by designers for its relationality,contributing toward versatility,ensuring flexibility,simplifying diversification,and for presenting programmatic solutions.As is seen in a number of areas,we have also begun to encounter the use of parametric designs produced with parametric design systems and wooden materials in urban landscaping.The purpose of this study is to examine the upper cover application and seating elements generated by taking advantage of parametric designs from wooden construction materials in urban landscaping areas,and examine the impact of wooden material characteristics while generating behavior and parametric structures of technologies.After researching parametric design and wooden material concepts,an attempt was made to reach conclusions through analyses conducted by examining parametric wooden designed pavilion and seating element specimens applied in various regions of the world.

Joinery and Structure:Cultural and Technical Comparison between Traditional Wooden Framing Systems in East Asia and Western Europe

Traditional wooden joinery is the craft of connecting wood pieces for buildings or producing utensils by utilizing only the geometry of the components and material properties of the wood,without other materials such as glue or metal connectors.In its thousands of years of tradition,this construction technique has achieved high accomplishment in both East Asian and European architectural civilizations.Although sharing the same basic principles,joinery techniques vary between regions and cultures,rooted in the geographical environment,available wood species and their material properties,characteristics of craftsmanship,tools,and structural systems.Wood framing systems from China,Japan,and Western Europe are selected for comparison to assess the relationship between wood joinery and other aspects of building technology.The main conclusions include:in East Asia,the building tradition pays great attention to the design and execution of joinery(sunmao榫卯),making it responsible for multiple functions including architectural mechanics and the stability of the entire frame,which leads to a broader role meant by the term“joint”itself,while in Europe joinery is treated as the“node”or literally“joint”of the structure.Although in both East Asia and Europe wooden joinery serves as an aesthetic factor of the structure,its expression in East Asia is subtle,veiled,and restrained,while in Europe it is explicit and direct.The most important lesson we learn from the study of traditional joinery technology is that it should be seen in the context of the building process as a whole,taking into account geographical environment,material resources,craftsmanship,tools,construction methods,structural form,and the structural system.

Lateral shear performance of sheathed post-and-beam wooden structures with small panels

Sheathed post-and-beam wooden structures are distinct from light-wood structures.They allow for using sheathing panels that are smaller(0.91 m×1.82 m)than standard-sized panels(1.22 m×2.44 m or 2.44 m×2.44 m).Evidence indicates that nail spacing and panel thickness determine the lateral capacity of the wood frame shear walls.To verify the lateral shear performance of wood frame shear walls with smaller panels,we subjected 13 shear walls,measuring 0.91 m in width and 2.925 m in height,to a low-cycle cyclic loading test with three kinds of nail spacing and three panel thicknesses.A nonlinear numerical simulation analysis of the wall was conducted using ABAQUS finite element(FE)software,where a custom nonlinear spring element was used to simulate the sheathing-frame connection.The results indicate that the hysteretic performance of the walls was mainly determined by the hysteretic performance of the sheathing-frame connection.When same nail specifications were adopted,the stiffness and bearing capacity of the walls were inversely related to the nail spacing and directly related to the panel thickness.The shear wall remained in the elastic stage when the drift was 1/250 rad and ductility coefficients were all greater than 2.5,which satisfied the deformation requirements of residential structures.Based on the test and FE analysis results,the shear strength of the post-and-beam wooden structures with sheathed walls was determined.

Oxidative mechanism of chicken wooden breast myofibrillar protein

To explore the oxidation mechanism of wooden breast myofibrillar protein(WBMP),oxidative breast MP(OBMP)was obtained from different doses(3,10,and 20 mmol/L)of H2O2 oxidized normal breast MP(NBMP).The results showed that the Zeta-potential,particle size,solubility,sulfhydryl,and carbonyl contents of OBMP-3(3 mmol/L,low-dose free radicals)and WBMP were similar.Fluorescence spectrum analysis showed that the oxidation of low-dose free radicals led to a significant increase in the surface hydrophobicity(from 214.03±10.03 to 393.50±10.33)and tryptophan fluorescence intensity(from 185.71 to 568.32).In addition,theα-helix content of WBMP decreased significantly from(37.46±1.15)%(NBMP)to(34.70±2.04)%,whileβ-sheet and random coil contents increased significantly(P<0.05)from(14.37±0.69)%and(22.24±0.78)%(NBMP)to(17.70±0.87)%and(25.20±1.47)%(WBMP).In summary,low-dose free radical oxidation attacks protein groups,inducing secondary and tertiary structural changes,leading to the formation of WBMP.This work will provide a theoretical basis at the molecular level for exploring the mechanism of functional degradation of WBMP.

Transformation of Traditional Wooden Houses in Rural Areas of Southwest China

By analyzing the status quo of traditional wooden houses in southwest China,it was proposed that although traditional wooden houses have many deficiencies in overall layout,type of flat,structure design,thermal protection and insulation,they are popular in southwest China due to particular resources and environment of the local areas,and advantages of wooden houses.It was stressed that the antiseismic structure of traditional wooden houses should be borrowed and modern materials applied to make residential buildings in rural areas more beautiful,comfortable,stable,energy-saving and environment-friendly.Problems of traditional wooden houses in planning,type of flat,structure design,thermal protection and insulation were analyzed,corresponding improvement measures were given,and advantages of improved wooden houses were concluded as "simple and quick construction;concise and beautiful style,favorable flat type;low-carbon and environment-friendly;high antiseismic capacity;low requirements on building materials,reusable materials".

Construction Techniques of Wooden Dwelling Column Frame in Tibetan Regions of Yunnan Province, China

Column frame of folk dwellings with slope roof in Tibetan regions of Yunnan Province was studied. Through field investigation and surveying, column frame timber, main components and construction techniques were introduced. The research showed that column frame of slope-roof dwelling in Tibetan regions of Yunnan is a regional construction technique using timber as the major materials, tenon-and-mortise work as the major connection, characterized by excellent structural expandability, and shock resistance, but it has no quantitative technical support. Scientific and systemic study is needed to improve safeness and livability of local dwellings.

The Challenges of Designing a Wooden Beam of Composed Section

This work describes details about the challenges and solutions encountered in the timber structure beam. The choice for wood is due to the fact that it is a better material suited for environments with high salinity and, in this context, to reduce maintenance costs. The entire roof was supported only by four columns, which forced the side and frontal beams to exceed spans over 18 meters without intermediate supports. This was the most important challenge of the project： to find a section to the beam which can attend the ultimate limit state and serviceability in wood to the dimensions in project. The answer was clear： It would need to have composed section. A computational model was constructed using the finite element method in order to obtain the efforts on the structural elements. It is important to emphasize that the design of a wood structure requires not only knowledge, but creativity as well, to overcome the challenges posed by the distinctive needs to the detailing of this material. In addition to that, it requires special attention during the construction execution, because of the difficulty that the carpenters have to read the specific plans.

Detection and Evaluation of a Migrated Timber Structure House

This article takes the inspection and appraisal of a certain migratory wooden structure as the backdrop, presents the inspection process of the wooden structure. Upon on-site examination, it was discovered that the connection (or node) construction mode of the building was correct. Only local surface flaws were present, and the operation was normal. The stress wave velocity of the randomly inspected wooden columns with surface cracking was close to the critical velocity, suggesting that no obvious cavities or decay defects existed within the measured wooden components. Based on the inspection outcomes, finite element computations were carried out for the wooden structure, arriving at the conclusion that the maximum stress value of the wooden members was smaller than the designed value of wood strength, and the vertical bearing capacity conformed to the requirements of the specifications. And rationally offered relevant treatment suggestions, providing a reference for the inspection and identification of such projects.

古建筑木结构无损检测内容与研究进展

中国拥有大量的木结构古建筑。合理有效地检测评估木结构的存在状况,是古建筑保护和修缮工作的重要需求。古建筑木结构无损检测是以无损检测和评估古建筑木结构安全性,以现场应用和实际需求为导向的木材材性检测评估技术,检测内容主要包括缺陷无损检测和木材物理力学性能无损检测两个方面。木结构、木构件隐藏缺陷的检测以及评估是古建筑木结构无损检测工作的重点和难点。本文首先介绍古建筑木结构的组成,总结其无损检测内容和目前常见无损检测方法;然后归纳总结古建筑木构件隐藏缺陷无损检测、古建筑木构件分等、腐朽对古建筑木材力学性能影响等应用和研究进展;最后归纳说明古建筑木材力学性能无损检测和自然老化对古建筑木材性质影响的研究状况。以期对从事木结构文物保护技术应用和科研工作的相关人员,有所启发和帮助。

考虑非结构构件的木结构古建筑抗震性能研究综述

木结构古建筑是我国文物建筑的主体,它以木材为主要承重构件,具有深厚的历史文化价值。本文根据已有研究,从结构试验、数值模拟、抗震性能评估方法 3个方面,总结了含有隔墙、隔扇、雀替等非结构构件的古木建筑抗震性能研究现状。研究表明,非结构构件可以限制榫卯节点拔榫,改善节点受力,不同程度提高结构的强度、刚度和耗能能力,降低了结构在地震作用下坍塌的概率。最后结合我国木结构古建筑的研究现状以及与其他国家的研究差异,给出了未来木结构古建筑抗震性能的可能研究方向。

模块建筑生态化木结构及轻量化铝结构研究进展

基于木结构模块重量较轻、成本低、节能与低碳等优点及铝结构模块重量轻、耐腐蚀、易折叠等优点,通过文献分析与工程案例,对木结构模块及铝结构模块的研究和应用进展进行梳理和总结,并提出木结构模块及铝结构模块未来发展建议。结果表明木结构模块建筑可应用于农村建筑,铝结构模块建筑适宜向沿海地区发展,二者均具有一定的发展潜力,但仍需对其结构、性能等进行进一步研究。

结构健康监测系统在木结构古建筑中的应用

文物木结构古建筑是一个国家文化的重要组成部分,代表着民族文化的自信与传承。然而由于长时间受到环境和人为侵蚀,木结构古建筑易遭到损坏。为更好地保存好木结构古建筑以及其代表的文化内涵,对其结构安全监测提出了迫切的需求,近年来对木结构古建筑的安全监测方法也得到了快速的发展。分别介绍了虚拟重建、红外热成像、地面激光雷达、超声波监测、光纤传感等技术的原理及在木结构古建筑监测中的应用,并总结了其各自的优势与劣势。针对木结构古建筑采光不足问题,总结了光导系统,尤其是光纤光导照明系统对自然光的引入,该类照明系统具有清洁、安全的特点,避免了烛火、电类照明系统为木结构古建筑带来的火灾风险。

大跨度木结构蒙古包的设计与工程实践

在我国“双碳”目标的实现和新时代中国民族建筑复兴的背景下,木结构建筑市场再次兴起。在原民族建筑文化内涵的基础上对结构进行创新,以满足现代市场的需求已成为新的研究方向。本文针对希拉穆仁草原景区设计了一座大跨度蒙古包,在不改变建筑材料的基础上,采用木网壳结构体系对传统建筑结构进行创新与优化,其最大跨度为23.5 m,最大高度为11.5 m,且整体结构稳定。在此基础上,利用有限元软件进行建模,对可能出现的各种工况进行静力计算和屈曲分析,验证了该结构的可靠性。本研究对我国大跨度木结构的发展和传统木结构建筑的创新具有重要的借鉴意义。

木材老化对古建筑木梁抗弯性能的影响分析

为研究木材老化对古建筑木梁抗弯性能的影响,分析了木材的老化机理,采用等效截面法并结合国内木梁老化深度经验公式,提出了老化木梁抗弯承载力退化模型,并对某古建筑的木梁进行了承载力退化评估。对未老化与老化木梁进行了单调加载数值模拟,并通过试验验证了模型的合理性;在此基础上,进一步分析了老化均匀度与老化深度对木梁抗弯性能的影响。结合《木结构设计标准》(GB 50005—2017)中受弯构件的承载力计算公式,提出了考虑老化影响的木梁抗弯承载力折减系数计算公式。结果表明:老化对木梁抗弯承载力的影响与老化均匀度呈线性相关,与老化深度呈一元二次多项式关系。老化深度越深且老化均匀度越大,木梁承载力越低。

CFRP布加固广府古建木结构残损箍头榫节点抗震性能研究

采用不同方案的碳纤维(CFRP,Carbon Fiber Reinforced Plastics)布,对6个经过抗震性能试验的残损箍头榫节点试件进行加固,并进行抗震性能试验.结果表明:有3个加固后节点试件的峰值承载能力超越了加固前试件的峰值承载能力,加固后节点的峰值承载力主要与梁榫原始损伤程度及加固量直接相关.加固后节点的初始刚度明显大于加固前的节点,而加固后试件的极限转角普遍小于加固前,但大部分试件极限位移转角均能达到1/21以上,说明此方法加固的节点具有良好的抗震变形能力.加固梁上侧与下侧的CFRP布,对受拉损伤的梁起了重要的补强作用.梁侧面CFRP布在节点区转角较大时退出工作,而L型CFRP布也随着节点转角的增大而逐步退出工作.

基于木质异型材的两自由度工作台研究

设计了一种两自由度可旋转工作台,用于辅助普通三轴数控机床对木质异型材进行复杂曲面加工。该工作台可通过两台电机控制工作台同时或分别进行X轴和Y轴方向上的旋转,左侧电机驱动蜗轮蜗杆传动实现工作台X轴向旋转,右侧电机驱动齿轮副传动实现工作台Y轴向旋转,通过互相配合实现多平面、多角度加工。通过对工作台关键支撑结构进行静力学分析与模态分析,确定工作台整体支撑结构合理性,为两自由度工作台结构设计提供参考。

多种荷载作用下的木塔结构优化与装配式设计研究

文章以第十五届全国大学生结构设计竞赛为题,以应县佛宫寺释迦塔为例,从基础构件设计、构件实验与优化、软件模拟与分析、装配式设计等方面入手,提出了木塔结构优化与装配式设计的相关建议,以期为同类木结构的设计优化与装配式应用提供参考。

华北地区古建筑木构件开裂类型与特征分析

木构件开裂是木结构古建筑中主要残损类型之一,影响古建筑安全性能。为研究古建筑木构件的开裂类型与特征,通过现场勘查对我国华北地区8处木结构古建筑的关键木构件开裂情况进行检测,获得古建筑木构件开裂残损的类型与形态、数量、尺寸等特征,并与自然干燥的现代材开裂情况进行比较,观察木材裂缝长时间的变化情况。研究结果表明:古建筑木构件开裂率约85%,裂缝按其形态与开裂原因可分为干缩裂缝与受力裂缝,干缩裂缝为主要类型;多数干缩裂缝开裂深度未至髓心,比例为78.16%;木构件干缩开裂特征受其形态影响,自然干燥现代材与古建筑木材开裂特征相同,达到平衡含水率后开裂特征基本不发生变化。