The Influence of Dowel-Bearing Strength in Designing Timber Pegged Timber Joints

ABSTRACT

The employment of timber pegs in timber structure joints is a widespread technology in the field of timber frame building in the United States, where the Timber Frame Engineering Council has published a special Standard to supplement the National Design Specification for Wood Construction. The authors have been studying the possibility of supplementing the Eurocode 5 design formulas, thought for timber joints with metal connectors, with specifications needed for a reliable design when employing timber pegs. The field of application envisaged is that of restoring timber structures and results obtained until now are quite encouraging. In this step of the research, more attention has been paid to deformation process: fir and chestnut samples have been tested to determine their dowel-bearing behavior with steel and ash timber peg while double-shear plane joints made of the same wood species, and fastened with steel as well as timber pegs, have been analyzed.     

Potential Use of Foamed Mortar (FM) for Thermal Upgrading of Chinese Traditional Hui-Style Residences

The Hui-style residence is an important architectural heritage of China. The hollow wall structures are widely used to build its exterior wall system. However, the thermal performance of the hollow wall is no longer able to meet the new energy-saving and environmental requirement. This article describes a laboratory study of the development of foamed mortar (FM), with the potential for use in thermal upgrading of the Hui-style hollow wall system without dramatically changing its traditional structure. The key early age, physical, mechanical and thermal properties were systematically measured. Two extended models were respectively developed to calculate compressive strength and thermal conductivity, as a function of porosity. Environment chamber test was also employed to investigate the effectiveness of this novel thermal upgrading approach and the results show that filling the voids with FM can effectively improve the overall thermal resistance of the hollow wall system by 44%, which is almost equal to the overall thermal resistance when using the more expensive commercial inorganic stucco system. In addition, the combination of these two methods yielded an overall thermal resistance of 0.701 m²·K/W, which is even higher than 0.67 m²·K/W for the code required in the hot summer/cold winter climate zone.     

山西省转型期旅游场强时空异质性特征及机制

以山西省转型期旅游发展为例,选取2005、2011和2017年17项指标构建城市旅游发展综合实力评价体系,基于改进场强模型,借助GIS技术和地理探测器模型,分析旅游场强时空异质性特征及演变机制。结果表明：①旅游场强高值区范围扩大、逐步形成叶脉状网络空间形态,突破了早期“人”形格局限制;②各地市旅游场强前期整体上升,后期集中在大西高铁沿线,城市绝对差异增加,高级别场强类型主要以太原市为中心向边缘扩散演替;③旅游场强空间格局演变具有时序性特征,主导因子经历了二元、三元主导和多元共同作用阶段,对于旅游产业后发省份构建区域旅游场强空间格局具有借鉴和指导意义。     

Stone Age fishhooks – how were they dimensioned? Morphology,strength test,and breakage pattern of Neolithic bone fishhooks from Ajvide,Gotland, Sweden

The late Stone Age Pitted Ware site at Ajvide, Gotland, in the Baltic Sea, Sweden, has revealed a large deposit of fishbone and approximately 400 bone fishhooks, complete and incomplete. Cod (Gadus morhua), which is one of the most abundant fish species in the bone assemblage, was probably caught with hook and line fishing. To investigate the fishhooks' field of application, a morphological and morphometric study was performed on 384 available hooks. Two sets of replicas made of four selected original fishhooks were submitted to a strength test. A breakage study of the incomplete hooks in comparison with the strength-tested hooks was carried out in order to distinguish fresh breaks from dry breaks. It seems that a certain morphology for fishhooks was preferred at Ajvide, indicating they were produced by skilled craftsmen for special usage. The strength test showed that the hooks had a weight bearing capacity more than the average size of cod caught at Ajvide. Using results of these tests, we predicted that the mean breaking strength of 46 intact Ajvide hooks was 96.6 ± 26.1 (s.d.) Newtons (equivalent to 9.85 ± 2.7 kg). The design of fishhooks changed somewhat over time, being slightly larger in the oldest layers of the site. The breakage patterns of the hooks show that the bow was the most common area of breakage. The design and weight bearing capacity of the hooks point to a specialized cod fishery from boats in deep water.     

一种新型古丝绸强度测定仪的研制

为了克服目前利用抗拉强度分析方法检测古丝绸老化强度的缺点,通过对古丝绸抗拉强度分析,利用电子天平的称量精度和记录、显示功能,结合控速、控力和固定试样的机械部件,对测定仪的机械、电路、软件部分进行了设计,研制出一种新型的古丝绸强度测定仪。用古丝绸强度测定仪对古丝绸进行了测试,结果显示古丝绸强度测定仪能很好地测定古丝绸的抗拉强度。该仪器为定量测定古代丝织品老化程度提供了一种较为精细的手段。     

EXPERIMENTAL BEHAVIOUR AND NUMERICAL MODELLING OF SMOOTH STEEL BARS UNDER COMPRESSION

Many existing reinforced concrete buildings located in seismic regions are characterised by internal steel reinforcement made of smooth bars and stirrups with inadequate spacing. These bars could be subjected to significant compression and eventually buckle. This paper deals with a comprehensive experimental campaign investigating the compressive behaviour of smooth bars for different values of the ratio L/D, L being the restraints distance and D the bar diameter. The stress-strain relationship is then modelled ranging from an elastic-plastic behaviour identical to that in tension (L/D=5) to the elastic buckling behaviour (L/D>20). The comparison between the experimental results and the outcomes of the model confirms the accuracy of the proposed stress-strain relationship.     

DESIRABLE STRENGTH DISTRIBUTION FOR ASYMMETRIC STRUCTURES WITH STRENGTH-STIFFNESS DEPENDENT ELEMENTS

Recent studies have shown that for many reinforced concrete lateral force-resisting elements (LFRE) stiffness is dependent on strength, and as a result strength assign-ment to these elements would affect both the strength and stiffness distributions in a structure. As a consequence, stiffness distribution cannot be considered known prior to strength assignment. This implies that in assigning strength to LFRE, the designer has the ability not only to prescribe the strength distribution, but also indirectly control the stiffness distribution in the structure. In this paper, a study is made on the seis-mic performance of a number of single-story structures to reconfirm that the “balanced CV-CR location” criterion, previously suggested by the writers, constitutes a desirable strength/stiffness distribution for minimising torsional response of asymmetric reinforced concrete structures.     

高分子彩绘类文物保护涂层材料的性能及应用研究

针对彩绘类陶器保护的特殊要求,筛选性能优良的保护材料。在人工气候箱中对所选择的9种有机高分子文物保护涂层材料进行人工老化试验,分别采用傅立叶红外光谱仪测量试验材料的分子结构,分光光度仪测量颜料的主波长、色纯度和高度的变化,粘接强度仪测量颜料的粘接强度变化。结果表明:PrimalAC33、B72、有机硅的耐老化性能好,颜色变化小,粘接强度高,能很好的起到保护彩绘文物的作用,建议在文物保护领域推广使用。     

Experimental characterization of the constitutive materials composing an old masonry vaulted tunnel of the Paris subway system

A significant proportion of the Paris metro tunnels comprise a masonry vault built out of stone blocks and mortar joints, and sidewalls and slabs made of unreinforced concrete. In order to provide the necessary data for future structural evaluation, an extensive laboratory testing programme has been conducted to characterize the materials of the tunnel separately, i.e., mortar, stone, and concrete. The tests, carried out on specimens taken from cores extracted from a 1930s tunnel, enabled to determine the mechanical properties, including direct tensile, shear strength, and mode I fracture energy, as well as the properties of the stone-mortar interface. Results show that the masonry mortar joints could reach 10 cm in width, and that blocks of stone varied in composition and porosity, thus producing a wide range of mechanical properties. The concrete was composed of large-sized aggregates and showed low stiffness and strength. Based on these experimental results, ratios between mechanical characteristics are hereby proposed. Perspectives on the use of this experimental data in a finite element model are then discussed.     

湘淮集团与19世纪60年代上海的崛起

19世纪60年代,是上海从"江南的上海"向"上海的江南"过渡的关键时期。这一时期,湘淮集团一方面通过解除太平军对上海围困,解决在此过程中产生的诸多社会问题,有效控制了上海的军政大权;另一方面通过采取系列的手段和措施,以处理日显复杂的上海中外关系,为上海的发展创造了一个相对安定和平的环境,从而成为了19世纪60年代上海崛起的一个重要因素。