Experimental Characterization of Ancient Metal Tie-Rods in Historic Masonry Buildings

Metal tie-rods play a decisive role in the control of horizontal thrusts in historic masonry buildings. The main goal of the present study is to investigate the relationship between metallurgical and mechanical properties of original tie-rods in order to contribute to a wider study on ancient building stability and their restoration protocols. This article presents the results of an experimental test campaign carried out on 14 historic tie-rods (dating back from 16^th–19^th century) recovered from restoration works or building demolitions. Stress-strain mechanical tests showed that the elastic modulus of the material is comparable to that of modern structural steel, while the strength and the elongation capability are significantly lower, with a large scatter. Further analyses based on metallography allowed us to assess that this mechanical behavior depends on the heterogeneous nature of the material, which can eventually be compared to a composite with vitreous elongated particles in a ferritic or ferrito-pearlitic matrix. The origin of such metallurgical condition is related to the iron making based on direct smelting from ores.     

Assessment of out-of-plane behavior of rammed earth walls by pull-down tests

This article reports pull-down tests performed on rammed earth construction in Bhutan. The pull–down specimens involved an old rammed earth building component as well as a newly prepared rammed earth wall. Both the wall specimens were tested in out-of-plane direction. Theoretical rigid body formulation and finite element (FE) models were developed to predict the response of the rammed earth structures under out-of-plane loading. The validated FE model was further extended to parametric study of material and physical characteristics of rammed earth construction and their effect on critical response quantities. The change in elastic modulus showed effect in the pre-cracking phase of the wall. Density of rammed earth on the other hand affected the post-peak response of the rammed earth wall. Furthermore, an increase in the physical characteristics, namely, the thickness of wall and the vertical superimposed load on top of the wall, enhanced the rocking resistance capacity of the out-of-plane loaded rammed earth walls.     

城市化水平与旅游发展之关系初探——基于我国改革开放三十年的时间序列动态计量分析

为了探求城市化水平与旅游发展之间的真实关系,本文以中国作为研究对象,将国际旅游收入和城市化率作为旅游发展水平和城市化水平的解释性指标,从时间序列角度出发,尝试构建两者间的关系模型。通过单位根检验,找到最佳的时间滞后期对数据进行平稳性的差分处理。得出结论为,中国城市化水平与旅游发展水平在滞后二期的情况下最为理想。在此基础上,为构建模型的合理性,进行格兰杰因果检验,但结果显示,两者不存在显著的互为因果的关系,即从长期来看,无稳定联系。最后文章对结果进行讨论并分析其产生的原因。     

Baseline Models for Two‐Mode Social Network Data

Baseline models have been used in the analysis of social networks as a way to understand how empirical networks differ from “random” ones. For the purposes of social network analysis, a “random” network is one chosen—at random—from a population of possible graphs derived from a given generating function. Although these principled hypothesis tests have a long history, many of their properties and extensions to multiple data structures—here, specifically two‐mode data—have been overlooked. This article focused on applications of different baseline models to two data sets: donations and voting of the 111th U.S. Congress, and organizations involved in forums on watershed policy in San Francisco, USA. Tests using each data set, but with different baseline reference distributions, will illustrate the range of possible questions baseline models can address and the differences between them. The ability to apply different models and generate a constellation of results provides a deeper understanding of the structure of the system.     

Microstructural Characterization and Mechanical Properties of Iron Reinforcements in Buildings from the Medieval and Modern Periods in France

This article presents an overview of the metallographic structures observed on the iron reinforcements of more than 20 buildings from the medieval and modern period in France, which are representative of the evolution of ironmaking techniques at that time (330 samples). Metallographic examinations show a great diversity of structures, even in the same sample: pure ferritic iron to low pearlitic steel, presence of phosphorus in solid solution (locally up to 0.5%wt), numerous slag inclusions of various sizes, porosities.

Tensile tests were performed on a representative set of samples from 4 buildings (46 samples). The results are in accordance with the metallographic observations: mechanical behaviors are very heterogeneous, even in samples taken on the same artefact. Failure happened at values as low as the yield stress up to 25% of the plastic strain. These reinforcements probably worked in the elastic domain at low stress (<150 Mpa). These mechanical properties are significantly beyond those of modern carbon steels and question the exact role of iron in the stability of monuments.     

Experimental and Analytical Investigation on the Corner Failure in Masonry Buildings: Interaction between Rocking-Sliding and Horizontal Flexure

ABSTRACT

The failure mechanism of corners in masonry buildings has frequently been observed in seismic scenarios, but only a few works and no experimental investigations devoted to it are available in the literature. In this aritcle, the experimental behavior of a simple masonry corner is first analyzed, by simulating the seismic horizontal actions through a progressive tilting of the supporting base. Then, the conditions of the onset of two possible failure modes are analytically formulated: they are the rocking-sliding and the horizontal flexure mechanism. A three-dimensional macro-block model with frictional joints is used to analyze these mechanisms, while the crack patterns and the load factors are derived through the kinematic approach of the limit analysis. The evaluation of the in-plane frictional resistances involved by the rocking-sliding mechanism is performed by applying a reliable criterion previously proposed, while for the torsion strength involved in the horizontal flexure mechanism, simplified yield conditions are adopted and a possible criterion is also introduced to take into account the actual reduction of the contact surfaces. Last, the experimental findings are compared and critically interpreted in light of the analytical results and the influence of the main parameters on the prevailing mechanism is highlighted.     

Improving the learning processes of Physical Geography through the use of landscape photographs in class

The use of alternative teaching methods to lectures is one of the keys to develop a more participatory and effective education. In the teaching of Geography, greater interaction of students with elements of the landscape through the active use of photography could be one of the ways to achieve this efficiency. This article describes an experiment conducted in 2016 with students of the subject Physical Geography of the Iberian Peninsula. Two different teaching methodologies were applied to two groups of students. The first one was based on dividing the time of each class between participatory comments of landscape photographs and imparting theoretical knowledge through lectures. The second methodology consisted only of lectures, following a more traditional approach. Additionally, some students from the first group actively participated by uploading and tagging their own field pictures to a photographic repository of the University of Seville. The effectiveness of the different activities in each group was assessed through four tests, performed monthly. The results indicate that the use of landscape photographs as a participative teaching resource allows a more efficient learning of theoretical concepts. Therefore, the proposed methodology should be considered by those interested in improving the quality and effectiveness of their teaching of Geography.