Analysis of the collapse mechanisms of medieval churches struck by the 2016 Umbrian earthquake

The 2016 Umbrian earthquake caused the collapse of several medieval churches, while it was noted that ordinary buildings only reported moderate or little damage. Researchers and technicians are looking to these religious constructions with the aim of understanding their structural behavior under seismic action. Depending on the direction of the seismic action, the typical collapse mode was the overturning of the side walls or of the church façade. This often produced the collapse of the roof structure. In many situations, the overturning was facilitated by a weak connection between the load-bearing walls. In this article, the collapse modes of three mediaeval churches are investigated. The article goes into some detail about what considerations are relevant when analyzing a historic masonry construction. The churches object of this study are located in Campi, a hamlet of Norcia, Italy. Between 2000 and 2004, a research team from the Technical University of Milan in collaboration with the Italian Ministry of Culture carried out an extensive investigation on the historic buildings of Campi, providing interesting data about the maintenance level and a summary of the structural state of the churches. These data were used in this article for a critical analysis of the causes of collapse, performed in combination with numerical simulations of the global behavior and local instability.     

Discrete Element Analysis of the Minimum Thickness of Oval Masonry Domes

This study focuses on domes the ground plan of which, instead of the more common circular shape, is an oval, and aims at finding the minimally necessary uniform wall thickness for domes of different geometries loaded by their selfweight. The discrete element code 3DEC was applied because of its capability of simulating the collapse mechanisms of masonry structures. Results on the minimal wall thickness, corresponding masonry volume and failure mechanisms for different dome geometries are presented. Three ranges of the friction coefficient were found. For very low frictional resistance collapse happens with pure frictional sliding, for any arbitrarily large wall thickness. In the range of relatively high (i.e., realistic) friction coefficients the structure collapses without any sliding if the wall is not sufficiently thick, and in the observed range of the friction coefficient the necessary wall thickness is nearly insensitive to its value (collapse initiates with hinging cracks only). Between the two domains an intermediate behavior was found: combined cracking and sliding collapse modes occur for insufficient wall thickness, and the minimal thickness strongly depends on the friction coefficient. The critical and transitional friction coefficients separating the failure modes were determined for different eccentricities of the groundplan.     

Quasi-Static Cyclic Tests of Two U-Shaped Reinforced Concrete Walls

U-shaped or channel-shaped walls are frequently used as lateral strength providing members in reinforced concrete (RC) buildings since their form does not only provide strength and stiffness in any horizontal direction but is also well suited to accommodate elevator shafts or staircases. Despite this popularity, experimental results on the seismic behavior of U-shaped walls are scarce. For this reason a research program with the objective to provide additional experimental evidence for such walls under seismic loading was developed. It included quasi-static cyclic testing of two U-shaped walls at the structural engineering laboratories of the ETH Zurich. The walls were built at half-scale and designed for high ductility. The main difference between the two walls was their wall thickness. The project was chiefly focusing on the bending behavior in different directions and therefore the walls were subjected to a bi-directional loading regime. This article discusses the design of the test units, the test setup and the test predictions. Finally the main results are summarized in terms of failure mechanisms and force-displacement hystereses.     

Monitoring façade soiling as a maintenance strategy for the sensitive built heritage

The color patterns generally found on the façades of architecturally sensitive buildings have an adverse impact on their aesthetics, to the detriment of their identity and potential economic value. A quantitative and qualitative study was conducted of the perception of aesthetic decay in the limestone on a heritage building. The study assessed building aesthetics between two façade cleaning operations, conducted in 1984–1986 and 2006–2008. Based on the calculation of the final or total soiling index, by means of in situ lightness measurement and three architectural design variables, the color distribution of the façades was quantified in 2006 and a model was developed to monitor façade soiling over time. The proposed model, a tool for planning preventive façade maintenance on architecturally sensitive buildings, advocates for sustainable cleaning operations. Its premise that periodic cleaning should only be conducted in areas where the limestone is affected by aesthetic decay redounds to minimised intervention and lower building management costs.     

Some considerations for the reburial of painted lime stucco façdesin the Maya region

Abstract

The conservation of Maya stucco façadesin humid tropical conditions poses significant challenges. Professionals in the region consider that reburial is one of the most easily accomplished and cost-effective conservation options; and reburial of modelled and painted lime plaster façades, in conjunction with the construction of exposed replica façadesoverlying the reburied originals, has been or is being considered as a preservation strategy at a number of sites in the region. This is illustrated by two case studies from Belize and one from Guatemala. However, more research is needed to fully understand the benefits and risks of reburial, and to determine the optimal conditions and techniques specifically suitable for wet tropical climates. The range of issues that must be considered for reburial of stucco façadesin this region include their conservation needs in relation to the susceptibility of ancient materials to climatic conditions, management issues such as visitor and interpretation needs and the problem of looting in the region, the feasibility of solutions in relation to available resources, choice of methods and materials used in interventions, and the impact of reburial on the significance of a site, amongst others.     

Rubble Stone Masonry Walls Strengthened by Three-Dimensional Steel Ties and Textile-Reinforced Mortar Render,Under Compression and Shear Loads

This article addresses the results of a structural strengthening solution for rubble stone masonry walls. The strengthening includes inserting three-dimensional steel ties across the thickness of the walls and a 30-mm layer of air-lime and cement mortar render reinforced with glass fiber mesh (textile-reinforced mortar), on both sides of the wall. The strengthening solution was found to be efficient for rehabilitating ancient rubble stone masonry walls due to the “three-dimensional” confinement, provided by the steel wires, by offsetting the low cohesive capacity of the mortar used in the walls and thus improving the mechanical resistance and delaying the collapse mechanisms. This study is part of an experimental research program carried out in Universidade Nova de Lisboa, to evaluate structural strengthening solutions for ancient rubble stone masonry buildings. To this end, three specimens of rubble stone masonry walls without strengthening (unreinforced masonry) and other three, with the mentioned strengthening solution, were subjected to compression and shear load tests. Building materials were also tested in order to characterize physical, chemical and mechanical properties.     

桃渚城城墙病害初步调研与保护对策探讨

临海桃渚城建于明代,是浙江保存最完好的抗倭卫所城址,全国重点文物保护单位。通过对桃渚城的现存状况进行调查分析可知,城墙目前存在局部垮塌、鼓闪、灰浆流失等病害,其本身的构造缺陷加上降雨和植物生长的共同作用是病害的主要成因。这类问题在东南沿海地区的古城墙中具有一定普遍性。针对这些病害以及桃渚城的构造特点,结合国内一些城墙保护的工程实例,提出桃渚城的保护策略:加强墙体的结构稳定性、加固墙芯填土、增设墙顶防水措施、及时疏改威胁本体安全的植物,可为后续以及同类城墙的保护工作提供参考。     

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.     

南京包山式城墙典型病害及整体坍塌预警分析

南京城墙作为现存的世界第一城垣，对其安全性进行科学评估尤为重要。包山式城墙为南京城墙的主要形式之一，由于其与土体相连，受力特点不同于常规的自承重城墙。本研究整理了包山式城墙的6种典型病害，并提出了包山式城墙的数值建模方法，将其简化为城墙-粘结界面-土体的模型。利用ABAQUS软件，结合工程实例模拟土坡强度折减后包山式城墙的鼓胀。研究结果表明：随着土体的强度下降，包山式城墙的位移不断增大形成鼓胀现象，最终发生倾覆坍塌，可通过墙体底部拉应力-顶点位移曲线中的明显拐点确立监测变形预警值；在此基础上，讨论土坡高度对整体坍塌的影响，并给出放坡角度的合理取值；城墙底部的积水浸泡会导致底部强度折减进而发生相对错动，可通过底部墙体达到极限抗拉强度时的最大相对位移确立监测变形预警值。最后，提出了包山式城墙的修缮保护建议。     

‘China-ware in the skies’: overlapping identities in the ornamental use of plates in Uruguay

Abstract

This is the study of a church where tableware manufactured in Great Britain was used to decorate the façade in the early 19th century. An argument is made that this one surviving case points to a larger regional tradition, now lost, whose greatest exponent was Montevideo Cathedral, Uruguay. The hypothesis presented here is that the use of British plates in religious façades shortly before the South American Wars of Independence was part of a search for identity in a region trying to break away from Spain, and in the process of becoming a small republic between the two larger countries of Argentina and Brazil.     

The Dynamic Behavior of the Basilica of San Francesco in Assisi Using Simplified Analytical Models

The Basilica of San Francesco in Assisi endured stronger earthquakes for centuries before 1997 earthquake, which generated the collapse of the two vaults. Experts blame as possible reasons of collapse the damage cumulated from previous earthquakes and/or the retrofitting made to the structure over its lifetime. This article presents the history of the retrofit interventions of the Basilica through the centuries, focusing mainly on the roof, which has been subjected to three major restorations through its life. It is shown using simple analytical models that the cumulative effects of the changes made to the roof of the Basilica affected the structure’s dynamic behavior in a negative manner, increasing the seismic loads on the existing structural members. In particular, the numerical results show that the 1958 roof intervention has stiffened the structure, redistributing the seismic loads on the façade and the transept. This overload might explain the collapse of the two Gothic vaults during 1997 earthquake.     

INVESTIGATING MATERIAL DECAY OF HISTORIC BUILDINGS USING VISUAL ANALYTICS WITH MULTI‐TEMPORAL INFRARED THERMOGRAPHIC DATA

This paper shows how visual analytics methodology can be used to facilitate interpretation of multi‐temporal thermographic imagery for the purpose of restoration of cultural heritage. We explore thermographic data in a visual environment from the unifying spatio‐temporal perspective in an attempt to identify spatial and spatio‐temporal patterns that could provide information about the structure and the level of decay of the material, and the presence of other physical phenomena in the wall. The approach is tested on a thermographic dataset captured on the façade of a Romanesque building from the 13th century—the Cathedral in Matera (Italy).     

单檐歇山式木构古建抵抗极端烈度地震试验调查研究

为更好地保护我国古建筑,基于《单檐歇山式古建筑抗震性能振动台试验》的相关成果,研究了强震作用下我国明清官式木构古建的抗震性能,制作了与该论文相同的试验模型,进行了振动台试验。通过对模型输入烈度逐渐增强的1940年El-centro波,并考虑地震波为水平双向作用,分析了强震作用下不同构造的试验现象,开展了详细的震后调查,获得了不同构造在强震作用下的抗震性能和震害机制。结果表明:强震作用下,我国明清官式木构古建的振动形式表现为柱架、斗拱、梁架及屋顶的近似同步往复摇摆;主要震害包括柱底偏移、榫卯节点开裂、拔榫、斗拱偏移及错位、额枋-垫板分离、墙体倒塌等,但承重木构架受损不严重,结构未产生倒塌。其良好抗震性能的原因与古建筑的构造特征密切相关。     

The Use of a Large-Scale Seismic Vulnerability Assessment Approach for Masonry Façade Walls as an Effective Tool for Evaluating,Managing and Mitigating Seismic Risk in Historical Centers

ABSTRACT

The vulnerability assessment of the building stock in a given territorial area, such as a city or an entire country, is a key prerequisite for evaluating risk, not only because of the potential physical consequences resulting from the occurrence of an event, but also because it is one of the few aspects in which engineering research can intervene. In fact, the rigorous vulnerability assessment of existing buildings followed by the implementation of appropriate retrofitting solutions can help to substantially reduce the levels of physical damage and economic impact of future events. Particularly regarding the seismic vulnerability assessment of historical centers, the amount of knowledge that has been accumulated over the past decades, together with the broad damage data obtained from post-earthquake damage surveys, provides a singular opportunity to develop and calibrate innovative large-scale seismic vulnerability assessment approaches, which can be used to outline and support risk mitigation and management strategies. This article addresses this issue by discussing the use of a large-scale seismic vulnerability assessment methodology for masonry façade walls as a tool for evaluating the potential benefit resulting from the application of different seismic retrofitting strategies, both considering their contribution to reduce post-event urban losses and accessibility.     

A Bronze Age Quarry in Eastern Crete

Abstract

The sandstone quarry at Mochlos is one of four major quarries in eastern Crete that were worked during the New Palace Period of Minoan civilization (ca. 1700–1450 B.C.) to produce large ashlar blocks for nearby Minoan sites. At that time sandstone, or ammoudha, as it is known locally, was especially valued as a building material, partly because of its distinctive color and texture, but mainly because of the ease with which it could be cut, and the stone was used extensively for exterior façades, for walls around interior courts, and for other architectural features of the more important buildings on these sites. This article describes the quarry at Mochlos in some detail, including the quarrying techniques employed, and argues that the destination of the stone from the Mochlos quarry was the Minoan palace at Gournia. The article ends with a comparison of the four ammoudha quarries in eastern Crete.     

OUT-OF-PLANE SEISMIC RESISTANCE OF MASONRY WALLS

Seismic vulnerability of unreinforced masonry buildings is studied by means of simplified out-of-plane collapse mechanisms that take into account connections with transversal walls. According to experimental evidence, the analysis assumes that failure is reached with a rigid body motion of a part of the facade that falls down. Two classes of mechanism are examined: the overturning of the facade due either to a vertical crack at the connection or a diagonal crack on the transversal wall, both defined resorting to a simple model of masonry fabric, viewed as a regular assembly of rigid blocks and elastic plastic joints with friction but no cohesion. The use of simplified mechanisms give rise to an explicit evaluation of the seismic resistance to changes in the geometry and in the masonry fabrics, that could be used by practising engineers. This formulation is developed for both static horizontal actions and ground velocity peak, in the belief that the latter probably gives a better approximation of seismic action, while also providing, by comparison with the results of static forces, an estimate of the behaviour factor for unreinforced masonry. Eventually, the analytical forecasts are compared with numerical results obtained by means of the distinct element method.     

Experimental Evaluation of Seismic Performance of Squat RC Structural Walls with Limited Ductility Reinforcing Details

This article describes an experimental study carried out on of reinforced concrete (RC) walls of less confining reinforcement than that recommended by ACI 318. A total of eight RC walls with boundary elements comprising of five walls with aspect ratio of 1.125 and three walls with aspect ratio of 1.625 were tested by subjecting them to low levels of axial compression loading and simulated seismic loading, to examine the structural performance of the walls with limited transverse reinforcement. Conclusions are reached concerning the failure mode, drift capacity, strength capacity, components of top deformation, and energy dissipation characteristics of walls on the seismic behavior with limited transverse reinforcement. The influences of axial loading, transverse reinforcement in the wall boundary elements, and the presence of construction joints at the wall base on the seismic behavior of walls are also studied in this paper. Lastly, reasonable strut-and-tie models are developed to help in understanding the force transfer mechanism in the walls tested.     

Degradation of mud brick houses in an arid environment: a geoarchaeological model

A common assumption in Near Eastern tell archaeology is that the majority of sediments originate from degraded mud bricks. Little is known about the mechanism of mud brick wall degradation. Here we present a detailed macro- and microscopic ethnoarchaeological study of the degradation of a mud brick house and propose a comprehensive mechanism for tell formation processes in arid environments. The study took place in southern Israel by trenching a ca. 60 year old abandoned mud brick house, followed by extensive sediment sampling. Macroscopic observations showed that mud brick walls degrade by collapse of single bricks and/or collapse of intact wall parts, either inwards or outwards. In addition, infill sediments within the house and outside it, in close proximity to its walls, form alternating sedimentary layers of various colors and textures. The degraded mud brick material lost its distinctive macroscopic structure, which makes it impossible to accurately identify this material by field observations alone. Mineralogical and elemental analyses established the sources of the house infill sediments, namely mud bricks and wind blown sediments. Alternating layers mostly originate from mixing between degraded mud brick material and wind blown sediments. Micromorphological observations revealed microscopic mechanisms of mud brick degradation and include processes of mud slurry gravity flows, sediment coatings and infillings, wind abrasion of walls, small-scale puddling, and bioturbation. This study provides a working scheme for site formation of abandoned mud brick structures in arid environments. It provides a set of criteria by which it is possible to differentiate floors from post-abandonment sedimentary features and thus improves the reliability of activity area research.     

Experimental analysis of rubble stone masonry walls strengthened by transverse confinement under compression and compression-shear loadings

Stone masonry walls of ancient buildings have reasonable resistance to vertical loads but lower resistance to shear forces and reduced tensile strength. However, to achieve such compressive strength the masonry must not disaggregate when subjected to loading. This can be achieved if during the construction of the walls larger stones, usually referred as “through stones”, are used, spanning the thickness of the wall, making it possible to improve the transverse confinement of the masonry. For rehabilitation projects and structural reinforcement of such buildings, the transverse confinement can be achieved by fixing steel elements perpendicular to the wall. This confinement technique is often part of a more comprehensive rehabilitation solution, which includes the application of mortar or concrete reinforced layers applied to the wall surface.

This article presents results of an experimental research on material properties and mechanical characterisation of stone masonry specimens strengthened by two transverse confinement solutions (independent steel reinforcing rods and continuous steel ribbons wrapping the specimen). Specimens were tested under compression and compression and shear loadings.

This experimental work is part of a major research project to study the mechanical behavior of URM and strengthened walls, and the characteristics of the building materials of such specimens.     

3D Digital Survey of Iron Tie-Rods in Masonry Buildings: Cross-Sections Analysis and Error Estimation

Ancient iron tie-rods are handcrafted elements with large geometric irregularities, due to production techniques (they are shaped by hammering and linked by hot-forging) and corrosion processes. In common practice, their cross section (that is one of the main parameter to assess their strength) is manually measured on site with a manual caliber. By analyzing a set of detailed three-dimensional (3D) digital surveys of real ancient tie-rods, this study provide an evaluation of the errors made by in-situ manual geometric measurements. In particular, it shows that, in some cases, manual on-site survey is sufficiently reliable and has errors that fall below 10%. Moreover, it shows that when tie-rods have high corrosion levels in hidden zones (typically those close or within the retaining walls) the on-site survey of visible parts only may produce far greater errors that exceed 100%, leading to a strong overestimation of the cross-section of the tie. The ongoing study is a first step toward the definition of correction coefficients to be applied to the on-site manual measurements of ancient tie-rods, with the final aim to improve the reliability of structural analyses.