Protecting the archaeological heritage from structural risks: some significant cases

In the present paper the “Three R” Strategy for archaeological consolidation is described, referring to some well-known historical examples and then to some significant cases on UNESCO sites performed by the author. The problem of conserving the constructive info of ancient structures along centuries is summarized, together with a set of recurrent structural problems. Three case studies of sites are explained, two located in Arabic Peninsula (Dhofar district, Sumhuram– Al Balid), one in Jordan (Petra district – Shawbak). The replacement of walls (with or without mortar joints) is performed, together with the strategy to assess a respectful, recognizable and reversible consolidation technique

Horizontally restrained rocking blocks: evaluation of the role of boundary conditions with static and dynamic approaches

The paper deals with the behavior of restrained rocking blocks under seismic actions. Structural or non-structural masonry or r.c. elements, such as building façades or pre-cast panels subjected to out-of-plane modes, may be assimilated to rocking blocks restrained by horizontal springs. Horizontal restraints can represent flexible floors or steel anchorages or any anti-seismic device designed to impede overturning probability. Their effect could improve, in most cases, the dynamic response of blocks in terms of reduction of rotation amplitude. Nevertheless, this effectiveness could vanish or, surprisingly, affect the response in negative way, resulting in overturning when low values of stiffness or one-sided motion in particular conditions are assumed. Two cases of horizontal restraints are analyzed: (1) concentrated restraint as single spring and (2) smeared restraint as spring bed with constant or linearly variable stiffness. The single stabilizing or destabilizing terms of the formulation are here analyzed and commented, providing practical evaluations to obtain enhancement of response in static and dynamic perspective. A numerical example of a masonry façade with non-linear boundary conditions has been provided highlighting how the choice of stiffness values affects the oscillatory motion and rebound effects. Finally, unit stiffness for masonry/concrete walls and retrofitting techniques, such as steel tie-rods, has been calculated

Low cost seismic constructions: design and dissemination in developing socio-economic areas

The paper describes a procedure for establishing and disseminating a sustainable technique for the construction of low-cost seismic structures, by using reinforced bamboo elements. The procedure is illustrated via the example of a small public building, suitable for use as a primary school or health centre. Furthermore, on the basis of sociolinguistic investigations, we propose a multi-pronged strategy for disseminating specific technical knowledge, involving different means of communication, and including various types of linguistic acts, that are appropriate to the various socio-economic segments identified in the local population

Rocking analysis of masonry walls interacting with roofs

This paper investigates the out-of-plane behavior of masonry walls interacting with roofs. Often, collapses of masonry portions supporting roofs may occur due to the roof thrust, which generates a destabilizing effect over motion. Nevertheless, the roof weight can produce a positive stabilizing effect for rotation amplitudes smaller than the critical value. The dynamics of a rocking masonry block interacting with roofs is discussed, by properly modifying the Housner equation of motion of the free-standing single degree-of-freedom block. The dependence of the restoring moment on the rotation angle is investigated and the minimum horizontal stiffness is calculated so that the same ultimate displacement as the system without roof thrust is obtained. Two case studies are presented as applicative examples of the proposed method: an unreinforced masonry structure tested on shaking table and a spandrel beam subjected to roof thrust that survived the Emilia Romagna earthquake. Inertia moments and radius vectors of different failure mechanisms are also provided to solve the equation of motion for different block shapes. Finally, a parametric analysis of a trapezoidal rocking block has been carried out by changing its geometrical shape. This analysis shows that the influence of the shape is relevant for the calculation of the failure load, although is not possible to determine an a priori most critical shape

Bamboo trusses with low cost and high ductility joints

Innovative solutions of joints for bamboo trusses are presented. Experimental tests show the performances and the high level of ductility of the proposed technique, joined with simplicity in the concept of the joints, low level of technology and low cost of all used materials. It can permit a proper dissemination and a sustainable maintenance in developing countries

Damage and restoration of historical urban walls: literature review and case of studies

Within this work, the causes of collapses and damages occurred in masonry artefacts have been evaluated to properly identify suitable monitoring and restoration methods. In this regard, a comprehensive literature review has been performed. Based on the results, the moisture has found to be a critical parameter, which affects the structural health of masonry artefacts. Diverse non-destructive methods were employed to measure the moisture and monitor the materials involved: the Infrared Thermography, the Electrical Resistivity Tomography and the Ground Penetrating Radar, the Laser Scanning and Digital Terrestrial Photogrammetry, the Global Navigation Satellite Systems, the Unilateral Nuclear Magnetic Resonance, the Laser-Induced Fluorescence technique, the Acoustic Imaging and the Acoustic Tomography, the Geographic Information System and on-site survey process as well as computer modeling of the structure with specific FEM software. Finally, the implementation of tie-beams, Fiber Reinforced Polymers layers, ventilation, draining systems, and high-quality materials are proposed as solutions for controlling the moisture effect and retrofitting

The “Triple R” approach on the restoration of archaeological dry stone city walls: procedures and application to a UNESCO World Heritage site in Southern Arabia

The ‘Triple R’ approach on the restoration of dry stone walls, using recognizable, reversible and respectful constructive techniques is here illustrated. A set of restoration procedures are explained and applied to a UNESCO World Heritage site in Al-Baleed (Salalah, Sultanate of Oman) in the ‘Land of Frankincense’. The procedures were adapted in an innovative way to take into account the climate features of the Indian Ocean area (specifically, the effects of the monsoon season). All the restoration procedures aimed at conserving the site’s original architectural features by using only suitable stones and materials found on-site. Specific procedures have been adopted to consolidate walls, gates, foundations and sloping surfaces. Simple on-site mechanical tests and evaluation methods have been developed for a quick assessment of the safety level of the restored walls to ease future archaeological excavations. The application is related to a waterfront side of the ancient city built around the ninth century and added to over the next five centuries. These restoration procedures allowed for further archaeological excavations with new findings is here described

Large-scale survey method for the integrity of historical urban walls: application to the case of Volterra (Italy)

Abstract Several relevant collapses of historical urban walls happened in Tuscany in the last ten years, due to rainfalls. The wide extension of the walls, with difficulties of proper monitoring, joined with lack of maintenance, contributed to the failures. This recalled the attention on their vulnerability, in view to ensure a proper safety level and appropriate cultural heritage protection. In this paper, a method of extensive and quick structural survey to identify the mechanical characteristics of an historical urban wall path is proposed. It is based on geographic method of management of the territory (GIS database, satellite data). The data are obtained throughout a discretization of the walls in a wide set of vertical sections. A reduced subset of sections is directly surveyed, while the others are indirectly identified via numerical procedure, with the help of GIS data. A specific form to take note of the most relevant features is edited. The method is tested on the entire perimeter of the Middle Age walls of Volterra (2,6 km), affected by two relevant collapses in 2014. The procedure of survey is conceived to perform structural analysis to evaluate the vulnerability to landslides and earthquake risks, in view to determine restoration strategies and consolidation or monitoring programs

Prolegomena to the Preservation of the Site of al-Wu’ayra (Petra, Jordan) and to the Restoration of the North-East Tower

The authors describe the importance of the site of al-Wu’ayra, at the east border of the ancient town of Petra (Jordan) where the Archaeological Mission “Medieval Petra” (University of Florence) is working since 1986. From the archaeological point of view, the physical conformation of the site is the main condition for the formation, during nearly two thousand years, of a highly significant archaeological deposit with a continuous chronological extension from Nabataean time up to Late Islamic and a high scientific potential. On the other hand, the site itself preserves the only still standing 12th century tower of the whole area of Petra, thus being a very significant element of the historical landscape and the only monumental evidence of a short but important season of the long history of the town. During the last three decades, the addition of human disturbance to the spontaneous and natural decay of buildings makes urgent a restoration and a protection programme for the whole site.

Structural Solutions for Low-Cost Bamboo Frames: Experimental Tests and Constructive Assessments

Experimental tests and constructive assessments are presented for a simple bamboo framed structure with innovative low-cost and low technology joints, specifically conceived for small buildings in developing countries. Two full scale one-storey bamboo frames have been designed by using the simplest joints solution among three different tested typologies. The entire building process is based on low-technology and natural materials: Bamboo canes, wooden cylinders, plywood plates and canapé rods. The first full scale specimen (Unit A) is a one-storey single deck truss structure subjected to monotonic collapse test; the second full scale specimen (Unit B) is a one-storey double deck truss structure used to evaluate the construction time throughout assembling tests. The first full scale specimen showed ductility in collapse and ease in strengthening; the second one showed remarkable ease and speed in assembling structural elements. Finally several constructive solutions are suggested for the design of simple one-storey buildings; they are addressed to four purposes (housing, school, chapel, health center) by the composition of the proposed full scale bamboo frames. Ease of use and maintenance with a low level of technology contribute to application in developing countries although not exclusively