Experimental Studies on Buried Barrel Vaults

The paper concerns an interaction problem between soil and masonry vaults in historic buildings. A particular emphasis was placed on the influence of finishing method of vaults extrados and fill material properties on the behavior of masonry vaults. The results of experimental studies on barrel vaults with and without backfill are presented. During the experiments three finishing methods of vaults extrados and three fill materials were investigated. The results of the experiments show that the presence of backfill and type of vaults extrados finish affect the behavior and load-carrying capacity of tested elements. Moreover, tests were performed on vaults without fill for comparative purposes. The comparison of experimental results obtained for specimens with and without fill shows that the presence of backfill in vault haunches modifies the failure mechanism and increases load capacity of the analysed models. The presented results confirm the importance of backfill as a structural element of vaulted structures.     

The Groin Vaults of St. John Hospital in Jerusalem: An Experimental Analysis on a Scale Model

The St. John Hospital is part of a larger complex of buildings known as the Hospitallers Quarter, located south of the Holy Sepulchre in Jerusalem. At present, the hospital looks like an irregular volume both in height and in plan; it is covered by ten groin vaults resting on very stocky pillars. Each vault is formed by intersecting double curvature surfaces. In order to verify the effectiveness of continuous carbon fiber reinforced polymer sheets reinforcement, bonded at the extrados of vaults, laboratory tests were carried out on a 1:5 scale model, built with materials and construction techniques similar to those of the real building. Experimental tests were performed on the unstrengthened and strengthened vault. The experimental results shown that the strengthening system is able to increase the collapse load of the vault, without substantial variation of the initial stiffness.     

Simulation of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (I): Displacement-based Approach Using Simple Failure Mechanisms

ABSTRACT

A displacement-based (DB) assessment procedure was used to predict the results of shake table testing of two unreinforced masonry buildings, one made of clay bricks and the other of stone masonry. The simple buildings were subject to an acceleration history, with the maximum acceleration incrementally increased until a collapse mechanism formed. Using the test data, the accuracy and limitations of a displacement-based procedure to predict the maximum building displacements are studied. In particular, the displacement demand was calculated using the displacement response spectrum corresponding to the actual shake table earthquake motion that caused wall collapse (or near collapse). This approach was found to give displacements in reasonable agreement with the wall’s displacement capacity.     

Historic Barrel Vaults Undergoing Differential Settlements

ABSTRACT

A principal reason of damage in historic masonry vaults consists in relative displacements of the vaults’ abutments. Excluding the case of seismic-induced damage, cracks are often produced by differential settlements generated by the lateral wall instability or soil degradation (e.g., due to stress concentrations, non-uniform soil stratigraphy, flooding phenomena etc.). When dealing with historic vaults, the effects of long-term deformation processes cannot often be linked directly to causes, which may also be unknown. In this article, the effects of differential settlements on historic masonry barrel vaults are investigated. An efficient 3D contact-based model was developed to reproduce experiments on a scaled pointed barrel vault (representative of a typology of late-medieval barrel vaults in Scotland) under non-uniform differential settlement. First, the numerical model is used to simulate the experimental campaign, achieving good agreement in terms of crack pattern (longitudinal shear) and transverse-longitudinal deformation profiles. Then, further analyses are carried out to gain insight on the effects of several plausible uniform and non-uniform settlement patterns on representative historic barrel vaults. Various settlement configurations were analysed and complex failure patterns observed. This study could help analysts in understanding the nature of on-going deformation process in historic masonry vaults and engineers in the design of strengthening strategies.     

Simulation of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (V): Discrete Element Approach

ABSTRACT

The analysis of the shaking table test of a 3-wall stone masonry structure performed with a discrete element model is presented. The numerical model, created with the code 3DEC, employed a rigid block representation and a Mohr-Coulomb joint model. Joint stiffness calibration to match the experimental natural frequencies is discussed, as well as the boundary conditions to simulate the shake table. Comparisons are made with the measured displacements at key locations, and the modes of deformation and fracture of the walls. The DEM model was able to reproduce important features of the shaking table tests. The experimental deformation and near collapse patterns were clearly identifiable in the numerical simulations, which produced displacements within the observed orders of magnitude, for the various levels of excitation.     

A Hybrid Masonry and Steel Mirror-Type Vault with Lunettes: Survey and Structural Analysis

ABSTRACT

The structural analysis of a mirror-type vault, consisting of a single- or double-curvature perimeter and a nearly flat part, is carried out. The vault is similar to a number of hybrid iron (or steel) and masonry vaults built between the late 19th century and the early 20th century to span large halls. The numerical analyses were preceded by an accurate geometrical survey and mechanical tests aimed at evaluating the properties of the materials. Thermography allowed the complex brick pattern of the vault to be detected. The influence of rib-walls (frenelli) and the material anisotropy on the stress and deformation of the vault is discussed. Eventually, attention is focused on one of the segmental vaults in the central part of the structure: it is found that the stress can be safely estimated by assuming its boundary to be fixed.     

Minimum Thrust of Rounded Cross Vaults

This study analyzes the static behavior of the rounded cross vaults based on the limit analysis approach developed for masonry structures and adopts a rigid no-tension constitutive model with no sliding. The kinematic theorem of the limit analysis with a compatible tridimensional mechanism is applied on these structures with the aim of evaluating the minimum thrust. In this way it was possible to build some abaci in which the ratio between the minimum thrust and the weight is plotted versus the geometrical characteristics of the vaults. Finally, the proposed abaci are used to calculate the thrust of the main vault of the Diocletian Baths in Rome.     

Effect of the joint type on the bearing capacity of a multi–drum column under static load

The results of an experimental study on the effect of the joints between the blocks on the ultimate bearing capacity of a multi-drum column loaded to centric vertical force and horizontal force in the middle of its height are shown. The column is approximately 2.5 m high, with one hinge at the top and another hinge at the bottom. Four types of joints between the blocks were considered: a dry joint (column C-DJ) and joints with stone powder (column C-SPJ), lead (column C-PBJ), and epoxy (column C-EPJ). The applied vertical and horizontal forces, horizontal displacement, vertical strains, and horizontal circumferential strains in the middle of the column height, as well as shortening of the column, were measured. Under axial compression, ratios between the ultimate load bearing capacities of tested columns were C-EPJ: C-DJ: C-SPJ: C-PBJ = 1: 0.68: 0.59: 0.51. The bearing capacity of the tested columns with regard to the horizontal force depended on the level of the applied centric compression force. Columns with soft joints (C-PBJ, C-SPJ) had the largest shortening and the largest horizontal displacements for the equal forces.     

Dynamic One-Sided Out-Of-Plane Behavior of Unreinforced-Masonry Wall Restrained by Elasto-Plastic Tie-Rods

Past earthquakes have shown the high vulnerability of existing masonry buildings, particularly to out-of-plane local collapse mechanisms. Such mechanisms can be prevented if façades are restrained by tie rods improving the connections to perpendiculars walls. Whereas in the past only static models have been proposed, herein the nonlinear equation of motion of a monolithic wall restrained by a tie rod is presented. The façade, resting on a foundation and adjacent to transverse walls, rotates only around one base pivot and has one degree of freedom. Its thickness is explicitly accounted for and the tie rod is modeled as a linear elastic—perfectly plastic spring, with limited displacement capacity. The model is used to investigate the response to variations of wall geometry (height/thickness ratio, thickness), tie rod features (vertical position, length, prestress level), and material characteristics (elastic modulus, ultimate elongation, yield strength) typical of historical iron. The most relevant parameter is the steel strength, whereas other characteristics play minor roles allowing to recommend reduced values for pre-tensioning forces. The force-based procedure customary in Italy for tie design is reasonably safe and involves protection also against collapse, although probably not enough as desirable.     

Numerical Study on the Peak Strength of Masonry Spandrels with Arches

This article presents a numerical study on the force-deformation behavior of masonry spandrels supported on arches which are analyzed using simplified micro models. The model is validated against results from quasi-static cyclic tests on masonry spandrels. A large range of spandrels with different arch geometries, material properties, and axial load ratios are studied. The numerical results are compared to peak strength values predicted with an existing mechanical model. Finally, estimates for the initial stiffness and the spandrel rotation associated with the onset of strength degradation are derived.     

Modeling the Seismic Response of Modern URM Buildings Retrofitted by Adding RC Walls

Modern unreinforced masonry buildings with reinforced concrete slabs are often retrofitted by inserting reinforced concrete walls. The main advantages of this technique are the increase in strength and displacement capacity with respect to masonry structures. This article presents two modeling approaches for evaluating such structures: a shell-element model and a macro-element one. The objective is to formulate practical recommendations for setting up a macro-element model using as input the geometry of the structure and results from standard material tests. Structural configurations of masonry buildings, in which the insertion of reinforced concrete walls is an efficient retrofit technique, are also investigated.     

Estimation of Vertical Floor Displacement Using a Wavelet De-Noising Method

The horizontal response of structural and nonstructural systems during seismic events has been studied for a long time. However, the effect of the vertical response of floors on building contents and nonstructural systems has still remained a topic of concern. A wavelet de-noising method along with the experimental data obtained from a full-scale test at E-Defense is used to estimate the vertical floor displacement of a five-story steel moment frame building in base-isolated and fixed-base configurations. Vertical displacements of slabs and beams are calculated from the experimental data and formulated based on their out-of-plane dominant frequencies. A curve fitting approach is then carried out to estimate vertical displacements at floors and stories. In these tests, partition wall damage such as buckling of studs occurred at slab displacements of about 1 in.     

Dynamic Analysis and Seismic Response of Planar Circular Arches with Variable Cross-Section

The aim of this paper is to investigate the dynamic response of planar circular arches with variable cross-section subjected to seismic ground motions. Arches have a wide range of application (e.g. bridges, roofs) thanks to their capacity to span large areas by resolving vertical actions into compressive stresses and confining tensile stresses. The full understanding of their dynamic response is a challenging technical and computational problem, especially when seismic loading is considered. For example, the assumption of axial inextensibility simplifies the differential equations but overestimates the vibration frequencies, especially those of shallow arches since axial forces are of paramount importance (as opposed to beams). In lieu of the above, our formulation incorporates the effect of axial extension, and the arches are modeled using a new generic curved beam model that includes both axial (tangential) and transverse (normal) to the arch centerline deformations, and is able to account for variable mass and stiffness properties, as well as elastic support or restraint. The resulting dynamic governing equations of the circular arch are formulated in terms of the displacements, and solved using an efficient integral equation method. Three circular arches with variable rectangular cross-section are analyzed in order to investigate their dynamic properties and seismic performance. Using both time history and modal analysis useful conclusions are drawn with regard to the contribution of each mode on the calculation of different response quantities.     

Earthquake Protection of Colonial Bell Towers in Colima,Mexico with Externally Prestressed FRPs

A methodology for the seismic vulnerability reduction of old masonry towers with external prestressing is presented. It is applied at the Colonial bell-towers of the Cathedral of Colima, Mexico, characterized for being a high seismic area (M>7.5). The 3D FE models are calibrated with experimental data and assessed through nonlinear static approaches including the seismic demand and an accurate validated masonry model. Based on an extensive parametric study on different configurations of old masonry towers, it is selected an optimal prestressing force and device. The Colonial towers are retrofitted with four prestressing devices of FRPs to convert them into a high energy-dissipative reinforced masonry. The external vertical prestressing is included at key points identified in the seismic vulnerability assessment. This technique is in compliance with the demand for architectural conservation and may be located without drilling and unbounded in order to be fully removable. The seismic performance is enhanced by increasing force, displacement, and internal confinement. It is observed an upgrading of 35% and 20% of displacement capacity. With these results it is corroborated that external vertical prestressing allows a substantial increment of ductility for seismic energy dissipation purposes.     

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.     

Source Modeling of the Kozani and Arnea 1995 Events with Strong Motion Estimates for the City of Thessaloniki

In Turkey, with the occurrence of almost every strong and even moderate earthquake, damage to masonry minarets is observed. In the present work, efficiency of vertical post-tensioning application to reinforce masonry minarets against earthquakes has been investigated. Considering a representative minaret and its post-tensioned counterpart, and performing spectral and time-history analyses, the effects of post-tensioning on the axial stresses, top lateral displacements and overturning safety have been determined. Obtained results have shown that vertical post-tensioning application is a very efficient method to reduce axial tensile stresses and lateral displacements, and to assure the overturning safety of masonry minarets against earthquakes.     

Seismic Assessment of a Historical Masonry Building in Switzerland: The “Ancien Hôpital De Sion”

This article presents the results of the evaluation of the seismic safety of the Ancien Hôpital de Sion, an important Swiss architectural heritage building, situated in the Canton of Valais, the region with the highest seismic hazard in Switzerland. Three-dimensional Applied Element (AEM) modeling of the whole structure has been performed and validated. The adopted modeling strategy, together with nonlinear dynamic analysis, was able to represent the actual behavior and failure mechanisms typical of complex masonry structures, in addition to a good computational efficiency compared to other available numerical approaches. The local collapse mechanisms have been also studied through a kinematic limit analysis based on rigid block rotation. Both linear and nonlinear approaches have been followed together with the capacity spectrum method. The results provided by the different methodologies have been compared with the aim to provide possible insights concerning a general procedure for the assessment of the safety of such type of structures.     

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.     

Discrete Element Modeling of Stone Masonry Walls With Varying Core Conditions: Prince of Wales Fort Case Study

The Prince of Wales Fort was constructed in the 18th century as a Vauban style stone masonry fortification where the Churchill River flows into Hudson’s Bay, across the river from Churchill, Manitoba, Canada. Since completion the fort has been exposed to harsh weather conditions, which have led to significant deterioration and deformations in the walls, with some cases of localized collapse. Recently, an increase in the rate of degradation has made preventative conservation an issue of interest. For this conservation to be possible, an understanding of the cause of failure of the walls is first required. Discrete element modeling (DEM) using the non-smooth contact dynamics (NSCD) method utilized in the Program LMGC90 has been used as a first step in understanding the failure mechanism of the wall system. The results of the modeling show that the rubble core of the walls can transition from stability to instability as the cohesion between the stones is altered. Grouting the core will alter the bond between stones, increasing the stability of the core, and is thus one possible conservation method.     

Integrating radar and laser-based remote sensing techniques for monitoring structural deformation of archaeological monuments

Ground-Based Synthetic Aperture Radar Interferometry (GBInSAR) and Terrestrial Laser Scanning (TLS) were purposely integrated to obtain 3D interferometric radar point clouds to facilitate the spatial interpretation of displacements affecting archaeological monuments. The paper describes the procedure to implement this integrated approach in the real-world situations of surveillance of archaeological and built heritage. Targeted tests were carried out on the case study of the Domus Tiberiana sited along the northern side of the Palatino Hill in the central archaeological area of Rome, Italy, and displacements of the monument were monitored over almost one year of acquisition. The GBInSAR – TLS integration provided updated information about the condition of the archaeological structures in relation to their history of instability mechanisms, and did not highlighted a general worsening for the stability of the entire monument. Point-wise and prompt detection of displacement anomalies and/or sudden changes in displacement trends proved the suitability of the method to support early warning procedures, also to evaluate effects on the masonry due to human activities.