Dr. Eng. Ahmed Elyamani

Historical structures are vital to the realization of how the technical, artistic, and scientific skills of the human kind have developed over time. These structures are one of the motors of the tourism industry, and therefore, the studies related to their conservation do not only have social benefits but as well economical ones. It is unfortunately that many countries rich with valuable architectural heritage are characterized by high seismic activity, Italy and Turkey are obvious examples. Due to earthquakes, many invaluable historical structures have been lost forever. Consequently, there is an increasing need for more research on the topic of seismic assessment and protection of this class of buildings. This work contributes to the methodological approaches adopted for the seismic assessment of historical structures. In many cases, due to the lack of knowledge about the assessed historical structure, it is essential to combine many investigation activities in such approaches. The aim is to minimize any possibly required seismic strengthening interventions (minimum intervention concept) by increasing the level of knowledge about the structure. In the current research, the employed experimental investigation activities are the dynamic identification tests and the dynamic monitoring. Most approaches for dynamic monitoring are based on the use of a threshold limit which is used to trigger the system when the parameters measured surpass the limit. Here, an alternative is considered that consists of a continuous monitoring system based on the permanent measurement of the ambient vibration. A thermography monitoring is used as a complementary system for the measurement of temperature. The integration between the dynamic investigation and the numerical modeling is essential and it includes two main features. On one hand, tentative structural analyses are carried out to identify important aspects of the dynamic tests and monitoring strategies such as critical points of the structure where to place the sensors. On the other hand, the results of the dynamic investigation are used to perform model updating until obtaining a satisfactory structural model adequately matching the measured dynamic properties of the structure. Once the structural model is validated, it is used to carry out the seismic assessment of the structure. This assessment is performed using different methods, to cross check the results, including the pushover analysis, the kinematic limit analysis and the nonlinear dynamic analysis. It is then possible with these assessments to identify the seismic behavior of the structure. Using the N2 method, the evaluation of the structural performance and its safety are carried out. Hence, the needs for any possible seismic strengthening are revealed, keeping in mind, the respect to the "minimum intervention" concept. As an application, the cathedral of Mallorca (Spain) is taken as a case study. This structure is one of the largest cathedrals built during the Middle Age. For each of the previously mentioned research steps, the followed criteria and the experience gained are transferred into recommended methodological approaches to be applied to other historical structures. Finally, the integration of these partial steps into one integrated methodology is discussed.

Barcelona Cathedral is one of the most important monuments not only in Spain but also all over the world. The construction of the Gothic cathedral started in 1298 under King Jaume II and in 1460 the main building was completed. The two architects Josep Oriol Mestres and August Font i Carreras completed the construction of the gothic façade in 1889 and the central spire in 1913, following the same design previously proposed by the French architect Charles Galters in 1408. The central spire reaches a height of 90 m over ground level which makes it very vulnerable when subjected to lateral loads like wind and earthquakes. Being finished at the beginning of the 20th century (when the concept of reinforced concrete was being widely spread) gave the builders the chance to centrally reinforce all masonry beams of the spire with steel ties and nowadays these steel ties are facing very severe problems due to corrosion. A complete project for restoration of the spire is being executed nowadays in which a complete dismantling and reconstruction will be carried out. The steel ties will be replaced with titanium ones in order to eliminate the corrosion problem. In order to understand wind and seismic performance of the spire and the role and strength contributions of the steel ties, the different applied loads on the spire which are self weight, wind loads and earthquake loads have been estimated ,then a numerical model of the spire has been created and analyzed using the finite element program DIANA. First a linear elastic analysis under the effect of spire self weight then a combination of spire self weight and wind loads and finally a combination of spire self weight and earthquake loads. The high tensile stresses in masonry beams under the effect of the combination of spire self weight and wind loads and the combination of spire self weight and earthquake loads meant that linear elastic analysis wasn't enough to describe the structure behavior and a nonlinear analysis was essential. A nonlinear analysis under the effect of spire self weight (using three different constitutive models to describe masonry nonlinear behavior) was investigated and it revealed an elevated safety margin as the spire can carry more than ten times its self weight. Then to investigate the seismic performance of the spire a nonlinear static pushover analysis (using two different constitutive models) has been carried out.As a conclusion of this study the steel ties are highly needed to carry the tensile stresses resulted from seismic actions and the spire would be able to resist a maximum base shear of 420 KN (16% of the spire self weight).

This research aims at throwing the light on one of the few survived examples of Ancient Egyptian vaulted structures; those are the storerooms of the temples of the Ramesseum and Sety I built in the 13th century BC. In the first case, only some of the adobe vaults and walls are still standing; whereas in the second case all the vaults collapsed and only the walls exist. Due to lack of maintenance and also scientific research on this topic, the survival remains may be lost forever. The research started with tracking the chronological development, the architecture and the construction of the adobe barrel vault in Ancient Egypt. The two case studies of the research were visually inspected and the existing damage symptoms and causes were reported and investigated. A structural analysis were carried out to understand the structural behavior and the causes of damage. Finally, a number of interventions were proposed that may help the existing ruins to survive.

The spire of Barcelona cathedral suffered from severe problems due to the corrosion of the steel ties used in reinforcing its stone masonry beams. Wide visible cracks were noticed in the stone beams and large parts were detached. Therefore, the full spire was dismantled and reconstructed using titanium ties to eliminate the corrosion problem. A finite element model of the spire was created and analyzed using DIANA software to support this decision. This analysis helped in understanding the role and strength contributions of these ties in resisting the applied loads on the spire, specifically, the lateral loads of earthquakes and wind. A nonlinear static (pushover) analysis was carried out to assess the spire capacity under the lateral loads. A number of constitutive models for modeling the masonry behavior were tried. Also, a number of seismic actions patterns were considered. As a main conclusion of this study, the ties were highly needed to carry the tensile stresses caused by earthquakes and wind loads. Therefore, in the reconstruction of the spire, such ties must be kept in the masonry beams.

Historic Cairo has been a UNESCO World Heritage Site since 1979. It has more than 600 historic structures, which require extensive studies to sustain their cultural, religious, and economic values. The main aim of this paper is to undertake dynamic investigation tests for the dome of Fatima Khatun, a historic mausoleum in Historic Cairo dating back to the 13th century and consisting of mainly bricks and stones. The challenge was that the structure was difficult to access, and only a small portion of the top was accessible for the attachment of accelerometers. Current dynamic identification procedures typically adopt methods in which the sensors are arranged at optimal locations and permit direct assessment of the natural frequencies, mode shapes, and damping ratios of a structure. Approaches that allow for the evaluation of dynamic response for structures with limited accessibility are lacking. To this end, in addition to in situ dynamic investigation tests, a numerical model was created based on available architectural, structural, and material documentation to obtain detailed insight into the dominant modes of vibration. The free vibration analysis of the numerical model identified the dynamic properties of the structure using reasonable assumptions on boundary conditions. System identification, which was carried out using in situ dynamic investigation tests and input from modelling, captured three experimental natural frequencies of the structure with their mode shapes and damping ratios. The approach proposed in this study informs and directs structural restoration for the mausoleum and can be used for other heritage structures located in congested historic sites.

The presented research aimed at studying the dynamic behavior of Mallorca cathedral (Mallorca Island, Spain) under ambient sources of vibration and seismic events. The cathedral is one of the greatest built masonry structures worldwide. It is characterized for its audacious dimensions and slender structural members. Because of it, the study of its dynamic behavior is a clear concern. The cathedral dynamic properties were firstly identified using ambient vibration testing. Afterwards, a dynamic monitoring system was implemented to continuously measure, record, and wirelessly transfer the acceleration records without having to set up an activating threshold. This monitoring type was implemented because of the low seismic intensity of Mallorca Island with a basic ground acceleration of only 0.04 g according to the Spanish seismic standard. The continuous monitoring allowed for capturing some seismic events and some drops in the natural frequencies were noticed because of a breathing crack effect. Using both ambient vibration testing and continuous monitoring system, global modes could be more accurately identified than more local ones. The identification of the global modes was more attainable than in the case of more local ones. The temperature was a more influential environmental parameter than humidity and wind for all of the identified modes except for one more directly depended on wind.

This paper presents an experimental investigation into the structural and material response of ambient-dry and wet clay-brick/lime-mortar masonry elements. In addition to cyclic tests on four large-scale masonry walls subjected to lateral in-plane displacement and co-existing compressive gravity load, the study also includes complementary tests on square masonry panels under diagonal compression and cylindrical masonry cores in compression. After describing the specimen details, wetting method and testing arrangements, the main results and observations are provided and discussed. The results obtained from full-field digital image correlation measurements enable a detailed assessment of the material shear-compression strength envelope, and permit a direct comparison with the strength characteristics of structural walls. The full load-deformation behaviour of the large-scale walls is also evaluated, including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a notable effect on the main material properties, including the shear and compression strengths, brick–mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses, and can lead to a loss of more than a third of the stiffness and strength. For the large scale wall specimens subjected to lateral loading and co-existing compression, the wet-to-dry reduction was found to be up to 20% and 11% in terms of stiffness and lateral strength, respectively, whilst the ductility ratio diminished by up to 12%. Overall, provided that the key moisture-dependent material properties are appropriately evaluated, it is shown that analytical assessment methods can be reliably adapted for predicting the response, in terms of the lateral stiffness, strength and overall load-deformation, for both dry and wet masonry walls.

The paper presents an integrated approach aimed at assessing the seismic safety of Mallorca cathedral. This cathedral is an extraordinary historical construction dating back to the middle ages. The experimental modal parameters of the cathedral were identified using Ambient Vibration Testing (AVT). The cathedral numerical model was updated using the identified modal parameters. This updated model was then used to study the seismic response of the cathedral using non-linear static (pushover) analysis. A sensitively analysis was carried out to reveal the dependency of the seismic capacity on the input materials properties. To assess the seismic performance and the safety of the cathedral, the N2 method was employed. It was found that the cathedral is safe when subjected to the earthquakes expected in Mallorca Island.

This work intends to provide seismic vulnerability analysis for a building stock in Al Khalifa District, Fatimid Cairo while focusing on the historic buildings in the area. The work represents part of an interdisciplinary study targeting the management and conservation of a UNESCO World Heritage Site. The project inspects several aspects including behavior of masonry walls, structural health monitoring of selected structures, conservation studies, in addition to influence of rising ground water. In the current study, seismicity of Egypt generally and Cairo specifically is reviewed. Afterwards, large-scale seismic vulnerability is adopted to calculate the vulnerability index for buildings within the study area. Data are collected through extensive on-site surveys for more than one hundred buildings. Observed typologies are listed alongside possible mechanisms of failure. Egypt has moderate seismic hazard; however, many buildings are prone to damage due to inadequate seismic design. This leads to retrofitting requirements to reduce seismic vulnerability and adhere to imposed seismic requirements in design codes. The study is intended to understand seismic risk of buildings within study area as part of a comprehensive study. Developed vulnerability map show that many buildings are prone to damage during seismic events.

This paper studies the response of unreinforced masonry (URM) members made of hydraulic lime mortar and fired clay bricks, commonly found in heritage structures, strengthened with textile reinforced mortar (TRM) overlays. The investigation includes URM and TRM-strengthened diagonal compression tests on square panels, and relatively large-scale wall specimens subjected to combined gravity and lateral cyclic loads. Complementary compression, tension, and interface material tests are also carried out. The diagonal panel tests show that the TRM effectiveness depends in a non-proportional manner on the overlays, render thickness, and substrate strength. The enhancement in stiffness, strength, and ultimate shear strain, using one to four mesh layers on each side, is shown to vary in the range of 49–132%, 102–536%, and 300–556% respectively. It is shown that strut crushing typically governs the response of such low-strength URM masonry elements confined by TRM overlays. The cyclic tests on the comparatively larger walls show that the TRM is effective, shifting the response from URM diagonal tension to rocking, and enhancing the stiffness, strength, and ultimate drift capacity by more than 160%, 30%, and 130%, respectively. It is shown that analytical assessment methods for predicting the response of TRM-strengthened and URM members in terms of stiffness, strength and load-deformation can be reliably adapted. The cumulative contribution of the URM and TRM components, in conjunction with a suitable fibre textile strain, is also found to offer an improved prediction of the shear strength compared to codified procedures. The findings enable the evaluation and improvement of analytical models for determining the main inelastic response parameters of TRM-strengthened masonry and provide information for validating future detailed nonlinear numerical simulations.

The paper presents the current state of an on-going research aimed at characterizing the seismic response of Mallorca cathedral. Mallorca cathedral is an audacious Gothic structure built in the island of Mallorca during 14th-16th centuries, characterized for its large dimensions and slender structural members. So far, experimental and numerical modal analysis, in addition to tentative model updating and seismic analysis, have been performed. The dynamic identification tests have been carried out by ambient vibration testing, while the frequency domain decomposition (FDD) technique has been used to obtain the modal parameters. A 3D Finite Element (FE) model has been used to determine the vibration modes. The model has been updated by modifying some structural parameters to improve the matching between experimental and numerical modal parameters. Once updated, the model has been utilized to study the seismic response of the cathedral using non-linear static pushover analysis. Conclusions on the possible collapse mechanisms and the seismic performance of the structure are presented.

The paper presents the application of continuous dynamic monitoring and thermographic monitoring to the study of Mallorca Cathedral, one of the largest medieval structures built in Europe. The dynamic monitoring has been carried out by means of a network of three strong motion tri-axial accelerometers installed in December 2010. This network has allowed the capture of seven seismic events characterized by different epicenter locations and frequency contents. The post-processing of the information recorded during these events has provided significant insight on the cathedral dynamic response. The paper also presents the post processing of raw data of nine months of continuous dynamic monitoring, allowing the characterization of the effect of temperature changes on the natural frequencies of different mode shapes. A complementary study undertaken by thermographic monitoring, in which a part of the cathedral has been monitored for at least two weeks in summer and also in winter using an IR camera, is also presented. The relation between the stone masonry temperature of different structural elements (columns, vaults, arches, walls) and natural frequencies has been investigated. This study is part of a more detailed research, still in progress, aimed at investigating the seismic behavior and vulnerability of Mallorca Cathedral.