The research presented in this doctoral thesis focuses on damage assessment in slender structures and on the methodology of reinforcement by means of composite materials. In particular, the dynamic behaviour of masonry belfries and industrial chimneys, as well as concrete buildings constructed in the coastal area of the Spanish east coast in the mid-20th century, has been analysed. These analyses have been carried out based on the study of several specific structures. In relation to the former, research has been carried out on the bell tower of Fiesole Cathedral, Italy. The main objective of the research is to evaluate the problems of dynamic interaction between the inertial forces associated with the swing of the bells and the main structure of the bell tower. In relation to the second structural typology, a study has been carried out to evaluate the origin of the current state of cracking of the industrial masonry chimneys, as well as to evaluate the damage associated with the problems of collapse that they present at the top of the chimneys. This study has focused on two industrial chimneys located in the municipality of Manises, Valencia, and Agost, Alicante. Finally, in relation to the third structural typology analysed, a third study was carried out on the Torre Adoc 10, located in the coastal area of the city of Alicante. The main objective of this research is to analyze the combined effect of corrosion and seismic action after forty years of corrosion processes on the structure, evaluating the distribution of the damage pattern by analyzing the capacity and demand curves. Finally, an analysis related to the seismic vulnerability of industrial masonry chimneys has been carried out, focusing on the chimney of Agost, Alicante. On the basis of this analysis the pattern of damage to the structure has been defined, and a system of reinforcement using composite materials capable of preventing the structural collapse of the stack has been proposed and sized. The content of this doctoral thesis has been structured in three phases according to the development of the work carried out. In this sense, the first phase is called "Phase of structural characterization", the second phase, "Phase of definition of the numerical model" and finally the third phase, "Phase of definition and analysis of variables". During the development of the first phase, the geometric characterisation of the structures is carried out, as well as the characterisation of the materials by means of laboratory tests or on the basis of the available literature. The results obtained from the process of characterisation of the materials allow the mechanical characteristics of the mortars and brick units to be known, but in addition, analysis at a microstructural level of the samples allows the presence of contaminating agents and expansive salts to be determined, which allows the problem of the damage analysed to be put into context later with the numerical models. Finally, the dynamic characterisation of the structures is carried out with the aim of finding out the modal parameters that allow the subsequent calibration of the numerical models. In the second phase, the numerical models are generated defining the behaviour of the materials in the linear and non-linear range. In addition, the models are calibrated from the experimental data obtained in the previous phase, or by means of experimental data from the consulted bibliography. During this phase the results of the calibration have been analysed using genetic algorithms of the Fiesole bell tower, and the influence of the lateral confinement of the tower on the modal response of the structure has been determined. Finally, during the third phase, the variables associated with the damage assessment of the modelled structures are analysed. In this sense, the first variable analyzed focuses on the effect of the swing of the bells. This study analyses the effect of the velocity, the angle of oscillation and the position of the bells along the height of the tower, in order to determine the range of operation of the bells to avoid damage to the structure. In addition, the influence of the harmonics of the inertial force of the bells on the determination of the real response of the structure is evaluated and compared with the simplified solution proposed by DIN 4178. The second variable focuses on the study of the origin of the current state of damage present in masonry industrial chimneys. This study is analysed from two points of view. On the one hand, the effect of the thermal action during the normal operation of the chimney is evaluated, and on the other hand, the effect of the increase in volume of the metallic elements due to corrosion, arranged on the inside of the chimney, is assessed. Finally, the third variable is related to the analysis of the seismic vulnerability of the Agost masonry industrial chimney, and the reinforced concrete building, Torre Adoc 10. This study analyses the seismic demand through the use of elastic response spectra, and compares the capacity of the structure through a sectional analysis, and through a non-linear pushover analysis. From the results, the damage pattern in both structures is analyzed, and the influence of corrosion in the case of the reinforced concrete building is evaluated. Finally, the results of the analysis of the seismic vulnerability in the industrial chimney allow us to propose a reinforcement system using composite materials capable of preventing the collapse of the structure.