Faculty of Civil Engineering

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    Static analysis of concrete dams by modeling of the structural joints
    (Ss Cyril and Methodius University, Civil Engineering Faculty – Skopje, 2015-07-24)
    Stevcho Mitovski
    The system da with reservoir lines up in structures with highest potential hazard for the environment. The prediction of the dam’s behavior during construction, first filling and service period is of primary importance in design stage of such complex structures and assessment of their stability. The stability analysis includes understanding of stress – deformation state in the dam body, as well and the interaction of the dam and the foundation. In the doctoral dissertation is presented advanced approach on numerical analysis of the stress – deformation state of concrete arch dam, based on the finite element method. The research within the dissertation are divided in three parts: (1) conveying of experimental laboratorial testing for determination of the strength parameters at contact on materials with different deformable properties (concrete – rock foundation and concrete - grouting mass); (2) numerical analysis of concrete arch dam and (3) comparation of the output results from the numerical analysis with monitoring data of the dam. The first part of the dissertation comprises series of experimental laboratorial testing of the contact concrete – grouting mass, carried out by Hoek’s apparatus, for de¬fining of the strength parameters of the contact presented by dependences tangential stress – displacement (σ-τ) and normal stress – tangential stress (σ–τ). Beside the carried out experimental testing, in the dissertation are also used results from already conducted terrain testing, by using Hook’s apparatus and by method of block – stamp (pressure application) , that determine the behavior of the contact concrete – rock foundation. On base of the obtained results from the conveyed testing, the input parameters for the interface elements, applied for simulation of the interaction of contact surfaces at materials with different deformable parameters within the numerical model, are adopted. The second part of the dissertation includes execution of spatial (three-dimensional) numerical analysis of concrete arch dam. For such purpose are prepared two numerical models: continuous model M1 (in which are modeled the dam and the rock foundation) and discontinuous model M2 (beside the dam and the rock foundation, within the model are included and the interaction zones concrete – rock foundation and concrete – grouting mass, by means of interface elements). The finite element method has been applied for performing of the numerical analysis, by software support of the program SOFiSTiK, which enables modeling of the structure and the foundation, simulation of the initial state, stage construction, reservoir filling and also simulation of the behavior of the contact of materials with different properties. For the materials in composition of the rock foundation is applied linear constitutive law, while the constitutive law for the concrete is adopted by Eurocode 2. Within the performed numerical experiment, the period after dam construction and reservoir first filling has been analyzed apropos following loading states are considered: (a) state after dam construction, (b) state upon primary grouting (only in case of numerical model M2), (c) state at beginning of reservoir filling and (d) state at full reservoir. By the numerical analysis is determined the distribution of the displacements and the stresses for the various loading conditions of the dam. In the third part of the dissertation the output results of the numerical analysis are compared with measured data from dam monitoring. The calculated and measured values show agreement, by what is obtained full picture for the dam behavior for the state after construction and at reservoir first filling. Such comparation also gives insight in the accuracy and precision of the monitoring instruments (the process of calibration of the model as well for the instruments is continuous process). The obtained data and acknowledgments from the dam monitoring during service period, will be used to update the numerical analysis that will provide model with high reliability, in order to follow the long-term behavior of the dam.
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    Experimental and Analytical Research of Strengthened Masonry
    (Faculty of Civil Engineering-skopje, 2012-06)
    Sergey Churilov
    The main structural elements in masonry buildings are the masonry walls. They are responsible for the load transfer and the global stability of the building when subjected to vertical and horizontal forces. The combination of the gravity and horizontal loads, such as seismic actions, attracts axial forces, bending moments and shear forces. All these contribute to the imbalance of the building and may lead to damage or collapse of the building. A large number of existing unreinforced masonry buildings are still present and operational throughout the world. Their presence in the building stock within area with high seismic activity requires careful assessment of their seismic behaviour and retrofitting. Moreover, the existing unreinforced masonry buildings are composed of inhomogeneous material, not capable to carry tension forces. Additionally, many masonry building do not satisfy the latest seismic design provisions. The seismic behaviour and resistance of unreinforced masonry buildings can be improved by strengthening or retrofitting in cases of seriously damaged walls. Usually, traditional strengthening methods are applied, with the common use of reinforced concrete jackets. However, there is insufficient knowledge about the seismic behaviour of jacketed masonry, due to lack of experimental and analytical investigations. The design of those walls is usually based on empirical relations which may result in over- or under-design. Therefore, this thesis focuses on two issues: (1) to compare the behaviour of the unreinforced and strengthened masonry with RC jackets subjected to lateral in-plane cyclic loads, and (2) to suggest a reliable analytical method for evaluation of the seismic resistance and performance of the jacketed masonry buildings. Based on the extensive literature review, an experimental test programme was established, aiming to identify the mechanical properties of masonry and its components. Based on the obtained results, the effects of variable wall geometry and precompression level were considered on the performance of the unreinforced and jacketed masonry walls, tested in real scale and subjected to alternating cyclic in-plane forces. The analytical models for reinforced masonry were used to investigate the capacity of the jacketed masonry due to the similarity of both structural materials and the similar behaviour when exposed to horizontal actions. The effectiveness of the strengthening method was verified experimentally and an increase in the seismic resistance of the strengthened masonry walls was obtained when compared to the resistance of the reference unreinforced walls. However, the ductility performance was not improved. An analytical model for evaluation of RC jacketed masonry walls was proposed, based on the contribution of the masonry and the horizontal reinforcement. The contribution of the vertical reinforcement to the resistance of the walls was ignored, because the tests were performed without anchorage of the vertical reinforcement in the top and bottom beams. This approach was used in order to study the behaviour of the strengthening structural material, rather than to investigate the behaviour of a strengthened structural element - wall. Based on the obtained results, the proposed method for evaluation of the seismic performance of jacketed masonry walls was used to study the strengthening effects on an existing building. The elasto-plastic force-deformation relations for unreinforced and strengthened masonry walls, based on the experimental results, were implemented in a displacement-based analysis software, through a newly developed analysis module. The capacity spectrum method was applied to validate the efficiency of the strengthened material and to assess the seismic resistance of the building. The research presented in the thesis follows the concept of the new generation of design codes for masonry buildings. The obtained results enable application of the analytical approach for design of masonry buildings in cases of strengthened masonry buildings.