الفهرس 
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Abstract
This research presents the structural investigation of four existing telecommunication towers located around Egypt. The towers are with different heights and sections. They can be classified into two triangular self-supported towers, one rectangular self-supported tower and one rectangular guyed tower. The investigation was carried out using experimental ambient vibration test (AVT) and seismic structural analysis. The study is to be considered one of the few studies for the dynamic testing of full scale towers using AVT techniques. The dynamic properties were identified for the full scale towers using a set that varies from three to sixteen of uniaxial accelerometers mounted in different positions and altitudes over the towers, roving of accelerometers took place during field measurements. The experimental modal results were identified in terms of natural frequencies and/or mode shapes. The Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification – Canonical Variate Analysis (SSI-CVA) methods were applied to extract the modal properties for some towers. The results obtained showed good agreement between both methods. Finite element models for each tower were updated based on the identified dynamic properties. Finally the structural analysis under seismic loads was also studied using time history analysis (Gulf of Aqaba 1995 earthquake). The results illustrate the success of AVT in identifying the actual dynamic properties of the full scale towers, where a finite element model was reliably updated to represent the actual dynamic behavior of the tower. The seismic structural analysis was enhanced using the updated model as the structural results expresses the real structural status of the existing tower using both the experimental and the analytical techniques.
The effect of seismic loads have been investigated on different parameters in this study, the effect of members deterioration is directly preoperational with both of the maximum drift and the maximum axial stresses on the mast. In addition, the effect of increasing geometrical dimensions is directly proportional with both of the maximum drift and maximum axial stresses on the mast. Also, the effect of increasing additional masses and the effect of different earthquakes with different patterns and magnitudes are investigated.