Demolition - Communication Tower
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Applied Science International (ASI), conducted a numerical study on the demolition of communication towers. ASI performed multiple demolition analyses to assess the influence of several factors that may alter the collapse behavior or the mode of failure. These factors included the fluctuation in the estimation of the tower’s self-weight, the uniformity of the tower mass, the effect of tower height, and the possible loss of the pretension in the guy cables.
The investigated communication tower is three-sided steel lattice with pretension guy wires at 8 levels of the mast. The lattice is made of solid round vertical legs, solid horizontal rods and solid diagonal rods. The guy wires were connected to six concrete footings, located at 45m and 90m from the face of each mast leg.
ASI used its proprietary Extreme Loading® for Structure, ELS software (LLC, 2004) to implement a 3D model for the structure and apply the demolition scenario. ELS is based on an innovative numerical methodology: Applied Element Method (AEM), which allows the creation of a detailed numerical model of the analyzed structure, simulating the complex structural behavior of reinforced concrete and steel structures, from the linear stage, passing through concrete cracking and reinforcement yielding, until the complete collapse is reached (Tagel-Din, 2009). The computational capabilities provided by the AEM allows the creation of high-fidelity models, accounting for the actual local behavior of constituent material in the global behavior of the structure.
The primary investigation involves the pre-weakened tower, with a weight of 58 tones, followed by cut of the guy wires in one of the three sides which leads to falling to the ground in the designated drop direction within approximately 14 seconds, reaching a distance of roughly 130 meters from the base of the tower.
The failure is observed in the tower bottom, where the weaking is applied for one leg. Increasing the self weight of the tower from 39 t to 58 t leads to an increase in stresses at the bottom leg by 15%.
ASI studied the Effect of different parameters on initiation of buckling of the tower. An analysis is conducted to evaluate the height effect. Two different heights were investigated(120m and 240m). Results showed that the high tower had larger buckling compared to the short one. Another analysis was performed ignoring the pretension of the upper cables. This scenario resulted in a slower collapse in the intended direction within 17 seconds. An analysis was carried out with nonuniform distribution of the total weight (39 ton) along the tower height. This scenario resulted in accelerating collapse and showed buckling compared to the uniform mass.