Time：May15 10:50 -11:15
Title: Innovative 3D Bracing System for Transmission Tower Structures/输电塔结构的新型三维支撑体系
Abstract: Many older transmission towers are designed based on tension-only bracing systems with slender diagonal members. However, the increased demand in power supply and changing global weather patterns mean that these towers require upgrading to carry the resultant heavier loading. The failure of a single tower can rapidly propagate along the line and result in severe damage that costs many millions of dollars. Hence, this research project aimed at developing efficient upgrade schemes using diaphragm bracings.
A nonlinear analytical technique for predicting and simulating the ultimate structural behaviour of self-supporting transmission towers under static load conditions was first developed. This method considered both the geometric and material nonlinear effects and treated the angle members in the tower as general asymmetrical thin-walled beam-column elements. Modelling of material nonlinearity for angle members was based on the assumption of lumped plasticity coupled with the concept of a yield surface in force space.
Tower strength improvement was then investigated by adding a series of diaphragm bracing types at mid-height of the slender diagonal members. Analytical studies showed that considerable strength improvements could be achieved using diaphragm bracings. They also showed the effects of different types of bracings, including those of joining the internal nodes of diaphragm members and the location of diaphragms. Experimental studies were undertaken using a tower sub-structure assembly that was strengthened with a variety of diaphragm bracings under two types of loading. The results confirmed the analytical predictions and allowed recommendations on the most efficient diaphragm bracing types. An upgrade scheme that used the most efficient diaphragm bracing type was successfully implemented on existing towers. This scheme used less steel than the replacement of the existing diagonal bracings, was easier to implement in practice, and led to improved tower performance.
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