Finally, my M.S. Thesis has been fully accepted. The full text can be viewed/downloaded from this link: http://docs.google.com/fileview?id=0B-NxRIz9HeFOZDM1OTBiMTAtY2IzMy00NGE2LTlmZDMtMzFiOGEzZWYzY2Uw&hl=en_GB
Codes from other countries use the term "lattice towers" instead of "trussed towers." Transmission towers and antenna towers are examples of trussed towers.
Highlights of the thesis include:
0. The main hypothesis of the study is that dynamic wind effects could not be neglected for trussed towers; for example typical trussed towers in the Philippines have aspect ratios around 7, and meanwhile the NSCP-01 requires that dynamic wind effects should be considered for structures with aspect ratios greater than 4.
1. The study suggested estimates of natural frequency, structural damping, aerodynamic damping, and mode shape exponent for trussed towers of different base shape (triangular/3-legged or square/4-legged), use or amount of antennas, wind zone, and wind terrain and topography. These are mostly based on results from full-scale experiments on actual trussed towers in other countries (mostly from Japan). These estimates are necessary parameters when estimating dynamic wind effects, embodied in the gust effect factor. Unfortunately, a gust effect factor formulation is not available in the NSCP-01.
2. The study suggested a gust effect factor (dynamic response factor) formulation specifically for trussed towers, based on Davenport's original gust response factor formulation for trussed towers, but modified for compatibility with the NSCP-01 (National Structural Code of the Philippines, 5th ed., 2001). Other formulations that were investigated where taken from ASCE7-02 and AS/NZS 1170.2:2002. Note that the NSCP-01 wind loading provisions is based on the ASCE7-95 provisions (excluding commentary).
3. Finally, the study illustrated using a simple and general 1DOF model, and then using a specific MDOF model of one actual tower, that non-consideration of dynamic wind effects (i.e. structure assumed as rigid; gust effect factor = 0.85) in trussed structures such as trussed towers could result in an under-estimate of the wind loads.