A methodology for site-specific wind contouring and hazard mapping: A case study in Surigao City

Around fifteen to twenty typhoons enter the Philippine Area of Responsibility every year. It is reported that ninety percent of the cost of damages are due to the effect of tropical storms. Structures normally resist wind load during extreme winds but the probability of damage increases as the wind velocity increases. The current structural code of The Philippines divides the country into three wind zones: 250, 200 and 125 Kph. Recent trends show that wind velocities are increasing and that the typhoon tracks are changing. In late 2012, the country was hit by typhoon 2Bopha3 that has a gust speed of 280 Kph. Typhoon 2Yolanda3 has also hit the archipelago in 2013. Both surpassed provisions of the current structural code causing severe damage. The objective of the study is to develop a methodology for a site specific wind contour and hazard map. This was done by applying a correction coefficient considering the shielding effect of structures. The model is a function of the horizontal, vertical and displacement angle of the structure. Wind is simulated through Generalization Extreme Value distribution to estimate the maximum wind speed and direction that can occur in different return periods. Coordinates of each structural group were determined through Global Positioning System. These points were the basis of the shielding coefficient that were determined through the theory established. The theory is validated by means of site investigation and actual wind speed determination of the shielding and the shielded structures. Analysis of Variance is done to take note of the level of significance between the theoretical and actual results. With the correction factor established per point location and the gust of different return period predicted, Geographic Information System database is used to do special analysis by means of Kriging Interpolation. The result are multiple contour and hazard maps. The study can serve as a reference to determine site specific wind speed of point in the area of interest. The author recommends this to be done in different areas because the method developed is more precise than that of a wind zone map