Mapping the vulnerability of low-cost house roofs in Malate, Metro Manila due to extreme wind speeds

• Main Authors: Garciano, Lessandro, Alvarez, Isiah Paul R., Colobong, John Anthony M., Decal, Christopher Q., Tan, Adam Benedict S.
• Format: text
• Published: Animo Repository 2013
• Subjects: Roofs—Aerodynamics; Wind-pressure; Civil Engineering
• Online Access: https://animorepository.dlsu.edu.ph/faculty_research/3352
• Institution: De La Salle University

Every year about fifteen to twenty typhoons enter the Philippine Area of Responsibility, causing devastating effects to residential structures in many parts of the country. The strong uplift force of the wind and the inadequate uplift resistance of the roof are the main reasons of roof failure during extreme wind speeds (typhoons). In this regard the authors investigated the probability of pullout and pullover failures of roof panels in low-rise residential structures when subjected to extreme wind speeds. The area studied is part of Malate Manila, Philippines, where many structures appear to be non-engineered or not designed according to applicable national structural codes. The extreme wind speeds were modeled using the generalized extreme value distribution (GEV) using 50 years of annual wind speed maxima from the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA). A survey was conducted on 42 residential houses in the study area. Galvanized iron roofs similar (rusted roofs) to the ones used in the study area were also tested for tensile strength. The roof panel resistance was obtained using the wind load provisions of the National Structural Code of the Philippines (NSCP 2010) while the wind uplift pressures for different typhoon return periods were obtained using NSCP 2010 and the GEV model. Finally the probability of failure for each roof was obtained by Monte Carlo simulation of the performance function, resistance minus load. The results obtained show that pullout failure is the main mode of failure attaining a maximum of 27.2% for a 150-year wind return period (200 km/h wind speed). A risk curve was also obtained using the annualized expected loss and the average annual exceedance probability of the wind speeds. Finally a map in Geographic Information System (GIS) format was developed that can help local authorities identify house roofs that are vulnerable to strong typhoons. This hazard map may also help residents strengthen their roofs to lessen damage during typhoons.