Evaluation of the environmental effects on a medium rise building

This article presents the variation of the dynamics properties due to environmental effects of the Central Tower at the Faculty of Physical and Mathematical Science of the University of Chile. This structure is a nine story, shear wall reinforced concrete building, 30 meters high, which has been monitored automatically and remotely since 2009 with a network of 8 uniaxial accelerometers and 9 environmental sensors. The network registers the ambient conditions, such as wind speed and direction, temperature, radiation, rainfall, ambient and soil humidity. The range of variation on environmental effect and modal properties is presented. Detailed analysis of the temperature effect on the properties is presented. The Principal Component Analysis (PCA) methodology has been utilized to reduce some environmental effects on the vibration frequencies to identify earthquake damage in the structure. The advantages and disadvantages of the method are presented. Typical variations in the range of 4% are observed related to temperature and 6% related to the rain and the surrounding soil humidity. Earthquake damage during the 2010 Mw=8.8 Earthquake is clearly identify from ambient vibration and earthquake records. Damage is considered low, with some visible cracking in structural wall. Variations due to this damage are in the order for 15 to 20% for predominant natural frequencies.