This work was supported by the National Natural Science Foundation of China (51076079, 51136002) and National Key Technologies Research & Development Program of China (2012BAJ02B03). We are grateful to Professor Yinping Zhang of the Department of Building Science, Tsinghua University and Professor Baizhan Li of the Faculty of Architecture and Urban Planning, Chongqing University for their excellent suggestions and comments on this work. We appreciate Louise B. Weschler for her modification on this article.