Behnam Shirkhanghah and  Vahid Shahbaznejhad-Fard and  Houshyar Eimani-Kalesar and  Babak Pahlevan,  Behavior Factor of Flat Double-Layer Space Structures.   journal   = {International Journal of Civil and Environmental Engineering}, [online]. World Academy of Science, Engineering and Technology.
    September 2012, vol. 69(9). 740 - 744
    [viewed 30 September 2020]. Available from: https://publications.waset.org/pdf/9387.