Ismail, Mahmud Rasheed, and Mohsin Juber Jweeg. “Natural Frequencies of Multi-Irregular Span Beams under Elastic Supports By Modal Analysis Method”. Nahrain University College of Engineering Journal, vol. 19, no. 2, Jan. 2017, pp. 353-62, https://oldjournal.eng.nahrainuniv.edu.iq/index.php/main/article/view/28.