Azhar, Afif Aiman, and Ahmad Fahmy Kamarudin. “Effect of Vertical Irregularity(Lower Level) of 5-Storey Laboratory Steel Tower Using Modal Parameters”. Recent Trends in Civil Engineering and Built Environment, vol. 2, no. 1, June 2021, pp. 362-71, https://publisher.uthm.edu.my/periodicals/index.php/rtcebe/article/view/1464.