Optimisation of hollow core slabs : Producing units of a smaller standard width

Abstract: The Swedish precast concrete company ‘Strängbetong’ produces a variety of Hollow Core slabs, with a standard width of 1200 mm. Quite often, the HC units are subjected to longitudinal cutting1, which takes place in the factory by a diamond blade, in order to achieve narrower elements. This results in a considerable material waste since the rest part of the HC unit cannot always be utilized. Regarding the cutting process, it requires a significant amount of time that slows down the production. Moreover, extra workhands are needed, while other factors such as the transfer and crash of unwanted pieces, contribute to a higher cost for the factory. Approximately 12% of the HC elements produced by Strängbetong are fillers. Aiming to achieve a more efficient and sustainable production, the reduction of the number of fillers is of vital importance.This thesis project investigates if a line producing smaller width elements would be more profitable. The study starts by investigating the most common width that HCs are cut, with the aim to create a line according to this width2. Then, the most promising width is determined, taking into account the possible alternatives and fillers’ width trends that have been found. To estimate accurately the possible cost saving, the impact of the smaller width line on the production and the possible increase of thru put3, the production of the factory in Kungsör, is simulated on MATLAB. Firstly, the current situation is simulated (8 lines, 1200-mm-wide) in order to evaluate the current efficiency. Then, the studied scenario is simulated (7 lines 1200-mm-wide and one 813-mm-line), to evaluate the advantages of this alteration. Both simulations start by imposing the HC production load of 2019. This thesis is completed by a repetition of the simulations, where the input data are modified, in an effort to calculate accurately the possible cost saving as a function of designers’ adaption to the 813-mm-line.The results show that if an 813-mm-line were used instead of a 1200-mm-line during 2019, the possible cost saving would be at least 1.0 million SEK annually. The suggested line leads to a more sustainable production, as concrete and steel waste can be decreased by 51.6% and 50.3%, respectively. A significant amount of time due to less longitudinal cutting can be saved while there is a slight increase of thru put. Moreover, the results show that the factory will be able to handle the pressure on the production, despite the decrease by 1/8 of the physical production capacity of 1200 mm units. Finally, if the designers adapt fast to the new width alternative, the possible cost saving would rise significantly. If it is possible to design 1 out of 5 future fillers as a full-width element, cost saving can reach 1.4 million SEK annually.