<![CDATA[Optimization of cold-formed steel construction materials in the form of merging two individualchannel into built up back-to-back channel. The use of cold-formed steel is increasingly applicable withvarying lengths used. Therefore, it is necessary to research the effect of variations in beam span lengthaffect the flexural strength of cold-formed steel beams arranged back to back. This study aims todetermine the load, deflection, and failure mode of back-to-back C channel beam with variations in beamspan length. The research uses quantitative methods through a laboratory experimental approach. Theresults of the study can be concluded as follows: (1) A load of back-to-back cold-formed steel beams hasdecreased with an increase in the length of the beam span in each variation code test specimen. Thedecrease in load compared to the shortest span length of 90 cm for the lengths of 120, 210, 240 cm are10,90%, 51,12%, and 62,39% respectively. The decrease in actual load is caused by a reduction offlexural rigidity, the presence of stress concentrations at the loading point that prevent the load from beingproperly distributed to the support, and the instability of the back-to-back or open sections, whichincreases as the length of the beam span increase. (2) Deflection of the beam due to transverse loadswhich act on back-to-back cold-formed steel beams increases as the span length increases for eachvariation code test spesimen. The beam deflection compared to the shortest span length of 90 cm for thelengths of 120, 210, and 240 cm increased by 17,26%, 73,11% dan 103,3% respectively. The decrease inbeam stiffness due to increased length of the beam span with a constant spreader beam size, which resultsin increased distance between the loading point and the support, is what causes the rise in verticaldeflection of the beam. The deflection that occurs in each length variation code exceeds the maximumdeflection limit, so it is necessary to take into consideration of the load applied to the back to back coldformed steel beam. (3) The failure modes that occured in the back-to-back cold-formed steel beam in eachvariation of the span length during the flexural test had the same failure, namely flange local buckling,distortional buckling, and lateral torsional buckling. The difference in failure modes among C channels inthe back-to-back beam was observed and there is an interaction of local buckling, distortional, and lateraltorsional buckling failure modes in one of C channel, while the other C channel only experiences lateraltorsional buckling]]>
