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An experimental program on built-up cold-formed steel beams carried out at The University of Sheffield is presented. The specimens were assembled from plain channel sections with nominal thicknesses of 1.2 mm and 1.5 mm. The specimens were tested in a four-point bending configuration and were designed to fail by local bucking within the constant moment span. Three different connector spacings were used to study their effect on the ultimate capacity of the built-up specimens and on the way the individual sections interact with each other as they buckle. Test coupons, extracted from the corners and the flat portions of the component sections, were tested in order to determine their material properties. The out-of-plane imperfections of each built-up specimen were also recorded using a laser sensor. The tests revealed that the interaction between the component sections is significantly affected by the connector spacing and that reducing the spacing between connectors results in an increase of the ultimate capacity.