Web crippling and combined bending and web crippling of cold-formed steel header beams

Cold-formed steel is widely used in residential and light commercial buildings for wall, floor and roof framing. This investigation studies the web crippling behavior of header beams for both I-beam and box-beam configurations in typical stud framed bearing walls. It is a continuation of a pilot study initiated in 1998 and combines the data of that study with the current testing program. The pilot study and testing done by the National Association of Home Builders has indicated that header beams have a greater strength than is predicted by current design procedures. This experimental study defines both web crippling strength and combined bending and web crippling strength for headers and shows that current design procedures for cold-formed steel header beams are conservative for interior-one-flange loading conditions. The specimens tested in this study were constructed, as they would be in a cold-formed steel stud framed wall based on the American Iron and Steel Institute (AISI) standard framing guidelines. Header beams consisting of C-sections and tracks were tested as an assembly. An appropriate design methodology that more closely represents the actual beam web crippling strength and combined bending and web crippling strength is proposed for I-beam headers. For box-beam headers, a modifier for web crippling strength and a new interaction equation for combined bending and web crippling have been developed and are proposed.