Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 48 1 1 Planes of bracing Figure 9.12 Detail showing additional bracing in the plane of the crane girder Table 9.1 Bracing requirements for crane girders Factored longitudinal force Bracing requirement Small (<15 kN) Use wind bracing Medium (15 - 30 kN) Use horizontal bracing to transfer force from the crane to plane of bracing Large (> 30 kN) Provide additional bracing in the plane of the longitudinal crane forces 9.3 Plan bracing 9.3.1 General Plan bracing is placed in the horizontal plane, or in the plane of the roof. The primary functions of the plan bracing are:  To transmit horizontal wind forces from the gable posts to the vertical bracing in the walls  To transmit any drag forces form wind on the roof to the vertical bracing  To provide stability during erection  To provide a stiff anchorage for the purlins which are used to restrain the rafters. In order to transmit the wind forces efficiently, the plan bracing should connect to the top of the gable posts. According to EN 1993-1-1, the bracing will have to satisfy the requirement of § 5.3.1, 5.3.2 and 5.3.3 for global analysis and imperfections within the bracing system. 9.3.2 Bracing using circular hollow sections In modern construction, circular hollow section bracing members are generally used in the roof and are designed to resist both tension and compression. Many arrangements are possible, depending on the spacing of the frames and the positions of the gable posts. Two typical arrangements are shown in