Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 62 The diameter of the bolt will generally be determined by consideration of the uplift and shear forces applied to the bolts, but will not normally be less than 20 mm. There is often generous over-provision, to allow for the incalculable effects of incorrect location of bolts and combined shear force and bending on the bolt where grouting is incomplete. The length of the bolt should be determined by the properties of the concrete, the spacing of the bolts, and the tensile force. A simple method of determining the embedment length is to assume that the bolt force is resisted by a conical surface of concrete. Where greater uplift resistance is required, angles or plates may be used to join the bolts together in pairs as an alternative to individual anchor plates. Calculations should be carried out by the designer at the final design stage to check the viability of the proposed bolt spacing. 11.3.5 Foundation design at the fire limit state If the foundation is designed to resist a moment due to rafter collapse in a fire, both the base plate and the foundation itself should be designed to resist the moment as shown in Figure 11.7(a). It may be possible to offset the base to reduce or eliminate the eccentricity generated by the moment to give a uniform pressure distribution under the base as shown in Figure 11.7(b). M M (a) (b) Figure 11.7 Foundation for portal frame in a fire boundary condition 11.4 Design summary  Moment-resisting connections should be arranged to minimise any additional local strengthening.  It is usually more economical to adopt nominally pinned column bases.  Experience has demonstrated that a four bolt connection with a relatively thin base plate may behave effectively as a pin, while still providing sufficient stiffness for safe erection.  Careful consideration needs to be given to resistance to shear forces, both in the column base and in the foundation.