Steel Buildings in Europe

Part 4: Detailed Design 4 – 14 very low torsional stiffness on plan, a situation which is unlikely to occur in practice). 2. Verify that all columns are tied into all attached beams by connections with a minimum resistance of 1,0% of the column axial force, i.e. that the tying resistance of the beam to column connection is at least 0,01 × N Ed,column. 3. Verify that all the equivalent horizontal forces in each column can be transferred into the relevant bracing system. Diaphragm action in the floor slab may be mobilised to satisfy this condition. In accordance with EN 1993-1-1, § 5.3.3(1), a reduction factor  m =        m 1 0,5 1 may be applied, where m is the number of columns to be restrained. 2.8 Design summary  ‘Simple’ design and construction provides the most economical approach for low and medium rise frames.  System(s) of triangulated bracing or concrete core(s) provide resistance to horizontal forces and overall frame stability.  ‘Simple’ connections have been proven by experience to provide sufficient strength, shear and rotation capacity to satisfy the assumptions of this method.  Beams are designed to span between grid lines.  Columns are designed for axial loading only, with no account of pattern loading and only nominal moments. The value of the nominal moments will be based on the equilibrium model adopted for the connections, as described in Section 3.3.  Concrete cores may generally be assumed to provide sufficient stiffness for all potential second order effects to be ignored.  For low-rise (2 or 3 storey) braced frames, designing the bracing for horizontal actions of 2,5% of vertical actions in accordance with section 2.6 will provide sufficient horizontal stiffness that all potential second order effects may be ignored.  Frames of intermediate stiffness, where 3 <  cr < 10, may be analysed by first order analysis, providing all relevant actions are amplified by the factor cr 1 1 1    Frames with  cr < 3,0 should be avoided.  The effects of sway imperfections and imperfections at splices may simply be addressed by applying equivalent horizontal forces of 1/200 of vertical forces, in accordance with Section 2.7.6 of this publication.