Designers' Guide to en 1992-1-1 and en 1992-1-2 Design of Concrete Structures Eurocode 2

DESIGNERS' GUIDE TO E N 1992- 1 - 1 AND E N 1992- 1-2

Fig. 3-3.Application of the effective geometrical imperfections: unbraced structure (number of vertically continuous members = 3 )

Fig. 3,4. Minimum tie force for perimeter columns

forces should be taken into account in the stability calculation. This is in addition to other design horizontal actions, such as wind. 3.3.3. Design of slender elements In the design of slender elements, which are prone to fail by buckling (e.g. slender columns), EN 1992-1-1 requires geometrical imperfection to be added to other eccentricities. For example, in the design of the columns, an eccentricity of 0,1,/2 is assumed for geometrical imperfection (where 1, is the effective length of the column). 3.3.4. Members transferring forces to bracing elements In the design of these elements (such as a floor diagram), a force to account for the possible imperfection should be taken into account in addition to other design actions. This additional force is illustrated in Fig. 3.4. This force need not be taken into account in the design of the bracing element itself.

Cjause 5.8.2(6)

As structures subject to lateral loads deflect, the vertical loads acting on the structure produce additional forces and moments. These are normally referred to as second-order effects. Consider a cantilever column shown in Fig. 3.5. The deflection caused by the horizontal load alone is A,. In this deflected state, the vertical loadPwill contribute a further bending moment and increase the lateral sway, and the final deflection will be A,. This phenomenon is also commonly referred to as the 'PA effect'. E N 1992-1-1 requires second-order effects to be considered where they may significantly affect the stability of the structure as a whole or the attainment of the ultimate limit state at critical sections. In the Application Rules, the code further states that for normal buildings, second-order effects may be neglected if the bending moments caused by them do not increase the first-