Tips for Resistant Systems in Seismic Design
Considering the extensive seismic zone in our territory and with it the requirements implied by the application of current regulations, we report some criteria that in our opinion are important in seismic design and in particular in the connections of structural elements that allow a greater dissipation of energy due to inelastic deformations when the event occurs.
- As structural systems for resistance to seismic actions, it is advisable to consider conventional non-bracing seismic resistant frames (OMF) formed mainly by beams, columns and beam-column nodes and concentric bracing frames (PSCAC) where seismic force is supported by axial forces in the braces. These systems, without being the only ones possible, allow apart from an adequate dissipation of energy in the event of a seismic action an appropriate and convenient design of the connections.
In conventional non-bracing frames, the design of the rigid beam-column joints must be carried out with a required flexural strength of at least 1,1.Ry.MP to recognize the possible overstrength and deformation hardening.
- In conventional non-bracing frames, the design of the connections of the beam-column connections must be carried out with a shear effort Vu obtained from the maximum action of the system for the combination of regulatory load plus the shear from an equal moment in value and opposite direction to the one defined in the previous point.
- Pay attention to the detail of the panel zone of the frame node in terms of its resistant capacity with respect to the design of the panel, welding and continuity plates.
- The PSCAC braced resistant systems with bar design so that they intersect at a point in the nodes without eccentricity of the connection. The recommended schemes are in X, V and V invert. The K shapes are not recommended and / or especially prohibited by the unbalancing of the load on the column.
- The design of the struts in the PSCAC systems must be carried out with a required resistance of Ry.Fy.Ag and with slenderness limitations for the struts.
- Bolted joints must be designed with high strength bolts and be fully tensioned.
- In general, due to the high resistance required, the connections result with a large number of bolts, so it is convenient:
- Shims must be considered for a more “comfortable” assembly according to the limits of the clearances and for the tolerances of supply and/or manufacture of built up profiles.
- In the joints of the braces, foresee if it is possible “splices” with a double shear plate, taking care of the assembly and foreseeing the slenderness of its parts in the case of braces that work to tension-compression.
- Pay attention to the welding of the continuity plates (stiffeners) in the panel zone and the joining plates in tensioned zones.
- Design the connection to foresee in the modeling the coherence of building and assembly to minimize the problems in work.