Fin plate rotation capacity

Fin plate connections derive their rotation capacity from:

• bolt deformation (in shear)
• hole distortions (bearing)
• out of plane bending of the fin plate

In order to achieve adequate rotational capacity, it is necessary to proportion fin plate connections so that the following failure modes are prevented:

• bolt shear
• weld rupture
• tensile tearing of the fin plate

Floor vibrations (ULS)

The issue of vibrations is considered to be a serviceability criteria.
However:
On some occations, the phenomenon can be an ultimate limit state consideration.
This is the case for high dynamic forces, such as:

• gymnasiums
• dance halls
• areas of aerobic activity.

Stub girders

Architectural demands for square column grids with spacings up to 12 m (almost 40ft) led to the development of stub girder construction.

The stub girder comprises of:

• a bottom chord which acts in tension
• a series of short beams (the stubs) which connect the bottom beam to ...
• ... the top chord which is the concrete slab and acts in compression.
• secondary beams which span across the bottom chord, designed as continuous beams
• the voids created are used for services.

The major disadvantage of the system is that it requires temporary propping until the concrete has gained adequate strength for composite action.

Castellated beams

Castellated beams can be used effectively for:

• lightly serviced buildings
• aesthetic reasons, where the structure is exposed

Composite action in castellated beams does not significantly increase the strength of the beams, but does increase their stiffness significantly.

Note finally that castellated beams have limited shear capacity and are thus best used as secondary beams.

LTB and cross-section

Cross-sections with:

• greater bending stiffness about the minor z-axis and
• greater torsional stiffness: 

have a greater lateral torsional buckling resistance.

CBF web members

In a braced frame, the principal function of web members is:

To resist the horizontal shear forces.

However, for brace configuration as in fig. (a), (b), the web members may pick up substantial compression forces as the columns shorten vertically under gravity loads:

SLS - joint slipping

If inelastic settlements of connections must be avoided in order to reduce the deformability of the structure:

The slipping resistance has to be obtained.

Its value depends upon bolt tightening and surface treatment.

Cantilever Buckling

The absence of out-of-plane restraints at the free end of a cantilever, changes the buckling mode:

In an end loaded cantilever, it is the tension flange which buckles.

(Note that in a simply supported beam, the compression flange buckles).

Dampers

Passive dampers (here viscous fluid dampers) can significantly enhance seismic performance of buildings by :

• reducing drifts 
• reducing inelastic deformations
• reducing the velocity and acceleration demands on non-structural components. 

Preheating

Rate of cooling is an important parameter in the control of hydrogen cracking of the heat-affected zone.

It is possible to reduce the cooling rate and so reduce the susceptibility to cracking by:

Preheating the elements before and during welding.

Stability check of members (avoid per EC3)

According to Eurocode 3, if

• second order effects in individual members and 
• relevant member imperfections

are totally accounted for in the global analysis of the structure, then:

No individual stability check for the members is necessary.