In high seismically areas, the code allows for some plan and vertical configurations irregularities but some others are not defined in the code. The problem with building irregularities and configurations is they tend to provide secondary stresses in the system that under severe seismic activity can causes failure of one small part that can eventually result in global failure.

Torsional irregularity - There will always be buildings with unique plans with odd- ball locations of lateral load carrying elements that result in torsional irregularities. The name of the game is to minimize the torsional irregularity. Secondly, always consider in the design of the lateral load carrying system that it's taking the tributary weight of the building in lieu of stiffness of lateral load carrying system. This should be considered in a concrete fill over metal deck diaphragm when the concrete yields and cracks up.

Re-entrant corners - Always consider that earthquakes are real and can be very large causing high tension loads, which in turn, can cause failure of the vertical framing members at the re-entrant corner. Therefore, always provide for secondary support system just in case there is failure.

Vertical irregularities

In-plane discontinuity in lateral load carrying element - The lateral load carrying system shall be continuous from ground to roof , no exceptions.

Mass irregularities and vertical configuration irregularity - The building masses should be uniform the full height of the structure. But in some cases this may not be possible, i.e., a tower atop a platform, where both conditions can not be avoided. Still the lateral load carrying system shall be full height of the building. The care should be taken on stiffness of the base lateral load carrying elements. They will be short and relativity stiff and tower lateral load elements very flexible.

Weak Story - A weak story is where there is less capacity in any one level  is less than the level above. Think about it, you are providing a weak link in the building. This should not be recommended in any case.

Soft story - This is the same as a weak story. Think about it, stiffness is not the issue.

Non-code irregularities

All the eggs in one basket - The plan location of the lateral force elements in any direction should not be located along one line and then  allowing the torsion effects to be resisted by the transverse elements. An example of this is a building with many shear walls all aligning along one column line and only on one column line.The reason for not allowing this concept is that under severe seismic motion the diaphragms will yield and crack up. Also the collector lines will have substantial forces. Third, there is only one line of defense and probably no redundancy.

50 - 50 Rule - There shall be approximately 50 % of the  concentric braced frame diagonal members sloping in each direction along the same brace line. Don't let the Architect  dream up a brace configuration that  provides all the brace diagonals in one direction. The reason for this rule is that if all the diagonals were in the direction they all will buckle leaving nothing on this bracing line and the net result is a collapse.

Middle of the road rule - All seismic  lateral system should never be located at one end of the bracing line or one end of the building. The collector or drag lines will be long and have significant axial deformation.

Drag for tension only - All collector or drag lines in an concentric braced frame building should be checked for the tensile capacity of the braces neglecting the compression braces. The compression braces will buckle and the  drag forces will redistribute to the tension members.