The following are rules for seismic design of new and existing structures

Compatibility: All building elements and their material properties should be able to sustain the maximum deformation without destructive interference.

Condition: Old Buildings: How the building has been maintained. Is there evidence of deterioration, decay, damage, settlement, or unauthorized modifications to the structure? New Buildings: Will the owner maintain the building or just invest the money for upkeep into something else?

Configuration: Are there irregularities in the building elevation or plan that could lead to concentration of excessive deformation or stress, such as soft or weak stories, or torsion due to eccentric location of resisting elements.

Continuity: There must be a continuous load path of structural elements and connections to carry gravity loads to the foundation, and to carry seismic inertial loads from the horizontal diaphragms to the lateral load-resisting shear elements and then to an adequate foundation.

Redundancy: The presence of a series of resisting elements or an additional backup system can provide extra assurance against collapse where the possible failure of a single element can occur due to design error, condition or construction weakness; the load initially taken by the failed element can be redistributed to the other elements in the lateral load-resisting system.

Strength: The existing lateral load-resisting capacity should be high enough to prevent sudden brittle failure or excessive inelastic yield distortion.

Toughness: Specific detailing should be provided to prevent excessive strength degradation of structural elements and connections due to the actual cyclic loading that leads to the maximum seismic deformation response.

Simple system: The building and the lateral load carrying system should be made simple. There should not be a complex lateral and vertical carrying system in the building. If you can not design the building using simple hand calculations then why use a computer to design a building when you can not justify the computer output with hand calculations. In other words, calculations are only a tool to set the limits of the design. You should not use the calculation process to justify a design.

Original Building Construction Quality: Good constuction quality and care helps in the seismic performance. Poor construction does not help in the seismic performance in the building. Poor construction practices around the world has contributed to many building failures and severe damage.

For the past few months, Al has been providing consulting structural engineering services at Telesis Engineers in Berkeley California.

There will be nonstructural damage in an earthquake. The exterior facade if not appropriately detailed and articulated will be damaged. No matter what the lateral system is used, the interstory drift will be considerable that if no seismic slip joint is used the exterior will be damage. Other damage will be the banging of different elements due to the pounding. The typical locations of pounding is the corners where stiff in-plane elements that do not move are pounded by the out-of-plane elements perpendicular to them. Even if all the exterior is adequately detailed and articulated, the damage to the facade will consist of replacing the sealant in the seismic slip joint.

Here is a list of some types of exterior wall finish and the potential damage:

precast and strip windows - there needs to be a minimum of one slip joint at one interface of components and there will  banging at the corners

precast and punched windows - there needs to be a slip joint at each floor between panels and there will banging at the corners

storefronts - these elements are usually design built by the contractor who may not know the potential inelastic drift in the building. Window walls are usually tall and are multi-story which than requires a much greater articulation. Corners are problems and the damage is life threading with falling glass.

metal studs and plaster/metal panel/etc - first the metal studs - these elements can rack in plane whether one or two stories but they can buckle in the out-of-plane direction when greater than two stories. This is due to the upper modal participation of the building dynamics. It is the exterior skin of plaster, metal panel etc if not articulated thay will be damaged..

brick veneer - this veneer is heavy and is brittle articulation is required..There are solutions to using brick veneer in high seismic zones. They are using thin units attached to a stiff structural elements or using full size units attached to a structural framing system similiar to a precast system.

stone veneer - this is the same as brick veneer and there are other solutions than noted under the brick veneer.

In summary, most of the exterior wall is design and detailed by an architect. Now comes the ugly part, many architects do not understand earthquake engineering and have to be taught how a building exterior needs to articulated. In some cases, the architectural design of the exterior may required to be completely re-designed.

Interior partition walls that are not appropriate detailed and articulated will be damage causing shelves to collapse, doors permanently fixed closed or open, gypsum board to fall, and ceilings to collapse.

Mechanical, plumbing, and electrical systems will be damaged if not adequately braced and anchored to the structure.

Standard Language for Structural Engineers for Earthquake damage

The following language should be stated to the Architect or building owner in letter form or on the contract documents. In letter form alone may not be enough, the letter could get lost.

In the event of an earthquake, there will be structural and non- structural damage. The extent of damage can not be determine at this time. The cost of damage, unknown at this time, may exceed the value of the building and it's contents. Furthermore, the extent of the damage may require the building official to not allow access into the building to retrieve the building contents.

There should be more and your attorney should be called to add further information if needed. Failure to communicate any language about damage to all parties could lead to further legal consequences. The same can be said if you say nothing at all.

For performance based design buildings, where the engineer designs the building for limited damage, the following language should be as follows:

Even though this building was design to a limited damage state, there will be structural and non-structural damage in the event of a earthquake. The extent of damage will be limited but can not be determine at this time. (Some language of the type of damage could be added here.) The cost of damage can not be determine at this time. Furthermore, the building official may limit the access to this building due to some dangerous hazardous condition that can not be determine at this time.

The future of structural engineering in California will depend on the result of the next large or great earthquake. It isn't the Northridge or Loma Prieta level earthquake, but a very large earthquake. The kind of earthquake where there is a large number of deaths and hundreds of billion dollars in damage. I believe the public is not ready for a large number of deaths like in Kobe earthquake  where 5500 died. Nor is the public ready for level of damage that will occur as a result of a large earthquake. Remember, the public thinks new buildings are being designed as "earthquake proof". Many new buildings will be damage but what will really pissed off the public will be the number of buildings that will collapse. Yes, there are many old buildings that will collapse but don't be surprise to see some relatively new buildings collapse. After that large earthquake, the structural engineers will be on the hot seat to explain to the public what went wrong and what we have learn. But, if the public is unhappy so will the politicians be unhappy. Heads will roll and new laws will be written.