Posteck Prestressing
Where qualities meet technical excellence

Where qualities meet technical excellence

WELCOME to our Seismic Design Forum. A new session dedicates to knowledge and technologies in seismic design and safety provisions for concrete buildings. This session contains specific Q&A, common and special analysis techniques used for seismic design, behavior of member joints and so on.  

Q: What are the roles of PT slab in seismic resistant system of concrete building? 

A: In the modern concept of seismic resistant design of concrete building in high seismic regions, PT slab has two main roles in seismic resistant concrete building. First it acts as rigid diaphragm to transfer lateral loads to lateral resistant system like structural walls, and special moment frames or dual systems. 
Second, it serves as gravity frame to carry any vertical loads from superimposed dead load to occupancy live loads. It is very important to design the slab-column connection to withstand lateral deformation of the lateral load system during seismic events. The slab shall be prevented from punching through column during cyclic deformation. it has to make sure that slab punching resistance is carefully designed with sufficient drift capacity. 
Posteck Prestressing is the first company who has introduced PUNCHGUARD (tm) to enhance drift capacity of slab-column connection with supported testing results. For more information about seismic consideration for post-tensioned slab building, please visit our blog page.   

Last updated 11.09.2016

What are drift limits used for different performance level?

According to SEAOC(1995), the permissible value of story drifts for each performacne level are listed below:

Last Updated 12.06.2016

Limit State
   Permissible max drift (%)
         Permissible    Permanent drift (%)
 Fully Operational
 Life Safety
 Near Collapse
What are performance objectives?

Performance objectives are suggested by SEAOC (1995) for seismic design guideline of buildings and other facility structures. SEAOC has classified the performance level of structures into 4 categories: Fully operational, Immediate Occupancy, Life Safety and Collapse Prevention according to level of damage to the structures. 

As shown, the performance objective increases (i.e. there should be less damage) for a high probability earthquake (one that may occur several times during the life of the structure) or for an important structure or dangerous occupancy (i.e. a hospital or dynamite plant). Conversely, more damage is acceptable for a rare, severe earthquake or for less critical or temporary facilities. Thus, a building would be expected to suffer more damage if it were subjected to a more severe, less likely earthquake. Also, a more critical building would be exepected to have less damage for the same earthquake probability.

A basic structure would be expected to have essentially no damage if subjected to an even with a 10% probability of occurence in 30 years whereas it would be near collapse if subjected to an event with a 10% probability within 100 years. One can substitute more appropriate numbers for a particular project, or upgrade the characterization of the structure (to an essential facility, for instance, where the structure would be designed to remain life safe during the very rare event).

This method removes some of the ambiguity from the current SEAOC recommendations. The method still needs to indicate what performance parameters to consider (drift, stress, plastic hinge rotation, acceleration, etc. and what limits are to be imposed to achieve a particular performance objective. Some information on performance parameters was provided in Vision 2000 for basically the first time, but it was for the most part based on consensus rather than on test data or quantitative field observation.

Fully Operational :
Continuous service. Negligible structural and nonstructural damage.

Immediate Occupancy (Operational):
Most operations and functions can resume immediately. Structure safe for occupancy. Essential operations protected, non-essential operations disrupted. Repair required to restore some non-essential services. Damage is light.

Life Safety:
Damage is moderate, but structure remains stable. Selected building systems, features, or contents may be protected from damage. Life safety is generally protected. Building may be evacuated following earthquake. Repair possible, but may be economically impractical.

Collapse Prevention (Near Collapse)
Damage severe, but structural collapse prevented. Nonstructural elements may fall. Repair generally not possible.


Last Updated 12.09.2016

What are the level of earthquake used in SEAOC's performance chart?

In SEAOC performance chart, 4 level of earthquake are classified:

Frequent earthquake 

     43 years return period p = 50% in 30 years


Occasional earthquake 

   72 years return period p = 50% in 50 years)

 Rare earthquake 

  475 years return period p = 10% in 50 years. ASCE 7-10 and Thailand's local seismic regulation currently demand the strength design based on this level of earthquake. 

Very rare earthquake 

 970 years return period p = 10% in 100 years). where p = probability of occurrence.

Last Updated 12.09.2016

Q: What is seismic response spectrum?

A:  Response spectra are very useful tools of earthquake engineering for analyzing the performance of structures and equipment in earthquakes, since many behave principally as simple oscillators (also known as single degree of freedom systems). Thus, if you can find out the natural frequency of the structure, then the peak response of the building can be estimated by reading the value from the ground response spectrum for the appropriate frequency. In most building codes in seismic regions, this value forms the basis for calculating the forces that a structure must be designed to resist (seismic analysis).


A research to define seismic risk zone in Thailand

A research by Charusiri et al. (1998) has draw a seismic risk zone map. From the map, zone 0 which corresponds to no seismicity, and zones 1 to 3 corresponding to mild, intermediate and strong quake intensities, respectively. 

Last updated 11.09.2016


Charusiri et al. (1998),  Review of active faults and seismicity in Thailand,  Ninth Regional Congress on Geology, Mineral and Energy Resources of Southeast Asia - GEOSEA '98 

Q: What are the active seismic faults near to us?

A: Based on the known researches, totally 13 active seismic faults can be located in Thailand.

The ones that are closest to Bangkok is fault no.10 Srisawat faults, Kanjanaburi about 200 km away. The maximum quake recorded in 22 April 1983 is 5.9 Mb (Charusiri etal., 1998).


Charusiri et al. (1998),  Review of active faults and seismicity in Thailand,  Ninth Regional Congress on Geology, Mineral and Energy Resources of Southeast Asia - GEOSEA '98