PROCEDURES FOR SEISMIC DESIGN FORCE

Equivalent Lateral Force (ELF) has been widely used due to both simplicity and efficiency. The National Structural Code of the Philippines (NSCP) uses ELF in the design of structures.

Under this method, three categories are followed referring to the structure configuration (208.4.8)



1. Simplified Static

Simplified static procedure is used for structures under Occupancy Categories IV and V. (208.4.8.1)

• Category IV.  Standard Occupancy Structures. All structures for housing occupancies  or having other functions not listed in Categories I, II, III, or V.
• Category V. Private garages, carports, sheds and fences of height over 1.5m.

2. Static

This procedure is used for the following structure configuration (208.4.8.2):

1. Structures, regular or irregular, located under Seismic Zone 2 and under Occupancy Categories IV and V.
2. Regular structures under Occupancy Categories I, II, III, rising under 75m and with specified force resisting frame systems.
3. Irregular structures NOT more than 20 meters (approx 5 stories) in height.
4. Structures with flexible upper portion but rigid lower portion.

3. Dynamic

The dynamic procedure of lateral force method is used for all other structures not falling under any between simplified static and static procedures (208.4.8.3).

1. Regular structures which are high rise, that is, more than 75m in height.
2. Structures having irregularity on stiffness, weight or geometric vertical configuration.
3. Irregular structures over 20 meters in height (five stories), or located in Seismic Zone 4.
4. Regular or irregular structures located on Soil Profile 
, which carries a period greater than 0.70s.