Seismic Load Computation

Seismic Load Calculations Group 6 This is basically a tutorial guide for students/aspirin students/aspiring g engineers for computing the seismic loadings of a certain structure.

Submitted by: JAZMIN, Allan Carlo LIM, Mark Hil MACAPAGAL, Dax Ulysses MAGISTRADO, John Paulo MOLINA, Jermaine VILLEGAS, Ralph Don

S. G. C. B. M. B.

Submitted to: Engr. Jonas Quero 8/1/2017

Seismic load computation As stated in the National Structural Code of the Philippines 208.5.2 “Static Force

Procedure”, the total base shear of the structure is determined using the following equation:

The total base shear should not exceed equation for the maximum total base shear which is:

The total design base shear should not be less than to the equation for minimum total base shear which is:

For seismic zone 4, the total base shear should not be less than the equation:

To solve the value of the total base shear (V), all the required variables for the equations should be determined.

Step 1 (Zone Factor, Z) As stated in the national structural code of the Philippines 208.4.4.1, the Philippine archipelago is divided into two seismic zones. The zone 2 covers only the provinces of Palawan, Sulu, and Tawi-tawi while the rest of the country is under seismic zone 4 (Figure 1). Each structure shall be assigned as seismic zone factor Z in accordance with Table 208-3.

Source: National Structural Code of the Philippines 2010

Figure 1. Seismic Zones of the Philippines


Step 2 (Importance Factor, I) The importance factor is based on the Occupancy Category. It is utilized in calculating flood, wind, snow, seismic, and ice design loads. The importance factor is a multiplier that increases or decreases the base design loads. For importance factor, base to the table 208-1 and determine the occupancy category.


Step 3 (Ductility Capacity Coefficient or Response Modification Coefficient, R) The response modification coefficient results from simplifying the seismic design process so that linear elastic, static analysis can be used for building designs. It is known from experience that structures can withstand large amplitude of forces, without excessive strength deterioration, than they were designed for through inelastic strength behaviour. To obtain this coefficient, refer to the table 208-11A.


Step 4 (Soil Profile Type) Soil Profile is determined as a vertical section of soil that is exposed by a hole that is dug from the surface of the soil to the underlying bedrock. There are six different soil profile types as seen in the NSCP. The soil profile type depends on the location of the structure. Refer to Table 208-2 for determine the soil profile types.


Step 5 (Seismic Coefficient, Ca and Cv) The seismic coefficients are dimensionless coefficients which represent the maximum earthquake acceleration as a fraction of the acceleration due to gravity. Those coefficients are determined in tables 208-7 and 208-8 using the given soil profile type.


Step 6 (Near Source Factors, Na and Nv) The near source factor is used as a multiplier to the seismic coefficient. It is used to determine the seismic coefficient related to both proximity of the building or structure to known faults with magnitude as set forth in tables 208-4, 208-5 and 208-6.


Step 7 (Elastic Fundamental Period of Vibrations, T) Elastic fundamental period of vibration is used to determine the design base shear as well as the exponent k that establishes the distribution of the shear along the height of the structure. To compute for the value of the elastic fundamental period of vibration of the structure in the direction under consideration, the formula stated in 208.5.2.2 method A is to be used:

where;  = 0.0853

for steel moment-resisting frames;

 = 0.0731

for reinforced concrete moment-resisting frames and eccentrically braced frames;

 = 0.0488 for all

other buildings and;

ℎ = the total height of the building

Step 8 (Total Seismic Dead Load, W) Refer to the provision 208.5.1.1 and 208.5.2.1 of National Structural Code of the Philippines 2010 to determine all the types of of load to be included for the total seismic dead load.

Step 9 (Seismic Load Distribution) To distribute the base shear to each floor of t he building, it must be multiplied to the ratio of the certain weight (W) and height (h) of the floor from the ground divided to the summation of all weights and heights of each floor as should in the formula:

Seismic Load Computation

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