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Eng.Salam Hatem eng.salamhatem@gmail.com

Earthquake loads:Definition of earthquake loads in ETABS according to UBC1997 Code ( The same method used by the Jordanian Code).1- Define the earthquake load as a static load case in both x & y directions as follow

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2- Modify Lateral Load

-Direction and eccentricity :

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-Direction and eccentricity :

• Choose to specify the X or Y direction of the seismic loading, or to specify

the direction with a percentage of eccentricity that is applicable to all

diaphragms.

• Use the % Eccentricity edit box to specify a value for eccentricity. Five

percent is the default and is entered as 0.05.

The eccentricity options have meaning only when diaphragms have been

assigned to joints or area objects. The program ignores eccentricities where

diaphragms are not present.

Where diaphragms are present, the program calculates a maximum width of

the diaphragm perpendicular to the direction of the seismic loading. This

width is calculated by finding the maximum and minimum X or Y coordinates

(depending on direction of load considered) of the points that are part of the

diaphragm constraint and determining the distance between these maximum

and minimum values.

After the appropriate diaphragm width has been determined, the program

applies a moment that is equal to the specified percent eccentricity times the

maximum width of the diaphragm perpendicular to the direction of the

seismic loading times the total lateral force applied to the diaphragm. This

moment is applied about the diaphragm center of mass to account for the

eccentricity.

-Seismic Coefficient:

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-Seismic Coefficient

•Soil profile type :

Soil Profile Types SA, SB, SC, SD and SE are defined in Table

below and Soil Profile Type SF is defined as soils requiring site-

specific evaluation.

-Seismic Coefficient

•Seismic Zone :

- Each site shall be

assigned a seismic zone

according to the

following map.

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-Seismic Coefficient

•Seismic Zone Factor:

- Then the Seismic zone factor (Z) assigned for the Structure.

Seismic response coefficients

Each structure shall be assigned a seismic coefficient, Ca, in

accordance with Table 16-Q and a seismic coefficient, Cv, in

accordance with Table 16-R..

-Seismic Coefficient

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-Time Period

The time an object takes to vibrate back and forth one complete cycle .

-Time Period

1. Method A:

For all buildings, the value T may be approximated from the

following formula:

T Ct (hn)3/4

Where:

Ct = 0.035 for steel moment-resisting frames.

Ct = 0.030 for reinforced concrete moment-resisting frames and

eccentrically braced frames.

Ct = 0.020 for all other buildings.

hn = height in (m) above the base to Level n.

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-Story Range

Story Range Choose the Top Story and Bottom Story to specify the

elevation range over which the automatic static lateral loads are to

be calculated. By default the bottom story is the base of the building

and the top story is the uppermost level of the building.

The bottom level would typically be the base level. However, if, for

example, a building has several below-grade levels, and the seismic

loads are assumed to be transferred to the ground at ground level, it

may be best to specify the bottom story to be above the base of the

building.

Note: No seismic loads are calculated for the bottom story. They are

calculated for the first story above the bottom story and for all stories

up to and including the top story.

-Near Source Factor

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-Near Source Factor

Na = near-source factor used in the determination of Ca in Seismic

Zone 4

Nv = near-source factor used in the determination of Cv in Seismic

Zone 4

-Over strength factor (R)

OVERSTRENGTH is a characteristic of structures where the

actual strength is larger than the design strength. The degree of

overstrength is material- and system-dependent.

R = numerical coefficient representative of the inherent over strength

and global ductility capacity of lateral force-resisting systems, as set

forth in Table 16-N or

16-P.

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-Structural Systems:

Structural systems shall be classified as one of the types listed in

Table 16-N .

• Bearing wall system. A structural system without a

complete vertical load-carrying space frame. Bearing walls or

bracing systems provide support for all or most gravity loads.

Resistance to lateral load is provided by shear walls or braced

frames.

• Building frame system. A structural system with an

essentially complete space frame providing support for gravity

loads. Resistance to lateral load is provided by shear walls or

braced frames.

• Moment-resisting frame system. A structural system

with an essentially complete space frame providing support for

gravity loads. Moment-resisting frames provide resistance to lateral

load primarily by flexural action of members.

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-Structural Systems:

•Dual system. A structural system with the following

features:

1. An essentially complete space frame that provides support

for gravity loads.

2. Resistance to lateral load is provided by shear walls or braced

frames and moment-resisting frames (SMRF, IMRF, MMRWF or

steel OMRF). The moment-resisting frames shall be designed to

independently resist at least 25 percent of the design base shear.

3. The two systems shall be designed to resist the total design

base shear in proportion to their relative rigidities considering the

interaction of the dual system at all levels.

.

-Importance Factor (I)

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-Base Shear (V)

The total design lateral force or shear at the base of a structure.

Shall be determined from the following formula :

The total design base shear need not exceed the following :

The total design base shear shall not be less than the following:

-Special seismic load combinations.The purpose of the special load combinations is to protect the gravity

load-carrying system against possible overloads caused by overstrength

of the lateral-force-resisting system. Either columns or beams may be

subject to such failure.

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-Rho Reliability/Redundancy:The value of this factor is either 1.0 or 1.5. This factor has an effect of

reducing the R factor for less redundant structures thereby increasing the

seismic demand.

When calculating drift, or when the structure is located in Seismic

Zone 0, 1 or 2, r shall be taken equal to 1.

-IBC2000 Seismic Design Category :

Omega Factor Ω:For specific elements of the structure, as specifically identified in this

code, the minimum design strength shall be the product of the seismic

force overstrength factor Ω and the design seismic forces.

Ω shall be taken from table 16-N .

-Dl Multiplier :the load effect resulting from the vertical component of

the earthquake ground motion and is equal to an addition

of 0.5CaID to the dead load effect, D.