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Reference Calculation Output

Name Date

Prepared by

Checked by

Approved by

Seismic Load Design Calculation per BS EN 1998-1 & 1998-6

Criteria for Regularity in Plan

For a building to be categorised as being regular in plan, it shall

satisfy all the conditions listed in the following paragraphs:

a. With respect to the lateral stiffness and mass distribution, the

building structure shall be approximately symmetrical in plan

with respect to two orthogonal axes.

b. The plan configuration shall be compact, i.e., each floor shall

be delimited by a polygonal convex line. If in plan set-backs

(re-entrant corners or edge recesses) exist, regularity in planmay still be considered as being satisfied, provided that these

setbacks do not affect the floor in-plan stiffness and that, for

each set-back, the area between the outline of the floor and a

convex polygonal line enveloping the floor does not exceed

5% of the floor area.

c. The in-plan stiffness of the floors shall be sufficiently large in

comparison with the lateral stiffness of the vertical structural

elements, so that the deformation of the floor shall have a

small effect on the distribution of the forces among the vertical

structural elements. In this respect, the L, C, H, I, and X plan

shapes should be carefully examined, notably as concerns thestiffness of the lateral branches, which should be comparable

to that of the central part, in order to satisfy the rigid

diaphragm condition. The application of this paragraph should

be considered for the global behaviour of the building.

d. The slenderness = Lmax/Lmin of the building in plan shall be

not higher than 4, where Lmax and Lmin are respectively the

larger and smaller in plan dimension of the building, measured

in orthogonal directions.

e. At each level and for each direction of analysis x and y, the

eccentricity eo and the torsional radius r shall be in accordancewith the two conditions below, which are expressed for the

direction of analysis y:

eox 0,30 rx and r x ls where,

eox is the distance between the centre of stiffness and the centre

of mass, measured along the x direction, which is normal to the

direction of analysis considered; rx is the square root of the ratio

of the torsional stiffness to the lateral stiffness in the y direction

(torsional radius); and ls is the radius of gyration of the floor

mass in plan (square root of the ratio of (a) the polar moment

of inertia of the floor mass in plan with respect to the centre ofmass of the floor to (b) the floor mass).

Hence, building is categorised as regular in plan.

Yes

Yes

Yes

Yes

Yes

3.0

compliance

Regularity

Seismic Page 3 of 17

7/29/2019 Seismic Load.pdf

2/2

Reference Calculation Output

Name Date

Prepared by

Checked by

Approved by

Seismic Load Design Calculation per BS EN 1998-1 & 1998-6

Criteria for Regularity in Elevation

For a building to be categorised as being regular in elevation, it

shall satisfy all the conditions listed in the following paragraphs:

a. All lateral load resisting systems, such as cores, structural

walls, or frames, shall run without interruption from their

foundations to the top of the building or, if setbacks at

different heights are present, to the top of the relevant zone of

the building.

b. Both the lateral stiffness and the mass of the individual storeysshall remain constant or reduce gradually, without abrupt

changes, from the base to the top of a particular building.

c. In framed buildings the ratio of the actual storey resistance to

the resistance required by the analysis should not vary

disproportionately between adjacent storeys.

Hence, building is categorised as non-regular in elevation.

Criteria for Structural Regularity

Yes Yes Planar Lateral force **

Yes No Planar Modal

No Yes Spatial Lateral force **

No No Spatial Modal

Category of Seismicity

ag = g

ag S = x

= g

If ag 0.04g (or) agS 0.05g, the site is categorised as 'very low seismicity'. NO

If ag 0.08g (or) agS 0.10g, the site is categorised as 'low seismicity'. NO

If ag > 0.08g (and) agS > 0.10g, the site is categorised as 'high seismicity'. YES

In this case, the site falls under 'high seismicity' category.

4.0

compliance

Regularity

Yes

Yes

No

Min.

appli-

cabi-

lity

5.0

Regularity

Method of Analysis

(Linear-elastic analysis)

Allowed Simplification

ModelElevationPlan

Behaviour Factor

(for linear analysis)

Table A: Recommended Structural Analysis Approach

Reference value

Reference value

Decreased value *

Decreased value *

Note: * basic behaviour factor, q o shall be reduced by 20% (see Table C for reduced value)

** applicable only if natural period, T1 4TC & 2s

6.0

0.1125

0.1125 1.35

0.15

Seismic Page 4 of 17