Seismic Load Calculation.pdf

Reference Calculation Output

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

Ground type =(deposits of loose-to-medium cohesionless soil...)

Soil parameters:S =TB = sTC = sTD = s

Viscous damping ratio, ξ = %

Damping correction factor, η = √[ 10 / (5 + ξ) ]= √[ / ( + ) ]= but ≥=

Horizontal Elastic Response Spectrum is as defined and plotted below:

0 ≤ T ≤ TB : = ag S [ 1 + ( T / TB ) ( η 2.5 - 1 ) ]

TB ≤ T ≤ TC : = ag S η 2.5

TC ≤ T ≤ TD : = ag S η 2.5 ( TC / T )

TD ≤ T ≤ 4s : = ag S η 2.5 ( TC TD / T2 )

5

10 5 51.00 0.55

D

1.350.200.802.00

Se (t)

Se (t)

Se (t)

Se (t)

1.00

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.00 0.20 0.80 2.00 4.00

Elastic Response Spectrum, S e(t) (g)

Vibration Period, T (s)

Response Spectrum Curve

Elastic Spectrum

Design Spectrum

Se(t) = agSη2.5

(TD)(TC)(TB)

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Criteria for Regularity in Plan

For a building to be categorised as being regular in plan, it shallsatisfy all the conditions listed in the following paragraphs:

a. With respect to the lateral stiffness and mass distribution, thebuilding structure shall be approximately symmetrical in planwith respect to two orthogonal axes.

b. The plan configuration shall be compact, i.e., each floor shallbe 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 thesesetbacks do not affect the floor in-plan stiffness and that, foreach set-back, the area between the outline of the floor and aconvex polygonal line enveloping the floor does not exceed5% of the floor area.

c. The in-plan stiffness of the floors shall be sufficiently large incomparison with the lateral stiffness of the vertical structuralelements, so that the deformation of the floor shall have asmall effect on the distribution of the forces among the verticalstructural elements. In this respect, the L, C, H, I, and X planshapes should be carefully examined, notably as concerns thestiffness of the lateral branches, which should be comparableto that of the central part, in order to satisfy the rigiddiaphragm condition. The application of this paragraph shouldbe considered for the global behaviour of the building.

d. The slenderness λ = Lmax/Lmin of the building in plan shall benot higher than 4, where Lmax and Lmin are respectively thelarger and smaller in plan dimension of the building, measuredin orthogonal directions.

e. At each level and for each direction of analysis x and y, theeccentricity eo and the torsional radius r shall be in accordancewith the two conditions below, which are expressed for thedirection of analysis y:

eox ≤ 0,30 rx and rx ≥ ls where,

eox is the distance between the centre of stiffness and the centreof mass, measured along the x direction, which is normal to thedirection of analysis considered; rx is the square root of the ratioof the torsional stiffness to the lateral stiffness in the y direction(“torsional radius”); and ls is the radius of gyration of the floormass in plan (square root of the ratio of (a) the polar momentof 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

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Criteria for Regularity in Elevation

For a building to be categorised as being regular in elevation, itshall satisfy all the conditions listed in the following paragraphs:

a. All lateral load resisting systems, such as cores, structuralwalls, or frames, shall run without interruption from theirfoundations to the top of the building or, if setbacks atdifferent 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 abruptchanges, from the base to the top of a particular building.

c. In framed buildings the ratio of the actual storey resistance tothe resistance required by the analysis should not varydisproportionately 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 ≤ 4T C & 2s

6.0

0.1125

0.1125 1.350.15

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Ductility Class and Behaviour Factor - for Concrete Buildings

Ductility class = (Ductility Class Medium)

Behaviour factor, q = qo kw

Basic behaviour factor, qo = Refer Table B if regular in elevation (or)

Table C if non-regular in elevation

Wall factor, kw =(conservatively)

Frame system, dual system,

coupled wall system

a) Frame or frame-equivalent

dual system

- one-storey buildings

- multistorey, one-bay

frames

- multistory, multi-bay

frames

- frame-equivalent dual

structures

b) Wall or wall-equivalent dual

system

- wall-equivalent dual, or

coupled wall systems

Uncoupled wall system

- wall systems with only two

uncoupled wall per

horizontal direction

- other uncoupled wall

systems

Torsionally flexible system

Inverted pendulum system

- 3.00 - 3.00

1.20

1.30 5.85 1.15 5.18

1.30 5.85 1.15 5.18

1.00 4.00 1.00 4.00

1.20 5.40 1.10 4.95

- 4.0αu/α1

- 2.00 - 2.00

1.10 4.40 1.05 4.20

1.10 4.95 1.05 4.73

5.40 1.10 4.95

- 4.0αu/α1

- 2.00

- 1.50

DCM

3.15

- 3.00 - 3.00

1.20 3.60 1.10 3.30

- 3αu/α1 - 3αu/α1

αu/α1

1.20 3.60

- 3.00

- -

1.10

- 4.5αu/α1 - 4.5αu/α1

DCH

Regular Non-regularStructural Type

Table B: Basic value of behaviour factor, qo, for systems REGULAR in elevation

in plan in plan

αu/α1 qo αu/α1 qo

3.30

1.30 3.90 1.15 3.45

1.30 3.90 1.15 3.45

7.0

DCM

1.10

αu/α1 qo

3.30

Regular

in plan

Non-regular

in plan

qo

1.05

1.0

2.00

1.50

-

-

-

-

- 3.00

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Frame system, dual system,

coupled wall system

a) Frame or frame-equivalent

dual system

- one-storey buildings

- multistorey, one-bay

frames

- multistory, multi-bay

frames

- frame-equivalent dual

structures

b) Wall or wall-equivalent dual

system

- wall-equivalent dual, or

coupled wall systems

Uncoupled wall system

- wall systems with only two

uncoupled wall per

horizontal direction

- other uncoupled wall

systems

Torsionally flexible system

Inverted pendulum system

- 2.40 - 2.40

- 1.20 - 1.20 - 1.60 - 1.60

Note: Shaded area denotes applicable q ̥ values

- 1.60 - 1.60

- 3.20

- 2.40 - 2.40 - 3.52 - 3.36

- 2.40 - 2.40 - 3.20

- 2.88 - 2.64 - 4.32 - 3.96

- 3.12 - 2.76 - 4.68 - 4.14

- 2.88 - 2.64 - 4.32 - 3.96

- 2.76 - 4.68 - 4.14

- 2.52 - 3.96 - 3.78

Table C: Basic value of behaviour factor, qo, for systems NON-REGULAR in elevation

Structural Type

DCM DCH

Regular Non-regular Regular Non-regular

in plan in plan in plan in plan

αu/α1 qo αu/α1 qo qoαu/α1 qo αu/α1

- 2.64

- 3.12

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Seismic Load Calculation.pdf