Seismic Loads

7/30/2019 Seismic Loads

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DETERMINATION OF LATERAL FORCES

1. Seismic Zone Factor (Z)Estimate of the applicable site dependent effective peak

ground acceleration expressed as a function of the gravityconstant.

2. Ground Response Coefficients Ca & Cv


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Parameters which reflect the potential amplification of theground vibration caused by different soil types.

3. Soil Profile Types, SA to SF


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4. Near Source Factors , Na & Nv


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5. Response Modification Factor, RA measure of the ability of the structural system to absorbenergy and sustain cyclic inelastic deformations withoutcollapse.


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6. Importance Factors, I

Importance of the structural element based on its occupancy


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7. Seismic Dead Load, W

The total dead load of the structure and that part of the

service load which may be expected to be attached to thebuilding, which consists of:

Twenty five percent of the floor live load for

storage and warehouse occupancies.

A minimum allowance of 0.50 kN/m2 for movable

partitions.


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The total weight of permanent equipment and

fittings.

Roof and floor live loads, except as noted above, are not

included in the value ofWas they are considered negligibleby comparison with the dead loads. In designing floormembers for gravity loads, the loading intensity for movablepartition is 1.0 kN/m2. This value allows for localconcentration of the partition, while the overall averagevalue of 0.50 kN/m2 is adopted for seismic loads. Forpermanent walls which are constructed of heavier materials,the actual weight of the walls shall be used.

8. Fundamental Period, TThe fundamental period of vibration of each structure, whichis the time required for one cycle of free vibration. The valuemay vary from 0.1 seconds for a single storey building toseveral seconds for a multi-storey building.

T = Ct(hn)3/4

Where:

hn = height in meter of the roof above the base,not including the height of penthouseparapets.

Ct= 0.0853 for steel moment-resisting frames.= 0.0731 for reinforced concrete moment-

resisting frames (the structure type of thiscase)

= 0.0488 for all other buildings.

9. Total Seismic Dead Load, W


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Superimposed Dead Load (Aside from the selfweightof assigned sections)

Weight of concrete = 23.6 kN/m3

TYPICAL FLOORSlab (100 mm thick) 2.36 kPaFloor Finish (40mm thick) 0.94 kPaMovable Partition 0.50 kPaCeiling (sus. Channel+accstc board) 0.15 kPaEE/ME/Plumbing Utilities 0.10 kPa

------------------------------------------TOTAL 5.05 kPa on floor area

CHB Walls (2 faces plastered)150 mm CHB exterior walls 3.30 kPa100 mm CHB interior walls 2.44 kPa

ROOF DECKSlab (100 mm thick) 2.36 kPaFloor Finish (40mm thick) 0.94 kPaCeiling (sus. Channel+accstc board) 0.15 kPa

EE/ME/Plumbing Utilities 0.10 kPa

------------------------------------------TOTAL 3.55 kPa on floor area

CHB Walls (2 faces plastered)100 mm CHB parapet walls 2.44 kPa

10. LOAD COMBINATIONS

Factored Loads


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The required strength U shall be at least equal to theeffects of the factored loads listed below. The effect ofone or more loads not acting simultaneously shall beinvestigated.

U = 1.4 ( D + F )U = 1.2 (D + F + T) + 1.6 ( L + H ) + 0.5 ( L or R )U = 1.2D + 1.6 ( L or R ) + ( 1.0 L or 0.8 W )U = 1.2D + 1.6 W + 1.0 L + 0.5 ( L or R )U = 1.2D + 1.0 Ex + 1.0 LU = 1.2D + 1.0 Ez+ 1.0 LU = 0.9 D + 1.6 W + 1.6 HU = 0.9 D + 1.0 Ex + 1.6 HU = 0.9 D + 1.0 Ez + 1.6 H

Unfactored Loads

U = D + LU = D + (0.75 L )

U = D + ( 0.7183 EX )U = D + ( 0.7183 EZ )

Where:U = required strength

D = Dead LoadsF = Loads due to weight and pressure of fluids

T = cumulative effects of temperature, creep,shrinkage

L = Live loadsH = Loads due to weight and pressure of soilR = Rain loadW = Wind loadEx = Seismic along x-axisEz = Seismic along z-axis

11. LOCAL COORDINATE SYSTEM (STAADEnvironment)


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A local coordinate system is associated with eachmember. Each axis of the orthogonal coordinate systemis also based on the right hand rule.

12. MEMBER END FORCES


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16.17.

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Seismic Loads