Situación de guarda del menor por un tercero

This Indian standard (part 1)(Fifth revision) was adopted by the Bureau of Indian standards, after the draft finalized by the Earthquake Engineering Sectional Committee had been approved by the civil Engineering Division council.

IS-1893-2002 has 5 parts

Part 1: General provisions and buildings

Part II: Liquid retaining tanks-elevated and ground supported Part III: Bridges and retaining walls

Part IV: Industrial structures including stack like structures Part V: Dams and embankments.

Our scope of the discussion is about the part-1 only

The following are the major and important modifications made in the fifth revision.. a) The seismic zone map is revised with only four zones, instead of five, zone I has

been merged to zone II

b) The factor s of seismic zone factors have been changed; these now reflect more realistic values of effective peak ground acceleration considering maximum considered earthquake and service life of structure in each zone.

c) Response spectra are now specified for three types of founding strata namely rock and hard soil, medium soil, soft soil.

d) Empirical expression for estimating the fundamental natural period Ta of multistoried buildings with regular moment resisting has been revised.

Ta=0.07h0.75 _{for RCC buildings}

=0.085h0.75 _{for steel buildings}

e) The concept of response reduction due to ductile deformation, or frictional energy dissipation in the cracks is brought in to the code explicitly by introducing the response reductions factor in place of the earlier performance factor.

f) Lower bound is specified for the design base shear of buildings based on empirical estimate of the fundamental natural period Ta.

g) The soil foundation factor is dropped instead a clause introduced to restrict the one of foundation vulnerable to differential settlements in severe seismic zone. h) Tensional eccentricity values have been revised upwards in a view of serious

damages observed in building with irregular plan.

i) Modal combination rule in dynamic analysis of building has been revised.

j) Other clauses have been redrafted where necessary for more effective implementation.

This standard (part 1) deals with the assessment of seismic loads on various structures and earthquake resistant design of buildings. Its basic provisions are applicable to buildings; elevated structures; bridges concrete masonry and earth dams; embankments and retaining wall and other structures

General principles and design criteria is given by the clause 6 of page 12 of the code 1893

6.1.1 Ground motion: The characteristics (intensity duration, etc) of seismic ground vibrations expected at any location depends upon the magnitude of earthquake, its depth of focus, distance from epicenter, characteristics of the path through which the waves travel, and the soil strata on which cause the structure to vibrate, can be resolved in any three mutually perpendicular directions.

Earthquake –generated vertical inertia forces are to be considered in design unless checked and proven by specimen calculations to be significant. Vertical acceleration should be considered in structures with large spans, those in which stability is a criterion for design, or for over all stability analysis of the structures.

6.1.2 The response of the structures to ground vibrations is a function of the nature of foundation soil; materials form size and mode of construction of structures and the durations and the characteristics of ground motion. This standard specifies design forces for structures standing on rocks soils, which do not settle, liquefy or slide due to loss of strength during ground vibrations. 6.1.3 The design approaches adopted in this standard is to ensure that the

structure posses at least a maximum strength

1. To with stand minor earthquakes which occur frequently, with out damage; 2. To resist moderate earthquake without significant structural damage though

some non structural damage may occur; and

3. Aim that structures withstand major earthquakes without collapse of the structures

6.1.4 Soil structure interaction: The soil-structure interaction refers to the effects of the supporting foundation medium on the motion of structure. The soil

structures interaction may not be considered in the seismic analysis for the structures supported on rock or rock -like material.

6.1.5 The design lateral force specified in this standard shall be considered in each of the two orthogonal horizontal directions of the structures.

6.1.7 Addition to existing structure: Addition shall be made to existing structures only as follows

An addition that is structurally independent from existing structures shall be designed and constructed in accordance with the seismic requirement for new structures.

6.1.8 Change in occupancy: When a change of occupancy results in a structure is being reclassified to a higher importance factor (I) , the structure shall confirm to the seismic requirement for a new with the higher importance factor

6.3. Load combinations: Load combination and increase in permissible stresses are

6.3.1.1 Load factors for plastic design of steel structures the following load combination can be accounted for

1) 1.7(DL+LL) 2) 1.7(DL+EL) 3) 1.3(DL+LL+EL)

6.3.1.2 Partial safety factors for limit state design of prestressed concrete and RCC structures

1) 1.5(DL+LL) 2) 1.2(DL+LL+EL) 3) 1.5(DL+EL) 4) 0.9DL+1.5EL

6.3.5 INCREASE IN PERMISSIBLE STRESSES

6.3.5.1 Increase in permissible stresses in materials: When earthquake forces are considered along with other normal design forces, the permissible stresses in material, in the elastic method of design, may be increased by one-third.

6.3.5.2 Allowable pressure in soils is given in table 1 of IS code 1893 6.4 Design spectrum: For the purpose of determining seismic forces the country is classified into four Zones

The design horizontal seismic coefficient Ah for the structure shall be determined from the following:

Ah=(Z/2) x (I/R) x (Sa/g)

7.5.3 Design base shear: The total design lateral force or design seismic base shear (Vb) along any principal direction shall be determined from the following expression

Vb = Ah x W

7.8 Dynamic analysis: Dynamic analysis shall be performed to obtain the design seismic force, and its distribution to different levels along the height of the building and to the various lateral load-resisting elements, for the following buildings:

a) Regular buildings: Those greater than 40m in height in zones IV and V, and those greater than 90m in height in zone II and III.

b) Irregular buildings: All framed buildings higher than 12m in zone IV and V, and those greater than 40m in height in zones II and III.

7.8.2 the dynamic analysis can be carried out in the following methods

7.8.3 Time history method: Time history method of analysis, when used, shall be based on an appropriate ground motion and shall be performed using accepted principles of dynamics.

7.8.4 Response spectrum method: Response spectrum method of analysis shall be performed using the design spectrum or by site- specific design spectrum.

7.8.4.1 Free vibration analysis: Undamped Free vibration analysis of the entire building shall be performed as per established methods of mechanics using the appropriate masses and elastic stiffness of the structural systems, to obtain natural periods (T) and mode shapes (φ) of those of its modes of vibration that need to be considered.

IS4326 – 1993 – E.Q. Resistant design and construction of