Different types of Load assessment during Earthquake Resistant (Seismic) design of the structure!!

Different types of load are to be assessed and studied during design and analysis of the earthquake resistant building or structure. Load assessment is a very important aspect of design and analysis of any structures. Some of important loads are explained below:

Dead load

The correct assessment and calculation of dead loads is the most important step. This can be done precisely if the architectural drawings are complete and include the roof, ceiling, floor, wall finishes, parapet and railings, overhead water storage tanks placed on the roof, position thickness and specifications of fixed partitions, etc.

The correct thickness/size of the structural member (i.e. slab, beams, and columns) cannot be ascertained before the structural analysis and design are finalized. Thus, some sizes need to be assigned by experience and architectural considerations to begin with, checked and modified during preliminary design, and finalized during analysis and checking.

Live load

These are to be chosen from codes as IS: 875(part 2) for various occupancies where required. These codes permit certain modifications in the load intensities where large contributory areas are involved, or when the building consists of many stories. For economy in design, such reductions should be utilized. Lateral and vertical loads on parapets and railings, and higher loads intensities on entrance halls, stairs, must be considered. It will be useful to mark the design load classes or intensities on a small- scale.

Wind load

Wind pressure occurs on all exposed surfaces and acts normal to the surface. The intensities of the pressure specified by the coefficient of wind pressure Cp in Is 875(part 3) depends on a large number of a parameter such as the direction of the wind relative to the axes of the building, its shape in plan and elevation, and size of exposed individual elements. The terrain and building height, the topography, etc IS 875(Part 3) is an attempt to codify the wind-tunnel experimental results by considering the various parameters. It gives a very exhaustive treatment and thus may appear complex for simple application to the building of usual shape and size.

Earthquake load

This load on a the structure is a function of the site dependent probable maximum earthquake intensity or string ground- motion and the local soil, the stiffness, and its orientation in relation to the incident seismic waves. For designing purpose, the resultant effects are usually represented by the horizontal and vertical seismic coefficient αh, αv. Alternatively, a dynamics analysis of the building is required under the action of the specified ground motion or design response spectra. Since the probable maximum earthquake occurrences are not so frequent, designing a building for such earthquake so as to ensure that they remain elastic and damage- free is not considered economically prudent. Instead, reliance is placed on kinetic energy dissipation in the structure through plastic deformation of elements and joints. Thus, the philosophy of seismic design is to obtain no collapse of the structure rather than no damage to the structure. This is a sound economic proposition for only the poor developing countries, but even for the developed one as well. To achieve a greater degree of protection, the critical and important buildings are designed for higher seismic factors by using an important factor I, (IS: 1893-3.4.2.3, table 4). Also, the effect of local soils and the type of different structural systems have shown varied behavior during past earthquakes, a performance factor k is also introduced (IS: 1893-4.2.1.1, table 5)

Thus, there is a lot of a possible variation on specifying the design seismic values for building in various seismic countries of the world have to make a choice depending on her economic the situation, skills in design, and their construction practice.

Earthquake causes impulsive ground motion, which is complex and irregular in character, changing in period and amplitude each, lasting for a small duration, horizontal components of the ground motion are generally more intense than vertical. The ground motion is random in nature. A qualitative schematization of earthquake effects is divided into different zones indicating the intensity of damage or frequency of earthquake occurrence. Suitable seismic coefficients were assigned based on an engineering judgment of the likely intensity in each zone and variation of these coefficients according to the ground condition. Through a reasonable estimate of the portable maximum is unit of the tectonic.