Dynamic Analysis of Blast Resistant Buildings

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Dynamic Method of Blast Analysis in Petrochemical Facilities and Study of IS 4991:1968.

Dr. Sidramappa V. Itti 1, Shishir S. Kadam 2

1 Head of Department, K.L.E. College of Engineering and Technology, Belgaum, India.

2 M.Tech (Structural Engg) Graduate, K.L.E. College of Engineering and Technology, Belgaum, India.

Email: ittisv@gmail.com 1, shishir.kadam@gmail.com 2

Abstract

Process plants in the petrochemical industries handle hydrocarbons and other fuels which may produce accidental explosion. Plants are designed to minimize the occurrence of such incidents. In today’s scenario the focus is on structural aspects of design or evaluation of buildings for blast resistance, establishing the design blast loads from overpressure, setting the structural performance requirements and designing the buildings and structures to withstand these loads within the required performance limits. This paper presents discussions on dynamic approach of design and analysis of a structure in petrochemical facilities, with numerical simulation study aiming to characterize the various structural effects of vapor cloud explosion. Numerical time integration method is used for caring out the analysis, where in an program has been written in MS EXCEL to carry out the incremental solution by solving the dynamic equilibrium equation for the displacement at each time step and results of previous time steps and the current time step are used with recurrence formulas to predict the acceleration and velocity at the current time step. A R.C.C. box structure is designed and analyzed by dynamic and static approach for various response ranges. Results show that dynamic analysis gives more economical and safer designs compared to other methods of analysis. Based on the understanding of results, a study on IS 4991:1968 is carried out and suitable suggestions have been given for its revision, by implementing new theories and research carried out in and around the world.

Keyword: Blast analysis; Petrochemical facilities; Vapor cloud explosion; Dynamic analysis; Static analysis; Blast overpressure; Numerical Integration; Equivalent static blast overpressure.

1. Vapor Cloud Explosion

The most destructive and dangerous explosions in chemical process industries are vapor cloud explosion (VCE). Typically this occurs when there is release of a flammable material at suitable conditions of pressure and temperature. These include liquefied gases under pressure, ordinary flammable liquids (especially at elevated pressure and/or temperatures), and flammable gases. When a flammable liquid spills, some or all of it will vaporize and form an aerosol. This dispersion is called vapor cloud. The explosion caused due to the ignition of vapor cloud is a primarily concern in petrochemical industry because there are no codes or industry standards for determining what blast overpressure should be used, the design blast loads are usually supplied by the facility owner, considering the wide variety of processes. The hazard levels are based on the material handled and the process used.

I. Dynamic Analysis

2. Blast Loading

For blast resistant, the most significant feature of explosion is the sudden release of energy to the atmosphere which results in a pressure transient, or blast wave. The blast wave propagates in a supersonic speed, the magnitude and shape of the blast wave depends on the nature of the energy release and on the distance from the explosion epicenter.

The two phase of blast waves are:

a. Shock Wave: This is a sudden, almost instantaneous rise in pressure above ambient atmospheric condition to a peak free field overpressure (Figure 1.a)

b. Pressure Wave: This has a gradual pressure rise to the peak side-on overpressure followed by a gradual pressure decay (Figure 1.b)

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