EVALUATING THE EFFECT OF UNEDRGROUND EXPLOSIONS ON

STRUCTURES

Submitted by U.V.Tejaswi(138WID8717)Under the guidance of sri V.Ramesh

ABSTRACT

• Underground explosions are caused by the detonation of explosive materials below the ground surface. These are due to civil engineering applications like rock excavation and also due to some accidental explosions.

• This project is to study the ground motion characteristics due to underground explosion and its influence on structures i.e. dynamic behaviour of structures.

• Effect of charge wt and depth of the explosions on structures will study by varying the charge wt and depth of the explosions. The soil below the ground is taken as sandy soil.

• Modelling of underground blast simulation will done by using the autodyn.

 

INTRODUCTION

• . An explosion is defined as a large-scale, rapid and sudden release of energy. Explosions can be categorized on the basis of their nature as physical, nuclear or chemical events.

• A number of important structures have been targeted by the terrorist attacks through the use of significant amount of explosives during the fast years. So these situations are lead to the blast resistant designs.

• The main parameters in underground explosions are ground motions. ground shock results from the energy imparted to the ground by the explosion.

• Blast induced ground vibrations are mostly depends on amount and the type of explosive used and sight distance.

• The most important parameters for explosion ground motion that affect structural response are its intensity and frequency content.

• The blast ground motion intensity is often measured by its PPV, where as the frequency content can be measured by the PF.

• The underground blast simulations are attenuates rapidly through the medium from charge centre.

• And it takes very short interval of time to reach the given point

LITERATURE REVIEW

(1) Chongqing Wu*, Hong Hao “Numerical study of characteristics of underground blast induced surface ground motion and their effect on above-ground structures. Part I. Ground motion characteristics”

• concluded as Ground motion attenuates rapidly when it propagate away from the charge centre. Surface ground motion has the large amplitude compare with free field at the some distance owing to surface reflection. The surface of PF has smaller frequency to the large charge loading at the same scaled distance

(2)Hong hao, changing wu* “Numerical study of characteristics of underground blast induced surface ground motion and their effect on above-ground structures. Part II. Effects on structural responses”

• This paper studies the response and damage characteristics of RC frame structures. It is found that structural responses are dominated by low frequency global vibration modes if ground motion frequency is low, and by first local elemental vibration mode if ground motion frequency is high.

(3) Chengqing wua,*, hong haoa , yong lu b , shangqing sun b “ Numerical

simulation of structural response on a sand layer to blast induced ground excitations” It s concluded as sand is a good base material for reducing the structural response & damage to blast induced ground motion.

• The response at all the targets on structures in terms of PV, PA, PD as well as the maximum equivalent strains decreases considerably with the placement of sand layer below the structure for both high frequency & lower frequency simulations.

 (4)H.J. Ma⃰ , S.T. Quek, K.K. Ang “ Soil–structure interaction effect from blast-induced horizontal and vertical ground vibration”  

• Under most circumstances but not always SSI reduces the structural response. Most of the time the soil act as low pass filter and effects the horizontal & vertical displacements.The base mass provides provides inertia against the input excitation. Bcz of this , the top horizontal displacement and base shear response decreases with increasing of base mass.

(5) Hong Haoa,*, Yaokun Wua, Guowei Maa, Yingxin Zhou “Characteristics of surface ground motions induced by blasts in jointed rock mass

• In this Accelerometers were placed along three lines at 00, 450 and 900 to the predominant rock joint strike direction, on rock surface. And concluded as The stress wav e attenuates slowest if it propagates in the direction parallel to the rock joint . set & attenuates fastest if it propagates in the direction perpendicular to rock joint set.

(6) Onur dogan a , zg anil b ,* ,sami o. “ Evaluation of blast induced groun vibration effects in new residential zone”

The measured PPV values for underground blasts are 47-95% smaller than those measured for surface blasts for a given site. Similarly the dominant frequencies are reduced by 37-78% for underground blasting operations compare to surface blasts. More then half of the frequencies lie in the interval of 10-15 Hz for under ground blasts. For surface blasts the frequency distribution is clustered in the range of 20- 30 Hz & 55-70 Hz

(7) Chongqing Waa, , Hong Haoa, Yong Lub “∗ Dynamic response and damage analysis of masonry structures and masonry in filled RC frames to blast ground motion”

Masonry walls which are perpendicular to the radial horizontal direction suffer severe damage and the walls which are parallel to the radial horizontal direction have less damage. i.e. out of plane damage is more severe than the in- plane wall damage. And the damage at first floor is more to strong ground vibrations induced by blasts.

METHODOLOGY

• A 2 storey RC framed structure will be considered and the soil below the ground level is taken as sand to study the response of structure to underground explosions. Later different types of soil will be considered for the study.

• The charge will be placed at a distance of 1Q^(1÷3)m from the ground level. (where Q is equivalent TNT charge wt in kilograms)

• And this distance will be changed to study the effect of buried depth on structure

• An explosive chamber of dimensions 10m×10m×10m will be considered at a distance of 10m from the structure in horizontal direction.

• In order to study the effect of loading density, the equivalent TNT charge wt varies with the loading densities of 10, 20, 50,100,200 kg/m3.

• The response is calculated first for 10 kg/m3 with different distances below the ground level i.e the response in terms of PPV or displacements against scaled distance are calculated.

• And next the loading densities are changed against the distance 1Q^(1÷3)m.

• Software ansys autodyn whis is based on Finite element Analysis is used for study and Loading is taken as non periodic loading.

• And the Soil is assumed as homogeneous &Isotropic

THANK YOU