BLAST LOAD EFFECT OF SIX STORIED FRAMEDSTRUCTURE WITH SHEAR WALLHanish Chundi, Graduate Student, CarletonUniversity, Ottawa ON Canada. Abstract: The main aim of thisreport is to show the lateral stability of a G+5 storied shear wall buildingunder blast loading condition. The basic interaction and stability of thestructure to the blast load is determined here.
This deals with determining thestructural stability in SAP 2000 using time history function. The framed shearwall building is subjected to a blast charge of 0.5 Ton, 0.4Ton, 0.3Ton,0.2Ton, 0.1Ton of TNT with stand offblast distance of 7m.
Total lateraldisplacement and inter story displacement are the main parameters to bediscussed here. The building is analysed with dynamic loading as non linearlyanalyzed structure with time history function. 1 Introduction Explosion is usuallydescribed as sudden burst or release of energy with excessive heat and freelyflying fragments either small or large depending on the intensity of the blast.Now a days separate codal provisions and standards are been given forstructures like public buildings, high rise buildings, economic institutes andother national heritages to withstand such unpredictable loads. Explosion isusually accidental or uncontrolled phenomenon’s while dealing with weaponssystems or highly explosive materials improperly.
Examples of such accidentsare burning or gas pipelines or flammable solutions due to improper handling ofsuch materials. Some organizations consider explosives as their strongestweapons for their dad to day work like building demolishers, etc. Detonation ofany kind of explosive in or around a structure can cause terrible impact onstructural integrity of the structure and degrades the strength of it structuralelements, sometime even loss of social life due to flying fragments of debrisand progressive collapse of structure and many other reasons. As importantcities and places has become a victim of blast either intentionally oraccidentally, it has been a major factor to study the structure when subjectedto blast pressure before construction or to study the stability of a structure incase or any explosion entire accidentally or intentionally. In this paper wehave described the available literature on blast load and interpreted theresults with an Structural analyzing software with nonlinear capabilities whichis SAP200 V-15.
2 Explosion Explosives are mostly used in:Defence applications, Construction or development works like demolition of oldbuildings, etc. It is one of the mostcommon weapon used by terrorist because it isaccessible easily. Table 1 shows the estimated quantity of explosivesthat can be fitted in various vehicles. Table 1 Estimated Quantity ofexplosions of various vehicles Vehicle Type Charge mass/Kg Compact car trunk 115 Trunk of a large car 230 Closed van 680 Closed truck 2270 Truck with a trailer 13610 Truck with two trailers 27200 In order to activate the explosives they haveto be stable and inert, which means the explosion is triggered effect ratherthan a spontaneous one. The explosion is a phenomenon where there will be arapid and abrupt release of energy.
Most of the explosions are detonated byexcitation of inert material which converts in to very hot, dense gas underhigh pressure which results in a release of strong explosion wave. One thirtythree percent of the total chemical energy is released by detonation while theremaining sixty six percent are slowly released during the blast as thesurrounding air and burnt debris mixes with the explosive product. Theexplosion effects are represented in a wave form of high intensity that growsoutwards from the detonation point to the surrounding air. As the wave passesit depletes its strength and speed as shows in Figure 1. Figure: 1 Variation of Blast Pressure withDistance 1 After a short period, the pressurewill drop below the ambient pressure in the front (figure 1).
During which anegative pressure phase, a partial vacuum is created, this is also accompaniedby high suction winds that carry the debris back to the demolition sourceleading to even more destruction to the surrounding elements. The time historyof blast wave is depicted in Figure 2 Figure: 2 Time History of Blast wave 2 3.Structural Response to Blast Loading Analyzing the dynamic response ofblast loading on structures is a complex process which involves the effect ofhigh strain rates, non-linear inelastic behavior of materials the timedependent deformation of structures and the uncertainty of blast loadcalculations. In order to simplify theanalysis various assumptions are taken related to the structural response andthe loads has been proposed and widely accepted. In order to simplify theanalysis procedure, the structure is considered as a single degree of freedom(SDOF) system and the relation between the positive duration of the blast loadwith the natural period of vibration of the structure is determined. Thisresults in idealization and simplifies the of blast loads calculation. 3.1Elastic Single Degree of Freedom The easiest way to solve a transientproblem is by means of Single degree of freedom approach.
The structure can bereplaced with an system of one concentrated mass at each level and one springrepresenting the resistance of the structure against deformation. A pictorialrepresentation of the above has been shown in figure 3. M represents structuralmass, the whole system is under the effect of external force F with respect totime t, i.e, F(t), with structural resistance R, vertical displacement isexpressed in terms of y, and spring constant as K. Figure:3 Representation of Single Degree offreedom system 2 The time history of the blast loadingcan be idealized as a triangular pulse having a force of Fm as peak force withpositive phase duration of Td as shows in figure 5.
The forcingfunctions are represented as The blastimpulse is approximated as the area under the force-time curve and is given as (2) The equationfor motion of un-damped elastic single degree of freedom for time ranging from0 to positive phase duration td,is given by Biggs (1964) as (3) Figure:4 Time History Graph 4 Structural Layout and Details TheG+5 storied framed shear wall concrete structure is modelled using SAP200 with 5rows of column in y direction and 3 bays in x direction each spanning 6 metersand 5 meters respectively. 5 meters is the ground floor roof lever from the groundlevel followed by 5 stories of 4 meter each. Shear wall is placed at the mid span through out theheight of the structure. Elevation of the structure is shown in figure 5. Thedimensions and design of the structural elements are designed according toIS-456 and SP-16 of India codes under normal loading conditions as momentresisting frame. The detailing of the elements are shown in the figure 6. Figure 5 Modelled structure in SAP2000 a) Typical Beam Detailing b) Typical Column Detailing c) Detaining of Shear wallFigure:6 Detailing of structural elements Grade of concreteused is M25 with HYSD 415 Steel rebars with a cover of 0.
03 m for all elements. 5 Blast Load Determination The method used tocalculate the blast pressure is developed by US Department of Defence underSection 5 of TMT – 1300 (1990): Structure to resist the effect of accidental explosion,for framed structure and its elements of a high-rise building. The loading parametersare calculated for 0.
5 Ton, 0.4Ton, 0.3Ton, 0.2Ton, 0.1Ton of TNT charge weight with stand off blast distance of7m from the base of the building along longer direction. The blast pressure calculatedis multiplied with area and converted into blast loads and evenly distributedto all the nodes at various levels at the face of the structure. For instance, the total pressure due toblast load on the top floor is multiplied with surface area of the requiredstructure, which has 5 columns on the front face.
Dynamic parameters of theblast loads which are duration, Time of arrival, shock front velocity, impulseare calculated accordingly Table 2 depicts the intensity of blast pressure inbay 3, along the height if the structure for a 0.1 Ton of TNT charge weightexploded at 7 m standoff distance. Table 2 Intensity of Blast Pressure on Bay 3 at differentlevels Bay 3 Height in m Angle in deg Arrival time in ms Duration of load in ms Pr in psi Load in kN Floor Level 6 25 69.8 24.99 9.09 17 578 5 21 64.4 20.1 6.85 26 865 4 17 57.9 15.05 6.85 37 1341 3 13 47.87 9.98 4.58 73 2534 1 9 36.87 7.87 3.17 151 5359 G 5 12.84 5.97 2.85 227 10997 Thegraph shown on figure 7 shows the time history function defined in SAP2000 foranalysing the structure for Blast pressure with varying load with respect totime