Hani A. Salim, Robert Dinan, Sam A. Kiger, Philip Trent Townsend, Jonathan Shull (2003) [2] The research reported in this paper is the incorporation of stud wall as a retrofit in existing structure to improve the blast resistance of the building. The Static Resistance Function (SRF) in Fig .1 implemented in the model is obtained from the experimental and analytical results. The ductile members should yield but also should absorb energy by plastic deformation. It is necessary that the stud wall deforms sufficiently and thus dissipates the energy by formation of plastic hinges. To achieve this criterion the connections should be designed properly to prevent premature failure. Predominantly screws are used but these connections are not sufficient to yield the studs fully. A connection should be checked for the following aspects.
- Failure due to shear of the stud to angle connection.
- Failure due to tension in the cross-section of stud/angle.
- The holes in the stud fail by block shear action.
- Failure of sections under the bolt holes by bearing..
Experiments were conducted and various configurations of bolts and thickness of angle plates were investigated. The results showed the angle plates of 12mm thickness with 6 bolts were required to yield the studs plastically. Furthermore experiments were conducted on Low Mass Wall (LMW) and High Mass Wall (HMW) to ascertain the response of mass of the wall to air blast effect. The LMW furnished with an EIFS sheathing and the HMW with a brick façade. The studs under EIFS sheathing ruptured, while the studs under the brick façade considerably deformed. This confirms that the larger the mass of the façade lesser the impact on the stud wall due to blast.
Jordan Wheeler Lane, Dr. Hani Salim (2003) [3] This paper provides the details of dynamic modeling. Dynamic modeling is a procedure to anticipate the post- blast condition of a structure subjected to a specific blast pressure. Pressure and .Impulse are the two significant criteria for dynamic loading. Failure is usually a behavior beyond the elastic limit. The plastic portion is an essential region in terms of blast design where the specimen absorbs a large amount of load thus proper parameters should be defined in the analytical model.
.For a complex system SRF has to be defined as a specific global stiffness becomes obsolete. The SRF curve is defined by an elastic region, softening region and an inelastic region. The portion AB is the elastic region, here the member regains its original cross-section after the removal of load. The permanent deformation starts from point B and is known as yield buckling. The portion BC is the stiffness loss region, the occurrence of stiffness loss region is not well defined.. The portion CD is called the tension membrane region where the stud begins to more resistance. In this region the studs absorbs maximum amount of energy and hence the static resistance function should be properly defined in this region. Furthermore two types of behavior have been noticed during experimentation. The first is a catenary action (upper limit response) where the tension membrane dominates immediately after the yield buckling. This also indicates that there is no formation of plastic hinge as the softening region is very small, here the studs deforms as an arch. The second behavior is where the bending action is less and the tensile action is more, the formation of plastic hinge is more predominant. The slopes of the curves AB, BC, CD give the Static Resistance function for the corresponding region.
Neuberger, S. Peles, D. Rittel (2007) [4] This two-part paper addresses scaling of the dynamic response of clamped circular plates subjected to close-range and large spherical blast loadings. In this study, similarity is obtained by using replica scaling for all geometrical parameters, while the blast effect is scaled by using the well-known Hopkinson scaling law. Also the overall effect of the strain rate sensitivity and variability of material properties with plate thickness on the response of the scaled model has been considered. This study presents numerical and experimental results from a series of controlled explosion experiments. The first part of the paper deals with spherical charges exploding in free air, while the second part deals with the same
Jessica Godinho, Arturo Montalva, Sharon Gallant (2007) [5] Present design practices neglect the instability of steel columns due to the application of axial load while considering blast load. The air pressure is usually assumed to be uniform along the length of the stud and the occurrence of plastic hinge is assumed to be at the midspan, this misinterpretation leads to miscalculation of the structural performance of the columns. During a blast the columns are exposed to large values of pressure that results in lateral deflections
The criteria for which the axial load effects are accounted for are given below,
- KL/r < 38 ; Axial load effects are neglected.
- <KL/r <75 ; ductility limit = 3 ; rotational limit = 3O ; Axial load effects are neglected.
- KL/r > 75 ; ductility limit = 3 ; rotational limit = 3O ; The columns are unacceptable.
During a close range explosion a non-uniform loading is expected to act on the column, thus this load shifts the plastic hinge below the mid height of the column, hence the failure mechanism will be oriented with shear rather than flexure.
T. Ngo, P. Mendis, A. Gupta & J. Ramsay (2007) [6]. In addition, major catastrophes resulting from gas-chemical explosions result in large dynamic loads, greater than the original design loads, of many structures. Due to the threat from such extreme loading conditions, efforts have been made during the past three decades to develop methods of structural analysis and design to resist blast loads.[15] The analysis and design of structures subjected to blast loads require a detailed understanding of blast phenomena and the dynamic response of various structural elements. The paper presents a comprehensive overview of the effects of explosion on structures. An explanation of the nature of explosions and the mechanism of blast waves in free air is given. The paper also introduces different methods to estimate blast loads and structural response..
Feng Zhua, Longmao Zhaoa, Guoxing Lua, Zhihua (2008) [7] Wang Metallic sandwich panels with a cellular core such as honeycomb have the capability of dissipating considerable energy by large plastic deformation under impact/blast loading. To investigate the structural response of sandwich panels loaded by blasts, a large number of experiments have been conducted, and the experimental results are reported and discussed in this paper. Quantitative results were obtained based on the safety systems. Loss of life and injuries to occupants can result from many causes, including direct blast-effects, structural collapse, debris impact, fire, and smoke. The indirect effects can combine to inhibit or prevent timely evacuation, thereby contributing to additional casualties. In addition, major catastrophes resulting from gas-chemical explosions result in large dynamic loads, greater than the original design loads, of many structures. [16] Due to the threat from such extreme loading conditions, efforts have been made during the past three decades to develop methods of structural analysis and design to resist blast loads. The analysis and design of structures subjected to blast loads require a detailed understanding of blast phenomena and the dynamic response of various structural elements. The paper presents a comprehensive overview of the effects of explosion on structures. An explanation of the nature of explosions and the mechanism of blast waves in free air is given. The paper also introduces different methods to estimate blast loads and structural response.
Stephen Hauser, Larry Abatiell (2008) [8] The research reported in this paper is about a light thin material that is blast resistant called as micro-reinforced concrete (DUCON) is found to resist extreme loads. Micro reinforced concrete is a composite material made from Portland cement of high grade, fine aggregate, cementitious materials and admixtures. It has a fine texture paste that is virtually impermeable when cured. The compressive strength is about 23000 psi and flexural strength about 11, 000 psi. It has very high resistance to compression andbending strength which makes it an effective blast and ballistic resistance sheathing material.
Bryan Bewick, John Hoemann, Eric Williamson (2010) [18] The primary aim of this research design stud walls that are available conventionally to absorb the impact of blast loads effectively. There are 2 primary issues in the current study 1. The efficiency of screwed stud-track with commercial clips has to be studied 2. Predent techniques do not involve the interplay of the veneer layer to increase the blast resistance. Experiment were conducted to occurs the following criteria
1. Elongation Action (EA) 2.Flexural Action (FA) 3.Crushing Action (CA).
The EA test is performed to determine the bond strength between the track and the stud. The selection of connection can be determined by EA test. The FA test examines the capacity of studs against rotation and shear by rendering one end boundary condition as fixed. The CA test assists to ascertain the amount of load that has been absorbed by shear in the studs.
Kumar P. Dharmasena, Haydn N.G. Wadley, Keith Williams, Zhenyu Xue, John W. Hutchinson (2011) [9] Small scale explosive loading of sandwich panels with low relative density pyramidal lattice cores has been used to study the large scale bending and fracture response of a model sandwich panel system in which the core has little stretch resistance.The panel responses are compared to those of monolithic solid plates of equivalent areal density. The impulse imparted to the panels was varied from 1.5 to 7.6 kPa s by changing the standoff distance between the center of a spherical explosive charge and the front face of the panels. A decoupled finite element model has been used to computationally investigate the dynamic response of the panels. It predicts panel deformations well and is used to identify the deformation time sequence and the face sheet and core failure mechanisms. The study shows that efforts to use thin face sheets to exploit FSI benefits are constrained by dynamic fracture of the front face and that this failure mode is in part a consequence of the high strength of the inertially stabilized trusses. Even though the pyramidal lattice core offers little in-plane stretch resistance, and the FSI effect is negligible during loading by air, the sandwich panels are found to suffer slightly smaller back face deflections and transmit smaller vertical component forces to the supports compared to equivalent monolithic plates.
Vasilis Karlos, George Solomos. (2011) [10] A sudden burst of hot gases and energy due to fast chemical reaction of a solid liquid or gas is defined as explosion. The resulting hot gases expand and radiate spherically from the point of detonation. This process pushes the air molecules surrounding the region with a great velocity. The resulting wave is termed as blast wave and shock front. The pressure value reaches its peak this is known as the peak overpressure and the pressure subsides to atmospheric pressure as time progresses this is termed as the positive phase. After this point the pressure drops below the ambient pressure and is called the negative phase and it lasts longer than the positive phase. The negative peak pressure value is much lesser than the positive phase and hence it is not considered for design. Another important parameter is the blast impulse this is the pressure on the particular structure at a small time interval. The area under the positive phase curve is the positive impulse and the area under the negative phase curve is the negative impulse. As there is an instantaneous change in the pressure values Friedlander formulated an equation to define the rate of decrease of pressure values.The air behind the blast wave moves at a smaller velocity and is responsible for the loading of the surface during the entire positive phase this is called as the dynamic coefficient.
S.E. Rigby, A. Tyas , T. Bennett (2013) [11] A commonly used approach for the engineering analysis of structures subjected to explosive loads is to approximate the problem as an equivalent Single-Degree-of-Freedom (SDOF) system and to use elastic e plastic response spectra. Currently, the response spectra that exist in the literature do not take into account the fact that blast wave clearing will occur if the target is not part of a reflecting surface that is effectively infinite in lateral extent. In this article, response spectra for equivalent SDOF systems under cleared blast loads are obtained by solving the equation of motion using the linear acceleration explicit dynamics method, with the clearing relief approximated as an acoustic pulse. The charts presented in this article can be used to predict the peak response of finite targets subject to explosions, and are found to be in excellent agreement with a finite element model, indicating that the response spectra can be used with confidence as a first means for predicting the likely damage a target will sustain when subjected to an explosive load. Blast wave clearing generally serves to reduce the peak displacement of the target, however it is shown that neglecting clearing may be unsafe for certain arrangements of target size, mass, stiffness and elastic resistance.
X.R. Liu , X.G. Tian, T.J. Lu, B. Liang (2014 [12] The dynamic responses and blast resistance of all-metallic sandwich plates with functionally graded close-celled aluminum foam cores are investigated using finite element simulations, and compared with those of ungraded single-layer sandwich plates[17] Upon validating the numerical approach using existing experimental data and introducing the present computational model, different graded sandwich plates under air blast loading are analyzed in terms of deformation and blast resistance. The effects of face sheet arrangements and interfacial adhesion strength between different foam layers are quantified. The results demonstrate that relative to conventional ungraded plates subjected to identical air blast loading, the graded plates possess smaller central transverse deflection and superior blast resistance, with further improvement achievable by optimizing the foam core arrangement. The blast resistance of both graded and ungraded sandwich plates subjected to the constraint of equivalent mass is also explored.
Lucia Figuli 1, Stefan Jangl 1, Daniel Papan (2016) [13] As a blasting agent in the blasting and mining engineering, has been using one of so called new generation of explosives which offer greater flexibility in their range and application, and such explosive is ANFO. The paper deals with the analysis of structure subjected to the blast load created by the explosion of POLONIT charge.. The real field tests of three different weight of charges and two different structures were done. The explosive POLONIT was used together with 25 g of ignition explosive PLNp10. Analytical and numerical model of blast loaded structure is compared with the results obtained from the field tests (is compared with the corresponding experimental accelerations). For the modelling structures were approximated as a one-degree system of freedom (SDOF), where the blast wave was estimated with linear decay and exponential decay using positive and negative phase of blast wave. Numerical solution of the steel beam dynamic response was performed via FEM (Finite Element Method) using standard software Visual FEA.
N. Jacob, S. Chung Kim Yuen, G.N. Nurick, D. Bonorchis, S.A. Desai, D. Tait (2004) [19] A series of experimental results on clamped mild steel quadrangular plates of different thicknesses (1.6, 2.0, 3.0 and4.0 mm) andvarying length-to-width ratios (1.0–2.4) subjected to localized blast loads of varying sizes is reported. Disc shaped explosive charges of varying charge diameter-to-plate width ratios (0.2–0.37) and charge heights (1.8–14 mm) are centrally positioned on quadrangular plates to provide impulses resulting in mid-point deflections in the range from two plate thicknesses to central plate tearing. The effects of varying both the loading conditions and the plate geometries on the deformation are described. A modified dimensionless number is presented for the quadrangular plate response when subjected to localised circular blast loading. In addition, numerical predictions are carried out and compared with experiments for a limited selection of plate geometries.
L.K. Stewart, A. Freidenberg, G. Hegemier (2013) [20] The blast effect is simulated using an air blast simulator. The effect of air blast on the stud wall system is studied and reported in this paper. Steel stud wall sheathed with a composite system of cement board is employed as the test specimen. A spectrum of specimen was used for the test with variation in the top and bottom connections. The various connections specified are angle, bearing washers, blast clips and L-brackets. The studs were spaced at 40.6cm and exposed to an air blast velocity of 15m/s. Two apt test results are 14 compared 1.The bottom connection is made of angle plates.2. The bottom connection is made of bearing washers with blast clips.
From the summary of literature review Individually model the components and perform static load test to determine the max capacity. Test the whole model and identify the failure mechanisms. Enhance the strength of the portion that is subjected to premature failure.6 bolts are required to yield the stud in static test.½” thick angle is required to prevent pullover of bolts .Provide lateral bracings at local zones. Provide shear stiffeners.
Provide a proper composite sheathing material