Finite Element Analysis of Blast Resistant Door

Finite Element Analysis of Blast Resistant Door Mr. Devidas Thorat

Mr. Prashant C.

Mr. Ajaykumar Jadhav

Sr. Manager Security Solution Division Godrej & Boyce Mfg. Co. Ltd

Sr. General Manager Security Solution Division Godrej & Boyce Mfg. Co. Ltd

Dy. Manager Security Solution Division Godrej & Boyce Mfg. Co. Ltd

Abstract This study is aimed at verification of performance of blast resistant door against Blast pressure and impulse with nonlinear explicit analysis using Altair Radioss solver. This paper describes development of a finite element model and subsequent analysis and simulation of a blast resistant door which consists of high strength door and replaceable sacrificing layer, designed by Godrej Security Solution Division Blast pressure time curve is used as input and performance parameters such as stress, deflection, energy, ductility ratio, elasto-plastic behavior etc. are analyzed and compared with permissible values. Blast resistant door- components, assemblies, contacts are modeled with appropriate methods. The results are also compared with analytical solution as elaborated in TM5-1300 with proper assumptions. Further, more attempts will be made to establish methodology to arrive at the pressure is time curve when inputs are weight of explosive and the distance of explosive from the entity of interest. It would also be relevant to carryout the ac tual blast test of the door and compare the results with software simulation

Introduction Now-a-days, the threats to the public security and premises security due to unexpected explosions are increasing because of prevailing of terrorism. Hence catering to the demand for blast resistant design for sensitive premises such as commercial building or military structures is urgent than ever before. Generally, constructions in these premises can be made strong by using reinforced concrete walls. However, the entrances need special attention to get sealed off and desired resistant to blast. Also in chemical laboratories, the research rooms working with chemicals are prone to explosions and surrounding premise need to be protected. Same is case for explosive items’ stores. Thus, a variety of blast resistant doors with sufficient explosion resistance need to be designed for various applications. Most of the blast door designs are as per the guidelines provided in the military technical manual TM51300 [1], NAVFAC P-397 [2],and the analysis is performed following the design criteria mentioned therein. Basically, the structural stiffness of blast door is estimated under blast loads and the blast resistance is evaluated according to the material strength, to check the performance of the door structure for explosion resistance. Generally, for the dynamic analysis as presented in TM5-1300, a simplified single-degree-offreedom system is considered to simulate the dynamic responses of the door structure under the blast shock wave, by which the maximum distortion, time-history of acceleration can be investigated. In this analytical approach, the load-mass factor and blast pressure-time relationship used for the calculation of the equivalent weight of structure can be available from literatures. The explosive loading characteristics such as peak pressure and loading duration of blast wave need to be established prior to analysis. Similarly, the blast door can also be designed under the guidelines provided in the Indian Standard IS 4991 [5].

1 Simulation Driven Innovation

Blast-resistant door could be constructed as solid plate door or door with stiffeners (built up door). Usually for higher pressure (50 psi or greater) solid plate door can be used and for lower pressure (10 psi or less) built up door is practical solution. Use of both solid plate and stiffener with proper thicknesses could be optimized where total moment of Inertia will be considered for strength of door. In addition to the main door plate, the sacrificing layer is provided from blast attack side. During the hit of blast wave onto the door, sacrificing layer gets deformed absorbing some of the blast energy and pressure. Then only remaining part of energy gets transferred to main door plate. Hence, sacrificing layer protects the door from larger loads and deformations. The deformed sacrificing layer can be replaced by new sacrificing layer, making the blast door functional and resistant again for blast threat. Earlier, the technology development of blast-resistant structure was limited to defense sector and could not be accessed for general application in industry. But now with the revolution in computer technology, a good number of analysis software packages have been developed and getting continuously improved to implement the mechanics and theory into finite element method and to provide an efficient tool to analyze the dynamic behavior of complicated structures This study was therefore aimed to investigate the blast resistance of a door structure with sacrificing layer by using finite element analysis with Altair Radioss. This approach can be used for blast resistant design simulation and validation in absence of actual blast test or for optimization of the door design.

Finite Element Analysis 1. Specifications of Blast Door

Blast resistant doors are designed to withstand a high pressure shock front of very short duration. The structure of this blast door consists of a 60 mm thick pressure plate built up with, additional stiffeners to increase the strength. The door is designed in seating condition so that the blast pressure coming onto pressure plate will get transferred to frame and then to wall. Fig. 1 shows the geometrical configuration of the door structure.


Fig. 1

Such a design can be constructed into a double leaf door or single leaf door as per requirement and application. The essential dimensions of the blast door used in this study are 1000 mm clear opening width and 2500 mm clear opening height. Stiffener thickness is 1.0 mm and sacrificing layers are 1.0 mm thick. 2. Finite Element Modeling

Fig. 2


Fig. 2 is the solid model of the blast door created for analysis. The elements used for this model are 3D brick element (P14_SOLID) for door plate and hinges, 2D shell element (P1_SHELL) for sheet metal components, and 1D rigid elements for welded connections. The material defined for all the components is steel with following properties: Young’s modulus E =200 GPa, Poisson’s ratio ν =0.30, density ρ = 7800kg/m3, Yield strength yield σ =250 MPa, ultimate tensile strength UTS = 550 MPa. The material model: M2_PLAS_JOHNS_ZERIL The frame is rigid (all degrees of freedom constrained). Other boundary conditions are defined by contact surfaces (TYPE_7) used for interfaces. The Load applied on the door surface is 20 bar pressure 0 ms and decreasing to 0 bar at 5ms. Design criteria for design of blast resistant door are Ductility ratio and edge rotation limits. A ductility ratio of 5 should be used for reusable door and for edge rotation 2 degree. When pressure is applied, the door structure should provide a least damage to its components and protect side occupants and contents; the deformation is restricted to the protection level prescribed in TM5-1300 [1]. In this study, the door leaf is allowed to deform with a rotational deformation of 2 degree at supports and can be reusable after explosions. For single leaf door, the maximum edge rotation θ is related to the maximum deflection δ and the door width W b y the equation; Tanθ = 2δ / W 3. Transient Analysis Firstly the plate is subjected to load calculated from pressure and surface area and then load step of 5ms is applied. After transient linear analysis, the stress found is 218 MPa and the deflection found is 3.67 mm (as shown in Fig. 3) δ = 3.67 mm = 0.144 in.

Fig. 3

Fig. 4

θ = tan-1(2δ / W) = tan-1(2*3.67 / 1000) = tan-1(0.00734) = 0.42 degrees


Following are the results from analytical calculations from TM5-1300 [1] Dynamic Design of Blast Resistant Door (fps system) (Solid) 290 psi (20 bar); 5 ms Door 2.5 m x1 m single leaf Door height (longer side) H, in Door width (shorter side) L in Over pressure Po=B psi Time To ms Plate Thickness d=t in Elastic section modulus S cu in / in Plastic section modulus Z cu in / in Static yield strength Fy ksi Dynamic increase factor c Dynamic yield strength Fdy ksi Plastic moment capacity Mp ksi / in Modulus of elasticity E psi Poisson's ratio nu Flexural rigidity of plate D H/L Deflection coefficient Gamma Equivalent elastic Stiffness KE psi / in L/H x/L Horizontal distance to yield line x in Negative moment capacity in horizontal direction M HN Positive moment capacity in horizontal direction M HP Ultimate unit resistance r u psi Equivalent elastic deflection XE in Load-mass factor K LM Acceleration due to gravity g in / s^2 Unit weight w lb / in Density rho lb / in^3 Unit Mass of plate m lb-ms^2/in^2 Effective unit of mass of plate m e lb-ms^2/in^2 Natural period of vibration Tn ms B/ru ru /B To/Tn Ductility ratio Xm/Xe Maximum deflection Xm in Maximum support rotation Theta deg

Fig 3.36/3.34

Fig 3.17

98.43 39.37 290.0 5 2.36 0.93 1.39 33 1.1 36.63 42.58 2.90E+07 0.3 3.50E+07 0.4 0.0026 5603.888 2.5 0.266 26.18110236 0

Table 3.13

Fig 3.54

42.58 310.62 0.055 0.65 386.4 0.67 0.2835 1733.14 1126.54 2.818 0.934 1.071 1.775 2.65 0.15 0.43

Table 1

The blast resistance of blast door plate is investigated using Altair Radioss solver. Analytical calculations and Finite Element Analysis is compared for maximum deflection which are satisfying the design criteria such as edge rotation limits as per blast data from TM5-1300 [1]. Maximum support rotation = 0.42 deg (By Radioss) = 0.43 deg (By TM5-1300).


4. Non-Linear analysis:

The full door model is analyzed using Radioss by applying pressure curve. When blast pressure is applied, it first hits onto sacrificing layer, which gets deformed and scrambled. When sacrificing layer completely collapses and touches to main door plate, it transfers remaining load to the door. The Energy and work done are plotted with respect to time to know the energy absorbed by sacrificing layer. When more factor of safety is desired, the thicknesses of top cover and sacrificing layer are increased to economical limit. And analyses are rerun to check the deflection and design criteria.

Fig. 5

Fig. 6


Results and Discussions

The energy plots before modification of thicknesses are generated and compared to see effectiveness of sacrificing layer for amount of energy absorbed to protect the main door. The total internal energy plots

Fig. 7

Fig. 8

Internal energy absorbed by Door plate = 6E+007 KJ

Fig.9


Internal energy absorbed by Door plate after modification = 5E+007 KJ The energy transfer to door plate is also delayed.

Fig.10

Further Scope of Study

Some times pressure curve may not be available as input loading condition. In that case, anticipated explosive weight and standoff distance need to be considered for simulation. There are methods to establish pressure and impulse parameters from this data. These parameters also highly depend on the surrounding layout, dimensions and atmospheric pressure. There are different types of cases depending on above variations such as open air blast, surface blast, confined blast, confined blast with venting, etc. The aim is to simulate these conditions with modeling of room, air, explosive at specified distance and workout the pressure parameters. Since the peak overpressure and duration of positive pressure can be expressed as the function of the scaled distance Z and explosive charge weight W , the details of the blast characteristics for various conditions can be derived from empirical charts or formulae in military technical manual TM5-1300. The results can be compared with the results from the Altair Radioss software. This comparison can be made for simple models for which formulae can be easily used. Radioss can be proven as efficient solving tool for complex models with good level of accuracy and reliability. Also the simulation results are to be verified with actual blast test results.


Conclusion

In this paper, RADIOSS has been used to model and simulate the blast analysis for Godrej blast resistant door. Linear transient analysis is carried out on door plate. The results are matching closely with the theoretical calculations and well within the limits of design criteria. Non linear dynamic analysis is also carried out on full door with sacrificing layers with varying thickness and results have been studied for effectiveness of sacrificing layer and found encouraging for th e use and further analysis. The work presented in this paper is in the early phases of ongoing work and it is important to note that these promising results will strongly demand more detailed analysis as mentioned in further scope for study.

ACKOWLEDEGMENTS The authors would like to acknowledge M/s. Godrej and Boyce Mfg. Co. Ltd. Security Solutions Division and Altair’s Technical support.

REFERENCES [1] Department of the Army, “Structures to resist the effects of acc idental explosive,” TM5-1300, [2] Department of the Navy, “Structures to resist the effects of ac cidental explosive,” NAVFAC P-397, Design Manual 2.08 [3] Department of Air Force, “Structures to resist the effects of a ccidental explosive,” AFR 88-22 [4] Altair HyperWorks Radioss v90 help Manual [5] Indian Standard “Criteria for blast resistant design of structures for explosions above ground” IS: 4991-1968,


Finite Element Analysis of Blast Resistant Door

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