Theoretical and Numerical Analysis for the Design of a Safety Barrier as Road Restraint System

Transcription

1 ANALELE UNIVERSITĂłII EFTIMIE MURGU REŞIłA ANUL XVII, NR. 1, 010, ISSN Constantin Vasile Bîtea, Gabriel Jiga Theoretical and Numerical Analysis for the Design of a Safety Barrier as Road Restraint System The aer deals with a theoretical background and with numerical studies achieved on an N safety barrier, with normal rotection. In order to determine the imact force, a model at a reduced scale was roosed. For the calculus of the dynamic load due to the imact, the corresonding maximum deflection was determined. In the same time, the equivalent stress distribution was lotted for the examined case. Keywords: safety barrier, numerical analysis, car crash 1. Introduction The safety barriers are situated on dangerous road regions from the oint of view of traffic safety, in order to rotect the vehicles against the unexected exits from the road latform on one side as their otical guidance on the other side. In the resent aer the authors intended to roos an adequate model for the designing of a N safety barrier and, in the same time, a resentation of the testing device destined for the imact testing of this model. In arallel, the exerimental model was analyzed using the finite element method.. Geometric characteristics of the safety barrier The authors considered a deformable N safety barrier, in conformity to the EU standard SREN 117-, with normal rotection as one can see in Fig.1. 18

2 A 0 10 A Figure 1. Deformable N safety barrier 40 0 The main comonents of a such safety barrier are: 1 Sheet iling rofile; Stirru made from cuing metallic rofile; Imact damer; 4 IE10 metallic ost. These tyes of barriers are subjected to imact, in conformity to imact tests TB11 and TB. The TB11 and TB standards foreseen the following criteria: Standard Imact seed [km/h] Imact angle α [ o ] Total mass M [kg] Vehicle tye TB car TB car The rotection caacity of N barriers, in conformity to the SR EN117-1 standard are: - the kinetic energy E c = 81,9 kj; - the deformation of the barrier side exosed to the car traffic and the corresonding mean force are resectively: 19

3 Kinetic energy [kj] Deformation of the side exosed to the traffic [m] 81,9 0,1 0,4 0,8 1, 1,6 F [kn] 11 79,4 57, 44,7 6,7 1,1 Related to Fig., the distance S n transited by the center of gravity is calculated with the formula: n ( cos α 1) Sb S = c sin α + b + (1) where S b is the dynamic dislacement of the safety barrier side exosed to the traffic. c b V S n α c sinα + b cosα S b b-s b Figure. Dislacement of the center of gravity in case of a lateral imact (α = 0 o ). Design of the model The model roosed by the authors, kee the same characteristics of the material. In this context two different scales have been chosen for the lengths (λ=15) as well as for the masses (K m = 00). The outut values are the force scale: K f λ K m = = 4,5 10 resectively the kinetic energy scale, K =, 1) E K m λ = = 67,5 10 =. () 0

4 The model of the ost a circular section has been chosen, due to the fact that an I shae is difficult to be manufactured. In order to determine the dimensions of the ost, a limit case corresonding to a limit moment M L calculated taking into account the Prandtl schematization (Fig.). σ σ c Figure. Prandtl schematization M L = σ S () c where, σ c reresents the yield limit and S the statically moment of the lastic zone. By equalizing the limit moment corresonding to the I shae ost with the circular corresonding one it results effectively an equalization of the statically moments S : πd S1 = S = 19,9 10 d 6 mm. (4) 6 The diameter of the ost model will be in this case: d 6 d m = = = 4,14 mm (5) λ 15 The dimensions of the sheet illing rofile, using the corresonding length scale λ = 15, are given in Fig. 4. ε 10,4 10,4 0, 5,6 7 Figure 4. Geometry of the sheet illing rofile 1

5 Starting from the revious model, a new metal foil with a thickness of 0,5 mm will be used leading to a modification of all dimensions (Fig.5). In order to determine these dimensions the static moment S of the rototye will be calculated with the relationshi: ' S " S =, λ (6) ' 8,4 8, 77 56,7 where: S = 4 + = 716 mm (7) " The static model will be therefore 47,46 o " 716 S = = 9,7 mm 15 8,4 77 8, 56,7 Figure 5. Aroximation of the illing rofile geometry Considering the corresonding height of the model, h m and by an equalization of the static moments, a value h m =,6 mm will be obtained. 47,46 o b a 0,5 0,8 h 1 h h m Figure 6. Determination of the real height of the rototye For the revious model (Fig.6), the values of a, b and " S will be resectively:

6 h1 hm h hm " 0,5h m a = = ; b = = ; S = 0 = 0,754h m h sinα sin47,46 sinα sin47,46 18 sin47,46 The final model is resented in Fig.7. A 1, ` m =,6mm. 50 9,7 Φ 4 0,7 A Figure 7. Presentation of the final model geometry of the safety barrier 4. Design of the device destined to the model testing The model will be fixed on a stiff late at an angle of 70 o. A great care will be taken into consideration so that every movement of the model will be inhibited (Fig.7). On this model a body having a mass m = 5 kg falls from the height h m. M The body mass m will be calculated with the relation: m=, where km =00 is the mass scale and M, the mass of the real car (M = 1500 kg). The height h of the droing mass m is determined equalizing the kinetic energy E c of the car with the strain energy E of its mass. Considering the deformation of the traffic side S b = 0,8 m (accordingly to the Standard SR EN117-1), one could exress: S = csin α + b cosα 1 + S 1,41. (9) k m ( ) m n b = The value 0,61 m has been obtained taking into account an energy value of 81,9 kj, a force F = 11 kn and the deformation of the traffic side S b = 0,1 m, using the mean force: M( vsin α) F = (10) csin α + b cosα 1 + S [ ( ) ] where v = 110 km/h and α = 0 o. The mass will dro from a height v h g 47,6 h m = = =,17 m λ λ 15 b

7 The design of the device destined for the model testing is resented in Fig.8. Droing mass m = 5 kg Post Φ ,6 1, 0 o 0 0 Sheet iling rofile 0 Stiff Figure 8. Design of the device destined for the model testing 5. Numerical results The model was meshed using a SHELL9 element as one can see in Fig.9. This element is articularly well suited to model curved shells. The element has six degrees of freedom at each node: translations in the nodal x, y, and z directions and rotations about the nodal x, y, and z-axes (UX, UY, UZ, ROTX, ROTY, ROTZ). The deformation shaes are quadratic in both in-lane directions. The element has lasticity, stress stiffening, large deflection, and large strain caabilities. The element is characterized by lasticity, stress stiffening and large deflections. Figure 9. SHELL9 element Only a art of the sheet iling rofile situated between two adjacent osts has been analyzed. An initial loading corresonding to a static force of 50 N (equivalent 4

8 to a mass of 5 kg) was alied in the midsan of the barrier. In order to calculate the dynamic load due to the imact, the corresonding maximum deflection was determined. In Fig. 10 the deformed shae of the iling rofile is resented. As one can see, the maximum deflection for the corresonding force was δ=8,944 m. Figure 10.Deformed shae The equivalent stress distribution, calculated for an imact force F = 4,9 kn is resented in Fig.11. Figure 11. Von-Mises stress distribution for the analyzed model 5

9 6. Conclusions The roosed model resented in this aer could be successfully alied for all the tyes of safety barriers (light, heavy and very heavy) and for all values of the traffic side deformation. The mean force F offers information on the interaction between the vehicle and the barrier during the imact. It is a useful measure for a first evaluation of the total force which acts on the anchorage devices of the barrier and of the vehicle in collision. References [1] Curtu, I. et.al., Mechanics of materials, Infomarket, Braşov, 00 [] Vasilescu, A., Praisler, G., Similitude of elastic systems, Ed. Romanian Academy, 1974 [] Euroean Standard 1948/1 [4] Euroean Standard SR EN [5] Euroean Standard EN Addresses: PhD.Eng. Constantin Vasile Bîtea, University Eftimie Murgu of ReşiŃa, PiaŃa Traian Vuia, nr. 1-4, 0085, ReşiŃa, bitea005@yahoo.com Prof. PhD Eng. Gabriel Jiga, University Politehnica of Bucharest, Slaiul Indeendentei, nr. 1, 06004, Bucharest, Romania,, gabijiga@yahoo.com 6