TANGENTIAL STRESS FACTOR COMPUTATION IN POINT MOUNTED STRUCTURAL GLASS

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 8, August 2017, pp , Article ID: IJCIET_08_08_086 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed TANGENTIAL STRESS FACTOR COMPUTATION IN POINT MOUNTED STRUCTURAL GLASS B. Venkatesh Department of Aerospace Engineering, RVCE, Bangalore, India Gowtham Reddy G Department of Aerospace Engineering, RVCE, Bangalore, India Benjamin Rohit Department of Aerospace Engineering, RVCE, Bangalore, India Syed Sharin, Department of Mechanical Engineering, PESIT-BSC, Bangalore, India ABSTRACT The main objective in this study is to compute the stress factors when the effect of countersinking a hole comes into play in comparison with the stress factors computed for a cylindrical straight bolt hole in accordance with DIN FEM analysis using 3-D volume elements were done with the commercially available software Abaqus. The study was carried out for various dimensional parameters of point mounted glass. This study has also carried out parametric sensitivity analysis for a single counter-sunk bolt hole and a double counter-sunk bolt to compute the increase in the tangential stress factor values when changing over from a straight cylindrical hole to a countersunk and a double countersunk hole. It was found that the stress factors increase when the hole is countersunk. Key words: DIN , Counter-Sunk Bolting, Double Counter-Sunk Cite this Article: B. Venkatesh, Gowtham Reddy G, Benjamin Rohit and Syed Sharin, Tangential Stress Factor Computation in Point Mounted Structural Glass, International Journal of Civil Engineering and Technology, 8(8), 2017, pp INTRODUCTION Glass is a highly brittle material but also an eco-friendly material used for construction of buildings to allow sunlight for lighting the interiors. But since it is highly brittle safety is always a point of concern. It is very difficult to analyze crack growth and crack propagation editor@iaeme.com

2 B. Venkatesh, Gowtham Reddy G, Benjamin Rohit and Syed Sharin Hence it is very much necessary to know the limits to which the stresses can be produced in the glass material. There is a lack of knowledge when it comes to simple design tools during the use of structural glass. This study deals with the development of efficient and linear tool for the design of glass bolting in point supported glass in accordance with DIN standard norms. The support conditions have been advanced for different type of boltings. As there is less work done in this field, there is very less literature available for point mounted glass in accordance with DIN DIN COMPUTATION OF STRESS FACTORS. Technical Experiment for Point mounted Glazing. For standard DIN 18008: the design value (limit stress) depends on the type of the glass. The maximum limit stress for thermally toughened glass is given by, =,. Where, : Construction Factor, : Characteristic limit stress value : Partial Factor Maximum limit stress for a glass which is not thermally toughened,, =,.. Where, is the correction factor. Now we will be discussing the stress factors due to the loading and at the bore of a point supported glazing. The stresses are calculated using the simplified method of the linear superposition of local and global stress components as shown in equation. =... Where, : Stress factor for Force : Reference thickness as per DIN Where, () () () : Thickness of the glass : Shear Force! = ", +, +, +. $, (%)! : Design value of Loading : Local Stress component resulting from the normal force in Z direction ",,, : Local Stress component resulting from the shear force in XY direction : Local Stress component resulting from the Bearing Torque. $, : Stress Factor k and Global stress component At the present this is only available for cylindrical hole bolting. We would like to expand this methodology to countersunk bolting and check for the increase in safety factors between cylindrical and countersunk holes editor@iaeme.com

3 Tangential Stress Factor Computation in Point Mounted Structural Glass Figure 1 Glass bolt model in accordance with St. Venant s principle [2] Stresses in the glass plate follow the Saint-Venant s Principle [Fig 1] which is evaluated only at a sufficiently large distance from the loading point. The global structural behaviour of the plate is taken by the global stress component. The local region is defined as a circular area cantered at each bore section surrounding the respective point holder. The radius of the sphere is three times the Bore diameter as shown in the figure. $ = $.& (=) (') Here we use FEM to study and calibrate the stresses to obtain the b-factors used in design for the countersunk bolting Hex mesh Vs Tet mesh In this analysis we have chosen hex mesh over tet mesh because of the reason that hex mesh have a higher degree of freedom than that compared to a tet mesh which provide a more accurate and practical results compared to a tet mesh Mesh Sensitivity We tried to put obtain the simulation results by increasing the mesh density along the edge of bolt by increasing the number of nodes. By plotting the results we find that the values of the stress factors converge to the DIN values [Fig 2]. In the test simulation cases we have applied a load of 1000N at an angle of 74 in the plane of shear lateral to the shank. Figure 2 Convergence to actual DIN value with increasing mesh density editor@iaeme.com

4 B. Venkatesh, Gowtham Reddy G, Benjamin Rohit and Syed Sharin Contact angle between bolt shank and hole A study on varying stress was done by applying a constant load by varying the angle in the plane of shear. We found that the Equivalent stress tend to increase at low angles and start decreasing as the angle of application of load is increased Stress factors for cylindrical bolted holes We have verified the results by attaining consistency with the values for cylindrical glass bolt. [2] Table 1 Variation of stress factors with the bolt bore diameter S.NO Bore diameter(mm) DIN Values FEM Results Deviation from DIN values STRESS FACTORS FOR COUNTER-SUNK AND DOUBLE COUNTER-SUNK BOLT We have used FEM modelling and simulation using commercially available software Abaqus [3] for the counter-sunk bolt [Fig 3] to predict the stress factors in shear stress conditions [Table 2]. In this the friction due to the contact between the bolt and the glass face is not considered. This could also add to the deviation. It is not in the scope of this paper to consider friction. We have done analysis in considerations with Von-Mises stress [Fig 4]. Figure 3.General dimension of the counter-sunk hole [4] Figure 4 FEM Analysis of counter-sunk hole# editor@iaeme.com

5 Tangential Stress Factor Computation in Point Mounted Structural Glass S.NO Table 2 Shear stress factors obtained from simulation for counter-sunk hole Bore diameter(mm) DIN Values FEM Results for Cylindrical for Cylindrical bolts bolts FEM Results for countersunk bolts Percentage increase in Stress factor Effect of varying angle of counter-sunk We then carried out variation in the parameter - angle of countersunk. We carried out this variation for a fixed bore diameter of 45mm maintaining constant thickness of the glass plate. Figure 5 Parametric sensitivity on angle of counter-sunk 3.2. Influence of the variation of shank in counter-sunk hole Varying the height of the counter-sunk hole region, we try to obtain the values for stress factors for the different values of the parameters. Figure 6 Parametric sensitivity of shank of counter-sunk hole editor@iaeme.com

6 B. Venkatesh, Gowtham Reddy G, Benjamin Rohit and Syed Sharin 3.3. Stress factors for double counter-sunk bolts We simulate and obtain the shear stress factors [Table 3] for varying diameter of the bore by giving double axis symmetry in x as well as in z direction. Figure 7 General dimensions of Double counter-sunk bolt S.NO Bore diameter(m) Figure 8 FEM analysis of double counter-sunk bolt Table 3 Stress Factors for double counter-sunk bolts DIN Values for Cylindrical bolts FEM Results for Cylindrica l bolts FEM Results for countersunk bolts Percentag e increase in Stress factor FEM Results for double countersunk bolts Percentag e increase in Stress factor RESULTS AND DISCUSSIONS Glass is a material which is of late being used in construction, despite the fact that there is lack of official standards and guidelines which can give details on design procedures and material strength characteristics. The oldest design principle is based on the factor of safety (fallowable = frupture/fos) [4]. Here we use the same principle to check the magnitude of FOS editor@iaeme.com

7 Tangential Stress Factor Computation in Point Mounted Structural Glass required while using a countersunk bolting. As there are no standard values for a countersunk bolting in DIN , we try to obtain stress factors for countersunk bolting to account for the increase in the safety factor when changing from cylindrical bolting to counter-sunk bolting and also when changing to double counter-sunk bolting we see the maximum stress factors induced in it. Equivalent stresses are found to be maximum in Double counter-sunk bolt. The maximum stress is found to occur in two different regions as shown [Fig 8].This is mainly because of the reason being that there is more surface in the inclined or angular region of the counter-sunk or double counter-sunk bolt which induces higher stress in the shank. We can note that as the bolt hole is being counter-sunk the degree of difference increases quadratically and tends to be linear in case of a cylindrical bolt, this phenomenon has to be studied in detail to be able to get a better understanding. Table 4 Shear stress factors of Counter-sunk bolting Hole Diameter(d) [mm] dt [mm] bfxy bfxy bfxy bfxy bfxy bfxy bfxy bfxy Table 5 Shear stress factors Double Counter-sunk bolting Hole Diameter(d) [mm] dt [mm] bfxy bfxy bfxy bfxy bfxy bfxy bfxy bfxy editor@iaeme.com

8 B. Venkatesh, Gowtham Reddy G, Benjamin Rohit and Syed Sharin 5. CONCLUSION Figure 9 Comparing the different type of bolts From the results obtained [Table 4] and [Table 5] above we conclude that the cylindrical bolts are more efficient in handling higher stresses, even when comparing cylindrical bolts with a normal counter-sunk bolt and the double counter-sunk bolts the cylindrical bolts are the ones which dominate as the stresses induced in them is less [Fig 9]. But at the same time the counter-sunk bolts are not exposed to the outer environment and are always within the surface of the glass whereas the cylindrical bolts protruding out and hence tend to spoil the outlook of the self-supporting skins. Therefore we can note that to have better looking structure with counter-sunk bolts we have to increase the margin of safety as indicated above. Hence there always exists a negotiable approach in choosing the appropriate bolt for the need and to satisfy the purpose. REFERNCES [1] Mark Porter, Aspects of Structural Design with Glass, Balliol College and the Department of Engineering Science,The University of Oxford, 2001 [2] Technische Regeln für die Bemessung und Ausführung punktförmig gelagerter [3] Verglasungen (TRPV), Schlussfassung August 2006, [4] DS Simulia. Abaqus Scripting Manual [5] Benjamin Rohit, Neel Sagar, Supreeth R, Dandapani P, Computation of Stress Factors for Counter-Sunk Bolt Fixings in Self Supporting Skins in accordance with DIN ,14 th International Conference on Developments in Science, Management and Engineering, 14 th & 15 th April 2017 [6] D. Rajesh, V. Balaji, A. De varaj and D. Yogaraj, An Investigation on Effects of Fatigue Load on Vibration Characteristics of Woven Fabric Glass/Carbon Hybrid Composite Beam under Fixed-Free End Condition using Finite Element Method. International Journal of Mechanical Engineering and Technology 8(7), 2017, pp [7] B. Anjaneyulu, G. Nagamalleswara Rao, Dr. K. Prahladarao and D. Harshavardhan. Analysis of Process Parameters in Milling of Glass Fibre Reinforced Plastic Composites. International Journal of Mechanical Engineering and Technology, 8(2), 2017, pp editor@iaeme.com