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INTRODUCTION

INTRODUCTION. Department Of Civil Engineering Govt. Poly. College, Bathinda Topic – Tension member Subject – Steel Structures Design Presenter- Er . Rani Devi B.E.(Civil), M.E. (Structures) Mob.- 9465265746. Introduction

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INTRODUCTION

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  1. INTRODUCTION Department Of Civil Engineering Govt. Poly. College, Bathinda Topic – Tension member Subject – Steel Structures Design Presenter- Er. Rani Devi B.E.(Civil), M.E. (Structures) Mob.- 9465265746 Punjab Edusat Society

  2. Introduction Steel structures are structures in which the members are made of steel and are joined by welding, riveting, or bolting. Because of the high strength of steel, these structures are reliable and require less material than other types of structures. In modern construction, steel structures are widely used such as industrial buildings, storage tankgas tanks, communication structures (radio and television towers and antennas), and power-engineering structures. Punjab Edusat Society

  3. The top beams in a truss are called top chords and are generally in compression, the bottom beams are called bottom chords and are generally in tension, the interior beams are called webs, and the areas inside the webs are called panels. Punjab Edusat Society

  4. Design for the steel frame of a twin-bay industrial building: (1) lattice, (2) column, (3) crane girder, (4) skylight, and (5) web members Punjab Edusat Society

  5. Tension Members Members which are subjected to direct tension are called tension members. The Members can be of any standard steel section e.g., angle iron, channel section etc. In case of frames and trusses, a tension member is called a tie. Punjab Edusat Society

  6. Types of Sections The types of section is governed by the nature and magnitude of stresses to which, it is subjected. The different type of sections are shown in figure and classified as: Rod, round or square :- These are used in buildings for the lateral and sway bracings, hangers, segmental arch floors and timber trusses etc. Punjab Edusat Society

  7. (2) Flats :- These are used as tension member in light trusses connected by welding at their ends. (3) Eye bars :- These are used in pin connected Structures. Punjab Edusat Society

  8. (4) Single angle sections :- These are used as tension member in light roof trusses, bracing members in plate girder bridges and light latticed girder bridges, not recommended as best tension member as they are subjected to bending stresses due to the eccentric loads. Punjab Edusat Society

  9. (5) Double angle section :- These are used extensively in roof trusses, may be connected to gusset plate on same or opposite faces i.e., by placing the gusset plate in between the two angles. The later type of end connection is preferred and more economical as it eliminates bending stresses. Punjab Edusat Society

  10. Punjab Edusat Society

  11. (6) T-sections :- These are used as a substitute of former type of double angles. (7) Double channel section :- These are used for heavy structures subjected to bending and direct stresses. Punjab Edusat Society

  12. Strength of a Tension Member The Strength of a Tie Member or load bearing capacity of a tension member is calculated as :- Strength of a Tension Member = Net area × Permissible tensile stress(σat). The strength depends upon net area. Permissible tensile stress(σat) for a tension member is generally taken as 150MPa Punjab Edusat Society

  13. Net Sectional Area Net sectional area of a tension member is the gross cross section area of the member minus the deduction for holes. Case 1 - For Plate : In determining the net sectional area of the plates, the arrangement of the rivets plays an important role. The riveting in plate can be of two types i.e.: (a)Chain riveting (b) Zig-Zag riveting. Punjab Edusat Society

  14. (a) Plates connected by Chain riveting : Let, Anet= Net cross sectional area along any section 1-1 b = Width of Plate n = number of rivets along the section under consideration Punjab Edusat Society

  15. d = Gross diameter of the rivets t = Thickness of the plate Anet = Gross area- area of plate lost in the process of making holes Anet = b t - nd t Anet = (b – nd) t Punjab Edusat Society

  16. (b) Plates connected by Zig-Zag or staggered riveting : Let, Anet = Net area of cross sectional b = Width of Plate n = number of rivets in the plane under consideration. Punjab Edusat Society

  17. n’ = number of gauge distance s = staggered pitch g = gauge distance t = Thickness of the plate Anet = Punjab Edusat Society

  18. Case 2 - For single angle connected by one leg only: Net effective area, i.e., Anet= A1 + A2K Where, Anet = Net cross-sectional area A1 = Net cross-sectional area of connected leg Punjab Edusat Society

  19. A1 = (length of leg – ½ t – nd) × t A2 = Gross cross-sectional area of outstanding leg A2 = (length of leg – ½ t) x t K = constant = Anet= A1 + A2K Punjab Edusat Society

  20. Case 3. For a pair of angles place over a single tee connected by only one leg of each angle to the same side of the gusset plate : Punjab Edusat Society

  21. Net effective area, i.e., Anet= A1 + A2K Where, Anet = Net cross-sectional area A1 = Net cross-sectional area of connected leg(flange of the tee) A2 = Gross cross-sectional area of outstanding leg(web of the tee) K = constant = Punjab Edusat Society

  22. A1 = 2 (length of leg – ½t – nd) × t A2 = 2 (length of leg – ½ t) × t In case of T section A1 = (bf - 2d ) × tf A2 = Gross area of web = tw × (overall depth(h) – tf) Punjab Edusat Society

  23. Case 4. For double angles or a tee placed back to back and connected to each side of the gusset or side of a rolled section. :- Punjab Edusat Society

  24. Deduction for rivet holes = number of rivets × gross diameter of one rivet × thickness of plate i.e., = n × d × t Net effective area, Anet = Gross area – Deduction for rivet holes Punjab Edusat Society

  25. Numerical Problems Problem 1: A plate 240mm wide and 12mm thick is connected by 20mm φ rivets as shown. Calculate the strength of the tension plate. Take σat= 150N/mm2 Punjab Edusat Society

  26. Solution: Nominal dia. of rivet (D) =20mm Gross dia. of rivet hole (d) = 20 +1.5 = 21.5mm Width of plat = 30 + 60 + 60+ 60 + 30 = 240mm s = 50mm g = 60mm Considering the failure of the plate along section line 1-2-3-4, we have; Anet1 = (b – nd) t t = 12mm, n = 2, b = 240mm, d = 21.5mm Punjab Edusat Society

  27. Anet1 = (240 -2 × 21.5) × 12 = 3564mm2 Now for area along staggered line 1-2-5-3-6-7 Anet2= Where b = 240mm n = 4 d = 21.5mm n’ = 3 t = 12mm Punjab Edusat Society

  28. Anet2 = = 2073 mm2 Minimum net area of section = Anet2 Strength of the plate = 2073 × 150 = 310950 = 310.95kN Punjab Edusat Society

  29. Problem 2: Calculate the strength of a tie composed of ISA 100 × 75 × 8mm with longer legs connected by 16mm dia. rivets. Take σat= 150N/mm2 Punjab Edusat Society

  30. Solution: Nominal dia. of rivet = 16mm Gross dia. of rivet = 16 + 1.5 = 17.5mm Net Area; Anet = A1 + A2K A1 = = 628mm2 A2 = 561mm2 K= constant = Punjab Edusat Society

  31. Anet = A1 + A2K = 628 + 561 × 0.77 = 1059.97mm2 Strength of ISA 100 × 75 × 8 = 1059.97mm2 × 150 = 158995.5N = 158.99kN Punjab Edusat Society

  32. Problem 3: Calculate the strength of a tie member composed of 2 ISA 125 × 75 × 8mm placed back to back connected by longer legs by 20mm dia. rivets on same side of the gusset plate. Take σat= 150N/mm2 Punjab Edusat Society

  33. Solution: Nominal dia. of rivet (D) =20mm Gross dia. of rivet hole (d) = 20 +1.5 = 21.5mm Anet = A1 + A2K A1 = = 1592mm2 A2 = = 1136mm2 K = constant = Punjab Edusat Society

  34. K = Net effective area Anet = A1 + A2K = 1592 + 1136 × 0.875 = 2586mm2 Strength of tie member = 2586 × 150 = 387900N = 387.9kN × Punjab Edusat Society

  35. Problem 4: Calculate the strength of a tie member composed of 2ISA 125 × 75 × 8mm placed back to back connected by longer legs by 20mm dia rivets on both sides of the gusset plate. Punjab Edusat Society

  36. Solution: From steel table, gross area of ISA 125 × 75 × 8mm = 15.38cm2 = 1538mm2 Net effective area = Gross area – Deduction for rivet holes Anet = 2[1538 – 21.5 × 8] = 2732mm2 Strength of tie member = 2732 × 150 = 109.8kN Punjab Edusat Society

  37. Problem 5: Determine the strength of ISHT 75 which is used as a tie member. It is connected through its flange by means of 20mm diameter rivets. Take σat= 150N/mm2 Solution: Data Given: Tie member consists of ISHT 75 Nominal dia. of rivet (D) =20mm Gross dia. of rivet hole (d) = 20 +1.5 = 21.5mm Punjab Edusat Society

  38. Thickness of Flange, tw = 8.4mm Thickness of web, tf = 9mm Overall Height = 75mm Punjab Edusat Society

  39. Case under consideration : Tee (or 2ISA) connected on same side of the gusset plate by riveting: Anet = A1 + A2K K = constant = Properties of ISHT 75 (From steel cables) Width of plate, b = 150mm Punjab Edusat Society

  40. Net Area of flange, A1 = (width of flange –nd) × tf = (150 – 2 × 21.5) × 9 (Since, number of rivets(n) = 2) = 963mm2 Gross area of web, A2 = (75 - 9) × 8.4 (Since, Area = Length of web × tw) = 554.4mm2 K = Punjab Edusat Society

  41. Net cross sectional area, Anet = A1 + A2K = 963 + 554.4 × 0.897 = 1460.29mm2 Tensile Strength of the T – section = Anet × σat = 1460.29 × 150 = 219043.5N = 219.04kN Punjab Edusat Society

  42. Design of Members Subjected to Axial Tension Step 1. Calculation of the required net area The axial pull (force) to be transmitted by the member and the allowable stress in axial tension ( permissible tensile force i.e. σat) are known for the steel with yield stress fy. Net sectional area required = Punjab Edusat Society

  43. i.e. Anet reqd. = Step 2. Selection of suitable section Try a suitable section, from steel tables having sectional area about 20 to 40% greater (in case of riveted joint) and 10% greater (in case of welded joint) than the required net area. In case the member selected is ISA, than select unequal angle and connect longer leg with gusset plate for getting more strength i.e. (load carrying capacity) Punjab Edusat Society

  44. Step 3. Calculate the net sectional (effective) area of the selected section (As discussed earlier) Step 4. Check for net Sectional area The net area calculated for trial section (in step 3) should be slightly greater than the required net area. If it is so then selected section is OK. Other wise try some other section. i.e. Net area of trial section > Net area required Punjab Edusat Society

  45. Step 5. Check for Slenderness ratio (λ). Slenderness ratio, is the ratio of effective length of member to the least radius of gyration. i.e. Slenderness ratio λ = The value of radius of gyration (rmin) can be obtained from steel tables. Punjab Edusat Society

  46. A tension member in which a reversal of direct stress due to load other than wind or seismic forces would occur, shall not have a slenderness ratio more than 180. • A member normally acting as a tie in a roof truss, but subject to possible reversal of stress resulting from the action of wind or seismic forces shall have slenderness ratio not greater than 350. Punjab Edusat Society

  47. Step 6. Design of end connections The end connections may be designed as a riveted connection or welded connection. • For riveted connection • Select suitable size of rivet and determine the rivet value ( i.e. least of Pband Pf) • Find the number of rivets by the relation ; Number of rivets required = Punjab Edusat Society

  48. (iii) The arrangement of rivets should be made in such a way that : • there is no eccentricity of loading. • The centre of gravity of the section coincides with the C.G. of group of rivets. Punjab Edusat Society

  49. (b) For welded connections • Find the minimum and maximum size of fillet weld and select the suitable size of weld (S) and find the value of effective throat thickness, t = 0.7 S • Calculate the strength of weld/mm length by the formula; = τvf× l × t Punjab Edusat Society

  50. Problems Based On Design of Tension Member Problem 1.Design a tension member subjected to pull of 165 kN using unequal angles placed back to back with their longer legs connected on both sides of gusset plate by 18mm diameter rivets. Use PDSR (Power Driven Shop Rivets). Take σat= 150N/mm2 Punjab Edusat Society

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