311 C H19

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311 C H19

  1. 1. <ul><li>X.) Bolted Connections (Steel) </li></ul><ul><li> A.) Introduction </li></ul><ul><li>1.) Types of bolts used with structural steel </li></ul><ul><li> a.) A307 - low carbon (lowest </li></ul><ul><li> strength) standard head size. </li></ul><ul><li>b.) A325 - high strength - heavy duty nut. </li></ul>
  2. 2. <ul><li>c.) A490 - high strength - heavy </li></ul><ul><li> duty nut. Sizes range from 1/2” to 1-1/2” in 1/8” increments. </li></ul>
  3. 3. <ul><li>2.) Types of Connections </li></ul><ul><li>a.) Tension/Compression Connection </li></ul><ul><li>(Axial Members - Trusses) </li></ul><ul><li>i.) Lap Joint - Bolts in single shear </li></ul><ul><li>- Eccentric - not as good </li></ul>
  4. 4. <ul><li>ii.) Butt Joint - bolts in Double Shear </li></ul><ul><li> - concentric </li></ul><ul><li>- better </li></ul>
  5. 5. <ul><li>b.) Shear Connection (Beams) </li></ul><ul><li>-Simple Support (No moment transferred at connection) </li></ul><ul><li> - Connect web only </li></ul><ul><li>- Bolts in Shear </li></ul>+ +
  6. 6. <ul><li>c.) Moment & Shear (Beam Connections) </li></ul><ul><li>- Fixed Support </li></ul><ul><li>- Connect Flange & Web </li></ul>+ + d.) Any combination of a.), b.), & c.) + +
  7. 7. <ul><li>B.) Possible Way a Bolted Connection could fail (failure modes) </li></ul><ul><li>1.) Bolts fail in Shear </li></ul>
  8. 8. <ul><li>2.) Member or Connection plates fail in </li></ul><ul><li> bearing or crushing </li></ul><ul><li> - making the bolt holes oblong </li></ul><ul><li>(crushing steel in plate) </li></ul><ul><li>- excessive deformation </li></ul>
  9. 9. <ul><li>3.) Member or Plates fail in tension </li></ul><ul><li>a.) failure by yielding on gross area is </li></ul><ul><li> b.) failure by fracture on net area </li></ul>Gross Area Net Area a. b.
  10. 10. <ul><li>4.) Member or Connecting plates fail by end or edge tear-out </li></ul>end distance too small or edge distance too small
  11. 11. <ul><li>C.) Design of Bolted Connections </li></ul><ul><li>- check all 4 possible failure modes: </li></ul><ul><li> 1.) Bolt Shear </li></ul><ul><li>2.) Member/Plate bearing failure </li></ul><ul><li>3.) Member/Plate tension failure </li></ul><ul><li>4.) Member/Plate end or edge tear-out </li></ul>
  12. 12. <ul><li> 1.) Bolt Shear </li></ul><ul><li> P V = A B  v,all Nn </li></ul><ul><li> N= __ P v ___ (solving for N) </li></ul><ul><li> nA B  v,all </li></ul><ul><li>P v = allowable load on connection, based on bolt shear (k) </li></ul><ul><li>A B = C.S.A. of one bolt (in 2 ) </li></ul><ul><li>N = No. of bolts in connection </li></ul><ul><li>n= number of shear planes </li></ul>
  13. 13. <ul><li> v,all = Allow. shear stress (ksi) ,Table 19-1 </li></ul><ul><li>a.) Slip Critical - when no slippage of joint can be permitted. </li></ul><ul><li>b.) Bearing Type - when slippage of joint </li></ul><ul><li>joint can be permitted so that bolts can bear on connected parts. </li></ul><ul><li>c.) Threads in or out of shear plane (for bearing connections only) </li></ul>
  14. 14. threads in shear plane threads not in shear plane
  15. 15. 2.) Member/Plate Bearing P P = dt  p,all N P P = Allowable load on connection based on bearing (k) d = Bolt diameter (in.) t = thickness of member/plate (in.) N = Number of bolts in connection
  16. 16. <ul><li>  p,all = allowable bearing stress of member/plate (ksi) </li></ul><ul><li> = 1.5  t,ult </li></ul><ul><li> = 1.5 (58ksi) = 87 ksi for A36 steel </li></ul><ul><li> t,ult in Table 19-2 for other materials. </li></ul><ul><li> </li></ul>
  17. 17. <ul><li>3.) Tension in member/plates -must satisfy </li></ul><ul><li>two requirements: </li></ul><ul><li>P all < A g (0.60  Y ) </li></ul><ul><li>P all < A n (0.50  t,ult ) </li></ul><ul><li> A g = Gross CSA of member or connection plate </li></ul><ul><li> Y = yield strength of member or plate </li></ul>
  18. 18. <ul><li> A n = Net CSA of member or plate = A g - A holes </li></ul><ul><li> t,ult = ultimate strength of member or plate </li></ul>
  19. 19. <ul><li>4.) Bolt Spacing Edge/End Distance </li></ul>P L B L end L edge L edge L B
  20. 20. <ul><li>a.) L end = distance from center of standard hole to end of connected part along the line of transmitted force. </li></ul><ul><li>Must satisfy two requirements: </li></ul><ul><li>L end > 2P B __ </li></ul><ul><li> t,ult (t) </li></ul><ul><li>L end > Table J3.5 </li></ul>
  21. 21. <ul><li> P B = Applied load per bolt = P/N </li></ul><ul><li> t,ult = ultimate strength of member/plate </li></ul><ul><li> t = thickness of member or plate </li></ul>
  22. 22. <ul><li>b.) L edge = distance from center of </li></ul><ul><li>standard hole to edge of connected part, perpendicular to line of force </li></ul><ul><li>L edge > Table J3.5 </li></ul>
  23. 23. <ul><li>c.) L B = Distance between centerlines of </li></ul><ul><li>standard holes. Again, two criteria </li></ul><ul><li>L B > 2.67 d (all directions) </li></ul><ul><li>L B > 2P B __ + d (in direction of load) </li></ul><ul><li>  t,ult (t) 2 </li></ul><ul><li>d = bolt diameter </li></ul><ul><li>P B  t,ult , & t defined previously </li></ul>
  24. 34. <ul><li>A.) INTRO. TO WELDED CONNECTIONS </li></ul><ul><li>1.) 6500 o F electric arc melts the weld electrode to the material being connected ( the base metal). </li></ul><ul><li>2.) Weld electrode must be compatible material for the base metal, i.e. same chemical makeup </li></ul>
  25. 35. <ul><li>3.) E60xx means 60 ksi ultimate strength </li></ul><ul><li>would use with low carbon (A36 or 1020) </li></ul><ul><li>steel. </li></ul><ul><li>4.) Weld geometry </li></ul><ul><li>a.) Groove welds: </li></ul><ul><li>- Full Penetration </li></ul><ul><li>- Partial Penetration </li></ul><ul><li>b.) Fillet Welds </li></ul>
  26. 36. <ul><li>B.) WELDED CONNECTION STRENGTH </li></ul><ul><li>1.) Groove Welds: Full strength of the connected part is developed if: </li></ul><ul><li>a.) full penetration </li></ul><ul><li>b.) full length </li></ul><ul><li>Edge prep. increases cost </li></ul>
  27. 37. <ul><li>2.) Fillet Welds </li></ul><ul><li>Required size (“a” dimension) of weld is controlled by: </li></ul><ul><li>a.) Minimum size is controlled by thickness of the thicker of two parts joined. (Table 19-4) </li></ul><ul><li>b.) Maximum size is controlled by the thickness of the welded edge. (Table 19-4) </li></ul>
  28. 38. <ul><li>2.) Fillet Welds </li></ul><ul><li>b.) Maximum size: </li></ul>a max t
  29. 39. <ul><li>2.) Fillet Welds </li></ul><ul><li>Required length of weld (L) is controlled by: </li></ul><ul><li>a.) weld shear strength: </li></ul><ul><li>P v =  v,all t e (units of lb/in) </li></ul><ul><li> = (0.3  t,u ) t e </li></ul><ul><li> t e = “effective throat thickness” </li></ul><ul><li> = a(sin45 o ) = 0.707a </li></ul><ul><li> P v =(0.3  t,u ) (0.707a ) </li></ul><ul><li>P v = 0.212  t,u a (units of lb/in of weld) </li></ul>
  30. 40. <ul><li>b.) L > 4a </li></ul><ul><li>c.) L > w </li></ul><ul><li>> width of part </li></ul><ul><li>d.) L > 5 t min </li></ul><ul><li>e.) Returns > 2a </li></ul>return L = weld length Section View w t min a

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