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SEISMIC LOADS LATERAL LOAD FLOW FRAMES and SHEAR WALLS

SEISMIC LOADS LATERAL LOAD FLOW FRAMES and SHEAR WALLS. SEISMIC LOAD. Determine Spectral Response Parameters at design location. At 37.80 N , -122.37 W : Ss = 1.50 S 1 = 0.60. Determine Site Coefficients. Site Class : D Ss > 1.25 Fa = 1.0 S 1 > 0.5 Fv = 1.5.

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SEISMIC LOADS LATERAL LOAD FLOW FRAMES and SHEAR WALLS

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  1. SEISMIC LOADS LATERAL LOAD FLOW FRAMES and SHEAR WALLS

  2. SEISMIC LOAD

  3. Determine Spectral Response Parameters at design location At 37.80 N , -122.37 W : Ss = 1.50 S1 = 0.60

  4. Determine Site Coefficients Site Class : D Ss > 1.25 Fa = 1.0 S1 > 0.5 Fv = 1.5 Determine Design Spectral Acceleration Parameters SMS = (1.0)(1.5) = 1.5 SDS = (2/3)(1.5) = 1.0

  5. Cs = SDS /(R/I) =1.0/(R/I) Class II : I = 1.0 Ordinary Moment Resisting Frame : R = 3.5 V = 1.0/3.5 W 0.3 W

  6. Seismic Load is generated by the inertia of the mass of the structure : VBASE Redistributed (based on relative height and weight) to each level as a ‘Point Load’ at the center of mass of the structure or element in question : FX VBASE Wx hx S(w h) VBASE = (Cs)(W) ( VBASE ) Fx =

  7. Total Seismic Loading : VBASE = 0.3 W W = Wroof + Wsecond

  8. Wroof

  9. Wsecond flr

  10. W = Wroof + Wsecond flr

  11. VBASE

  12. Redistribute Total Seismic Load to each level based on relative height and weight Froof Fsecond flr VBASE (wx)(hx) S (w h) Fx =

  13. Load Flow to Lateral Resisting System : Distribution based on Relative Rigidity Assume Relative Rigidity : Single Bay MF : Rel Rigidity = 1 2 - Bay MF : Rel Rigidity = 2 3 - Bay MF : Rel Rigidity = 3

  14. Distribution based on Relative Rigidity : SR = 1+1+1+1 = 4 Px = ( Rx / SR ) (Ptotal) PMF1 = 1/4 Ptotal

  15. Lateral Load Flow diaphragm > collectors/drags > frames

  16. STRUCTURAL DIAPHRAGM A structural diaphragm is a horizontal structural system used to transfer lateral loads to shear walls or frames primarily through in-plane shear stress Basically, combined with vertical shear walls or frames IT ACTS LIKE A LARGE I-BEAM

  17. STRUCTURAL DIAPHRAGM Flexible or Semi-flexible Type: Plywood Metal Decking

  18. STRUCTURAL DIAPHRAGM Rigid Diaphragm Type: Reinforced Concrete Slab Concrete-filled Metal Deck composite Slab Braced/horizontal truss

  19. STRUCTURAL DIAPHRAGM Rigid Diaphragm: Almost no deflection Can transmit loads through torsion Flexible Diaphragm: Deflects horizontally Cannot transmit loads through torsion

  20. COLLECTORS and DRAGS

  21. COLLECTORS and DRAG STRUTS A beam element or line of reinforcement that carries or “collects” loads from a diaphragm and carries them axially to shear walls or frames. A drag strut or collector behaves like a column.

  22. COLLECTOR FRAME DIAPHRAGM COLLECTOR FRAME Lateral Load Flow diaphragm > collectors/drags > frames

  23. COLLECTOR FRAME LATERAL LOAD DIAPHRAGM COLLECTOR FRAME Lateral Load Flow diaphragm > collectors/drags > frames

  24. COLLECTOR FRAME LATERAL LOAD DIAPHRAGM COLLECTOR FRAME Lateral Load Flow diaphragm > collectors/drags > frames

  25. LATERAL LOAD COLLECTOR FRAME FRAME COLLECTOR DIAPHRAGM COLLECTOR COLLECTOR FRAME

  26. LATERAL LOAD RESISTING: MOMENT frames BRACED frames SHEAR WALLS

  27. INSTABILITY OF THE FRAME

  28. STABILIZE THE FRAME FIX ONE OR MORE OF THE BASES

  29. STABILIZE THE FRAME FIX ONE OR MORE OF THE CORNERS

  30. STABILIZE THE FRAME ADD A DIAGONAL BRACE

  31. RELATIVE STIFFNESS OF FRAMES AND WALLS LOW DEFLECTION HIGH STIFFNESS ATTACTS MORE LOAD HIGH DEFLECTION LOW STIFFNESS ATTRACTS LESS LOAD

  32. BRACED FRAMES

  33. BRACED FRAMES

  34. SHEAR WALLS

  35. SHEAR WALLS

  36. SHEAR WALLS

  37. SHEAR WALLS

  38. SHEAR WALLS

  39. MOMENT FRAMES

  40. MOMENT FRAMES

  41. MOMENT FRAMES INDETERMINATE STRUCTURES SOLVE BY “PORTAL FRAME METHOD”

  42. MOMENT FRAMES FIXED BASE =6 UNKNOWNS, 3 AVAILABLE EQUATIONS OF EQUILIBRIUM STATICALLY INDETERMINATE TO THE 3RD DEGREE SOLVE BY “PORTAL FRAME METHOD”

  43. MOMENT FRAMES PINNED BASE =4 UNKNOWNS, 3 EQUATIONS, STATICALLY INDETERMINATE TO FIRST DEGREE SOLVE BY “PORTAL FRAME METHOD”

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