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Flexural Strength of Exterior Metal Building Wall Assemblies with Rigid Insulation

Flexural Strength of Exterior Metal Building Wall Assemblies with Rigid Insulation. Tian Gao and Cris Moen The Charles E. Via, Jr. Dept. of Civil & Environmental Engineering Virginia Tech www.moen.cee.vt.edu SSRC Annual Conference Grapevine, Texas, April 18 , 2012. Outline:.

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Flexural Strength of Exterior Metal Building Wall Assemblies with Rigid Insulation

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  1. Flexural Strength of Exterior Metal Building Wall Assemblies with Rigid Insulation TianGao and Cris Moen The Charles E. Via, Jr. Dept. of Civil & Environmental Engineering Virginia Techwww.moen.cee.vt.eduSSRC Annual ConferenceGrapevine, Texas, April 18, 2012

  2. Outline: • Introduction • Suction/Uplift Loading • Design Methods • Experiments • Ongoing Study

  3. Introduction: Metal building • Low rise, light weight and long span building. • Many cold-formed steel members are used. Metal Building Metal Building Metal Building Metal Building

  4. Wind loading: Gravity/Pressure Gravity Pressure

  5. Wind loading: Uplift/Suction Our focus! Uplift Suction

  6. Inside of the building: Primary frame

  7. Inside of the building: Purlins (Roof) Primary frame Girts (Wall)

  8. Inside of the building: Sheathing Purlins (Roof) Primary frame Girts (Wall) Sheathing

  9. Inside of the building: Sheathing Purlins (Roof) Simple Primary frame Continuous Girts (Wall) Sheathing

  10. Design variables: Purlin Girt Zee Cee . . . X None Fiber glass Rigid board X Through-fastened Standing seam X X Continuous Simple X Uplift/Suction Gravity/Pressure

  11. In this study, we will cover: Purlin Girt Zee Cee . . . X None Fiber glass Rigid board X Through-fastened Standing seam X X Continuous Simple X Uplift/Suction Gravity/Pressure

  12. Loading: Wall/Suction Wall panel Wall panel screw girt girt A A Section A-A

  13. Loading: Wall/Suction Bending + Rotation Wall panel Wall panel girt girt X X

  14. Loading: Roof/Uplift Bending + Rotation Roof Panel B X B X Section B-B kФ

  15. Design Methods: Analytical approach Peköz, T.B., and Soroushian, P. (1982). “Behavior of C- and Z-purlins under wind uplift.”Proc., 6th International Specialty Conference on Cold-Formed Steel Structures, Rolla, MO. • Peköz’s model • EuroCode q K w

  16. Design Methods: Analytical approach Peköz, T.B., and Soroushian, P. (1982). “Behavior of C- and Z-purlins under wind uplift.”Proc., 6th International Specialty Conference on Cold-Formed Steel Structures, Rolla, MO. • Peköz’s model • EuroCode q ??? Test kФ K w

  17. Design Methods: Analytical approach Peköz, T.B., and Soroushian, P. (1982). “Behavior of C- and Z-purlins under wind uplift.”Proc., 6th International Specialty Conference on Cold-Formed Steel Structures, Rolla, MO. • Peköz’s model • EuroCode q ??? Test kФ K w Gao, T., and Moen, C.D. (2012). “Rotational restraint prediction method for through-fastened metal building wall girts and roof purlins.”Thin-Walled Structures.

  18. Design Methods: Experimental approach • R-factor method • AISI • AS/NZS Wall/roof flexural capacity in a full scale test (Vacuum Test) Fully braced girt/purlin capacity

  19. AISI R-factor: Z C d

  20. 50 Vacuum Tests @ VT: • Motivation: Energy efficiency (*ASHRAE-90.1). • Determine the R-factor for the case when the rigid board insulation is used. Metal panel Metal panel Girts Girts Metal panel Girts 25mm Rigid Board 50mm 100mm * ASHRAE-90.1. (2010). American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA.

  21. Test setup: Girts Rigid insulation Panel Vacuum Girts Rigid insulation Panel Vacuum

  22. Results: Stocky • Failure modes • (4) failure modes • Effect of cross-section local slenderness • Stocky (200 mm deep, 2.5 mm thick) • Slender (250 mm deep, 1.5 mm thick) • R-factors Slender

  23. Failure mode-1: Panel failure

  24. Failure mode-2: Panel pull over • Thick rigid board = “Washer”. • Can prevent panel pull over.

  25. Failure mode-3: Screw bending/fracture • If the rigid board insulation is used, and the girt is thick enough to clamp the screw. Board Thickness

  26. Failure mode-3: NOT for slender girt • The girt is too thin to clamp the screw.

  27. Failure mode-4: Girt/Purlin failure • Rotation + Yielding • Rotation + Local Buckling

  28. Slender Z-section, 50mm rigid board(Video) http://www.youtube.com/user/drcrismoen

  29. Local slenderness • Slender cross-section: the connection becomes not that important, because all action happens in the girts. • Stocky cross-section: connection failure. Slender Z-section Stocky Z-section

  30. R-factors for Z-section, bare panel Slender Failure modes: Panel failure Panel pull over Screw failure Girts failure 2 4 4 2 2 2

  31. R-factors for Z-section, bare panel • Panel pull over dominates for locally stocky Z-sections. Stocky Failure modes: Panel failure Panel pull over Screw failure Girts failure 2 4 4 2 2 2

  32. R-factors for Z-section, rigid board • For slender Z250, No reduction in R-factor. Failure modes: Panel failure Panel pull over Screw failure Girts failure 4 4 4 4

  33. R-factors for Z-section, rigid board • For slender Z250, No reduction in R-factor. • For stocky Z200, R-factor is reduced from 0.65 to 0.5. Failure modes: Panel failure Panel pull over Screw failure Girts failure 4 3 4 4 4 4 4 2 2 3 4

  34. R-factors for Z-section, rigid board • For slender Z250, No reduction in R-factor. • For stocky Z200, R-factor is reduced from 0.65 to 0.5. • Gao, T., Moen, C.D. (2011). “Flexural strength of exterior metal building wall assemblies with rigid Insulation.” Virginia Tech Research Report No. CE/VPI-ST-11/01, Blacksburg, Virginia. kФ LOW! Failure modes: Panel failure Panel pull over Screw failure Girts failure 4 3 4 4 4 4 4 2 2 3 4

  35. R-factors for C-section, rigid board • For slender C250, No reduction in R-factor. • For stocky C200, R-factor is reduced from 0.65 to 0.4. Failure modes: Panel failure Panel pull over Screw failure Girts failure 4 4 4 4 2 3 3 4 2 3

  36. Summary: • Bare panel: • Rigid insulation: • Slender cross-section: • Stocky cross-section:

  37. Summary: • Bare panel: • Rigid insulation: • Slender cross-section: • Stocky cross-section: • Panel pull over

  38. Summary: • Bare panel: • Rigid insulation: • Slender cross-section: • Stocky cross-section: • Panel pull over • Prevent panel pull over • Screw bending/fracture • Lower kФ

  39. Summary: • Bare panel: • Rigid insulation: • Slender cross-section: • Stocky cross-section: • Panel pull over • Prevent panel pull over • Screw bending/fracture • Lower kФ • Girt/Purlin body

  40. Summary: • Bare panel: • Rigid insulation: • Slender cross-section: • Stocky cross-section: • Panel pull over • Prevent panel pull over • Screw bending/fracture • Lower kФ • Girt/Purlin body • Connection

  41. Ongoing study (Limit State Design): Panel failure: Panel pull over: Screw bending/fracture: Girt/Purlin failure:

  42. Ongoing study (Limit State Design): • Use Direct Strength Method (DSM) to predict the panel flexural capacity. Panel failure: Panel pull over: Screw bending/fracture: Girt/Purlin failure: • DSM is using the buckling strengths (local, distortional and global) to predict the capacity.

  43. Ongoing study (Limit State Design): Panel failure: Panel pull over: Screw bending/fracture: Girt/Purlin failure: • Panel-flange connection study. • Panel connection failure. AISI E4.2.2. Pull-Over Gao, T., and Moen, C.D. (2012). “Rotational restraint prediction method for through-fastened metal building wall girts and roof purlins.”Thin-Walled Structures.

  44. Ongoing study (Limit State Design): Panel failure: Panel pull over: Screw bending/fracture: Girt/Purlin failure: • Gao, T., Moen, C.D. (2011). “Flexural strength of exterior metal building wall assemblies with rigid Insulation.” Virginia Tech Research Report No. CE/VPI-ST-11/01, Blacksburg, Virginia. • Board-flange connection study. • Flange thickness & screw. • Fastener bending study.

  45. Ongoing study (Limit State Design): Panel failure: Panel pull over: Screw bending/fracture: Girt/Purlin failure:

  46. Ongoing study (4. Girts/Purlin failure): • Finite strip analysis • (Mcrl, Mcrd, Mcre) DSM kϕ Mn • EuroCode • Peköz Gao, T., and Moen, C.D. (2012). “Rotational restraint prediction method for through-fastened metal building wall girts and roof purlins.”Thin-Walled Structures. Bare panel • Gao, T., Moen, C.D. (2011). “Flexural strength of exterior metal building wall assemblies with rigid Insulation.” Virginia Tech Research Report No. CE/VPI-ST-11/01, Blacksburg, Virginia. Rigid insulation

  47. Primary results: DSM prediction • 46 simple span Vacuum Tests, uplift/suction loading. • Z and C-sections, bare panel only, girt/purlin failure. Mean=1.01 COV=19%

  48. Questions This presentation is @ www.moen.cee.vt.edu

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