Fall Protection Systems Fall Arrest Anchor Analysis

Fall Protection Systems Fall Arrest Anchor Analysis Aaron Randal Andy Cash Tiruneh Haile December 7, 2005 Introduction Existing Roof and Anchor Cond...
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Fall Protection Systems Fall Arrest Anchor Analysis Aaron Randal Andy Cash Tiruneh Haile December 7, 2005

Introduction Existing Roof and Anchor Conditions

Anchor Protruding Through Roof Sheeting and Weather Proofing

Interior View of Beam Rafters, Roof Purlins and Existing Anchor

Close-up View of Anchor and Attachment Loop

Goal Statement To evaluate the condition of the existing roof anchor and verify compliance with OSHA regulations for Fall Arrest Systems. Analysis Action Plan ¾ Identify Parameters of Interest ƒ Deflection ƒ Maximum Stress ƒ Verify Elastic Range Model ƒ Supporting Conditions ¾ Eliminate Unnecessary Part Features ƒ Attachment Loop ƒ Roof Sheeting ƒ Purlins ¾ Determine Applicable Loads – OSHA Summary

OSHA Summary ¾ Working heights of 6 FT or more require fall protection ¾ Fall Protection Methods o Engineering Control ƒ Platforms and Railing o Fall Protection ƒ Fall Arrest ¾ Fall Arrest System o System Components ƒ Full Body Harness ƒ Connection Devices • Dee-rings • Lifelines (Steel Cable) • Lanyards ƒ Tie-off Point (Steel Pipe Anchor and Underlying Structure) ¾ Fall Arrest System Requirements o Lanyard (Shock Absorbing) ƒ 5,000 lb minimum breaking strength ƒ 1800 lb maximum arrest force during deployment o Lifeline ƒ 5,000 lb minimum breaking strength o Tie off Point ƒ Rigid and not deflect greater than 0.04 IN (1mm) for an applied force of 2,250 lb (10 kN)

Theoretical Background Linear Stress Strain Relation Ship

σ = E *ε Stress, Force and Area Relation

σ = F/A Strain Relation

δ = ∆l / l Force and Deformation Relation

AE F =( ) * ∆l l Load Matrix

{F } = [K ]{U }

Shape Function for Solid92

Analysis Details Material Properties Modulus = 29e6 10^6 psi Yield Strength = 36 ksi (tension), 21 ksi (shear) Ultimate Strength = 58 ksi (tension)

Static Analysis Single Pipe Run

Pipe Material and Size Verification 4” Nominal Pipe Size Deflection < 0.04” Existing anchor pipe fixed to 1 ft square steel plate. The plate is an extruded with a 1 in thickness. The volume was free meshed at the default setting. All nodes in the four side planes and bottom plane were then fixed with zero displacement in all degrees of freedom. A 2250 lbf was attached to a single node at approximately the center of the top of

the anchor. The analysis was run and the results were reviewed. The pipe section was found to satisfy the displacement limitations.

Boundary Conditions, Mesh and Load Application

Post Processing Results Pipe and 36” Beam Section Run – Displacement/Yield Test

36” W12x50 Wide Flange Beam – 2250 lbf Load in Positive X Direction Displacement at Tip Exceeds Allowable 0.04” – Reinforcement or Redesign Required

36” W12x50 Wide Flange Beam – 2250 lbf Load in Positive X Direction Von Mises Stress Not Exceeding σY = 36,000 lbf/in2

Reinforced Pipe/Beam System – Displacement/Yield Test

Reinforced W12x50 Wide Flange Beam with 2250 lbf Maximum Allowable Tip Displacement (0.04”) Exceeded by Factor of 2

Reinforced W12x50 Wide Flange Beam with 2250 lbf Load Von Mises Stress Not Exceeding σY = 36,000 lbf/in2

Reinforced Pipe/Beam System – Fracture Test

W12x50 Wide Flange Beam Von Mises Stress 5000 lbf Static Force – Ultimate Strength (50 ksi) Exceeded at Pipe and Beam Connection

W12x50 Wide Flange Beam Tip Displacement - 5000 lbf Static Force

Summary The pipe anchor alone complies with OSHA requirements. When connected to the standard wide flanged beam the tip displacement of the anchor exceeds the allowable dimension. After reinforcing the sides of the beam by welding quarter inch plating the anchor system no longer deflects excessively at the tip. With an applied load of 5000 lbf the stresses in the anchor system exceed the ultimate strength for this material. Further reinforcement of the anchor system is required or more appropriately the system should be redesigned with higher grade materials.

Acknowledgements I.

Finite Element Analsys, Moaveni 2003

II. Mechanics of Materials, Beer & Johnston 2002 III. ANSYS Manual IV. www.machinedesign.com V.

U.S. Department of Labor

VI. Lab Safety Supply