Micropile Bearing Plates: Are they Necessary? Presented by: Nadir - PowerPoint PPT Presentation

Micropile Bearing Plates: Are they Necessary? Presented by: Nadir Ansari, P.Eng. Peter Sheffield & Associates Ltd.

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Outline -Reasons for Test -Test set up -Instrumentation -Our Findings Peter Sheffield & Associates Ltd.

Reasons for Test and Analysis Program - Cost - Time/ Schedule impact - Difficult to ensure plate to grout contact - Plates impede concrete placement beneath - Plates provide smooth interface where cracks may propagate - Tests by the Ohio DOT in 1947, suggest large plates may weaken pile caps Peter Sheffield & Associates Ltd.

Test Set Up 800 mm 1000 mm 1800 mm 1200 mm Dial Gauges Area of micropile Is 0.0294 m^2 Air Pocket Peter Sheffield & Associates Ltd.

Test Set up Dial Gauges Peter Sheffield & Associates Ltd.

Test Set Up Concrete Strain Gauge Rebar with Strain Gauges Compressible Material Peter Sheffield & Associates Ltd.

Test Set Up 30 MPa Concrete Cylinders Peter Sheffield & Associates Ltd.

Cyclic Loading for One Micropile LT1- Micropile Compression Test 4500 4000 3500 3000 Load (kN) 2500 2000 1 500 1 000 500 0 0 5 1 0 1 5 20 25 30 35 40 45 50 55 Movement (mm) -8050 kN ultimate load on cap -2.33 Design Load -50 mm movement -136 MPa based on MP area Peter Sheffield & Associates Ltd.

Results - Actual Cracking Pattern Peter Sheffield & Associates Ltd.

Actual Cracking Pattern Peter Sheffield & Associates Ltd.

Column Base Plate Cracking Pattern in one quarter of the cap Peter Sheffield & Associates Ltd.

Strut and Tie Model Used to Determine Required Reinforcement A1 Compression A2 Strut Tension Tie Peter Sheffield & Associates Ltd.

Vertical Stress Peter Sheffield & Associates Ltd.

Vertical Stress Peter Sheffield & Associates Ltd.

Horizontal Stress in Reinforcement Plane Peter Sheffield & Associates Ltd.

5 0 Results- -5 Rebar Stress Stress (MPa) -10 -15 Test Analytical -20 -25 -30 0 1 2 3 4 5 6 7 8 9 10 Load (1000 kN) Peter Sheffield & Associates Ltd.

Our Findings -Bearing plates were not necessary -Based on area the bearing strength was 4.5 times the concrete compressive strength much higher than allowed by codes -Class A analysis predicted failure within 5% -The concrete strut was parabolic, not linear Peter Sheffield & Associates Ltd.

Findings Continued -Longitudinal rebar was in Compression in the middle of the pile cap -Rebar can be spaced evenly across pile cap -Further research for other geometries is necessary Peter Sheffield & Associates Ltd.

Ontario College of Art and Design Peter Sheffield & Associates Ltd.