ML12153A393
| ML12153A393 | |
| Person / Time | |
|---|---|
| Issue date: | 06/01/2012 |
| From: | Office of the Chief Human Capital Officer |
| To: | |
| References | |
| Download: ML12153A393 (87) | |
Text
ology and Codes ology and Codes Reinforced Concrete Reinforced Concrete Concrete Techno Concrete Techno
Outline Outline z Basic Material Properties Concrete Reinforcement z Reinforced Concrete l
2 Flexure Bond Shear Creep and Shrinkage z Prestressed & Post-tensioned Concrete
Compression Machine Compression Machine 3
Compression Testing to Compression Testing to Failure Failure 4
Definitions Definitions psi
)
in
(
Area
)
lbs
(
Load Stress 2 =
=
Area Load gth D
5
.)
in
(
Length Original
.)
in
(
n Deformatio Strain Stress Maximum Strength
=
=
Leng
High High--Strength Concrete Strength Concrete 6
Compressometer Compressometer 7
Strain Gage on Cylinder Strain Gage on Cylinder 8
Direct Tension Test Direct Tension Test Specimen Specimen 9
Direct Tension Test Setup Direct Tension Test Setup 10
Direct Tension Failure Direct Tension Failure 11
Splitting Tensile Test Splitting Tensile Test 12
13
Characteristics of Characteristics of Concrete Concrete z Basic Concept Strong in Compression Weak in Tension 14 Factor of 10!!
Load Load--Deformation Characteristics Deformation Characteristics for Concrete for Concrete 15
Demonstration Demonstration z Slotted Styrofoam Model z Model Beams 16
Styrofoam Beam Styrofoam Beam -- Loaded Loaded Compression 17 Tension
Plain Concrete Beam Plain Concrete Beam (no rebar)
(no rebar) 18
Plain Concrete Beam Plain Concrete Beam 19
Reinforced Concrete Beam Reinforced Concrete Beam 20
Load Load--Deformation Deformation Characteristics for Characteristics for Reinforcing Steel Reinforcing Steel 21
Why Steel?
Why Steel?
z Strong in tension z Does not react with concrete 22 z Compatible thermal expansion and contraction z Ductile z Bond strength
Reinforced Concrete Reinforced Concrete Beam Beam 23
Load Load--Deformation Deformation for Plain and for Plain and Reinforced Beams Reinforced Beams 24
Reinforced Concrete Beam Reinforced Concrete Beam (steel at top)
(steel at top) 25
Case Case Study Study 26 Stairway Landing Pair of Precast Ledger Beams If you look underneath.
Case Study Case Study 27 Remember, this is from underneath!
Rebar Development Rebar Development 28
~ 1 3/8
- 14 9/8
- 9 3/8
- 3
Rebar Development Rebar Development 29 Why the ribs?
Rebar Development Rebar Development 30
Bond and Development Bond and Development Length Length z Mechanical Bond z Adhesion Bond 31
Mechanical Bond Mechanical Bond 32
Headed Bars in Tension Headed Bars in Tension Headed Bars Can Reduce Rebar Congestion Trump Tower Chicago 33 Courtesy ERICO
Shear and Stirrups Shear and Stirrups Crack (Saw Cut) 34 Stirrup (Bungee Cord Thru Drilled Hole in Beam)
Shear and Stirrups Shear and Stirrups After Concrete Cracks Shear Load Supported by Stirrups (stretching 35 by Stirrups (stretching bungee cord)
Held Together by Stirrup
Diagonal Tension Due to Diagonal Tension Due to Shear Shear 36
Headed Shear Stud Headed Shear Stud Reinforcement Reinforcement 37 Courtesy of Hai Dinh, Univ. of Michigan
Creep and Shrinkage Creep and Shrinkage The Rocket Science of Structural Concrete 38 Short-term Elastic Behavior Superimposed over Long-term Inelastic Behavior
Creep and Shrinkage Creep and Shrinkage Determine the Important Parameters Use Analogy of Inflatable Mattress 39
Creep and Shrinkage Creep and Shrinkage Short-term Loads = Elastic 40
Creep and Shrinkage Creep and Shrinkage Long-term Loads = Inelastic 41
Creep and Shrinkage Creep and Shrinkage Important Parameters Scale of Element 42
Creep and Shrinkage Creep and Shrinkage Important Parameters Scale of Element 43
Creep and Shrinkage Creep and Shrinkage Important Parameters Size of Openings = Age and Strength of Concrete 44
Creep and Shrinkage Creep and Shrinkage Important Parameters Pressure Differential 45
Creep and Shrinkage Creep and Shrinkage Pressure Differential = Relative Humidity 46
Predicted Vertical Shortening vs. Story at 30 Years
Demonstration Demonstration z Styrofoam Blocks (Prestressed) 48
Prestressed Concrete:
Prestressed Concrete:
General Principles General Principles 49 Tension Compression No Tension
Methods of Prestressing Methods of Prestressing Concrete Members Concrete Members
- Pretensioning 50
- Post-Tensioning
Prestressed Concrete Beams Prestressed Concrete Beams 51
Precast Girders After Detensioning Precast Girders After Detensioning 52
Unloading Girders from Flat Unloading Girders from Flat Bed Rail Car Bed Rail Car 53
Test to Destruction Test to Destruction 54
Flexural Cracks Flexural Cracks 55
Sudden Shear Failure Sudden Shear Failure --
No Shear Reinforcement No Shear Reinforcement 56
Advantages of Post Advantages of Post--tensioned tensioned Structures Structures z Reduced structural depth for lower story heights and reduced dead load Additional savings in labor and material for M/E/P, elevator and cladding cladding z Long economical spans z Wide flexibility and variation in design z Reduced cracking z However, additional inspections are required
Unbonded Tendons Unbonded Tendons z The prestressing strand is prevented from bonding, and is free to move, relative to the surrounding concrete 7 wire strands (0 5 dia )
7-wire strands (0.5 dia.)
Sheathing Anchor
Unbonded Tendons Unbonded Tendons z Prestressing force can only be transferred to the concrete through the anchorage Casting: 5 x 2 1/4 typical Wedges
Unbonded Tendons Unbonded Tendons
Typical Tendon Typical Tendon Profile Profile
Banded Tendon Distribution Banded Tendon Distribution z Resembles a one-way slab (uniform tendons) supported by an embedded beam (banded tendons) along column lines z Tendons grouped in flat bundles of 4 to 5 z Accommodates irregular column pattern
Placement at Column Placement at Column z #4 bars, typical to match tendon diameter z Place transverse reinforcing steel below the banded below the banded reinforcing steel
Curving Curving Banded Tendons Banded Tendons
Extreme Curves Extreme Curves
Curves in Plan Cause:
- Increased Losses
- High Internal Forces
- Cracking at Openings Extreme Curves Extreme Curves
Corrected Layout Extreme Curves Extreme Curves
Punching Shear Punching Shear z Detail with tendon group running directly through l
column core z 2 minimum required per ACI Code z Headed shear stud reinforcement Adolphson
& Peterson
Short Short Column Effect in Ramps Column Effect in Ramps Crack in Column
Improper Improper Conduit Conduit
Acceptable Conduit Acceptable Conduit
Beam Column Beam Column Joint Joint -- Interior Interior z Tendons and beam top steel compete for placement at top of beam
Beam Column Beam Column Joint Joint -- Exterior Exterior z Beam hooked tops bars compete for space with PT anchorages
Beam Column Beam Column Joint Joint -- Corner Corner z Two beams framing in at a corner column have even more congestion issues z Coordinate Coordinate Coordinate!
Anchorage Zones Anchorage Zones z Beam-column connections have limited space for anchoring tendons Wider columns for ease of construction Consider column vertical steel configuration
Beam Column Joint Beam Column Joint -- Exterior Exterior z Congestion + Poor consolidation
= Problems
Beam Column Joint Beam Column Joint -- Exterior Exterior z Congestion + Poor consolidation = Problems
Consolidation at Anchors Consolidation at Anchors
Blow Blow Out Prevention Out Prevention z One tendon exerts ~33,000 pounds of force at the anchor or about the weight of 10 cars z Remove penetrations near the anchorage zone z Proper concrete consolidation is crucial
Restraint Crack Restraint Crack
Restraint Crack Restraint Crack
Special Inspections Special Inspections z Pre-Pour Verify PT c.g.s off structural drawings Supports, midspan, anchors Verify minimum number of tendons intersect center of column in both directions Remove conduit, penetrations, etc., by the anchors
Special Inspections Special Inspections z Pre-Pour Look for tendons with extreme bends, reverse curvature, or odd curvature, or odd configurations Inspect for damage to sheathing
Special Inspections Special Inspections z During and after stressing operation Inspection of the stressing operation is to be continuous, NOT periodic A deputy inspector is required for each stressing
(
h j k) crew (each jack)
Measurement of strand tails
Elongation Record Elongation Record
Building is Human Nature 86
?