ML12153A393
| ML12153A393 | |
| Person / Time | |
|---|---|
| Issue date: | 06/01/2012 |
| From: | Office of the Chief Human Capital Officer |
| To: | |
| References | |
| Download: ML12153A393 (87) | |
Text
Concrete Techno ology and Codes Reinforced Concrete
Outline z Basic Material Properties Concrete Reinforcement z Reinforced Concrete Flexure l
Bond Shear Creep and Shrinkage z Prestressed & Post-tensioned Concrete 2
Compression Machine 3
Compression Testing to Failure 4
Definitions Load Area Load ( lbs )
Stress = 2
= psi D Area ( in. )
Leng gth Strength = Maximum Stress Deformation ( in.)
Strain =
Original Length ( in.)
5
High--Strength Concrete High 6
Compressometer 7
Strain Gage on Cylinder 8
Direct Tension Test Specimen 9
Direct Tension Test Setup 10
Direct Tension Failure 11
Splitting Tensile Test 12
13 Characteristics of Concrete z Basic Concept Strong in Compression Weak in Tension Factor of 10!!
14
Load-Deformation Characteristics Load-for Concrete 15
Demonstration z Slotted Styrofoam Model z Model Beams 16
Styrofoam Beam - Loaded Compression Tension 17
Plain Concrete Beam (no rebar) 18
Plain Concrete Beam 19
Reinforced Concrete Beam 20
Load-Deformation Load-Characteristics for Reinforcing Steel 21
Why Steel?
z Strong in tension z Does not react with concrete z Compatible thermal expansion and contraction z Ductile z Bond strength 22
Reinforced Concrete Beam 23
Load-Deformation for Plain and Load-Reinforced Beams 24
Reinforced Concrete Beam (steel at top) 25
Case Study Pair of Precast Ledger Beams If you look underneath.
Stairway Landing 26
Case Study Remember, this is from underneath!
27
Rebar Development
~ 1 3/8 9/8 3/8
- 14 #9 #3 28
Rebar Development Why the ribs?
29
Rebar Development 30
Bond and Development Length z Mechanical Bond z Adhesion Bond 31
Mechanical Bond 32
Headed Bars in Tension Headed Bars Can Reduce Trump Tower Chicago Rebar Congestion Courtesy ERICO 33
Shear and Stirrups Crack (Saw Cut)
Stirrup (Bungee Cord Thru Drilled Hole in Beam) 34
Shear and Stirrups After Concrete Cracks Shear Load Supported by Stirrups (stretching bungee cord)
Held Together by Stirrup 35
Diagonal Tension Due to Shear 36
Headed Shear Stud Reinforcement Courtesy of Hai Dinh, Univ. of Michigan 37
Creep and Shrinkage The Rocket Science of Structural Concrete Short-term Elastic Behavior Superimposed over Long-term Inelastic Behavior 38
Creep and Shrinkage Determine the Important Parameters Use Analogy of Inflatable Mattress 39
Creep and Shrinkage Short-term Loads = Elastic 40
Creep and Shrinkage Long-term Loads = Inelastic 41
Creep and Shrinkage Important Parameters Scale of Element 42
Creep and Shrinkage Important Parameters Scale of Element 43
Creep and Shrinkage Important Parameters Size of Openings = Age and Strength of Concrete 44
Creep and Shrinkage Important Parameters Pressure Differential 45
Creep and Shrinkage Pressure Differential = Relative Humidity 46
Predicted Vertical Shortening vs. Story at 30 Years Demonstration z Styrofoam Blocks (Prestressed) 48
Prestressed Concrete:
General Principles Compression Tension No Tension 49
Methods of Prestressing Concrete Members
- Pretensioning
- Post-Tensioning 50
Prestressed Concrete Beams 51
Precast Girders After Detensioning 52
Unloading Girders from Flat Bed Rail Car 53
Test to Destruction 54
Flexural Cracks 55
Sudden Shear Failure -
No Shear Reinforcement 56
Advantages of Post Post--tensioned 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 z Long economical spans z Wide flexibility and variation in design z Reduced cracking z However, additional inspections are required
Unbonded Tendons z The prestressing strand is prevented from bonding, and is free to move, relative to the surrounding concrete 7-wire 7 wire strands (0.5 (0 5 dia.)
dia )
Sheathing Anchor
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 Typical Tendon Profile 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 z #4 bars, typical to match tendon diameter z Place transverse reinforcing steel below the banded reinforcing steel
Curving Banded Tendons Extreme Curves Extreme Curves Curves in Plan Cause:
- Increased Losses
- High Internal Forces
- Cracking at Openings
Extreme Curves Corrected Layout
Punching Shear z Detail with tendon group running directly through column l core z 2 minimum Adolphson
& Peterson required per ACI Code z Headed shear stud reinforcement
Short Column Effect in Ramps Crack in Column
Improper Conduit Acceptable Conduit Beam Column Joint - Interior z Tendons and beam top steel compete for placement at top of beam
Beam Column Joint - Exterior z Beam hooked tops bars compete for space with PT anchorages
Beam Column Joint - Corner z Two beams framing in at a corner column have even more congestion issues z Coordinate Coordinate Coordinate!
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 - Exterior z Congestion + Poor consolidation
= Problems
Beam Column Joint - Exterior z Congestion + Poor consolidation = Problems
Consolidation at Anchors Blow 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 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 z Pre-Pour Look for tendons with extreme bends, reverse curvature, or odd configurations Inspect for damage to sheathing
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 crew (each
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Measurement of strand tails
Elongation Record Building is Human Nature 86
?