ML12153A393

1500 - E117 - Concrete Technology and Codes - 17 - Reinforced Concrete

ML12153A393
Person / Time
Issue date:	06/01/2012
From:	Office of the Chief Human Capital Officer
To:
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Download: ML12153A393 (87)

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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

1. 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

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