Building Code Requirements for Structural Concrete ACI 318

Building Code Requirements for Structural Concrete (ACI 318 M-11) Design of Structures with High-Strength Concrete by ACI 318 David Darwin Vietnam Institute for Building Science and Technology (IBST) Hanoi and Ho Chi Minh City December 12 -16, 2011

This morning Slender columns Walls High-strength concrete

High-strength concrete Background ACI 318 provisions that apply to high-strength concrete

Background High strength concrete = ?

1920 s > 20 MPa 1950 s > 35 MPa 1990 s > 60 MPa

> 70 MPa

100 – 135 MPa

High-strength concrete Small % Important Columns in high-rise buildings

The tallest building in the world is constructed of reinforced concrete

Compressive behavior

cylinder size 100 x 200 mm vs. 150 x 300 mm molds

f'c(4 x 8 in. ) = 1. 016 f'c(6 x 12 in. ) f'c(100 x 200 mm) = 1. 016 f'c(150 x 300 mm)

End condition

Stress-strain curves

Behavior in compression tests

Strength versus age

Strength gain - example 28 days 91 days % gain absolute gain 20 MPa 35 MPa 75 % 15 MPa 64 MPa 92 MPa 44 % 28 MPa

Tensile and fracture behavior

Relationship between tensile and compressive strength

Fracture The energy required to open a crack once the tensile strength has been reached

Fracture energy vs. compressive strength

Structural behavior Bond Shear

Bond 1. 83 m 4. 88 m

Splices w/o confining reinforcement

Splices w/ confining reinforcement

Asfs/f′c 1/2 (Test), in. 2 Asfs/f′c 1/2 (Prediction), in. 2

Asfs/f′c 1/4 (Test), in. 2 Asfs/f′c 1/4 (Prediction), in. 2

Shear

Creep and shrinkage

Specific creep

Creep coefficient

Shrinkage

ACI 318 provisions that apply to highstrength concrete Required average strength Evaluation and acceptance of concrete Stress block parameter Limits that apply to shear, torsion, and bond Transmission of column loads through floor systems

Required average strength

Evaluation and acceptance of concrete (a) Arithmetic average of all sets of three consecutive strength tests* equals or exceeds (b) No strength test* falls below by more than 3. 5 MPa when is 35 MPa or less; or by more than when is more than 35 MPa *Test = average strength of three 100 200 mm cylinders or of two 150 300 mm cylinders

Stress-block parameter 1

Limits that apply to shear, torsion, and bond Shear and torsion

Bond

Transmission of column loads through floor systems

Summary Background ACI 318 provisions that apply to high-strength concrete

51

Figures copyright 2003 by Pearson Education, Inc. Upper Saddle River, NJ USA Figures copyright 2010 by Mc. Graw-Hill Companies, Inc. 1221 Avenue of the America New York, NY 10020 USA Figures copyright 2011 by American Concrete Institute 38800 Country Club Drive Farmington Hills, MI 48331 USA Duplication authorized for use with this presentation only.

The University of Kansas David Darwin, Ph. D. , P. E. Deane E. Ackers Distinguished Professor Director, Structural Engineering & Materials Laboratory Dept. of Civil, Environmental & Architectural Engineering 2142 Learned Hall Lawrence, Kansas, 66045 -7609 (785) 864 -3827 Fax: (785) 864 -5631 daved@ku. edu