AECT250-Lecture 33

AECT250-Lecture 33 - Lecture 33 - Page 1 of 14 Lecture 33...

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Unformatted text preview: Lecture 33 - Page 1 of 14 Lecture 33 Columns Concrete Columns: Concrete is good at resisting compression but poor in resisting tension. So, it might make sense that concrete would be the material of choice for columns. It is true that concrete IS used for compression members such as columns, piers, bearing walls and pedestals. Members under pure compression could then (theoretically) be unreinforced. These members are often subject to additional forces such as moment that would put some tensile forces into the member and would thus necessitate the addition of tension reinforcement. Most columns have combined compression and bending . They are essentially a beam-column. The compression capacity of a reinforced column is reduced by the bending stresses on the column and vice-versa. A graph of the axial load capacity of a column vs. the moment capacity of a typical column is shown below: Axial compression capacity Bending moment capacity Pure compression Pure bending Lecture 33 - Page 2 of 14 Types of Concrete Columns: There are two types of reinforced concrete columns tied and spiral and refer to the type of confining bars used to contain the interior core of concrete. It has been shown that unconfined concrete core will carry MUCH LESS load than a confined core as shown below: Unconfined core Load Concrete & vert. bars explode outward Load Insufficient ties Lecture 33 - Page 3 of 14 A confined concrete core will carry substantially more load and will NOT explode outward like the unconfined concrete section will. Tied Column: A Tied concrete column is one in which individual rebar ties are used to wrap completely around the vertical bars to confine the interior core. These ties are usually #3 or #4 bars spaced per ACI requirements: Tie Spacing = smaller of Additionally, the ACI dictates that there must be a minimum of 4 vertical bars having a minimum area of 1% of the column cross-sectional area and a maximum of 8% of the column cross-sectional area. From a constructability standpoint, 4% is the upper maximum that can be readily achieved because of rebar congestion....
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This note was uploaded on 05/05/2009 for the course AE AE250 taught by Professor Hultenius during the Fall '08 term at SUNY Delhi.

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AECT250-Lecture 33 - Lecture 33 - Page 1 of 14 Lecture 33...

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