AECT250-Lecture 39

AECT250-Lecture 39 - Lecture 39 Prestressed Concrete Prestressed concrete refers to concrete that has applied stresses induced into the member

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Lecture 39 - Page 1 of 12 Lecture 39 – Prestressed Concrete Prestressed concrete refers to concrete that has applied stresses induced into the member. Typically, wires or “tendons” are stretched and then blocked at the ends creating compressive stresses throughout the member’s entire cross- section. Most Prestressed concrete is precast in a plant. Advantages of Prestressed concrete vs. non-Prestressed concrete : More efficient members (i.e., smaller members to carry same loads) Much less cracking since member is almost entirely in compression Precast members have very good quality control Precast members offer rapid field erection Disadvantages of Prestressed concrete vs. non-Prestressed concrete : More expensive in materials, fabrication, delivery Heavy precast members require large cranes Somewhat limited design flexibility Small margin for error More complicated design Typical Precast Prestressed concrete members
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Lecture 39 - Page 2 of 12 Pre-Tensioned Prestressed Concrete : Pre-tensioned concrete is almost always done in a precast plant. A pre- tensioned Prestressed concrete member is cast in a preformed casting bed. The BONDED wires (tendons) are tensioned prior to the concrete hardening. After the concrete hardens to approximately 75% of the specified compressive strength f’ c , the tendons are released and axial compressive load is then transmitted to the cross-section of the member. “Live” end “Dead” end Tendons tensioned between bulkheads Prestress force P s Casting bed Tendons anchored at “Live” end and “Dead” end Fresh concrete placed in bed Tendons released at “Live” end and “Dead” end creating an axial force along length of precast member Prestress force P s Hardened concrete Step 1 Step 2 Step 3
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Lecture 39 - Page 3 of 12 Post-Tensioned Prestressed Concrete : A post-tensioned member has UNCOATED tendons cast into concrete in draped patterns. After the concrete hardens to about 75% f’ c , the tendons are tensioned and try to straighten out. This creates an upward camber of the member which offsets anticipated downward deflection due to gravity
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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 39 - Lecture 39 Prestressed Concrete Prestressed concrete refers to concrete that has applied stresses induced into the member

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