What is the modulus of elasticity of concrete?
The modulus of elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. The elastic modulus of the hardened paste may be in the order of 10-30 GPa and aggregates about 45 to 85 GPa.
What are 3 properties that are important for a prestressing strand to have?
Have good bonding properties, low relaxation, good resistance to corrosion. Be economical and easy to handle. Prestressing reinforcement can be in the form of single wires, strand composed of several wires twisted to form single element, and high strength bars.
What is the purpose of stress relieving prestressing wires and strands?
The strander works in tandem with the straightening and stress-relieving equipment and this assures a high degree of toughness and elasticity in the strand. The straighter the strand, the easier it is to place and tension, and less likely that it will become tangled on the job.
What is CGC in prestressed concrete?
Figure 2-1.1 Areas for prestressed members CGC = Centroid of concrete = Centroid of the gross section. The CGC may lie outside the concrete (Figure 2-1.2). CGS = Centroid of prestressing steel = Centroid of the tendons.
What is the modulus of concrete?
The elastic modulus of hardened cement paste is around 10 to 30 GPa and that of aggregate is between 45 to 85 GPa. Concrete generally have an elastic modulus varying between 30 to 50 GPa.
How modulus of elasticity of concrete is determined?
Modulus of elasticity of concrete is defined as the ratio of stress applied on the concrete to the respective strain caused. The accurate value of modulus of elasticity of concrete can be determined by conducting a laboratory test called compression test on a cylindrical concrete specimen.
What are strands in concrete?
PC Strand, or prestressed concrete steel strand, is a twisted steel cable composed of 2, 3, 7 or 19 high strength steel wires and is stress-relieved (stabilized) for prestressed concrete or similar purposes.
What is Strand in wire?
A strand is when two or more wires are wound concentrically in a helix. These strands are typically wound around a center wire and then around the core. The lay of the strand is the direction that the wires orbit the core.
What is stress-relieved strand?
What important benefit was achieved by the introduction of high strength strands and wires?
Higher bond strength in early-age concrete will speed production and allow more economical fabrication. To promote this, pre-tensioned tendons are usually composed of isolated single wires or strands, which provides a greater surface area for bonding than bundled-strand tendons.
Which type of losses are considered in concrete?
In pretensioned concrete, the four major sources of prestress losses are elastic shortening (ES), creep (CR), shrinkage (SH) and relaxation (RE).
What is elastic shortening of concrete?
1.In a structural member, a decrease in the length (under an imposed load) which is linearly proportional to the load. 2. In prestressed concrete, the shortening of a member which occurs immediately on application of forces induced by prestressing.
What is the standard SPECIFI-cation for prestressed concrete?
Special equipment and some experi- ence in the details of its use are re- quired to obtain the necessary degree of accuracy in testing 7-wire prestressed concrete strand, ASTM A416 is the Standard Specifi- cation for Uncoated 7-Wire Stress- Relieved Steel Strand for Prestressed Concrete.
How does prestressing work in the drawing process?
Technically, prestressing strand develops high strength and excellent creep characteristics through cold drawing. During the cold drawing process, the grain structure is elongated and aligned into a condition resulting in specific physical and mechanical properties.
What is the instantaneous camber of precast concrete?
Instantaneous camber, which occurs at the time of release of the prestressing force from the bed to the concrete member, is well defined. The prestressed concrete member cambers upward because the upward bending due to initial prestress is generally larger than the downward deflection due to member self-weight.
Do you Fuse the ends of a post tensioned strand?
If the wires are properly dimensioned and the wires are not lubricated, it should not be necessary to fuse the ends of the specimen. After all, the center wire of an unbonded post-tensioned strand is gripped only by the outer wires of the strand and the ends are often cut off with a carborundum wheel rather than with a torch.