Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders (2022) / Chapter Skim
Currently Skimming:
Pages 1-26
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 1... ...
1 1.1 Introduction In the United States, seven-wire prestressing strands conforming to ASTM A416/AASHTO M203 (ASTM, 2015a) are used to pretension concrete bridge members.
|
From page 2... ...
2 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders 1.2 Motivations for Using 0.7-In.
|
From page 3... ...
Background 3 increase clearances beneath the bridge. Once again, clearance is a major design issue in urban areas of many states or for bridges over waterways where the bridge limits the hydraulic opening.
|
From page 4... ...
4 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders By comparing the results from the pretensioned and nonpretensioned strands, Cabage attempted to identify the contribution of radial expansion to bond capacity.
|
From page 5... ...
Background 5 In Girder A, vertical No. 3 hairpins spaced at 3 in.
|
From page 6... ...
6 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders length could not be determined due to insufficient instrumentation.
|
From page 7... ...
Background 7 strands were, therefore, debonded to control initial cracking stresses; the maximum debonding ratio was 0.29. A total of twenty-four 0.7-in.
|
From page 8... ...
8 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders that AASHTO Bridge Design Specifications Article 5.9.4.4.1 (AASHTO, 2020)
|
From page 9... ...
Background 9 were used. Nevertheless, the authors concluded that confinement steel could reduce this possibility.
|
From page 10... ...
10 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders 4.
|
From page 11... ...
Background 11 1.5.2 Strand Spacing in U.S. Practice and the Transition from 0.5-In.
|
From page 12... ...
12 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders (Unay et al., 1991)
|
From page 13... ...
Background 13 Eq. 1.1 can be rewritten as ( )
|
From page 14... ...
14 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders 1.5.3.1 NCHRP Report 603 Ramirez and Russell (2008)
|
From page 15... ...
Background 15 This confinement must extend at least 1.5d into the span and consist of no less than No. 3 bars spaced at 6 in.
|
From page 16... ...
16 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders with No.
|
From page 17... ...
Background 17 1.6 Overview of Bond Characteristics Like any bonded internal reinforcement, stress is transferred between concrete and prestressing strand by bond. Bond forces are developed by chemical adhesion, friction, and mechanical interlock between deformed bars and the surrounding concrete (Figure 1.4a)
|
From page 18... ...
18 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders described by Machida and Durelli (1973)
|
From page 19... ...
Background 19 but varies as seen in Figure 1.5a and, therefore, the diameter of the tendon varies similarly. As the tendon stress is reduced (toward the free end of the member)
|
From page 20... ...
20 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders fpz = axial stress in prestressing strand a distance z from the free end of the concrete embedment vc = Poisson's ratio of concrete Ec = Young's modulus of concrete fcz = axial stress in concrete a distance z from the free end: = 02 2f f r ccz pz Eq.1.7 c = radius of concrete cylinder; c = clear cover + r0 From the interface pressure, the radial (σr)
|
From page 21... ...
Background 21 the geometry of an unstressed prestressing strand as one in which the helical wires are "slightly elliptical," resulting in a small clearance between the center wire and the helical wires if the diameters of all wires are the same. It is not clear from Machida and Durelli whether this geometry and the associated annular space apply to both stress-relieved and low-relaxation strand.
|
From page 22... ...
22 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders considered in terms of the potential for rollover and the susceptibility to excessive deformations causing concrete stress limits to be exceeded.
|
From page 23... ...
Background 23 1.8.2 Hanging Girders The hanging girder condition corresponds to that in which a girder is supported (by a crane) from above by cables attached to the girder web or top flange.
|
From page 24... ...
24 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders The factor of safety against failure, which must exceed 1.5, is calculated as: ( )
|
From page 25... ...
Background 25 The rotation angles θmax and θ′max are those given by Eq.
|
From page 26... ...
26 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders the girder.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.