The user wants an OCR conversion of an engineering standard PDF page to HTML.
The page contains a table of contents (partially visible, red text) and the beginning of "CHAPTER 1—INTRODUCTION".
The text is in two columns.
I need to follow strict HTML rules:
- Allowed tags: p, h2, h3, h4, h5, strong, em, b, i, u, s, sup, sub, table, caption, thead, tbody, tfoot, tr, td, th, ol, ul, li, blockquote, span, pre, code, hr, br
- Allowed classes: align-center, align-right, indent, small-note, layout-columns, formula
- No style attributes.
- No , tabs, multiple spaces.
- No Markdown fences.
- No forbidden tags (h1, div, etc.).
- No attributes on ol/ul/li.
- Only td/th can have rowspan/colspan.
- Must start with
(page title).
- Must end with
2
.
- pre only contains code.
- Two-column layout ->
Let's analyze the layout:
Left column:
4.2—Prestressing tendon materials selection
4.3—Corrosion protection for prestressing systems
4.4—Cathodic protection
Chapter 5—Field evaluation, p. 222.2R-25
5.1—Introduction
5.2—Evaluation goals
5.3—Pretensioned systems
5.4—Post-tensioned systems
Chapter 6—Remediation techniques, p. 222.2R-30
6.1—Introduction
6.2—General
6.3—Grouted post-tensioned systems
6.4—Ungrounded post-tensioned systems
Chapter 7—Field performance of prestressed concrete structures, p. 222.2R-32
7.1—Introduction
7.2—Corrosion of prestressing strand before construction
7.3—Pretensioned structures
7.4—Unbonded post-tensioned structures
7.5—Bonded post-tensioned structures
Chapter 8—References, p. 222.2R-38
8.1—Referenced standards and reports
8.2—Cited references
CHAPTER 1—INTRODUCTION
1.1—Background
While several attempts were made during the 1800s to prestress concrete, the modern development of prestressed concrete is credited to E. Freyssinet of France in 1928 (Lin and Burns 1981). Freyssinet understood the importance of using high-strength steel for prestressing to avoid prestressing losses that can significantly reduce the applied prestressing force. Use of prestressed concrete began in the United States with circular-wrapped prestressed tanks in 1941 (Schupack 1964). The first prestressed bridge in the United States was located in Tennessee and opened to the public on Oct. 28, 1950. The Walnut Lane Bridge, located in Pennsylvania, was completed in the fall of 1950 and opened to traffic in Feb. 1951 (Manning 1988). Since that time, applications of prestressing in bridge and building construction have spread rapidly. In the United States prestressed concrete has proven to be a very successful method of construction. Its benefits include increased load-bearing capacity, improved crack control, and slenderness of elements.
Corrosion is not as well documented in prestressed concrete structures as in non prestressed concrete structures. Corrosion of these structures appears to be restricted to specific circumstances, including construction details, improper design, and construction practices. The potential for widespread problems still exists, however. Indeed, in environments contaminated with known corrosion promoters, such as chloride ions and hydrogen sulfide, it is imperative that prestressing steel be protected.
A number of surveys provide information concerning the potential for corrosion of prestressed structures. Burdekin
Right column:
and Rothwell summarized current practice, specifications, and corrosion mechanisms (1981). Failure to follow proper construction details and practices, as well as poor-quality materials, account for the vast majority of poor performance. Schupack reached similar conclusions in two additional surveys (1978a; Schupack and Suarez 1982).
Because corrosion in prestressed concrete members potentially has more serious consequences than in nonprestressed concrete, more information needs to be developed and disseminated. The magnitude of the corrosion problem, its projected extent, and measures that can be taken to resolve it are of vital concern to designers, contractors, owners, and form the basis of this report.
Prestressed concrete is used in several forms. It is important to the discussion of corrosion of prestressed concrete that the basic differences in these forms of construction be described.
Pretensioned concrete refers to systems in which high-strength wire or strand is stressed before placement of the concrete. Concrete is cast around the prestressing steel (bonding the steel to the concrete) and allowed to cure to a specified strength. Tension in the steel is then released, placing the member in compression. Pretensioning is common practice for both standardized bridge beams and on building elements, such as solid joists, solid and hollow-core planks, and single-and double-tee joists.
Post-tensioned concrete is prestressed after the concrete is placed and allowed to cure to a specified strength. This term is used for both bonded and unbonded tendons. Bonded post-tensioning requires that deformed tubes or ducts be placed in the forms before concrete placement. After the concrete is placed and cured to a specified strength, bundles of strand, wire, or bar (the bundle is referred to as a tendon) are placed in the duct and are stressed against and anchored to the concrete.
After the tendons have been installed and stressed, ducts are usually injected with grout (a fluid mixture of portland cement, water, and perhaps admixtures) with a grout pump. Ducts can be metallic or nonmetallic and include uncoated or coated steel, high-density polyethylene (HDPE), and polypropylene. The injected grout fills the spaces among the individual elements of the tendon and between the tendon and duct. Grout injection provides two benefits: corrosion protection for the tendon with the highly alkaline environment provided by the grout, and bond between the concrete and the tendon. This form of prestressing is popular on structures such as bridges, buildings, dams, tanks, and tie-backs.
The other post-tensioning technique, unbonded post-tensioning, mainly uses single-strand tendons. Each strand is placed inside an individual sheath, and the annular space is filled with a corrosion-inhibiting grease or wax. The tendon is installed in the formwork before placement of concrete. The sheath provides a barrier between the greased strand and the concrete, allowing the strand to be stressed after concrete placement. In general, the anchors are cast into the concrete along with the tendon. Unbonded multistrand tendons have also been used extensively in nuclear pressure vessels. Multiple wire or strands are placed in a cast-in-place duct,
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开头（页面内标题）".
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2 Scope
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开头".
Let me re-read: "每页输出必须以
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If there is no h2 at the top, maybe I should make the first heading an h2? "CHAPTER 1—INTRODUCTION" is an h2.
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Let's look at the example:
2 Scope
This Australian Standard deals with...
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If I have to start with h2, I will put
CHAPTER 1—INTRODUCTION
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开头".
I will output
CHAPTER 1—INTRODUCTION
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Let me look at the example again. The example page starts with "2 Scope", which is an h2.
What if the page starts with a table of contents? I will just start with
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CHAPTER 1—INTRODUCTION
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