The National Academies Press

Currently Skimming:

Pages 35-52

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 35... ... 35 C H A P T E R 3 Review of NCHRP 534 Approach Introduction Since its publication in 2004, NCHRP NCHRP Report 534 "Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel Wire Cables" (herein referred to as NCHRP Report 534) , has provided a standardized method for use by owners and investigators to inspect and evaluate main cables and has been applied on suspension bridges worldwide. Read the entire page →
From page 36... ... 36 • Wedging and preparing the cable for inspection, • Recording the stage of corrosion of all exposed wires, • Recording the location of any broken wires, along with the gap distance between the wire ends (where possible) , • Removal of sample wires for testing, and recording the gap distance between cut ends, • Repair of broken wires (if applicable) Read the entire page →
From page 37... ... 37 at the 12:00, 1:30, 3:00, 4:30, 6:00, 7:30, 9:00, and 10:30 positions (clock positions are referenced to a standardized direction along the cable, i.e. "looking upslope") Read the entire page →
From page 38... ... 38 Stage 1: Spots of zinc oxidation on the wires (like-new condition) ; Stage 2: Zinc oxidation over the entire wire surface (no ferrous rust) Read the entire page →
From page 39... ... 39 wires is not typically known prior to the investigation (unless the cable has been evaluated previously) , it is appropriate to err on the conservative side. Read the entire page →
From page 40... ... 40 A detailed summary of all construction activities performed as part of the cable investigation, including the dates on which they were performed should be documented by the construction inspection team for future reference. Laboratory Testing Sample wires extracted from the main cable are delivered to a laboratory for testing. Read the entire page →
From page 41... ... 41 Oftentimes, wires will break outside the 10" gage length (this is typical of main cable wires due to the residual stress caused by the "cast" of the wire resulting from the fabrication process) Read the entire page →
From page 42... ... 42 The primary purpose of the fractographic evaluation is to evaluate the wire specimen fracture surfaces generated by tensile testing for wires with pre-existing cracks. All specimens are visually examined under a stereoscopic microscope in accordance with FHWA Guidelines for "Inspection of Fracture Critical Bridge Members" of Cable Suspension Bridges (FHWA-1P-86-26) Read the entire page →
From page 43... ... 43 multiple segments along the panel. Note that this procedure assumes that wires remain parallel (the wire stays in the same ring) Read the entire page →
From page 44... ... 44 Assigning Sample Wires to Groups For bridges where it is observed that the corrosion stage varies along the length of the wire, it is important to categorize the wire corrosion stage on the basis of an inspection of the individual specimens after they are cut from the wire. In some cases, the corrosion stage determined in this manner may result in assigning a higher corrosion stage to a wire than had been assigned in the field. Read the entire page →
From page 45... ... 45 The bottom line is that it is not necessary to test all sections along a sample wire to determine the properties of the wire. NCHRP Report 534 recognizes that visual corrosion rating allows one to minimize the number of tests while obtaining sufficiently accurate results. Read the entire page →
From page 46... ... 46 from bridges in service, the use of the nominal wire diameter appears to be more appropriate for the purpose of reporting test results. Wire Redevelopment Length Wires that are broken in adjacent panels are redeveloped in the panel under investigation through friction. Read the entire page →
From page 47... ... 47 Estimation of Cable Strength The properties of the test specimens determined from the tensile tests are used to establish the ultimate strength and strain of the wires composing each group per Article 4.4 of NCHRP Report 534, as follows: 1. The ultimate strength (strain) Read the entire page →
From page 48... ... 48 for that group. The assumed stress is then multiplied by the area of the remaining wires and estimates of the force in wires broken in other panels and redeveloped in the panel under consideration are added to determine the total force in the cable. Read the entire page →
From page 49... ... 49 Evaluation of Accuracy of Strength Estimation The process of developing an estimate of the strength based on cable inspection necessarily relies upon several assumptions. Only the wires along the wedge lines are inspected, and the results are used to estimate the condition of the rest of the wires inside the cable. Read the entire page →
From page 50... ... 50 cables, Cases 4 and 5 were considered to see how extremes of wire strength distribution may affect the accuracy of the strength estimates. Table 2. Read the entire page →
From page 51... ... 51 2. weather and temperature 3. Read the entire page →
From page 52... ... 52 9. verbal description of method used to calculate cable strength; table of calculated strengths 10. Read the entire page →

From page 35...

... 35 C H A P T E R 3 Review of NCHRP 534 Approach Introduction Since its publication in 2004, NCHRP NCHRP Report 534 "Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel Wire Cables" (herein referred to as NCHRP Report 534) , has provided a standardized method for use by owners and investigators to inspect and evaluate main cables and has been applied on suspension bridges worldwide.