C - SECTION 4.4 FLEXURAL STRENGTH OF ... order to give satisfactory service a prestressed monoblock...
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C C O O M MM ME E N N T T A A R R Y Y ( ( 2 2 0 0 1 1 5 5 ) ) The purpose of this part is to furnish the technical explanation of various Articles in Chapter 30. In the numbering of Articles of this Section, the numbers after the “C-” correspond to the Section/Article being explained. C C - - S S E E C C T T I I O O N N 4 4 . . 4 4 F F L L E E X X U U R R A A L L S S T T R R E E N N G G T T H H O O F F P P R R E E S S T T R R E E S S S S E E D D M MO O N N O O B B L L O O C C K K T T I I E E S S Monoblock ties are stiff structural members that are loaded by the rails from the top and are supported on the ballast at the bottom. The loads applied at the top combined with the support reactions at the bottom will produce flexure in the ties. Maximum flexure occurs at the rail seats and at the center. Flexure is influenced by a number of factors discussed in Section 4.1, General Considerations. C C - - W WH H E E E E L L L L O O A A D D S S In order to give satisfactory service a prestressed monoblock concrete tie should be capable of withstanding without cracking the maximum loads likely to be found in service. C C - - R R A A I I L L S S E E A A T T L L O O A A D D a. The rail seat load is that load transmitted by rail to the rail seat of the tie. In order to determine the rail seat load, a maximum axle load (AL) of 82 kips (365 kN) was chosen. Therefore, using a distribution factor (DF) of 0.505 for concrete ties spaced at 24 inch (610 mm) centers from Figure 30-4-1 and an impact factor (IF) of 200% from Article 4.1.2.4, the calculated rail seat load (R) is, = 1 + = 1 2 82 0.505 1 + 2.00 = . ( ) b. This rail seat load is used to determine the flexural requirements in Article 4.4.1, for monoblock ties. The design flexural performance values for monoblock ties for other than 24 inches (610 mm) spacing may be determined directly from Figure 30-4-3 and by applying the appropriate speed and tonnage factors. Henry 10/14/14 6:02 PM Deleted: 2002 Henry 10/14/14 5:58 PM Deleted: 78 kips Henry 10/14/14 5:58 PM Deleted: 347 Henry 10/14/14 6:07 PM Deleted: : Draft Not Yet Approved
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Transcript of C - SECTION 4.4 FLEXURAL STRENGTH OF ... order to give satisfactory service a prestressed monoblock...
CCOOMMMMEENNTTAARRYY ((22001155)) The purpose of this part is to furnish the technical explanation of various Articles in Chapter 30. In the numbering of Articles of this Section, the numbers after the “C-” correspond to the Section/Article being explained. CC -- SSEECCTTIIOONN 44..44 FFLLEEXXUURRAALL SSTTRREENNGGTTHH OOFF PPRREESSTTRREESSSSEEDD MMOONNOOBBLLOOCCKK TTIIEESS Monoblock ties are stiff structural members that are loaded by the rails from the top and are supported on the ballast at the bottom. The loads applied at the top combined with the support reactions at the bottom will produce flexure in the ties. Maximum flexure occurs at the rail seats and at the center. Flexure is influenced by a number of factors discussed in Section 4.1, General Considerations. CC -- WWHHEEEELL LLOOAADDSS In order to give satisfactory service a prestressed monoblock concrete tie should be capable of withstanding without cracking the maximum loads likely to be found in service. CC -- RRAAIILL SSEEAATT LLOOAADD a. The rail seat load is that load transmitted by rail to the rail seat of the tie. In order to determine the rail seat load, a maximum axle load (AL) of 82 kips (365 kN) was chosen. Therefore, using a distribution factor (DF) of 0.505 for concrete ties spaced at 24 inch (610 mm) centers from Figure 30-4-1 and an impact factor (IF) of 200% from Article 4.1.2.4, the calculated rail seat load (R) is, 𝑅𝑅 = 𝐴𝐴𝐴𝐴 𝐷𝐷𝐷𝐷 1 + 𝐼𝐼𝐼𝐼
𝑅𝑅 =1282 𝑘𝑘𝑘𝑘𝑘𝑘 0.505 1 + 2.00 = 𝟔𝟔𝟔𝟔.𝟏𝟏 𝒌𝒌𝒌𝒌𝒌𝒌𝒌𝒌 (𝟐𝟐𝟐𝟐𝟐𝟐 𝒌𝒌𝒌𝒌)
b. This rail seat load is used to determine the flexural requirements in Article 4.4.1, for monoblock ties. The design flexural performance values for monoblock ties for other than 24 inches (610 mm) spacing may be determined directly from Figure 30-4-3 and by applying the appropriate speed and tonnage factors.
Henry 10/14/14 6:02 PMDeleted: 22000022
Henry 10/14/14 5:58 PMDeleted: 78 kips
Henry 10/14/14 5:58 PMDeleted: 347
Henry 10/14/14 6:07 PMDeleted: :
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CC -- RRAAIILL SSEEAATT PPOOSSIITTIIVVEE BBEENNDDIINNGG MMOOMMEENNTT a. The rail seat positive bending moment (MRS+, given as B in Figure 30-4-3) for an 8’-6” tie at 24” center-to-center spacing is calculated using the following assumed support conditions.
Where the bending moment is calculated using, 𝑀𝑀 = 1.1 and rounded up to the nearest 5 kip-in. The 10% increase accounts for prestress losses. Where: R=rail seat load (as calculated above) L=length of tie g=rail center spacing
𝑀𝑀 = 1.162.1 𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘 102" − 60"
4 102"= 𝟑𝟑𝟑𝟑𝟑𝟑 𝒌𝒌𝒌𝒌𝒌𝒌 − 𝒊𝒊𝒊𝒊 (𝟑𝟑𝟑𝟑 𝒌𝒌𝒌𝒌𝒌𝒌)
CC –– CCEENNTTEERR NNEEGGAATTIIVVEE BBEENNDDIINNGG MMOOMMEENNTT a. The center negative bending moment (MC-) is calculated using the following assumed support conditions.
Where the bending moment is calculated using, 𝑀𝑀 = 1.1 − 𝑅𝑅𝑅𝑅 + − and rounded up to the nearest 1 kip-in. Where: R=rail seat load (as calculated above) g=rail center spacing L=length of tie l=center support region=2g-L α=percentage reduction in center support region reaction=1.0 - 0.61 = 0.39
𝑀𝑀 = 1.1 −1262.1 𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘 60" +
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62.1 𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘 102"102" − 0.39𝑥𝑥18"
−14
0.39 62.1 𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘 18"102" − 0.39𝑥𝑥18"
= 𝟐𝟐𝟐𝟐𝟐𝟐 𝒌𝒌𝒌𝒌𝒌𝒌𝒌𝒌 − 𝒊𝒊𝒊𝒊 (𝟐𝟐𝟐𝟐 𝒌𝒌𝒌𝒌𝒌𝒌)
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