Development Length: Compression Bars

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1 CHAPTER Reinfored Conrete Design Fifth Edition DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS A. J. Clark Shool of Engineering Department of Civil and Environmental Engineering Part I Conrete Design and Analysis 5b FALL 2002 By Dr. Ibrahim. Assakkaf ENCE Introdution to Strutural Design Department of Civil and Environmental Engineering University of Maryland, College Park CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 1 Development Length: Compression Bars Deformed Bars in Compression The method for determining the development length in ompression l d involves finding the the basi development length l db and multiplying it by appliable modifiation fators. The modifiation fators reflet speial onditions. Note: l d shall not be less than 8 in. 1

2 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 2 Development Length: Compression Bars Basi Development Length (ompression) The basi development length in ompression is given by l db f y 0. d (1) b f = 02 But it shouldn t be less than f y d b aording to the ACI Code, Setion CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 3 Development Length: Compression Bars Modifiation Fators (Compression) The following modifiation fators may be applied to the basi development length for ompression bars: 1. Reinforement in exess of that required: As A s required provided 2. Bars enlosed within a spiral that is not less than ¼ in. in diameter and not more than 4 in. in pith or within No. 4 ties and spaed at not more than 4 in. on enter: USE

3 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 4 Development Length: Compression Bars Tables 1a through 1 gives values of the basi development length l db for ompression bars in inhes for the following ombinations of f and f y : f : 3000, 4000, 5000, and 6000 psi f y : 40,000, 50,000, and 60,000 psi CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 5 Development Length: Compression Bars Table 1a. Basi Development Length l db for Compression Bars (in.) for f y = 40,000 psi Bar Size f (normal-weight onrete), psi

4 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 6 Development Length: Compression Bars Table 1b. Basi Development Length l db for Compression Bars (in.) for f y = 50,000 psi Bar Size f (normal-weight onrete), psi CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 7 Development Length: Compression Bars Table 1. Basi Development Length l db for Compression Bars (in.) for f y = 60,000 psi Bar Size f (normal-weight onrete), psi

provide mehanial anhorage at the end of the bars 9 Need for

5 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 8 Need for Hooks In the event that the desired development length in tension annot be furnished, it will be neessary to provide mehanial anhorage at the end of the bars CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 9 Need for Hooks Hook l d l d Column Figure Hook Beam 5

6 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 10 Types of Hooks Anhorage for main or primary reinforement is usually aomplished by means of 90 or 180 hook. The dimensions and bend radii for these hooks have been standardized by the ACI Code. Standard reinforement hooks are shown in Fig. 2. CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 11 Types of Hooks Figure 2a. Standard Hooks 6

7 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 12 Types of Hooks Figure 2b. Standard Hooks CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 13 Types of Hooks Figure 3. Standard Hooks 7

8 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 14 ACI Code Speifiations The ACI Code speifies that the development length l dh (see Fig. 2) for deformed bars in tension, whih terminate in a standard hook, be omputed as the produt of a basi development length l hb and any appliable modifiation fators. Mathematially, this may expressed as l l MF (2) dh = hb CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 15 ACI Basi Development Length, l hb For a hooked bar with f y = 60,000 psi, l d b hb = 1200 (3) f Table 1 (Table A-13, Textbook) provides values for l hb. 8

9 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 16 ACI Modifiation Fators (MF) Modifiation fators are to be used if appliable: 1. Bars with f y other than 60,000 psi, USE MF f y = (4) 60, Conrete over for No. 3 through No. 11: Side over (normal to the plane of the hook ) 2 ½ in. and, for 90 hooks, over on bar extension beyond the bend 2 in.: USE 0.7 for MF CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 17 ACI Modifiation Fators, MF (ont d) 3. Ties or stirrups: For No. 3 through No. 11 with hook enlosed vertially of horizontally within ties or stirrup ties spaed along the full development length l dh not greater than 3d b : USE MF = Reinforement in exess of that required, where anhorage or development for f y is not speifially required: MF A required A provided s = (5) s 9

10 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 18 ACI Modifiation Fators, MF (ont d) 5. Lightweight aggregate onrete: USE MF =1.3 (6) 6. Epoxy-oated reinforement: USE MF =1.2 (7) CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 19 ACI Modifiation Fators, MF (ont d) The basi development length l hb must be multiplied by the appliation fators outlined in the previous viewgraphs. In no ase may l db be less than 8d b or 6 in., whihever is greater. 10

11 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 20 Example 1 Determine the anhorage or development length required for f the onditions shown in the figure. Use = 3,000 psi (normalweight onrete) and f y = 60,000 psi. The No. 8 bars may be ategorized as top bars. Assume a side over on the main bars of 2 ½ in. minimum. Bars are unoated. CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 21 Example 1 (ont d) Column (minimum) l d (minimum) l d 14 2 lear #8 bars 18 3-#8 bars 2 lear 24 Stirrups Beam #4 5 o.. 11

12 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 22 Example 1 (ont d) Anhorage into the exterior olumn: 1. Establish values for the multiplying fators α, β, γ, and λ: a. α = 1.3 (the bars are top bars). b. β = 1.0 (the bars are unoated).. γ = 1.0 (the bars are No. 8) d. λ = 1.0 (normal-weight onrete used) 2. The produt α β= 1.3 < 1.7 (OK) CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 23 Example 1 (ont d) 3. Determine. Based on over (enter of bar to nearest onrete surfae), onsider the lear over, the No. 4 stirrups diameter, and one-half the diameter of the No. 8 bar: 1.0 = = 3.0 in. 2 Based on bar spaing: 14 2( 2.0) 2( 0.5) 2( 0.5) = 2( 2) = 2.0 in. Therefore, use = 2.0 in (smallest) Controls 12

13 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 24 Table 2. ASTM Standard - English Reinforing Bars Bar Designation Diameter in Area in 2 Weight lb/ft #3 [#10] #4 [#13] #5 [#16] #6 [#19] #7 [#22] #8 [#25] #9 [#29] #10 [#32] #11 [#36] #14 [#43] #18 [#57] Note: Metri designations are in brakets CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 25 Example 1 (ont d) 4. The figure shows stirrups in the beam. However, there are no stirrups in the olumn, and K tr an be taken as zero for the olumn anhorage. 5. Chek ( + K tr )/d b 2.5: + K d b tr = = 2.0 < 2.5 USE The aess reinforement an be ignored and the fator applied an be omitted. 13

14 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 26 Example 1 (ont d) 7. Calulate l d : l l d d = = f y αβγλ d f + ktr db 60, , ()()() 1 1 ( 1.0) 53.4 in. 12 in. OK Sine 53.4 in > 24 in. (olumn width), use a standard hook, either a 90 hook or a 180 hook. b = > CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 27 Example 1 (ont d) Anhorage using a standard 180 hook: 1. The basi development length l hb for the standard hook shown in the figure an be omputed from 1200d 1200() 1 l hb = f b = = 21.9 in.(also hek Table1) The only appliable MF is based on side over of 2 ½ in. Therefore, USE MF =

15 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 28 Table 1. Basi Development Length l db for Compression Bars (in.) for f y = 60,000 psi Bar Size f (normal-weight onrete), psi CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 29 Example 1 (ont d) 3. The required development length is then alulated from l = l MF = 21.9( 0.7) = 15.3 in. dh hb Chek minimum : minimum l 8d b dh = 8d 6 in. = 8 in. < 15.3 in. OK The minimum width of olumn required is = 17.8 in. < 24 in.(olumn width) Therefore, the hook will fit into the olumn. b OK 15

16 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 30 Example 1 (ont d) Anhorage into beam: The development length required if bars are straight an be taken as 53.4 in. as determined previously. However, this number is onservative (K tr = 0). To determine a more aurate value, we have to take into onsideration the transverse reinforement index K tr beause there are stirrups in the beam. CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 31 Example 1 (ont d) Atr f yt 0.4( 60,000) Ktr = = 1500sn 1500()() 5 3 l l d d Area of 2 #4 stirrups = Ktr = = 3.07 < 2.5 USE 2.5 db f y αβγλ = db 40 + f ktr db = , , ()()() 1 1 ( 1.0) 42.7 in. 12 in. OK = > 16

17 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 32 Table 2. ASTM Standard - English Reinforing Bars Bar Designation Diameter in Area in 2 Weight lb/ft #3 [#10] #4 [#13] #5 [#16] #6 [#19] #7 [#22] #8 [#25] #9 [#29] #10 [#32] #11 [#36] #14 [#43] #18 [#57] Note: Metri designations are in brakets CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 33 Example 1 (ont d) Anhorage into beam (ont d): The development length required if bars are straight is 42.7 in. Therefore, the bars must extend at least this distane into the span. Figure 4 shows the detailed sketh for the development length. 17

18 CHAPTER 5b. DEVELOPMENT, SPLICES, AND SIMPLE SPAN BAR CUTOFFS Slide No. 34 Example 1 (ont d) 1 Required = 15.3 min. 2 over l db Hook #8 bars 18 Column 24 Beam Figure 4. Detailed Sketh for Example 1 18

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