Bond, Anchorage, and Development Length - Bond Stresses in Beam - Development Length - Standard Bar Hooks - Bar Cutoff of Bend Points in Beams

Bond Stresses in Beam Greased or lubricated Free slip es น ec Concrete Reinforcing bar P End slip Greased or lubricated Free slip es น ec Bond_02

Bond forces acting on concrete Bond forces acting on steel Bond_03

Tied-arch action in a beam with little or no bond (Round bar reinforcing) Mmax j d Little or no bond Bond_04

Bond Stress Based on Simple Cracked Analysis jd T + dT V C + dC T C dx O [ SMO = 0 ] j d (dT ) = V (dx ) 1 [ SFx = 0 ] u So dx = dT 2 T T + dT u 2 1 Elastic Cracked Section Equation Bond_05

เหล็กเสริมข้ออ้อยรับแรงดึง: Nominal Bond Strength เหล็กเสริมข้ออ้อยรับแรงดึง: เหล็กบน เหล็กอื่น เหล็กเสริมข้ออ้อยรับแรงอัด: * สำหรับเหล็กข้อกลมผิวเรียบให้ใช้กำลังครึ่งหนึ่งแต่ไม่เกิน 17.6 กก./ซม.2 Bond_06

Steel Force and Bond Stress M u stresses on bar Cracked concrete segment steel tension T bond stress u Bond_07

Actual Distribution of Flexural Bond Stress Actual T Actual u Bond_08

Source of Bond Strength R DT Reaction of concrete on ribs u DT Friction & chemical adhesion between concrete and steel R Forces exerted by ribs on concrete Bond_09

Vertical cracking of bottom cover Failure modes R V-notch failure Side-split failure R Vertical cracking of bottom cover Bond_10

Ultimate Bond Strength Cylindrical zones of circumferential tension Reinforcement Radial component of bearing pressure Circumferential tensile stresses Bond_11

Minimum Bar Covering and Spacing cb Minimum bar covering ( cb ) cs Minimum bar spacing ( 2cs ) 2cs Bond_12

Splitting of concrete along reinforcement Bond_13

Requirement: l ณ ld : development length Embedment length to develop full tensile strength of bar a ld T = Ab fs T = 0 Requirement: l ณ ld : development length Factors influencing ld - Tensile strength of concrete fct - Steel covering - Bar spacing - Stirrup Bond_14

Development of Tension Reinforcement Bonding Sources: - Embedment length - Bar Hook - Mechanical anchorage - Chemical bonding Bond_15

ระยะฝังของเหล็กเสริมรับแรงดึง v ระยะฝังของเหล็กเสริมรับแรงดึง a ld fs = fy fs = 0 ld Ab fy un Bond_16

ACI Code for Development Length = Transverse reinforcement index s = Max. spacing of stirrup n = number of bar c = smaller of edge and one-half c-c distance Bond_17

Modifiers for ld /db a Bar location: (a) Top reinforcement a = 1.3 (b) Bottom bars a = 1.0 b Coating factor: (a) Epoxy-coated cover < 3db or b = 1.5 clear spacing < 6db (b) All other epoxy-coated b = 1.2 (c) Uncoated reinforcement b = 1.0 Note: a ด b need not be taken > 1.7 Bond_18

(a) Lightweight aggregate l = 0.3 concrete g Bar-size factor: (a) DB20 and smaller g = 0.8 (b) DB25 and larger g = 1.0 l Lightweight aggregate factor: (a) Lightweight aggregate l = 0.3 concrete (b) Normal weight concrete l = 1.0 Reduction for excess reinforcement: As,req/ As,sup Reduction for large cover and wide bar spacing: 0.8 Heavily confined reinforcement: 0.75 Bond_19

Simplified Equation for Development Length DB20 and smaller (g = 0.8) DB25 and larger (g = 1.0) Case A: (1) covering = db clear c-c = db min. stirrup (2) covering = db clear c-c = 2db Case B: others Bond_20