1、Section 8 REINFORCED CONCRETE* Part A GENERAL REQUIREMENTS AND MATERIALS 8.1 APPLICATION 8.1.1 General The specifications of this section are intended for de- sign of reinforced (nonprestressed) concrete bridge mem- bers and structures. Bridge members designed as pre- stressed concrete shall conform
2、 to Section 9. 8.1.2 Notations A a ab = depth of equivalent rectangular stress block (Article 8.16.2.7) = depth of equivalent rectangular stress block for balanced strain conditions, in. (Article 8.16.4.2.3) = shear span, distance between concentrated load and face of support (Articles 8.15.5.8 and
3、8.16.6.8) = effective tension area, in square inches, of concrete surrounding the flexural tension re- inforcement and having the same centroid as that reinforcement, divided by the number of bars or wires. When the flexural reinforce- ment consists of several bar or wire sizes, the number of bars o
4、r wires shall be computed as the total area of reinforcement divided by the area of the largest bar or wire used. For cal- culation purposes, the thickness of clear con- crete cover used to compute A shall not be taken greater than 2 inches. = area of an individual bar, sq. in. (Article 8.25.1) = ar
5、ea of core of spirally reinforced compres- sion member measured to the outside diame- ter of the spiral, sq. in. (Article 8.18.2.2.2) = area of concrete section resisting shear trans- fer, sq. in. (Article 8.16.6.4.5) a, AC“ area of reinforcement in bracket or corbel re- sisting moment, sq. in. (Art
6、icles 8.15.5.8 and 8.16.6.8) gross area of section, sq. in. area of shear reinforcement parallel to flex- ural tension reinforcement, sq. in. (Articles 8.15.5.8 and 8.16.6.8) area of reinforcement in bracket or corbel re- sisting tensile force N, (Nu$), sq. in. (Articles 8.15.5.8 and 8.16.6.8) area
7、of tension reinforcement, sq. in. area of compression reinforcement, sq. in. area of reinforcement to develop compres- sive strength of overhanging flanges of I- and T-sections (Article 8.16.3.3.2) area of skin reinforcement per unit height in one side face, sq. in. per ft. (Article 8.17.2.1.3). tot
8、al area of longitudinal reinforcement (Articles 8.16.4.1.2 and 8.16.4.2.1) area of shear reinforcement within a dis- tance s area of shear-friction reinforcement, sq. in. (Article 8.15.5.4.3) area of an individual wire to be developed or spliced, sq. in. (Articles 8.30.1.2 and 8.30.2) loaded area (A
9、rticles 8.15.2.1.3 and 8.16.7.2) maximum area of the portion of the support- ing surface that is geometrically similar to and concentric with the loaded area (Articles 8.15.2.1.3and8.16.7.2) width of compression face of member perimeter of critical section for slabs and footings (Articles 8.15.5.6.2
10、 and 8.16.6.6.2) width of cross section at contact surface being investigated for horizontal shear (Arti- cle 8.15.5.5.3) *The specifications of Section 8 are patterned after and are in general conformity with the provisions of AC1 Standard 318 for reinforced concrete de- 189 sign and its commentary
11、, AC1 3 18 R, published by the American Concrete Institute. 190 HIGHWAY BRIDGES 8.1.2 bw C cm d d d“ db dC E, EI ES fb fC f, fct ff fmin f1 = web width, or diameter of circular section (Article 8.15.5.1.1) = distance from extreme compression fiber to neutral axis (Article 8.16.2.7) = factor relating
12、 the actual moment diagram to an equivalent uniform moment diagram (Article 8.16.5.2.7) = distance from extreme compression fiber to centroid of tension reinforcement, in. For computing shear strength of circular sections, d need not be less than the distance from ex- treme compression fiber to cent
13、roid of ten- sion reinforcement in opposite half of mem- ber. For computing horizontal shear strength of composite members, d shall be the dis- tance from extreme compression fiber to cen- troid of tension reinforcement for entire com- posite section. = distance from extreme compression fiber to cen
14、troid of compression reinforcement, in. = distance from centroid of gross section, ne- glecting the reinforcement, to centroid of ten- sion reinforcement, in. = nominal diameter of bar or wire, in. = distance measured from extreme tension fiber to center of the closest bar or wire in inches. For cal
15、culation purposes, the thick- ness of clear concrete cover used to compute d, shall not be taken greater than 2 inches. = modulus of elasticity of concrete, psi (Article 8.7.1) = flexural stiffness of compression member (Article 8.16.5.2.7) = modulus of elasticity of reinforcement, psi (Article 8.7.
16、2) = average bearing stress in concrete on loaded area (Articles 8.15.2.1.3 and 8.16.7.1) = extreme fiber compressive stress in concrete at service loads (Article 8.15.2.1.1) = specified compressive strength of concrete, psi = square root of specified compressive strength of concrete, psi = average
17、splitting tensile strength of light- weight aggregate concrete, psi = fatigue stress range in reinforcement, ksi (Ar- ticle 8.16.8.3) = algebraic minimum stress level in reinforce- ment (Article 8.16.8.3) = modulus of rupture of concrete, psi (Article 8.15.2.1.1) = tensile stress in reinforcement at
18、 service loads, psi (Article 8.15.2.2) = stress in compression reinforcement at bal- anced conditions (Articles 8.16.3.4.3 and 8.16.4.2.3) = extreme fiber tensile stress in concrete at ser- vice loads (Article 8.15.2.1.1) = specified yield strength of reinforcement, psi = overall thickness of member
19、, in. = compression flange thickness of I- and T- sections = moment of inertia of cracked section trans- formed to concrete (Article 8.13.3) = effective moment of inertia for computation of deflection (Article 8.13.3) = moment of inertia of gross concrete section about centroidal axis, neglecting re
20、inforce- ment = moment of inertia of reinforcement about centroidal axis of member cross section = effective length factor for compression mem- bers (Article 8.16.5.2.3) = additional embedment length at support or at point of inflection, in. (Article 8.24.2.3) = development length, in. (Articles 8.2
21、4 through 8.32) = development length of standard hook in ten- sion, measured from critical section to out- side end of hook (straight embedment length between critical section and start of hook (point of tangency) plus radius of bend and one bar diameter), in. (Article 8.29) = thb X applicable modif
22、ication factor = basic development length of standard hook in = unsupported length of compression member = computed moment capacity (Article 8.24.2.3) = maximum moment in member at stage for which deflection is being computed (Article 8.13.3) = nominal moment strength of a section at bal- anced stra
23、in conditions (Article 8.16.4.2.3) = moment to be used for design of compression member (Article 8.16.5.2.7) = cracking moment (Article 8.13.3) = nominal moment strength of a section = nominal moment strength of a section in the = nominal moment strength of a section in the = factored moment at sect
24、ion tension, in. (Article 8.16.5.2.1) direction of the x axis (Article 8.16.4.3) direction of the y axis (Article 8.16.4.3) 8.1.2 DIVISION I-DESIGN 191 = factored moment component in the direction of the x axis (Article 8.16.4.3) = factored moment component in the direction of the y axis (Article 8.
25、16.4.3) = value of smaller end moment on compression member due to gravity loads that result in no appreciable sidesway calculated by conven- tional elastic frame analysis, positive if mem- ber is bent in single curvature, negative if bent in double curvature (Article 8.16.5.2.4) = value of larger e
26、nd moment on compression member due to gravity loads that result in no appreciable sidesway calculated by conven- tional elastic frame analysis, always positive (Article 8.16.5.2.4) = value of larger end moment on compression member due to lateral loads or gravity loads that result in appreciable si
27、desway, defined by a deflection A, greater than e,/1500, cal- culated by conventional elastic frame analy- sis, always positive. (Article 8.16.5.2) = modular ratio of elasticity = ESEc (Article 8.1 5.3.4) = design axial load normal to cross section oc- curring simultaneously with V to be taken as po
28、sitive for compression, negative for ten- sion and to include the effects of tension due to shrinkage and creep (Articles 8.15.5.2.2 and 8.15.5.2.3) = design tensile force applied at top of bracket of corbel acting simultaneously with V, to be taken as positive for tension (Article 8.15.5.8) = facto
29、red axial load normal to the cross sec- tion occurring simultaneously with Vu to be taken as positive for compression, negative for tension, and to include the effects of ten- sion due to shrinkage and creep (Article 8.16.6.2.2) = factored tensile force applied at top of bracket or corbel acting sim
30、ultaneously with Vu, to be taken as positive for tension (Arti- cle 8.16.6.8) = nominal axial load strength of a section at bal- anced strain conditions (Article 8.16.4.2.3) = critical load (Article 8.16.5.2.7) = nominal axial load strength of a section at zero eccentricity (Article 8.16.4.2.1) = no
31、minal axial load strength at given eccen- tricity = nominal axial load strength corresponding to M, with bending considered in the direction of the x axis only (Article 8.16.4.3) = nominal axial load strength corresponding to Mny, with bending considered in the direction of the y axis only (Article
32、8.16.4.3) = nominal axial load strength with biaxial load- ing (Article 8.16.4.3) = factored axial load at given eccentricity = radius of gyration of cross section of a com- pression member (Article 8.16.5.2.2) = spacing of shear reinforcement in direction parallel to the longitudinal reinforcement,
33、 in. = spacing of wires to be developed or spliced, in. = span length, ft = design shear force at section (Article 8.15.5.1.1) = design shear stress at section (Article 8.15.5.1.1) = nominal shear strength provided by concrete (Article 8.16.6.1) = permissible shear stress carried by concrete (Articl
34、e 8.15.5.2) = design horizontal shear stress at any cross section (Article 8.15.5.5.3) = permissible horizontal shear stress (Article 8.15.5.5.3) = nominal shear strength (Article 8.16.6.1) = nominal horizontal shear strength (Article = nominal shear strength provided by shear re- = factored shear f
35、orce at section (Article = weight of concrete, lb per CU ft = distance from centroidal axis of gross sec- tion, neglecting reinforcement, to extreme fiber in tension (Article 8.13.3) = quantity limiting distribution of flexural rein- forcement (Article 8.16.8.4) 8.16.6.5.3) inforcement (Article 8.16
36、.6.1) 8.16.6.1) a (alpha) = angle between inclined shear reinforcement and longitudinal axis of member af = angle between shear-friction reinforcement and shear plane (Articles 8.15.5.4 and 8.16.6.4) b (beta) = ratio of area of reinforcement cut off to total area of reinforcement at the section (Art
37、icle 8.24.1.4.2) = ratio of long side to short side of concentrated load or reaction area; for a circular concen- trated load or reaction area, c = 1 .O (Articles 8.15.5.6.3 and 8.16.6.6.2) c 192 HIGHWAY BRIDGES 8.1.2 d Pi x Ps PW ab = absolute value of ratio of maximum dead load moment to maximum t
38、otal load mo- ment, always positive = ratio of depth of equivalent compression zone to depth from fiber of maximum com- pressive strain to the neutral axis (Article 8.16.2.7) = correction factor related to unit weight for concrete (Articles 8.15.5.4 and 8.16.6.4) = coefficient of friction (Article 8
39、.15.5.4.3) = tension reinforcement ratio = A,/b,d, As/bd = compression reinforcement ratio = Ad = reinforcement ratio producing balanced strain conditions (Article 8.16.3.1.1) = ratio of volume of spiral reinforcement to total volume of core (out-to-out of spirals) of a spirally reinforced compressi
40、on member (Article 8.18.2.2.2) = reinforcement ratio used in Equation (8-4) and Equation (8-48) = moment magnification factor for members braced against sidesway to reflect effects of member curvature between ends of compres- sion member = moment magnification factor for members not braced against s
41、idesway to reflect lateral drift resulting from lateral and gravity loads = strength reduction factor (Article 8.16.1.2) 8.1.3 Definitions The following terms are defined for general use in Section 8. Specialized definitions appear in individual Articles. Bracket or corbel-Short (haunched) cantileve
42、r that projects from the face of a column or wall to support a concentrated load or beam reaction. See Articles 8.15.5.8 and 8.16.6.8. Compressive strength of concrete (fi)-Specified compressive strength of concrete in pounds per square inch (psi). Concrete, structural lightweight-A concrete contain
43、- ing lightweight aggregate having an air-dry unit weight as determined by “Method of Test for Unit Weight of Struc- tural Lightweight Concrete” (ASTM C 567), not exceed- ing 115 pcf. In this specification, a lightweight concrete without natural sand is termed “all-lightweight concrete” and one in w
44、hich all fine aggregate consists of normal weight sand is termed “sand-lightweight concrete.” Deformed reinforcement-Deformed reinforcing bars, deformed wire, welded smooth wire fabric, and welded deformed wire fabric. Design load-All applicable loads and forces or their related internal moments and
45、 forces used to proportion members. For design by SERVICE LOAD DESIGN, de- sign load refers to loads without load factors. For design by STRENGTH DESIGN METHOD, design load refers to loads multiplied by appropriate load factors. Design strength-Nominal strength multiplied by a strength reduction fac
46、tor, 4. Development length-Length of embedded reinforce- ment required to develop the design strength of the rein- forcement at a critical section. Embedment length-Length of embedded reinforce- ment provided beyond a critical section. Factored load-Load, multiplied by appropriate load factors, used
47、 to proportion members by the STRENGTH DESIGN METHOD. Nominal strength-Strength of a member or cross sec- tion calculated in accordance with provisions and as- sumptions of the STRENGTH DESIGN METHOD be- fore application of any strength reduction factors. Plain reinforcement-Reinforcement that does
48、not conform to the definition of deformed reinforcement. Required strength-Strength of a member or cross sec- tion required to resist factored loads or related internal moments and forces in such combinations as are stipu- lated in Article 3.22. Service loa-Loads without load factors. Spiral reinfor
49、cement-Continuously wound reinforce- ment in the form of a cylindrical helix. Splitting tensile strength (%)-Tensile strength of con- crete determined in accordance with “Specifications for Lightweight Aggregates for Structural Concrete,” AASHTO M 195 (ASTM C 330). Stirrups or ties-Lateral reinforcement formed of in- dividual units, open or closed, or of continuously wound reinforcement. The term “stirrups” is usually applied to lateral reinforcement in horizontal members and the term “ties” to those in vertical members. Tension tie member-Member having an axial tensile force suffici
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