STRUCTURAL DESIGN HIGHLIGHTS OF ACI 318-19 PART 2 ..., Exercises of Design

Download STRUCTURAL DESIGN HIGHLIGHTS OF ACI 318-19 PART 2 ... and more Exercises Design in PDF only on Docsity! 1 STRUCTURAL DESIGN HIGHLIGHTS OF ACI 318-19 PART 2 of 2 CHAPTERS 11 – 27 By: Michael Folse, P.E. ABSTRACT: This presentation is a chapter by chapter review of ACI 318-19 “Building Code Requirements for Structural Concrete”, released in August 2019 to replace ACI 318-14. Highlighted are the code provisions which the author of this presentation has used most often while engaged in the design of industrial, marine, and commercial reinforced concrete structures. Figures and short example problems illustrating use of the provisions are included. The emphasis is on non- prestressed, non-seismic structures designed by traditional methods. 2 5 From Chapter 2: “wall” = a vertical element designed to resist axial load, lateral load, or both, with a horizontal length-to- thickness ratio greater than 3, used to enclose or separate spaces. 11.1 SCOPE 11.1.1 This chapter shall apply to the design of nonprestressed and prestressed walls including: cast-in- place, precast in plant, and precast on site including tilt-up. 11.1.2 Design of special structural walls: Chapter 18 11.1.3 Plain concrete walls: Chapter 14 11.1.4 Cantilever retaining walls: Chapter 13 6 11.2 – GENERAL 11.2.1 Materials: Concrete properties Chapter 19; Reinforcement properties Chapter 20 7 11.4 – REQUIRED STRENGTH (CONT’D) 11.4.2 Factored axial force and moment Factored axial force at a given eccentricity shall not exceed the capacity given in 22.4.2.1. Moments must include slenderness effects (second order elastic presumed) 11.4.3 Factored shear: Design for in-plane and out-of-plane 10 1 CODE COMMENTARY Steoderness effects stall be calculated in accor RILALS The forces typically actieg on x wall are iltee- 1 3 Fe OA, GT, of GR. Altwastively, otof-plase — teviot m Fig, RIALS, sonbysis shall be permitted using 114 for walls the requivereents of thal section. Area of tramsverse wepleen {te lecies J) retmforament shea P i per verhatinch Va oa &h e +8) hev 4,73 for hu) Sis = “ >2.0 thickness < =Ag=hhw hus is entire a Ay . : if multi story. Fig. RILALI-—forplime ond out-of ptunve forres a HALA Walls shall be dexigeed for exxettrio rxcel boads 8d sexy lateral or other hoosks to waked they are sxbrjectod. 14.2.1 Walls shall bo designed fo the rrsccisrarn factored mersent M, thet can acccenpany the factored axial force far tech applicable toad combinatinn. The factored axial force Menderes effects in eccoedance with 6.6.4, 67, of 68 BAIAS Faced shew 114.3.8 Walle sbetl irasan iephwse “a nas zie osigreat foe the crore 29) ‘strength General {.SA.0 For cach applicable Stoned nad combination, atreegtt at wit nectices sball sity @S.> Ui, inctateng Hereagh (c). Interaction between socid loud andl sneeneth te considerent 1 11.5 – DESIGN STRENGTH 11.5.1 General: Consider axial force, moment, and shear 11.5.2 Axial load and in-plane or out-of-plane flexure: Bearing walls 22.4 or 11.5.3; Moment in nonbearing walls 22.3 12 11.5.4 - IN-PLANE SHEAR (CONT’D) 11.5.4.3 Nominal wall in-plane shear capacity calculated by: For normal weight concrete with wall height to length ratio LE 1.5: Vn = (Gross wall area in a horizontal section) (3sqrt(f’c) + steel yield stress times the area of horizontal steel reinforcing per vertical inch / wall thickness) The “3” in the above equation is reduced to “2” at hw/lw = 2 and above, and as low as zero if the wall has axial tension. 11.5.5 Out-of-plane shear: Nominal capacity according to 22.5 15 11.6 – REINFORCEMENT LIMITS Table 11.6.1 Minimum reinforcement cast-in-place and precast walls, transverse and longitudinal steel ratios required: values range 0.001 to 0.0025 (safe to use minimum values 0.0025 for both) 16 11.7 – REINFORCEMENT DETAILING 11.7.1 General: Cover 20.5.1; Development lengths 25.4; Splices 25.5. 11.7.2 Spacing of longitudinal reinforcement 11.7.2.1 Spacing s of longitudinal bars in cast-in-place walls shall not exceed the lesser of 3h and 18 inches. If shear reinforcement is required for in-plane strength, spacing of longitudinal reinforcement shall not exceed lw/3. 17 11.7 – SPACING OF REINFORCEMENT (CONT’D) 11.7.4 – LATERAL SUPPORT 11.7.5 OPENINGS 11.8 – ALTERNATE ANALYSIS 11.7.4 Lateral support of longitudinal reinforcement: If longitudinal reinforcement is required for compression and exceeds one percent of the gross concrete area, it shall be laterally supported by transverse ties. 11.7.5 Reinforcement around openings: Add #5 bars developed at corners. 11.8 – Alternate method for out-of- plane slender wall analysis: Simply supported axially loaded member subject to an out-of-plane uniformly distributed lateral load, with maximum moments and deflections occurring at midheight. 20 21 CHAPTER 12 – DIAPHRAGMS (Generally cast-in-place floor slabs acting as thin deep beams to transfer lateral loads) 12.1 SCOPE 12.2 GENERAL 12.1 - Scope: Nonprestressed and prestressed cast-in place slabs, topping slabs on precast slabs, other precast systems. Diaphragms in Seismic Design Categories D, E, and F must also satisfy 18.12. 12.2 - General: Design shall consider: In- plane forces due to lateral loads; transfer forces; forces at connections to vertical framing or bracing; out-of-plane forces due to gravity or other source. Consider effect of slab openings. Concrete properties according to Chapter 19. Steel properties according to Chapter 20. 22 12.5 - DESIGN STRENGTH (CONT’D) 12.5.3 Shear In-plane shear; capacity reduction factor 0.75. Nominal in-plane shear strength for cast- in-place slabs of normal weight concrete: Vn = (slab thickness)(slab plan dimension in the direction of the load – openings = “depth”)( 2sqrt(f’c) + (area of steel reinforcing parallel to load per inch of slab width perpendicular to load / slab thickness) (steel yield stress)) f’c LE 100psi ; Vn limited to (0.75)(8)sqrt(f’c)( slab thickness) (slab depth) 25 12.5 -DESIGN STRENGTH (CONT’D) 12.5.4 Collectors 12.5.4.1 Collectors shall extend from the vertical elements of the lateral-force-resisting system across all or part of the diaphragm depth as required to transfer shear from the diaphragm to the vertical element. 12.5.4.2 Collectors shall be designed as tension members, compression members, or both, in accordance with 22.4. 26 12.6 – REINFORCEMENT LIMITS 12.6 – Reinforcement limits: Shrinkage and temperature according to 24.4 can also be used to resist diaphragm in-plane forces; one-way slab limits in 7.6; two-way slab limits 8.6 27 30 CHAPTER 13 – FOUNDATIONS 13.1 SCOPE 13.1 – Scope: Strip footings, Isolated footings, Combined footings, Mat foundations, Grade beams, Pile caps, Piles, Drilled piers, Caissons, Cantilever retaining walls, Counterfort and buttressed cantilever retaining walls. 31 13.2 GENERAL 13.2.1 Materials: Concrete properties Chapter 19; Steel reinforcement Chapter 20; Embedments 20.6. 13.2.2 Connection to other members: 16.3 13.2.3 Earthquake effects: 18.2.2.3; Seismic Design Categories C, D, E, F 18.13. 13.2.4 Slabs-on-ground: If part of seismic-force-resisting system 18.13. 13.2.5 Plain concrete: Chapter 14. 32 13.2.7 – CRITICAL SECTIONS 13.2.7 Critical sections for shallow foundations and pile caps Table 13.2.7.1 Supported member: Location of critical section for Mu Column or pedestal: Face Column with steel base plate: Halfway between face and edge of steel base plate Concrete wall: Face Masonry wall: Halfway between center and face of masonry wall 35 13.2.7 – CRITICAL SECTIONS (CONT’D) 13.2.7.2 The location of critical section for factored shear in accordance with 7.4.3 and 8.4.3 for one-way shear or 8.4.4.1 for two-way shear shall be measured from the location of the critical section for Mu . 13.2.7.3 Circular or regular polygon-shaped concrete columns or pedestals shall be permitted to be treated as square members of equivalent area when locating critical sections for moment, shear, and development of reinforcement. 36 eel! Mus Mn Check L2D+L6L [2D +1. OL +.0(W ore) 0.4D+1.0 (w one) Stem Toe —~ Key (optional) Heel Fig. RI3.1.1—Dpes of foundations, 13.1.2 Foundations excluded by 1.4.7 are excluded from 37 13.3 – SHALLOW FOUNDATIONS (CONT’D) 13.3.3 Two-way isolated footings 13.3.3.1 Must also satisfy Chapters 7 and 8. 13.3.3.2 In square two-way footings, reinforcement shall be distributed uniformly across entire width of footing in both directions. 40 13.3 – SHALLOW FOUNDATIONS (CONT’D) 13.3.3.3 In rectangular footings: (a) Reinforcement in the long direction distributed uniformly across width. (b) In short direction, fraction 2/( 1+ ratio of long footing dimension to short dimension) of total steel reinforcing required shall be uniformly distributed over a strip of short footing dimension centered on the column. Remainder of reinforcing uniformly distributed over areas outside this strip. 41 13.3 – SHALLOW FOUNDATIONS (CONT’D) 13.3.4 Two-way combined footings and mat foundations 13.3.4.1 Must also satisfy Chapter 8. 13.3.4.2 Direct design method not permitted. 42 13.4 – DEEP FOUNDATIONS (CONT’D) 13.4.2.1 It shall be permitted to design a deep foundation member using load combinations for allowable stress design in ASCE/SEI 7, section2.4, and the allowable strength specified in Table 13.4.2.1 if (a) and (b) are satisfied: (a) The deep foundation member is laterally supported for its entire height (b) The applied forces cause bending moments in the deep foundation member less than the moment due to an accidental eccentricity of 5 percent of the member diameter or width. 45 13.4 – DEEP FOUNDATIONS (CONT’D) Table 13.4.2.1 – Maximum allowable compressive strength of deep foundation members Uncased cast-in-place concrete drilled or augured pile: Pa = 0.3f’cAg + 0.4fy As … Precast prestressed concrete pile: Pa = (0.33f’c – 0.27fpc) Ag 46 13.4 – DEEP FOUNDATIONS (CONT’D) 13.4.3 Strength design 13.4.3.2 The strength design of deep foundation members shall be in accordance with 10.5 using the compressive strength reduction factors of Table 13.4.3.2 for axial load without moment, and the strength reduction factors of Table 21.2.1 for tension, shear, and combined axial force and moment. The provisions of 22.4.2.4 and 22.4.2.5 shall not apply to deep foundations. 47 13.4 – DEEP FOUNDATIONS (CONT’D) 13.4.5.6 Minimum transverse reinforcement enclosing longitudinal reinforcement: Least horizontal pile dimension LE 16 inches: W4,D4 16 to 20 inches: W4.5, D5 Over 20 inches: W5.5, D6 Maximum spacing: First five ties or spirals each pile end, 1 inch center to center; end 24 inches, 4 inch; rest of pile, 6 inches. 50 13.4 – DEEP FOUNDATIONS (CONT’D) 13.4.6 Pile caps 13.4.6.1 Minimum “d” for bottom steel 12 inches. 13.4.6.2 Pile reactions may be assumed to be concentrated at the pile centroid. 13.4.6.3 Except for pile caps designed in accordance with 13.2.6.5, the pile cap shall be designed such that (a) is satisfied for one-way foundations and (a) and (b) are satisfied for two-way foundations. 51 13.4 – DEEP FOUNDATIONS (CONT’D) (a) 0.75 Vn GE Vu , where Vn shall be calculated in accordance with 22.5 for one-way shear. (b) 0.75 vn GE vu , where vn shall be calculated in accordance with 22.6 for two-way shear. (Note: Vu and vu references to 13.4.2.7 are errors since there is no such section.) 52 55 CHAPTER 14 – PLAIN CONCRETE 14.1 SCOPE 14.1.3 Plain concrete shall be permitted only in cases (a) through (d): (a) Members that are continuously supported by soil or other… (b) Members for which arch action provides compression under all conditions of loading. (c) Walls (d) Pedestals 56 14.1 SCOPE (CONT’D) 14.2 GENERAL 14.1.4 Further restrictions for Seismic Design Categories D, E, F 14.1.5 Plain concrete shall not be permitted for columns and pile caps. 14.2 General: Concrete properties Chapter 19; Steel reinforcement Chapter 20; Embedments 20.6. 57 14.5 – DESIGN STRENGTH 14.5.1.3 Tensile strength of concrete shall be permitted to be considered in design.(5sqrt(f’c)) 14.5.1.6 No strength shall be assigned to steel reinforcement. 14.5.6 Bearing: Bn = 0.85 f’c A1 or up to double this if supporting surface is wider on all sides than the loaded area ( increase factor is sqrt(A2/A1) ) 60 61 CHAPTER 15 – BEAM – COLUMN AND SLAB – COLUMN JOINTS 15.1 – SCOPE 15.2 GENERAL 15.1 - Scope: This chapter shall apply to the design and detailing of cast-in-place beam-column and slab-column joints. 15.2 - General 15.2.1 Beam-column joints shall satisfy the detailing provisions of 15.3 and strength requirements of 15.4. 15.2.2 Beam-column and slab- column joints shall satisfy 15.5 for transfer of column axial force through the floor system. 62 15.3 – DETAILING OF JOINTS (CONT’D) 15.3.1.1 Beam-column joints shall satisfy 15.3.1.2 through 15.3.1.4 unless (a) through (c) are satisfied: (a) Joint is considered confined by transverse beams in accordance with 15.2.8 for all shear directions considered (b) …..not part of a designated seismic-force-resisting system (c) …..not …. SDC D, E, or F 65 15.3 – DETAILING OF JOINTS (CONT’D) 15.3.1.4 Spacing of joint transverse reinforcement s shall not exceed 8 in. within the depth of the deepest beam framing into the joint. 15.3.2 Slab-column joint transverse reinforcement 15.3.2.1 Except where laterally supported on four sides by a slab, column transverse reinforcement shall be continued through a slab column joint, including… 66 15.4 – STRENGTH REQUIREMENTS 15.4 – Strength requirements for beam-column joints 15.4.1 Required shear strength 15.4.1.1 Joint shear force Vu shall be calculated on a plane at mid- height of the joint using flexural tensile and compressive beam forces and column shear consistent with (a) or (b): 67 15.4 – STRENGTH REQUIREMENTS (CONT’D) 15.5 TRANSFER OF COLUMN AXIAL FORCE (a) Beam width plus joint depth (b) Twice the perpendicular distance from longitudinal axis of beam to nearest side face of the column 15.5 – Transfer of column axial force through the floor system 15.5.1 If fc’ of a floor system is less than 0.7fc’ of a column…. 70 71 CHAPTER 16 – CONNECTIONS BETWEEN MEMBERS 16.1-16.5 16.1 - Scope: Precast concrete; foundations; brackets and corbels. 16.2 – Connections of precast members 16.3 – Connections to foundations 16.4 – Horizontal shear transfer in composite concrete flexural members 16.5 – Brackets and Corbels 72 17.1 – SCOPE 17.1.2 Provisions of this chapter shall apply to the following anchor types (a) through (g): (a) Headed studs and headed bolts…. (b) Hooked bolts… (c) Post-installed expansion anchors… (d) Post-installed adhesive anchors… (f) Post-installed screw anchors… (New to ACI 318) (g) Attachments with shear lugs.. (New to ACI 318) 75 17.2 – GENERAL 17.2.1 Anchors and anchor groups shall be designed for critical effects of factored loads calculated by elastic analysis. If nominal strength is controlled by ductile steel elements, plastic analysis is permitted… 17.2.1.1 Anchor group effects shall be considered if two or more anchors loaded by a common structural element are spaced closer than the spacing required for unreduced breakout strength… 76 17.3 – DESIGN LIMITS 17.4 REQUIRED STRENGTH 17.3.1 The value of fc ‘ LE 10 ksi for cast-in anchors LE 8 ksi for post-installed. 17.4 – Required strength: Chapter 5 Load Combinations; Also section 17.10 for Seismic Design Categories C, D, E, and F, 77 CODE tw E { tL [ ce (0) Stoel failure (i) Pullout an rh COMMENTARY {™ {" Singie {iv) Concrete spitting (v) Side-face blowout (09) Bond tallure (a) Tensile loading v at v v — Meal [eae (9 Steal failure preceded —_(i) Concrete pryout for bby concrete spall ‘anchors far from froe 6090 (b) Shear loading Fig, R17.5.1.2—Failure modes for anchors, 175,13 Strength of anchors shall be permitted to be deter- ined in aooordance with 17.6 for 17-5.1.2(a) through (©), nd 17.7 for 17-5.1.2(4) theongh (b). For adhesive anchors that resist sustained tension, the requirements of 17,522 shall apply. RITSA.3 The method for concrete breakout esis deemed to comply with the requirements of 17.5.1.2 6% ‘developed from the concrete capacity design (CCD) (Buchs et al. (1995); Fligehusen and Balogh (1995), woieh coca dnptation ofthe Kappa Method (Eligehause #0 Fuchs 1988; Eligehausen et al. 20060) with a breakout failure surface angle of approximately 35 degrees ee 80 17.5 – DESIGN STRENGTH (CONT’D) 17.5.2.1 The design strength of anchor reinforcement shall be permitted to be used instead of the concrete breakout strength if (a) or (b) is satisfied. (a) For tension, if anchor reinforcement is developed in accordance with Chapter 25 on both sides of the concrete breakout surface. (b) For shear, if anchor reinforcement is developed in accordance with Chapter 25 on both sides of the concrete breakout surface, or encloses and contacts the anchor and is developed beyond the breakout surface. 81 17.6 – TENSILE STRENGTH 17.7 SHEAR STRENGTH 17.6 – Tensile strength – based on 35 degree angle between breakout surface and exterior surface, 1:1.5. This gives a square plan view of the breakout surface of dimensions 3hef x 3hef where hef is the effective embedment depth of the anchor. 17.7 – Shear strength: 35 degree breakout angle also applies for shear. 82 CODE QB Anchoring simiar Fig. R17.$.2.16()—Halrpin anchor reinforcement for shear. siti is @ay 85 eiemelciss CODE 4.3.1 Anchoc group effects shall be considered wher- ‘or more anchors have spacing less than the crit- 3.1, where only those anchors 4 Strength of anchors shall be permitted to be based m test evaluation using the 5 percent fractile of applicable results for 17.5.1.2 (a) through (th). COMMENTARY 17.5.1.30 and b), Itis considered to be sufficiently accurate, + relatively easy to apply, and capable of extension to ireg- ula layouts. The CCD Method predicts the strength of an “2 ‘anchor or anchor group by using a basic equation fortension << in cracked concrete, which is multiplied by factors that gq ‘account for the sueber of anchors, edge distance, spacing, eccentricity, and absence of cracking. For sbear, « similar approach is used. Experimental and numerical investigations have demonstrated the applicability of the CCD Method to adbesive anchors as well (Eligebausen et al. 2006a). Pig. RI7.5.1.3b—Breakout cone for shear: RI7.S.14 Sections 17.5.1.2 and 17,5.2.3 establish the performance factors for which anchor design models are required to be verified. Many possible design approaches exist, and the user is always permitted to “design by test" using 17.5.1.4 as long as sufficient data sre available to verify the model. Test procedures can be used to determine the single-anchor breakout strength in tension and in shear, ‘The test results, however, are required to be evaluated on a basis statistically equivalent to that used to select the values for the concrete breakout method considered to satisfy provisions of 17.5.1.2. The basic strength cannot de taken jai aaa aa @als 86 Peper) EMRE nenentcnn cen cian CODE COMMENTARY on, Shy ‘The critical edge distance for headed studs, ae headed bois, expansion anchors, screw ‘anchors, and undercut anchors is 1.5!tgy Ane 15h 15th v =~ Weg; <1.Blgg Ga < 1 ‘Section through faiture cone Aye = (G4 + 1.50tgd) X (2X 1.5!r¢9) —__4,— Aveo Cu 8, Shoe jem > >| Ane J $.5lg 1.5er | 15 ier | 1.5!tep | — — | It egy < 1.5!qp Pd 84< ge ! 4- A, Aue = (Cqi + $+ 1.5ltgd X (2X 1.5led } Cay 8, 1.5 ! 1.5lgy 15h = | Plan \4 Abico = (2% 150g) «(2 K 15th) = Bye Ane 4 1 Shey | {se ow Gq AN Gye < 1.5 2p and 8 and 8 < 3g Avie = (Cys + 8+ 1.50Mgd) X (Cqo + 89+ 1-5ltel (a) ® | Fig. R17,6.2.1—(a) Calculation of Ayu and (2) calculation of Ax. for single anchors and anchor groups. American Conceots bstiule ~ Copytigied © Nerd — worn concrete on 18.1 - SCOPE 18.1.1 This chapter shall apply to the design of nonprestressed and prestressed concrete structures assigned to Seismic Design Categories B through F…. 18.1.2 Structures designed according to the provisions of this chapter are intended to resist earthquake motions through ductile inelastic response of selected members. 90 18.1 - GENERAL 18.2 – General: SDC B shall satisfy 18.2.2; SDC C shall satisfy 18.2.2, 18.2.3, and 18.13; SDC D, E, and F shall satisfy 18.2.2 through 18.2.8 and 18.12 through 18.14. 18.2.1.6 Structural systems designated as part of the seismic- force-resisting system shall be restricted to those designated by the general building code… (a) through (h) shall be satisfied… 91 18.2 - GENERAL (CONT’D) (a) Ordinary moment frames 18.3 (c) Intermediate moment frames 18.4 (e) Special moment frames 18.2.3 through 18.2.8 and 18.6 through 18.8. (g) Special structural walls 18.2.3 through 18.2.8 and 18.10 92 18.13 - FOUNDATIONS (CONT’D) 18.13.4.3 Where required, foundation seismic ties shall have a design strength in tension and compression at least equal to 0.1 SDS times the greater of the pile cap factored dead load plus factored live load unless… 95 96 CHAPTER 19 CONCRETE: DESIGN AND DURABILITY REQUIREMENTS 19.2 – CONCRETE DESIGN PROPERTIES 19.2 – Concrete design properties 19.2.1 Specified compressive strength: f’c based on 28-day tests 19.2.2 Modulus of elasticity: For normal weight concrete, Ec, ksi = 57sqrt(f’c psi) 19.2.3 Modulus of rupture: For normal weight concrete, fr, psi = 7.5sqrt(f’c psi) 97