CHAPTER 13 CONCRETE COLUMNS

Transcription

1 CHAER 13 CONCREE COUMNS ABE OF CONENS 13.1 INRODUCION YES OF COUMNS DESIGN OADS DESIGN CRIERIA imit States Forces AROXIMAE EVAUAION OF SENDERNESS EFFECS Moment Magnification Method COMBINED AXIA AND FEXURA SRENGH Interaction Diagrams ure Compression Biaxial Flexure COUMN FEXURA DESIGN ROCEDURE ongitudinal Analysis (CBridge) ransverse Analysis (CSiBridge) Column ive oad Input rocedue Wind oads (WS, W) Braking Force (BR) restress Shortening Effects (CR, SH) restressing Secondary Effect Forces (S) Input oads into WinYIED Column Design/Check COUMN SHEAR DESIGN ROCEDURE ongitudinal Analysis ransverse Analysis Chapter 13 Concrete Columns 13-i

2 Column ive oad Input rocedure COUMN SEISMIC DESIGN ROCEDURE DESIGN EXAME Design Column One at Bent wo Flexural Check of Main Column Reinforcemen (A s ) Shear Design for ransverse Reinforcement (A v ) NOAION REFERENCES Chapter 13 Concrete Columns 13-ii

3 CHAER 13 CONCREE COUMNS 13.1 INRODUCION Columns are structural elements that support the superstructure, transfer vertical loads from superstructure to foundation, and resist the lateral loads acting on the bridge due to seismic and various service loads YES OF COUMNS Columns are categorized along two parameters (Chen, 2014 and MacGregor, 1988): shape and height: Columns sections are usually round, rectangular, solid, hollow, octagonal, or hexagonal. Columns may be short or tall. he column is called either short or tall according to its effective slenderness ratio (Kl u /r). where: K = effective length factor l u = unsupported length of a compression member r = radius of gyration 13.3 DESIGN OADS he considered design loads as specified in AASHO are: Dead loads (DC) Added dead loads (DW) Design vehicular live loads: 1. Design vehicle H-93 shall consists of a combination of (ruck + ane) or (design tandem + ane) including dynamic load allowance (IM). 2. ermit vehicle (15) including the dynamic load allowance (IM). Wind loads (WS, W) Chapter 13 Concrete Columns 13-1

4 Braking force (BR) hermal effects (U) restress shortening effects (CR, SH) restressing secondary effects (S) 13.4 DESIGN CRIERIA Columns are designed for Service, Strength, and Extreme Event limit states (AASHO, 2012 and Caltrans, 2014). he Extreme Event I limit state must be in accordance with the current the Caltrans Seismic Design Criteria (SDC) version 1.7 (Caltrans, 2013). Columns should be designed as ductile members to deform inelastically for several cycles without significant degradation of strength or stiffness under the design earthquake demand (see SDC seismic design criteria chapters 3 and 4 for more details). Columns supporting a superstructure that is built using balanced cantilevered construction, or other unusual construction loads, are not addressed herein imit States Forces As stated above, columns are designed for three limit states: Strength imit State Service imit State Extreme Event imit State Bridge columns are subjected to axial loads, bending moments, and shears in both the longitudinal and transverse directions of the bridge AROXIMAE EVAUAION OF SENDERNESS EFFECS he slenderness of the compression member is based on the ratio of Kl u /r (AASHO ), while the effective length factor, K (AASHO ), is to compensate for rotational and transitional boundary conditions other than pinned ends. heoretical and design values of K for individual members are given in AASHO able C Slenderness s effect is ignored if: Kl u /r < 22 (members not braced against sidesway) Chapter 13 Concrete Columns 13-2

5 Kl u /r < (M 1 / M 2 ) (members braced against sidesway) where: M 1 = smaller end moment, should be positive for single curvature flexure M 2 = larger end moment, should be positive for single curvature flexure l u = unsupported length of a compression member r = radius of gyration = 0.25 times the column diameter for circular columns = 0.3 times the column dimension in the direction of buckling for rectangular columns If slenderness ratio exceeds the above-mentioned limits, the moment magnification procedure (AASHO b) can approximate the analysis. Note: If Kl u /r exceeds 100, columns may experience appreciable lateral deflections resulting from vertical loads or the combination of vertical loads and lateral loads. For this case, a more detailed second-order non-linear analysis should be considered, including the significant change in column geometry and stiffness Moment Magnification Method he factored moments may be increased to reflect effects of deformation as follows: M c = b M 2b + s M 2s (AASHO b-1) where: M c = magnified factored moment M 2b = moment on compression member due to factored gravity loads that result in no sideway, always positive M 2s = moment on compression member due to factored lateral or gravity loads that result in sideway,, greater than l u /1500, always positive b s = moment magnification factor for compression member braced against sidesway = moment magnification factor for compression member not braced against sidesway he moment magnification factors ( b and s ) are defined as follows: b Cm u 1 k e 1 (AASHO b-3) Chapter 13 Concrete Columns 13-3

6 1 s u 1 k e (AASHO b-4) For members braced against sideway s is taken as one unless analysis indicates a lower value.for members not braced against sideway b is to be determined as for a braced member and s for an unbraced member. u = factored axial load e = Euler buckling load, which is determined as follows: e 2 E I c ( Kl ) 2 u E c = the elastic modulus of concrete I = moment of inertia about axis under consideration k = stiffness reduction factor; 0.75 for concrete members and 1 for steel members C m = a factor, which relates the actual moment diagram to an equivalent uniform moment diagram, is typically taken as one However, in the case where the member is braced against sidesway and without transverse loads between supports, C m may be based on the following expression: C M 1b m (AASHO b-6) M 2b o compute the flexural rigidity EI for concrete column in determining e, AASHO (AASHO, 2012) recommends that the larger of the following be used: EI EI c g EsI 5 1 E I c g d s (AASHO ) EI 2.5 (AASHO ) 1 d where: I g = the gross moment of inertia (in. 4 ) E s = elastic modulus of reinforcement (ksi) = moment of inertia of longitudinal steel about neutral axis (ksi) I s d = ratio of maximum factored permanent load moment to the maximum factored total load moment, always positive Chapter 13 Concrete Columns 13-4

7 13.6 COMBINED AXIA AND FEXURA SRENGH Interaction Diagrams Flexural resistance of a concrete member is dependent upon the axial force acting on the member. Interaction diagrams for a reinforced concrete section are created assuming a series of strain distributions and computing the corresponding moments and axial forces. he results are plotted to produce an interaction diagram as shown in Figure o c = Compression Controlled s y = c = b ension Controlled Balanced Strain Condition s = y = c = Mo Mb Mn s Figure ypical Strength Interaction Diagram for Reinforced Concrete Section with Grade 60 Reinforcement When combined axial compression and bending moment act on a member having a low slenderness ratio and where column buckling is not a possible mode of failure, the strength of the member is governed by the material strength of the cross section. For this so called short column, the strength is achieved when the extreme concrete compression fiber reaches the strain of In general, one of three modes of failure will occur: tension controlled, compression controlled, or balanced strain condition (AASHO ). hese modes of failure are detailed below: Chapter 13 Concrete Columns 13-5

8 ension controlled: Sections are tension controlled when the net tensile strain in the extreme tension steel is equal to or greater than just as the concrete in compression reaches its assumed strain limit of Compression controlled: Sections are compression controlled when the net tensile strain in the extreme tension steel is equal to or less than the net tensile strain in the reinforcement ( y = 0.002) at balanced strain condition at the time the concrete in compression reaches its assumed strain limit of Balanced strain condition: Where compression strain of the concrete ( c = 0.003) and yield strain of the steel (for Grade 60 reinforcement y = 0.002) are reached simultaneously, the strain is in a balanced condition ure Compression For members with spiral transverse reinforcement, the axial resistance is based on: r = n = o = f c A g A st A st f y (AASHO For members with tie transverse reinforcement, the axial resistance is based on: r = n = o = f c A g A st A st f y AASHO where: r = factored axial resistance n = nominal axial resistance, with or without flexure = resistance factor specified in AASHO o = nominal axial resistance of a section at zero eccentricity f c = specified strength of concrete at 28 days, unless another age is specified A g = gross area of section A st = total area of main column reinforcement f y = specified yield strength of reinforcement Chapter 13 Concrete Columns 13-6

9 Biaxial Flexure AASHO specifies the design of non-circular members subjected to biaxial flexure and compression based on the stress and strain compatibility using one of the following approximate expressions: For the factored axial load, u 0.1f c A g 1 rxy 1 rx 1 ry 1 o (AASHO ) where: o = 0.85f c (A g A st ) + A st f y (AASHO ) For the factored axial load, u 0.1f c A g M M ux rx M M uy ry 1 (AASHO ) where: rxy = factored axial resistance in biaxial flexure rx = factored axial resistance determined on the basis that only eccentricity e y is present ry = factored axial resistance determined on the basis that only eccentricity e x is present u = factored applied axial force M ux = factored applied moment about x axis M uy = factored applied moment about y axis M rx = uniaxial factored flexural resistance of a section about x axis corresponding to the eccentricity produced by the applied factored axial load and moment M ry = uniaxial factored flexural resistance of a section about y axis corresponding to the eccentricity produced by the applied factored axial load and moment Chapter 13 Concrete Columns 13-7

10 13.7 COUMN FEXURA DESIGN ROCEDURE Column flexure design steps for permanent and transient loads are presented in the following sub-sections ongitudinal Analysis (CBridge) erform a longitudinal analysis of the bridge under consideration using Caltrans CBridge software. Results will determine: Axial load (A x ) and longitudinal moment (M z ) at top of the column for DC and DW Maximum unfactored axial load (A x ) and associated longitudinal moment (M z ) of design vehicular live loads for one lane per bent Maximum unfactored longitudinal moment (M z ) and associated axial load (A x ) of design vehicular live loads for the one lane per bent ransverse Analysis (CSiBridge) erform a transverse analysis of bent cap (BD Chapter 12, Bent-Cap) using commercial software CSiBridge. Results of the analysis is used to determine: Column axial load () and transverse moment (M 3 ) for DC and DW Maximum axial load () and associated transverse moment (M 3 ) for design vehicular live loads Maximum transverse moment (M 3 ) and associated axial load () for design vehicular live loads Note: WinYIED (Caltrans, 2008) uses the x-axis for longitudinal direction and y- axis for the transverse direction. he CBridge output renames M z as M x and A x as. he CSiBridge output renames the transverse moment, M 3, as M y Column ive oad Input rocedure Output from ongitudinal 2D Analysis (CBridge) Column unfactored live load forces and moments for one lane from longitudinal analysis (CBridge) are summarized in able below: Chapter 13 Concrete Columns 13-8

11 able Unfactored Bent Reactions for One ane, Dynamic oad Allowance Factors Not Included Design Vehicle ermit Vehicle Maximum axial load and associated longitudinal Maximum axial load and associated moment longitudinal moment A x (kip) M z (kip-ft) A x (kip) M z (kip-ft) ruck A max C M z assoc C A max C M z assoc C ane A max C M z assoc C Maximum longitudinal moment and associated Maximum longitudinal moment and associated axial load axial load A x (kip) M z (kip-ft) A x (kip) M z (kip-ft) ruck A assoc C M z max C A assoc C M z max C ane A assoc C M z max C where: A max C = maximum axial force for truck load M z assoc C = longitudinal moment associated with maximum axial force for truck load A max C = maximum axial force for lane load M z assoc C = longitudinal moment associated with maximum axial force for lane load A max C = maximum axial force for permit vehicle load M z assoc C = longitudinal moment associated with maximum axial force for permit vehicle load M z max C = maximum longitudinal moment for truck load A assoc C = axial force associated with maximum longitudinal moment for truck load M z max = maximum longitudinal moment for lane load A assoc C = axial force associated with maximum longitudinal moment for lane load M z max C = maximum longitudinal moment for permit vehicle load A assoc C = axial force associated with maximum longitudinal moment for permit vehicle load Chapter 13 Concrete Columns 13-9

12 Output from 2D ransverse Analysis (CSiBridge) Axial forces presented in able are converted to two pseudo wheel loads including dynamic allowance factor to be used in transverse analysis (see BD Chapter 12) to be used in transverse analysis. Include dynamic load allowance factor for able Column reaction = 1.33(reaction/2) for truck = 1(reaction/2) for lane = 1.25(reaction/2) for -15 he transverse analysis column forces for pseudo truck and permit wheel loadings are presented in able able Unfactored Column Reaction, Including Dynamic oad Allowance Factors Design Vehicle ermit Vehicle Maximum axial load and associated transverse moment Maximum axial load and associated transverse moment (kip) M 3 (kip-ft) (kip) M 3 (kip-ft) ruck max CSi assoc 3 CSi max M CSi 3 assoc CSi Maximum transverse moment and associated axial load Maximum transverse moment and associated axial load (kip) M 3 (kip-ft) (kip) M 3 (kip-ft) ruck assoc CSi M 3 max CSi assoc CSi M 3 max CSi where: max CSi = maximum axial force due to pseudo truck wheel loads M 3 assoc CSi = transverse moment associated with maximum axial force due to pseudo truck wheel loads. max Csi = maximum axial force due to pseudo permit wheel loads M 3 assoc CSi = transverse moment associated with maximum axial force due to pseudo permit wheel loads M 3 max CSi = maximum transverse moment due to pseudo truck wheel loads assoc CSi = axial force associated with maximum transverse moment due to pseudo truck wheel loads Chapter 13 Concrete Columns 13-10

13 BRIDGE DESIGN RACICE FEBRUARY 2015 M 3 max CSi = maximum transverse moment due to pseudo permit wheel loads assoc CSi = axial force associated with maximum transverse moment due to pseudo permit wheel loads CBridge output including Dynamic oad Allowance Factors Multiply dynamic allowance factor for values in able divided by number of bent columns to get reactions per column (able ). able Unfactored Column Reactions for One ane, Including Dynamic oad Allowance Factors Design Vehicle ermit Vehicle Maximum axial load and associated longitudinal Maximum axial load and associated moment longitudinal moment (kip) M x (kip-ft) (kip) M x (kip-ft) ruck max C M x assoc C max C M x assoc C ane max C M x assoc C Maximum longitudinal moment and associated axial Maximum longitudinal moment and load associated axial load (kip) M x (kip-ft) (kip) M x (kip-ft) ruck assoc C M x max C assoc C M x max C ane assoc C M x max C ruck and ane oads for ransverse Analysis (CSiBridge) Split truck reactions results of transverse analysis (able ) into truck and lane loads as follows: Ratio of truck load per design vehicle = Ratio of lane load per design vehicle = max C max C max max C max C C max C R1 R2 Unfactored column reactions (able ) including dynamic load allowance (CSiBridge): R1 = truck load ratio of design vehicle (values of able ) R2 = lane load ratio of design vehicle (values of able ) Chapter 13 Concrete Columns 13-11

14 able Unfactored Column Reactions, Including Dynamic oad Allowance Factors Design Vehicle ermit Vehicle Maximum axial load and associated transverse Maximum axial load and associated transverse moment moment (kip) M y (kip-ft) (kip) M y (kip-ft) ruck max CSi M y assoc CSi max CSi M y assoc CSi ane max CSi M y assoc CSi Maximum transverse moment and associated axial Maximum transverse moment and associated load axial load (kip) M y (kip-ft) (kip) M y (kip-ft) ruck assoc CSi M y max CSi M assoc CSi y max CSi ane assoc CSi M y max CSi Combination of ongitudinal and ransverse Output Combine forces and moments of ables and Case 1: Maximum M y (able ) Case 2: Maximum M x (able ) Case 3: Maximum (able ) able Case 1: Maximum ransverse Moment (M y ) M y (kip-ft) M x (kip-ft) -truck H-truck ane y CSi M y max CSi M y max CSi M max assoc CSi M x assoc assoc CSi. C max C max C M x assoc C assoc CSi max C (kip) assoc CSi assoc CSi assoc CSi M x assoc C Chapter 13 Concrete Columns 13-12

15 able Case 2: Maximum ongitudinal Moment (M x ) M y (kip-ft) M x (kip-ft) (kip) -truck H-truck ane assoc. C M y. assoc. CSi M y assoc. C. assoc. CSi max C M max C assoc. C max C max CSi M x max CSi. max C max C M x. max C max CSi max C max C assoc. C assoc. C max. CSi assoc. max. CSi max C max able Case 3: Maximum Axial oad () M y M (kip-ft) y assoc CSi M x (kip-ft) C -truck H-truck ane M. y assoc. CSi M y max CSi M x assoc max CSi. C max C M x assoc. C max CSi max C max max C C C M assoc. CSi (kip) max CSi max CSi max CSi M x y. assoc. CSi x. max C max. CSi assoc. C WinYIED ive oad Input ransfer ables , , and data into able , which will be used as load input for the WinYIED program. able Input for Column ive oad Analysis of WinYIED rogram. M y rans M x ong Axial Case 1: Max ransverse (M y ) ane -truck H-truck oad Case 2: Max ongitudinal (M x ) ane -truck H-truck oad Case 3: Max Axial () - truck H-truck ABE Data ABE Data ABE Data ane oad Chapter 13 Concrete Columns 13-13

16 Wind oads (WS, W) Calculate wind moments and axial loads for column (see BD Chapter 3) Braking Force (BR) Calculate braking force moments and axial load for column (see BD Chapter 3) restress Shortening Effects (CR, SH) Calculate prestress shortening moments as shown in design example (13.10) restressing Secondary Effect Forces (S) Calculate secondary prestress moments and axial loads (from CBridge output) Input oads into WinYIED ransfer all loads into WinYIED s load table Column Design/Check Run WinYIED to design/check the main vertical column reinforcement. Chapter 13 Concrete Columns 13-14

17 13.8 COUMN SHEAR DESIGN ROCEDURE Column shear demand values are calculated from longitudinal and transverse analyses ongitudinal Analysis erform a longitudinal analysis (CBridge) to determine: ongitudinal shear (V y ) and moment (M z ) for DC and DW at top and bottom of the column. Maximum longitudinal shear (V y ) and associated moment (M z ) for design vehicular live loads at top and bottom of the bent unfactored reactions for one lane as shown in able able ongitudinal Unfactored Bent Reactions for One ane, Dynamic oad Allowance Factors Not Included. Design Vehicle ermit Vehicle Maximum longitudinal shear and associated longitudinal moment at top of the column Maximum longitudinal shear and associated longitudinal moment at top of the column V y (kip) M z (kip-ft) V y (kip) M z (kip-ft) ruck ((V y ) max ) C ((M z ) assoc ) C ((V y ) max ) C ((M z ) assoc ) C ane ((V y ) max ) C ((M z ) assoc ) C Maximum longitudinal shear and associated longitudinal moment at bottom of the column Maximum longitudinal shear and associated longitudinal moment at bottom of the column V y (kip) M z (kip-ft) V y (kip) M z (kip-ft) ruck ((V y ) max ) C ((M z ) assoc ) C ((V y ) max ) C ((M z ) assoc ) C ane ((V y ) max ) C ((M z ) assoc ) C where: ((V y ) max ) C = maximum longitudinal shear at top and bottom of column for truck load ((M z ) assoc ) C = longitudinal moment at top and bottom of column associated with maximum shear for truck load ((V y ) max ) C = maximum longitudinal shear at top and bottom of column for lane load ((M z ) assoc ) C = longitudinal moment at top and bottom of column associated with,aximum shear for lane load ((V y ) max ) C = maximum longitudinal shear at top and bottom of column for permit load ((M z ) assoc ) C = longitudinal moment at top and bottom of column associated with maximum shear for permit load Chapter 13 Concrete Columns 13-15

18 ransverse Analysis erform a transverse analysis (CSiBridge) to determine: Column transverse shears (V 2 ) and associated moment (M 3 ) for DC and DW Maximum transverse shear (V 2 ) and associated moment (M 3 ) for design vehicular live loads at top and bottom of the column with dynamic load allowance factors included, as shown in able able ransverse Unfactored Column Reactions Including Dynamic oad Allowance Factors Design Vehicle ermit Vehicle Maximum transverse shear and associated transverse moment at top of the column Maximum transverse shear and associated transverse moment at top of the column V 2 (kip) M 3 (kip-ft) V 2 (kip) M 3 (kip-ft) ruck ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi Maximum transverse shear and associated transverse moment at bottom of the column Maximum transverse shear and associated transverse moment at bottom of the column V 2 (kip) M 3 (kip-ft) V 2 (kip) M 3 (kip-ft) ruck ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi where: ((V 2 ) max ) CSi = maximum longitudinal shear at top and bottom of column for truck load ((M 3 ) assoc ) CSi = transverse moment at top and bottom of column associated with maximum shear for truck load ((V 2 ) max ) CSi = maximum transverse shear at top and bottom of column for permit load ((M 3 ) assoc ) CSi = transverse moment at top and bottom of column associated with maximum shear for permit load Column ive oad Input rocedure Output from ongitudinal 2D Analysis (CBridge) Include dynamic load allowance factors per column for CBridge output (able ) and summarize the results in able Chapter 13 Concrete Columns 13-16

19 able Unfactored Column ongitudinal Shear and Associated ongitudinal Moment for One ane, Including Dynamic oad Allowance Factors (CBridge) Design Vehicle ermit Vehicle Maximum longitudinal shear and associated longitudinal moment at top of the column Maximum longitudinal shear and associated longitudinal moment at top of the column V y (kip) M z (kip-ft) V y (kip) M z (kip-ft) ruck ((V y ) max ) C ((M z ) assoc ) C ((V y ) max ) C ((M z ) assoc ) C ane ((V y ) max ) C ((M z ) assoc ) C Maximum longitudinal shear and associated longitudinal moment at bottom of the column Maximum longitudinal shear and associated longitudinal moment at bottom of the column V y (kip) M z (kip-ft) V y (kip) M z (kip-ft) ruck ((V y ) max ) C ((M z ) assoc ) C ((V y ) max ) C ((M z ) assoc ) C ane ((V y ) max ) C ((M z ) assoc ) C Output from 2D ransverse Analysis (CSiBridge) Reform able to split truck reactions of CSiBridge analysis (able ) into truck and lane loads ( ) as shown in able able Unfactored Column Reactions, Including Dynamic oad Allowance Factors (CSiBridge) Design Vehicle ermit Vehicle Maximum transverse shear and associated longitudinal moment at top of the column Maximum transverse shear and associated longitudinal moment at top of the column V 2 (kip) M 3 (kip-ft) V 2 (kip) M 3 (kip-ft) ruck ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi ane ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi Maximum transverse shear and associated longitudinal moment at bottom of the column Maximum transverse shear and associated longitudinal moment at bottom of the column V 2 (kip) M 3 (kip-ft) V 2 (kip) M 3 (kip-ft) ruck ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi ((V 2 ) max ) CSi ((M 3 ) assoc ) SA ane ((V 2 ) max ) CSi ((M 3 ) assoc ) CSi Chapter 13 Concrete Columns 13-17

20 Since the longitudinal shears and associated longitudinal moments are per one lane from CBridge, the total longitudinal shears and associated longitudinal moments should be calculated as shown in able able otal ongitudinal Shear (V y ) and Associated ongitudinal Moment (M z ) -truck H-truck ane (V y ) max max CSi (kip) V y max CSi max C max C V y max CSi max C max C V max C (M z ) assoc. max CSi (kip-ft) M z assoc max CSi C max C Mz z assoc max CSi C max C M z max C y max C assoc C Determine factored shear and associated factored moment for Strength I and Strength II imit States. Design for shear for controlling case as per AASHO he following example in Section will demonstrate the shear design in details COUMN SEISMIC DESIGN ROCEDURE Column seismic design and details shall follow the Caltrans Seismic Design Criteria DESIGN EXAME he bridge shown in Figures and are a three-span S/CI box girder bridge with 20º skew and two column bents. he superstructure depth is 6.75 ft. Columns heights from top of footing to superstructure soffit are 44 ft at bent two and 47 ft at bent three. he columns are round with a diameter of 6 ft. he centerline distance between columns is 34 ft. Chapter 13 Concrete Columns 13-18

21 Design Column One at Bent wo Figure Elevation View of Example Bridge. Chapter 13 Concrete Columns 13-19

22 Figure ypical Section of Example Bridge. Chapter 13 Concrete Columns 13-20

23 Flexural Check of Main Column Reinforcement (A s ) ongitudinal Analysis From CBridge output, determine M z for Dead oad (DC) and Added Dead oad (DW). able Dead oad Unfactored Column Forces able Additional Dead oad Unfactored Column Forces. Controlling moments, M z, are as follows: DC M z = kip-ft DW M z = kip-ft Chapter 13 Concrete Columns 13-21

24 Design Vehicular ive oads From CBridge output, determine bent two unfactored reactions for one lane (no dynamic load allowance factors) for the design vehicle as: Maximum A x and associated M z at top of the column Maximum M z and associated A x at top of the column able ive oad, Controlling Unfactored Bent Reactions From the CBridge output, determine unfactored bent two reactions for one lane (no dynamic load allowance factors) of permit vehicle load as follows: Maximum A x and associated M z at top of the column Maximum M z and associated A x at top of the column Chapter 13 Concrete Columns 13-22

25 able Bent 2 Reactions, RFD ermit Vehicle ransverse Analysis From CSiBridge output, determine the axial loads and transverse moments for DC and DW. able Axial loads and ransverse Moment for Dead oad and Added Dead oad Chapter 13 Concrete Columns 13-23

26 ive oads From CSiBridge output, determine the unfactored column reactions for design vehicle including the dynamic load allowance factors which are: Maximum and associated M 3 Maximum M 3 and associated able Maximum Axial oad () for Design Vehicle able Maximum ongitudinal Moment (M 3 ) for Design Vehicle From CSiBridge output, determine the unfactored column reactions for permit vehicle including the dynamic load allowance factors which are: Maximum and associated M 3 Maximum M 3 and associated Chapter 13 Concrete Columns 13-24

27 able Maximum Axial oad () for ermit Vehicle. able Maximum ongitudinal Moment (M 3 ) for ermit Vehicle. Chapter 13 Concrete Columns 13-25

28 Output from ongitudinal 2D Analysis (CBridge) Column unfactored live load forces and moments for one lane from longitudinal analysis (CBridge) are presented in able able Unfactored Bent Reactions for One ane, Dynamic oad Allowance Factors Not Included Design Vehicle ermit Vehicle Maximum axial load and associated longitudinal moment Maximum axial load and associated longitudinal moment A x (kip) M z (kip-ft) A x (kip) M z (kip-ft) ruck ane Maximum longitudinal moment and associated axial load Maximum longitudinal moment and associated axial load A x (kip) M z (kip-ft) A x (kip) M z (kip-ft) ruck ane Output from ransverse 2D Analysis (CSiBridge) wo pseudo wheel loads including dynamic allowance factor to be used in transverse analysis (see Section ). he transverse analysis column forces for pseudo truck and permit wheel loadings are presented in able able Unfactored Column Reaction, Including Dynamic oad Allowance Factors. Design Vehicle ermit Vehicle Maximum axial load and associated transverse moment Maximum axial load and associated transverse moment (kip) M 3 (kip-ft) (kip) M 3 (kip-ft) ruck Maximum transverse moment and associated axial load Maximum transverse moment and associated axial load (kip) M 3 (kip-ft) (kip) M 3 (kip-ft) ruck Chapter 13 Concrete Columns 13-26

29 Unfactored Column Reactions for One ane, Including Impact (CBridge) Multiply dynamic allowance factor for values in able and calculate reaction per column (able ). able Unfactored Column Reactions for One ane, Including Dynamic oad Allowance Factors (CBridge) Design Vehicle ermit Vehicle Maximum axial load and associated longitudinal moment Maximum axial load and associated longitudinal moment A x (kip) M z (kip-ft) A x (kip) M z (kip-ft) ruck ane Maximum longitudinal moment and associated axial load Maximum longitudinal moment and associated axial load A x (kip) M z (kip-ft) A x (kip) M z (kip-ft) ruck ane Unfactored Column Reactions, Including Dynamic oad Allowance Factors (CSiBridge) Split the truck reactions results of transverse analysis (Section ) into truck and lane loads as follows: Ratio of truck load per design vehicle = (76.2) / ( ) = Ratio of lane load per design vehicle = (49.6) / ( ) = ruck load of design vehicle = (values of able ) ane load of design vehicle = (values of able ) able summarizes the truck and lane loads for both design and permit vehicles of transverse analysis. able Unfactored Column Reactions, Including Dynamic oad Allowance Factors (CSiBridge) Design Vehicle ermit Vehicle Maximum axial load and associated transverse moment Maximum axial load and associated transverse moment (kip) M 3 (kip-ft) (kip) M 3 (kip-ft) ruck ane Maximum transverse moment and associated axial load Maximum transverse moment and associated axial load (kip) M 3 (kip-ft) (kip) M 3 (kip-ft) ruck ane Chapter 13 Concrete Columns 13-27

30 Combine load results as shown in ables , , , and to get WinYEID input loads as shown in able able WinYIED Column ive oad Input Case 1 Max ransverse- Case 2 Max ongitudinal- M y-rans (kip-ft) M x-ong (kip-ft) -Axial (kip) - ruck M y H- ruck ane oad -ruck M x H- ruck ane oad - ruck Case 3 Max Axial- H- ruck ane oad Wind oad (WS, W) Wind on structure (WS): Average bridge height = ft Assume bridge is in Open Country, from AASHO able V o Z o V DZ = 8.2 mph = 0.23 ft V Z 2.5V ln o 30 (AASHO ) VB Z o V DZ ln mph (design wind velocity) 2 V DZ D B VB for wind skew direction = 0 (AASHO ) From AASHO able B = 0.05 for superstructure (skew angle of wind = 0 ) B = 0.04 for columns (skew angle of wind = 0 ) D ksf 100 (Superstructure) D ksf 100 (Columns) he base wind pressure, B, for various angles of wind directions may be taken as specified in AASHO able (AASHO, 2012). Chapter 13 Concrete Columns 13-28

31 where: B = base wind pressure, corresponding to V B =100 mph D = wind pressure on structures, RFD equation V DZ = design wind velocity (mph) at design elevations V B = base wind velocity of 100 mph at 30 ft height V o = friction velocity (mph), RFD able Z = height of structure (ft) at which wind loads are being calculated as measured from low ground, or from water level, > 30 ft Z o = friction length (ft) upstream fetch, RFD able he wind pressure, D, is calculated at various angels using the base wind pressure, B, as per AASHO able able lists the wind pressure, D, at various angles of wind. able Wind ressure at Various Skew Angles of Wind Superstructure Columns Skew angle of wind (degrees) ( D ) rans (ksf) ( D ) ong (ksf) ( D ) rans (ksf) ( D ) ong (ksf) oad on span = ( ) D oad on columns = (6) D oads on both superstructure and columns at various winds skew directions are shown in able : able Wind oads at Various Skew Angles of Wind Superstructure Columns Skew angle of wind (degrees) ( D ) rans (kip/ft) ( D ) ong (kip/ft) ( D ) rans (kip/ft) ( D ) ong (kip/ft) Chapter 13 Concrete Columns 13-29

32 Model wind as a user-defined load in CBridge as shown below: Figure User Defined oads for Wind oads From CBridge output: o Case of maximum transverse wind takes place at wind direction with skew = 0 o Case of maximum longitudinal wind takes place at wind direction with skew = 60 Chapter 13 Concrete Columns 13-30

33 able User oads, Unfactored Column Forces, WS rans Skew 0 able User oads, Unfactored Column Forces, WS rans Skew 60. Chapter 13 Concrete Columns 13-31

34 Wind on live load (W): Apply 0.1k/ft acting at various angles (AASHO able ) as shown in able : able Wind on ive oad (W) at Various Angles Skew angle of wind (degrees) Normal component (k-ft) arallel component (k-ft) Using CBridge for wind on live load, the results are: o Case of maximum transverse wind takes place at skew angle of wind = 0 o Case of maximum longitudinal wind takes place at wind direction with skew = 60 able User oads, Unfactored Column Forces, W rans Skew 0 Chapter 13 Concrete Columns 13-32

35 able User oads, Unfactored Column Forces, W rans Skew 60 able Summary of Wind oads Reactions for Column 1 at Bent 2 Wind on Structure Wind on ive oad Max. rans. Max. ong. Max. rans. Max. ong. M y (kip-ft) M x (kip-ft) (kip) Braking Force (BR) he braking force (AASHO 3.6.4) shall be taken as the greater of: 25% design truck = 0.25(72) = 18 kips 25% design tandem = 0.25(50) = 12.5 kips 5% design truck + lane = 0.05[ (412)] = 16.8 kips 5% design tandem + lane = 0.05[ (412)] = 15.7 kips Controlling force = 18 kips Number of lanes = [ (1.42)]/12 = 4.66 Use four lanes, MF = 0.65 otal breaking force = 18(4) (0.65) = 46.8 kips Apply the braking force longitudinally then design for the moment and shear force effects. he braking force can be modeled in CBridge as a user defined load in the direction of local X direction as shown below: Chapter 13 Concrete Columns 13-33

36 Figure User Defined oads for Braking Force Braking forces output from CBridge are shown in able able User oads, Unfactored Column Forces, Braking Force Chapter 13 Concrete Columns 13-34

37 hermal Effects (U) For a three-span bridge, the point of no movement is shown in Figure : oint of No Movement Figure oint of No Movement Design temperature ranges from 10 to 80 F (AASHO able ) For normal weight concrete F (AASHO ) oad factor for moment in column due to thermal movement U = 0.5 (AASHO 3.4.1) hermal movement = 100 ft)(12) = in. /100 ft ' E 33,000K w c fc (AASHO ) For f c = 3.6 ksi, E ,000 (1)(0.15) ksi I g r 4 4 for circular column For 6 ft diameter column, I g (3) ft 4 4 oint of no movement calculation: 3EI k, = k then, 3EI 3 3 I (two columns per bent) = 2(63.6) =127.2 ft 4 4 (1) Bent2 3(3637)(127.2)(12) 3 (44(12)) 4 (1) Bent 3 3(3637)(127.2)(12) 3 (47(12)) kips kips Chapter 13 Concrete Columns 13-35

38 where: coefficient of thermal expansion k = column stiffness = lateral displacement = column height Bent2 = lateral force due to lateral displacement () of 1 in at bent-2 Bent3 = lateral force due to lateral displacement () of 1 in at bent-3 able oint Of No Movement Units are kips and ft Abut1 Bent2 Bent3 Abut4 SUM at 1inch. (kip) Distance (D) (ft) D (kip-ft) 0 24,633 47, ,790.6 Distance from C of support at Abut (X) = ( / 355.9) = ft Distance from point of no movement from Bent 2 = = ft Note: he point of no movement can be read directly from the CBridge output. For this example, the point of no movement is ft from bent two, as shown in Figure Figure oint of No Movement hermal displacement ( ) = (0.504 / 100) (75.72) = 0.38 in. M H 3EI g H 2 U 4 3(3637)(63.6)(12) (0.38) = 0. 5 = 9807 kip-in. = 817 kip-ft 2 (44(12)) Chapter 13 Concrete Columns 13-36

39 (M H ) x = M cos cos(20) = kip-ft (M H ) y = M sin sin(20) = kip-ft where: M H = column moment due to thermal expansion U = skew angle = load factor for uniform temperature restress Shortening Effects (Creep and Shrinkage) he anticipated shortening due to prestressing effects occurs at a rate of 0.63 in. per 100 ft (MD 7-10). Displacement = 0.63 (75.72 / 100) = 0.48 in. M csh 3EI g 2 p = 4 3(3637)(63.6)(12) (0.48) 2 0.5=12387 kip-in.=1032 kip-ft (44x12) (M csh ) x = M cos cos(20) = 970 kip-ft (M csh ) y = M sin sin(20) = 353 kip-ft where: M csh = column moment due to prestress shortening (creep and shrinkage) p = load factor for permanent load due to creep and shrinkage restress Secondary Effects (S) he secondary effect of prestressing after long term losses is shown in able able restressing Secondary Effects Chapter 13 Concrete Columns 13-37

40 WinYIED Input for Column 1 at Bent 2 Design of column reinforcement is performed by running WinYIED starting by general form as shown in Figure Figure WinYIED General Form Chapter 13 Concrete Columns 13-38

41 Column form for circular column with diameter of 72 inches is shown in Figure Figure WinYIED Column Form Chapter 13 Concrete Columns 13-39

42 Material form (Figure ) shows concrete specified compressive strength, fʹc = 3.6 ksi and steel rebar specified minimum yield strength, f y = 60 ksi. Figure WinYIED Material Form Chapter 13 Concrete Columns 13-40

43 Figure shows the rebar form with: Out to out distance = 72 2(2) = 68 in. (for cover = 2 in.) Assume #14 bundle total 36 and #8 hoops oop radius = [72 2(2) 2(1.13) 2(1.88/2)]/2 = 31.9 in. Figure WinYIED Rebar Form Chapter 13 Concrete Columns 13-41

44 Use AASHO Chapter 4 to determine K x and K y, considering AASHO C to be used in load-1 form (Figure ). Figure WinYIED oad-1 Form Chapter 13 Concrete Columns 13-42

45 oad-2 (Figure ) input data is taken from able Figure WinYIED oad-2 Form WinYIED Output Winyield output sheet (Figure ) shows the steel reinforcement required for the column. Figure WinYIED Output Results he final design could be summarized as: rovided number of bars = 18 bundle > required number of bars = 10.6 (OK) Min. clearance and spacing for #14 bundle horizontally = 7.5 in. Distance between bundles = 2(31.93) / 18 = 11.1 in. > 7.5 in. (OK) Chapter 13 Concrete Columns 13-43

46 Shear Design for ransverse Reinforcement (A v ) he procedure of determining column transverse reinforcement is presented in consequent sections ongitudinal Analysis From CBridge output (ables and ), determine longitudinal shear (V y ) and moment (M z ) at top and bottom of columns for DC and DW. Combine output in able able Dead oad, Unfactored Column Forces able Additional Dead oad, Unfactored Column Forces Chapter 13 Concrete Columns 13-44

47 able ongitudinal Shear (V y ) and ongitudinal Moment (M z ) for DC and DW op of Column Bottom of Column DC DW DC DW V y (kip) M z (kip-ft) Determine maximum longitudinal shear (V y ) and associated moment (M z ) for design vehicular live loads at top and bottom of the bent unfactored reactions for one lane as shown in able able Unfactored Bent Reactions For Design Vehicle Determine maximum longitudinal shear (V y ) and associated moment (M z ) for permit vehicular live loads at top and bottom of the bent unfactored reactions for one lane as shown in able Chapter 13 Concrete Columns 13-45

48 able Unfactored Bent Reactions For ermit Vehicle Re-arrange the longitudinal shear and moment output from CBridge are for two columns (able ). Chapter 13 Concrete Columns 13-46

49 able Unfactored Bent Reactions for One ane, Dynamic oad Allowance Factors Not Included Design Vehicle ermit Vehicle Maximum longitudinal shear and associated longitudinal moment at top of the column Maximum longitudinal shear and associated longitudinal moment at top of the column (V y ) max (kip) (M z ) assoc (kip-ft) (V y ) max (kip) (M z ) assoc (kip-ft) ruck ane Maximum longitudinal shear and associated longitudinal moment at bottom of the column Maximum longitudinal shear and associated longitudinal moment at bottom of the column (V y ) max (kip) (M z ) assoc (kip-ft) (V y ) max (kip) (M z ) assoc (kip-ft) ruck ane Apply dynamic allowance factor to able for one column as shown in able able Unfactored Column ongitudinal Shear and Associated ongitudinal Moment for One ane, Including Dynamic oad Allowance Factors. Design Vehicle ermit Vehicle Maximum longitudinal shear and associated longitudinal moment at top of the column Maximum longitudinal shear and associated longitudinal moment at top of the column (V y ) max (kip) (M z ) assoc (kip-ft) (V y ) max (kip) (M z ) assoc (kip-ft) ruck ane Maximum longitudinal shear and associated longitudinal moment at bottom of the column Maximum longitudinal shear and associated longitudinal moment at bottom of the column (V y ) max (kip) (M z ) assoc (kip-ft) (V y ) max (kip) (M z ) assoc (kip-ft) ruck ane Chapter 13 Concrete Columns 13-47

50 ransverse Analysis CSiBridge output for load cases of dead load (DC) and added dead load (AD) is shown in able able ransverse Shear (V 2 ) and Moment (M 3 ) at op and Bottom of Columns due to Dead oad (DC) and Added Dead oad (DW) Combine output in able able ransverse Shear (V 2 ) and Moment (M 3 ) for DC and DW op of column Bottom of column DC DW DC DW V 2 (kip) M 3 (kip-ft) CSiBridge output for maximum shear (V 2 ) and associated and moment (M 3 ) for design vehicle including dynamic load allowance as shown in able Chapter 13 Concrete Columns 13-48

51 able Maximum Shear (V 2 ) and Associated Moment (M 3 ) for Design Vehicle CSiBridge output for maximum shear (V 2 ) and associated and moment (M 3 ) for permit vehicle including dynamic load allowance as shown in able able Maximum Shear (V 2 ) and Associated Moment (M 3 ) for ermit Vehicle Re-arrange the transverse shear and moment output from CSiBridge in able Chapter 13 Concrete Columns 13-49

52 able Unfactored Column Reaction, Including Dynamic oad Allowance Factors Design Vehicle ermit Vehicle Maximum transverse shear and associated transverse moment at top of the column Maximum transverse shear and associated transverse moment at top of the column (V 2 ) max (kip) (M 3 ) assoc (kip-ft) (V 2 ) max (kip) (M 3 ) assoc (kip-ft) ruck Maximum transverse shear and associated transverse moment at bottom of the column Maximum transverse shear and associated transverse moment at bottom of the column (V 2 ) max (kip) (M 3 ) assoc (kip-ft) (V 2 ) max (kip) (M 3 ) assoc (kip-ft) ruck Use the procedure shown in and arrange output in able able Unfactored Column Reactions, Including Dynamic oad Allowance Factor Design Vehicle ermit Vehicle Maximum transverse shear and associated longitudinal moment at top of the column Maximum transverse shear and associated longitudinal moment at top of the column ruck ane Maximum transverse shear and associated longitudinal moment at bottom of the column Maximum transverse shear and associated longitudinal moment at bottom of the column (V 2 ) max (kip) (M 3 ) assoc (kip-ft) (V 2 ) max (kip) (M 3 ) assoc (kip-ft) ruck ane otal ongitudinal Shear and Associated Moments otal column longitudinal total shear and associated moment as per is presented in able able Unfactored Column otal ongitudinal Shear and Associated ongitudinal Moment, Including Dynamic oad Allowance Factors Design Vehicle ermit Vehicle Maximum longitudinal shear and associated longitudinal moment at top of the column Maximum longitudinal shear and associated longitudinal moment at top of the column (V y ) max (kip) (M z ) assoc (kip-ft) (V y ) max (kip) (M z ) assoc (kip-ft) ruck ane Maximum longitudinal shear and associated longitudinal moment at bottom of the column Maximum longitudinal shear and associated longitudinal moment at bottom of the column (V y ) max (kip) (M z ) assoc (kip-ft) (V y ) max (kip) (M z ) assoc (kip-ft) ruck ane 17 0 Chapter 13 Concrete Columns 13-50

53 Summary of Column Shear oads Column shear loads are summarized in able able ongitudinal Shear and Associated ongitudinal Moment oad Case op of Column Bottom of Column (V y ) max. (kip) (M z ) assoc (kip-ft) (V y ) max. (kip) (M z ) assoc (kip-ft) DC DW H-ruck ane ruck able ransverse Shear and Associated ransverse Moment. oad Case op of Column Bottom of Column (V 2 ) max (kip) (M 3 ) assoc (kip-ft) (V 2 ) max (kip) (M 3 ) assoc (kip-ft) DC DW H-ruck ane ruck Since this example uses circular columns, the design shears and moments should be taken as the square root of the sum of the squares: able Square Root of the Sum of the Squares oad Case op of Column Bottom of Column V (kip) (M) assoc (kip-ft) V (kip) (M) assoc (kip-ft) DC DW H-ruck ane ruck Strength Shear imit States Determine strength I and strength II limit states for shear and associated moments. Strength I: V u = 1.25 (23) (3) ( ) = 119 kips (controls) M u = 1.25 (1034) (112) ( ) = 5248 kips Strength II: V u = 1.25 (23) (3) (20) = 60 kips M u = 1.25 (1034) (112) (886) = 2,657 kip-ft Chapter 13 Concrete Columns 13-51

54 V n = V c + V s (AASHO ) Av f ydv Vs cot s (AASHO ) v u Vu (AASHO ) b d v v Column loop radius = in. (from WinYIED input) Using simplified procedure for nonprestressed sections (AASHO ) f b d kips 119 kips V c c v v where: A v = area of shear reinforcement within a distance s (in. 2 ) b v = effective web width d v = effective shear depth s = spacing of transverse reinforcement measured in a direction parallel to the longitudinal reinforcement (in.) V c = concrete shear capacity V n = nominal shear capacity V s = transverse shear reinforcement capacity V u = factored shear force M u = factored moment = factor indication ability of diagonally cracked concrete to transmit tension and shear as specified in article Use minimum shear reinforcement (AASHO ). A v f c bv s min f y A v = 0.79 in. 2 for #8 hoops, so 0.79 s min 11 in. (Use s = 6 in.) Check maximum spacing: x in. 2 /in. Chapter 13 Concrete Columns 13-52

55 vu For f c BRIDGE DESIGN RACICE FEBRUARY 2015 S max = 0.8 d v 18 in. (CA ) vu fc S max = 0.4 d v 12 in. (AASHO ) vu Since , then S max = 0.8 (50.16) = 40.1 in. > 18 in. f 3.6 c S max = 18 in. > 11 in. (OK) Note: Use #8 6 in. Seismic shear demands should be checked per the current SDC. Column confinement/shear steel, in most normal cases, will be governed by the plastic hinge shear. Check shear-flexure interaction: Af M u VU 0.5V cot d v s y s 5248(12) 117 2(18)(2.25)(60)³ + -0 cot45 0.9(50.16) 0.9 (AASHO ) 4860 kips 1525 kips (OK), then #14 tot. 18 bundle as shown in Figure are OK Chapter 13 Concrete Columns 13-53