![Page 1: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/1.jpg)
Seismic Pier Designfor
Steel Pipe Pile Extensionswith Concrete Cap Beam
State of Alaska
Department of Transportation &Public Facilities
Bridge Section
![Page 2: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/2.jpg)
Overview
■ The purpose of this document isto assist in the design anddetailing of Multiple Column /Pile Extension Piers
■ The basis of this document isfounded on the “Full-Scale Testof a Three Column / Pier CapBridge Substructure SystemUnder Simulated SeismicLoading” by Seible, et al.
![Page 3: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/3.jpg)
Typical Pier
Figure 1
![Page 4: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/4.jpg)
Step 1
■ Collect the dead load forces inthe pier cap and columns due tostructure self weight, asphalt,utilities, etc
■ These forces should include:
P - axialVy and Vz - shearMy and Mz - moment
![Page 5: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/5.jpg)
Step 2
■ Collect the seismic forces in thepier cap and columns frommultimodal computer analysis orother methods
■ These forces should include:
P - axialVy and Vz - shearMy and Mz - moment
■ Consider both Load CombinationI (100%L + 30%T) and LoadCombination II (100%T + 30%L)
![Page 6: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/6.jpg)
Step 3
■ Determine the combined axial,shear and moment forces
■ Note that the responsemodification factor, R, appliesonly to seismic moments inductile members (i.e. whereplastic hinges form)
![Page 7: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/7.jpg)
Step 4
■ Using the worst case loadcombination, determine theamount of longitudinalreinforcement required in thecolumn, Asc
■ Do not over reinforce the column- this will lead to more cap beamand joint reinforcement
■ Use φ factorsas defined inAASHTO
plastic strength
![Page 8: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/8.jpg)
Step 4■ There are many computer
programs to aid in the design ofconcrete columns,
Recol_M Imbsen & AssociatesULTCOL Washington DOT
■ Print out the P-M interactioninformation for later use in thecap beam design
■ Note that AASHTO specifies acolumn reinforcement ratio
1% < ρ < 4%
but 3% is a practical upper limitdue to joint reinforcementlimitations
![Page 9: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/9.jpg)
Step 5■ The ultimate applied shear, Vult,
is the minimum of either thedesign EQ shear or the shearassociated with plastic hinging ofthe column, Vp
■ Include the column overstrengthfactor for the concrete “gap”portion of 1.3 and 1.25 for thesteel pipe when calculating Vp
■ If the required moment capacityof the column is close to thebalance moment, use thebalance moment in subsequentcalculations
![Page 10: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/10.jpg)
Step 5■ The shear associated with plastic
hinging is calculated as shownbelow. It is good practice to use theVp for design if practical
Vp = M1 + M2 He
where:M1 = moment at top of column
= Mn * 1.3 - concrete columnM2 = moment at bottom of column
= 1.25 * Mp - steel pipeHe = effective height of column = H + lm (see figure 1)
![Page 11: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/11.jpg)
Step 6■ Determine the size and pitch of
the spiral in the column
Vult < φ * Vn
where: φ = 0.85 (16th) 0.9 (LRFD)Vn = nominal shear capacity
see AASHTO code or UCSD shear design equations
D = column / pile diameter
![Page 12: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/12.jpg)
Step 7
■ Determine the amount of the capbeam steel required noting that:
■ the height of the cap beam, hb,must be greater than thedevelopment length of thecolumn longitudinal steel and
D < hb < D * 1.15
■ the width of the cap beam, bj,must satisfy the following:
D + 12 in < bj < D + D/2
■ Use the maximum overstrengthmoment of the column to “load”the cap beam (i.e., Mp at Pmax)
![Page 13: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/13.jpg)
Step 7
■ The required development lengthof the longitudinal columnreinforcement is:
ld = 0.025*db*Fy/ √ (f’c)
where:db = diameter of barFy = rebar yield strength (psi)f’c = concrete strength (psi)
■ To use this length, welded hoop orspiral reinforcement must be usedin the joint (defined in step 9)
■ Always extend longitudinal columnbars to the top of the cap beam
![Page 14: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/14.jpg)
Step 7
ϕ *Mn > Mult
Where: ϕ = 0.9 for bending
Mn = nominal bending capacity
Mult = Mp + Mdl
Mp = plastic moment capacity of
column associated with Pmax
Check that the cap beam is not over orunder reinforced and that temperature andshrinkage steel requirements are satisfied
![Page 15: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/15.jpg)
Step 8
■ Determine the size and spacingof shear stirrups required in thecap beam
Vult < φ * Vn
where: φ = 0.85 (16th ed.) 0.9 (LRFD)Vn = Vc + VsVult = Vdl + Vp-capVp-cap = shear in cap beam
due to plastic hinging of column
= 1.5*Mp (approx.) Scol
■ Use shear at “d” from face ofcolumn
![Page 16: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/16.jpg)
Step 9
■ Determine the size and spacingof welded hoops required in thejoint region of the cap beam
■ This steel is needed to providedevelopment length andconfinement for the columnlongitudinal steel
s = 4*Ah < hb D’*ρs 4
where:s = welded hoop spacingAh = area of welded hoop
e.g. #5 hoop = 0.31 in2
![Page 17: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/17.jpg)
Step 9
■ Continued
la = anchored length of AscAsc= Area of column longitudinal steel rebarhb = height of cap beam λo = overstrength factor = 1.4 ρs = 0.3*λo*Asc / la2 > 3.5*√(f’c)/ FyD’ = core diameter of column
■ Provide a cap beam height greaterthan the anchorage length requiredfor the column longitudinal steel(see step7)
![Page 18: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/18.jpg)
Welded Hoop Steel
S < 4 * Ah < hb
D’ * ρs 4
Typically these bars will be field weldedafter placement
![Page 19: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/19.jpg)
Step 10■ Determine the average principal
tensile stress in the joint
pc,t = (fv+fh) + (fv-fh)2 + v2j
2 4
where:fv = Pc__
bj*(D+hb)
![Page 20: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/20.jpg)
Step 10■ Continued
fh = Vc_ bj*hb
vj = Mc _hb*D*bj
Mc = moment in the columnVc = shear in the columnPc = axial load in the columnD = column diameterhb = height of cap beambj = width of cap beam and
< √ 2 * D< D + hb
■ Always check your signs (+/-)
![Page 21: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/21.jpg)
Step 10■ Use Mc,Vc, and Pc which result in
maximum principal tension, pt
■ If the principal tension (pt) isgreater than 3.5*√(f’c) thenadditional joint reinforcement isrequired - that is:
If pt < 3.5* √(f’c) then done
If pt > 3.5* √(f’c) then provide theadditional reinforcement definedin the following steps
If pt > 15* √(f’c) then joint will notwork - try different pier geometry
![Page 22: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/22.jpg)
Strut and Tie Model■ The model developed by UCSD
(shown below) was used togenerate the following jointdesign procedure
■ Area of steel to resist tensileforces (Tes, Tbb and Tc) isdetermined from joint geometryand reinforcement pattern
AovjAi
vj
∆AB
![Page 23: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/23.jpg)
Step 11■ Determine the extra amount of
shear reinforcement (pairedhoops) required outside the jointregion, Ao
vj
■ Space the stirrups evenly in aregion equal to the cap beamheight. Total area Ao
vj to eachside of the column
Aovj > 0.125 * λo * Asc
where:Asc = area of column
longitudinal steel λo = overstrength factor = 1.4
![Page 24: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/24.jpg)
Shear Reinforcement Outside Joint
Avjo > 0.125 * Asc * λo
Put the paired hoops on each side of the joints
![Page 25: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/25.jpg)
Step 12
■ Determine the amount of shearreinforcement (paired hoops)required in the joint, Ai
vj
■ Space these bars evenly withinthe joint region over the column
Aivj > 0.095 * λo * Asc
where:Asc = area of column
longitudinal steel λo = 1.4
![Page 26: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/26.jpg)
Shear Reinforcement Inside Joint
Avji > 0.095 * Asc * λo
Space paired hoops evenly within joint region
![Page 27: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/27.jpg)
Step 13■ Additional top and bottom
longitudinal reinforcement isrequired to develop the jointstrut-and-tie mechanism
■ Add the following amount of capbeam longitudinal steel, ∆Ab,inaddition to what is required toresist bending alone, to both topand bottom
∆Ab > 0.17 * λo * Asc
where:Asc = area of column
longitudinal steel λo = 1.4
![Page 28: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/28.jpg)
Additional Longitudinal BeamReinforcement
∆Ab > 0.170 * Asc * λo
Put additional longitudinal bars on top ANDbottom
![Page 29: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/29.jpg)
Step 14
■ Provide seismic “J’ bars withinthe joint regions to preventbuckling of the longitudinal steelin the cap beam and to provideadditional confinement of thejoint region
■ Two or three “J” bars perlongitudinal cap beam bar shouldbe adequate for most cases
■ Space the bars evenly within thejoint so as to prevent buckling oflongitudinal cap beam bars
![Page 30: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/30.jpg)
Transverse Seismic “J” Bars
Place two or three three “J” barsper longitudinal cap beam barwithin joint region
Could use welded, headed bars if desired
![Page 31: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/31.jpg)
Detailing Notes
■ Provide concrete core down pipepile below the depth of effectivefixity (point of maximum moment)by at least 3 pile diameters or tothe point where the pile momentis about half the maximummoment
■ Make sure that the longitudinalcap beam bars are fullydeveloped - may need to provide90o hooks
■ Use headed reinforcement inplace of the “J” bars and on theends of the longitudinal capbeam bars if space is tight
![Page 32: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/32.jpg)
Detailing Notes
■ Use paired shear stirrups (hoops)in pier cap beams. This providesbetter confinement of concreteand a more even distribution ofsteel within joint region to bettercarry the loads
■ Generally, more smaller bars arebetter than few larger bars forserviceability. However, you muststill meet bar spacingrequirements for concreteplacement
■ Although the earthquake loadcase often governs the pierdesign, you must still examinethe other load combinations(strength and serviceability)
![Page 33: Seismic Pier DesignSeismic Pier Design for Steel Pipe Pile Extensions with Concrete Cap Beam State of Alaska Department of Transportation & Public Facilities Bridge Section Overview](https://reader030.vdocuments.net/reader030/viewer/2022040212/5e87a187680d881a3d3bd7e1/html5/thumbnails/33.jpg)
References■ Nilsson et al Reinforced Concrete Corners
and Joints Subjected to Bending Moment(1976)
■ Park and Paulay Reinforced ConcreteStructures (1976)
■ Schlaich, Schäfer, and Jennewein Towardsa Consistent Design Methodology (1987)
■ Collins and Mitchell Prestressed ConcreteStructures (1991)
■ James G. MacGregor Reinforced Concrete;Mechanics and Design (1992)
■ Priestley, Seible, and Calvi Seismic Designand Retrofit of Bridges (1996)
■ AASHTO AASHTO LRFD Bridge DesignSpecifications (1996)
■ ASCE-ACI Committee 445 RecentApproaches to Shear Design of StructuralConcrete (1998)
■ Silva, Sritharan, Seible, and Priestley Full-Scale Test of the Alaska Cast-in-Place SteelShell Three Column Bridge Bent (1999)