Bolt Group Coefficient for Eccentric Loads
Introduction
This application calculates the bolt coefficient for eccentrically loaded bolt groups using the Instantaneous Center of Rotation method (also known as the Ultimate Strength method).
The bolt coefficient C is the ratio of the factored force (or available strength) of the bolt group Pu and the shear capacity of a single bolt φr__n,
C = P__uφr__n
Once the coefficient is known, a bolt group can be designed for any load.
Traditionally, bolt group coefficients are extracted by using tabulated values in the AISC Steel Construction Manual. However, these tables are limited to common bolt patterns, and specific load eccentricities and angles. Non-tabulated values must be extracted by using linear interpolation.
This Maple worksheet, however, calculates the bolt group coefficient for any bolt and load configuration by implementing the theory used to generate the tables.
The results agree with those presented in AISC Manual of Steel Construction: Load and Resistance Factor Design, 2nd Edition.
restart: withUnitsSimple:
Parameters
The following commands define the bolt locations and plot them.
boltLoc≔−1.5|−3,1.5|−3,−1.5|0,1.5|0,−1.5|3,1.5|3inch:
plotconvert~~boltLoc,unit_free,style=point,symbol=solidcircle,symbolsize=40
The shear strength of a single bolt (kip):
φr__n≔96081N:
The horizontal component of force eccentricity with respect to the centroid of bolt group (in):
e__h≔2inch:
Force angle to horizontal axis (deg):
β≔75 π180.0
β≔1.308996939
Calculations
Translate the bolt locations so that the centroid is at the origin.
X≔boltLoc..,1−~addi,i in boltLoc..,16:Y≔boltLoc..,2−~addi,i in boltLoc..,26:
The eccentricity:
e≔e__h sinβ
e≔1.931851653in
Adjusted beta:
β≔βe>0β+0.5πotherwise
Instantaneous center of rotation (ICR):
X__0≔−L__0 sinβ−m__0 cosβ:
Y__0≔L__0cosβ−m__0 sinβ:
Bolt angle to ICR (rad):
θ≔arctan~ Y -~ Y__0, X -~ X__0 -~ Pi/2:
Bolt distance to ICR (inches):
d≔X−~X__0~2+Y−~Y__0~2~12: dmax≔maxd:
Bolt displacement (inches) from Crawford and Kulak (1971):
Δ≔d~dmax⋅0.34:
Load-deformation relationship from Crawford and Kulak (1971):
Rn≔φr__n⋅1−~ⅇ~−10⋅Δ~0.55:
Optimization
The sums of the bolt forces in the vertical and horizontal directions are equal to the applied shear and axial loads.
forceX≔P__0⋅sinbeta+addi,i in Rn⋅~sin~θ=0:forceY≔P__0⋅cosbeta+addi,i in Rn⋅~cos~θ=0:
The moment of the bolt forces about the ICR is equal to the moment of the applied load.
moment≔P__0⋅L__0+e−addi,i in Rn⋅~d=0:
res≔fsolveforceX,forceY,moment,P__0=1N,m__0=1m,L__0=1m
res≔L__0=0.09115169826m,P__0=429160.9378N,m__0=−0.004661726525m
Results
Ultimate tensile strength of bolt group
P__u≔evalP__0,res2
P__u≔429160.9378N
Bolt coefficient:
C≔P__uφr__n
C≔4.466657693
References
Behavior of eccentrically loaded bolted connections, Crawford S. F., Kulak, G. L. (1968)
AISC Manual of Steel Construction: Load and Resistance Factor Design 2nd Edition
http://www.bgstructuralengineering.com/BGSCM14/BGSCM004/BGSCM00403.htm
https://engineering.purdue.edu/~jliu/courses/CE591/PDF/CE591eccentric_shear_F13.pdf
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