Post on 13-Jan-2016
description
analysis of moment resisting connections
basic principles of connection designProvide as direct a load path as possibleAvoid complex stress conditionsWeld in the shop, bolt on site
Welded connections
moment connection of an I-BeamBending moment is carried mainly by the flangesTherefore connect flanges for moment transfer
moment connection of an I-BeamWelded connectionFillet weldsFull penetration weldsCompression transfer can also be accomplished through direct bearing
shear connection of an I-BeamShear is carried mainly by the webTherefore connect the web for shear transfer
shear connection of an I-BeamFillet welds in shear are commonly usedConnect entire web and adjust weld size to suit shear load
moment connection of a plateStress in weld = M (d/2) / I= M (d/2) / (ad3/12) [kN/m2]q= a= M (d/2) / (d3/12)= M (d/2) / I [kN/m]WhereI= I/a
Then choose a weld size a that will carry q
q = .a where a = weld sized
moment connection of a plateCan also use simplified approach:
Break moment into a force coupleChoose a suitable weld sizeThen calculate the required length of the weld to carry the tension force T
q = T/l where l = weld lengthdResultant tension force T = M/dC = T
welded shear plate
simplified approachBreak eccentric load up into a vertical force along the vertical weld and a pair (couple) of horizontal forces along the horizontal weldsThen choose lengths of welds to carry the calculated forcesVV.e/dV.e/dVde
Stress calculations+
Stress calculations for vertical force VDivide shear equally amongst all the weld lines
q = V / (total length of weld)
Choose a weld size that can carry the stress q
Note q is actually a force per length [kN/m]qV
Stress calculations for Moment M = V.eTreat the weld group as a cross-section subjected to a torsional moment
Ip2 = Ix2 + Iy2where I = I/a
qAx = M yA / IpqAy = M xA / Ip
qAM = (qAx2 + qAy2)0.5
Similarly for point BThen select weld size for max. q
qAx qAy qBx qBy yAxBxAyBA B qAM qBM
Stress calculations for combined V and MVM = V.eqAx qAy qAV qA Combine the weld stress components from the vertical force and the torsional moment
qA = [qAx2 + (qAV + qAy)2]0.5
Similarly for point B or any other point that might be critical
Then select weld size for the maximum value of q
A B
example of a complex connectionColumn tree for Times Square 4, NYC
bolted connections
moment splice in a column
moment splice of an I-BeamBolted connectionDivide tension and compression resultant equally between bolts
shear connection in bridge diaphragm girder
(Alex Fraser Bridge)
shear connection of an I-BeamBolted connections to transfer shear are commonly usedConnect entire web to avoid stress concentrations and shear lag
shear connection via end plateCoped flanges to fit in between column flangesEnd plate
moment connection with and end or base plate
moment connection with fully welded end plateMhihmaxTiTmaxTi = Tmax (hi / hmax)
M = Ti hiC = Ti
pre-tensioned moment connection
pre-tensioned Moment ConnectionApply both tension and compression forces to pre-tensioned bolts. Compression force can be seen as a release of the tension force.M=
bolted shear plate
vertical loadPVPVPDivide the force by n, the number of bolts
VP = P / n
moment M FxMFyMFMiyixiTreat the bolt group as a cross-section subjected to a torsional moment
Ip = i A ri2 = i A (xi2 + yi2)
and with IP = IP/A
FxM = M yi / IpFyM = M xi / Ip
FMi = (FxM2 + FyM2)0.5
Then select a bolt size for the maximum force FM
ribolt area Abolt i
combined vertical force and momentFxMFyMVPFmax
Fmax = [FxM2 + (FyM + VP)2]0.5
Then select a bolt size for the maximum force Fmax