Design and strength assessment of a welded connection of a plane frame

Structural connections Structural connections of a plane frame must be able to transfer 1) internal forces between beam and beam 2) internal forces between beam and column 3) reaction forces between column and ground These are typical permanent connections and can be riveted, bolted or welded The basic criterion in the design of connections include - assessment of their static strength and endurance - assessment of the right transfer of the internal forces The welded connection at point B must be designed Advanced Design for Mechanical System Pract04

Reaction and Internal moments Reaction forces and internal moments can be evaluate: using handbook formulae for a similar structure loaded with distributed load or concentrated load, and then applying the superposition principle. applying the Principle of Virtual Work by means FEM model of the frame The suggestion is to evaluate reaction forces and internal moments by means of handbook formulae and to compare results with results obtained by Principle of Virtual Work or FEM analysis Advanced Design for Mechanical System Pract04

Moment for distributed load: handbook formulae* *Manuale for mechanical engineer, Hoepli edition 1994, (in italian). Advanced Design for Mechanical System Pract04

Moment for concentrated load: handbook formulae Advanced Design for Mechanical System Pract04

Principle of virtual work for frames For plane frame Mt=0 and the deformations due to the axial and the shear forces are negligible, only the internal bending must be taken into account Advanced Design for Mechanical System Pract04

The examined plane frame The plane frame is symmetric only half of the frame have to be considered Q/2 Q/2 p p RE B E B E ME h RE and ME: hyperstatic unknown A A l/2 The structure is two times hyperstatic The internal moment M(x) on the real structure is M(x)=M0(x)+RE*M1(x)+ME*M2(x) Advanced Design for Mechanical System Pract04

Internal moment M(x) on the real structure Q/2 p 1 B B B E E E 1 Isostatic structure Auxiliary structure n.1 Auxiliary structure n. 2 RA A A 1 A MA 1 1*h M0(x) M1(x) M2(x) M(x)=M0(x)+RE*M1(x)+ME*M2(x) Advanced Design for Mechanical System Pract04

PVW for the auxiliary structure n. 1 Advanced Design for Mechanical System Pract04

PVW for the auxiliary structure n. 2 Advanced Design for Mechanical System Pract04

Hyperstatic unknown The system allows the calculation of RE and ME Advanced Design for Mechanical System Pract04

FEM Analysis Deformed shape Model 20000 N/m 20000 N Constrains: Point A U1=U2=UR3=0 Point E U1=UR3=0 Deformed shape Model Advanced Design for Mechanical System Pract04

Example of results Moment at nodes 31420 Nm 10370 Nm The same cross section IPE 330 has been used for the beam and for the column Advanced Design for Mechanical System Pract04

The cross section of the beam and of the column Cross sections can be choose on the basis of the bending moment only On each cross section act the bending moment due to the distributed load constant and the bending moment due to the concentrated load Q varying sinusoidally with time y x E z Mb,p Mb,Qsinwt Maximum of Mb,p and Mb,Qsinwt z x y Advanced Design for Mechanical System Pract04

Bending stress on the cross section at point E We consider the cross section at point E where both Mb,p and Mb,Qsinwt are maximum. The bending stresses result linearly varying with the distance from the neutral axis: and sinusoidally varying with time a Aa a a a a A a A a Advanced Design for Mechanical System Pract04

It is maximum at the points that are most distant from the neutral axis of the section The condition where  is the safety factor and slim can be obtained from the Haigh diagram of the material allows the calculation of Jxx of the beam section. Advanced Design for Mechanical System Pract04

Bending Haigh diagram sa sa,f slim sa,max sm sm,max UTS Advanced Design for Mechanical System Pract04

Design of the structural node M2 The node between the column and the beam, realized with a double T section, must be designed in order to realize a clamped constrain. The aim is to transfer the boundary moment M1, from the transverse beam to the vertical column ht M1 hc M3 Advanced Design for Mechanical System Pract04

The welded connection The end of the horizontal beam, upper plate, lower plate and web are welded to the upper plate of the column The weld is a fillet weld type Advanced Design for Mechanical System Pract04

Moment transfer In the double T sections, if subjected to flexural moment in the plane of the web, the axial forces that originate from the flexural moment are transmitted by the upper and lower plate. As a consequence the upper plate of the column receives the normal forces of the flexural moment from the transverse beam, and deflects, except close to the web. An overview of the deformations of the node is given in the figure, as result of a finite element analysis. The level of deformation, in absence of any reinforcement, is quite high, and not acceptable. Advanced Design for Mechanical System Pract04

Reinforcements From the previous considerations, it is intuitive that local reinforcements are needed, to correctly transfer the flexural moment to the upper and lower plate of the column. Advanced Design for Mechanical System Pract04

Adopted solution In the adopted solution, the node is considered as a group of four beams, plus a diagonal member, all hinged at their ends. Advanced Design for Mechanical System Pract04

D C E A St Sd Sc Let M be the moment to be transmitted to the column. Axial load on the upper and lower plate of the beam, transferred to the reinforcement results Axial load on the upper and lower plate of the column D C E A St Sd Sc On the diagonal AD acts the force: If the contribution of the web of the column is take into account, by means of the coefficient h: Advanced Design for Mechanical System Pract04

The comparison between the reinforced node (a) and the one without reinforcement (b) allow to visualize their different behavior. (a) (b) Advanced Design for Mechanical System Pract04

Verification of the beam-column welded joint In the following the verification of the welding is reported. Let the two profiles be a IPExxx for the beam and for the column. The reference sections of the fillet of the welding are place as shown in figure below. TB MB J is the moment of inertia of the resistant section of the welding MB and TB are the bending moment and the shear that must be transmitted by the welded joint Advanced Design for Mechanical System Pract04

So that the reference stress results: At the edges of the fillets welding along the web, where bending and shear are present, the stresses are So that the reference stress results: The corresponding safety coefficients then results: At point A (top of the horizontal fillet) only sT due to bending is present and he corresponding safety coefficients results: Advanced Design for Mechanical System Pract04