Connections checks - Fixed column base

[Anonymous]

Hello:

I have three doubts about the fixed column base connection check with hook type anchorages:

1.- The defined concrete of the foundation is H-30 (Spanish denomination) with a characteristic resistance of 30 MPa (see “Material Definition” picture), although, in the results , the characteristic resistance indicated is 45 MPa (see “Results detail 1” picture).

2.- The check of pull-out failure is carried out with the bond stress of the anchorage with the equation of the Eurocode (EN 1992-1-1 8.4.2 (2)), see “Results detail 2” picture. This equation is for ribbed bars but, what happens if the anchorage is a plain bar? , Is it this check correct for plain bars anchorages or only for ribbed bars?

3.- I do not know where is the check of the tensile resistance of an anchor in the results. I can see the tensile resistance of an anchor (see “Results detail 3” picture) but not the load of an anchor and neither the check comparing the two values.

Best Regards

Pablo Escario

[Artur.Kosakowski]

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@Anonymous wrote:

Hello:

1.- The defined concrete of the foundation is H-30 (Spanish denomination) with a characteristic resistance of 30 MPa (see “Material Definition” picture), although, in the results , the characteristic resistance indicated is 45 MPa (see “Results detail 1” picture).

Could you attach this example?

2.- The check of pull-out failure is carried out with the bond stress of the anchorage with the equation of the Eurocode (EN 1992-1-1 8.4.2 (2)), see “Results detail 2” picture. This equation is for ribbed bars but, what happens if the anchorage is a plain bar? , Is it this check correct for plain bars anchorages or only for ribbed bars?

I'm not aware of a formula for plain bars in EC so perhaps you should ask the authors of the code 

The old Polish code defined it as:

fbd is the design resitance of the plain bar.

3.- I do not know where is the check of the tensile resistance of an anchor in the results. I can see the tensile resistance of an anchor (see “Results detail 3” picture) but not the load of an anchor and neither the check comparing the two values.

What you indicated is the resistance of the single anchor bolt which is one of many resistances connsidered during the verification of the conmnection which includes among others concrete resistance against compression, base plate resistance for bending etc. It is the combination of these resistances that leads to determine the capacity of the connection for tension or bending (see: 6.2.8.3 of EN 1993-1-8). 

For the example of a base connection under tension only with 4 anchor bolts with 49 kN capacity each:

As yiu cabn see in the note below Robot calculates the resistance of the base plate in the tension zone Ft,pl,Rd, which is the result of analysing 3 possible failure modes. Two first are for breking the plate wheres the 3rd one is breaking of anchor bolts in the analyzed part of the plate.  In this example the bolts are the weakest component therefore the capacity for tension is Ft,pl,Rd = 2*49 = 98 kN as two bolts are in the analysed part of teh plate.

For pure tension Njrd is then double this value as tere are two identical zones:

Nj,Rd = 2*Ft,pl,rd = 196 kN.

This is the value that goes to the final verification formulas. For acting force Nj,Ed = 100 kN the obtained ratio is NJ,Ed/Nj,Rd = 0.51 <  1.00

Just to let you know I'm not going to make hand calcs for Mjrd (6.2.8.3  EN 1993-1-8) 

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[Anonymous]

Thanks for your answer:

I am going to comment the points:

1.- I send you an attached example.

2.- Looking concrete EC I can see that it does not cover the use of plain reinforcement (EN 1992-1-1, 1.1.2 (4)).

If you use the equation of the old Polish code indicated (I suppose than fck is in MPa units), the value obtained for fbd is significantly lower than the value obtained with the program equation.

3.- I understand the checking in the example you send but if you have compression (negative Nj,Ed), what is the meaning of the checking Nj,Ed/Nj,Rd<1.00? (you can see it in the example attached for the point 1).

In the other hand I suppose this check correspond with the equation (6.24) of the EC of joints (EN 1993-1-8, 6.2.7.1 (3)), but in the code it is a different check (combined axial force and moment).