STeelCON - for steel connections

Moment connections with 4 bolt rows (extended end plates)

Design Assumptions

This connection type is not considered in the Eurocode EN 1993-1-8:2005. The assessment methods adopted follow the Eurocode design assumptions and methods as far as possible. For tension, all bolts near the beam flange under tension can be taken into account for bending moment resistance calculation (a1-4 and b1-4), see Fig. 1. The bolts c2 and c3 could also be considered. However the bolts c1 and c4 cannot be considered to transfer tension due to the limited stiffness of the end plate. These bolts together with the bolt row d could be useful in shear.

Depending on the size of the end plate and bolt spacing, there is several possibilities for yield line patterns for bolts in rows a and b. The bolt row a can be considered as bolt row outside tension flange of the beam. The simplified approach of EN 1993-1-8 can be adopted with modifications of yield lines for the bolt group. The design procedure requires the following assumptions:

• The use of horizontal stiffeners is obligatory. Without stiffeners the outer bolt columns (1 and 4) cannot form T-stub in the column flange, so all the tension is received by the inner columns (2 and 3). This downgrades the connection to a 2 bolt columns connection (as refers to moment resistance), so there is no need to use 4 bolt columns.
• The program expects that the tensioned stiffener will transfer all the tension (in the area between the first two rows a and b), and no tension will pass through the column’s web.  This can be made sure provided the distance of the inner column from the web (0.5*w2) is less  than the distance of the  yield  line towards the columns web,  1.73*mx+0.5*Stiffener thickness. If this condition is not true for any of the bolt rows near the stiffener, the program informs the user with warning messages.
• For the calculation of the moment resistance in the weak axis, the program does not take into account the outer bolt columns.

Known differences between STeelCON and “Typisierte Anschluesse”.

a.       Moment Resistance.

1. In “Typisierte Anschluesse” only the tension resistance of the first bolt row is calculated. The resistance of the second bolt row is considered equal to the first. The third bolt row is considered always as under compression. In STeelCON all the bolt rows are calculated separately.
2. In “Typisierte Anschluesse” there is no examination of the  formation of prying forces.  In 1998-1-8 at table 6.2, is clearly stated that the design resistance of a T-stub depends if prying forces may develop or not. If prying forces cannot develop then the design resistance of the T-stub may be 50% smaller (EC3 adds a fourth failure mode the ‘F1-2’). This may result in major differences between  the moment resistance of the connection that STeelCON calculates.
3. The calculation of forces FTrd6 and FTrd7 of the book, are different from those in 1998-1-8 at table 6.2.
4. STeelCON default connection is assumed to be in the last floor. This leads to a smaller effective length of the T-stub formed at the column flange in the upper bolt row region, comparing to the book.  The solution is to give a small force at the upper column so the program will assume that the column is continuous. 

b.      Shear Resistance.

1. In “Typisierte Anschluesse” several componetnts are checked to determine the strength of the connection in shear (Bolts in shear, plates in bearing, plate in shear fracture) , welds in shear, 50% of Beam web in shear. STeelCON only calculates Bolts in shear acting together with tension, and plates in bearing. The welds are checked independently but do not participate in the shear resistance value calculation.
2. According to 1998-1-8, 3.7(1), the design resistance of a group of fasteners should be taken as the number of fasteners multiplied by the smallest design resistance of any of the individual fasteners (except only if all the fasteners fail under bearing). This leads to very small shear resistances compared to those of the book.