The joining of two sections of a steel column to form a single, longer column is known as a steel column splice. Splices are used to replace a damaged part or to increase a column’s length.
For multistory steel buildings, column splices are desirably placed 4 feet above finished floors to permit the attachment of safety cables to the columns, as may be required at floor edges or openings. This offset also enables us to keep the splices from interfering with the beam and column connections.
The AISC Manual’s Table 14-3 contains numerous further instances. For load transfer purposes, the column ends are typically milled to provide for firm contact between them. A significant portion, if not all, of the axial compression can be transferred through the contacting areas when the contact surfaces are milled.
Typical steel column splices
In most cases splice connection is provided either through splice plate or a bearing plate. Both cases may or may not involve use of bolts and welds.
Typical steel column splices using splice plates is shown in following figure:
Typical steel column splices using bearing plates is shown in following figure. Note that clip angles are provided for column proper orientation.
Do we need to use steel column splice plates all the times?
Even when the columns make complete contact and carry only axial loads, builders still require splice plates. For example, they must keep the two sections of the column together both during and after erection. The designer relies on experience and judgment to determine the necessary measures for maintaining their stability.
Splice plates become even more essential when columns experience shears and moments due to off-center loads, lateral forces, and other factors.
What is difference between tension and compression steel column splice?
There is, obviously, a great deal of difference between tension splices and compression splices. In tension splices, all load has to be transferred through the splice, whereas in splices for compression members, a large part of the load can be transferred directly in bearing between the columns. The splice material is then needed to transfer only the remaining part of the load.
What should be the design load for steel column splice plates?
It is challenging to predict how much load the splice plates will have to support. The plates should be made to support 100% of the weight if the column ends cannot be machined. It is possible to anticipate that the plates will bear between 25 and 50 percent of the total load when the surfaces are milled and only axial loads are involved. Perhaps 50 to 75 percent of the total load may need to be supported by the splice material if bending is present. The AISC Specification lacks the meticulous splice requirements for compression members that are outlined in the bridge specifications.
AISC specification take on steel column splices
The AISC Specification’s Section J1.4 lists a few general requirements as well. A snapshot of these specification is given below:
Practice related to steel column splices
The first figure above shows a splicing that can be applied to columns with essentially the same nominal depths. According to the AISC Manual, W forms of a specific nominal size are separated into groups that are rolled using the same set of rolls. Although their overall depths may vary significantly, the obvious lengths between the flanges for each form in that group are always the same due to the fixed size of each set of rolls.
For example, each of the 28 designs (from the W14 X 61 to the W14 x 730) has an inside distance of about 12.60 inches, although their overall depths range from 13.9 inches to 22.4 inches. (Note that for the W14 X 90 through the W14 x 730, the T values—the distances between the fillets’ web toes—are all 10 in.) The simplest splices, as seen above, are the most cost-effective. Using a single set of shapes for as many stories of a structure as feasible makes this task simple.
For example, we might choose a specific W14 column section for a building’s top story or top two floors, and as we move down the structure, we might continue to choose bigger and heavier W14s for that column. As we proceed down the building, we might also transition to stronger steel columns, which would allow us to continue using the same W series for additional floors.
Filler plates
It will be necessary to use filler plates between the splice plates and the upper column if the upper column has a total depth significantly less than that of the lower column.
Splice connection in significantly different depth columns
Another option is to employ bearing plates in such case. The butt plate is shop-welded to the lower column, while the clip angles needed for field erection are shop-welded to the upper column. In the field, the erection bolts are placed, and the top column is welded to the butt plate. The horizontal welds on this plate resist shears and moments in the columns.
Splice connection on all sides
Sometimes, splices are applied to all four sides of columns. The web splices are bolted in place in the field and field-welded to the column webs. The flange splices are shop-welded to the lower column and field-welded to the top column. The web plates might be referred to as shear plates, while the flange plates are known as moment plates.
Is it better to avoid column splices?
Columns for multistory buildings can be fabricated for one or more stories. In theory, column thickness can be adjusted at each floor level to get the lightest total column weight. The splices required at each story will be fairly expensive, so it is normally more cost effective to use the same column widths for at least two storeys, even if the total steel weight will be more. Because three-story columns are difficult to install, the same diameters are rarely employed for more than two storeys. Most of the time, the two-story heights are ideal.
