Notice: Location of splices in structural steel frames 

Splices play a vital role in steel structures. 

They ensure that components like beams and columns can be joined to achieve the required lengths and configurations when continuous sections are impractical due to fabrication, transportation, or onsite assembly constraints. 

In large-scale projects, steel sections used for very long beams, such as portal frame rafters and for columns often come in limited dimensions, necessitating the use of splices. Welded splices, typically involving complete joint penetration butt welds, are a common choice because they offer high strength and a seamless finish. Alternatively, bolted splices may also be used, depending on design and construction preferences.

The placement of splices is critical for both structural integrity and construction efficiency. Poorly located splices can increase stress concentrations and reduce the overall strength of the structure. Standards such as NZS 3404 and AISC 341 provide specific guidelines for determining optimal splice locations to mitigate structural stresses on splices and enhance their performance in practical applications. 

Placement of column splices according to the NZS 3404 standard 

According to Clause 12.9.6.1 of NZS 3404 standard, column splices should generally be located within the middle third of the story height. This recommendation is based on minimising bending moments at the splice location and avoiding high-stress regions in the columns. In addition, the standard specifies that splices must be placed clear of any yielding regions, which are zones where significant plastic deformation could occur under load.  

The most likely source of plastic deformation is severe earthquakes. Typically, the inelastic demands on columns in a severe earthquake are minimised through capacity design, with elements other than columns chosen to become inelastic before any columns become inelastic. However, even here, the implications of inelastic action in the most highly stressed regions of the columns must be considered.  

The length of a yielding region within the member is determined using Table 12.6.1 of the NZS 3404 standard. Locating splices away from these areas ensures that the structure can dissipate seismic energy without failure at the spliced connections and compromising its structural integrity. Note that when this is done, the splices do not need to develop the full strength of the columns being spliced in order to make the columns effectively continuous – the minimum actions for splices located within the middle third of the column are expressly given in NZS 3404. 

It is also important to note that the column splice location in NZS 3404 is a recommendation and there may be architectural or structural reasons to place column splices at the floor level. In this case, the splice must be designed to resist the capacity design derived design actions, when capacity design is undertaken, or the overstrength column capacity, when capacity design is not undertaken. This generates actions, especially moments, much larger than the minimum specified splice actions from NZS 3404 meaning larger and more expensive splice components.

Comparison of column splice locations in AISC 341 and NZS 3404 

A comparison of NZS 3404 and AISC 341-10 shows that both standards are largely consistent regarding the location of column splices. Clause D2-5a, in AISC 341-10 standard, requires that column splices be located at least 1.2 meters (4 feet) away from beam-to-column flange connections to reduce the effects of flexure and improve accessibility during construction. 

Exceptions are provided for columns with clear heights under 2.4 meters, where splices can be placed at half the clear height. Additionally, exceptions apply to column splices joined by complete-joint-penetration groove welds, where the splice can be positioned closer to beam-to-column flange connections, provided the distance is not less than the depth of the column. 

The general recommendation in AISC 341 is that the column splice should be positioned within the middle third of the story height, as outlined in the commentary section of the standard for Clause D2-5a, which aligns with the NZS 3404 standard. 

Optimal placement of beam splices according to the NZS 3404 standard 

Beam splices require careful consideration as well. According to Clause 12.9.6.2 of NZS 3404 standard, the preferred location for a beam splice is near a point of contraflexure, where the bending moment is minimal. This reduces the load on the splice, enhancing its performance.  

In seismic frames, beam splices (like column splices), must be located outside the yielding region in accordance with Clause 12.9.6.2. 

Recommended splice locations for brace members under the NZS 3404 standard 

Brace members, which provide lateral stability in a steel frame, also have specific splice location requirements.  

Splices in braces should be positioned as close as possible to the quarter points of the brace length and must be located outside any yielding regions, in accordance with Clause 12.9.6.1 of the NZS 3404 standard. This placement minimises the impact on the brace’s load-carrying capacity and ensures that the splice does not interfere with the brace’s ability to resist lateral loads. 

Summarising the key takeaways  

1. Column splices, including fully bolted, fully welded, and combined bolted and welded types, should be placed within the middle third of the story height. Minimum splice actions will typically apply to ensure effective column continuity.  

2. Fully welded column splices may be positioned closer to beam-to-column flange connections, provided the distance is not less than the length of the yielding region as defined in Clause 12.6.2.1 in NZS 3404 standard.  

3. For columns with a clear height of less than 2.4 m between beam-to-column flange connections, it is recommended that splices be located at half the clear height. 

4. Beam splices should be located as close as possible to the point of contraflexure, as determined through static or modal analysis. If this is not feasible, the beam splice must be placed outside the yielding region, as specified in Clause 12.6.2.1 of the NZS 3404 standard. 

5. Splices in brace members should be located as near as practicable to the quarter points of the brace and must be placed outside any yielding regions. 

6. All splices must be placed away from any yielding regions. 

7. All welded splices shall meet essential tolerance requirements for Class 1 of AS/NZS 5131. 

8. All welds shall meet the quality requirements of weld category SP to AS/NZS 1554.1 and the Construction Category (CC) to AS/NZS 5131 specified. 

Why does this matter for your projects? 

The correct location of splices is essential to ensure that steel structures comply with AS/NZS 3404.  

Understanding this notice’s summary of the relevant requirements for columns, beams, and braces enables you to be able to follow proper splice location practices so that structural elements in your structural steel project can perform as expected under various loading conditions contributing to the overall safety and durability of the building. 

Need more information? 

Please refer to the following documentation below: 

1. Standards New Zealand (1997/2001/2007). Steel structures standard (NZS 3404: Part 1 and 2:1997), New Zealand. 

2. American Institute of Steel Construction (2010). Seismic provisions for structural steel buildings (ANSI/AISC 341-10), Approved by the American National Standard Institute (ANSI).