We often assume that the load span tables featured in our lintel guide are easy to understand, which for those with knowledge; probably are. However, for anyone starting out in the industry, getting to grips with interpreting the load spans for prestressed concrete lintels and steel lintels is not always straight forward.
This post examines the load span tables featured for both concrete and steel lintels and will demonstrate how you should interpret the values within them. This post is not going to help you with the calculations to arrive at what loads you need the lintel to bear – that is for another blog post.
Lintels are independently tested
The first point we need to make is that the load span tables in this post are based on our own products. These products are CE marked, and in order to obtain this accreditation, lintels are subject to the most stringent tests under the Construction Products Regulation (CPR). This means they are independently tested. The values in our own tables have been independently verified by a third party.
Lintel load span definitions
We will look at the load span tables for two steel lintel products at either end of the ‘strength’ spectrum. Initially we will make sure we know what values are included in the table.
Standard Lengths – This is pretty self-explanatory, and simply means the length of the lintel. As standard our steel lintels increase in length by 150mm, the two values represent the length of the lintel that the values in that column relate to. If it is 600 | 1200 it means the load span details can be applied to any lintel between 600mm and 1200mm.
Nominal height – The height of the lintel in mm.
Weights – The weight of the lintel in kg per metre.
SWL – This means Safe Working Load, but can also be referred to as Serviceable Working Load. This value is the load in kiloNewtons (kN) and simply means the load that this particular lintel can safely bear.
RM – This means Resistance Moment. RM is quite difficult to explain, and quite frankly is best described by a qualified engineer. In very simple layperson terms it is the force (as measured by kiloNewtons metre; kNm) at which point the lintel breaks. You can find out more about resistance moment here.
Understanding lintel load ratios
The SWL values in our load span tables are often subject to load ratios. These ratios represent the ratio of load that the lintel can bear as inner leaf to outer leaf. The ratios are different for the different applications.
- 1:1 – Lintels supporting masonry only
- 3:1 – Lintels supporting masonry and timber floors
- 5:1 – Lintels supporting concrete floors
- 19:1 – Lintels for eaves applications
How these ratios are applied will be demonstrated in the examples below.
Steel lintel load span tables
This first load span table is for a standard 50mm cavity lintel. The second table is for a 50mm composite extra heavy duty (CXHD) lintel.
|SWL 1:1 | 3:1||(kN)||16||17||22||23||24||28||28||28||28|
|SL50 CXHD 225||Standard Lengths||600|
|SWL 1:1 | 3:1||(kN)||89||71||55||42||37||32|
Let’s assume you need a 900mm lintel, you would look at the details of the first column of each of the two tables.
A 900mm SL50 has a height of 95mm, and weighs 6.2kg per metre.
Looking at SWL figures you can see that if your floor load is a 1:1 ratio (so the same weight is applied on both the inner leaf and outer leaf, then this SL50 at 900mm can take a load of 16kN on each leaf.
If you needed your lintel for an eaves application, then you would use the 19:1 ratio, which means this lintel would take an inner leaf load of 11.4 kN and an outer leaf load of 0.6 kN (rounding up). In reality; this is probably not the best lintel for the job.
Looking at the CXHD lintel, you can see the SWL for 19:1 is 75 which equates to approximately 71kN on the inner leaf and 4kN on the outer leaf. This level is used for extreme loads.
Like I said at the start of the post, the calculations for working out what your load will be is for another post, but once you know this (and the other factors affecting lintel selection) then you will be able to quickly see which sort of lintel you need to use for the job.
Prestressed concrete load span tables
The load span tables for prestressed concrete lintels are very similar to the steel lintel tables with the exception of two values.
UDL means uniformly distributed load which is measured in kiloNewtons per metre (kN/m). The principle is the same however; the higher the value, the better the load bearing capabilities on the lintel.
kNm or kN/m?Note: Do not confuse kNm with kN/m. kNm is a force measurement kiloNewtons times metres, kN/m is kiloNewtons per metre (or divided by metre).
Clear span is very simply the length of the opening. If you have a clear span of 1200mm, you will need a 1800mm length lintel to accommodate the required 150mm span on each side of the opening.
The R15 is a popular concrete product; here you can see the load table values up to a length of 1800mm.
|R15 140 x 100||Standard Lengths||1050||1200||1350||1500||1650||1800|
*This UDL value is restricted by shear, which means the UDL would be higher where it not for the shear force which would snap the lintel first.
Hopefully this will have provided a simple introduction to lintel load spans and what the values in the load span tables mean. However, if you have any questions about lintel selection, load span calculations or lintel specification, our technical team are more than happy to assist. Contact them at firstname.lastname@example.org.