When builders and self-builders order structural steel for a project, attention naturally focuses on the main beam—the universal beam or column that does the primary structural work. The supporting hardware receives less thought, and sometimes none at all, until a problem emerges on site. Bearing plates and RSA angles are two of the most commonly overlooked components in structural steelwork packages, yet both perform specific structural functions that the main beam alone cannot. Installing a steel beam without considering whether these elements are needed—and specifying them correctly when they are—is a gap in structural thinking that can create problems ranging from minor remediation work to significant structural defects.
This guide explains what bearing plates and RSA angles are, the structural roles each performs, when they are required, how they are specified, and how to order them correctly. It is aimed at builders, structural contractors, and technically-minded self-builders who want to understand not just what to order, but why.
Bearing Plates: Distributing Concentrated Loads
A bearing plate is a flat steel plate positioned between the end of a steel beam and the masonry or concrete substrate on which it rests. Its purpose is straightforward: to distribute the concentrated reaction force at the beam end over a larger area of substrate, reducing the bearing stress to a level the substrate can safely carry.
Why Bearing Plates Are Needed
When a loaded beam bears on a wall, it exerts a concentrated force at each bearing point—the beam's reaction load. This force divided by the bearing area gives the bearing stress. If the bearing stress exceeds the compressive capacity of the substrate, the substrate crushes, cracks, or progressively fails.
The bottom flange of a universal beam is the surface in contact with the substrate. For a 152x89 UB16, the flange width is 89mm. If that beam bears 100mm onto brickwork, the bearing area is 89mm × 100mm = 8,900mm². If the beam reaction is 30kN, the bearing stress is 30,000N ÷ 8,900mm² = 3.4 N/mm². Standard facing brick has an allowable bearing stress of approximately 1.5-2.5 N/mm² depending on quality—so this installation is marginal or overstressed without intervention.
A bearing plate extends the contact area. A 200mm × 150mm bearing plate under the same beam increases the bearing area to 200mm × 150mm = 30,000mm², reducing bearing stress to 30,000N ÷ 30,000mm² = 1.0 N/mm²—well within facing brick capacity. The same load is now safely transferred to the substrate.
Bearing plates do not change the load. They change how that load is distributed, reducing peak stress at the contact interface. This is their entire structural function.
When Are Bearing Plates Required?
Your structural engineer's calculations will specify whether bearing plates are required and what dimensions they should be. However, understanding the conditions that typically trigger their use helps builders identify when to raise the question with the engineer if plates haven't been specified but conditions on site suggest they may be needed.
Weak substrate. The most common trigger. Concrete blocks below 7N compressive strength, standard facing bricks (as opposed to engineering bricks), aerated blocks (Thermalite, Celcon), or any masonry in poor condition may have insufficient bearing capacity for beam reactions without load spreading. Bearing plates—or padstones—are required.
High beam reactions. Heavily loaded beams exert larger reactions at bearings. Even on relatively strong substrates, high reactions may exceed bearing capacity with the beam flange area alone. Bearing plates extend the contact area to bring stress within limits.
Short available bearing length. Where physical constraints limit how far the beam can extend onto the supporting wall—narrow walls, tight structural arrangements, or existing openings close to the bearing point—bearing plates compensate for the reduced length by increasing width.
Hollow sections bearing on masonry. Rectangular and square hollow sections (RHS/SHS) have thin walls and small contact areas at their ends. End plates welded to hollow section ends distribute load over a larger area—these are a specific application of the bearing plate principle.
Steel-on-steel bearing. Where a secondary beam bears on a primary beam, or where a beam sits on a steel column cap plate, bearing plates ensure load transfer is controlled and stress concentrated on web or flange is managed.
Bearing Plates vs Padstones: What's the Difference?
These terms are sometimes used interchangeably, which causes confusion. They perform the same structural function—distributing beam end loads over a larger area—but they are different elements constructed differently.
A bearing plate is a steel plate, typically 10-20mm thick, positioned directly under the beam flange. It is a steel-to-masonry interface element. Its dimensions in plan distribute the load over the masonry below it, and its thickness provides rigidity ensuring load distribution is uniform rather than concentrated on edges or high spots.
A padstone is a concrete or engineering brick block, typically 100-215mm deep, positioned under the beam bearing and spreading load both in plan (like a bearing plate) and vertically through its depth into the masonry below. Padstones distribute loads over multiple brick or block courses rather than just the immediately bearing course, which matters on weak or hollow substrates where load needs to spread to adjacent material.
In practice, structural engineers specify one or the other—or occasionally both together for very high loads or weak substrates. Bearing plates are more common for steel-on-concrete situations and where limited depth is available. Padstones are more common for masonry walls where load needs to be spread through height as well as plan area.
Bearing Plate Specification
Bearing plates are specified by their plan dimensions (length × width) and thickness. Standard specification involves:
Plan dimensions are determined by the required bearing area. The structural engineer calculates the minimum area needed to reduce bearing stress to within substrate capacity, then sets dimensions that achieve this while fitting within the physical constraints of the bearing location. Common dimensions for domestic steelwork range from 150×100mm to 300×200mm.
Thickness must be sufficient to distribute load uniformly without bending or deforming under the beam reaction. Thin plates may deflect locally, concentrating stress rather than distributing it. Minimum thickness for bearing plates is typically 10mm for light loads; 15-20mm for heavier applications. The engineer's calculation will determine the required thickness based on load and plate dimensions.
Steel grade is normally S275 (structural steel, 275 N/mm² yield strength) for bearing plates—the same grade as most structural beams. S355 may be specified for high-stress applications but is rarely necessary for domestic bearing plates.
Surface preparation and coating should match the requirements for the main beam—if the beam is primed, the bearing plate should be primed with a compatible system. Plates in contact with damp masonry need at least a basic primer to prevent early corrosion.
When ordering from a steel stockholder or fabricator, bearing plates are typically cut from flat plate or flat bar stock. Specify dimensions, thickness, and quantity. If holes are required (for anchor bolts in some applications), these need to be included in the order description.
Installation of Bearing Plates
Bearing plates are positioned on the prepared bearing surface before the beam is lowered into place. Key installation points:
The bearing surface must be level and flat. Place the bearing plate on a full mortar bed ensuring complete contact between plate and substrate—no voids or high spots that would create uneven load distribution. The plate should be bedded level in both directions.
The beam is then lowered onto the bearing plate. The plate should be centred under the beam flange, with the beam sitting squarely on the plate across its full width. Check that the beam flange does not overhang the plate edges—the plate must be wider than the beam flange for proper load distribution.
In some details, bearing plates are tack-welded to the beam flange in the fabrication shop, arriving as an integral assembly. This simplifies site installation—the beam is lowered into position with the plate already attached—and ensures correct positioning. If your project involves a fabricated steelwork package, confirm with the fabricator whether plates are pre-attached or supplied loose.
RSA Angles: Versatile Structural Connectors
RSA stands for Rolled Steel Angle—a structural section with an L-shaped cross-section consisting of two flat legs meeting at 90 degrees. The legs may be equal (both legs the same width, designated as equal angles) or unequal (legs of different widths, designated as unequal angles). In UK structural practice, RSA angles are one of the most versatile elements in the structural steel range, used in a wide variety of connecting, supporting, and framing applications.
Angles are designated by leg dimensions and leg thickness: for example, 100×100×10 RSA is an equal angle with 100mm legs and 10mm leg thickness. 150×90×12 RSA is an unequal angle with a 150mm longer leg and 90mm shorter leg, both 12mm thick.
Common Uses of RSA Angles in Building Projects
Beam-to-beam connections (cleats). Where secondary beams frame into the web of a primary beam, angle cleats welded or bolted to the primary beam web provide the bearing and connection for the secondary beam ends. This is one of the most common uses of angles in structural steelwork. The secondary beam end sits on the outstanding leg of the cleat, transferring its reaction load to the primary beam. Cleat angles are typically welded to the primary beam in the fabrication shop and arrive on site ready to receive secondary beams.
Beam-to-wall connections (shelf angles / supporting angles). Where a beam needs to be connected to or supported by a masonry or concrete wall without the beam sitting directly on top of the wall, a supporting angle bolted or chemically anchored to the wall face provides a ledge for the beam end. This is common in situations where the beam must be at a specific height relative to the wall, where the wall cannot be cut to receive the beam end, or where the structural arrangement requires it.
Lintels. Pairs of equal angles back-to-back (or occasionally a single angle) are widely used as lintels over non-structural or lightly-loaded openings in masonry. A back-to-back angle lintel provides a bearing ledge for masonry on both faces of the wall. For structural lintels carrying significant loads, universal beams are appropriate—but for partition walls and lightweight internal openings, angle lintels are efficient and economical.
Trimmer framing around openings. Where openings are formed in steel or timber floor structures, trimmer framing around the opening perimeter often uses angles to provide connections and support for cut joists. Angles welded or bolted to main beams provide bearing for trimmer joists or secondary beam ends at opening edges.
Bracing and restraint. Angles are commonly used as diagonal bracing members in steel frames, and as restraint members preventing lateral movement of beams or columns. Their compact section and ease of connection make them practical for these secondary structural roles.
Shelf angles for masonry support. In mixed steel-frame and masonry-clad construction, shelf angles welded to the steel frame support the weight of masonry cladding panels at each floor level, preventing masonry from hanging unsupported over multiple storeys. This application is more common in commercial construction than domestic projects, but the principle appears in various residential mixed-structure situations.
Stiffeners and gussets. Angles are used as local stiffeners at beam ends and column bases, and as gusset plates at connections. Welded to webs or flanges, they prevent local buckling and reinforce connections under concentrated load.
General framing and support. Floor void framing, mezzanine edge trims, roof purlin cleats, handrail posts, equipment supports, stair stringers—the breadth of applications reflects the angle's versatility as a structural element that can be bolted, welded, or screwed to almost any substrate in almost any orientation.
Selecting the Right Angle Section
RSA angles are available in a wide range of sizes, from small 25×25×3 sections (25mm legs, 3mm thick) to large 200×200×24 sections used in heavy structural work. Selection depends on the structural role:
For beam-end cleats, the angle must be deep enough to provide adequate bolt edge distances and weld lengths, and thick enough to carry the shear force from the beam reaction. Structural engineers calculate cleat sizes; common domestic-scale cleats use 90×90×10 or 100×100×10 equal angles, though smaller and larger sections are used depending on loads.
For shelf angles supporting masonry or beam ends, the outstanding leg length must be sufficient to support the beam end or masonry properly, and the thickness must resist bending under the supported load. The required leg size and thickness are calculated based on load and projection.
For lintels, paired back-to-back angles must have sufficient combined section properties to carry the masonry load over the span without excessive bending or deflection. Span tables for angle lintels are published by the Steel Construction Institute and by lintel manufacturers—for anything beyond straightforward short spans carrying a few courses of masonry, an engineer's check is advisable.
For bracing, angles in tension are straightforward to size based on axial capacity. Angles in compression require checking for buckling, particularly if slender (long relative to section size). Engineers will specify the appropriate section for these applications.
For domestic projects where the structural engineer has specified angles by size and grade, ordering is straightforward—specify the section designation, length, steel grade (S275 standard), and quantity. For projects where angle requirements emerge on site without pre-specification, describe the application to your supplier who can advise on appropriate section selection, and have any structural decision verified by the engineer before committing.
Unequal Angles: When the Longer Leg Matters
Equal angles (equal leg lengths) are the most common general-purpose choice and suit most connection and framing applications. Unequal angles are specified when the geometry of the connection requires different leg lengths—typically when one leg must project further than the other to reach a fixing surface, clear an obstacle, or provide a longer bearing ledge.
A common application: a shelf angle supporting floor joists on a steel beam flange where one leg is bolted through the beam web and the other projects horizontally to support joist ends. If the joist ends need a 100mm bearing but the beam web connection requires only 75mm, an unequal angle (100×75 or similar) provides the right geometry. Using an equal angle in both directions would either provide excessive projection on the connection side or insufficient bearing on the support side.
When specifying unequal angles, clearly identify which leg is which—the longer leg is listed first in the designation (150×90 means 150mm longer leg, 90mm shorter leg). Confirm the orientation intended (long leg vertical, long leg horizontal, long leg fastened to the beam) to avoid ambiguity in the fabrication or ordering process.
Connection Methods: Bolted vs Welded Angles
Angles can be connected by welding, bolting, or a combination. The appropriate method depends on the situation:
Shop welding is most common for angles that form part of a fabricated steelwork assembly—cleats welded to beams, angles welded to column bases, gussets welded to connections. Welding in a fabrication shop under controlled conditions produces high-quality, fully inspectable connections. Shop-welded angles arrive on site as part of the beam or column assembly, requiring only bolted site connections to complete the structural joints.
Site bolting is used for connections made on site. Bolted connections require pre-drilled holes in the angle and in the connecting element. For structural connections, bolt grade matters—Grade 8.8 bolts are standard for structural steel connections; do not substitute lower-grade fixings. Bolt hole positions are set by the engineer's connection design; standard hole spacing and edge distances must be maintained for the connection to achieve its designed capacity.
Chemical anchors and mechanical fixings are used where angles are fixed to concrete or masonry—shelf angles fixed to concrete walls, angle supports bolted into blockwork, and similar applications. The fixing capacity must be verified for the load being transferred; chemical anchor suppliers publish characteristic values for different substrates, embedment depths, and anchor diameters that are used in design calculations.
Ordering RSA Angles: What to Specify
When ordering RSA angles from a steel stockholder, provide:
- Section designation: Leg dimensions and thickness (e.g., 100×100×10 RSA, or 150×90×12 RSA). Equal angles are specified with two equal dimensions; unequal with two different dimensions.
- Length: Cut length required in millimetres. Most stockholders can supply cut lengths to order, avoiding waste from standard 6-metre mill lengths. If ordering full lengths for site cutting, specify 6m lengths and arrange on-site cutting.
- Steel grade: S275 for most structural applications. S355 for higher-strength requirements (specified by engineer).
- Quantity: Number of pieces at the specified cut length.
- Surface preparation: Primer or as-rolled, matching your project specification.
- Any fabrication requirements: Drilled holes (specify hole diameter, position from specified datum), notching, or other preparation.
For site-cut angles, an angle grinder with cutting disc or cold saw produces clean cuts. Confirm cut ends are deburred (sharp edges removed) before installation—particularly important where angles are handled frequently or where sharp edges could damage adjacent materials.
Bearing Plates and Angles Together: How They Work as a System
On many projects, bearing plates and angles appear together as part of an integrated connection solution. Understanding how they interact clarifies why both elements may be specified simultaneously.
Consider a secondary beam framing into a primary beam at mid-span. The secondary beam end sits on angle cleats welded to the primary beam web—the angle carries the secondary beam reaction. The primary beam, carrying its own loads plus the secondary beam reactions, bears at its ends on the supporting walls. At each bearing point, a bearing plate distributes the primary beam's (now increased) end reaction over the masonry. The angle manages the beam-to-beam connection; the bearing plate manages the beam-to-masonry interface. Each element has a defined structural role.
Or consider a steel beam bearing on a blockwork wall where physical constraints mean the beam cannot simply sit on top of the wall—perhaps the floor level requires the beam soffit to be at a specific height. A shelf angle chemically anchored to the wall face provides a bearing ledge at the correct height. A bearing plate between the angle leg and the beam end distributes the load from the beam into the angle, reducing contact stress on the relatively thin angle leg. Again, both elements serve distinct functions in the load path from beam to wall.
When reviewing a structural engineer's drawings, look for these elements in the connection details—typically shown in enlarged scale detail drawings or annotated sections. If you cannot find specification for bearing plates or connection angles and you believe they may be required based on the above discussion, raise the question with the engineer before ordering steel. Adding these elements at order stage is straightforward; adding them after installation is significantly more complicated.
Where to Find Bearing Plates and RSA Angles
Both bearing plates and RSA angles are standard structural steel products available from steel stockholders alongside universal beams, columns, hollow sections, and other structural sections.
Bearing plates are cut from flat plate or flat bar stock. Flat bar (a flat rectangular section with a defined width and thickness) is often the most practical source for bearing plates—order flat bar in the required width and thickness, cut to bearing plate length. Alternatively, plates can be cut from sheet or plate stock if non-standard widths are required.
RSA angles are stocked in a comprehensive range of sizes and are one of the most widely available structural sections. Most steel stockholders carry the common equal angle sizes (40×40 through 150×150) in standard lengths, with less common sizes and all unequal angles available to order. Cut lengths are typically available to order without significant premium for standard sizes.
Ordering bearing plates and angles alongside your main beam order—at the same time, in a single enquiry—is the most efficient approach. It avoids separate deliveries, allows you to plan your site programme around a single steel delivery, and gives your supplier full visibility of the project so they can flag any apparent omissions or conflicts in the specification.
Conclusion: The Supporting Cast That the Structure Depends On
Bearing plates and RSA angles occupy a supporting role in structural steelwork—neither element is the main structural member, and neither receives much attention in typical project discussions. But both perform structural functions that the main beam cannot perform alone. A beam correctly specified, correctly delivered, and incorrectly installed without proper bearing distribution or connection hardware is a structural defect waiting to develop. The small additional cost and planning effort involved in specifying and ordering these elements correctly at the outset is repaid many times over in installations that perform as the engineer intended and pass Building Control inspection without remediation.
Pratley's Builders Beams stocks flat plate and flat bar for bearing plates and the full range of RSA equal and unequal angles alongside our universal beam, universal column, hollow section, and channel ranges. When you enquire about steel for your project, tell us about the full structural package—beams, columns, bearing plates, angles, and any other elements specified—and we'll supply everything you need in a single order and delivery. Contact us to discuss your requirements.
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