Pad Stone Sizes + Calculations
Pad Stone Sizes
What are Pad Stones?
Pad Stones Sizes are an important structural element to consider when installing steel beams while removing load bearing walls. They are used to reduce the beam reaction concentrated loads to an acceptable level which is less than the compressive resistance of the masonry below the pad stone – expressed as a value in N/mm2. The stresses are distributed through the padstone in a forty five degree angle and spread over the masonry underneath the pad stone. Pad stones are commonly factory made precast concrete units, in accordance with BS 8500-2:2015 – the complementary British Standard to BS EN 206:2013, achieving a compressive strength of 50N/mm2. However there are a number of alternatives which are listed below:
The Importance of Pad Stone Calculations
Do not assume that pad stone sizes are to be taken for granted, selecting any off the shelf pad stone may not suitable for your project. Your Building Control Inspector will expect to see pad stone size calculations to justify what has been used – If the calculations can’t reflect what has been used Building Control have the powers to make you alter the pad stones which is problematic once installed and the acrow props have been removed. Even worse scenario if the building work is complete and decorated to a high standard. So its always essential to have the pad stones designed before they are installed. Get it right first time!
Our Pad Stone Calculations
The padstone calculation contained within our steel beam calculation documents is an important part of the steel beam design and installation process. The pad stones are designed in accordance with BS5628-1 specifically to reduce concentrated loads applied by the ends of the beam(s) or the beam bearing to an acceptable level depending on the masonry/mortar type used to construct the walls. This ultimately ensures that the supporting masonry walls do not fail by crushing or cracking under the applied loading from the steel beam reactions. It is worth remembering, however, that not all beams require pad stones. If the masonry a beam is bearing onto has a high compressive strength and the applied loads are relatively low then the pad stones could be omitted. However, the masonry would still be subject to a design check which your Building Control Inspector would require.
Common choices for pad stones we specify are:
- Pre Cast Concrete Pad Stones
These are factory made concrete units achieving a declared compressive strength of 50N/mm2. They are manufactured in accordance with BS 8500-2:2015 – the complementary British Standard to BS EN 206:2013. The pad stone sizes come in a wide variety to suit most applications and the quality of manufacture can be relied upon. - Engineering Bricks
These bricks have a high compressive strength and low water absorption. Engineering bricks are classified as either Class A or Class B. Class A have a minimum declared compressive strength of 125N/mm2 and Class B have a minimum declared compressive strength of 75N/mm2. Class B is the most common brick specified for pad stones and other structural applications such as masonry columns. Engineering bricks are manufactured in accordance with BS EN 771-3: 2011 so the manufacture quality and declared strength can be assured. - Steel Spreader Plates
As the title suggests an option to support the beam bearing can be with steel plates. These are quite simply steel plates at varying lengths and thickness determined by design. We would tend to specify steel spreader plates in loft conversions as often space is tight and a pad stone may need to extend down below the existing ceiling level. Steel spreader plates are designed in accordance with BS5950-1. - Pre Cast Reinforced Concrete Lintels
As with pre cast concrete pad stones these are factory made concrete units and come in a wide range of depths and lengths. Common sizes are 65mm deep – 140mm deep and 215mm deep in varying lengths. These work to brick/block coursing dimensions so are easily cut to size and built in as work progresses on-site. As they are reinforced they offer the ability for reduced depth pad stones.
EXAMPLE OF OUR CAD DETAILING SHOWING REQUIREMENTS FOR PAD STONE PLACEMENT UNDER BEAMS – THESE ARE USEFUL SO THE BUILDER ENSURES THAT THE WORK ON SITE IS IN ACCORDANCE WITH THE DESIGN/CALCULATIONS.
; ?>)
