Mezzanine floors: Baseplate design

July 29, 2010

How are the loads from mezzanine floors dispersed?

Mezzanine floors recessed baseplate

Mezzanine floors recessed baseplate in pocket

Loads from freestanding mezzanine floors are all supported through columns and base plates by the concrete floor slab, which is in turn supported by the subsoil below it.

 The object when designing a mezzanine floor is to ensure that the loads applied down the columns are adequately distributed over the subsoil so that they are less than its ‘subsoil bearing capacity’. The load is then safely dispersed through the ground without settlement, subsidence, shear or any associated building damage.

  A typical mezzanine floor supports a design load of around 5kN (approx. half a tonne) per square metre, uniformly distributed load, on a column grid of around 4m x 5m. This means that a column in the middle of such a floor will support half a tonne on each square metre of the 20 square metres that it supports, making a total of 10 tonnes down the column. Typically this will be applied to the concrete floor on a base plate 300mm (1 foot) square. 

It is generally assumed when designing mezzanine floors that the load will be evenly applied over the whole area, and such a load is referred to as a uniformly distributed load or UDL. 

Load dispersal is affected by the construction of the slab itself. The thickness of the slab, the amount of reinforcement and the depth of hardcore below the slab affect how the load applied by the column is distributed to the subsoil.

 The subsoil in turn can vary from made up ground, through clays, sands and gravels to chalk, limestone and granite which have greatly varying subsoil bearing capacities, and therefore the mezzanine floor loads may need to be distributed over different sized areas in order to ensure they are kept below the ‘subsoil bearing capacity’. 

Mezzanine floor base plates are designed by first calculating the load applied down each column, and based upon the subsoil and slab construction a suitable mezzanine floor base plate size can then be calculated to safely disperse the applied load. Plate sizes will vary to suit the load applied to each column, depending on the area of mezzanine flooring that it supports.

Depending on the site location, history and age, information regarding the slab construction and type of subsoil may be readily available, or may need to be obtained by investigation and test. An old riverside location with an old slab is likely to need some trial holes or cores and penetration tests to obtain the relevant data, whilst a brand new site in a chalk downland location would be expected to come with full specifications.

Mezzanine floors trial hole

A typical trial hole through slab

The first port of call for documentation is the landlord or owner, followed by the local authority. If no documentary information is available, conservative assumptions may be acceptable to approved inspectors and building control officers, failing which visual inspection of trial holes and testing of subsoil by independent geotechnical engineers may be necessary.

The poorer the ground quality and the higher the mezzanine flooring loads, the more likely trial holes and testing will be necessary, and the more likely that the slab alone will not be adequate to accommodate the applied loads and independent foundations may be needed, though the percentage of mezzanine floor applications where these factors combine is low.

This general information relates to the design of mezzanine floor base plates and is intended for guidance only. Each project needs to be assessed on its own merits.

It is always prudent to discuss your specific project with an approved inspector or building control officer prior to commencing work, a task with which your mezzanine floor contractor will be prepared to assist.

If you would like advice regarding the specific requirements for your project, someone to liaise with building control on your behalf, or a quotation for your project call Llonsson Ltd on 01883 622068.

 

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Mezzanine floors: Bracing

July 22, 2010

To brace or not to brace – is that the question?

Mezzanine floor bracing

Mezzanine floor bracing

It is always necessary to design mezzanine floors to accommodate a degree of dynamic and side loading, and bracing will always be required to resist any sideways loading.

Mezzanine floors are designed to be freestanding – that is they will remain in place even if the building in which they are located were to be removed. This allows them to be added or removed without needing to apply load to the building structure or involve a structural engineer in checking wall loadings.

Bracing can take a number of forms, a “panel or cross brace”, “knee brace” or “floor brace” and can be fabricated from flat, angle or tubular material.

The panel or cross brace comprises a pair of straps forming a cross, which are bolted to lugs at the top and bottom of an adjacent pair of columns. Panel bracing is very effective, but has the disadvantage of obstructing access between the columns where the brace is located.

Knee braces usually link a lug at the top of a column with a lug on a beam at an angle of 45 degrees. They are not as effective as panel braces, and locally reduce clear headroom and project below fire protection.

Floor braces are like an inverted knee brace, but usually are fixed to a lug at the top of a column, and fixed to the concrete floor slab at the bottom. Floor braces are inclined steeply from floor to column to minimise obstruction of the space between columns.

When no obstructions between the mezzanine floors columns are acceptable, bracing can be achieved by using heavier sections and designing structural bolted connections that can accommodate sideways loading. This is usually a more costly solution.

The removal of  a mezzanine floors braces following installation in order to facilitate access will at the very least apply sideways loads to the building fabric which could result in damage or invalidate insurances, and in the worst case where the mezzanine floor is unrestrained, could lead to collapse of the mezzanine floor and crushing of people below.

For further advice regarding the design of your mezzanine floors, call Llonsson Ltd on 01883 622068

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Mezzanine floors: Staircase and handrail design

July 21, 2010

Staircase and handrail design for mezzanine floors and part K of the building regulations. 

Medieval staircase in use

Medieval staircase

A recent visit to Eastern Europe reminded me how we take for granted the safety offered by compliance with Building Regulations at home.

Part K1 of the regulations deals with the design of stairs, ladders and ramps whilst part K2  deals with protection from falling from exposed edges, and it is only these parts that relate directly to mezzanine floors.

Stairs need to be designed to suit the quantity of people using them, the nature of the environment in which they are used, and the people within that environment, so widths can vary as can the length and height of treads and the incline of the staircase within the specified ranges of the regulations that ensure comfort in use.

The one rule of thumb within these ranges is that the length and height of treads should be consistent in order to prevent users stumbling.

Hand railing also needs to be designed appropriately for the quantity and type of people using it. When guarding a mezzanine floors edge, hand railing needs to comply with the height requirements set out in the regulations.

Depending upon the application, the handrail will either require a hand and knee rail at specified heights and kick plate in industrial environments or where access is open to the public and children, infill of some kind will be required with no horizontal elements that could be climbed by children. If vertical elements are used, then they must be spaced to comply with the regulations, so that not only is there no risk of falling through but also children are not able to get their heads stuck between them.

Different hand rail load bearing ability will also be required depending upon the environment in which the handrailing is being used to ensure there is no risk of collapse should it be exposed to crowding.

To access a free copy of the Building Regulations from the Governments planning portal click below:

Approved document K – Protection from falling collision and impact (1998 edition)

Mezzanine floors, stairs, handrailing and balustrading designed by Llonsson Ltd will always take account of the environment in which they are being used and will be designed to fully comply with the building regulations.

 For help with the design of your mezzanine floor call Llonsson Ltd on 01883 622068

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Mezzanine floors: Part ‘K’ and Part ‘M’ staircases

July 12, 2010

Does your mezzanine floor need a part ‘K’ or part ‘M’ staircase?

Mezzanine floor staircase

Mezzanine floors

Part ‘K’ and part ‘M’ refer to the parts of the building regulations that deal with the design of staircases. Part ‘K’ relates to standard staircases, whilst part ‘M relates to ‘ambulant’ staircases designed for disabled access.

In principle it should be possible for anyone with a disability to gain access throughout your premises, however there are circumstances where this is not necessary.

If a mezzanine floor is used for a purpose where staff must be able bodied to undertake their duties such as storage, then an access statement can be made as part of the building regulations application and a part ‘K’ stair should suffice.

If the mezzanine floor is to be used for office space, then a part ‘M’ ambulant staircase will usually be necessary, however a part ‘K’ staircase may suffice if the uses on the mezzanine are duplicated elsewhere so that a disabled employee could undertake the same role in a more accessible location.

If  there is  public access to the mezzanine floor, as in retail applications, then the main staircase should be of part ‘M’ ambulant design.

If more than one staircase is required, then additional stairs can usually be part ‘K’.

Bear in mind that part ‘M’ staircases occupy more plan space as they are wider, shallower and have intermediate landings.

These are general guidelines relating to mezzanine floor staircases, and do not address requirements for stairlifts or personnel lifts which may be required for larger floors.

It is always prudent to discuss your specific project with the approved inspector or building control officer prior to commencing work.

If you would like advice regarding the specific requirements for your project and someone to liaise with building control on your behalf, call Llonsson Ltd on 01883 622068.

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Mezzanine floors and public liability insurance

July 8, 2010

Is public liability insurance important?

Mezzanine floors

Mezzanine floors

Installation of mezzanine floors is a potentially dangerous business. Forklift trucks unloading heavy materials, lifting them to heights. Manual handling of heavy items. People working in close proximity to fork lift trucks. People working at height. Using electrical power tools, creating noise, vibration and dust.

Often this work needs to be carried out in occupied premises. It is easy to see that there are potential risks posed by the installation of mezzanine floors.

These risks are mitigated by the employment of competent installation teams who are trained and experienced and who are equipped with the safest tools and personal protective equipment and trained in its use, however risk is never totally eliminated and sometimes things can go wrong.

 Llonsson Ltd recognises this and has public liability cover of £5 million as a matter of course as we think that adequate insurance when installing mezzanine floors is extremely important.

 For advice or a quotation for your mezzanine floor project call Llonsson Ltd on 01883 622068

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Mezzanine Floors: How much do they cost per square metre?

July 6, 2010

It’s a question that we often get asked, but it’s difficult to answer because:


Cost depends on many factors such as:

  • The extent of the mezzanine floor and associated economies of scale.
  • The load capacity for which the structure is to be designed.
  • The deflection limit to which the floor is to be designed.
  • The column grid required.
  • The maximum depth of the structure itself.
  • How many, and what kind of means of access are required.
  • Are any landings required?
  • Is fire protection required?
  • Are materials being delivered, and if so where to?
  • What material is to be used for the decking?
  • Is the mezzanine to be installed on a clear and level site or over existing equipment?
  • Is installation required?
  • Is installation to be undertaken during normal working hours or at weekends or evenings?

Mezzanine floors

Mezzanine floors

Basic headline costs per square metre may exclude necessary staircases, hand railing, delivery, installation, and are likely to assume a most economic grid and low load bearing capacity, low deflection limits.

With this many variables, a cost per square metre is relatively meaningless and buying on the basis of a low cost per square metre is ill advised unless the application is extremely undemanding, you have low expectations and are prepared for a bill for extras.

Our preferred approach is to discuss actual requirements with our clients and to quote on the basis of a specification that fully meets these requirements.

If you are planning a mezzanine floor project and would like advice or a quotation, call Llonsson Ltd on 01883 622068.


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Mezzanine floors: surplus handrail posts

July 2, 2010

Galvanised steel handrail posts

Galvanised steel handrail post

Anyone need some galvanised steel ball and tube handrail posts? These are surplus from a large contract and could be used either on mezzanine floors or for a barrier/handrail.

They are special, in that they are 1000mm high, so for perimeter edge protection would need to be mounted on 100mm plinth.

We have 38 off available, with 48.3mm dia. (40mm nominal bore) shank posts and balls to suit 42.4mm dia. (32mm nominal bore) galvanised gas barrel. Balls are at 500mm and 1000mm crs above base. 170mm x 80mm baseplates set perpendicular to handrail axis with 14mm dia. holes at 120mm centres.

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Mezzanine floors: New or used

July 1, 2010

Are second hand mezzanine floors worth considering ?

Mezzanine floors

Mezzanine floors

Under the right circumstances, buying second hand can save money and is undoubtedly environmentally friendly. Under the wrong circumstances it can be a disaster.

A second hand mezzanine that can be viewed in situ, is of adequate load capacity for the new application, and has the benefit of its original drawings and calculations that can be dismantled, transported to a new site and re-erected by the same experienced team without reconfiguration should provide a cost saving.

In these circumstances it may be necessary to provide steel spreader plates if the new site has a floor or subsoil with lower load bearing capacity. A new Building Regulations application will need to be made, using the information from the original documentation, or new drawings and structural calculations will have to be professionally prepared.

At least some new decking will be required to make up for pieces damaged during dismantling, and often with an older structure, all the decking will require replacement, as swelling of the boards makes dismantling impractical without damage and reassembly difficult and time consuming.

The main saving achieved is therefore the cost of the steelwork, against which the cost of dismantling has to be set. If the mezzanine has to be transported to a different site for temporary storage or rework then additional transport handling and rework costs must also be offset against the saving on steelwork cost.

The type of construction of the second hand mezzanine should be considered if height is critical. Inset (slim line) construction will occupy less vertical space than ‘over the top’ construction.

If a significant amount of site alteration is required to make the second hand mezzanine floor suit a new site, then it can swiftly become uneconomic to consider this as an option. If, for example, the floor is too low, some steels are too long or the load capacity is unsuited then some steelwork will either need to be double handled to rework it off site, or will need to be reworked on site with associated risks (is the site insured for hot works?).

Rework should be undertaken to an acceptable standard – a new mezzanine floor from a reputable supplier will not have any structural members that have been welded together from off-cuts, but will comprise prime steel cut to size.

If documentation is not available, then research will be necessary to obtain relevant beam data. Structural calculations prepared by a mezzanine floor supplier with relevant data at hand will be far more cost effective than those prepared by a structural engineer from first principles.

An initial assessment of the feasibility of reuse of a mezzanine can usually be made by bearing the above points in mind. If it appears viable assistance from a professional supplier is best sought for confirmation.

A professional supplier of mezzanine floors will provide an impartial opinion for a fee and may be willing to undertake dismantling and relocation.

Llonsson Ltd  (T 01883 622068) are happy to provide advice regarding your new or used mezzanine project.

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Llonsson Ltd

49 Court Farm Road,
Warlingham,
Surrey,
CR6 9BL United Kingdom

T: 01883 622068 F: 01883 623280

Registered No: 2389444

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