Examples (Previous Projects):
The Design Structural Steelwork for a House
Based North of Wisbech, just outside of Throckenholt, a client wanted some structural alterations to be designed for his property. The design itself was extensive, requiring the removal of both internal and external load bearing walls, thereby opening up the property and introducing a new entrance route into the building itself.
Removal of the internal load bearing wall meant that a steel frame would have to be used in its place (image left). Simply introducing a steel beam would result in loads being transferred into outer walls and the foundations to the property were not considered adequate to accommodate the additional bearing pressures. Additionally, the existing wall that the steelwork would replace was there to support the outer wall as it resisted wind loading (you've probably seen sagging walls with steel plates in them- the sag it due to wind loading and the plate is there to tie it back to floor joists). Floor joists to the first floor spanned parallel to the outer wall in this location, so the horizontal span of the wall had to be kept low- hence the column provided some thing for it to "lean" against!
As a result, I had to design a "picture frame" which would act in the same way as the wall it was replacing. The top steel beam carried the loads from above, transferring them into columns and down into another beam, located on top of the existing footings, distributing vertical loads evenly over the length of the footings. Without the beam to the bottom, stresses would have been so high that by the time they reached the underside of the footings, they would have caused the ground to subside over time as it "consolidated" under the additional load.
A similar solution was designed for the first floor to the front of the property, allowing for complete removal of the first floor front wall. However, this particular steelwork was also designed to carry horizontal loads, imposed by wind loading to a new steel frame that would enclose the front of the house and be encased in a glazed finish. As a result, the "picture frame" steelwork replacing the old front wall had to be positioned so that the horizontal wind loads would be evenly distributed back into the roofs rafters and first floor timber floor joists.
Why didn't I just design the glass front to be bolted onto the side elevations protruding out of the house? One of the biggest issues I had was that to the left of the house (above image), the extension was circa 100 years old and to the right circa 150 years old.
Construction techniques differed considerably during this era and both fronts could inadvertently move to different degrees when heated and cooled by sunlight. In effect, I was aware that there was a risk of "differential movement" and didn't want the new steel glazed frame to suffer as a result.
Footings to the new steel frame had to be designed to avoid transferring loads into the existing corbelled footings to the base of the existing house. In order to do this, I designed a reinforced concrete beam that would span over the top of the new footings, cantilevering out each end so that the steelwork could be positioned up against the existing house but all vertical loads would be carried by the new footings. A compressible membrane could be used in the void between new and existing, removing the risk of "foundation interaction".
As can be seen in the image on the right, the foundations to the new steelwork appear to be deigned in two stages, with brickwork in between. This was intentional as it allows loads to be carried by the top reinforced concrete beam. These loads are then transferred through "bearing" into the brickwork, which in turn bears directly onto a 6540mm wide strip footing founded 750 mm below ground level. The bearing pressure to the underside of this strip footing is less than 30kPa and at the depth shown will not suffer from any dessication or swelling of the clay that it is founded on.
The Design of a Load Bearing Steel Beam
A client contracted me to design a steel beam, to act as a replacement of an existing load bearing wall. In effect, a simple process of designing a beam and the padstones to either end, thereby providing support to the floor joists above in bending and transferring the same loads into the supporting walls through bearing. An initial design resulted in a 152 x 152 UC 23, spanning onto Engineering Bricks to either end, set in Cat II mortar. Design stressed in the existing Blockwork wall indicated that the padstone had to be 400mm wide in order to prevent crushing. 3 Courses of Engineering bricks would distribute loads from the underside of the beam so as to reduce the applied stresses sufficiently. However, having reviewed the existing structure, it soon became apparent that a window to the ground floor kitchen would inadvertently prevent the formation of a padstone to the cavity wall of the building. In effect, the concrete lintel over the window spanned at such a height and in such a location that it ended right in the middle of where I would locate the padstone. In addition, the lack of further partitions running perpendicular to the external wall was of concern. With the internal partition removed, the external wall would span some 7 meters, unrestrained and floor joists ran parallel to it. As a result, a pier would have to be formed from the internal blockwork wall, meaning that not all of it could be demolished. The second iteration of the design incorporated the pier, avoiding the need to form a padstone in the location of the Lintel but the stresses introduced in the pier by the steel beam would result in crushing of the concrete blockwork. At the same time, stresses to the underlying footings would not be evenly distributed and without sufficient information on allowable bearing capacities, the potential for failure in the footings had to be considered a possibility. The resultant solution aimed to solve all these issues in as elegant way as possible. A steel hanger, formed from a 120 x 120 x 10 RSA was designed to sit within the internal leaf of the cavity wall. It would be inserted just above the line of the Lintel and an end plate would connect back to the steel beam. The RSA would have it's downstands removed where it did not coincide with the beam, thereby allowing the wall to be re-rendered and plastered. Boxing in of the steel beam would also hide the remaining downstand and connection back to the beam, thereby leaving a clean finish once completed.
The Completed works: The left hand picture below shows a steel hanger protruding from the wall, carrying the steel beam. The right hand picture below shows the detail (above), with brick pier retained as a wind post. The steel beam is hung from the rolled steel angle (RSA) with a side plate welded onto it. M16 bolts fix the beam back to the side plates. Note that the wind post is formed from remains of the existing load bearing wall. This is important because the bricks need to be tied back (cross bonded) into the inner leaf of Gable end cavity wall. Without the cross bonding, the pier offers no resistance against wind loads.
Grade II* listed Georgian Property in a Conservation Area
The North Brink in Wisbech is synonymous with Georgian Architecture, much of which was designed and commissioned by the Peckover Family. I was contracted by the owners of North Brink Medical Practice as Structural Engineer to a project that would see the internal re-modeling of the third floor to this historic structure. The work involved was considerable and involved:
- Removal of the existing Plaster and Lathe Ceiling
- Installation of a new Ceiling at a height that allowed full use of the new space.
- Removal of an internal single skin brick partition
An initial site visit allowed me to carry out an inspection of the existing ceiling timbers and notably, two of these formed ties to the wall plate, thereby preventing the spread of the walls due to roof loads. The ties also acted as main structural supports, carrying the ceiling loads themselves.
My key concern when carrying out the designs for this project was to retain the existing historic features of the structure as far as possible. This meant limiting structural alterations so that the original fabric of the building remained intact.
The construction techniques used in a building of this age clearly dictate it's longevity. Timbers were included in the construction of it's external walls, providing some "elasticity" that would otherwise not be present in a building with walls formed from "bricks and mortar". The existing masonry still retains it's original lime mortar with pozzolan clearly defined against the white of the lime on freshly "opened up" faces. Timbers were ungraded at the time of construction but appear denser than those used in modern construction today. Lead flashing is thicker than the gauges employed in roofing today. Movement and true levels in the building itself, whilst clear against straight edges, is lost through the use of skilled construction techniques and use of traditional building materials.
In designing the new ceiling, it was important to check that the existing timber rafters could accommodate the new loads imposed by new joists that would be attached to them. Vertical loading at the connections could quite feasibly cause undue sagging of the roof. Purlins spanning perpendicular to the rafters could be subjected to greater stresses in bending and these needed to be checked. Loads on these were determined using the "Stiffness Matrix" method, whereby the rafters were analyzed for spanning over four supports.
Interestingly, the new joists were slender about their minor axis, so I introduced Noggins between them to prevent buckling. This had the added benefit of making the new connections between the joists and rafters act in shear, taking out the risk of the timbers failing at the new connections. With stress in the timbers being within tolerable limits, a final design was drawn up that would inadvertently strengthen the existing structure for years to come!
However, the removal of the internal wall, which clearly was not carry any vertical load proved an eye opener to all those involved in the project. In carrying out wind load calculations, it soon became apparent that the wall did indeed carry loads- horizontally! In effect, the central wall, formed from a single skin of brickwork, acted as a support to the main external wall when buffeted by wind from the South. It prevented the wall from bowing out as the wind tried to "suck" at it and took load when the wind tried to "push" on it. My solution to this was to design a single column, fixed to the spine wall of the building below and rafters above. Formed from a Structural Hollow section (SHS), the column was fixed back to the wall at every fourth brick course and acts as a mid-span support to the wall itself.
I was recently engaged by an Architectural Technician in Kings Lynn. The client required the assessment of a series of timber floor joists, each 225mm deep and spanning 4.4 meters. Part of a renovation project, the joists had been cut and spliced some 1.6 meters from the end support. The splicing had been flagged by the Local building Control officer who wanted an inspection by a Structural Engineer to ensure that they were structurally strong enough. Each joint incorporated 10mm diameter grade 8.8 bolts set into a 600mm long splice. Having carried out a site inspection, I felt that calculations would be required to prove the capacity of the joint.
The joists were spaced at 400mm centers and carried self weight, a permanent load and variable load. Initial calculations proved fruitless and implied (even with load sharing) that when we did our site inspection, the timbers should have collapsed under our feet! On speaking to the client, it became apparent that toothed connectors had been incorporated into the joints when they were formed. In re-calculating with the greater surface area in compression (parallel to the grain), the joists were found to be adequate. Building control were notified and issued with a copy of the calculations and works were allowed to continue.
Last week, I was asked to carry out yet another Structural survey. Having completed the survey, I didn't think it was worth repeating myself and putting anything up on the examples page. There were a few cracks to the property which certainly weren't of concern.
One of the cracks, top the underside of a window followed a plane of weakness in the brickwork, where builders had inadvertently lined up bed joints vertically. The same crack appeared around brickwork to the top of the window.
However (and this is a big however), whilst visiting an event in Whittlesea, I happened upon a long freestanding wall (about 30 meters long) which had a vertical crack that had propagated the entire height of the wall.
That got me thinking- Had the addition of a new UPVC window on a South Westerly facing wall inadvertently introduced a plane of weakness in the wall itself, allowing a restraint crack to develop? This form of cracking is typical in a wall 30 meters in length but not very common in a detached bungalow.
It's the reason why Building regulations specify the need for vertical movement joints in long walls- to allow for expansion and contraction due to changes in temperature!. However, the size of the opening for the window and the changing of the window frame to UPVC as opposed to timber could have caused restraint in the wall so that as it expanded and contracted, the weakest point in the wall failed. The issue with that hypothesis was that the crack was nearly 800mm from the edge of the window frame. However, it did happen to coincide with an internal partition that was in turn restrained by the chimney breast and a line of weakness in the brickwork itself.
Either way, the vertical alignment of mortar joints (see image right) clearly points to a vertical plane of weakness in the masonry. As can be seen in the image, a bed joint, one course down from the window cill is poorly pointed and this line of mortar has cracked and spalled. The crack runs horizontally right under the entire window and then down the wall. Thankfully in this instance, it's clear from the brickwork below the Damp Proof Course (the bottom course is Engineering Bricks with DPC over) that there hasn't been any movement in the foundations, meaning that this can be easily rectified with little extra cost.
Structural Survey & Renovation
I was recently engaged by a client to carry out the survey of a property for restoration. Purchased at auction, the property was in a significant state of decay, with previous building works partly completed. Sections of the property were at risk of collapse due to a lack of suitable temporary supports and other parts of the property's interior had been constructed using inadequate structural beams for supports. A short schedule of works was drawn up as part of the survey and presented to the client, so that a builder could be contracted to rectify structural defects before the weather deteriorated. These works included the shoring up of an existing external wall, precariously supported on "cantilevered" Acro Props some 3 meters in length. The temporary supports, which were positioned incorrectly already showed signs of having moved under the weight of masonry they were supporting and a crack, 1 inch in width had opened up to the interior of the supported brickwork skin.
As a consequence of the survey, I advised the client to engage the services of an Architect, who would produce preliminary plans, against which I could produce Structural Calculations for internal steelwork beams, timber floor joists and masonry walls. Given that the roof to the property had been completely removed and new trusses fitted, tiles, battens and felt could not be laid until a suitable planning application was granted by Fenland District Council. This would cause significant delay to the commencement of any works on-site, leaving the existing building at risk from further decay, as it was not watertight. It was therefore imperative that a design, commensurate with the surrounding properties was produced, so as to facilitate a quick and painless planning approval, thereby allowing works on the property to commence in earnest.
Initial Layout/ Architectural Layout:
A client requested the initial design of a series of 3 dwelling units, designed to fall within the curtiledge of an existing steel portal Framed Farm Building. Falling under the Guise of a Class Q Change of Use, a suitable design would be provided with "Deemed Consent", automatically meeting the requirements of Planning.
The initial appraisal of the Portal Framed Barn took the form of a site visit and survey, so as to obtain existing section sizes of the steel members, the dimensions of the portal frame bays and dimensions of the Haunches at both Apex and Eaves.
An analysis of the structure to both BS5950 and Eurocode 3, revealed that the Portal frames could accommodate suitable loads from a cladding system that would provide adequate insulation. Sway was found to be L/200 and this dictated the initial layout of the retro-fitted interior.
Layout: The building's overall residential area is constrained by Class Q to less than 450 square meters on plan.
Instep areas, employing a timber cladding system were devised, off-setting the external appearance of the Steel cladding. Large windows, allowing for extensive lighting were included, thereby allowing for the orientation of the building, which was found to be in a Northerly Direction.
Internal Masonry, comprising Blockwork was included to allow for disproportionate collapse of the building, thereby protecting occupants of adjacent dwelling units, should one of the units collapse due to fire or accidental damage.
The floor to the existing building was raised by 500mm so as to allow for the building being in a "Flood Zone 3".
This property is located within the curtiledge of a Growth Village, meaning that it stands a "better" chance of being granted "Change of Use" consent. The consent itself takes into account other factors other than external appearance.
This includes the vicinity to services including water, gas, sewage and electricity, the location or vicinity to "special" areas and whether the property or land has, within a given period, been used for Farming.
A client requested my assistance with a Structural Engineers Survey of his Semi Detached Property. The property, which had been placed on the Market, had previously remained unsold, with a prospective buyer "pulling out" of the sale shortly after having received a Structural Engineers report on the property.
Prior knowledge of the report produced by a local Structural Engineer meant that I approached this survey with trepidation. Professional indemnity can inadvertently result in the Engineer being overly Cautious when carrying out a survey for a prospective buyer, thereby finding faults in the property when there are none to be found. In conducting this survey for the vendor, I surveyed the entire exterior of the property, finding little more than a covered Air vent to the underside of the floating timber floor to the front elevation of the property.
A Resin injected DPC to the rear was unfortunately installed to a solid brick wall and whilst correctly corresponding to an internal concrete ground bearing slab, would do little for a property of this age. However, further inspection revealed moss to the exterior face of the wall, extending up to the underside of the original DPC but no further, This indicated that masonry above the original DPC remained dry and free of internal moisture.
The interior of the property was similarly immaculate and the lack of cracks, damp, movement or dry rot within the property itself indicated that it was in sound condition.
A client was in the process of extending his property with a bespoke Brick and timber single storey extension. Having produced preliminary drawings and specifications and obtained both Planning and Building regulations approval, he felt that a Vaulted Ceiling would be more in keeping with the property than a trussed roof. I was engaged to design a steel beam over a series of bi-fold doors, allowing for a ridge beam to run the full length of the extension, thereby supporting rafters and a series of velux windows set into the roof.
In designing this new roof, I had to consider the entire structure, including rafters, ridge beam, steel post to the ridge beam and steel beam over the bi-fold doors. I first analyzed loading on the roof to Eurocodes, taking into account snow loading and drifted snow loading, wind on the dominant face of the building and Dead (permanent) loads from self weight. The roof, even with the load from concrete tiles would be subject to Uplift, so wall ties running the length of the wall were necessary.
Designing the timber members to the roof meant considering deflection in the members first- the finishes were brittle and included glass!. They were then checked to Eurocode 5 to make sure they could take the design load.
The steelwork beam and post was again designed for deflection and checked for the Ultimate Limit State. This time, I wanted to make sure the bi-fold doors continued to work even when the weather had turned poor during the winter!
Although not a complicated design, it's important to note the need to consider deflection of structural members as the critical design factor in this project. I could have quite easily used smaller structural members but deflection in excess of span/360 would have meant redecorating within 5 years and doors and velux roof lights that were forever sticking!
Waste Management, Health & Safety and an Environmental Management Systems:
Many operators of Waste Management facilities are unaware of the risks posed by their activities to the Environment, Personnel and the General Public as a whole. I was tasked with the review of one such client's operations with a view to implementing changes and improvements to their operations. The client, who had been in operation of six years, employed 15 operatives under an "exempt" activity. He had to consider areas of improvement with a view to expansion through ISO registration.
Upon first assessment, I found that the client lacked sufficient Health and Safety documentation and had not carried out risk assessments or produced method statements to reflect the various activities and tasks his employees had to perform. Similarly, the operation, given that it was a waste management activity, was carried out without sufficient reporting to the previous holders of the waste or the Environment Agency itself
The client had considered a number of he key Health and Safety regulations, providing Welfare facilities, avoiding slips, trips and falls, but had not considered the primary Health and Safety at Work Act 1974, implemented a record keeping system for Accidents or sickness, provided suitable PPE for employees or considered the ramifications of Contractors working on his property.
In implementing an EMS, I took into account all aspects of his operations, from the consumption of energy to the waste outputs, their storage, transport and disposal. Vehicle movements and on-site storage were drastically changed to reflect the fugitive emissions that were being produced and the risks posed by the stored outputs to employees and the general public entering the site.
Overall, the site lacked forethought on the part of the operator, posed a risk to employees and to the local environment. Implementing the changes took the client three months, after which, he was able to progress his operations to ISO 9001, ISO14001 and ISO 27001 registration successfully.
Building a Floating Hearth:
Have you ever wondered how a Floating hearth is constructed? It's not as complicated as you may think. If it's a single plinth that you intend to hang over the fireplace, all you need are sufficiently large dowels and epoxy resin to anchor them in place. Here's how I hung ours:
- I find threaded bar is very suitable for this. The thread itself provides a greater surface area in friction. You'll need three lengths of M10 threaded bar (1/2 inch in old money will also do). Threaded bar has to protrude 100mm into the brickwork and 100mm into the floating hearth.
- You'll need a suitably long drill bit for use on masonry. The drill bit has to be able to drill a hole 100mm deep into the hearth. Make sure the drill bit is no more than 1mm wider than the threaded bar.
- First mark your drill points on the wall and on the floating hearth so that they will line up.
- Drill out the holes in the wall first. The dust in them needs to be cleaned out- use a vacuum and a can of clean air. Don't go poking around in the hole- it'll make it wider!
- Next drill out the holes on the floating hearth using a suitable drill bit. Blow out the holes.
- Mix your epoxy and fill the holes in the wall so that there is plenty in them. Insert the threaded bar into each hole, turn the bar and make sure the epoxy covers the space between the metal and the wall.
- Cover the protruding part of the threaded bars with epoxy and line up the holes on your floating hearth with the rods. Now slide your floating hearth over the threaded bars until it fits snuggly against the wall.
- Allow the epoxy to cure before you put any weight on the hearth
Here's the finished product that I installed last winter. The Timber is European White Oak, weighing about 40 Kilograms. I sanded it with 80 grit, then 120 and finished it with 200 grit sandpaper to achieve a good finish before applying a coat of beeswax. The most important parts of this job are edge distances to the timber (make sure the threaded dowel is at least 20mm from an outside edge), embedment length of the steel dowel in the brickwork and the timber and the use of plenty of epoxy. Finally, just so we're clear on this, this solution only works on solid brickwork walls. It won't work on dry lined walls or walls made from lightweight blockwork.
In-experienced Building Works
I was engaged by a local client with a view to carrying out a Structural Survey of her recently completed detached Garage. Built from Single skin Brick, with trussed roof, the structure had been initially designed by an Architect and included Brick Piers integral with the walls. The builder had unfortunately opted to build the Garage differently, opting for a single skin brick wall with blockwork piers, affixed back to the brickwork with wall ties in the Mortar Bed Joints.
The key issue with this solution wasn't the fact that the blockwork piers had separated from the masonry walls though. It was the fact that the piers, which should have been built up in a "stretcher" and "bearer" fashion from brickwork, so that it formed an integral part of the masonry, was included in the original design to prevent flexure on of the brickwork horizontally. It was on these grounds that I advised the client to withhold further payment to the builder until works were rectified, citing the fact that the building was "not fit for purpose".
However, the building suffered from other significant defects including a concrete floor that had been poured and troweled so poorly that it was uneven and had "dusted" in places, exposing an uneven, rough finish that was exhibiting excessive wear and had a weakened surface. Laid with a view to carrying vehicular traffic, the surface would have continued to wear to a point where aggregate could be dislodged. During poor weather conditions, vehicles entering the garage would introduce road salts and water to the concrete surface which, given it's sub-standard finish, would be excessively porous, thereby allowing chemical attack and more deterioration.
I advised the client that the existing surface to the concrete would require grinding back to expose the harder underlying concrete and a bonded screed, suitable for vehicular traffic, poured. This would also remove the issue of the finished floor level being uneven and have the added benefit of achieving the desired finished floor height, thereby minimizing ingress of surface water from the driveway to the front of the building.