“When we build, let us think that we build for ever. Let it not be for present delight, nor for present use alone; let it be such work as our descendants will thank us for”.
John Ruskin
Refurbishment engineers and big data need to talk
In the 21st Century, the age of technological advancement, refurbishment projects are still frequently seen as the province of the grey-haired engineer. To truly enable the current retrofit zeitgeist, It is time to reframe the evaluation of existing structures, using tech-clarity to modernise, streamline and illuminate the process (and those grey haired engineers).
The focus on retention of structure links directly to the industry drivers initiated by the climate emergency: reduction of embodied carbon and waste. However, the case for preservation rarely hinges on a proposals environmental impact, even now. Cost is not the motivator for structural retention either, on a major reworking of an asset as the savings usually pale in comparison to the risk attributed to “unknowns”. Retention primarily makes commercial sense for small interventions or restoration schemes. For more ambitious schemes, commercial viability assessments are usually the biggest inhibitor to structural retention. This is due to perceived limitations on design, fear of “hidden” costs associated with temporary works/the construction process and the risks associated with “unquantifiable” uncertainty. We believe that the reduction, management and quantification of that uncertainty can swing the balance.
Historically the driver for refurbishment/retrofit projects has been low planning risk, quick programme and (all too frequently) low ambition. There is value associated with the building’s character and history, reduced construction programmes and a reduced carbon footprint. This holds true whatever the scale of the proposal. Early definition of opportunity and risk are essential in defining the viability of retaining an existing structural frame.
We will talk about the key influences that have developed exponentially over recent years. In this article we will try to fling open the doors for radical interventions, underpinned by considered strategic assessments, facilitated by the capability modern tools have brought to data management.
Technology is enabling the reuse of structures through:
· Visualization of the opportunity
· Defining and testing the buildings capacities and limitations
· Rapid study of the influence of interventions
· Controlling and quantifying risk
The big steps in structural technology, outlined below, can release the opportunity held by our existing building stock. But, we can do more. We should view remodelling of structures as the first of many refurbishments, and design as preparation for the future life of the building. If done correctly, a refurbishment project should be an enabler for future alterations to be delivered more freely, more cost-effectively and with lower risk.
Figure 1 - Layering of constraints to optimise interventions
1: Forensic capability in structural analysis
Over the past 40 years, the phenomenal advancement in structural analysis has been woefully under-utilised in the reuse of existing structures.
Understanding of variability in existing structures takes experience. Structural opportunity and risk differ between building typologies and vary through materiality, era of construction and the status of the original build. The quality and nature of workmanship, as well as time, influence different buildings differently. Experience builds this repertoire of understanding. Once this is in place, the variables are ripe for parametric assessment.
Ingraining digital assessment with this understanding of the variables associated with existing building creates a powerful tool to define the range of opportunity, the factors influencing that opportunity and the triggers holding it back. As these triggers are identified, physical solutions for overcoming them can be developed. Their impact on program and cost can be assessed against the quantum of additional area that can be delivered.
If you link a massing model to a potential range of results from either a geotechnical or material investigation, you can determine how important they are. If you add in the potential for localized enhancement of the structure, perhaps an extension of the core, you can instantly visualize how much additional mass this will enable you to achieve.
Rapid automation of these assessments, coupled with visualization models, enable massing opportunity to be assessed against design variables such as lightweight construction, column strengthening etc. This identifies the limiting structural factors in achieving massing and allows these to be correlated to factors such as planning, rights of light and value.
2: Programme-linked design assessments
Advances in high rise construction over recent years have been supported by construction sequence-linked analysis options within structural engineering packages. This staged analysis includes iterative assessments of structural performance in relation to construction activities. The link between site operations and structural assessments can be used to enable detailed temporary works sequence assessments, minimizing the level of intervention and unnecessary and complex temporary works.
This process can be utilized to work with the building, to orchestrate the works so that the building maintains its stability and integrity, whilst a phased work sequence is delivered. This along with detailed localized modelling assessments of specific interventions can mitigate temporary works requirements.
Temporary works are too frequently unaccounted for in both cost and carbon assessments of redevelopment projects. Bringing these to the fore by incorporating them in early-stage assessments is essential in making the right decision. This can be done through integrated design assessments. Coupling these with staged analysis gives an understanding of where stresses get locked into structures and where they are shared between new and retained elements. This leads to efficiencies in the scheme and suggests sequencing to enable these to be realised.
3: Innovation in geotechnical assessment
Geotechnical analytical modelled and the accuracy of in-situ testing has leapt forward in the past 20 years. Modelling of soil/ structure interactions eliminates a degree of uncertainty, enhances accuracy and makes savings in new build projects by utilizing the stiffness of the entire structure in the design of the basement box and foundations. In-situ testing of geotechnical properties has enabled more certainty in results, reducing safety factors on design and enabling greater design capacity. Previously removal of samples from site for testing had an inherent risk of deterioration during the testing, accounted for in the test results. This has led to many existing buildings having conservative assumptions ingrained into their foundation design.
Due to the nature (and cost) of foundation strengthening, this combination of better test data and enhanced analysis capability is an essential step in unlocking the capacity of our existing building stock.
Using these developments in testing equipment and digital capability massive capacities within existing building foundations can be identified. Linking this to a staged design assessment can identify how movements relate to sensitive elements- such as the façade, internal partitions, tunnels and adjacent utilities. This understanding can be considered in initial studies as to whether to re-clad buildings or not, whether to phase any excavation works and the impact of varying degrees of demolition. If removing the cladding enables an extra two or three storeys to be added, the value model will shift. Evaluating this alongside programme and sequencing impacts should account for intermediate solutions as well, such as a partial re-clad or a risk pot to deal with cracks which will save the cladding.
4: Material advances
The scale of structural intervention required to overcome a limitation is intrinsically linked to the material and installation technologies associated with structural strengthening works. Extensive refinement and testing of carbon fibre technologies has been a major contributor to the progress in its use for structural enhancement works. Carbon fibre’s widespread use by major infrastructure firms, such as Network Rail, has enabled increased commercial viability and more widespread adoption.
Fibre-reinforced concrete is having a similar impact, enabling higher increases in element capacity. Prefabricated plates can be installed at a fraction of the thickness of traditional concrete column strengthening, reducing impact on floor areas.
5: Building surveys
Familiarity with advances in dimensional surveys is widespread through the industry. However, the capacity of non-intrusive investigations to give clarity to a structure has been underplayed. Non-intrusive investigations have has developed significantly and continue to be refined with tools such as ferro scanners now able to produce 3D reinforcement models. Whilst unlikely to be adopted for full building surveys, local use could save areas of concrete that might otherwise be removed due to uncertainty of reinforcement quantity and condition, and so increased the assessed capacity.
Non-intrusive surveys give opportunity for a staged investigation to be conducted, which can identify unknowns and risks prior to vacant possession. When program is a key project driver, having to wait until the building is vacant to perform investigations can be problematic. It can add months to the design program for the retrofit option, which in turn can impact the viability of retention and remodelling vs. demolition and new build significantly.
How the industry can do better
Whilst progress has been profound, there are always ways to improve. Three crucial areas are presented below.
Firstly, retrofit projects should be seen as the first of many on a building. Using reversible mechanical connection details and introducing new structure as genuine demountable soft spots is fundamental to this. Consideration of future extension/ alteration of the structure should be a Stage 2 exercise to define the scope and outline cost impacts. A section within the Operations & Maintenance manual, left with the building’s owner/ occupier, should identify residual structural capacity, structural demount ability and future construction opportunity.
Secondly, data is king in advancing technology-driven approaches. The capability to monitor existing structures is available. Installation of these technologies into new build developments is happening, but retrofitting into existing building stock is not- and it should be. Monitoring of new developments provides data for redevelopment in 20 years. Existing buildings are being adapted now. Installing stress gauges and looking at how we use these to influence refurbishments can be done now, but will need investment to enable a sufficient scale to justify changing the design codes. This includes weighing demolished materials to determine the load relief, whilst monitoring retained elements to see the impact of this change.
The combination of enabling future adaptation and the historic buildings capacity has value. It should be considered as a benefit to potential purchasers, increasing the value of the asset to account for the residual opportunity that it holds.
The final point in need of progress is legislative. We have heard and support the campaigns for VAT relief on refurbishment. However, as we have seen above, there are other key factors in the decision-making process. By creating accelerated planning processes for retrofit schemes over new build, it enables a developer to vacate a building where it is necessary to progress retrofit schemes, knowing that the time the building will be off the market will be limited.
Here at London Structures Lab we are seeing the progress this approach is bringing to unlocking the potential of our projects. Retention and remodelling of existing structures is an essential component of the reduction in our use of natural resources and the response to the Climate Emergency. The combination of London’s design culture, vibrant and varied historic building stock and data resources is enabling us to be at the forefront of what has to become a global trend.