Substructure Design
Structural engineers assess the use of the proposed building and selected substructure type to plan what Superstructure elements would be best suited
There are many different types of superstructure systems the structural engineer can choose from. These options will be explored in our next post - Types of Substructure.
We will be exploring a reinforced concrete frame for the remainder of this post but the design principles can be applied to other systems.
As with all elements of work, my recommendation would be to start by finding the relevant drawings.
In the case of Superstructure, these will be under the Structural Engineer section and likely labelled 'First Floor General Arrangement Plans' and 'General Elevations'.
Example Upper Floor GA Drawing
Things to note
1. If there are no setting out dimensions given off gridlines (GL) for the element, this means it is to be set out central to gridlines. In the example above all elements are on gridlines except the column on GL 3B.
2. 'FFL' stands for 'finished floor level and 'SSL' stands for structural slab level. This means concrete is poured to a level of 54.900 AOD from on half of the building above and there are 100mm of floor finishes which gets you to the 55.000 shown.
3. There is a step in the slab between gridline 3 and 4. The size of the step can be calculated by taking the difference between the two structural slab levels i.e. 54.900 - 54.700 = 200mm slab step.
4. Section A-A drawing would show you a section through the stair core.
5. A cross inside of a box like the one on GL 1-2 B-C means there is a penetration through the slab so this must be formed before concrete is poured for the slab.
6. There is a red line showing masonry support. This is usually formed of metal and will be covered in depth in future posts. It is usually designed by the supplier of the support.
7. Each column has a reference - you would expect to find a schedule accompanying this drawing which should show: C01, for example being a 200mm x 600mm RC column.
8. A 100mm fire collar needs to be cast into the slab at GL 5B. This is usually to allow for something to penetrate through the slab like a pipe to take foul waste.
9. GL 9 - 10 has a dotted line which references the down downstand beam running underneath the slab.
10. Along GL G there is a concrete upstand drawn.
You would expect a number of section and detail drawings accompanying the plan drawings if they are not included as extracts on the main GA.
Structural Engineers considerations when designing Superstructure
1. Load Analysis: Determine the loads the superstructure must support. This includes dead loads (permanent), live loads (temporary), wind loads, if there's any seismic loads, etc.
What is the weight of the structure?
What will be in the building? How much loading will it impose?
What are the average wind levels in the area? Is there a lot of snow that could load the roofs?
Sometimes the load during the construction phase is higher than what the building has been designed to take in the permanent state. For example, the structural engineer would need to run a calculation to check if the structural slab can take the weight of a pallet of plasterboard which needs to be loaded onto it.
Pallet of plasterboard
2. Foundation Compatibility: Coordinating the superstructure design with the foundation design to ensure they work together effectively in supporting the building's loads.
Do my superstructure elements correspond with the foundation design?
3. Structural Materials: Choose the right materials, such as concrete, steel, or timber, considering strength, durability, and compatibility.
Which material would be best suited for a buildings size?
4. Structural System: Integrate the superstructure design with the building's architectural vision and functional requirements.
How many columns are required in the building?
Is any of the concrete going to be exposed?
5. Buildability: Design elements that are feasible to construct, considering construction methods, equipment, and labour availability.
Do the site logistics allow the superstructure types chosen to be constructed safely?
Are there any neighbouring properties that could be affected?
6. Sustainability: Incorporating sustainable design principles to reduce the environmental impact of the superstructure and improve energy efficiency.
Is there a more efficient way this building could be designed to prevent waste?
7. Expansion and Contraction: Account for thermal expansion and contraction of materials in the design to prevent cracking and structural issues.
8. Resilience: Design for the long-term resilience of the superstructure against potential changes in use, loads, or environmental conditions.
9. Cost Effectiveness: Strive for an efficient design that balances performance and costs while meeting safety requirements.
Definitions
Reinforced concrete frame - A structural system using steel reinforcement bars embedded in concrete to take loadings from a building down to the foundations
Setting out dimensions - Specific measurements and locations for elements to be built given off a known reference point
AOD - Above Ordinance Datum. height of a point or location above a reference point called "Ordnance Datum"
Section - a drawing that displays a vertical or horizontal cut through the element. Shows details and dimensions.
Fire collar - passive fire protection device used in buildings to seal openings and prevent the spread of fire, smoke, and hot gases between compartments
Downstand beam - a type of reinforced concrete beam that extends below the slab or the floor it supports
Upstand - raised or elevated structural element
Dead Load - the permanent, unchanging weights imposed on a structure. These include the weight of the structure itself, fixtures, finishes and any non-moving equipment.
Live Load - also knows as imposed or variable loads. Temporary and dynamic forces on a structure including occupants, furniture, movable equipment and any moving vehicles.
Thermal Expansion - tendency for materials to expand when heated and contract when cooled. Alters their dimensions due to more or less molecular activity.
Posts to Follow
We plan to go into more details on Superstructure and add sections on:
Types of Substructure
Logistics
Temporary Works
Build Sequence
Health, Safety & Environment
Quality
Programme
Commercial
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