Types of Superstructure
There are a number of different superstructure systems which can be used to support a building or structure.
Determining the most suited superstructure (informally referred to as the frame) is critical to a job as it determines the design for the rest of the building including the facade, roof and internals.
The selection is usually made by the Structural Engineers with input from the Architects and Main contractor.
One of the key elements that need to be considered is compatibility with the selected substructure (or foundations) and use of the building.
Options available fall into, but are not limited to, the following three main categories:
Reinforced concrete (RC) superstructure
The most commonly used type of superstructure. If an RC frame is selected, the following elements can form part of it:
Example of a reinforced concrete frame
1. Slabs - These form the 'floors' of the building. They are supported by beams, columns, walls or other structural elements.
The method of slab construction can be decided with the main contractors input. The following are options:
Reinforced concrete slab as concrete pour is happening
1.1 Reinforced Concrete (RC) In-situ Slabs - most common slab casting method. Concrete is poured over steel reinforced which has been laid.
Pre-cast concrete plank
1.2 Pre-cast - manufactured in 'planks' off-site and lifted into place to form the slab. Usually they require a concrete topping to be cast above with mesh.
2 Columns - structural elements which support vertical loads, such as the weight of a building. Reinforced concrete columns are made by encasing a steel framework (reinforcement) within a concrete core.
You may hear the term 'starter bars' used on site. This refers to the reinforcement which is tied into a structural element like a slab.
Starter bars for a column which have been cast into an RC slab
Similar to slabs, there is the option of using pre-cast reinforced concrete columns which are manufactured off site.
These are lifted onto the starter bars and grout is poured into hollow tubes which have been installed in the factory and encase the steel.
3 Beams - structural elements designed to carry and distribute loads, such as the weight of the building. Typically used to support the floors, ceilings, and roof of a structure.
RC Beams
4 Load Bearing Walls - serving the same purpose of columns they support the vertical loadings exerted on a structure.
There are few key types of load bearing wall:
4.1 Shear Wall - a specific type of load-bearing wall designed to resist lateral forces, such as those generated by wind, seismic activity, or other horizontal movements.
They are strategically placed to provide stability and prevent the building from swaying or tilting during such events.
4.2 Core Wall - also referred to as a shaft wall. These can also be non-load-bearing wall and are designed to enclose vertical service elements, utilities, or other components such as elevators, stairwells, plumbing, electrical components, and mechanical systems.
View inside an RC shaft wall
They are often used as they create a dedicated and protected space for utilities while maintaining fire and smoke containment.
Steel superstructure
Steel superstructures are made up of some of the same basic elements as a reinforced concrete one, except they are constructed from steel manufactured off site. Namely, columns and beams.
A steel framed building
Slabs within a steel frame tend to be precast planks. This is referred to a composite slab:
Precast concrete slabs on a steel frame
A composite slab comprises of steel decking and a concrete topping is poured on top - usually with a layer of mesh.
Composite slab detail
As steel is delivered in sections which are limited to what vehicles can deliver them, they consist of many connections as below:
Example connection between steel column and beams
Steel frame buildings have become increasingly popular in modern construction due to their many advantages. They are used in a wide range of building types, from warehouses, factories, and high-rise office buildings to residential homes and sports facilities.
Timber superstructure
The primary structural framework of a timber superstructure consists of timber members, such as beams, columns, trusses, and joists. These components provide support for the floors and roof.
A timber frame building
Floors in a timber frame building may include timber joists or engineered wood products, which support the floor finishes and the loads placed on them.
Example of timber joints forming the floor
Masonry superstructure
A masonry superstructure consists of building elements made from materials like bricks, concrete blocks, or stone, which are bound together with mortar.
Reinforced block wall
Floors in a masonry superstructure building can consist of precast concrete blocks or beams that are placed horizontally across the span between load-bearing walls.
These blocks or beams are typically made from reinforced concrete.
View from the underside of a block and beam floor
Combination
In many cases, the final solution is a combination the above options. Some examples include:
Reinforced Concrete Slabs with Steel Vertical Elements: slabs are made of reinforced concrete, but the vertical elements like columns and beams are constructed using steel. This combination is used when steel's strength is required for the vertical load-bearing elements.
Masonry Walls with Reinforced Concrete Slabs: Masonry walls can serve as vertical elements, while the slabs are constructed using reinforced concrete. This combination is often seen in buildings with masonry load-bearing walls and concrete floor slabs.
Masonry Walls with Timber Slabs: Similar to the previous combination, masonry walls can be combined with timber slabs. This is common in traditional construction where masonry provides structural support.
Timber Frame with Reinforced Concrete Slabs: In some cases, a timber frame may be used for vertical elements (walls and columns), while the slabs are constructed using reinforced concrete.
Masonry Walls with Steel Slabs: Masonry walls can be combined with steel deck slabs to create a hybrid structure. This is less common but can be used in specific design scenarios.
Definitions
Substructure - the lower portion of a building or structure that is below ground level that supports the superstructure
Reinforced Concrete - concrete with embedded steel inside to increase strength and durability.
Timber trusses - structural framework composed of wooden members, typically arranged in a triangular configuration, that is designed to support the roof or the upper portion of a building
Joists - maximum weight/loading that a soil can support without excessive settlement or failure
Mortar - a paste-like substance that hardens over time and provides structural cohesion to building elements. Composed of three primary ingredients: water, a binder (cement, lime or a combination of both), and aggregates (sand or other fine granular materials).
Posts to Follow
We plan to go into more details on Superstructure and add sections on:
Logistics
Temporary Works
Build Sequence
Health, Safety & Environment
Quality
Programme
Commercial
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