Constructing a multi storey building requires careful coordination between design disciplines, site preparation, structural framing, and finishing trades. Each phase must be executed with precision to ensure safety, durability, and compliance with building codes. The process begins with the design of key structural components – formwork systems, staircases, deep beams, and slabs are all detailed before any ground is broken. Architectural and structural drawings must be cross-checked for consistency regarding column locations and beam alignments. Modern analysis tools such as SAP2000 and ETABS model the structure to verify that all members satisfy strength, deflection, and serviceability limits. Understanding how types of bracing systems in multi storey steel structures provide lateral stability is one critical part of the design, but the overall workflow spans everything from foundation excavation to finishing works. This article outlines the essential stages involved in bringing a multi storey building from concept to completion.
Excavation, Layout and Foundation Preparation
Once the design is finalised and approvals are obtained, site work begins with excavation. This involves digging trenches and pits for foundations and basements using heavy machinery such as JCB excavators, typically hired on an hourly basis. The excavation depth is set to precise levels determined by the structural drawings – the formation level at an escape site, for instance, might be set at 219.825 mm. After digging, the exposed surface is levelled through a process called surface dressing.
Plain cement concrete (PCC) is poured over the levelled area to create a clean, firm working platform. Once the PCC has set, the column and foundation layout is marked on the surface. Reinforcement for raft foundations and column footings is then laid in position according to the structural drawings. For a full breakdown of the sequence from ground slab to roof, a guide on how to construct a concrete building a step by step guide provides a detailed walkthrough of every stage.
Critical checks during excavation and layout:
- The layout dimensions should be verified against the approved architectural plans before any concrete is poured.
- Any mismatch between architectural and structural drawings regarding column positions must be flagged and resolved immediately.
- The stability of adjacent temporary structures near the excavation edge must be inspected before proceeding.
- Before laying raft reinforcement, a brick shuttering wall should be constructed, with soil backfill on the outer side for lateral support.
- The orientation of chair bars in the raft must be checked to ensure correct top and bottom cover is maintained.
Column Reinforcement and Casting
Column construction begins as soon as the foundation concrete has gained sufficient strength. The process starts with marking the column positions on the raft surface and fixing starter bars that anchor the column reinforcement to the foundation below.
Key steps in column reinforcement and formwork:
- Column ties and link bars are positioned according to the column reinforcement schedule and general specification notes.
- Where displacement of main bars occurs, L-shaped bars are provided to maintain the correct cover and alignment.
- The plumb of the column formwork is checked with a spirit level or laser plumb before concreting begins.
- The exact height of each pour is calculated to avoid cold joints between successive lifts.
- Caps at the top of column forms are avoided where possible to simplify concrete placement and vibration.
Slab, Beam and Formwork Construction
Once columns for a given storey are completed, construction moves to the slab and beam system for that level. The sequence follows a standard pattern:
- Beam bottom forms are placed on the column heads first, followed by slab formwork spanning between the beams.
- Reinforcement steel for beams and slabs is laid in accordance with the bending schedule, with care given to cover blocks and chair supports.
- A camber of approximately 5 mm is provided at the centre of long-span slabs to offset dead load deflection.
- The casting of the slab is discontinued at L/3 from the beam support to control cracking at the critical moment region.
Shuttering systems must be designed to support the full weight of wet concrete, reinforcement steel, and construction live loads. Table forms, flying forms, and conventional timber shuttering are common choices depending on floor area and repetition of layout between storeys. Proper stripping times must be observed based on concrete cube test results to avoid overstressing the young concrete.
As the building frame rises, attention must also turn to the building envelope. The building wrap selection installation and performance of weather resistive barriers for modern building envelopes should be planned early so that facade installation keeps pace with structural work. Integrating weather barriers into the construction schedule prevents delays and protects interior finishing from moisture damage.
Formwork for columns relies on steel or plywood shutters held in position by yokes, bolts, and bracing. The system must resist the lateral pressure of wet concrete without excessive deflection. Once the concrete reaches adequate strength, the formwork is stripped and wet curing begins, typically for a minimum of seven days. Understanding how horizontal structural elements connect to the vertical load path is essential at this point. The floor systems used in multi storey steel structure buildings differ from those in reinforced concrete frames, but in both cases the column-to-floor connection must effectively transfer gravity and lateral loads.
Joints, Water Bars and Interface Treatments
Several important detailing elements must be incorporated into multi storey buildings to accommodate movement and prevent water ingress at construction joints.
Key in Columns
Since the height of a column is typically too large to cast in a single operation, construction joints are necessary between successive pours. A key is a small depression intentionally left on the concrete surface at the joint location. This key provides mechanical interlock between the old and new concrete, ensuring a sound structural bond.
Expansion Joints
Concrete undergoes volume changes due to temperature fluctuations and drying shrinkage. Expansion joints relieve the internal stresses produced by these movements. Buildings longer than approximately 45 m are typically provided with one or more expansion joints. The joint filler material is usually an armour board with a thickness of 25 mm, which compresses to accommodate movement while maintaining a seal.
Water Bars
Water bars are installed in retaining walls and basement slabs at construction joints to prevent moisture from migrating through the joint into the building interior. They are typically made from rubber or PVC and are placed at mid-depth of the concrete section. Water bars are especially important at joints between adjacent tower blocks or between retaining walls and the main structural frame.
Binding Materials at Material Interfaces
The junction between concrete and masonry is vulnerable to cracking because the two materials have different coefficients of thermal expansion. Chicken wire mesh embedded at this interface controls crack development and ensures better bonding. Similarly, where drainage pipes pass through outer walls, lead keys are used to accommodate differential movement between pipe and concrete. In toilet and kitchen areas where the slab is sunken, all joints are packed with waterproof, non-shrinkable sealant to prevent leakage into floors below.
| Component | Primary Function | Common Material |
|---|---|---|
| Key in Columns | Ensure bond between successive concrete pours | Depression formed in wet concrete |
| Expansion Joint | Relieve thermal and shrinkage stresses | Armour board (25 mm) |
| Water Bar | Prevent moisture migration through joints | Rubber or PVC strip |
| Binding Mesh | Control cracking at concrete-masonry interface | Chicken wire mesh |
| Lead Key | Seal around pipe wall penetrations | Lead |
For existing multi storey buildings that require structural upgrades or have experienced deterioration, building retrofitting structural strengthening methods for seismic upgrades and building rehabilitation offer proven techniques for improving the capacity of columns, beams, and beam-column joints. Techniques such as jacketing, fibre-reinforced polymer wrapping, and steel bracing can extend the service life of a structure significantly.
Waterproofing and Protective Treatments
Waterproofing remains one of the most technically demanding aspects of multi storey building construction. The use of plasticisers, superplasticisers, and air-entraining agents in the concrete mix reduces permeability by lowering the water-cement ratio, which improves resistance to water ingress. Approved waterproofing compounds available in the market include pidilite, cico, fosroc, baushimine, and unitile. Waterproof cement paint such as super snowcem can be applied to exposed external surfaces for added protection.
Waterproofing sequence for garden and terrace areas:
- The terrace surface is levelled and compacted to achieve maximum soil density.
- A layer of plain cement concrete mixed with a waterproofing compound such as Tape Crete is laid as the base.
- Fibrous plaster is applied over the PCC layer to create a smooth substrate.
- Bituminous sheets are heat-welded onto the plaster to form a seamless waterproof membrane.
- Drainage pipes are placed over the bituminous layer with a suitable slope and covered with geotextile fabric.
- A second plaster layer is applied above the drainage pipes for protection.
- 40 mm aggregates are spread over the plaster as a drainage layer.
- Another layer of geotextile fabric is placed over the aggregates, followed by a layer of sand.
- Topsoil mixed with fertiliser is placed on top for landscaping and planting.
This multi-layer waterproofing system provides redundancy against potential leaks. The combination of a bituminous membrane, geotextile separation layers, and graded aggregate drainage ensures that water is directed away from the structural slab and into the drainage network. Regular inspection of the waterproofing layers during construction is essential because defects at this stage are extremely difficult to rectify after landscaping is complete.
The construction of a multi storey building demands careful attention at every stage, from foundation excavation and column casting to joint detailing and waterproofing. Each phase must be executed with proper quality control measures, consistent supervision, accurate interpretation of drawings, and strict adherence to material specifications. The success of the entire project depends on the seamless integration of these stages. For projects of a smaller scale that still require thoughtful structural planning, building a multi purpose guest suite ADU with vaulted ceilings and reclaimed materials demonstrates how the same principles of structural integrity, joint detailing, and waterproofing apply across different project scales. Understanding the full construction sequence helps builders, engineers, and project managers deliver safe, durable, and code-compliant multi storey buildings.