What Does a Structural Consultant Do?

Most people meet a structural consultant for the first time when an approval form asks for an engineer’s signature. That is late. The structural decisions that matter most, from the type of foundation to the size of the ground floor columns, are made long before anyone signs a drawing. This article explains what a structural consultant does, in the order the work happens, and what to ask before you appoint one. For the wider picture of a building project, see the six disciplines DDA covers.

Who does what on a building project

Three roles are often confused, and a decision that lands with the wrong person costs money.

Architectural and structural design work best when they proceed together, so a column the structure needs does not land in the middle of a living room, and a room the client wants does not demand a beam the frame cannot give.

What a structural consultant does, in five parts

The work runs in a fixed order, because each step depends on the one before it.

• Load analysis. Every load the building carries is traced from the roof down to the soil: the weight of the structure itself, the people and furniture in it, and the sideways push of an earthquake. Engineers call these gravity and seismic loads.
• Foundation design. The foundation spreads all of that load into the ground. Firm ground can often take a shallow foundation, such as a pad footing under each column. Soft ground needs a deep foundation, such as a group of piles. The soil decides which.
• Concrete and steel detailing. Concrete is strong when squeezed and weak when pulled, so steel bars go where the pull is. Detailing sets the size, number, spacing and position of every bar, and how much concrete covers it.
• Construction drawings. All of this becomes drawings: framing plans, sections and reinforcement details. These are what the contractor works from on site.
• The code check. The design is checked against the Bangladesh National Building Code before it is issued.

That last step is not paperwork. BNBC 2020 replaced the 2006 edition, came into force at once, and sets minimum standards for design, construction and the quality of materials. It also says who is responsible. Under the code, the design documents for a building are prepared and signed by the engineer responsible for its structural design, and every structural drawing carries that engineer’s signature and date. The full code is available to download from the Housing and Building Research Institute.

Why every design in Bangladesh allows for earthquakes

Bangladesh sits where the Eurasian, Indian and Burmese plates meet, as a 2022 seismic hazard and microzonation study sets out. The region has a record of large earthquakes, including the 1897 Shillong earthquake, which the same study puts at moment magnitude 8.1. BNBC 2020 itself notes that earthquakes stronger than magnitude 7.0 have affected parts of Bangladesh in the last 150 years.

The code turns that history into numbers. It divides the country into four seismic zones, each with a zone coefficient that sets how strong a shaking the design must allow for. Dhaka falls in the moderate zone, with a coefficient of 0.20. Chittagong falls in a severe zone, at 0.28.

Why the soil test comes before the foundation

A foundation is designed for the ground under it, and nobody can see that ground from the surface. Two neighbouring plots can sit on very different soil.

BNBC 2020 makes the investigation a requirement. Sub soil investigation, describing the character, nature, load bearing capacity and settlement of the soil, is to be done before a new building is constructed, and before the foundation of an existing one is altered. A soil report gives the structural consultant three things:

• Bearing capacity. How much load the ground can carry before it gives way.
• Settlement. How far the ground will compress under the building, and whether it will compress evenly.
• The layers below. What lies at depth, which decides how deep piles must go if they are needed.

Without that report, the foundation is a guess. A guess either spends money on a foundation bigger than it needs to be, or saves money on one that is too small. Neither shows until the building is standing.

What changes when the building changes

Can a contractor add a floor if the columns look strong enough? No. A frame is designed for a stated number of floors and a stated use. Add a floor and every column, beam and footing below it carries more than it was designed for. Turn a home into a warehouse or a factory and the floor loads change too.

The cost of getting this wrong is on record. When the Rana Plaza building collapsed on 24 April 2013, the International Labour Organization reported 1,127 lives lost. A 2019 qualitative study of survivors, drawing on earlier reports, records that floors were being added to the top of the building at the time of the collapse, weakening the overall structure.

• Extra floors. An added storey needs the whole frame and the foundation rechecked before work starts.
• Change of use. A new use with heavier floor loads needs the same check.
• Removed walls or columns. Taking out a column or a load bearing wall to open up a room moves load somewhere the design did not plan for.
• A half built project. The existing drawings and what has already been built are reviewed before an engineer accepts responsibility for the structure.

What to ask before you appoint a structural consultant

• Will the structure be analysed for gravity and seismic load to BNBC 2020
• Will a soil investigation be done, or an existing soil report interpreted, before the foundation is designed
• Will the engineer responsible sign the structural design documents
• Do the drawings include full reinforcement details, not only member sizes
• Who checks on site that the work built matches the drawings issued
• Who issues structural certification when the building is complete

DDA follows the same sequence on every project: a free consultation, then survey and soil, design and drawings, and supervision and certification. More than 200 buildings across Bangladesh have gone through it since 2009, and the portfolio shows a selection. You can read more about DDA and its six disciplines.

The first step costs nothing. Bring the plot size, the intended use and the number of floors to a free consultation, and you get a written response within 24 hours setting out which disciplines the project needs.

Frequently asked questions