HOW TO READ STRUCTURAL DRAWINGS: A DEEP DIVE FROM A TO Z

Structural drawings are a series of pages which explain and illustrate the structural framing of a building or structure including its strength, member size and stiffness characteristics.

If you are in the construction industry or renovating your own house, the ability to read structural drawings and plans is a very important skill to have and its relatively easy to learn.

When I was a wee Structural Engineer studying at university, reading structural drawings was not a skill my course provided. I found myself as a graduate engineer staring at linework having no idea what I was looking at

It wasn’t until several months into my career that I started to understand what it all meant and how to read Structural Drawings. This was largely a process of osmosis for me as being part of a busy structural engineering consulting firm I didn’t receive the “Structural Drawings 101” course, however dear reader, this is what I will endeavour to provide for you in this article.

As always, we need to properly define what we are going to learn before jumping in…

What are Structural Drawings?

Structural drawings are a series of pages which explain and illustrate the structural design intent of a building or structure. The aim of a good set of structural drawings is to provide the reader with enough information to:

  • Construct that building or structure if you are a contractor
  • Provide enough information to understand the size, shape and layout of the structural framing if you are an architect, part of the wider design team or a developer/owner.

To construct a building, many disciplines need to be coordinated, not just the Structure and Architecture. A set of structural drawings are usually read along with drawings from these other disciplines including:

  • Mechanical: Ducts for heating and cooling, ventilation and smoke systems etc.
  • Hydraulic: Sewer, hot and cold water supply, fire sprinkler system etc.
  • Electrical: High and Low voltage power, lighting etc.
  • Data: Smart building systems, building management system, security system etc.
  • Vertical Transport: Lifts, elevators, dock levellers, travellators etc.
  • Civil: Road and pavement details as well as storm water drainage.

Structural drawings are not to be confused with architectural drawings, these separate drawing sets provide very different pieces of information…

What is the Difference Between Architectural and Structural Drawings?

In general terms, Structural drawings show detailed information on the building elements which provide support and stability to the structure including material strength grades and reinforcement while Architectural drawings provide detailed information on the buildings aesthetics and usage such as colours, patterns and finishes.

For example, a load-bearing column is shown on both the Structural and Architectural drawings however the information provided for that column between the two sets of drawings is quite different:

  • In the case of Architectural drawings, the dimensions and appearance of the column are important to the architecture of the building so information such as the following is illustrated:
    Dimensions: Length, width or diameter.
    Appearance: Paint colour if its a painted finish or details on the materials if cladding is required.
  • In the case of Structural drawings, the strength and stiffness characteristics of the column are important so information such as the following is illustrated:
    Concrete/Steel Grade: The strength grade of the material used weather it be concrete, steel or timber.
    Reinforcement: In the case of a reinforced concrete column; the quantity, size and grade of the vertical reinforcement and ligatures.

Here is an example of an Architectural (top) and Structural (bottom) drawing illustrating the same office floor in the same building…

Example of an architectural plan drawing
Example of a structural plan drawing.

These examples are taken from a typical floor in an office building. At the bottom of the drawings is the location of the lift/stair shaft including the bathroom facilities.

You can see that the architectural drawing goes into much more detail on the look and usage of this zone with specifications on toilet pan locations, tiling, cubicle doors and so on. All of these elements are non-structural so they don’t appear at all on the structural drawing. only the structural slab thickness is shown (in this case 250mm thick or 9.84inch thick for those playing at home in the US).

Outside of the lift/stair shaft on the top of the drawings is the office floor plate. Its planned to be an open space office ready for the tenant to fitout exactly how they like with flexibility for partition walls for meeting rooms, office cubicles etc. That means that the base architecture for the office floor plan layout is carpet and ceiling with little else. The structural drawings on the other hand appears to have a bit more going on in this area, with slab thicknesses indicated (180-200mm or 7.08-7.87inch) as well as some additional dashed lines… this we will get into more detail later on.

General Drawing Elements

First we will go through the general drawing elements which are usually common across the disciplines.

Drawing Reference Grids:

Reference grids are like the glue that ties all of the engineering and architectural drawings together. They provide reference points which helps the reader identify the same locations on each disciplines drawing set.

The reference grids are read similar to the old fashioned game of battle ship; a row of grids following sequential numbers (for example running horizontally) and a row of grids following sequential letters (for example running vertically).

This means that a grid reference of E2 on the architectural drawing should be the exact same location in the building as the grid reference E2 on the structural drawing (you sank my battle ship, or in this case, column!)

Drawing reference grids are read similar to the old school game of battleship
A grid reference of E2 on the Architectural drawings (left) is the exact same location within the building as grid reference E2 on the Structural drawings.

Face Sheet / Title Page:

Building drawings are read similar to a book, and just like a book the drawings need a cover page. This is often referred to as a Face Sheet or a Title Page.

The face sheet will often contain a drawing contents table (similar to a book; a list of drawing titles and their corresponding drawing number).

The Face Sheet will also have the name of the project (often simply the project address or if the developer has started to brand the development, it may be the projects brand name).

The consultant may also use this opportunity to show an overall site plan to give the reader context of where the site is located and the neighbouring buildings nearby.

If the project has been documented by the consultant in a 3D modelling package, a 3D perspective view of the building or structure may be displayed on the face sheet as well.

Example of a face sheet which is the first drawing in the structural drawing set.

Title Block:

A title block is usually included on every drawing in the structural drawing set (and all other discipline’s drawings for that matter)

An example of a drawing title block.

The title block is located on the bottom boarder of the drawing or the right hand side (depending on the drawing size/orientation and set-up) and will generally include the following key information…

  1. Revision Box: This portion keeps track of the revision history of that particular drawing. Here you can see the revision number/letter history, a brief summary of what the changes were for that revision (in the amendment section) and the date that that revision was issued.
  2. Consultants Company Logo: Here may include the organisations logo, address, discipline and professional registration number (required for practicing engineers dependant on the state and country they are in).
  3. Copyright Disclaimer: There is generally an inclusion of some form of intellectual property statement protecting the rights of the drawing creator.
Example portion of a drawing title block

4. North Point Indicator: In the case of a floor plan, this shows the orientation of that plan in relation to true north. This is generally left blank for detail drawings, elevation drawings and general notes drawings.
5. Development Address: Contains the projects address and sometimes is development name as well.
6. Name of the Drawing: An explanation of what the title of the drawing is.
7. Name of the Client: Generally the name of the person or company who has engaged the consultant to produce the drawings and the design.
8. Drawing Size and Scale Details: Two pieces of information; the intended drawing sheet size and the scale the drawing is at when printed at that sheet size (more on drawing scales later on).
9. Quality Assurance Information of the Drawings: Contains the QA and administrative information for the drawing including the initials of the people who drew it and checked it. This section may also include the project number which is usually a number assigned by the engineering consultant firm which follows its company project numbering system. Finally the drawing number and revision is also provided.

General Notes:

After the face sheet, a series of general notes sheets then follow and make up the first few sheets of the drawing set.

General notes drawings provide very important information on the structural detailing of the building. The general notes provide project-wide specifications and, for efficiency purposes, they are provided in a consolidated location to prevent the need to repeat them on later drawings multiple times. This information may include the following (and more!):

  • Concrete cover/grade/slump
  • Structural steel grades
  • Reinforcement and post-tensioning grades
  • Specifications for the performance of formwork
  • Founding depth and material for foundations
  • Standard lap lengths of reinforcing bar
  • Performance specification for shoring systems
  • Structural loading assumptions
  • General notes and guidance on how to read and interpret the drawing set

Typical Details:

Immediately following the general notes section are a series of typical standard detail sheets. These standard details are usually typical repetitive details which will be adopted at multiple locations on the project. These details also generally match the common construction approach used by the local industry where the drawings were produced and therefore are usually used from project to project on multiple occasions.

Below is a standard detail which you may find in the typical standard details portion of the drawing set, it is a cross-section looking through a slab with an edge beam located to the left. You will notice that reinforcing bar sizing and spacing is not provide, however the general arrangement of the reinforcement and the lapping requirements are. This allows the detail to be adopted at multiple locations on the project, with the detailed bar spacing and size requirements being illustrated at the specific location later in the drawing set.

Example representation of a typical structural detail.

General Arrangement Plans

Now that we are familiar with the general elements which make up the drawing set, lets start to get into details.

A structural general arrangement plan is a birds-eye view of the floor, roof or foundation arrangement (depending on which plan it is). It gives the reader a visual representation of the structural framing requirements for that level.

Lets take a look to see how a concrete framed floor may look on a structural general arrangement plan (often called a GA plan), lets not overwhelm ourselves and just look at a small portion of a larger floor plan…

Ok there’s a lot going on here! lets break it down into individual elements…

  1. Grid System: Easy, we know this already!
  2. Revision Cloud: The revision cloud is usually coupled with a revision “bubble” (the upside-down triangle with the letter “C” in it). The revision cloud outlines a portion of the drawing which has been altered, in this case something within this clouded zone has either been added, deleted or modified since the last revision (which would have been revision “B”). Since the revision cloud bubble says “C” that would make the drawing that this snapshot has been taken from also revision “C”. In order to see exactly what has changed at this location, you will need to reference the revision “B” drawing and compare the two.
  3. Beam Tags: This is the “name” of the beam and usually it starts with a letter “B” (for beam) followed by a number. The GA plan is usually provided with a beam schedule, which is a table of beam tags with their corresponding beam depths/widths (an example is shown further below). The reason for not providing the dimensions of the beam on the general arrangement plan itself is to reduce the visual mess on the drawing to make it easier to read (although some engineering consultant firms will provide the dimensions on the GA and not use a schedule, depending on that offices drawing standard).
  4. Slab Depth Tag: Simply provides the structural depth of the slab.
  5. Column Tag (Under): Similar to a beam tag, the column tag is the columns “name” and usually starts with a “C” for column. The “U” in this case indicates that this is the column tag for the column beneath this floor. This is another main difference between structural and architectural drawings; since the columns beneath are what supports this very floor, it is an important structural element as far as this floor is concerned. So therefore structural drawings will often show the reader what is happening not only above the floor but beneath it as well.
  6. Column Tag (Over): Same for Column Tag (Under) however this is for the column above the floor.
  7. Soffit Step Line: A slab soffit is simply the bottom surface of the slab. A soffit step line is an indication that the slab soffit is stepping up/down at this location. Any steps or structure beneath a floor is usually shown as a dashed line.
  8. Top Surface Step Line: This is also a step line, however instead of occurring on the bottom surface of the slab, it is a representation of a step which is occurring on the top surface of the slab.
  9. Step Indicator Tag: It is sometimes not clear which portion of the slab either side of a top surface step line is the high side or the low side. For this reason, a step indicator tag is provided which shows a mini cross-section view of how the step is orientated. in this example above the left-hand-side of the top surface step line is higher than the right-hand-side.
Example of a structural beam schedule
Example of a reinforced concrete column schedule

Lets take a look at another floor with a different structural framing type this time. The following image is a snapshot of another typical office floor however the structure is a composite steel floor system. Also the drawing is produced by a different engineering consultant firm, you can see there are some slight variations in the beam and column tag format with all letters instead of a mixture of letters and numbers.

  1. Beam Tag: The same as previous however notice “SB” is used instead of “B” (different engineering firms have different drawing standards). The beams are indicated as dashed lines as they are beneath the composite slab. Each beam is shown as three separate dashed lines, the outer lines represent the extremes of the beam flanges and the centre line indicating the centre-line of the beam.
  2. Beam Tag: Same as previous
  3. Column tag: Same as previous
  4. Slab Depth Tag: Indicates the depth of the composite slab, and is also coupled with a symbol which looks like something Zorro may have written. This arrow type symbol indicates the span direction of the metal tray deck (in this case the span direction is up/down of screen).

Lets take a look at another drawing example but this time with a couple new symbols…

Example portion of a structural drawing indicating void cross and section bubble.
  1. Void Cross: Two solid crossing lines generally represent a void in the structure (better known as a hole). The example above is showing a large rectangular hole in this floor slab.
  2. Section Bubble: A section bubble indicates that a cross-section has been drawn for a specific slice of the slab and is located within the drawing set. There are a few pieces of information here… the section is given a unique identifier (in this case G.04 which is basically the name of the section). The bubble also gives a drawing reference where this section is located (in this case the drawing number is S-P3-N-2114). The orientation of the bubble which is pointing left of screen indicates that the cross section has been drawn assuming that the viewer is looking to the left of screen. The corresponding section bubble tail indicates how wide the section has been drawn (the extent of the section).

Turning to drawing number S-P3-N-2114 in this example drawing set and looking for section G.04 allows us to see what this section looks like in order to better understand what is shown on this general arrangement plan…

Now we can see the section view of this slice, we can also see our large hole/void within the slab which was indicated on the GA plan.

What are Drawing Scales?

A scaled drawing is a drawing which properly represents an objects size and proportions reduced or enlarged by a certain percentage. The scale of that drawing is an indication of the percentage that the drawing is smaller or larger than the real-world object. The scale is represented by a unit length on the drawing, followed by a colon (“:”) then by the corresponding length of the real-world object.

In order for structural drawings to fit on a manageable sized drawing sheet, the drawing is usually a small fraction of the real-world size. A scale of 1:100 is a very common scale to use for a structural framing plan. That is, a 1mm measurement taken on the drawing represents a 100mm length of the real-world object.

It is very important to understand scales when measuring off from printed drawings. If the drawing is not printed on the correct sheet size the intended drawing scale is not accurately represented. Sometimes it is preferable to print a drawing on a smaller sheet size as smaller sheets are easier to store and carry. If you would like to have a hard copy of the drawing on a smaller sheet size, it can still be measured using a scale ruler, however the scale needs to be converted accordingly depending if the sheet you are printing to is smaller or larger than the required original drawing sheet size….

Drawing Scale Converter

SizeA0A1A2A3A4A5A6
A0100%71%50%35%25%18%12.5%
A1141%100%71%50%35%25%18%
A2200%141%100%71%50%35%25%
A3283%200%141%100%71%50%35%
A4400%283%200%141%100%71%50%
A5566%400%283%200%141%100%71%
A6800%566%400%284%200%141%100%

Conclusion

That was a run through of what I learned in my first few months being a structural engineer fresh out of University all those years ago. I hope some of you out there have found this useful and sped up your learning experience into this small fraction of the art of structural engineering.

Please feel free to leave a comment below on topics you would like to see covered on future posts on Sheer Force Engineering.

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Quentin Suckling is a full time practicing Structural Engineer based in Melbourne Australia. He has been practicing in the local market at tier 1 engineering consulting firms over the last 16 years.

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