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Common Structural Design Mistakes beginners make


Many aspiring Structural Engineers asks me about the most important skill that they should possess for success. There are many things that one has to do to be successful. However, there are also a few things that you need to adopt early in your career to ensure you are not a failure. Again, there are many things to be mentioned about this. However, in this blog am discussing about the need of introducing a process to identify errors a structural engineer can make early in career.

Everyone makes mistakes but be sure that someone shouldn’t pay for your mistakes. Silly negligence or ignorance in the design of structure may become a reason for the loss of lives, money and property. The collapse of a building may be due to insufficient strength, improper construction, use of defective materials, environmental factors, and faulty design of structures. As we know Prevention is better than cure, we should be attentive while doing the analysis and design. In this blog, we will see some general mistakes in the process of designing and detailing and how you can avoid making them. Practice this check process to ensure you don’t make mistakes.

Wrong Measurements and unit conversion

Sometimes the dimensions in drawings may be wrong. Blindly following the values for design will result in structural issues and problems and sometimes structural failure. For example, the spacing between the columns may be wrongly measured from a drawing while doing the analysis model. This error if not captured, will result in wrong force interpretation and structural design. This can be some times conservative and many times critical resulting in structural issues and failure.

Faulty unit conversions and incorrect scales also result in defective design. If the software makes everything an automated process, don’t think that it is always error free. it’s better to check all the proper measurements before starting a project.


Solution:

  • Never be casual while modelling and analysis. Be away from distractions like phone.

  • Ensure the drawing you follow are the latest, coordinated and checked by you and a senior.

  • Never measure a drawing and adopt dimensions unless you have validated it to be in scale.

  • Ensure you check the active dimension style if you are using AutoCAD

  • Ensure you logically appreciate the column positions, dimensions and so on.

  • Try to import the plan from AutoCAD than measuring the drawing and modelling.

  • If the drawing is in a different unit than what you are using for analysis, do the conversion in CAD itself than manually converting it each time you measure.

  • Use the best system and software for analysis. Long time and laborious work can irritate you and that can affect your attention level. This is a proven fact.

  • Use tools like Revit for drawing production to reduce mis matches and discrepancies.

Mistakes in Modelling


The structural units used as explained above is a reason for many modelling mistakes. There are many other reasons of modelling errors. Modelling errors can be classified in to 2 types.

  • One due to real modelling errors.

  • One due to lack of technical understanding.

Modelling errors

This arises to real modelling errors due to lack of concentration and attention. Overlapping of beams and slabs etc. can be classified as this type of error. Other examples are listed below.

  • Wrongly assigned materials and properties.

  • Missing Assigning supports.

  • Geometric measurement errors.

  • Load application errors.


There are many more errors that can occur varying from user to user.

If you are using ETABS, the geometric errors can be captured by an etabs error check. However, many don’t know how to check errors in ETABS in the correct way. You can see the video to understand how to check error in ETABS. Subscribe to the Youtube channel.


Error due to lack of understanding of Structural concepts


These errors occur when one doesn’t have enough experience and enough technical understanding. Experience and knowledge cannot be replaced by quick fixes or software. You need to know structures fundamentally to appreciate it and use the design software to suit the real performance at site. Some examples of points that you should know to use software like ETABS or STAAD Pro is mentioned below. Without knowing these basic principles, there is no meaning in learning an analysis software alone.

  • How do I decide the column positions?

  • How do I orient columns in a project?

  • When do I use membrane option for slabs and when shell thin?

  • When to fix and when to pin the base of a column?

  • What is stiffness modification? Should I modify stiffness?

  • When should I release moments? Note : I have a separete blog & video in the blog section

  • Do I need a shear wall in a building?

  • Releasing torsion without proper understanding

  • Using wrong methods to rotate columns. Many rotate columns in STAAD Pro by defining the smaller dimension of columns as depth instead of using beta angle. Same mistake many civil engineering students do in ETABS modelling also and this results in swapping of major moments and minor moments in columns. I will be making a video regarding this soon. You can subscribe to my mail list if you are keen to receive this structural design tutorial.

There are many more structural errors that can occur based on user’s structural design experience and understanding.


Mistakes in load calculations


If a single error happens in the calculation, it will entirely affect the final result. The design of the structure includes many computations starting from the basic dimensions, load take down, shear, bending moments, and many values. I have seen many students still lack basic mathematical concepts. As calculations, values taken down for each calculation should be in proper units and accurate.

Many are still confused with the load calculations. General confusions and mistakes are listed below.

  • How to calculate the stair loading

  • How to calculate and apply water tank loads

  • Some at entry level are confused when to use kN and kN/m2

  • Mistakes while adopting Live load reductions.

Even though everything is now computed with software, one should be aware of the proper values.


Wrong Load paths & Alternate Load Paths


Loads on a structure are transferred to foundations and finally to the ground. Every load may take a continuous path between the elements of a structure. Everyone is likely to take the shortest route and hence the load too. Structures always perform well if there is no interruption in the vertical and horizontal load path. There should be a continuous and direct way for loads which arises the need for a symmetrical and simple plan of structure. Such loads will ensure the adequate strength and relative stiffness of a structure. Improper connection, large openings, and defective elements of structure may disrupt the smooth transfer of loads. Specific provisions for many structural elements like walls, diaphragm, connections are adopted as per the seismic code. While designing, you should consider the proper load path and of course the proper load combination and safety factors. Imposed loads on the structures depend on the occupancy and type of buildings.

Many times, the importance of the building demands provision of alternate load paths for bridging a local failure. Disproportionate collapse control is to be looked up on by removing key elements. I will be creating a new video to explain this. Join my structural workshop list at the end of this blog to get regular updates.

Neglecting basic code provisions


Every element of the structures should be designed as per provisions in the code. Many of the cases illustrated in codes are getting neglected over the general practice of design methods. One should be aware of proper code provision before starting a design project.

There are some lesser-known code provisions which many structural engineering consultants miss out. Note : I have a separete blog & video in the blog section about this topic

Other than that, many fail to appreciate many code provisions involving the points listed below.

  • Minimum column sizes as per 13920 ductile detailing clauses

  • Stability calculations and requirement

  • Stiffness modifications as per 1893 2016

  • Column beam capacity ratio – Many ignore this IS 13920 code provision for ensuring ductility.

  • Calculation of effective length of column as per IS 456 – IS 456 adopts moment magnification method for accounting slenderness moment. To decide if a column is slender, one needs the effective length. After this for calculation of slenderness moment too, we need the effective length. Most engineers calculate this effective length wrongly with out accounting the sway index calculation.

Result Interpretation


If you are using tools like ETABS or STAAD Pro, you need to know how to interpret the results from it. You also need to know how to provide the right input parameters to get the correct results. Both of these are inter-related and quite important. Without properly appreciating these you can have quite a lot of errors in your design. Common mistakes listed below.

  • Wrong parameters as effective length for column design.

  • Not reducing the moments to the face of the columns. ETABS does this automatically

  • Using moment envelopes wrongly for design of columns

  • Taking down reactions from force envelopes for sizing of Foundations.

There are many more common result interpretation questions. If you have any more points to add to this structural blog, please log in and comment.


Mistakes in detailing and drawing



Drawings are a design engineers communication tool. Whatever good things you do in design won’t be conveyed or even appreciated unless your drawings are not the best. Many young engineers consider drawing as a non-engineering job. You are failing yourself by doing this. The last bit but the most important for 2 reasons.

  • Your client probably doesn’t know ETABS or STAAD Pro or your struggle to meet that desired mass participation. He has only one means to appreciate what you do and that is a drawing.

  • A wrong drawing can create even a failure.

Here are some points you need to be careful and understand.

  • Many times, incomplete drawings, improper labeling, and annotation can confuse the site.

  • Notes, specifications, and details should be properly mentioned in a drawing.

  • A proper bending schedule should be included. Label the diameter of bars, spacing, and other details properly.

  • It’s recommended to use available grades and the size of bars.

  • If any beam and column joint, wall intersections, corners, openings, etc., try to give an enlarged view of those details.

  • Proper cover values should be mentioned.

  • The mistake may happen while editing the drawings.

  • It is very common to omit some edited works while preparing detailed drawings.

  • The diameter of bars should be checked in plan and sections properly.

  • Checking and proofreading should be done thoroughly before sending the drawings to a site.

  • Ensure anchorage lengths are properly calculated and conveyed

  • Ensure the laps are staggered. See the blog section for another blog on this topic.

  • Use a modern BIM tool like Revit to ensure there are no discrepancies and latest revisions are tracked.

Less attention to soil investigation reports


As Structural engineers, we should thoroughly check the geotechnical investigations from where we get the parameters for foundation design. Errors in soil reports may lead to incorrect soil strata and water table identification and further incorrect Bearing Capacity and adoption of wrong type of footings.

The type of foundation and its depth can be determined based on the bearing capacity, settlement values of the soil. If the structure rest on some weak soil strata, recently filled strata, shallow depth or soil with no preloading history results in the subsequent movement of the structure and causes uniform or differential settlement. There are a lot of examples of building failures due to such differential settlement. Swelling and shrinkage properties of soil also need to account while designing the structure. For such type of soil, i.e., expansive soils, foundation design criteria will be different. Inadequate detailing of reinforcement, construction joints, and movement joints, settlements, unequal supports also fails Foundation.

It is mandatory to have a Geotechnical consultant on board. He can take correct decisions on the points listed below

  • Number of bore holes needed for a project

  • Kind of soil

  • SBC of soil

  • Subgrade modulus of soil (The spring constant while modelling in ETABS)

  • Recommendation on type of footing.

  • Stability of slopes

  • Earth retaining methods

I have written another blog on soil parameters in the blog section.

Lack of proper communication & coordination


A structure is a result of a team work. Proper communication between an architect and a structural engineer and all stake holders including the contractor is of importance for the wellbeing of the structure.

The general challenges in coordination are as below

  • Engineers are late to be on board and many times architects would have frozen the architectural scheme. So, if we are late, attend to the scheme on priority and point out the deficiency so that any needed correction can be done as soon as possible

  • Be a great listener, client’s perception of load and structural design is different from yours. You need to pick every detail from what he says.

  • You need to ask the right questions at the right time.

  • You can have considerations but not assumptions. Read more in another specific blog

  • Detect clashes with services pipes and communicate in advance where you can probably provide sleeves.Read more in another specific blog

  • Co-ordinate real time using BIM tools like Revit

  • Always explain the additional value for your structural suggestions

Buildability

Many engineers never care if what you design has a challenge in construction. If you push some thing which is not buildable, that can result in mistakes at site and create structural issues.

Some common challenges of buildability are listed below.

  • Congested detailing of column beam junctions

  • Lack of proper studies of site interfaces

  • Clashes with existing adjacent footings

How can you avoid errors?


As a beginner, it is difficult to ensure not to make errors. However, one should do the best to reduce the errors. You can set a personal standard for focusing on the kind of errors you are making and work up on improving. Just follow a standard any company follows in their consulting process at your individual level too. Some of the good practices below.

  • Always focus on your work without distractions.

  • Take enough breaks to increase your attention.

  • Ensure you know your strength and weaknesses

  • Seek help when in doubt. There is nothing wrong in seeking help.

  • Keep a check list for your modelling process on what you have erred before

  • Use easy cross checks to validate your results like matching reactions with a quick hand calculation

  • Ask your seniors to validate your work

  • Keep engaging in discussions

  • Study as many drawings and visit sites to get a feel of what is built in general.

Summary

There are many more things that an aspiring structural engineering student should focus. You can join my community here to be mentored on these kinds of structural concepts. I provide daily and weekly tips on structural concepts in civilera forums and structural groups. If you are looking for civil engineering internship or civil engineering workshops, you should definitely join our forums as I provide more value in the forum discussions than what you might find in a non-structured civil engineering internship.

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