Structural layout plan or Structural Scheme of a building is very important for the structural performance of buildings. Structural layout preparation involves deciding positions of structural members.
Many young structural engineers don’t give adequate importance for this aspect and starts modelling in ETABS without developing the structural beam layout. Positioning structural members is always a challenge for beginners.
To help take some of that mystery on beam positioning and beam location, I have some tips for you about what to look for and how to best determine your beams in a building!
With this knowledge you can start preparing your structural beam layout.
Why beams are needed in a Building?
There are many reasons that a beam may have to be provided in a building. However, there are 3 distinct and common reasons. It is good for entry level engineers, architects, MEP Engineers and all who are planning to build a home to understand this requirement.
This understanding helps entry level engineers and Architects to co-ordinate the requirement better with other stakeholders or each other and reduce abortive work there by speeding up the project. A well-coordinated structural beam layout speeds up the design phase of any project.
For dividing the slabs
The functional loads in a building are primarily transferred to the slab and the slab transfers it to the beam, then to columns and footings and then to the ground.
All the structural members need sufficient sizes to ensure it can take the forces developed in it. Slab is a flexural member and its thickness depends on the bending moments and the shear force developed in it. For a given load, span of the slab decides the forces in the slab. In other words, span of the slab decides its thickness. For normal buildings a thickness range of 100mm to 150 is sensible and any thing more is not advisable. So, to keep the thickness of the slab with in this range, we have to limit the spans of the slabs. Beams are provided to split the slabs in to manageable thickness.
For supporting walls above the slab
In many buildings, the wall layout at lower levels and upper levels need not be in a same vertical line. The walls, when not matching in different levels, will have to sit on the slab. While it is possible to design the slab by considering the wall load and presence of wall, many times it becomes uneconomic to do so especially when the wall thickness is large. So where ever possible, a beam is introduced below the wall to support the wall.
It is not that, you introduce a beam where ever there is a wall. You need to balance between the first reason I mentioned and this reason so that the beams are not too close. One need to have sufficient experience to decide these.
For tying the columns
It is preferable that all columns in the buildings are tied to the nearest column or beam in either direction. This tying of columns is needed for lateral resistance. Whole of India is seismically active and it is mandatory to design all buildings for appropriate seismic resistance. Tying of columns increases the lateral resistance of the building.
If untied, the columns will be slender and the lateral sway in the building will be much higher. Also, the slenderness moments will increase in the column. This will increase the column size requirement and often the reinforcement requirement in the building.
Sometimes, due to architectural reasons a beam may not be possible to be provided. A beam provided, will be visible in the bottom floor if not in line with a wall and it will be aesthetically unpleasant. In such cases, if unavoidable to provide a beam, a concealed beam of same thickness as that of slab can be provided to tie the columns. The reinforcement in this concealed beam should be through and through to ensure tie action. Most important thing to remember is that, concealed beams are not really stiff and hence should not be treated as a support for the slab. The slab panel shall not be considered split at this concealed beam. Concealed beam is just a tie. You call it a beam as it is easier to show it in a column beam layout.
The above 3 points are the most common and important reasons for having beams in a floor slab. Other than this, there can be many projects specific, construction and construction sequence specific or even site situation-based reasons to provide beams. Also depends on if it is a new work or old and so on. Some of them are listed below.
When a repair is needed in a building like additions or adding a stair or changing the functional use of the building, more beams may have been added newly to suit the requirement.
Cut-outs & shafts
Many times, there will be large openings and shafts in a building. You may need additional beams around the openings to support the slabs. Your beam layout depends on the real conditions and positions of the openings.
Sometimes, there will be an un avoidable structural reason to provide a beam and this may clash with the aesthetics of the floor when you look up from the room below. To cover this up, you may have to provide additional beams to make it more pleasing aesthetically.
There can be many more miscellaneous reasons that will result in requirement of beams in a floor. If you have any questions on this, please leave a comment below this blog and I will answer.
How to improve your skills to scheme
Some of these points above can be mastered only by spending enough time by doing projects. Here below, I have listed a few things young engineers can do to improve their skills on deciding beam positions.
Study Structural Layout
Study as many structural layouts as possible and try to understand the structural scheme. Emphasis should be given in understanding the architectural requirement as well as MEP requirement. This will help you to improve your understanding and scheming ability.
Visiting sites helps you to visualize things better. You can physically see how and where the structural members are provided. If you have any doubts, ask a senior and find out the reasons. Exploration in this way helps to develop visualization skills.
Work on real projects
There is nothing like learning by working with an experienced structural engineer. If you get an opportunity that will be the best to learn the nuances of structural consulting including structural scheme development. You can also learn from structural courses where you get a chance to do real project. See the below section for the structural design courses.
Learn from Structural Design courses
Learning from well structured structural design courses will have the same effect of working with a consultant, provided, the course covers real project and a mentor guiding you.