Design of Fire Rated Wood Beams Exposed three sides based on “Lie Method”

There are several methods have been developed since early 70’s when T. T. Lie developed a simplistic method to design heavy timber beams exposed on three sides for fire resistance at NRCC [1].

I have performed several design examples for calculating endurance time for beams exposed to three sides for various sizes based on the equations provided in technical literature provided by AF&PA [2] and below are my calculated results*. The sizes which has endurance time of 1 hour or more are highlighted in green.



Design Results for Fire Resistance of Wood Beams Exposed on Three Sides


1. “Calculating Fire Resistance of Exposed Wood Members” By AF&PA – Technical Report 10.

2. “Design for Code Acceptance” by AF&PA.

*”These results shall not be used directly for any design without performing a design and analysis by a structural engineer and confirmed by a professional engineer. This blog is for educational purposes only and are based upon calculations done based on formulas provided in technical literature by AFPA [2]”

100% 75% <=50%
b d t
1.5 9.25 14.62 16.45 19.01
3 9.25 28.01 31.51 36.41
4.5 9.25 40.16 45.18 52.21
1.5 11.25 14.73 16.57 19.15
3 11.25 28.45 32.00 36.98
4.5 11.25 41.15 46.29 53.49
1.75 9.5 16.96 19.08 22.05
3.5 9.5 32.28 36.32 41.97
5.25 9.5 45.97 51.72 59.76
7 9.5 58.02 65.27 75.42
1.75 11.875 17.12 19.27 22.26
3.5 11.875 32.94 37.06 42.82
5.25 11.875 47.44 53.38 61.68
7 11.875 60.64 68.22 78.83
1.75 14 17.22 19.38 22.39
3.5 14 33.34 37.50 43.34
5.25 14 48.34 54.38 62.84
7 14 62.23 70.01 80.90
1.75 16 17.29 19.46 22.48
3.5 16 33.62 37.82 43.70
5.25 16 48.96 55.09 63.65
7 16 63.34 71.26 82.34
1.75 18 17.35 19.52 22.55
3.5 18 33.83 38.06 43.98
5.25 18 49.45 55.63 64.29
7 18 64.21 72.23 83.47

Material Properties in Revit Structure!!!

Many times when we download Revit Libraries from online resources we do not find the right material that we need. In order to have the right material properties selected you can follow below procedures.

1. Open the .rfa (Family) file

2. Go to Manage >> Material tab from menu bar

3. Click on Material will open below window >> Add New Material (See very bottom left)

4. By clicking this icon it will ask you to duplicate material >> Click OK >>

5. Now…Look at right side of new window >>you will need to set up Material properties such as Graphic >> As shown below…

6. In Graphics Tab >> chose the material color (RGB code) or chose color from pallet. You can also select surface pattern.

7. Now we will select rendering of material…in this example its for wood material (Make sure to keep the same for entire library)…Please note that the RGB code for rendering may be different than your regular graphics RGB Code.

8. Now we will create identity of material….which is in our case>>>wood so it will not have manufacturer specific identity which may be the case in order to create manufacturer specific material properties.

8. Now we will add Physical properties, now this is very important in case of Revit Structure because if we want to incorporate in to any structural analysis software these properties may be transferred to the analysis program and hence modeling need to be done only once.

9. Hit Apply>>>OK. You are all set with your new material. Select elements of the revit family and apply this material.

The world is changing an Engineer has to be a “Reviteer” now !!! Go Revit Structure !!

As the world is moving forward and technology is changing drastically which makes our life easier but at the same time requires great deal of knowledge in dealing with new technology. One of it is Revit, which I am working on since many years but with 2011 version it has given me everything that I need. Yes….it was behind for structural engineers than architects but its almost there now. We can do almost anything we want with Revit Structure. Model Concrete, Steel or wood structure. Here is one of the samples I am preparing for wood structure…its just an exercise and experiment towards excellence. Nothing related to any particular project but just a pure “Research work”. Will keep updating as I move on. Here is one of the model I am preparing with framed walkout basement and concrete foundation wall with I joist framing. I am not sure if architecturally how efficient the plan will be, but I have pretty good idea of what I am modelling structurally and what I am planning to test and once its done should be a good example with details and everything.

Design of structures for lateral loads

There are three methods to figure out wind loads for structure by wind loads

1. Simplified Procedure ( height < 30 ft, Slope < 10 degrees)

2. Analytic Procedure

This includes Main Wind Force Resisting System ( MWFRS) in which the wind loads are applied to structure from more than one direction while on Component & Cladding, wind load is being applied to cladding and then transferred to structural components

3. Wind Tunnel

This method is useful to analyze complex conditions, such as Y, L or T shaped non symmetric structures or where the wind loads are heavy and accurate dynamic analysis is required. The scaled models of structures are applied with wind loads thru wind tunnel and dynamic analysis is performed using test results.

(the above article is based on ASCE-05 code and are interpreted per best of author's knowledge, any suggestions or corrections are greatly appreciated.)

Kaushal Kansara, P.E.