Today we bring you moment, shear, deflection stuff! Sharing some basic VBA functions for determining the moment, shear and deflection of a simply supported beam (with or without cantilever) under almost any typical loading scenario imaginable.
Point loads, variable length uniformly distributed loads (constant, triangular, trapezoidal), etc [the only thing not implemented is a point moment, because it’s not that common in typical beam design… never needed it, not that practical].
I created these because I tend to start off working some weird loading out by hand using formulas instead of throwing it into some analysis program quickly, because I [falsely] thought it would be quicker by hand. I never learn.
But then the loading changes (made some error or multiple point loads, etc… go figure), or the span of the member changes (bloody architects usually), and by the time I’m finished it would have been quicker just to throw it into an analysis program and redo the analysis in an instant if things change.
Under weird load cases like triangular or trapezoidal cases when combined with point loads or constant UDL’s finding the maximum by hand is not that quick, so you’re almost forced to reach for an analysis program to get you to the end game.
Simplifying the end game..
Well, I finally got round to simply throwing something together in Excel so doing it by hand is much quicker than firing up an analysis program and plugging it in. The bonus is you can integrate it in any spreadsheet and use the output instead of manually transferring results from your black box program of choice to your spreadsheets.
I was knocking up some spreadsheets to design composite beams to the new AS/NZS2327 composite structures standard, and you really need more than a constant UDL if you’re serious about designing them correctly.
The modules are built with the plotting of results in mind to visualise the results, and to aid in extracting the min/max values if you calculate a sufficient number of points along your member. The results can be calculated at any ‘resolution’. By ‘resolution’ I mean the dimension step along the member at which you’re working out the design actions or deflections. Theres no solving for the absolute maximum, but if you divide a beam into 25mm chunks you’re going to get close enough for practical design. Theres virtually no overhead going to even smaller steps if you desire further accuracy.
So basically, the code create an array of values from beginning to end of the member at some specified regular intervals, like 0.1 meters or 0.00001 meters, up to you. Adds in the other points of interest at point load locations and the beginning and ends of the UDL loading and points some small distance either side of the point loads (to calculate & plot the step in the shear force diagram and accurate values at any discontinuities in UDL loading). Then these points of interest are run through modules for calculating moment, shear, deflection, and spit out some results as a dynamic array. Job done.
The end result is these moment, shear, and deflection plots (a 4.0m beam with 2.34m cantilever with some random loads):-
Loads are entered in a format of load and location arrays similar to shown below for UDL’s and point loads on main span and cantilever (if required), these form the inputs for the overarching BEAM_analysis function. The below configuration is setup for 3 UDL’s on both the main span and the cantilever span, and 3 point loads on the main span and the cantilever. You can specify any number of loads of any one type, just add more rows to the individual input arrays if required:-
So, with one function BEAM_analysis using the above inputs, you can get a dynamic array returned with the location, moment, shear and deflection for your given scenario! Easier than by hand.
Now that I’ve dangled the carrot, you’ll have to wait for part 2 where I’ll cover the functions and provide an example worksheet and Github repository. You can either copy the sheet into your own spreadsheets and/or start your own plots/layout of inputs from scratch. Over to you for the win.
Laters, until part 2 (sometime next week probably) …. UPDATE – Part 2 can be found here