Truss analysis marathon

arman · 9 Nov 2009, 3:03 PM

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Ok, I though it would help if we all did some truss analysis questions

to start off with an easy one:

Determine reactions R1 and R2

[edit: btw NOT to scale, all angles are meant to be 60deg (all equilateral triangles)]

ShowStopper · 9 Nov 2009, 3:07 PM

Quote:

Originally Posted by arman

Ok, I though it would help if we all did some truss analysis questions

to start off with an easy one:

Determine reactions R1 and R2

lol, cbf writing it all out

R1= 270 N
R2=180 N

arman · 9 Nov 2009, 3:13 PM

Quote:

Originally Posted by ShowStopper

R1= 270 N
R2=180 N

ok, now for something harder

determine force in member BG for the same truss

btw, feel free to post any truss questions you have

just draw the truss in paint or similar and upload to 'imageshack dot us' - no signup or anything and press on 'insert image' when you reply on bos, copy and paste link and its done

ShowStopper · 9 Nov 2009, 3:20 PM

using method of sections

BG =242.48 N (C) ( may be an error in calculations, as i used ipod calculator lols

)

Kaos1 · 9 Nov 2009, 3:20 PM

ShowStopper's right... R1 = 270 & R2 = 180

he just assumed that all the members were 1 unit long, and did a simple members equation to figure out each reaction

eg.
R1 = 300 x .5 + 30 x 1 + 120 x 1.5 - R2 x2
therefore
R2 = 360 / 2
R2 = 180
R1 = 450 - 180
R1 = 270

Whats happening in member FG?

arman · 9 Nov 2009, 3:32 PM

Quote:

Originally Posted by ShowStopper

using method of sections

BG =242.48 N (C) ( may be an error in calculations, as i used ipod calculator lols

)

I got answer as BG = 138.67N

arman · 9 Nov 2009, 3:35 PM

Quote:

Originally Posted by Kaos1

ShowStopper's right... R1 = 270 & R2 = 180

yes you are both correct

Quote:

Originally Posted by Kaos1

Whats happening in member FG?

I found FG using method of joints and got 34.64N
Used this to find BG when sum the horizontals

ShowStopper · 9 Nov 2009, 3:44 PM

joints is easy, sections with this q is :S

arman · 9 Nov 2009, 3:46 PM

Actually, there are two ways to do this:

method of joints, requires you to find horizontal and vertical components of AF and FG, then sum to find BG

method of sections, cuts through BG, FG and FE, consider LHS of truss, take moments about external point between ED (at 30N down): takes into account R1, 270N up, 300N down and BG across

(note, although no distances are given, assume 1 member length is 1 (as equilateral, and then use relative distances, such as 0.5 for half a member)

arman · 9 Nov 2009, 3:49 PM

Quote:

Originally Posted by ShowStopper

joints is easy, sections with this q is :S

actually, working for sections is easy

(270*1)-(300*0.5)+(BG*0.87)=0 (BG assumed in tension)
BG= -120/0.87
=-137.93N
therefore assumed direction incorrect

BG = 137.93N in compression

(note: I got 138.57N compressive, using method of joints

ShowStopper · 9 Nov 2009, 3:50 PM

omg i left the height as root 3 on 2! arghhh

arman · 9 Nov 2009, 3:51 PM

Now:

Question: determine force in member CH

ShowStopper · 9 Nov 2009, 3:56 PM

sections is easy can yu do joints? im confused as to why thats the answer, my direcitons are confusing the shit out of me!

Kaos1 · 9 Nov 2009, 3:58 PM

WOA WOA WOA!! STOP!!

i get the 272*1-300*.5 part ... but where the hell did .87 come from?!

ShowStopper · 9 Nov 2009, 4:00 PM

cos 60 = 0.866..

i thought itd be root 3 on 2

9 Nov 2009, 3:03 PM	#1 (permalink)
arman Member HSC: 2009 Gender: Male Join Date: Apr 2008 Posts: 101 Last Activity: 7 Mar 2010, 6:13 PM	Truss analysis marathon You can hide this advertisement by registering. Ok, I though it would help if we all did some truss analysis questions to start off with an easy one: Determine reactions R1 and R2 [edit: btw NOT to scale, all angles are meant to be 60deg (all equilateral triangles)]

9 Nov 2009, 3:20 PM	#4 (permalink)
ShowStopper Member HSC: 2009 Gender: Male Join Date: Jan 2008 Posts: 100 Last Activity: 17 Feb 2010, 12:59 AM	Re: Truss analysis marathon using method of sections BG =242.48 N (C) ( may be an error in calculations, as i used ipod calculator lols ) __________________ SELLING LOADS OF TEXTBOOKS= GOOD CONDITION AND CHEAP http://community.boredofstudies.org/...48#post4690248 HSC 2009 Subjects:Advanced English, 3Unit Maths, IPT, Engineering Studies, Physics, UAI Aim: 85+ - Bachelor of Civil Engineering UNSW

9 Nov 2009, 3:20 PM	#5 (permalink)
Kaos1 Assistant Member HSC: 2010 Gender: Male Join Date: Aug 2009 Posts: 60 Last Activity: 2 Feb 2010, 10:39 PM	Re: Truss analysis marathon ShowStopper's right... R1 = 270 & R2 = 180 he just assumed that all the members were 1 unit long, and did a simple members equation to figure out each reaction eg. R1 = 300 x .5 + 30 x 1 + 120 x 1.5 - R2 x2 therefore R2 = 360 / 2 R2 = 180 R1 = 450 - 180 R1 = 270 Whats happening in member FG?

9 Nov 2009, 3:44 PM	#8 (permalink)
ShowStopper Member HSC: 2009 Gender: Male Join Date: Jan 2008 Posts: 100 Last Activity: 17 Feb 2010, 12:59 AM	Re: Truss analysis marathon joints is easy, sections with this q is :S __________________ SELLING LOADS OF TEXTBOOKS= GOOD CONDITION AND CHEAP http://community.boredofstudies.org/...48#post4690248 HSC 2009 Subjects:Advanced English, 3Unit Maths, IPT, Engineering Studies, Physics, UAI Aim: 85+ - Bachelor of Civil Engineering UNSW

9 Nov 2009, 3:46 PM	#9 (permalink)
arman Member HSC: 2009 Gender: Male Join Date: Apr 2008 Posts: 101 Last Activity: 7 Mar 2010, 6:13 PM	Re: Truss analysis marathon Actually, there are two ways to do this: method of joints, requires you to find horizontal and vertical components of AF and FG, then sum to find BG method of sections, cuts through BG, FG and FE, consider LHS of truss, take moments about external point between ED (at 30N down): takes into account R1, 270N up, 300N down and BG across (note, although no distances are given, assume 1 member length is 1 (as equilateral, and then use relative distances, such as 0.5 for half a member)

9 Nov 2009, 3:50 PM	#11 (permalink)
ShowStopper Member HSC: 2009 Gender: Male Join Date: Jan 2008 Posts: 100 Last Activity: 17 Feb 2010, 12:59 AM	Re: Truss analysis marathon omg i left the height as root 3 on 2! arghhh __________________ SELLING LOADS OF TEXTBOOKS= GOOD CONDITION AND CHEAP http://community.boredofstudies.org/...48#post4690248 HSC 2009 Subjects:Advanced English, 3Unit Maths, IPT, Engineering Studies, Physics, UAI Aim: 85+ - Bachelor of Civil Engineering UNSW

9 Nov 2009, 3:51 PM	#12 (permalink)
arman Member HSC: 2009 Gender: Male Join Date: Apr 2008 Posts: 101 Last Activity: 7 Mar 2010, 6:13 PM	Re: Truss analysis marathon Now: Question: determine force in member CH

9 Nov 2009, 3:56 PM	#13 (permalink)
ShowStopper Member HSC: 2009 Gender: Male Join Date: Jan 2008 Posts: 100 Last Activity: 17 Feb 2010, 12:59 AM	Re: Truss analysis marathon sections is easy can yu do joints? im confused as to why thats the answer, my direcitons are confusing the shit out of me! __________________ SELLING LOADS OF TEXTBOOKS= GOOD CONDITION AND CHEAP http://community.boredofstudies.org/...48#post4690248 HSC 2009 Subjects:Advanced English, 3Unit Maths, IPT, Engineering Studies, Physics, UAI Aim: 85+ - Bachelor of Civil Engineering UNSW

9 Nov 2009, 3:58 PM	#14 (permalink)
Kaos1 Assistant Member HSC: 2010 Gender: Male Join Date: Aug 2009 Posts: 60 Last Activity: 2 Feb 2010, 10:39 PM	Re: Truss analysis marathon WOA WOA WOA!! STOP!! i get the 2721-300.5 part ... but where the hell did .87 come from?!

9 Nov 2009, 4:00 PM	#15 (permalink)
ShowStopper Member HSC: 2009 Gender: Male Join Date: Jan 2008 Posts: 100 Last Activity: 17 Feb 2010, 12:59 AM	Re: Truss analysis marathon cos 60 = 0.866.. i thought itd be root 3 on 2 __________________ SELLING LOADS OF TEXTBOOKS= GOOD CONDITION AND CHEAP http://community.boredofstudies.org/...48#post4690248 HSC 2009 Subjects:Advanced English, 3Unit Maths, IPT, Engineering Studies, Physics, UAI Aim: 85+ - Bachelor of Civil Engineering UNSW

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