• Hi Diane,

I hope this diagram I drew helps.  It's a beam with a load.  The shape will bend the beam (slightly).  The top is in compression and the bottom is in tension.  Tension is like a tug of war on a wire.

The question you showed is a sideways version of this.  So the 'top' is the left (in compression), and the bottom is where the bolts are.  So the bolts are in tension.  They are going to try to pop out.

I hope this helps you visualize the condition.

Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses

• No. All three bolts are in tension. Look at them and ask yourself are they "stretching" or "squishing". . . all three are stretching so they are in tension. The amount of tension is roughly proportional to the distance from the top bolt. All of the compression is happening at the butt of the post, where it squishes up against the walkway.

• I already said that…. Yes, the bolts are in tension. 🙄

• Hi Diane,

You really should read up on tension/compression in Ballast and the Building Construction by Mehta book.

I definitely remember a section on trusses in compression/tension in the Ballast book, and here's a basic diagram.

Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses

•  the 3 holes in the steel angle are slightly bigger than the bolt. and if the bolts are your fingers holding the steel angle in place.

do you feel that the steel angle is pushing or pulling on your fingers ?

• How do you know the direction of the tension on the bolts at the right side? It seems like if someone was leaning against the railing that all the bolts would be pulled into tension from the same direction no matter the side.
The amount of tension makes sense but i don't know how you understand the direction. Is this when the tug of war analogy comes into play? (Or equal & opposite force?)

• Maybe I don’t understand the confusion, Diane…are you asking about the arrows on the right side of the bolts? If so, arrows pointing outward, one on each side of the bolt, is the way we describe tension…the red arrows pointing inward toward one another means compression. (If you knew that already, my apologies). It’s not an absolute direction thing…it’s a stretching or squeezing thing that we are trying to show with the arrows.

• unscrew the nut on the right hand side. hold the bolt with your hand. which direction do you tug to keep the steel angle in place ? tug of the nuts.

keep asking more of these questions. you are on your way to become a very good physicist.

• Yeah (i low key feel enlightened), clearly I didn't understand that pointing the arrows outward at either side of the bolt explained tension.
I confused this with the direction that the bolt would be moving as a result of the tension.

Thanks. I don't know why I had such a hard time understanding that.... Now I want to see if I can tackle a problem that asks about the direction of a chord on a prefabricated truss.

• wow ! professor michael and professor rebekka have chimed in. free education. thank you all.

where is professor black spectacles and others ?

in addition to the pulling, do you feel that the weight of the steel angle is pushing down on your fingers ?

this stuff is getting more interesting. hope your fingers anatomy is strong enough to hold the steel angle in place.

• no worry. mr isaac newton was confused about the direction of the apple falling from the tree.