anyway, the most important question we must answer is...
if the secondary beam doesn't go beyond a certain Vu shear loading and there is no compression fan... is the secondary beam loading still towards the bottom portion of the girder and hanger still required? Most of the books says it is a...
But if you used the second diagram which is the standard or normal practice...
Then all such primary-secondary beam joint already automatically have hanger reinforcement even if the designer didn't originally intent it.... is it not?
For girder with concentrated load such as secondary beam framing into it. Are you saying that some designers provide close uniform stirrups but only up to:
I know the following is what should be done providing 4" spacing of stirrups throughout the entire girder and I will always do it (no...
I think the following solves the puzzles of why in spite of ACI lack of provision for hanger stirrups.. millions of beams don't come crushing down...
See illustration:
This thread shows that for inclined crack that forms vertically or very steep within 'd' from midspan (within the red...
If no compression fan forms in the supported beam.. then the loading would be uniform top to bottom of the supporting beam? Can others confirm what is the case?
According to Macgregor. This occurs due to the compression fan. (?)
But according to Macgregor.. the provision is waived if the shear, Vu2, at the end of the supported beam is less than 3 sqrt (fc bw2 dw)... quoting:
"The additional hanger reinforcement,Ah, is placed in the supporting beam to intercept
45° planes starting on the shear interface at one-quarter...
I need figures. You mean after concrete reaches the modulus of rupture of about 475 psi, there would be no crack (even hairline) if the reinforcement is doing its job?
I think the right way to think is after reaching the modulus of rupture, there would be hairline crack that won't widen...
I'm not arguing about why there are cracks.. but arguing that these should be common yet even when I climb up the beams in many buildings.. i can't see any cracks.. even hairline.. according to Dolan in page 75:
"If the section were to remain uncracked, the tensile stress in the concrete would...
To continue with the above. In the book "Design of Concrete Structures" by Dolan & Co, an example used in page 79 is thus...
For 60,000 psi longitudinal bars
in the uncracked tension load, the stress in the rebar is 2870 psi corresponding to modulus of rupture of 432 psi (out of the 475 psi...
Is this the normal where you must anticipate the actual loading to be less than the design load?
I have a friend working in a structural company. They seldom see cracks. So whenever they see cracks. They immediately demand retrofit saying crack shouldn't occur even hairline... the cracks is in...
I know it's taken by rebar. I wonder what strain/stress values before the concrete cracking occurs.. even so.. it is still at low loading... even halfway from ultimate load. I mean, at low load, the stress/strain of rebar and concrete is proportional.. at low loading, the concrete should crack...
Here's a mystery. The tensile stess in bending or modulus of rupture of 4000 psi concrete is about 475 psi. This is very small stress compared to the available strength of the materials. Here's the weird part. In most buildings and malls I saw (including my house). I haven't seen any flexural...
A single concentrated load on the beam occurs when secondary beam frames into it at midspan. For example.
This is the common stirrups spacing I saw in structural designers drawing. Many designers neglect to use uniform stirrups spacing which I will surely do in any design. In evaluating...
BA,
You mean it is common to have inclined diagonal cracks, but in most buildings and malls I saw, I haven't seen a single inclined diagonal crack.. maybe they were purposedly overdesigned? How many percentage of buildings you have built was there inclined diagonal cracks? If minimal.. can you...
Thanks BA.
In the case of regular inclined shear cracks at the sides.
I want to ask about design methodology.
Supposed your factored shear forces (1.2 DL + 1.6 LL) is 20 kips (or about 90 kN). Should you find concrete sizes that will have Vc that completely enclose it.. that is.. finding...
Thanks BA. In short. Any crack that occurs *within* (meaning from bottom to up even inclined inside) 'd' each side of the concentrated load is flexural crack, right? Illustration:
The red inclined crack occurs within 'd' from midspan concentrated load.. so can we say any crack within 'd' is...
This thread is about the standard shear diagonal cracks and not study of one occurring at midspan so let me post this separately to avoid confusion.
Please post all the shear diagonal cracks you have ever seen.
Why does these occur less frequency than flexurable cracks?
Now about design...
For concentrated load at midspan and constant shear diagram from support to midspan.. uniform stirrup is needed. No problem about it. But some just didn't follow it reasoning that no shear failure could occur at midspan and it's flexural failure only. I was asking what degree or angles of...
