Base plate with hooked rebar inserts 4

[Dano1996]

Hi everyone,

I'm working on my first independent structural engineering job right after university. I have to design a 2-story steel house, using tubular sections for the columns and IPE sections for the beams. Initially, I was thinking of designing the base plate with 4 anchor rods, as I was taught in university. However, because we are using steel framing in the house, I'm forced to use a solution like the one in the picture, with hooked smooth bars. The architects told me that they use this solution often in houses, but I'm a little bit worried about how I should calculate the moment resistance of the insert. I'm thinking of using the classic resistance Mn for a beam and using the development length to estimate the length of the rebar.

I don't know if that is the right approach for designing that kind of insert, or if you suggest using another solution for the base plate. I also don't know if I should consider the base plate fixed in both directions depending on the distance between the inserts.

Excuse my English; it's not my first language, and it's a little bit rusty.

 

[dik]

I'd never used hook smooth bars... always deformed and also weldable. If you are actually developing a moment, I'd consider using headed studs. I assume you cannot use normal anchor rods and nuts?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[HTURKAK]

The size of the base plate ( 150X150 mm) and thickness( 8 mm) implies that ,this connection could be simple base connection having limited moment resistance.
You may calculate the resistance of base plate with basic principles as you have stated.
AFAIK , the use of plain bars is forgotten and many codes prohibit their use in RC and allow their use only for transverse
spirals, stirrups, and ties smaller than 10 mm in diameter.
I do not have any idea for the code applicable in your zone and will suggest you to look your codes and if the plain bar is allowed , model the structure with pinned end columns .
P.S. = The lap length 45Φ seems a little bit less , i remember 50Φ .



Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[dik]

I didn't know that HTURKAK... I've never used them for any projects, nor have I seen them used. Most steel codes still use smooth 'J' or 'L' bars for anchor rods, which I haven't used on any of my projects for 3 decades. I use headed anchor rods, for all my work.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[haynewp]

Hooked smooth anchor bolts were discouraged by AISC a long time ago. I think the concrete crushes at the front and back of the hook part and then slips out if I remember correctly. I wouldn't use those in moment or tension resisting conditions.

 

[dik]

I haven't used them for decades. I design connections for steel fabricators and about 90% of those I encounter still use 'J' or 'L' type anchors... I don't like A307... but like F1554 Grade 55 S1. These are a lot stronger for little added cost... and weldable. If headed rods are spec'd they are usually A307... I have the EOR confirm my alternative (so I don't take ownership of the alternative). Been using them, almost forever... When I first encountered headed anchor rods, and found out they were much stronger and more predictable; I immediately switched and haven't gone back.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[HTURKAK]

As far as is remember , ACI prohibited the use of plain reinf. bar at mid 70's. Regarding previous practice, i found the following page from the book Foundations of structures ( C. DUNHAM , 1960 )

I agree with haynewp (Structural) and i refrained in moment or tension resisting conditions.




Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[Dano1996]

Thanks to all for the responses.

To provide context, here in Chile, for concrete, we follow our NCh430 standard (a "copy" of the ACI 318-08 with some requirements from ACI 318-11 added after the 2010 Earthquake [

https://earthquake.usgs.gov/earthquakes/eventpage/official20100227063411530_30/executive

]). Currently, it's in the process of being updated to align with ACI 318-19. Unfortunately, we struggle to keep pace with changes in ACI due to legislative issues, a topic that requires a separate discussion. For steel, we use our NCh427 standard (a "copy" of AISC 360-10).

Dik, we could use anchor rods and nuts, but they should be embedded in the concrete because of the steel framing positioning (see Picture 1). I don't know if leveling them in concrete is an easy task; I would assume it's easier to level from the base plate, but I admit my ignorance on that matter.

I agree with haynewp regarding the behavior of smooth hooked bars.

Clearly, I should use headed studs. Do you have any examples of headed studs calculations?

Maybe I can consider the solution in Picture 2 (with weldable rebar), but I don't know if it's suitable for a highly seismic region. The challenge is to hide it or ensure it doesn't interfere with the steel framing above.

 

[dvd]

You are welcome to look at this spreadsheet - no guarantees are stated or implied

 

[dik]

Check with your locals... it's done all the time here... likely 95% of all projects or more (I don't know the numbers, just a WAG, but anchor rods are used in nearly all projects sitting on 1" grout (or thereabouts). [correction] A lot of the projects, in this area, still use 'L', and 'J' bolts but with threaded nuts for attaching the column. It's generally less costly to install a column with bolts than to have the crane 'hang around' supporting the column for it to be welded.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

dvd... haven't checked the sheet in detail, but it is an excellent sheet.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

Thanks, I've sealed connections on projects within the last few days that use smooth A307 'L' bars (20"long, 3" hook and threaded 4" end)... It's not prohibited in these environs, and is still common.

a) is still common, and I add a caution about using jam nuts.

INSTALLATION OF ‘JAM’ NUTS (NOT RECOMMENDED):
(REFER TO:

https://www.boltscience.com/pages/twonuts.htm)

THE INNER JAM NUT SHALL HAVE A THICKNESS OF NOT MORE THAN 75% OF THE OUTER NUT;
THE INNER NUT SHALL BE INSTALLED FIRST AND SNUGGED TO 50% OF THE TORQUE VALUE;
THE OUTER JAM NUT SHOULD BE INSTALLED SNUG TO THE INNER JAM NUT;
THE INNER NUT SHOULD BE RESTRAINED TO KEEP FROM ROTATING AND THE OUTER JAM NUT SHOULD BE FULLY TORQUED TO IT; AND
WRECK THE THREADS BELOW THE NUT.

I use d) most of the time without a plate washer at the base.


-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Dano1996]

I'm currently considering these two options. I believe that when the column is embedded, it will bear against the concrete, and the free body diagram (FBD) will change, affecting the design methodology.

 

[dik]

Option 1, provide a pocket for the column... that's often done in these environs. Option 2 with headed studs if you really want to weld the column... both totally feasible.

I would rely on the anchor rods/headed studs for providing the moment resistance. I would not rely on the column bearing on the concrete. Base plate may have to increase in thickness. Pocket may be 3" deep.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[haynewp]

I've done both of those before, prefer Option 1 since you can provide leveling grout under the plate for tolerances.

 

[dik]

trickier with headed studs... have to level in place. One of the reasons for Option 1.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Dano1996]

In the case of Option 1, the pouring should be a two-stage process then. First, pour to the level where the grout sits, and then pour to the top of concrete defined? The reinforcement should be stopped before reaching the anchors, or it should be caged?

Does anyone have a picture of a process like that?

 

[NOLAscience]

If this is your first independent structural engineering job out of uni, you should be working under a P.E. (or equivalent in Chile). Will a P.E. review your final design?

 

[Dano1996]

NOLAscience, in this type of project (2-story private house), there's no need to have the review from a P.E.. The review from a P.E. doesn't depend on the engineer's experience but rather on the classification of the structure:

1) Buildings for public use.
2) Housing complexes whose construction has been contracted by the Ministry of Housing and Urban Planning
3) Social housing complexes with 3 or more stories.
4) Housing complexes with 3 or more stories that are not social housing.
5) Buildings with 3 or more stories intended exclusively for private office use.
6) Buildings that must remain operational in emergency situations, such as hospitals, fire stations, police stations, buildings designated for control centers of energy and sanitation service companies, and telecommunication broadcasting stations.
7) Buildings whose structural calculations are based on foreign standards, which must be declared at the time of permit application.

 

[NOLAscience]

, I just figured that if this guy was involved, then the project required an "engineer", which I took to be a P.E.