Verco Deck - Changes have happened - TUNE IN online

So, imagine my surprise when i went online to www.vercodeck.com, and printed out some W2 and W3 concrete pandeck sheets from home... only to find those numbers in all those columns were ALL different from the numbers in my (2001) catalog...!

Having heard neither hide-no-hair about any changes to the Verco catalogs. I called up our rep Holly S. She mentioned that YES there are changes. These are NEW. They go as follows:

1. The grade has been changed to Fy=50ksi (vs Fy=30/38ksi). So while the materials have goten thinner (due to the rolling process with higher grade materials), the actual decks load and span charateristics have improved favorably. So, if you have a new job... check online for latest info!
2. The questions of 1-2-3 span conditions refers: Holly says that the limiting factors are the shear transfer between the decking metal and the concrete, and that the span conditions do not particularly apply. (?) She volunteered to send over some data from which the span tables were derived. I received that, and stuck it on the server at the followiung link - G:\LIBRARY\DETAILS\MFR\verco. But regardless, she confirms the basic thought that the 3-span condition refers to all spans over 2 spans - regardless of the end-span condition... (it was my contention that end span conditions needed to be treated as a 2-span condition since the moments are similar). The point is mostly moot, as there is NO difference between the 1-2 or 3 span conditions for the majority of cases (unless shoring is required)...

Retaining wall - Creative solution

So what do you do when you have a 20ft situation that needs to be retained... and the solution that comes up is a (huge) concrete cant'd wall with a big key...? Add to that a building surcharge of 4 stories or so, and you're into serious head-scratching mode... right...?

In my meeting with GRE a few weeks back, the contractor Bruce Moe and the geotech ganged up to come up with the following idea... It makes use of geotextile materials to reinforce the dirt, and take care of the surcharge loads from the building. All that, and my active goes down to 15psf... Looks like a good deal... Will let you know how the design turns out!

Energy Efficiency - WTH!!?

So I wanted to start a dialog about energy efficiency, and how this appears to be making inroads into our engineering life...  It is!

The latest effort appears to try to have architects "insulate" the edges of exposed (elevated) slabs by installing 2" (or so) rigid insulation at the edge of the (PT) slab and directly under the sole plate of an exterior wall... thereby affecting the bearing of the sole plate, reducing edge distances potentially to anchor bolts and holdowns, and possibly exacurbating a corner shear break-out condition... all in the name of "energy efficiency"...

There appear to be 2 camps of thought in our office on this score concerning wherther to "entertain" this type of condition. There seems to be some resistance to accepting this as a status quo - i agree with this approach... It seems that the "tale is waggin" the dog on this one... surely the structural aspects of the building design should take precedence over this type of "energy assault"...

The goal of this dialog is to try to "faciliate" the desire for energy efficiency, but to do it in an informed manner that can legitimately point to other aspects of construction that are not as invasive, but can still get the "savings" needed for the energy budget...

I think the SOG insulation is in a similar situation and needs to be discussed... particularly where we "buttress" the bottom of soil retaining walls with the SOG....

Comments please...?

PT Design: Stud Rails: Limited capacity!!!

Recent discussions about studrail design refers.

Note that Ram Concept has the ability to design studrails according to the provisions of the ACI 318-08 (or previous versions if you're so inclined) . Previous codes had "speed bumps" allocated such that

• Vc =< 2(f'c)^0.5 (Concrete strength) and,
• Vn =< 6(f'c)^0.5. 

 In current (08) code, this has been bumped up to

• Vc =< 3(f'c)^0.5 and 
• Vn =< 8(f'c)^0.5. 

 (See ACI 318-08 [11.11.3](general shear rebar condition) and [11.11.5] (New section for headed stud rails). This change is in line with comments from ACI 421-99 which has some suggestions for parameters for studrails applicability.

The issue is this: The Decon Studrail ICC report limits the Vc to =< 1.5(f'c)^0.5...!!!! WTH... That means that we could conceivably design stud rails all the way at 3(f'c)^0.5 - when in fact the product to be installed (including all look-alikes) are limited to 1.5(f'c)^0.5 by approved ICC docs. ICC claims that this limit is inherent in the ACI 421 code which references that limit in relation to earthquake loads... not sure of the context... do not have a copy of this doc...!

So given the lack of clarity and direction on this issue at this point (i called Decon and ICC - no real direction coming from any of them!) - we have decided at CTE to limit our studrail designs to the 318-05 version - which includes the 2* and 6* limits...

PT Design: Ram Concept: Tips and Tricks

I've designed a few PT slabs recently, and have battled a bit with the software, and its various tweaks. Here's what i've learned recently (if you know this stuff... sorry in advance!):

1. Steps in slabs are awkward: Concept does the modelling OK and comes up with the FE units easily enough, but then it tries to get smart and figure out the sections along each design strip to be able to apply design rules and calc stresses. There are various kinds of "section trimming" methods that are available in the "design strip" manager/editor, and these can be confusing. This "trimming" can lead to bogus results or unreasonable steel/section requirements. I've had conditions where i have to check punching shear using one type of trim and tensile rebar using another type of trim. Not sure what the solution here is, but we should discuss design methodology going forward so we have some kind of standard out there.
2. Setting of tendon profiles: It seems that Concept snaps tendons at the slab perimeter to slab mid-height - so no need to spec a profile point here - FYI
3. Concept Rebar Design to "code": Concept can design rebar to "code" requirements(set under the "design strips"). Only problem is that when it does, you sometimes get unusual results. Like all things, we have to apply judgement to each case. In reading the manual, i noted that this option can be set to none (ie don't apply code reinforcement rules). This does NOT have the effect of leaving off the rebar, but merely stops Concept from trying to apply the "code rules" and coming up with bogus or "collated" results. It will still come up with steel requirements but only at the locations where stresses dictate - not coordinated with code rebar rules... not rocket science (i don't think)... (ps the reason they are trying to approximate the code design is to better approximate rebar quantities in their take-off - thats my take anyway...)... (pps - the manual says that this should produce results similar to v2.1)
4.  Notes on Design Methodology: In the overview of design in PT, i still look to deflections and top rebar requirements to adjust and "massage" tendons - also looking at mid-height prestress to check on P/A (or do a hand calc). Once the slab is behaving OK, then i would look to design strips for determining appropriate rebar requirements. As mentioned, you may need to consider 2 "trim methods" in order to determine -punching - span rebar - other min/max stress related rebar...

 Anyway - thats all i got for now... Feel free to set me right if i "strayed off the path..."

Build it Green - Advanced Framing

 Today i was asked about "Advanced Framing" and whether it would affect our design and our fee. I asked Chuck. We did not know what that meant. That made us feel dumb!

So i called up Hugh Schaeffer and asked him about it. The link below describes a bit more about it. 
http://www.builditgreen.org/attachments/wysiwyg/22/Advanced-Framing.pdf

The idea is to use "smart techniques" to minimize use of materials, and to maximize energy efficiency in "common sense" ways...

I'd be interested what y'all think about this... Of course the overriding question is... LEED or no LEED?

ENERCALC V6 - slender masonry walls - maximum reinforcement ratio

Ever wonder how much steel you can stuff in slender masonry walls these days. Did you think that ENERCALC V6 would perform an internal check? Think again. See my question and ENERCALC's responce (for your enjoyment).


MY QUESTION:

Dear Technical Support:
video and users guide is silent relating to the max % of rho balanced entry under the material properties of the general tab.
Please see attachment (ACI-530-08)Commentary section 3.3.3.5. How is the program determining rho balanced? I assume that the equations in the attached commentary section are used with alpha = 1 (1.0*yield strain). I also assume that P/db in the numerator of the equations is calculated according to the service level load combination P=D+.75L+.525Qe. Please comment on the value assumed for the third term (ie .525Qe). Thanks


Benjamin J. McCann P.E.
bmccann@ctengineering.com

CT ENGINEERING Inc.
Structural Engineers
▪ 180 Nickerson Street ▪ Suite 302 ▪ ▪ Seattle, Washington 98109 ▪ ▪ Phone: 206-285-4512 ext: 312 ▪ Fax: 206-285-0618 ▪


ENERCALC REPLY:

Good Morning Ben,

Sorry for the delay in getting back to you on this one, but it is an excellent question and one that has required some research on my part and some conversations with the developers.

The answer is that the Masonry Slender Wall module is currently using reinforced concrete concepts (and 1.0 x steel yield strain) to determine rho balanced. It then respects the user-specified "max % of rho balanced" as the upper limit on reinforcing. This is workable, provided that the user observes the calculated value of rho balanced and enters a meaningful factor as the "max % of rho balanced" to arrive at the desired upper limit.

I'm glad you asked the question, though, because it has given me reason to propose to the developers that we should implement the provisions in ACI 530, which are more specific to concrete masonry. So I would expect that we will soon be seeing the reference to rho balanced disappear from masonry modules, as that term is not used in ACI 530. I would also expect that we will soon be determining the upper limit on reinforcing in masonry sections by using 1.5 x steel yield strain, along with usable masonry strains as defined by ACI 530 rather than as defined for concrete sections in ACI 318.

At present, none of the masonry modules are incorporating the axial load from the specified load combination into the determination of rho max.

· The Masonry Lintel module does not perform a check on the reinforcing limits. I’m going to provide the developers with some recommendations on this. But even if a reinforcing limit check gets implemented in this module, it will not consider the axial load from the specified load combination, because the beam modules in the Structural Engineering Library do not incorporate axial load in any way.
· The Masonry Column module currently bases its maximum reinforcing limit check on 0.04An. ACI 530 specifies that value as an absolute upper limit on the area of reinforcing in a column, but it also says that designs should still respect the value of the upper limit as determined in section 3.3.3.5. I’m going to provide the developers with some recommendations on this, including the incorporation of the axial load effects from the specified load combination.
· As mentioned above, the Masonry Slender Wall module is basing its maximum reinforcing limit check on the user-specified "max % of rho balanced" multiplied by the calculated value of rho balanced. I’m going to provide the developers with some recommendations on this, including the incorporation of the axial load effects from the specified load combination.

Finally, you asked for comment on the value assumed for the 0.525Qe term in the load combination specified for determining axial load on masonry elements. The factor of 0.525 occurs in Basic Combination #6 in section 2.4.1 of ASCE 7-05, which is (Equation 16-13) of IBC 06 and IBC 09. However, the combination specified for determining axial load on masonry elements differs slightly from the equation in ASCE 7 and IBC, because it omits the roof live load or snow term. So I will need to provide the developers with some guidance on how to handle this requirement, and at the present time, I think I am going to point them to the expanded form of this equation as presented in section 12.4.2.3 of ASCE 7-05. I think I will eliminate the roof live load or snow load term, and ask that they calculate a value of axial load based on all of the remaining terms, including the vertical component of the seismic load.

Thanks for raising great question, and keep your eyes peeled for some nice enhancements in the masonry modules as a result.

Cheers,
Chris

Chris Conrad, P.E.
Director of Development
ENERCALC, Inc.
cconrad@enercalc.com
Technical Services: 949-645-0441
Fax: 949-645-3881
Business Office: 949-645-0151, 800-424-2252
Web : www.enercalc.com