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?
Thursday, July 7, 2011
Tuesday, July 5, 2011
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
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
Wednesday, June 29, 2011
Shoring Alternative from Craig!
fyi - an alternate shoring design that Rob Ward is advocating for house addition in west seattle I'm working on.
From: John McDowell [mailto:JohnM@PileKing.com]
Sent: Tuesday, June 28, 2011 7:19 AM
To: croberts@ctengineering.com
Subject: driven wide flange shoring
Sent: Tuesday, June 28, 2011 7:19 AM
To: croberts@ctengineering.com
Subject: driven wide flange shoring
Hi Craig,
Please see attached a general description of the driven wide flange shoring system as well as a few pictures of jobs we have done.
Beams are driven using a hydraulic impact hammer that strikes the pile at about 250-400 blow per minute. For temporary cuts up to 8’ cantilever we oftentimes see W6x25 beams at 2’ centers, but for deeper excavations we recommend a W8x31 or W8x35. Lastly, the maximum length beam we can drive without a splice is 30’.
At the end of the job beams are left in the ground as sacrificial. If necessary beams may be cut off several feet below grade to insure they don’t interfere with future landscaping.
If you have any comments or questions then please do not hesitate to call or write.
Regards,
John McDowell
McDowell
Monday, June 27, 2011
Pre fabricated wood stairs
Here are a few photos from my "Seattle stair and design" field trip last Friday afternoon. Contact information on card photo.
These guys are craftsmen to say the least and have been in business in the local area for around 30 years.
If this post works I can follow up with some more information.
Ben
Friday, June 24, 2011
Check the links to the CTE blog
You all should be getting the links to postings whenever they now arise... (there were some bugs!)
Should all be good now!
Should all be good now!
Mech'l Equipment - Design requirements
Kudo's to Anne for info on this topic.
The graphic from "mybuildingpermits.com" is very helpful. This seems to imply in some cases that we should be providing design support for some items over 75 pounds.... WTH!!!
It may be that this issue should come to a head... Due to the "unknowable nature" of some of these items, maybe we should be specifically excluding these items from our design services, and insert them as an additional service on an hourly basis... There is no way that our clients will know that we have to do all this crap... if we seperate it out, maybe they will...? any thoughts?
The graphic from "mybuildingpermits.com" is very helpful. This seems to imply in some cases that we should be providing design support for some items over 75 pounds.... WTH!!!
It may be that this issue should come to a head... Due to the "unknowable nature" of some of these items, maybe we should be specifically excluding these items from our design services, and insert them as an additional service on an hourly basis... There is no way that our clients will know that we have to do all this crap... if we seperate it out, maybe they will...? any thoughts?
Friday, June 3, 2011
PT Design and standards in the CT Office
So the question has come up over the last few weeks about PT design and bonded rebar in PT slabs.
The current status of the CTE design philosophy is wrapped up in a FE calc done using RAM Concept that typically aims at the minimum prestress levels required by code. Code requires 125psi min in slabs... we generally aim at 150 to 200psi depending on column layouts, significant on-off spans etc...
As you know, the benefits of maintaining the code min prestress is that you get to "write-off" some of the "speed-bumps" that you'd otherwise run into for normal RC design... such as min bonded rebar spacings, distribution of rebar in beams and slabs, requirements for 2-way slabs and so on. So its important to get those benefits when designing PT. However, it is (more-or-less) common knowledge that our PT designs are generally quite conservative. We have all witnessed the fact that we get tendons cut on our projects (routinely)... we make a big fuss about it and yell at the contractor... the truth is that it almost never causes any heartburn... the slab works fine without that tendon.... WHY?!
The fact of the matter is that we have in the past used any combination of bottom rebar mats on our projects: #4 @18"; #4@24; #5@18; #5 @24, and so on... In many cases with PT design, rebar requirements for the most part are minimal in our PT slabs except for unusual conditions and spans that require "a bit more attention". So it is evident that our use of rebar at the bottom mat is generally VERY conservative, leading to a high steel tonnage in our slabs -which is part of the reason that we can weather the "tendon cuts" so well.
If we were at the other end of the spectrum where we max out the P/A at 4-500 psi with minimal bonded, then i think you would notice a snapped cable more...
All this to say - we should come up with a bottom mat configuration that we're confortable with that still gives us good use of materials and an efficient design...
Since the code ACI[18.12.4] will let us go to 8d or 60" for tendon spacing, and [18.9] spells out some minimum requirements for bonded rebar, we should consider relaxing our "strangle-hold" on the #5 @ 24"oc and ooch a little over toward say... #5 @ 36"oc?
Somebody...?
The current status of the CTE design philosophy is wrapped up in a FE calc done using RAM Concept that typically aims at the minimum prestress levels required by code. Code requires 125psi min in slabs... we generally aim at 150 to 200psi depending on column layouts, significant on-off spans etc...
As you know, the benefits of maintaining the code min prestress is that you get to "write-off" some of the "speed-bumps" that you'd otherwise run into for normal RC design... such as min bonded rebar spacings, distribution of rebar in beams and slabs, requirements for 2-way slabs and so on. So its important to get those benefits when designing PT. However, it is (more-or-less) common knowledge that our PT designs are generally quite conservative. We have all witnessed the fact that we get tendons cut on our projects (routinely)... we make a big fuss about it and yell at the contractor... the truth is that it almost never causes any heartburn... the slab works fine without that tendon.... WHY?!
The fact of the matter is that we have in the past used any combination of bottom rebar mats on our projects: #4 @18"; #4@24; #5@18; #5 @24, and so on... In many cases with PT design, rebar requirements for the most part are minimal in our PT slabs except for unusual conditions and spans that require "a bit more attention". So it is evident that our use of rebar at the bottom mat is generally VERY conservative, leading to a high steel tonnage in our slabs -which is part of the reason that we can weather the "tendon cuts" so well.
If we were at the other end of the spectrum where we max out the P/A at 4-500 psi with minimal bonded, then i think you would notice a snapped cable more...
All this to say - we should come up with a bottom mat configuration that we're confortable with that still gives us good use of materials and an efficient design...
Since the code ACI[18.12.4] will let us go to 8d or 60" for tendon spacing, and [18.9] spells out some minimum requirements for bonded rebar, we should consider relaxing our "strangle-hold" on the #5 @ 24"oc and ooch a little over toward say... #5 @ 36"oc?
Somebody...?
Subscribe to:
Posts (Atom)