how do you find errors? 6

[rowingengineer]

Having a bit of time on my hands I have decided to put together a “Tips manual” This is my first post out of the manual, I will probably post more of the manual (even the whole thing) as I go along, depending on the response.

Part of this manual is checking to find errors, how to identify errors in calculations.

I found these ten questions on the web, and I was wondering if anyone had a particular method for checking or prompting checking,I don't want a check list like faq507-229 , more general prompts. Thus that engineering judgement is used.

While I have a method for design that involves using butter paper and beam runs ect, I am more interested in checking of the cals than the finished product.

Ten Questions for Identifying Presence of Errors
Is the deflected shape consistent with what was expected? When reviewing displaced shape from analysis software, look for beams that have rotates at beam-column connections; evaluate whether you intended for the connections to be rigid or not. Verify that the beams you expected to deflect most actually do. Verify that the frames you expected to deflect most under lateral actually do.

If most beams are the same size, why are the others not? Evaluate whether you would expect the different beam to be bigger, smaller or the same.

Are the moment diagrams consistent with what was expected? When reviewing moment diagrams from analysis software, look for columns not part of the lateral load resisting system that have moment at the base; evaluate the supportst. Look for torsion in girders; evaluate whether you intended for the beam-girder connections to cause torsion or not. Verify that the locations where you expected negative have negative moment. Verify that the locations of points, points of zero moment, are where you expected them.

Is the beam depth consistent with standard rules-of-thumb?

For lateral load in any direction, do the connections and bracing provide a continuous load path to the foundation? This is why it is good to Draw cross-sections through the entire structure.

Does the building weigh what you anticipate?

Does total base shear equal total applied lateral load?

Do connection details match the assumptions used in the analysis? Identify locations in the structure where you intended to have a rigid or semi-rigid connection

Are the primary structural member sizes similar to members in similar projects?

Do beams deflect more than permitted?



When in doubt, just take the next small step.

 

[racookpe1978]

Does it "look right"? Does it "feel right" based on your experience, or are you fighting to sell it to yourself; and trying to justify something that "doesn't pass the smell test"?

Intuitively and instinctively, would you want to walk under it, live above it, and climb on it?

 

[DaveAtkins]

rowingengineer,

I love your list. Where I work, we have calculations and drawings go through a quality review, but I don't expect the reviewer to find math errors. I do expect him or her to find things that don't make sense.

When I review the work of others, I generally catch such things as joints in a computer model showing up as supports when they should really be free, or a bolt being checked for double shear when it is in single shear.

DaveAtkins

 

[abusementpark]

I like to visual load paths to see if there are any flaws in the lateral system.

There are a lot of rules of thumb for beam depth as related to span, that can indicate if something is grossly underdesigned, (i.e. I don't need to see the numbers to know that a W12x16 on a 40' span is wrong, it should most likely be at least a W18).

 

[youngstructural]

rowingengineer: Doesn't relate directly to your "finding errors" question, but have you checked out

http://www.eng-tips.com/viewthread.cfm?qid=233677&page=2

It's a thread I started on Stuctural Tips & Tricks. Might be useful for your tips manual...

Also, are you intending to post the Manual as a FAQ?

Cheers,

YS

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!

 

[graybeach]

I review a lot of calculations that involve attaching something to an existing structure. The thing I find the most mistakes with is the load path for lateral loads. I see many calculations that do not address all or part of the load path. The whole load path should be checked, including the underlying structure. So this is where I start checking first.

 

[csd72]

You should google it. some items that came up are:

http://books.google.co.uk/books?id=...esult&ct=result&resnum=5#v=onepage&q=&f=false

http://www.structuremag.org/article.aspx?articleID=758

http://cedb.asce.org/cgi/

http://WWWdisplay.cgi?8803277

http://www.fitzroy.com/people/verifying.pdf

http://www.lga.sa.gov.au/webdata/re...lculations_-_Discussion_Paper_-_Apri_2008.pdf

http://www.istructe.org/publications/pubdetails.asp?pid=108

http://www.duke.edu/~hpgavin/ce130/Bulleit-2008.pdf

http://www.modernsteel.com/Uploads/Issues/March_2008/032008_30775_schwinger_web.pdf

http://www.ipenz.org.nz/ipenz/forms/pdfs/Practice_Field_Guidelines-Structural_Final_version.pdf

I have also come across some others which I will try and find. I wanted to do this myself for training the junior engineers at my previous position but never got around to it. I will be happy to help more if you need it.

 

[rowingengineer]

Everyone thanks thus far, I am thinking of posting the manual in the FAQ area, but I will probably put a few more chapters in threads first.
The other chapters are:
1. What is an engineer, how do you fit into the design process? (this will be my next post)
2. Some good engineering quotes
3. Design methodology (concept)
4. Preliminary design
5. Rule of thumbs
6. Identifying errors
7. Checklists (I am yet to decide how detailed this will be or if it will be a chapter)
8. Cover sheet

The chapter Identifying errors is the one I am having most trouble with, struggling to tell someone with no experience how to develop experiences is hard, hence the questions idea.

I especially like the “Intuitively and instinctively, would you want to walk under it, live above it, and climb on it”, this will be added. And the lateral loads idea’s are good, will be putting a complete page on checking of lateral loads I think now.

YS,
Thanks for the thread tip but I had already gone through this and a few other threads with a fine tooth comb, there were some really good posts, am using a few in other chapters.

csd72,
I have been doing heaps of goggle searches for information, but you managed to get three that I hadn’t already viewed, thank you. But if you know of more I would be more than grateful.


When in doubt, just take the next small step.

 

[JedClampett]

Where I work, we are a multi-discipline firm with mechanical, architectural, civil, electrical and structural on the same project. Many of our structures are repetitive (boxes, single story buildings, etc.) and there are very few strict structural errors, like not enough reinforcing, beams too small and poor load path understanding. These are easy to check with experience. Where I find the biggest errors is where disciplines interface. Pipe penetrations, HVAC supports, electrical manholes, civil elevations and locations and the like. Has the conduit been considered? If you overlay the plans, do things line up. Are there dimensional errors between discipline drawings? The most common error I've found is the locations of building using coordinates. If you check the coordinates on the corners of a building, does the dimensions match the structural drawing?

 

[IDS]

As a young engineer I was given what was possibly the best advice I have ever received.

Before passing on any work to the next stage ask yourself, are you happy with it?

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[rowingengineer]

I would take the chance to thank everyone for their input thus far, I have start to post the first chapters in the FAQ, Just thought you would like to know.

When in doubt, just take the next small step.

 

[ishvaaag]

I usually find errors by continuously thinking again what at hand. I use to say I am the man that after having thought something 1000 times I think it once more. For example I am looking now for a post where I omitted the flexure strength of the section in favor of just the LTB critical moment (something that came to me in bed, thinking the worksheet I was using maybe was one of those NOT including such check -I have so many) as it was the case, to post a correction. Now I can't find the thread, some compassionate gnome must have seen my error and mandated it out of sight (solving some student problem?). But I will stay looking, I do not like errors known and standing.

 

[rowingengineer]

Parts of the "rule of thumb" section of the grad manual are posted in the FAQ. Still have footing, caps and fire (and a few others) to go, but alas I am out of time for now, so this now goes on the back burner until such time I get another grad student.

Feel free to comment, suggest amendments ect.

When in doubt, just take the next small step.

 

[Ron]

JedClampett hit one of the most common issues I see....multidiscipline "exclusion". What he has described is a constructability and compatibility check. In my opinion, this requires more experience than the other "checks". You have to know how a building is put together, bottom to top, and you have to know the sequencing of construction. I see so many post-construction failures that result from a lack of this type of checking on the front end. A common example is mechanical and electrical penetrations in a roof that don't get sealed, because the roofing subcontractor has already finished the roof and left the site. There are numerous others as well.

 

[rowingengineer]

Ron,
This chapter is a bit raw, and was having a hard time convincing myself to put it up, due mostly to the fact that I am not happy with it as of yet, need a fair it of editing and is a bit here and there. But I will post it for comment.

Consider needs to be given to the coordination of mechanical, electrical, plumbing, egress, architectural, civil, landscaping, ?re protection, security and more. You need to account for others disciplines requirements of your structure coordination area’s are: plumbing and process piping engineering disciplines, including but not limited to various water, waste and drainage systems, process and fuel gasses, medical gasses, vacuum services, special process fluids, as well as associated fixtures, equipment, controls and appurtenances. Service cores should be of a size sufficient size and in vertical alignment.
Examples are
• Beam penetrations are provided for duct work and piping;
• Slab edges are designed and detailed to accept the fascia;
• Floor openings are coordinated with the stairs and elevators;
• Openings are provided for mechanical shafts; and
• Floor to ?oor height is developed considering building usage, utility and ceiling requirements.
• roof geometry must suite the projected usage of the facility; considering such constraints as utilities, security, piping and suspended loading.
• Depth of roof must accommodate suspended HVAC units and other process related equipment.
• Maximum shipping depth varies based on shop location and site location, local ordinance, over-the-road clearances, trucking availability, shop capacity or size restrictions.
• Maximum shipping length varies based on trucking availability, local ordinance, shop crane capacity, shop size restrictions, site laydown area, installation crane capacity, and handling and lateral stability requirements.
• Maximum weight of shipping piece varies based on trucking availability, local ordinance, shop crane capacity and installation crane capacity.
• Bracing geometry should suite the usage of the facility, considering openings, and other penetrations and circulation requirements in the ?nal facility.
• Elevations must be coordinated with the ?nal usage of the facility or ?nished elevation requirements.
• Shoring requirements, special erection needs, design assumptions very helpful additions to the design documents.
• The lateral stability of the structure is a function of the initial design assumptions, the erection sequence and the erector- installed temporary bracing. Regardless of the nature of the structure, the erector is responsible for the lateral stability as it is installed. The erector’s temporary bracing must therefore sustain the forces imposed on the structure during the installation process. For the erector to accomplish this, the documentation should identify the lateral-load-resisting system and connecting diaphragm elements that provide for lateral strength and stability in the completed structure; and any special erection conditions or other considerations that are required by the design concept, such as the use of shores, jacks or loads that must be adjusted as erection progresses to set or maintain camber, position within speci?ed tolerances or prestress
Concrete
Design of concrete framed facilities also requires a similar under- standing of the construction process and coordination. Variables such as those listed below are examples of such considerations:
• Shoring and re-shoring requirements.
• Loading and support of concrete.
• Form de?ection limits.
• Concrete ?nish requirements.
• Joint location and details in slabs on grade and walls.
• Precast shipping restrictions or trucking availability.
• Cold or hot weather concreting procedures noted within the design documents.
• Layout of column anchor bolts including the foundation rein-forcing provides the basis for accurate initial construction.

Simple considerations such as the selection of wall thicknesses must be done in concert with structural engineering needs as well as accommodating mechanical and electrical elements within the walls. Allowances for the depth of framing, piping, ductwork, suspended ceilings and similar concealed items must be considered as part of the overall design, especially if any of the systems must be stacked within a space. Mechanical systems including heating, ventilation and air conditioning, gas and water pipes and vents, and fire protection systems where applicable generally present the greatest impact on structural systems. The size of ductwork and piping elements and accommodation for the changes in direction of these systems requires provision for openings, chases and horizontal bulkheads that impact placement of structural framing.

Electrical systems which include electric power, lighting, communications (voice, media and data) and controls generally fit within the structural framing without major problems due the small size and flexibility of wiring and conduits. However, these systems have become increasingly more complex in terms of the amount of wiring. This complexity is of particular concern with advanced systems like Structural Insulated Panels or other closed panel products. In addition, lighting appurtenances such as fixtures, control panels, built-in components and similar features occasionally create problems which must be resolved by altering the framing design, moving framing elements or moving the electrical wiring or devices.
The coverings that make up the typical structural system also interact in direct and indirect ways with the ability to keep moisture from becoming a problem in the building. The selection of certain materials that either attach to the structural system or are part of it can create a situation in some climates where the material acts as an unintended vapor retarder and thus retains moisture from either inside or outside the building. Bulk water movement into the building also can be influenced by the structural system. For example, it often is necessary to cut through the structural sheathing to run plumbing and mechanical vents. To reduce the potential for leaks, the design of the venting systems should be coordinated with the structural system design. Even the slope of the roof’s structural members can impact water penetration and should be considered.

In addition to the space limitations relative to mechanical systems discussed previously, there must also be adequate provision in terms of wall, floor, or roof thickness to accommodate insulation.

Foundation’s impact on utilities and moisture
The foundation system can interact in at least two significant areas with other systems in the building moisture management and utilities. The elevation of the foundation can be too low for proper placement of utilities, or it can be placed to preclude effective drainage. The first case can lead to bulk water entry into the basement or crawlspace. It can also result in failure of the sanitary sewer if the slope is too low for adequate gravity discharge. In addition, just the very presence of utility openings creates potential routes for water entry. In the second case, the flow of water toward the building is one of the most common reasons for wet basements.
Utilities can also be damaged or destroyed if the foundation is not designed to accommodate them. Piping that runs through a foundation is a good example where the allowance for a sleeve should be part of the structural system design. Otherwise, it is not uncommon for plumbing supply and sewer pipes to be sheared at the point of entry through the foundation. Failures can also occur if copper piping is buried in aggressive soils or directly in contact with concrete. The structural system should consider these types of systems interactions in the design stage.
Finally, the foundation system can interact with the thermal envelope to create moisture problems under the right conditions, especially with crawl space construction. Placement of insulation in the floor of a crawlspace typically requires foundation ventilation. Under the right circumstances, this approach can contribute to the very moisture problems it is intended to prevent. Thus, an economical structural solution may create a negative outcome because of failure to reconcile it with the thermal envelope design.


When in doubt, just take the next small step.

 

[vandede427]

reference the Hammurabi code