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In the recent discussion on SE licensure reference was made to complex structures. Given that what may be complex to one engineer may be routine to another what are examples of complexity that cause pause and why? See this link for background discussion. https://collaborate.asce.org/integratedstructures/discussion/why-se-licensure#bm910d013d-ab5a-4c00-8ba5-2858ae527f59
I'm so glad you brought this up. I've been trapped on a time vampire of a project for a couple weeks which has got me thinking about this. It's a sprawling two-story-plus-basement community center, built cheap in the late 50's, nowhere near any legal threshold for a complex or significant structure. We're modifying the gravity and lateral systems pretty extensively. There are no fewer than seven distinct flat roof elevations. The floors are a hodgepodge of structural slab, slab on metal deck, hollowcore plank and prestressed masonry tile plank, mostly on CMU bearing walls. To say that the span direction changes every bay is misleading, as it implies that there is anything resembling a regular bay system. The architect is putting new openings in the walls and wanted to know which ones are structural. When I went through the existing drawings to find out, this is what I got out the other side (deleting the ex. drawings underlay for anonymity):
A contrasting example: one of my favorite new buildings in Chicago is 150 N Riverside. If you haven't seen it, it's worth looking up (virtually and, if you get the chance, in person). It's a glass tower built over some railroad tracks that necks down to a third its width in the weak direction right at the base. It's a beautiful piece of structural engineering that sets peoples' teeth on edge. My cousin once played a concert in the lobby; he was terrified the whole time.
The thing is, the shearwalls are regularly spaced. The transfer trusses are symmetric. The core is dead center of the floor plate. Now, this is an MKA building and I'm sure they used complicated design procedures to make it super efficient. But I suspect a lot of engineers could've designed this building safely, perhaps with a little more material. It's a complicated building, but there are other 54-story towers a lot more complicated.
Looking forward to hearing more on this topic!
In the recent discussion on SE licensure reference was made to complex structures. Given that what may be complex to one engineer may be routine to another what are examples of complexity that cause pause and why? See this link for background discussion.https://collaborate.asce.org/integratedstructures/discussion/why-se-licensure#bm910d013d-ab5a-4c00-8ba5-2858ae527f59
Though there can be many different types of complex structures, the term is colloquial with regard to SE Licensure. In SE Licensure, we typically talk about a threshold structure as opposed to a complex structure, but the intent is similar.
The goal of SE Licensure is to provide reasonable protection to the public in extreme conditions, and to be effective, a building department official needs to be able to objectively recognize which structures are beyond the threshold and should be designed by an SE. In New York, our proposal with regard to buildings that require an SE is as follows:
Clearly, with this definition of the threshold structure, the vast majority of buildings and even the majority of constructed area will not require an SE; however, a hospital, for instance, would.
I am looking at the proposed criteria for the stratified PE/SE reqirement. I am curious why an SE would need to design a wast treatement headhouse or wet well, SBR tank, etc. for waste treatment or water treatment. These are Risk 3 structures, yet aren't complex.
Likewise for an educational building. A competent PE is capable of designing a three or four story school building - these aren't complex buildings. To establish a requirement that only SEs could design the building implies a PE isn't competent.
In this NY proposed criteria, I see deligated design isn't included. How then does this square with the concpet? A PE for all intent and purpose could be the steel framing connection designer. The SE in this instance is accepting that a PE is competent for the task when the deligated design is submitted for conformance.
An SE can be authorized to design those threshhold structures but may not have the requisite experience for a spcific design type. It is once again incumbent on the licensed design professional to practice within one's competency. That is no different than having a PE license.
A statement was made that the criteria can inform a building code official which appropriate dsign professional should be designing the structure. This puts an licensure law enforcement obligation on the BCO. Enforcement of the licensure law is not an authorized (by legislation) responsibility of the building code process. In my experience, give a BCO an inch and they will take a mile. I see no reason to extend their perceived jurisdiction. ------------------------------Robert R Desmarais Jr, PEPresidentrrd pe corp313 West Liberty Street, Suite 101Lancaster, PA 17603------------------------------
------------------------------Brian Falconer P.E., S.E., M.ASCEPrincipalSeverud AssociatesNew York NYOriginal Message:Sent: 03-09-2023 03:49 PMFrom: Mitchell WinklerSubject: What is a complex structure and why?
------------------------------Mitch Winkler P.E., M.ASCEHouston, TX------------------------------
The proposed requirements assume that SEs will have upgraded structural engineering skills and experience relative to PEs. The proposed thresholds could create a situation where nearly similar structures have unequal levels of structural reliability in a hypothetical. What is the thinking here?
SE's will still need to work within their competency area as horizontal structure experience does not necessarily translate to vertical structure experience and vice versa-Ditto for different materials. Unless the SE is differentiated, how will this be any different than the responsibility already placed on PEs that they must work in their competency area?
How has peer review been considered in the deliberations for the proposed requirements? Even the best of us can make mistakes. Here, I think of William LeMessurier and his design of the Citicorp Center structure.
Is any periodic review planned to ensure the new requirements achieve the desired end?
A statement was made that the criteria can inform a building code official which appropriate dsign professional should be designing the structure. This puts an licensure law enforcement obligation on the BCO. Enforcement of the licensure law is not an authorized (by legislation) responsibility of the building code process. In my experience, give a BCO an inch and they will take a mile. I see no reason to extend their perceived jurisdiction.------------------------------Robert R Desmarais Jr, PEPresidentrrd pe corp313 West Liberty Street, Suite 101Lancaster, PA 17603Original Message:Sent: 03-10-2023 01:48 PMFrom: Brian FalconerSubject: What is a complex structure and why?
SE's must have to have 3 to 4 years of experience in designing threshold structures. PE's can have 3 to 4 years of any engineering experience. Most SE's have a PE and an SE. Discussing the comparative reliability between non-threshold structures and threshold structures is a complex discussion, but definitively I can say that the intent is to make threshold structures more reliable.
Engineers always need to work within their competency, but when you have less directly relevant experience, you know less of what you don't know. When you have more relevant experience, anyone makes better decisions about their own competency. The SE's will be making the decision of if they are competent to design a waste treatment head house, a 60-story office building, or a hospital.
Structural peer review is considered a separate issue from SE Licensure. Some jurisdictions have SE, some jurisdictions have peer review, and some have both. Peer review has been something that has proved to me the value of SE Licensure.
SE Licensure is a state-by-state law; so, any state can legislate it how they want it. I would be curious to hear an idea for periodic review - keeping in mind that we are sometimes designing for 50-to-2500-year events. These events are ultimately going to demonstrate who knew what they were doing, and who did not.
------------------------------Brian Falconer P.E., S.E., M.ASCEPrincipalNew York NY------------------------------
Not to put too fine a point on it, but is it improved structural reliability that is being sought or improved accuracy that the reliability levels of today's codes and standards are consistently met? I think the latter. If you want improved structural reliability, this needs to be done via upgrades to the existing codes and standards to maintain the proper balance between public safety and owner costs.
CROSS could provide an indication of of the efficacy of enhanced licensure, e.g., by comparing safety issues before and after implementation of SE licensure, but unfortunately it does not look like CROSS is being widely used - or I have misread the information on the website https://www.cross-safety.org/us.
The point that enhanced licensure makes one aware of what they don't know is the most compelling argument I've heard for SE licensure.
------------------------------Brian Falconer P.E., S.E., M.ASCEPrincipalNew York NYOriginal Message:Sent: 03-14-2023 02:22 PMFrom: Mitchell WinklerSubject: What is a complex structure and why?
While I don't think there are perfect lines to draw to cover every critical structure, I believe there is a rational behind ASCE 7, and I think that the proposed threshold structure is tied closely to that. Risk Category 3 and 4 structures have a greater value to society; therefore, they are intended to meet a better performance in a design event like an earthquake, a hurricane, or a blizzard. While we may not perceive the design of them to be disproportionately difficult, we as an industry have deemed their failure to have more implications for our society.
If a waste treatment head house fails in a design blizzard, what will be the implications to the water supply and local environment? By requiring a waste treatment head house to be designed by an SE, the intention is that waste treatment head house structure will be designed by an engineer that has been trained to design other waste treatment head houses and similar structures. I think that someone who has designed Risk Category 3 and 4 structures is more competent to design a Risk Category 3 or 4 structure than someone who has not.
With regard to school buildings, many in New York are intended to be used as shelters during a public emergency. Other parts of the country may not place the same value on school buildings.
With regard to the delegated design, the EOR always determines what can be delegated and what cannot, the EOR provides the loads for design, and the EOR is required to review the work of the delegated designer. In the case when the EOR must be an SE, the delegated designer can be a PE because they are being guided by the SE. With regard to steel framing connection design, the responsibility of the SE would be consistent with the AISC Code of Standard Practice.
The intent is not to make most structural design to require an SE, but it is to ensure better design of critical structures and better performance of those structures in extreme events.
I really appreciate your thoughtful and cogent comments on this topic. It seems like the "threshold" has to do with the importance of the building moreso than the complexity. Buildings which use simple structural systems and facilitate ordinary use can bump into RCIII based on large occupancies, on the very apt logic that the stakes are higher and we should take greater caution in ensuring that only an extraordinarily unlikely event could cause failure. A corrolary to Mitch's question that I'm still wondering about is: with importance-adjusted code requirements already in place, does it make sense for buildings which are equally complicated but of different sizes to require different qualifications?
As an alternative, here is a set of complexity-based criteria that I have pulled out of thin air (not necessarily advocating for this, just for discussion):
- Buildings implementing performance-based design
- Buildings using structural systems not explicitly addressed in ACI 318, AISC 360, or NDS
- Buildings where nonlinear push-to-collapse analysis is required
- Buildings detailed as special moment frame, special structural wall, or mass timber lateral force resisting system
- Buildings with a structural aspect ratio above 1:6
- Buildings with a horizontal irregularity as defined in ASCE 7
- Buildings relying on sharing of lateral load among elements with relative stiffness of 5x or more between distinct lines of resistance
- Buildings designed using semi-rigid diaphragms
- Modifications to existing buildings more than 30 years old which fall outside of Level 1 or 2 Alteration per IEBC
- Buildings subject to tornado loading or FEMA P-361 shelter design
One problem with this list: how would an owner know what kind of structural engineer to hire?
I think that most of the conditions that you have suggested as an alternative would be directly or indirectly covered by the threshold definition. I also think that most complexity is in threshold structures. The benefit of the simpler threshold descriptions is that they are more easily implemented by building officials, architects, and owners who are not structural engineers. That makes it easier to know who is supposed to be engaged to do the work. It is also easier for the PE to know when an SE needs to be the EOR.
In general, the assumption is that structures below the threshold are common, are constructed in a common fashion, and many involved start with a good idea of what is required to construct it safely. Many individuals involved with the design or construction could catch an error. When we cross over into the threshold structures, forces are magnified, members are bigger, there are more bolts, more welding, more rebar, longer anchors, more complex systems, and higher performance requirements. In this instance, not only does the SE have a higher degree of design difficulty, but the SE has less support from the industry to assure that the structure will not only be designed but also constructed adequately.
There will always be non-threshold structures that for other reasons are complex and could benefit from the direction of an SE, but that argument is making the perfect the enemy of the good. If you have a better definition of threshold structure, there are many ways to get engaged in the discussion though. NCSEA and SEI are good places to start.
Hi Mitchell, good afternoon. I found some answers inside this document: Oak Brook Accords Consensus Document regarding Geo-Structures and SE Licensure - November 25, 2015 I "Structural Engineering (SE) is intended to be applied to designated significant structures. It is expected that designated significant structures will typically represent a relatively small number of all buildings and structures within a given jurisdiction. Those buildings and structures that fall outside of established thresholds could be designed by any appropriately qualified and licensed professional engineer."
II Complex Structures can be also defined by some genius that have designed such as structures…"
One example is Jörg Schlaich (born 1934-2021), a German structural engineer and was known internationally for his ground-breaking work in the creative design of bridges, long-span roofs, and other complex structures.
"Making the difficult easy and the heavy light: Jörg Schlaich - structural artist and teacher"In this is the Article , you might find the answer that some of us, is trying to understand (for what is possible):Is it his open, interdisciplinary way of thinking and the vividness which he explains complex structures?
III In my view creativity is about unordinary structures systems, it means that might exist as rare as conventional. Its requires experience, divergent thinking some times to design those types of structures, use of non-linear analysis, simulation/computational skills and advanced models, predict behaviors and findings patterns, better understanding of truss systems on transparent design, exploration of geometries and shapes, considering performances objectives… Structural Art by itself can carry a lot of those Concepts and Contents (Ideas). Because Humanity tell us about evolution, you have to search for inspiration at times, using your brain sometimes something collapses for the start of a new!