Integrated Buildings & Structures

As I was binge-reading the pile of recent structural engineering magazines on my desk this afternoon, a number of articles about performance-based structural engineering attracted my attention:

1. Article 1 (Feb 2019 Structure magazine): Performance-based design is the future
2. Article 2 (March 2019 Structure Magazine): How performance-based design will shape our future
3. Article 3 (March 2019 Structure Magazine): The Story of a Survivor (which is an excellent example of what performance-based design can do.) 

I understand the value of performance-based design in areas of high-seismic and wind, as well as for "high importance" structures. Article 1 above makes the point that "Performance-based design approaches are not needed for most structures." This led me the following questions for which I'd like your input. ( @Donald Dusenberry @John Dal Pino @Anne Ellis Thank <g class="gr_ gr_5084 gr-alert gr_gramm gr_inline_cards gr_run_anim Grammar only-ins replaceWithoutSep" id="5084" data-gr-id="5084">you</g> writing the above listed articles!)

1. What do you think the future of performance-based design will be for buildings that are not in high-seismic and high-wind <g class="gr_ gr_3643 gr-alert gr_gramm gr_inline_cards gr_run_anim Punctuation only-del replaceWithoutSep" id="3643" data-gr-id="3643">areas,</g> and don't serve a critical function (i.e. the vast majority of buildings built, at least in the USA)?
2. Are you seeing high-performance design gaining traction in your projects, and if so please share the (general) types of projects and locations, especially if they are NOT in high-wind, high-seismic areas. (I want to better understand the current state of the industry.)​​​​

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Stephanie Slocum P.E.
Founder & CEO
Engineers Rising LLC
www.engineersrising.com
------------------------------

While PBEE has provided structural engineers with a methodology to design structures in seismic regions, it has managed to make it more difficult to obtain a true picture of the ultimate capacity of new buildings.  While past codes were complex, at least it was feasible to figure out what the requirements were.  In today's practice, it is common to describe the capacity of a building in years (often 2,500).  Of course, saying that a building is constructed for the 2,500-year ground motion is not adequate information to describe the capacity of a structure.  Typically, what it actually means is that a structure is designed such that a finite element model of the proposed design does not collapse in a suite of ground motions that have response spectral amplitudes similar to the US National Probabilistic Seismic Hazard Maps (USNPSH).  The determination that a design meets the PBEE intent is ultimately decided by a peer-review committee.  The actual structural reports for buildings are intended to remain confidential.  This makes it difficult to discover the true capacity of new PBEE-designed buildings.  In the end, the appropriateness of the PBEE design strategy depends heavily on the adequacy of USNPSH.  If one wishes to design reliable structures, then it is important to consider infrequent earthquakes (e.g., large earthquakes close to the building).  Naturally, it is the things that happen rarely that we know least about; the science is just not there to extrapolate current data sets to infer infrequent events.  I personally believe that the current hazard maps seriously underestimate the potential for large near-source ground displacements that are potentially dangerous to modern high-rises.  Someday there will be a large earthquake that attacks a major city with high-rise buildings.  I seriously doubt that we will be advertising the advantages of PBEE after that time.  You can read a little more about this at  https://authors.library.caltech.edu/35612/1/183.full.pdf

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Thomas Heaton Ph.D.,M.ASCE
Director of the Earthquake Engineering Research Laboratory
Caltech
Pasadena CA
heaton@...
heaton.caltech.edu
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Just to add my two cents and that's regarding performance-based structural design; many codes available to design as according to performance  of structures and these codes provide design criteria for all seismic zones, perhaps  with a bit difficulties in designing at high seismic zones. If the question turned out to be: is performance-based structural design  just responding for low seismic zone then what the answer might be.
No. performance based designs cover almost all level of seismic zones to design based on. It's cost, material, and customer satisfaction driven. The future with performance based structural design, seem  the design industry is shifting toward light, flexible and stiff material to design based on. As it seem the steel design and that in specific the metal decks are all over.

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Sayed Maqsood
Oakland CA
(510)395-4361
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Performance based design has always been an aspect of engineering design, especially when there is need for specific details as mentioned. Performance is activity oriented, which in design involves the functionality of the structure (ie, loading), environment (ie, location), and cost (ie, quality engineering). 

Basic engineering design criterion is to sure that the process of optimizing the criterion will provide a suitable, and safe structure hence the need to adequate preempt all possible condition of loading expected on the structure for a through structural analysis to determine the internal forces and displacement actions, that will meet the strength ability of the material, and other permissible service conditions.  

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Olusegun Afolabi R.Eng
Lagos
234803 4248600
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​To answer the original two questions:

1. The future of performance-based designs in non-high-seismic and wind areas?  I think PBD will allow flexibility with designs that realistically meet the intent of the code but not the prescriptive letter.  Honestly, I think that already happens now either with formal discussions or negotiations with building officials or with an engineer's own calculations to show that a design is equivalent to or exceeds code requirements.

2. Am I seeing PBD gaining traction, and in what type of projects?  I can't say I've seen it formally gaining traction.  For as long as I've been practicing, though, other engineers and I have made the sorts of judgment calls the designers of the Mexico Beach house made.  Going back 10-20 years, there were a lot of things that weren't covered in ASCE 7/BOCA/UBC/SBC that required judgment calls. 

I think some of the claims (ie. that performance based design is our future....) are a bit overstated.  There's a good reason for prescriptive code provisions.  Everyone is not an expert in everything, and it protects people from what they don't know.  Everyone goes through that phase - especially with the ever-increasing complexity of codes - and prescriptive provisions guide you safely through the 'gaining experience' phase of your career (and I'm not sure that phase ever really ends).  As you become more proficient, you start questioning the 'why' of some code provisions and delve deeper into the Commentary section of codes and other outside literature.  THAT's when you're ready for performance based design.

Honestly, too, our business is very different from that of Ford or Boeing, where a team of engineers may work for a decade optimizing a new design like the Dreamliner which will then be mass-produced.  Our designs are typically one-off, and are typically under financial pressure for low design fees.  Certain projects for certain clients may warrant a high level of performance based design.  Others may warrant a soft-PBD approach, like the Mexico Beach house (and I think that already occurs)

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Greg Thein, PE
Cleveland, OH
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Stephanie, 

Another use of performance-based design is for fire. For many structures, this approach can be very advantageous compared to prescriptive design for fire resistance.​

To answer your first question, however, the vast majority of buildings will still be designed using conventional approaches and performance-based approaches will be limited to certain types of buildings and occupancies.

For the second question, the answer depends on how general you intend the term performance-based design to be used. It is becoming more common to see bridges and some other structures, mostly for government entities, designed with a specified design service life of 75 or 100 years, which may require the use of service life modeling and ultra high performance concrete. This should be considered performance based design and is an area that is gaining traction.

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Brian Kehoe
bkehoe@...
------------------------------

​Thank you for your interest.

There are at least three loads for which performance based design is being examined in detail.  Seismic is perhaps the most established, with wind and now fire response following in step.  But it really isn't the load source or site location that determines the merits of design according to performance.  Performance based design could be used legitimately for any structure for all loads, with the benefit being 1) a better understanding of the actual performance expectations, 2) more flexibility to address multiple and potentially competing performance goals, 3) greater efficiency in the selection and use of materials, and 4) potentially even lower total cost in most cases.  These benefits and others need to be demonstrated through study and practice, and such efforts are underway.

That said, it is not obvious that performance based design would be the best approach for all structures.  I can imagine that design phases for time-critical routine projects could be shorter following conventional design than for performance based design.  In fact, the profession is nearing a state of automated design for such structures.  Performance based design might also entail peer reviews and more intensive code compliance assessments than are needed now for conventional design.  At the same time, the overall savings for routine structures might not justify the pursuit.  But it depends on what you value.

I expect that performance based design will be used first for structures that show clear promise for benefit, and these (and large bridges) might be the ones you list.  However, as the construction industry's familiarity with the process increases and building codes become more progressive, we are likely to witness the threshold for structures that would receive net benefit lowering.

On your second question, we are pursuing performance based design for seismic and fire exposures.  I anticipate that the frequency with which we engage in performance based design will increase substantially in the next few years.

------------------------------
Donald Dusenberry F.SEI, F.ASCE
Consulting Principal
Simpson Gumpertz & Heger Inc.
Waltham MA
(781) 907-9237
dodusenberry@...
------------------------------

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Stan R. Caldwell, P.E., SECB, F.ASCE, F.SEI, F.AEI
Plano, Texas
www.StanCaldwellPE.com
stancaldwell@...
------------------------------

Original Message:
Sent: 04-02-2019 13:54
From: Donald Dusenberry
Subject: What do you think about performance-based structural design?

​Thank you for your interest.

There are at least three loads for which performance based design is being examined in detail.  Seismic is perhaps the most established, with wind and now fire response following in step.  But it really isn't the load source or site location that determines the merits of design according to performance.  Performance based design could be used legitimately for any structure for all loads, with the benefit being 1) a better understanding of the actual performance expectations, 2) more flexibility to address multiple and potentially competing performance goals, 3) greater efficiency in the selection and use of materials, and 4) potentially even lower total cost in most cases.  These benefits and others need to be demonstrated through study and practice, and such efforts are underway.

That said, it is not obvious that performance based design would be the best approach for all structures.  I can imagine that design phases for time-critical routine projects could be shorter following conventional design than for performance based design.  In fact, the profession is nearing a state of automated design for such structures.  Performance based design might also entail peer reviews and more intensive code compliance assessments than are needed now for conventional design.  At the same time, the overall savings for routine structures might not justify the pursuit.  But it depends on what you value.

I expect that performance based design will be used first for structures that show clear promise for benefit, and these (and large bridges) might be the ones you list.  However, as the construction industry's familiarity with the process increases and building codes become more progressive, we are likely to witness the threshold for structures that would receive net benefit lowering.

On your second question, we are pursuing performance based design for seismic and fire exposures.  I anticipate that the frequency with which we engage in performance based design will increase substantially in the next few years.

------------------------------
Donald Dusenberry F.SEI, F.ASCE
Consulting Principal
Simpson Gumpertz & Heger Inc.
Waltham MA
(781) 907-9237
<maskemail>dodusenberry@...</maskemail>
------------------------------

I hope Performance Design is the wave of the future. I see the potential of improving the design of structures no mater what the loading level is used.

I believe one of the major challenges of Performance Design is understanding the probability behind the loading versus the resistance.  I would really appreciate having a document detailing the basis of the probably behind the loads and load combinations, in combination with what is the expected probability of failure of the resistance.  At the moment I do not see that understanding properly explained especially for wind loads and wind load combinations.


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David Thompson M.ASCE
KTA Structural Engineers Ltd.
Calgary AB
(403) 246-8827
------------------------------

Original Message:
Sent: 04-03-2019 02:09
From: Stan Caldwell
Subject: What do you think about performance-based structural design?

Well stated, Don. Your summary is right on target.

------------------------------
Stan R. Caldwell, P.E., SECB, F.ASCE, F.SEI, F.AEI
Plano, Texas
www.StanCaldwellPE.com
<maskemail>stancaldwell@...</maskemail>
------------------------------


Original Message:
Sent: 04-02-2019 13:54
From: Donald Dusenberry
Subject: What do you think about performance-based structural design?

​Thank you for your interest.

There are at least three loads for which performance based design is being examined in detail.  Seismic is perhaps the most established, with wind and now fire response following in step.  But it really isn't the load source or site location that determines the merits of design according to performance.  Performance based design could be used legitimately for any structure for all loads, with the benefit being 1) a better understanding of the actual performance expectations, 2) more flexibility to address multiple and potentially competing performance goals, 3) greater efficiency in the selection and use of materials, and 4) potentially even lower total cost in most cases.  These benefits and others need to be demonstrated through study and practice, and such efforts are underway.

That said, it is not obvious that performance based design would be the best approach for all structures.  I can imagine that design phases for time-critical routine projects could be shorter following conventional design than for performance based design.  In fact, the profession is nearing a state of automated design for such structures.  Performance based design might also entail peer reviews and more intensive code compliance assessments than are needed now for conventional design.  At the same time, the overall savings for routine structures might not justify the pursuit.  But it depends on what you value.

I expect that performance based design will be used first for structures that show clear promise for benefit, and these (and large bridges) might be the ones you list.  However, as the construction industry's familiarity with the process increases and building codes become more progressive, we are likely to witness the threshold for structures that would receive net benefit lowering.

On your second question, we are pursuing performance based design for seismic and fire exposures.  I anticipate that the frequency with which we engage in performance based design will increase substantially in the next few years.

------------------------------
Donald Dusenberry F.SEI, F.ASCE
Consulting Principal
Simpson Gumpertz & Heger Inc.
Waltham MA
(781) 907-9237
<maskemail>dodusenberry@...</maskemail>

These are all great answers! ASCE Plot Points, a podcast that tells the robust story of civil engineering one civil engineer at a time, is in Season 2 and is looking for answers on this topic. If interested, email your answer as a voice memo (keep to around 60 seconds) to ascenews@... for a chance to be featured on a future episode!

I submitted an answer to one of the featured questions last year, so feel free to respond here or message me with any questions!

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Danielle Schroeder EIT, A.M.ASCE
Associate Engineer
Pennoni Associates
Philadelphia PA
------------------------------

Original Message:
Sent: 04-03-2019 20:56
From: David Thompson
Subject: What do you think about performance-based structural design?

I hope Performance Design is the wave of the future. I see the potential of improving the design of structures no mater what the loading level is used.

I believe one of the major challenges of Performance Design is understanding the probability behind the loading versus the resistance.  I would really appreciate having a document detailing the basis of the probably behind the loads and load combinations, in combination with what is the expected probability of failure of the resistance.  At the moment I do not see that understanding properly explained especially for wind loads and wind load combinations.


------------------------------
David Thompson M.ASCE
KTA Structural Engineers Ltd.
Calgary AB
(403) 246-8827
------------------------------


Original Message:
Sent: 04-03-2019 02:09
From: Stan Caldwell
Subject: What do you think about performance-based structural design?

Well stated, Don. Your summary is right on target.

------------------------------
Stan R. Caldwell, P.E., SECB, F.ASCE, F.SEI, F.AEI
Plano, Texas
www.StanCaldwellPE.com
<maskemail>stancaldwell@...</maskemail>


Original Message:
Sent: 04-02-2019 13:54
From: Donald Dusenberry
Subject: What do you think about performance-based structural design?

​Thank you for your interest.

There are at least three loads for which performance based design is being examined in detail.  Seismic is perhaps the most established, with wind and now fire response following in step.  But it really isn't the load source or site location that determines the merits of design according to performance.  Performance based design could be used legitimately for any structure for all loads, with the benefit being 1) a better understanding of the actual performance expectations, 2) more flexibility to address multiple and potentially competing performance goals, 3) greater efficiency in the selection and use of materials, and 4) potentially even lower total cost in most cases.  These benefits and others need to be demonstrated through study and practice, and such efforts are underway.

That said, it is not obvious that performance based design would be the best approach for all structures.  I can imagine that design phases for time-critical routine projects could be shorter following conventional design than for performance based design.  In fact, the profession is nearing a state of automated design for such structures.  Performance based design might also entail peer reviews and more intensive code compliance assessments than are needed now for conventional design.  At the same time, the overall savings for routine structures might not justify the pursuit.  But it depends on what you value.

I expect that performance based design will be used first for structures that show clear promise for benefit, and these (and large bridges) might be the ones you list.  However, as the construction industry's familiarity with the process increases and building codes become more progressive, we are likely to witness the threshold for structures that would receive net benefit lowering.

On your second question, we are pursuing performance based design for seismic and fire exposures.  I anticipate that the frequency with which we engage in performance based design will increase substantially in the next few years.

------------------------------
Donald Dusenberry F.SEI, F.ASCE
Consulting Principal
Simpson Gumpertz & Heger Inc.
Waltham MA
(781) 907-9237
<maskemail>dodusenberry@...</maskemail>