Facade Structural Engineering

Steven Sletten: Insights into Facade Structural Engineering

Today’s guest is Steven Sletten, a Licensed Professional Structural Engineer and Project Manager for Larson Engineering in New York. 

 Steve has great experience in the Façade and Curtain Wall Industry and has licenses from New York and Minnesota states. Has been involved in many great projects such as Transbay Transit Center, the Star Statue at Mall of America, Lantern House on NYCs Highline, One Madison Ave in NYC and many more. Works for Larson, one of the biggest firms in the field with 11 offices across United States.


Skyline: What are the important items in a Facade Structural Reports and where do you give the most attention? 

Steven: There are many important aspects of a façade structural report that bear mentioning.  The most critical items that should never be overlooked or discounted, are those pertaining to design loads and applicable building codes/standards.  The codes used today are established to provide an appropriate level of safety factor, in order to ensures a design is safe.  There are aspects of the design and engineering that can be up to the engineer’s judgment, however the minimum standard of care should always be to meet or exceed load/building code requirements.

The second most important aspect, in my opinion, is providing an efficient design that will meet the project specifications.  This includes working closely with the client (fabricator/glazier/etc) to determine any project specific design criteria or specification requirements, including serviceability limit states, that may impact the design. These are important as they impact the clients’ bottom line, as well as owner satisfaction with the end product.  If specifications are not met, there is potential for the owner rejection resulting in rework or potential back charges to the client. 

The engineer’s goal should be to have an efficient design.  The project may have high corner zone wind pressures, but may only occur on a small percentage of the building.  It may be possible to get by with reinforcing system(s) only in corner wind regions, or maybe the loading is high enough in all regions, such that a change to the system extrusions/depths is warranted.

Additional engineering time spent may be well worth the effort in order to provide the most efficient design for the client. Considering the additional cost of labor and material resulting from an excessively conservative or quick engineering design, may far exceed the cost associated with a more thorough engineering design. Each aspect of the overall design, should be reviewed with respect to the project specifications, applicable codes, and consideration for both the engineering and client budget.

Skyline: Are the specifications and wind loads getting over-designed?

Steven: Wind and code loadings are an ever-changing topic in the structural engineering industry. As more testing is executed, and more information is learned by the code agencies, the more accurate the resulting requirements become. 

This is paired in the facade industry with the need to be as efficient in design as possible.  These factors combined have led to our current codes and results in wind loads being dependent on many project specific factors, including but not limited to:  project profile (Manhattan skyscraper versus two-story building in Iowa), project complexity (unique building footprint vs box building), project location (Suburban area in Pennsylvania vs the coast line of Florida), applicable building codes for the project location, and also overall building design/construction.

Typically, if a project is a low profile, simple building, the design wind loading for the project, likely wouldn’t be much different from older to newer codes much from older building codes. 

Skyline: What software you use for Facade Structural Reports?

Steven: Wind and code loadings are an ever-changing topic in the structural engineering industry. As more testing is executed, and more information is learned by the code agencies, the more accurate the resulting requirements become. 

This varies within in the industry, but typical software includes:

– Mathcad or similar engineering math software which is used in the creation of many calculation

 templates.

– Use of Microsoft excel sheets, can be used in similar fashion, but may not be as friendly to the reviewer.

– RISA or other similar 2D/3D structural analysis software.

– RFEM or other Finite Element Analysis software.

– AutoCAD or similar drafting software.

– Bluebeam Revu or similar pdf editing software.

Depending on your firm / expertise, you may have other complimentary software as well, used to support thermal analysis, acoustic analysis, etc.

Skyline: What is the typical academic background for a Facade Structural Engineer?

Steven: It is standard that a Facade Structural Engineer will have at minimum a Bachelor’s degree in Civil Engineering – Structural emphasis.  It is also common for some firms to require a Master’s degree.

Most engineers will have completed and passed the EIT exam, either prior to starting full-time, or during their first years as an engineer.  Most engineers will go on to take either the PE or SE exams for their respective state, and other states as required for the company/position.

Skyline: What is the most challenging project you have worked and why?

Steven: The most challenging project so far in my career, was a façade replacement for a high rise in New York City.  Due to damage on a portion of the elevation high up on the building, there was a need to remove and replace multiple bays of curtain wall system in an occupied building. 

The project was a testament to collaboration, as there were no drawings provided from the building owner, and also required to get an exact match to the adjacent existing curtain wall.  Careful consideration for site access and safety was maintained throughout the project, and the final product met all project requirements.  To this day, an unknowing eye, will most likely not be able to see that anything had been replaced. 

Overall, it was an exciting and challenging experience, as we spent more time than normal coordinating directly with members of the design team, the project building envelope consultant, and also a contracted façade designer that aided in all of the not structural items/requirements.

Skyline: Do you need individual PE stamp for every state and how you deal with it?

Steven: In the U.S. each state will have its own requirement for PE licensure.  For each individual engineer, it is not common to have multiple state licenses.  A majority will have the state in which they live/work, and where the take the PE exam.  Some may look to get reciprocity licensure in other states, if they move companies, move states, gain clients / work in other states, etc.

It is also common for engineering firms to have most/all states licensed by only a few senior engineers in the company. 

Skyline: What is a Facade Structural Engineer actually doing?

Steven: The Facade Structural Engineer is an engineer that provides structural analysis /review /confirmation of the many aspects and components of the building façade / envelope.  This typically includes all elements/components from the structure to anything attaching to the main façade system; including but not limited to the facade framing, glazing/panels, attached components (fins, etc.), and the anchorage/embeds to structure.  The engineer is to be knowledgeable in the applicable building codes for the project location, while preparing calculations sufficient to prove the system(s) is capable of withstanding all applicable design loads and project specification requirements.

The goal of the engineer is to provide an efficient design for their client, while ensuring the design is structurally safe.  As the engineer’s primary responsibility is to hold public safety paramount. 

Skyline: Lately we see bigger and bigger openings, let it be cladding panels or glazing. What challenges does this imply for structural engineers?

Steven: The increase in daylight openings on projects has provided many challenges and changes to the systems aesthetically and how they are calculated by the structural engineer. 

The larger openings typically have led to the use of thicker glass or use of single/double IGU’s to meet deflection and/or thermal criteria.  This in turn leads to a larger overall weight of the system, which can impact the system framing, system internal connections, and anchorage back to structure. 

The larger glass has not necessarily led to a direct increase / change to a project’s system or quantity of anchors.   This is dependent on the accuracy of the contract documents, and if the client estimated/bid appropriately. 

Many times, the larger DLO is pushing the boundary of the intended use of a client’s chosen system. Therefore, careful consideration should be made by the façade engineer to ensure an adequate load path exists for these larger loads back to the building.