The importance of structural simplicity
Every profession has stereotypical complaints regarding their industry. Structural engineers are not different (in this regard, at least), and aside from the personal aspersions often cast our way regarding our personalities (or lack thereof), the most common is that we overdesign everything. Overdesign can mean multiple things and in its use to describe our services, it is used in almost all those ways. From designs that are uniquely complicated to execute in real life, to the specification of materials that seem to be larger and more costly than needed based on the experience of the people in the field building the design. With construction costs, both labor and materials, reaching new highs over the last year, and rapidly rising interest rates, the pressure on our industry to produce affordable housing has never been greater.
One of the core tenets that we teach engineers in our firm, is that if you are a competent engineer, there is no need to overdesign. Designing structures to meet the minimum requirements of the code will rarely get a structural engineer in trouble. Where we find ourselves challenged is when the geometry of the building makes it difficult to support the loads required by the code with normal construction techniques. There has been an evolution in aesthetic standards in housing over the last 30 years, moving away from relatively smaller window openings in exterior walls, to today’s “window walls.” At the same time, interior living spaces have morphed from specific rooms for specific uses, separated by interior walls, to large, expansive interior spaces that allow functions to cross over and mingle within each level of the home, sometimes even between levels.
The interior walls that were present in the past provided redundancy for lateral force resisting systems (“LFRS” – shear walls to resist wind/seismic forces) and the smaller window/door openings provided ample shear walls at the exterior of the building. It was relatively rare that homes in the affordable category required a complicated or unusual LFRS design. Likewise, the interior walls separating the spaces provided many bearing locations, allowing joist spans to be reduced and smaller framing members to be used.
Combined with the evolution in architectural styles, there is a greatly increased level of supervision provided by building departments. Where previously they checked to see that the plans were stamped and that the right codes were referenced, it’s not unusual for them to produce their own independent calculations to check the structural design and they generally do so using the most restrictive interpretation of the code. To further complicate things, there is an army of plaintiff’s attorneys and experts looking for any possible reason to initiate a claim against all involved in the design and construction process.
Structural simplicity is necessary. Too often, the structural consultant is brought into the project after the project Owner has become enamored with the architectural design, or even worse, after an architectural review board has approved a design, making changes difficult to incorporate. While almost anything can be accommodated through structural design, the general rule is that if it is costly and complicated to engineer, it will be costly to build. Structural engineers have to work within the code, and we can’t violate the laws of physics. You also need to understand how engineers communicate—we desire to please and hate to share bad news. If your engineer says, “Well, I can design this, but it’s going to be a challenge,” what you should hear is “You really don’t want to go down this road, because after I design it and you bid it, you’re not going to want to pay to build it, and then I’m going to have to design it again.” Bring in your structural engineer early in the project design (at the schematic design stage) if not during conceptual design. Listen to your engineer, (s)he just wants to help. When contemplating affordable housing, keep the priority on using any public funds to maximize the result, which means providing as many people quality housing as possible with the funds available, not winning a prize for most unique design.