Getting a structural engineer involved early on in a project’s development can make a difference —” not only for the structure, but financially as well. The knowledge of an owner or facility manager greatly varies, and an architect’s experience with the construction of a structure maybe limited. Structural engineers involved in the initial design phase —” and even before —” can help to ensure the project is constructed cost-effectively.
Before any construction begins, the owner or facility manager has responsibilities to manage, including securing required pre-construction testing. The owner is the one responsible for obtaining site surveys and soil-engineering services, which include test borings or pits, soil-bearing values, percolation tests, and ground-water levels. Experienced owners and facility managers understand the need for these tests. Less experienced owners may need more help along the way, from explanations of the tests and why they are done to who to hire for the tests. The structural engineer should step in to explain the tests to the owner, and could recommend quality geotechnical firms in the area.
Additionally, for any building structure, the owner must secure any required technical tests during construction, such as concrete strength tests. The owner must also find an on-site project representative and obtain the necessary legal, auditing, and insurance counseling services needed to fulfill these responsibilities, as outlined in AIA documents B141 and A201. Even the most knowledgeable owner or facility manager may not be aware of all the tests and requirements. A structural engineer guides and makes recommendations along the way to ensure that the structure meets the necessary requirements.
Where the structural engineer begins
An effective structural engineer starts by meeting with the owner or facility manager and architect in the initial design stage of a structure. The structural engineer wants to understand not just the building itself, but the site and expectations. This includes the building’s location, geography of the site, adjacencies to existing buildings, the building’s use, budget, and what is anticipated for the building’s basement and the number of underground levels.
After the initial pre-construction soil test borings are made, the structural engineer will counsel the owner on the site class designated by the test and whether any additional testing would change the designation. Soil borings are geologic engineering tests to determine the capability of the soil and the underlying rock to support proposed improvements. These tests are necessary to determine the conditions of the soil and rock as they may impact the foundation design. The geotechnical firm conducts the tests and interacts with the owner and the structural engineer.
Site classes range from A to F, with A being the best class to resist seismic activity. Site-specific site class is found by measuring the type of soil and the depth of rock. The rock affects how deep the seismic waves can propagate. Shallow rock effects the propagation of seismic waves.
If additional testing is deemed advantageous, the geotechnical firm will perform more tests —” for additional fees —” to confirm or change the site class. With a better site class, less bracing and structural support is needed, which reduces the project cost.
The structural engineer advises the owner of this and the possible cost savings. The structural engineer also works with the geotechnical engineer to determine the best foundation system for the building. This is based on soil and site conditions, the desired performance of the foundation, the structural system and loading of the building, and the cost.
By involving the structural engineer in design/pre-construction process, it is possible to save costs and begin construction with the most cost-effective design.
Case Study: Nationwide Children’s Hospital
Nationwide Children’s Hospital in Columbus, Ohio, strives to be a place where a child can receive the best care anywhere in the world. The hospital says it’s “the place where curing and caring go hand-in-hand.” It’s a mission that’s important to the hospital and the people of Columbus. To uphold this pledge, a massive expansion of the hospital’s current facilities is necessary.
The $840 million expansion consists of several facilities: a new main inpatient hospital, Clinical Research center, West Campus research center, expanded green space, Livingston Avenue garage, central energy plant, and the Ronald McDonald House. The expansion will be completed in phases over several years. The first phase began five years ago. Now the hospital is ready to break ground on another phase, the Research Building 3, part of West Campus.
In the case of this hospital expansion, the owner was very savvy and worked well with the structural engineering firm from the beginning, knowing that the structural engineer was there to implement cost savings.
As Nationwide Children’s Hospital began to work on their next phase, Shelley Metz Baumann Hawk structural engineers met with the owner and architect in the design phase to learn about the structure and make recommendations. They coordinated with the work done by the geotechnical service company, including the soil borings.
Soil testing — Soil testing is always done before construction is done on a structure, even if structures are being constructed side by side. Never assume that the site classes are the same.
While a soil boring test is standard, additional soil tests are sometimes necessary and/or advantageous to reduce the seismic loading on the building. In this case, the next phase of construction was a research facility, not a patient building, so different seismic requirements were possible. After the standard blow count test method in the deep hole resulted in Class D identification, SMBH recommended that additional soil testing to explore the possibility of reducing the site class, and thus the seismic loading on the building.
This testing is an additional expense to the owner —” approximately $5,000 —” and the savings could only be recouped if the facility was changed to a different class. It was up to SMBH to explain to the owner why we felt the additional expense was necessary and how the testing could save millions in the structure. The owner did end up approving the additional expense, and the testing was performed using the refraction microtremor method, a surface-performed geophysical survey that evaluates surface waves by dropping a heavy weight on the ground.
The result of this additional testing was a change in status to class C, which will save an estimated $1-2 million dollars on this facility. With this change, less bracing is needed for mechanical/ plumbing/engineering (MEP) design and less structure is needed to resist the lower seismic loads.
Because the soil was tested upfront and not later in the design process, this project got off on the right foot in determining the foundation and lateral load systems. It is prudent to complete the testing early in the design process. If testing is not done early in the design process, it is possible that work may need to be redone when the information is available.
Each area of the country has different building codes. The structural engineer is aware of the building codes that could affect the structural design, as well as the tests that can be done to the soil to see if a structure must meet certain codes.
For example, Ohio is fairly active seismically, but the events are not considered major earthquakes. The nearest fault to Columbus is located in Nashville, Tenn.; however, the building code in Ohio requires that structures meet certain seismic requirements. For that reason, it is important to pay attention to soil testing and when the site class can be changed. Having a structural engineer on the job who understands this is essential.
Stephen Metz, P.E., is a principal at Shelley Metz Baumann Hawk in Columbus, Ohio. He can be reached at 614-481-9800.