What is a Structural Engineer

by Rick Abbott, PE, SE

I often meet people who do not have a clear understanding of structural engineering or the purpose of a structural engineer.  This article will provide a short description of what a structural engineer is and the role they play in the construction, evaluation, and repair of a building.

A PE is a Professional Engineer.  A SE is a structural engineer.  Structural engineering is normally offered in the Civil Engineering Department of colleges and universities; however, structural engineering has somewhat broken off from Civil Engineering and has its own designation because the work of a structural engineer has become more specialized over the past few years.Often times, structural engineers are confused with architects.  Architects perform a distinctly different role than structural engineers.  Architects are normally the head of the design group.  They understand the whole picture of creating a building, and lead a design group in the creation of a building that serves the needs of the owner and the community.  Lead architects understand mechanical processes, electrical needs, ascetics, safety, health issues, work flow, people movement, air quality, and most every aspect needed to make the building a success.  The architect understands these systems, but is not necessarily responsible for the detailing or specifying every system.  That is why architects rely on mechanical engineers, electrical engineers, interior designers, civil engineers, landscape architects, and yes, the mysterious structural engineer.

Architects work directly with owners to design (configure) the interior layouts and make sure the building will function as intended.  At the same time, architects creatively design the building to attract and appeal to the human eye.  The architect designs interconnecting spaces that work together with one another to create a building that serves many different functions.  These functions may change over time.  The placement of rooms, doors, windows, and necessities such as entrances, hallways, and utility rooms along with finishes and views has infinite effects on people.  Architects are also responsible for developing and designing the exterior of the building, which is strongly affected by the interior layout.  The exterior finishes, material types, and colors associated with the building are their responsibility.  The architect is truly the chief grand builder.

Structural engineers are basically technical trained and licensed professionals that focus on the design of structural elements.  Structural engineers are responsible for the bones of the building; the skeleton that holds the building together.  Structural engineers are responsible for determining how the building will stand up due to its own weight and the forces of nature that imposes load on them.  Forces of nature include wind, rain, snow, soil, and earthquakes.  Structural engineers hide their system within the confines of the architectural spaces.  Structural engineers use a form of physics, called statics, to determine what forces will be on the stationary components of the building; stationary component such as walls, columns, beams, and joists.  Then using knowledge that has been developed though years of testing and experience of materials, structural engineers design (select and size) each of the components of the building based on the chosen material.  For example, some columns are constructed of concrete and some of steel or wood.  Structural engineers must design (select) a column that will resist the anticipated loads that will be present and make sure it won't fail and cause the building to collapse.

Structural engineers must pay attention to the "serviceability" of the components.  Members must not deflect or vibrate too much to be noticed by eye or by feeling.  Serviceability refers to the everyday performance of a building component.  For example, if a roof beam is undersized, it may deflect more than desired and can lead to cracks in wall finishes or a leaky roof.  Serviceability also refers to vibration.  When beams are not designed for serviceability, they may vibrate and be noticed by the occupants.  Although they are capable of carrying the loads, they don't handle vibration well and cause some discomfort to those who are sitting still within the building as they feel the floor moving up and down when others are walking nearby.

After the members are designed (specified and sized), the information is communicated onto structural drawings.  These drawings look similar to the architectural drawings, but they have specific information on them that show what the structural components of the building will be and how they connect together.  The structural drawings show specific and required information about the foundations, the walls, the columns, the floor framing members, and the roof framing components.  Structural drawings have specific information on sizes of the components, the strengths of the materials, and how the components will be connected.  Structural drawings show the amount of rebar needed in the concrete components and where it needs to be located.  Structural drawings show the welds and bolts that are needed to hold steel components together.

Most of the time, new residential homes don't require a structural engineer to design them.  There are a number of reasons for this.  The most predominant reason is that governing building codes have recognized certain construction practices that have proven to be adequate.  Therefore; there are industry accepted practices that have made their way into the code, and produce safe structures.

Another reason structural engineers are not required is that the building codes, manufacturer’s standards have provided design tables which specify member sizes that can be used at certain spans or heights.  Since the loads are consistent and relatively small, the structural engineering has already been done on these tables.  The person responsible for the construction can check to see, that for a certain span and spacing, the minimum size has been provided.  This leads to safe, but often “over-designed” or “conservative” systems.

In certain instances, when the structural system to be used doesn't have specific information located in the building code or the system is atypical or complicated, a building official will require the homeowner or contractor to get the project documents “stamped” by a licensed professional engineer.  In this instance, a registered professional structural engineer needs to analyze the components and verify that they are adequate to carry the design loads.  By affixing their “stamp” on the calculations or drawings, the building official has verification that the components have been designed by a licensed professional capable of taking responsibility for the safety of the building structure.

Existing building that have been damaged may or may not require a structural engineer for repair.  It is a judgement call based on the complexity of the building and complexity of the damage.  Simply replacing a few damaged components with new identical components in a newer uncomplicated building probable will not require a review from a professional structural engineer.  A complicated structure that required a structural engineer to design the building in the first place, will most likely need the original structural engineer or a new structural engineer to evaluate the damage.  A contractor familiar with shoring can shore a small portion of a building based on years of experience; however, elaborate shoring most likely will require a licensed professional engineer to design or review.

Building codes are constantly changing; therefore, it is a given fact, that older building “don’t make code.”  This does not necessarily mean that any component that does not meet current code must be replaced.  It has always been the intent of modern building codes to allow building owners to maintain and repair their buildings.  Of course, any component that is determined to be a life safety issue, wither it is damaged or not, must be repaired, replaced, or modified to safeguard the general public.  Structural engineers understand building materials.  They understand how building materials are attached to a building, and their function within a building; therefore, structural engineers are good at evaluating damage, extent of damage, and giving recommendations for repair.

The process of requiring licensed professional structural engineers to design (specify and size) building repairs and modifications protects all involved.  It protects current and future owners, and anyone who may enter or be near the structure throughout the service life of the building.

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