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High-Profile recently caught up with Sergio Guindon, senior structural engineer I at e2 engineers, to discuss how he approaches restoration and historic preservation projects, and the process of evaluating existing buildings to ensure successful outcomes.
High-Profile: What are the first things you look for to understand the condition of the building, and how do you decide what can be saved versus what needs to be strengthened or replaced?
Sergio Guindon: This is a great question. The easiest way for me to answer this is to outline the general steps that I take when working on an existing building project.
One of the first steps is to determine if the project will fall under the definition of a rehabilitation, preservation, or restoration as defined by the Secretary of the Interior’ s Standards for the Treatment of Historic Properties. Looking at those definitions, you’ ll note that all approaches generally promote some aspect of preserving significant features. For the most part, as the structural engineer, I rely on the expertise of other design professionals such as architects or preservation consultants to help identify significant features either as dictated by the standard, local historic ordinances, or as requested by the client. Understanding the type of project can be particularly important both in developing
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Sergio Guindon
strategies for conducting a condition assessment and in developing repair or reinforcement strategies. For example, on a rehabilitation project, we may be able to remove finishes and access almost all surfaces of the structural skeleton of the building for assessment and repair, while in a preservation or restoration project, we may need to be more targeted and discrete in our approach.
Similarly, understanding the desired architectural program is important in determining if there will be local increases in gravity loading or if there will be triggers for lateral analysis. Understanding the intended uses for each area of the building helps us to perform a code review and to anticipate the extent of evaluation, analysis, and retrofits that may be required.
Another important step when working
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with existing buildings is conducting background research into the building, ideally before arriving on site for a condition assessment. Some of the most basic information you can obtain are the location, dates of construction, primary structural materials, and structural scheme. Each one of those elements provide a clue as to what types of failure mechanisms or known deficiencies to be mindful of on site.
The extent of available existing documentation always varies, but it’ s important not to be discouraged if the building owner doesn’ t have a set of 200-year-old structural as-build drawings. The more you get into the habit of conducting research, the more familiar you will become with the resources available for you. You’ d be amazed by the insights you learn to uncover by starting with a Google search, reading the National Register of Historic Places inventory nomination forms, reading publications from a Google book search, and working with archivists.
If you don’ t have access to existing drawings, your project may have access to a 3D scan of the building and / or architectural drawings. If so, I always recommend studying those before getting out to the site. Once you’ re out at the site, you will need to document the existing framing as well as the condition of each structural element.
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As a structural engineer, the condition evaluation is intended to be an impartial effort focused on documenting the existing conditions – how much of the existing cross section remains sound, and what are the material properties. That said, the more you expand your structural expertise working with antiquated structural systems or niche materials( for example terra cotta or stone masonry), the more often you will be able to provide your client with options that lead to additional capacity and more sensitive reinforcement methods. Generally speaking, whenever the structure requires additional capacity, due to an increase in design loads or decrease / deficiency in the existing capacity, I try to use as much of the existing structure as possible and make the structure behave compositely. This approach reduces the amount of new structural material required to carry the additional load.
To summarize, some of the requirements of what can be saved or need to be strengthened will be driven by the intended treatment; some of the requirements will be a reflection of changes to the design loads or as triggered in the codes for substantial changes in program; and, ultimately, the structural engineer will use their tool box of evaluation, analysis and reinforcement techniques to fit the prior defined requirements.
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