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Inspecting for Structural Defects

Recent events have highlighted the engineers' role in determining the structural safety of a building. Just what does an engineer look for to make such a determination? When and why does he do it? There are a number of reasons for performing a structural inspection:

  • as part of normal due diligence when purchasing or refinancing
  • when required by an insurance company
  • in anticipation of a change in use (a new use of the building is contemplated that involves greater loading than the present use)
  • because of visible signs of a structural problem
  • due to concerns about older buildings, built before building codes were adopted
  • when there are municipal requirements such as those in New York City and Miami
  • post-disaster (after a fire, flood, earthquake, explosion etc.) - to determine if a building is still structurally sound.

Whatever the reason, the owner or manager should make certain that the person performing the inspection is qualified to do so. Only a qualified, licensed Professional Engineer (or in some states, a Registered Architect) is legally allowed to make a determination of the structural capacity of any building.

Initial inspections are generally limited. 

The engineer’s objective is first to determine if there really is a structural problem, then to determine the cause of the problem if there is one, and finally to suggest a remedy. Unless there are obvious signs of structural problems with a building, the engineer will usually start with a limited structural inspection. This inspection is based on evidence gathered in the course of:

  • a document review,
  • a walk-through visual examination of readily-accessible portions of the structure,
  • interviews with people who have knowledge of the property and the municipal authorities.

Let’s look at what is involved in each of these, and what the engineer learns from them.

A document review is the first step.

Document review. Usually one of the first things the engineer will do in the course of the investigation is to review available and relevant documents such as drawings, specifications, construction reports, soils reports, and previous studies. This review serves two purposes. The first is to gain an understanding of the structural system. Since many structural elements are covered, the exact details of construction may not be evident from a visual inspection. The second purpose is to alert the engineer to possible problems in the design or those discussed in previous reports. The engineer may also search municipal records for code violations and inspections that might have relevance to the problem

A visual inspection comes next.

Visual Examination. Because most of the structural elements in all but the simplest buildings are hidden by exterior and interior finishes or, in the case of foundations, buried, the engineer must base his investigation on whatever other information is available. The investigative process involves piecing together a puzzle.

The first piece is visible signs that may indicate structural distress. Often the first sign of movement is a door or window that won’t close properly. Other indicators include signs of settlement, components out of level or plumb, cracking, bowing, heaving, etc. These signs may appear in the structural elements of the building or be telegraphed to the interior or exterior finishes or other components of the building.

One sign of structural distress in a building is displacement. A building or one of its components may settle, heave, tilt, sag, deflect or otherwise exhibit signs that it has moved. Movement that is not uniform is easier to detect than uniform motion. If one corner of a building has settled, it is more likely to be noticed than if the whole building has settled together. Unequal settlement or deflection is likely to cause other visible signs of distress such as cracking of structural elements or finishes, and separation of components.

However, not all displacement is a sign of a structural problem. Buildings move for a number of reasons such as changes in temperature and humidity. Determining the cause and significance of displacement is not always a straightforward procedure. An engineer’s trained eye is often required.

In assessing the significance of displacement the engineer will consider such things as the amount of displacement, the apparent cause of the displacement, and the likely consequences if the deficiency is not remedied. One common sign of displacement is cracking in the structural member itself. A few hairline cracks in a concrete foundation are usual and are not likely to have any structural significance. Checking in timber structures caused by the drying of the wood is also common and may or may not be significant. However, cracking in steel structural members or concrete beams or columns usually has great structural significance.

Interviews shed additional light.

Interviews. The engineer will interview people such as building engineers, maintenance people, the owner, tenants, service contractors etc. who have knowledge of the property. The purpose of the interview process is to gain insight into the history of the building’s performance from a structural point of view. While there may be direct evidence of structural problems, often the evidence is indirect.

A limited structural inspection may not be enough. 

Often a limited structural inspection will be adequate. Sometimes, however, questions about the cause of the problem, its extent, and its significance cannot be determined from a limited inspection. In these cases a comprehensive structural investigation is needed. A comprehensive inspection involves the same process as a limited inspection but is a more in-depth investigation and may involve intrusive inspections, detailed measurements, specialized testing, and engineering calculations. Defining the scope of a comprehensive investigation is more difficult than that for a limited inspection because the comprehensive inspections are, by their nature, more open ended.

Volume 13, Number 1

March 2002

Copyright © 2002

The Engineering Advisor is intended to enhance your knowledge of technical issues relating to buildings.  For additional information on any subject, please feel free to call us.  Our commitment is to provide you with timely, accurate information.