Structural Condition Assessment — An Introduction

Abstract

Structures, like people, never get younger. Structures, like people, can maintain their good health with age, if properly cared for, examined, and treated when needed. Structures, like people, need periodic check-ups as part of their preventive care to ensure their fitness; and need examination when exhibiting signs of illness. Interestingly, structural condition is often referred to as fitness-for-service. This paper is an introduction to a series of eight papers on structural condition assessment, delivered at the 2006 Structures Congress in St. Louis, Missouri, and published in the Proceedings of the Congress. It is based heavily on the Preface written by the author in the book, Structural Condition Assessment, Robert T. Ratay, Editor, John Wiley & Son, 2005. The authors of these papers are the authors and co-authors of the corresponding eight of twenty-one chapters in the book. The seven topics were selected for this series of papers because they represent the most frequently assessed building-type structures and construction materials. It may be said that a structure that has withstood the combined effects of use, abuse, loads and environmental conditions over time has, in effect, proven itself. However, buildings, bridges, parking structures, stadiums, and all other structures do deteriorate with time as the result of repeated loadings, exposure to the elements, aging of materials, wear-and-tear from normal use, abuse, inadequate maintenance, and other factors. We design structures for strength, stability and deformation, but the most common problems that occur are those of deteriorations, durability and serviceability. The deterioration may progress to the point, or one or more individual debilitating events may have the consequence, of compromising the structure's strength, stability or serviceability. Evaluating the condition of structures is an area of professional practice within the field of structural engineering. It is an increasingly active business driven in part by the need for maintenance, repair and rehabilitation of buildings, bridges and other deteriorating infrastructure; by change in ownership; by the choice of adaptive reuse of facilities; by the necessity of retrofitting for ever-changing code compliance; by damage sustained as the result of natural hazard; and, particularly for corporate and public buildings, by the need for increased physical security. In simplified terms, structural condition assessment consists of activities of visual observation, measuring, photographing, probing and sampling, field and laboratory testing, engineering analyses, record keeping, documentation, and report preparation. Appropriateness and accuracy of field measurements, testing and analyses notwithstanding, the reliability of the condition assessment lies in the interpretation of the collected and generated data and in the judgments converting them to accurate conclusions and recommendations. Condition assessment may be made of apparently "healthy" as well of visibly "damaged" structures. It is not to be confused with forensic investigation of structures, which is the determination of the causes and modes of failure (where failure is not only collapse but also the unacceptable difference between intended and actual performance). A very important part of the evaluation and reporting, particularly if the structure will be repaired and/or restored, is the recognition of the adverse condition as being a "defect" or "deterioration". Defects are usually errors in design or shortcomings in construction or imperfections in materials; deterioration is the gradual loss of original properties; and defects often enhance deterioration. Both the predicted consequences and the recommended remediation are influenced by whether the condition is the result of a defect or deterioration. While "a structure is a structure", each is unique in the combination of its design, construction, history of use and abuse, and quality of its maintenance. Therefore, while there are "typical" signs that indicate "obvious" conditions, some unrecognized details may distort one's conclusions. There is the need in the structural engineering profession to instruct the novice and guide the experienced engineer in performing the condition assessment of structures and their materials: how to conduct the assessment; how to inspect the structure; how to recognize various conditions; what to look for; what methods of field examination, laboratory testing, and analytical evaluations are available; how to report the findings; and what to recommend. This series of presentations and papers are intended to fill at least part of that need. They include description of assessment strategies, methodologies, techniques and equipment.