Since the sudden collapse of Champlain Condominium Towers South in Florida, increased scrutiny has been placed on the structural conditions of reinforced concrete ocean-front high-rises. Built-in 1981, the building was known to have deteriorated conditions, yet no action was taken when engineering reports recommended that extensive repairs be completed.
Marine environments often create conditions conducive to concrete deterioration that can cause reduced structural capacity in building framing. For this reason, special consideration must be given to the management of older, reinforced concrete structures in coastal areas. Cyclic investigations by qualified, licensed structural engineers can greatly reduce the likelihood of deterioration in these buildings and ensure they remain safe and structurally sound for many years.
Preliminary Aspects of a Concrete Structure Investigation
Engagement of a structural engineering team with experience in concrete structure testing, assessment, repair and rehabilitation is key to a successful structural integrity investigation. Concrete structure investigations typically begin with a preliminary assessment to develop an initial understanding of the structure’s design and behavior, condition and performance over time. Engineering teams will review available construction, repair and maintenance documents (e.g., drawings, specifications), identify building code requirements in effect at the time of design and construction (i.e., the “design code”) and meet with stakeholders to establish scope and expectations for the building evaluation.
Structural Observations and Condition Survey
Following a preliminary assessment, the engineering team will conduct a field investigation to document structural observations and verify the accuracy of information obtained from the document review. A condition survey should also be completed at this time to evaluate the physical condition of the as-built structure. Utilizing visual observations of conditions and construction materials testing, the survey should document the approximate extent and severity of distress or deterioration of the concrete structure as well as conditions that could adversely affect its strength, load-carrying capacity, durability, or service life.
Testing the Structure
Engineers may use a variety of nondestructive and laboratory testing methods and instruments to augment the building assessment. Nondestructive testing uses methods like corrosion detection, ground-penetrating radar and ultrasonic pulses to help verify original construction or repairs as well as any existing conditions.
Laboratory testing is often used to determine concrete strength (e.g., compressive, tensile, flexural) and evaluate various concrete properties (e.g., air content, carbonation, permeability). Building owners tend to resist laboratory testing, since it involves drilling holes into the existing structure to obtain multiple concrete core samples. Regardless of their concerns, the engineer needs to be able to persuade the owner that a testing program is essential to the project.
Evaluation, Reporting and Recommendations
Upon completion of a field investigation and testing, the engineering team will evaluate the findings to assess the overall condition of the building, the significance of observed conditions, effects of concrete conditions on load-carrying structural capacity and the structure’s remaining service life.
Data and evaluation results from the investigation should then be compiled in a comprehensive illustrated report summarizing the significance of the observed conditions of the structure’s various components as well as the results of materials testing and analysis. Follow-up recommendations and a suggested schedule for building repair and maintenance should be included along with a cost estimate.
Repair and Rehabilitation
As the assessment project proceeds, the engineering team must keep the building owner or manager informed of its general progress and impress upon them the imperativeness and urgency of recommended repairs. Surprises at the end of investigations are not advisable and can lead to delays in implementing repairs.
Moreover, since the assessment team has comprehensive knowledge of the building’s condition, structural functions and reasons for deterioration, it is advisable that the team be commissioned to design the repair program after the assessment is complete.
Managed properly, reinforced concrete high-rise buildings can be maintained safely and in good working order for decades. Evaluating and addressing structural problems long before significant deterioration occurs is essential to maintaining structural integrity and prolonging service life.