By K. Nam Shiu

Structures represent a major capital investment for owners. They expect their structures to be durable and generally have a service life of 30 to 40 years. Parking structures represent a particular challenge to achieve the desired lifetime as they are exposed to exceptionally harsh environments. Although most parking structures are constructed with reinforced concrete, premature corrosion-related deterioration is common. As a result, preventive maintenance and corrective actions are required to achieve the desired useful life of concrete parking structures in a cost-effective manner.

Parking facilities are becoming structurally more complex than ever. Challenges facing the repair designer include:

§         Integration of parking facility operational and structural features;

§         Special attention for structural maintenance to ensure long-term structural integrity;

§         Multi-use facilities or high-rise structures with integrated parking that demand life expectancy well beyond 40 years; and

§         A service environment that is more severe and potentially more destructive than conventional structures are capable of withstanding.


Parking structures in the U.S. frequently show signs of deterioration within ten to 15 years. Removal of the loose and cracked concrete will expose corroded reinforcing bars and in some locations, reinforcement bars may have complete section loss. Such deterioration would need to be repaired to maintain acceptable levels of serviceability and safety in the structure. 

The advantages of addressing deterioration early before the rate of deterioration accelerates are obvious. After that, restoration and repair costs are significantly higher.  It is difficult and costly to catch up after deterioration in the structure starts to accelerate.   As the deterioration progresses, the cost of repairs increase and their effectiveness decreases. When repairs are delayed, you will regain less life before further repairs are necessary.


A systematic approach is essential to successfully rehabilitate and restore parking structures. An effective project delivery system is shown in Figure 1. Similar approaches are described in the American Concrete Institute (ACI) Committee 362(4) “Guide for Structural Maintenance of Parking Structures” and the ACI Committee 364(5) “Guide for Evaluation of Concrete.” This systematic approach thoroughly documents deterioration, identifies root causes, and investigates alternatives so that the owner can make an informed decision regarding the optimal replacement alternatives after considering their requirements and resources.

First, the owner must have a condition assessment performed by an engineer specializing in restoration and refurbishment. It is imperative to understand the root causes of the observed deterioration before remedial actions can be prescribed. Too often, remedial actions are undertaken without the necessary evaluation documenting why the material is deteriorating. The result is that the repair fails prematurely and the distress re-occurs shortly after the repair. Therefore, it is more cost-effective to complete a thorough investigation and evaluation prior to jumping into remedial actions. 

The amount of deterioration and the type and size of the structure will impact the time and effort required for the investigation.  For all structures, however, the first step is a visual examination of the current conditions, coupled with an examination of any project records or drawings that may be available. The need for laboratory material testing varies depending on the nature and extent of deterioration and the type of structural system. Exploratory openings may also be necessary to further investigate or confirm important details or subsurface deterioration. Once the visual examination has been completed, the need for further material testing or exploratory openings can be established based upon the objectives of the condition appraisal. Once the condition appraisal is completed, a comprehensive restoration and refurbishment program can then be developed.

In addition to the more obvious technical issues, it is important to develop a management plan for implementing the repair program. This must address the following key questions:

§         How extensive and severe are the problems?

§         Can the problems be corrected or mitigated?

§         What is the cost for performing the repair?

§         What is the desired remaining service life of the structure?

§         How big is the impact of repair construction to the normal operation?

Management plans become extremely important when dealing with multiple parking structures. The repairs must be planned and systematically programmed to address the repair priorities, budget constraints, number of parking stalls to be vacated, revenue loss, and impact on facility operations. Walker generally develops repair planning and programming over a period of three to ten years.


Repair design consists of selecting appropriate repair schemes, repair materials and methods based on the findings and observations of the investigation.  Preparation of complete contract documents and providing resident services during construction are also essential for proper implementation of the repairs. A structural restoration and refurbishment program will focus on addressing the following key technical issues:

§         Repair deteriorated construction materials to re-establish structural integrity;

§         Perform repair and strengthening to underlying structural members including slabs, beams, columns, and other structural elements for continued safe use of the facility; and

§         Enhance durability by providing protection to extend the useful service life of the structure.

Several repair methods are used to address existing deterioration of structural members and to provide protection to extend the service life of the refurbished structure. 

When considering alternative repair approaches, an important question to ask is “How long should the repair last or how long should the structure last?”  The answer will have a significant impact on the repair design.  If the owner does not intend to keep the structure for more than five years, repairs can be selected to last a relatively short term. Not only will the owner save money up front, but the turnaround time for the repair will also be shorter.  On the other hand, if the owner wants to keep the structure for more than 20 years, long-term repairs and redundant protection should be the design approach. Though the repair may be more costly, take longer to implement, and have a greater impact on patrons, the long-term life-cycle costs would be less. To lessen the adverse impact, it is common to phase major refurbishment work over several years.

Of course, a thorough and appropriate repair design is only the first step in having a successful repair program. There are two key factors for the successful implementation of repair work:

§         A competent repair contractor; and

§         Regular repair observations by an engineer.


The work doesn’t end once the repairs are complete. In order to obtain the full benefit of a repair program, a maintenance program should be implemented after the repairs have been completed. Restoring a structure does not eliminate all the adverse conditions that contributed to the premature deterioration of the facility in the first place.  Some of the built-in deficiencies can be corrected and many other conditions improved.  The structure will, however, require more maintenance in comparison to a newly constructed facility.  The repairs will lower the deterioration rate of the refurbished structure. However, it’s important to note that it will continue to deteriorate at an increased rate compared to a new facility.

Parking facility maintenance allows proper and timely preventive actions that reduce premature deterioration of structural elements and equipment failures.  Maintenance activities are simple and less expensive than implementing repairs. Simple activities include implementing a semi-annual wash-down of the parking structure. This will significantly enhance the life of the repairs. 

So make maintenance a part of facility management and avoid, or at least keep repairs at bay for a while.

1.      Bhuyan, S.; Sabnis, G.M.; and Shiu, K.N., “A Systematic Approach to Extending Service Life of Parking Structures,” Indian Concrete Journal, V. 75, No. 1, Jan. 2001, pp. 58-63.

2.      Parking Garage Maintenance Manual, 4th Edition, National Parking Association, Washington, D.C., 2004, 111 pp.

3.      ACI Committee 362, “Guide for Structural Maintenance of Parking Structures (ACI 362.2R-00) (Reapproved 2005),” American Concrete Institute, Farmington Hills, Mich, 2005, 15 pp.

4.      ACI Committee 364, “Guide for Evaluation of Concrete”

5.      “Structures before Rehabilitation, 364.1R-07,” American Concrete Institute, Farmington Hills, Mich, 2007.

Selected for reader interest by the editors.
K. Nam Shiu, FACI, is Vice President of Walker Parking Consultants, a firm that provides specialized restoration and waterproofing consulting, experienced restoration engineering, and state-of-art restoration and preservation strategies and services, helping building owners extend the service life and value of their structures. He is actively involved in a number ACI technical committees, including being a member of ACI Committees 209, Creep and Shrinkage in Concrete; 364, Rehabilitation; 365, Service Life Prediction; 437, Strength Evaluation of Existing Concrete Structures; and 444, Experimental Analysis for Concrete Structures. He is also a member of the Strategic Development Council (SDC) Membership Committee.