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11 The process of undertaking renewal for an in-use airport park- ing structure is summarized in a flow chart shown in Figure 9. There are four major components in the renewal planning: a history and condition evaluation; selection of appropriate renewal design and approaches; preparation of construction documents; and detailed plans for construction administra- tion and monitoring. This chapter presents effective practices in documenting airport parking structure existing conditions and renewal history. Documentation of the history and condition of the airport parking structure includes a physical description, including the type of construction, geographic location and environ- mental exposure, age, deterioration, and built-in deficiency; and existing conditions and renewal history. Questionnaire responses indicated that all surveyed air- port hubs are keeping records on the existing conditions at their parking structures. However, respondents indicated that the physical description and renewal history data are usually retained by the facility department rather than the parking operations department. TYPES OF CONSTRUCTION The most common types of airport parking structure construc- tion, used in 49 of 51 surveyed structures, are steel and con- crete construction. Steel structures were reported to be 22 and 26 years old. The common concrete structural systems are pre- stressed (post-tensioning) cast-in-place concrete; precast con- crete; and conventionally reinforced concrete (short span). GEOGRAPHIC LOCATIONS AND EXPOSURE Parking structures are subjected to harsh and corrosive envi- ronments (7), including: ⢠Exterior weathering (thermal cycles, ocean salt sprays, freezing and thawing cycles, and water damage, etc.) ⢠Wear and tear from vehicular traffic ⢠De-icing chemicals that promote corrosion of embed- ded steel ⢠Mechanical damage from snow removal operations. The primary deterioration experienced by concrete park- ing structures is corrosion of embedded reinforcement steel (8) such as mild steel bars (rebar) and high strength pre- stressed steel tendons. Chloride ion-induced corrosion is ranked first among causes of steel corrosion in concrete; the second most prevalent factor is freezing and thawing damage. Concrete parking structures are categorized and designed for the following five zones recommended by the ACI and shown in Figure 10 (8): ⢠Zone IIIâExposed to moisture with freezing and thaw- ing cycles and de-icing salts ⢠Zone IIâExposed to moisture with freezing and thaw- ing cycles but no de-icing salts ⢠Zone IâExposed to moisture; that is, all others except Zones CC-I and CC-II ⢠Zones CC-IâAreas within 1 mile of salt water bodies ⢠Zone CC-IIâAreas within 2 to 5 miles of salt water bodies. Parking structures located in Zone III are expected to be exposed to harsher environments than Zones I, II, or CC-I and CC-II. Consequently, parking structures in Zone III are antici- pated to experience accelerated deterioration. Airport parking structure renewal plans would need to account for climatic exposure (8). Proportionally, renewal intervals in areas of cli- matic extremes are typically shorter and the renewal and cumu- lative costs higher (see Figure 6). AGE OF FACILITIES The age of the parking facility has a direct impact on the type and frequency of renewal plans (7). More age-related deterioration equates to more frequent, more extensive, or more costly renewal. Additionally, the timing of renewal and the existence of built-in deficiencies in structures are factors in deterioration. Timing of Renewal The rate of deterioration for airport parking structures accel- erates with time. An empirical deterioration curve is shown in Figure 11 (7). The x-axis represents the time since con- struction and the y-axis indicates the level of sustained dete- rioration or repair/restoration costs. Each parking structure would have its own specific deterioration curve. chapter three DOCUMENTATION OF HISTORY AND EXISTING CONDITIONS
12 FIGURE 9 Parking facility renewal plan.
13 Deterioration necessitates regular renewal. At point A on the curve in Figure 11, a renewal plan is undertaken, reducing the level of deterioration down to point A1. The distance from A to A1 represents the renewal costs. However, if the renewal program is not carried out until point B, the parking structure will have sustained more deterioration (point B is noticeably higher than point A). At that point, costs for renewal would be larger than that at point A (point B to point B1 is longer than point A down to A1). Even then, the deterioration level at point B1 would still be higher than the deterioration level at point A1 and the cost greater with less improvement. In summary, Figure 11 illustrates that the earlier the renewal FIGURE 10 Climatic exposure zones for parking structures (8). Note: Hawaii and Alaska were not included in the documented figure [Source: American Concrete Institute (ACI) Technical Committee 362 ]. FIGURE 11 Parking structure deterioration curve (Source: Parking Structures: Planning, Design, Construction, Maintenance and Repair) (7 ).
14 process starts, the more cost-effective the renewal process will be. There are different models simulating the deterioration of parking facilities (7, 9). However, almost all of them are empirical, and more research is needed to develop a typical deterioration curve for airport parking structures. Built-in Deficiency Older airport parking structures have built-in deficiencies that were not recognized by design professionals at the time of design and construction. Prior to the 1970s, corrosion-related deterioration in concrete structures was not fully understood, and had not been identified as the prime deterioration cause for concrete structures. Consequently, parking structures built in the 1970s do not have the same level of protection against corrosion for embedded steel as those built in later years. For example, concrete cover over reinforcing steel was speci- fied at ¾ inch in the 1970s instead of the current 1½ inches (5, 10). With less concrete cover protection, the reinforcing bars are more likely to be exposed to chloride ions. Conse- quently, local delamination and spalls are more commonly found on parking floor slabs built in the 1970s than those in newer structures. For pre-stressed concrete construction, new developments in the past 25 years are more distinct and significant. From 1955 to 1975, a single high-strength wire with a button head anchorage was used. The wire was protected with rust- inhibiting grease wrapped inside paper sheathing. This sys- tem, though effective and functional, provides little to no protection against corrosion. From 1975 to 1985, the paper sheathing was replaced with plastic. The plastic sheathing provides much better corrosion protection against chloride ion contamination. After 1985, a new encapsulated seven- wire strand system was introduced. Full encapsulation fur- ther reduces the possibility of unanticipated tendon exposure during the stressing operation in construction. The result is that newer pre-stressed concrete structures experience far less deterioration than their earlier counterparts. As building technology evolves, designs for parking struc- tures become more sophisticated. Commonly encountered deterioration is mitigated with newer hardware and better practices, resulting in more durable parking structures that require less frequent renewal. Survey respondents provided two examples of major renewal for airport parking structures. The parking structure at Chicago OâHare International Airport (ORD) was built in 1969 and underwent a major three-year renewal program beginning in 1995, when it was 26 years old. The airport parking structures at Denver International Airport (DEN) were built in 1993 with pre-topped precast concrete double- tee girders and underwent sealant replacement in phases for all joints between 1998 and 2009, beginning when the parking structure was about five years old. Both airports are located in the ACI climatic exposure Zone III. EXISTING CONDITIONS AND RENEWAL HISTORY Survey respondents indicated that airports are keeping main- tenance records for their parking structures, which provide managers information on what has been done and what needs to be scheduled in the future. Records include condi- tion appraisal reports, repair construction documents, repair contracts, repair construction field reports, and records of renovation and component replacement. Airport operators often perform annual walk-throughs to visually evaluate the condition of their parking structures. This information can be used to understand the condition of the structure and approximately what stage the deterioration has reached. However, periodic and more in-depth evalu- ations of the parking structures are needed. The industry standard evaluation process is outlined in the attached flow chart as shown in Figure 12 (11). The process starts with a preliminary evaluation or condition survey. The purpose of the preliminary evaluation is to: ⢠Document visible distress such as cracking, exposed corroded reinforcement, water stains or leaks through cracks or expansion joints, spalled concrete, and corro- sion staining. ⢠Assess condition of previous repairs, if applicable. ⢠Evaluate performance of routine and preventive main- tenance items. ⢠Identify areas that may need further investigation and/ or repairs. Survey respondents indicated that preliminary investiga- tions are commonly performed annually by in-house staff. In some airports, managers engage engineering consultants to provide both the preliminary and subsequent in-depth evalu- ations and investigations. During detailed investigations, unusual conditions are high- lighted and evaluated. For example, when previous repairs are not performing as expected, the root cause(s) for the premature failure of the repair or the reasons for continuing deterioration are investigated, and then a new repair approach is developed. A typical case is one reported at OâHare. Parking struc- ture replacement expansion joints failed within two years after installation, although the anticipated service life of the expansion joints was 10 years. Investigation into the likely causes of the observed distress resulted in specifying more durable replacement expansion joints to be installed that suc- cessfully corrected the unexpected low performance of the failed expansion joints. More detailed information about this case history can be found in Appendix B.
15 FIGURE 12 Evaluation process [Source: American Concrete Institute ACI Committee 364.1R (11)].
