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Parking Garage - News from Archives
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PARKING GARAGES AND RESTORATION
| BY KEVIN SHAW, B.TECH July, 1982 An Ounce of Prevention is Worth a Pound of Cure With parking garages perhaps the most costly item for a condominium to maintain, the cost of a survey by an engineering firm specializing in building science technology can save the corporation a great deal of money and inconvenience in the long run. The purpose of a parking garage survey is to review the existing conditions of the various components of the structure and develop a plan for its maintenance and repair. The components include structural elements (slabs, columns and beams), waterproofing systems (membranes), expansion joints and mechanical/electrical systems (drainage, snow melting, exhaust and fire safety). Critical to the Functionality The various elements, whether they are structural, mechanical/electrical or protective waterproofing membranes, are all critical to the functionality of the parking garage. They are all susceptible to deterioration by a number of factors inherent in the design and use of the structure. Environmental Issues The two main factors that affect the life expectancy of parking structures are the environment in which the garages are built and the environment related to their use - car parking. Parking garages are subjected to a number of environmental conditions whether they are constructed above or below grade. In garages constructed above ground, the concrete structure is exposed to the effects of precipitation. Rain and snow can penetrate the exposed concrete elements and cause deterioration of the structure through the effects of freeze-thaw cycling. This causes spalling/delamination when moisture trapped within the structural elements expands and contracts with the changing temperatures, thereby fracturing the concrete. Those constructed below grade must be shielded from the surrounding environment. Moisture within the soil will penetrate the concrete structure if it is not protected by a waterproofing membrane that prevents moisture from entering the concrete and causing deterioration of the reinforcing steel. Moisture is Main Contribution to Deterioration Parking garages are also subjected to a harsh environment caused by their traffic. During the winter months, cars bring in moisture and deicing salts that drip onto the reinforced concrete structure. Moisture, particularly when combined with deicing salts, is the main contributor in the deterioration of reinforced concrete within parking garages. Steps must therefore be taken to protect the structure from the effects of these. The most common solution is the installation of a water-proofing membrane over the surface of a suspended slab. Structural Elements Reinforced concrete is very long-lasting with a proven record of performance as a structural material. Concrete is, however, susceptible to deterioration as a result of the corrosion of the reinforcing steel within the concrete elements. Corrosion occurs as a result of moisture and salts migrating through cracks and defects in the slabs. Corroded reinforcing expands as a result of the accumulation of rust. The deteriorated reinforcing exerts pressure on the surrounding concrete and eventually causes cracking and delamination of the surface material. If this process is left unchecked, and allowed to continue, the structural capacity of the component can be significantly reduced as a result of the deteriorated reinforcing steel. A survey of the concrete structural elements should include a visual examination of the garage roof deck, beams, columns, perimeter walls, suspended slabs, parking ramps and slabs-on-grade. The purpose of the visual inspection is to identify existing conditions, such as cracks, spalling, delamination and signs of water leakage. Findings should be copied to a plan of the parking garage to track the affected areas. Structural defects or concerns noted during the inspection should be reviewed by a structural engineer to determine if remedial action is required. Existing Condition of Components Based on the visual survey, site testing may be undertaken to provide the consultant with empirical data regarding the existing condition of the structural components. Testing is normally under-taken only if the visual survey has uncovered defects in the concrete elements (i.e., spalls, delaminations or water leakage). Based on the results of the visual survey and the site testing, recommendations can be made regarding if or when repairs should be undertaken. If the deterioration is limited, repairs may be deferred with the understanding that the structure will be regularly monitored. Site testing results are one of the tools that can be used to track the progress of defects by comparing findings from tests conducted at intervals. Site testing can provide information on a number of factors affecting the life expectancy of the structural components and can be divided into two categories, destructive and nondestructive. The destructive tests require the removal of core samples from the concrete components (typically slabs). Samples are normally 4 inches in diameter and are cored through the component with an electric drill equipped with a coring bit. The core samples are then submitted to a laboratory for testing. The locations from which the samples are removed must be repaired to prevent moisture entry into the surrounding concrete. Non-destructive tests can be performed on the existing structure without causing any damage to the components. Chain-Drag Survey Non-destructive testing may be undertaken to verify the following: Extent of Delamination. A chain-drag survey can be used to determine the extent of surface delamination in a concrete slab. The test involves swinging a single length of heavy chain side to-side over the concrete surface. Delaminated sections can be detected by a hollow sound when the chain passes over the upper surface. Hammer tapping vertical (columns, walls) and overhead (soffit slab) surfaces can also be used to detect pockets of spalled concrete. Chain-drag tests are not normally performed on slabs-on-grade as these contain less reinforcement than structural slabs and are therefore less susceptible to the effects of corroding steel. Depth of Concrete Cover over the reinforcing steel in a structural element is integral to its life expectancy. The concrete cover aids in reducing the amount of moisture migrating toward the steel and increases the forces required for deteriorated reinforcing to crack or delaminate surface material. The depth of concrete cover can be measured using an electronic cover meter. Core samples and laboratory testing may be undertaken to verify the following conditions: Chloride Content. Core samples taken from the concrete can be analyzed in a laboratory to determine the amount of chloride ion present. Chloride content can aid in determining if corrosion of the steel within the concrete is likely to occur. Compressive Strength. Concrete cores taken from the structure can be tested in a laboratory to determine the compressive strength of the material. Knowing this is important if repairs to the structure are necessary. Air Entrainment. In concrete, air entrainment can be calculated in the laboratory from a core sample. This is an important measurement in calculating concrete durability. Air-entrained concrete has a greater resistance to freeze-thaw cycling. Corrosion Potential can be determined by taking half-cell measurements at various positions on the concrete structure. These measurements can determine if conditions are right for corrosion to take place within the concrete element. Testing requires that the concrete slab be cored to expose the reinforcing steel. Waterproofing Membranes The purpose of incorporating waterproofing membranes into the design of parking structures is twofold: to prevent water penetration into the garage and to protect the reinforced concrete structure. Waterproofing membranes come in a variety of forms and materials and are applied to the various components of the structure based on their performance characteristics. Membranes are typically installed on the foundation walls, the garage roof deck slab, suspended slab ramps and intermediate/suspended slabs within the garage. Membranes are not normally installed on slabs-on-grade (i.e., lowest garage floor level) as there are typically no steel reinforcing bars within the slab. Prevent Water Penetration Membranes prevent water penetration through the structure, thereby protecting vehicles and the mechanical and electrical equipment inside. Membranes also keep water/moisture away from the concrete thereby preventing the corrosion of the reinforcing steel within the structural components. Because waterproofing membranes are installed to protect the concrete, they are exposed to the same environmental conditions as the concrete as well as the added effects of structural movement and vehicular and pedestrian traffic. It is therefore critical that the membranes be routinely examined for signs of deterioration and wear. With the exception of traffic toppings installed on suspended slabs, the examination of the majority of the membranes is hindered by their location under site landscaping (sod, asphalt or concrete). Depending on the outcome of the interior inspection of the structural elements, the consultant may recommend that a portion of the overburden be removed on the exterior of the structure (i.e., create a test pit), to examine the condition of the membrane installed on the garage roof deck. The waterproofing membranes are examined to determine a number of factors: Type of System. As design drawings often do not specify the exact type of waterproofing to be installed, a visual examination determines the membrane type. For membranes installed on the exterior of the structure, a test pit (as described above) must be prepared in order to expose them. Membranes installed on suspended or intermediate slabs (traffic-bearing systems) are more easily inspected as they are typically installed on the surface of the slab. Traffic bearing systems can be divided into two broad categories: thin and thick. Thin systems are more easily inspected as they consist of an elastomeric membrane with a wearing course. The combined thickness of the two layers averages approximately 60 Mils (1/16 in). As the two layers are bonded together, observable defects suggest a failure of both the waterproofing and wear course layers. Thick systems normally consist of a bituminous waterproofing membrane protected by an asphalt or mastic wearing course. Visual examination of the wearing course can provide clues as to the condition of the membrane below, but a more thorough investigation may require coring through the wearing course and membrane. A core can reveal the condition of the membrane as well as the bond between it and the slab below. Existing Condition As membrane systems have the potential to be damaged by a number of factors, a thorough examination by a consultant can identify potential and existing problem areas. Waterproofing membranes installed on the exterior of the structure are susceptible to damage from debris in the overburden, such as tree roots. A test pit allows the consultant to inspect the membrane for cracks, scrapes and ponding water. It also provides the consultant with the opportunity to verify that the membrane is bonded to the concrete deck and to determine if the concrete slab below the membrane is delaminated. Traffic-bearing systems are inspected in critical areas such as drive lanes, turning radii, ramps and parking stalls to itemize damage or deterioration caused by vehicular and pedestrian traffic. Accelerating, braking and turning can exert tremendous forces on membrane systems installed over the structural slabs and can lead to their premature failure. Expansion Joints are incorporated into a structure to prevent distortion, cracking and breaks in building materials by allowing for possible movement that may occur due to expansion and contraction of these materials and/or building settlement. Expansion joints within a parking garage must also be waterproofed to prevent the entry of moisture into the structure. As an expansion joint is required to accommodate movement within the structure while remaining waterproof, it can often be an area where water leakage occurs early in the lifespan. Visually Inspected The expansion joints within the parking garage should be visually inspected as part of a condition survey. Any areas of water leakage noted during the inspection should be copied to the plans of the garage for reference when preparing a repair solution. Mechanical and Electrical Systems A number of mechanical and electrical systems are incorporated into the design of a parking garage, several of which are integral to the life expectancy of the structure. Critical systems include drainage and snow melting systems. For the review of mechanical and electrical systems, the consultant often relies on information from the property manager and site staff regarding their operation. and maintenance. For example, a large portion of a snow melting system cannot be visually inspected as it is located within the ramp slab or beneath the traffic bearing membrane. The consultant must therefore depend on the manager and/ or site superintendent for information regarding its current operation. It is therefore recommended that managers keep accurate records of maintenance repairs and possible failures of all electrical and mechanical systems. A review of the parking structure should' include observations of the drainage condition of the garage roof deck, intermediate and lower floor slabs. Standing water can be a leading cause of deterioration of waterproofing membranes, as well as the reinforced concrete structure. Areas of ponding water and negative sloping, as well as observations of blocked drains and damaged grates, should be noted and copied to the parking garage plans. A thorough survey can determine if changes to the drainage system (e.g., additional drains) are required to shed water from the horizontal surfaces properly. Snow-Melting Systems Ramps for parking garages are an important element as they are typically the main access route for vehicles. Exterior ramps must be equipped with snow-melting systems to maintain a safe driving surface during the winter months. The snow-melting systems are critical as icy surfaces could lead to personal injury and/or damage to the structure and/or vehicles. Snow-melting systems consist of electric cables or hot water/stream/glycol filled pipes. The systems are either embedded within the concrete slab or installed between the concrete slab and a traffic bearing system. The operation is essentially the same; the cables or pipes heat the surrounding materials to prevent the build-up of ice or snow on the upper surface of the ramp. Parking ramps should be inspected for signs of cracks, and or movement in the slab or wearing course, as these may indicate possible stress or damage to the snow melting system embedded in the slab below. The control and operating systems can also be reviewed for signs of deterioration due to moisture ingress and physical damage. Managers should be aware that some municipalities require garage lighting to be updated based on current codes. The current edition of the Ontario Building Code requires a minimum illumination level of 50 lux. (4.6 ft. candle) within garages. Lighting levels within the parking garage can be verified by the consultant using a light level meter for measurements taken at floor level. Review Air Intake and Exhaust The exhaust of carbon monoxide fumes from the interior of the garage is essential for the protection of condominium residents. Air intake and exhaust areas should be reviewed during the survey and comments regarding possible problems noted in the written report. A survey of the parking garage by an experienced consultant is an invaluable tool to aid in the identification of potential and existing problems. Routine evaluation of a parking. structure can identify potential problems and provide a condominium with the valuable time that is necessary to prepare for the inevitable repair costs associated with parking garage rehabilitation. The preparation of a maintenance and repair strategy is important, for once a concrete structure has begun to deteriorate the problems only increase. Moisture and salts will migrate through the structural elements and increase the extent of the repairs that will eventually be necessary for the structure to remain functional. Many condominiums elect to defer repairs due to the high cost of rehabilitation, but delay will only lead to increased repair costs in the future. The repair of concrete structures is a costly and time-consuming undertaking A thorough review of the parking garage components by a qualified consultant, on a regular basis beginning early in its lifespan, can assist a condominium in preparing a comprehensive strategy for maintenance and repair. Kevin Shaw, B. Tech. (Arch.Sc.) is Project Manager with the consulting engineering firm, Coulter Building Consultants Ltd., Consulting Engineers & Building Scientists, based in Oakville Ontario. Coulter Building Consultants Ltd. provides engineering services to multi-unit residential communities including condominium corporations and non-profit housing, in the fields of building envelope and structural engineering, reserve fund studies, building condition surveys, technical/performance audits. The firm is a member of the Canadian Condominium Institute, Golden Horseshoe Chapter, the Association of Condominium Managers of Ontario and the Ontario Non-Profit Housing Association | | ||||