ACI MNL-3-2016 Guide to the Code for Assessment Repair and Rehabilitation of Existing Concrete Structures (Second Edition).pdf

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1、An ACI / ICRI Manual Guide to the Code for Assessment, Repair, and Rehabilitation of Existing Concrete StructuresA Companion to ACI 562-16MNL-3(16) Guide to the Code for Assessment, Repair, and Rehabilitation of Concrete BuildingsSecond EditionUpdated by Khaled Nahlawi, ACI Senior Engineer, under th

2、e review and approval of an ACI/ICRI review group consisting of Chair Jay H. Paul and members Eric L. Edelson, Fred R. Goodwin, Keith E. Kesner, and Antonio Nanni. The first edition was prepared by the team from Wiss, Janney, Elstner Associates, Inc., of Project Manager Richard A. Walther, Stephen W

3、. Foster, Gary J. Klein, and Richard C. Reed with comments by ACI Committee 562, Evaluation, Repair, and Rehabilita-tion of Concrete Buildings, and ICRI Committee 150, ICRI Notes on ACI 562 Code Requirements. Guide to the Code for Assessment, Repair, and Rehabilitation of Concrete Buildings2ndEditio

4、nFirst Printing: September 2016ISBN: 978-1-945487-20-0Copyright 2016 by the American Concrete Institute and theInternational Concrete Repair Institute.All rights reserved.Managing Editor: Khaled Nahlawi, Ph.D., P.E.Art Program: Claire HiltzPhoto Editor: Ken Lozen, FICRI, FACIManager, Publishing Serv

5、ices: Barry M. BerginProduction Editors: Carl R. Bischof, Tiesha Elam, Kaitlyn J. Hinman, Kelli R. SlaydenPage Design therefore, safety for the workers in these areas was paramount. Weekly safety meetings were held on site with all crews and subcontractors to make everyone aware of the specific safe

6、ty concerns present in their work areas. Work proceeded concurrently on multiple levels of the garage and extra precautions were taken and monitored to ensure workers were safe from falling debris from the extensive coring operation above. Exterior shear wallsIFourth-Level Crack Repair and Phase 1 F

7、oundationsThe first phase of the repair was to fix the large shear failure crack within the fourth-level transfer slab, which spanned four column bays. The repair comprised conventional selective demolition and replacement along with epoxy injection. This would further weaken the already damaged tra

8、nsfer slab, so additional shoring was installed. Additional steel was added to the repair areas where concrete was removed, and the floor was re-placed to its original level. Simultaneously, work began on Phase 1 of the foundation strengthening, which consisted of areas that fell outside of the exis

9、ting shoring and could easily be accessed. The foundation work consisted of demolishing and removing the slab-on-ground concrete, excavating down to the existing concrete pile caps, installing new steel helical piles, placing steel reinforcement, and placing of the new expanded pile caps. During exc

10、avation of the first pile cap location, it was discovered that the existing cap was only 16 in. (406 mm) deep. However, the original construction as-built drawings showed a pile cap depth of 29 in. (737 mm). The same was true for 10 out of 12 of the Phase 1 pile caps. Based on these existing conditi

11、ons, the structural engineers had to revise their original designs.IILevel 3 Drop Panels and Upper-Level Exterior Shear WallsThe second phase of the project was to install the post-tensioned drop panels on the underside of the fourth-floor slab. The ceiling was prepped using hydrodemo-lition, and th

12、en column enlargements were installed on Level 3. Six-hundred 8 in. (203 mm) holes were cored through the fourth-level slab to install “shear lug keys.” These would tie the new drop panel to the fourth-level overlay, creating a new composite slab. The area of the drop panel construction was over 770

13、0 ft2 (715 m2) and was split up into four subphases. The process took over 2 months, 400 yd3 (305 m3) of concrete, 22,000 ft (6705 m) of post-tensioning cable, and over 42 tons (38,000 kg) of reinforcing steel to complete. Because access within the formwork was limited, self-consolidating concrete w

14、as used. The steel cages for the new drop panels were hung from the lug keys, and the post-tensioning cables were installed within the cage. Post shores were installed underneath the drop panel formwork and across 100% of the tower area on all three levels of the garage. This shoring would support t

15、he new construction of the drop panels and overlay. In total, 2800 post shores and 200 shoring towers were used for the drop panel and overlay construction. Also during the second phase, exterior wall segments at the four corners of the building were converted to concrete shear walls. The existing w

16、indows and 4 Project CompletedThe Dolphin Tower project was very challenging and used many interesting and groundbreaking design concepts. Constant communication be tween the contractor, design engineer, and owner was a necessity to adapt to continuously changing condi-tions, which required quick so

17、lutions to maintain the aggressive schedule. Despite many challenges, the repairs were completed on schedule and under budget.concrete masonry unit (CMU) walls were removed, reinforcing steel was installed, and concrete was placed. IIILevel 4 Overlay Slab, Interior Shear Walls, Upper-Level Shear Rep

18、airsThe third phase commenced with construction of the fourth-level overlay slab. The overlay was roughly 13,500 ft2 (1250 m2) split into two subphases. Over 68 tons (61,700 kg) of reinforcing steel and 300 yd3 (230 m3) of concrete was used. Additionally, because the floor height was being increased

19、 by 6 in. (152 mm), the two elevator doors required relocating. After the overlay slab was completed, interior shear wall construction began starting on the fourth level and continuing up to the penthouse. In conjunction with the installation of new interior shear walls, upper-level slab overstress

20、was relieved through jacking. Once the concrete cured, the shoring would be released, redirecting stresses in the floor to the new shear wall. To supplement lateral wind load capacity and address upper-floor punching, existing CMU walls were filled with grout and 108 steel “T-columns” were installed

21、 at various locations. Originally, these columns were to be placed-in-place concrete, much like those done on the garage levels. IVPhase 2 FoundationsThe final stage of work was to finish the second phase of the new foundation pile capsthose areas which were previously inaccessible due to the substa

22、ntial amount of shoring required for the fourth-level repairs. For these foundations, the existing pile caps were 4 ft (1.2 m) or more below the upper slab-on-ground, resulting in excavations extending 2 ft (0.6 m) or more below the water table. Consequently, undermining of the slab surrounding the

23、excavation areas was a major concern. Temporary sump-pump pits were created to lower the water table level and reduce soil erosion. Several large concrete piers buried within the existing foundations were discovered, making it very difficult to install helical piles, so these had to be removed. The

24、final foundation area to be completed was within a subgrade mechan-ical pump room. Due to limited headroom, holes were punched in the ramp slab above to install the helical piles. Because of the depth of this excavation, the water was again an issue and undermining of the surrounding slab needed to

25、be controlled. Therefore, soil grouting was used to maintain support of the existing mechanical units and prevent further erosion. Steel overlayDolphin Tower CondominiumsOwnerDolphin Tower Condominium AssociationSarasota, FLProject Engineers/DesignersKarins EngineeringSarasota, FLMorabito Consultant

26、sSparks, MDRepair ContractorConcrete Protection applicability of the code; responsibilities of the licensed design professional, including submittals to building officials and the owner; and development of maintenance recommendations. Chapter 1 also specifies the requirements for performing a prelim

27、inary evaluation by examining the available information and determining if the proposed changes, imposed changes, or both, are safe, followed by how the structure will be affected by these changes. 1.1GeneralACI 562 Code is written to the licensed design professional (LDP) and provides guidance and

28、consistency when assessing, designing, repairing, and rehabilitating concrete structures. It is intended to supplement the International Existing Building Code (IEBC), as part of a locally adopted code governing existing buildings or structures, or as a stand-alone code for existing concrete structu

29、res. The intent of the Code is to address minimum safety requirements and provide some uniformity and standardization to the industry for assessing existing concrete structures. The mostly performance requirements included in the Code direct the design professional to 11satisfy specific requirements

30、, while providing some leeway, flexibility, and direction with the repair and rehabilita-tion of concrete structures. Concrete structures constructed before 1971 that require repair, rehabilitation, or strength-ening were probably designed based on the allowable stress approach whereas the demand an

31、d capacity requirements of ACI 562 are based on strength design. The demand and capacity requirements in ACI 562, however, are based on the strength design approach. The engineer is encouraged to consider strength design provisions of this Code as a check when assessing existing structures originall

32、y designed with allowable stress methods. An existing structure, as defined in Chapter 2 and consis-tent with the definition in the International Building Code (IBC)/IEBC, is one for which a legal certificate of occu-pancy has been issued, or one that is finished and permitted for use. If no certifi

33、cate of occupancy has been issued, or the building has not been permitted for use, the building is still considered new construction, and provisions of ACI 318 used in its design will govern.Licensed design professionalThe LDP, as defined in the Code and consistent with ACI Concrete Terminology (CT)

34、, refers to an individual for a project who is licensed to provide design services as defined by the statutory requirements of professional licensing laws of the state or jurisdiction in which the project is to be executed and who is in responsible charge of the structural assessment, rehabilitation

35、 design, or both. The LDP should exercise sound engineering knowledge, experience, and judgment when interpreting and applying ACI 562. 1.2Criteria for the assessment and design of repair and rehabilitation of existing concrete structuresDetermination of applicable building codesBefore performing an

36、 assessment, repair, rehabilitation, or strength-ening of an existing concrete building or concrete structural element, the LDP of the project should first determine the building codes applicable to the project, understand their relevance to assessment and repair, rehabilitation, and strengthening d

37、esign decisions, and the relationship between the different standards. Per ACI 562, the LDP should iden-tify the following codes per the specific section numbers of ACI 562:a. Current building code (1.2.2)b. Original building code (1.2.3) c. Existing building code (1.2.1)d. Design basis code (1.2.4)

38、In the U.S., the current building code is usually based on an edition of the IBC, which was first published in 2000; a few large cities have their own customized building codes. The current building code establishes the design and construction regulations for new construction and provides limits tha

39、t need not be exceeded if designing new construc-tion or assessing and designing repairs and rehabilitation of existing structures. For the design and construction of new concrete structures, IBC references ACI 318. The code used to initially design the building is referred to as the original buildi

40、ng code and is typically identified in the construction documents, or may be obtained by contacting the local juris-diction and requesting information regarding the building code in effect at the time of original construction. The most common original codes prior to the IBC in the U.S. include the B

41、uilding Officials Code Administrators National Building Code (BOCA/NBC), the Uniform Building Code (UBC), and the Standard Building Code (SBC) that typically reference previous versions of ACI 318 with modification.In the U.S., the existing building code is most often based on an edition of the IEBC

42、, which was first published in 2003. As of January 2016, the IEBC has been adopted in approxi-mately 80 percent of the states, Guam, and Puerto Rico (Inter-national Code Council 2014). Chapter 34 of the IBC, before the 2015 edition, also covers existing structures and has similar provisions as IEBC

43、that permit the use of the original code for rehabilitations, and when it is required to upgrade an existing structure to the current code. Chapter 34 has since been deleted from the 2015 IBC. The intent of ACI 562 is that existing building code refers to IEBC and not sections of other current build

44、ing codes that contain provisions pertinent to existing construction. For jurisdictions that have not adopted an edition of the IEBC or the IBC with Chapter 34 version before 2015, that jurisdiction is considered to have no existing building code. In this case, the provisions of Appendix A of ACI 56

45、2 and any chapters in the current building code that address existing buildings must be met.Once the original building code and current building code have been identified, the LDP can use the flowchart presented in Fig. 1.2 as a guide to determine the design basis code for repair, rehabilitation, or

46、 strengthening design. The design basis code is dependent on the adoption of an existing building code within the jurisdiction of the project. If a juris-diction has not adopted an existing building code, Appendix A of ACI 562, is used to determine the design basis code. In jurisdictions that have a

47、dopted an existing building code, the design basis code is determined in accordance with Chapter 4 of ACI 562. The Project Examples included within this guide illustrate how Fig. 1.2 is used to determine the design basis code. Chapter 4 and Appendix A provide the design-basis criteria for the repair

48、 and rehabilitation work. Designing new members and their connections to existing structures must be based on ACI 318-14.1.3Applicability of the CodeACI 562 is applicable to existing concrete structures including the concrete elements of buildings; nonbuilding structures; building foundation members

49、, both plain and reinforced concrete; soil-supported structural slabs; concrete portions of composite members; and prestressed and precast concrete structures including cladding, which transmits lateral loads to diaphragms or bracing members. ACI 562 includes provisions specific to performing assessment, repair, reha-bilitation, and strengthening of existing concrete elements of buildings or nonbuilding concrete structures. The LDP can exceed the minimum requirements of ACI 562, such as those for progressive collapse resistance, redundancy, or integrity provisions. Regulations of t