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File: Reinforced Concrete Water Tank Design Pdf 84700 | D Fromexp Holmberg July091
from experience how did you do that reinforced concrete tank design by mark w holmberg p e reinforced concrete tanks have been used analysis for water and wastewater storage and ...

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                        From ExpEriEncE
                         “how did you do that?”
       Reinforced Concrete Tank Design
       By Mark W. Holmberg, P.E.                                                                                                                      ®
        Reinforced  concrete  tanks  have  been  used                   Analysis
       for water and wastewater storage and treatment       Analysis of reinforced concrete slabs 
       for decades. Structural engineers are asked         and walls is a complex finite element 
       to  design  a  variety  of  square,  round,  and    exercise. ACI 350 suggests three de-
       oval reinforced concrete structures that may        sign aids that can simplify the analysis                                                                
       be above, below, or partially below ground.         of liquid containing tanks:
       Design of reinforced concrete tanks requires          •  Rectangular Concrete Tanks, 
       attention not only to strength requirements,            Portland Cement Association,         Figure 1: Commerce WWTP Aeration Screen, Walkway and 
       but also to crack control and durability. The           1994                                 Hoist Bridge.
       challenge for the structural engineer is to de-              Copyright
       sign concrete liquid containing structures that       •  Circular Concrete Tanks                                           Details
       will resist the extremes of seasonal temperature        Without Prestressing, Portland  
       changes and a variety of loading conditions,            Cement Association, 1993                         Proper detailing of reinforcing and joints 
       and remain watertight.                                •  Concrete Manual, U.S. Department of            has as much to do with durability of a liquid 
                                                                               th                              containing structure as properly applying the 
        Design and construction of the Bear Creek              Reclamation, 8  edition, 1981
       Waste Water Treatment Plant (WWTP) Ex-               The two Portland Cement Association (PCA)          provisions of ACI 350 and correctly analyzing 
       pansion located in Hampton, Georgia and the         publications include coefficients for calculating   the structure. End fixity of a section affects 
       Commerce Georgia WWTP are used to illus-            moments, shears, tension, and deflection for        location and magnitude of maximum moments, 
       trate code requirements, tank analysis, design      a variety of aspect ratios and end conditions       and joint location affects the amount of mini-
       details, and construction of liquid containing      of plate and circular elements. Engineering         mum shrinkage and temperature reinforcing 
       reinforced concrete tanks.                          judgment of the designer is required to select      required. The PCA design tables include both 
                                                           the proper design tables, detail sections to        fixed and hinged base conditions. The com-
                Code Requirements                          resemble the boundary conditions selected           mentary states that either extreme is rarely 
                                                           and recognize that ideal boundary conditions        achieved in the field. The detail in Figure 2 is 
                                       R U C T U R E
        ACI 350-06 Code Requirements for Environ-          are rarely achieved in the field. In addition, the  typical for a hinged base condition and was 
       mental Engineering Concrete Structures extends      engineer must recognize conditions, beyond          used in several of the Bear Creek WWTP 
                             T
                                                           the limitations of the PCA data, that require       structures. A compression type waterstop was 
       the basic ACI 318 Building Code Requirements 
                                                    magazine
       for Structural Concrete with additional service-    special analysis.                                   installed  near  the  inside  face  of  the  wall.  A 
            S                                               Liquid containing tanks often support heavy        PVC bulb type waterstop is not practical at this 
       ability  requirements for crack width control 
       due to flexure, shrinkage of concrete, and tem-     equipment requiring special design of equip-        location due to the location of slab reinforcing. 
       perature movement. The commentary of ACI            ment support and surrounding walls. The              Prior to completing the Bear Creek WWTP 
       350 makes it clear that ACI 318 requirements        structural engineer must obtain vertical and        structures wall details, it was determined that 
       alone will not produce watertight structures. ACI   vibration loads of equipment, and design for        the maximum allowable length between con-
       350 serviceability requirements include:            possible restraint of temperature movement of       struction joints would be 50 feet, and that 
         •  Reduced working load stresses, and             supporting concrete.                                Grade 60 reinforcing steel would be specified. 
           requirements for size and spacing of             Figure 1 is an example of equipment that           Figure 3, from the PCA Circular Concrete Tanks 
           reinforcement                                   restrains or induces temperature movement in        Without Prestressing noted above, is a useful aid 
         •  Increased minimum reinforcement for            the reinforced concrete structure.                  for proportioning shrinkage and temperature 
           temperature and shrinkage movement,                                                                    reinforcing based on joint spacing. ACI 350 
           which is dependent on the grade                                                                        notes that concrete sections over 24 inches 
           of reinforcing steel and the length                                                                    thick must have shrinkage reinforcing at 
           between shrinkage dissipating joints                                                                   each face based on a 12-inch thick section.
         • Waterstop requirements at all joints
         • Concrete mix design requirements                                                                                       Concrete
         •  Increased cover requirements                                                                           Specifying and supplying a concrete mix 
           compared to ACI 318                                                                                    that minimizes shrinkage is critical to the 
         •  Commentary suggestions for use of                                                                     durability of liquid containing structures. 
           shrinkage compensating concrete                                                                        Concrete shrinkage is dependent on several 
           per ACI 223                                                                                            factors, including cement content and aggre-
        Properly designed, specified, and detailed                                                                gate. To insure that design assumptions are 
       structures applying the requirements of the                                                                valid, the engineer should specify shrinkage 
       ACI 350, along with engineering judgment                                                                   requirements (0.04% to 0.03%), and that 
       and quality construction, should have a                                                                    the concrete supplier provide shrinkage test 
       useful life of 50 to 60 years.                                                                             results prior to approving the mix design. 
                                                       Figure 2: Hinged Base Detail.                              Where large tank walls or slabs are required 
                                                    STRUCTURE magazine           22 July 2009                                                                                                                            STRUCTURE magazine
                                                                   bility of the structure. Almost all form systems 
                                                                   require through-wall form ties that create po-
                                                                   tential for leaks, and weak planes where cracks 
                                                                   may occur. Proper concrete mix design and 
                                                                   appropriate  add  mixtures  will  assure  that 
                                                                   concrete  is  easily  consolidated.  Proper  cur-
                                                                   ing of concrete will reduce the potential for 
                                                                   shrinkage cracking.                                                                                      ®
                                                                     Figure  4  shows  small  temperature/shrinkage 
                                                                   cracks  in  the  Bear  Creek  WWTP  Aeration 
                                                                   Basin Tank wall located at form tie holes. The 
                                                                   contractor injected the cracks and applied 
                                                                   a  specified  waterproofing  membrane  to  the 
                                                                   inside of the tank walls.                                                                                              
        Figure 3: Minimum Temperature and Shrinkage                                  Conclusion                                Figure 4: Tank Wall Cracks at Tie Hole.
        Reinforcement.                                               Proper application of ACI 350 design require-
                                                                             Copyright
        without expansion joints, shrinkage compen-                ments, appropriate structural details, properly 
        sating concrete may be specified; however, the             specified and supplied concrete, and quality                  Mark W. Holmberg, P.E. is Vice President 
        structural engineer must account for concrete              construction will assure long life for reinforced             and Civil Manager for Heath & Lineback 
        expansion movement.                                        concrete tanks that will be subjected to harsh                Engineers, Inc. in Marietta, Georgia. Mark is 
         ACI requirements for hot and cold weather                 environmental and use conditions. The structural              also a member of the STRUCTURE Editorial 
        concrete placement must be specified because               engineer and the contractor must work together                Board, representing CASE. He can be reached 
        construction of a large project can take place             to produce reinforced concrete liquid containing              at mholmberg@heath-lineback.com.
        over a year or more. One concrete mix design               tanks that are as watertight as possible.▪
        will not be adequate for all pour conditions.                                                             Project Team
                        Construction                               Process Design Engineer and Construction Observation – Stevenson & Palmer Engineers, Inc.
         Formwork, concrete placement and curing                   Structural Engineer – Heath & Lineback Engineers, Inc. 
        are obviously critical to the quality and dura-            Contractor – Choate Construction
                                            R U C T U R E
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             ©2009Simpson Strong-Tie Company Inc.  SSW09-S
                      Now 2006 IBC Code-Listed (ICC-ES ESR-1679)
July 2009     SSW09_S_7_1-2x4_3-4.indd   1                  STRUCTURE magazine               23 July 2009                                                      6/12/2009   4:16:21 PM
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