Internal Bracing Design Guide For Masonry Walls Under .
INTERNATIONALMASONRYINSTITUTEInternal Bracing Design Guide forMasonry Walls Under ConstructionPreface: Masonry under construction must be temporarily braced until the final lateral supportsystem is in place. The importance of this bracing is paramount to the safety of both the generalpublic and those involved with the project under construction. The Standard Practice forBracing Masonry Walls Under Construction provides engineering principles and properties forrationally design bracing systems for masonry walls under construction. Internal bracing, orusing the developing strength of the masonry assembly, can provide significant benefits to aproject team. To support the engineering community in the use of structural masonry, includingeffective and efficient temporary bracing, the International Masonry Institute has funded thisguide.Date: May, 20131st edition
About Bracing Masonry Walls Under Construction (from International Masonry Institute)This Guide has been developed by the International Masonry Institute (IMI) for use by engineersand other qualified persons designing masonry bracing systems. It provides an outline of theprocess and illustrates the application of engineering principles for bracing masonry walls usingthe wall’s inherent strength rather than external bracing elements. This concept is known as‘Internal Bracing’ and has been successfully applied in numerous projects with short to very tallwalls.Bracing masonry walls under construction is a life safety necessity that is mandated by eachstate’s legally adopted building code through the referenced masonry standards. The 2011‘Specification for Masonry Structures’ (TMS 602/ACI 530.1/ASCE 6) was adopted by the 2012International Building Code for masonry construction and contains requirements for the masoncontractor to ‘Design, provide, and install bracing that will assure stability of masonry duringconstruction.’ Bracing is also part of federal occupational safety requirements including nationalregulations -- OSHA Safety and Health Regulations for Construction (CFR 29) Part 1926.706and locally adopted regulations -- Michigan’s MiOSHA Construction Standard Part 2, as anexample. Bracing protects project workers as well as the general public who may access the site,be passing by, or even occupying adjacent facilities or spaces.Masonry bracing is typically designed by an engineer retained by the project’s mason contractor,although there is some movement in the industry to incorporate Internal Bracing capacity into theproject’s construction documents prepared by the Engineer of Record. There is an industrystandard for bracing masonry walls: ‘Standard Practice for Bracing Masonry Walls UnderConstruction’, 2012, sponsored by IMI and the Mason Contractors Association of America(MCAA) and published by MCAA. There also are compiled examples and technical literatureavailable through industry sources as well as proprietary information for external bracingsystems. This Guide applies the content of the Standard and other documents along withknowledge gained through experience to provide users with one approach to designing internallybraced masonry walls.About International Masonry Institute (IMI)The International Masonry Institute offers quality training for craftworkers, professionaleducation for masonry contractors and free technical assistance to the design and constructioncommunities. IMI is a strategic alliance between the International Union of Bricklayers andAllied Craftworkers (BAC) and their signatory contractors to promote quality masonryconstruction.Team IMI consists of architects, engineers, construction managers, skilled craftworkers andinstructors, offering what no other group can: expertise in training, craftsmanship, design,installation and marketing. That means buildings built by union craftworkers and contractors getbuilt the right way.AuthorScott W. Walkowicz, PE, NCEESscott@walkowiczce.com Walkowicz Consulting Engineers, LLCCopyright 2013 of International Masonry Institutei
DisclaimerIMI and Walkowicz Consulting Engineers, LLC disclaim all warranties, expressed or implied,including but not limited to implied fitness for a particular purpose, with respect to this manual.All designs resulting from the processes defined in this manual should be verified to the user’ssatisfaction. The contents of these written materials may include technical inaccuracies ortypographical errors and may be revised without notice.This document is intended for the use of industry professionals who are competent to evaluatethe significance and limitations of the information provided herein. This publication should notbe used as the sole guide for masonry Internal Bracing design and construction.ThanksIMI and Walkowicz Consulting Engineers, LLC would like to thank Dailey Engineering, Inc.,Bergmann Associates, Davenport Masonry and Koch Masonry for their willingness to shareideas based on their work with internally braced masonry walls under construction and forphotographs and figures shared to better illustrate the concepts presented herein. Additionalthanks are extended to Dailey Engineering and Bergmann Associates for their time and effortspent reviewing this document.Copyright 2013 of International Masonry Instituteii
Internal Bracing Design Guide for Masonry Walls Under ConstructionTable of Contents:Table of Figures: . 1Section 1: Concepts for Bracing Masonry Walls Under Construction . 21.General. 22.External Bracing . 23.Internal Bracing . 24.Communication Between the Engineer and the Mason Contractor . 35.Modifying Requirements Shown in the Construction Documents . 56.The Role of Special Inspection . 6Section 2: Short Term Design Approach . 71.General. 72.Masonry . 93.Foundation and Soils . 10Section 3: Internal Bracing Design . 121.Analysis . 122.Deliverables . 13Section 4: Design Examples . 161.Component Software (Structural Masonry Design System, V5.0.1) . 172.Finite Element (Ram Elements) . 22Section 5: Concluding Remarks. 26Table of Figures:Figure 1: Cantilevered Wall Diagram . 7Figure 2: Sample Bracing Plan Graphics, Notes and Legend . 15Figure 3: Design Basis Menu – Codes tab . 17Figure 4: Design Basis Menu – Concrete Masonry tab . 17Figure 5: Out of Plane Wall Design – Design Data tab . 18Figure 6: Out of Plane Wall Design – Construction Data tab. 18Figure 7: Out of Plane Wall Design – Load Data tab . 19Figure 8: Analysis Results – Interaction Diagram Showing Insufficient Capacity . 19Figure 9: Return to Design Basis – Modify masonry strength . 20Figure 10: Analysis Results – Interaction Diagram Showing Sufficient Capacity. 21Figure 11: Data Input Field - Masonry Properties . 22Figure 12: Data Input Field - Geometry . 22Figure 13: Data Input Field - Masonry Criteria . 23Figure 14: Data Input Field - Loads . 23Figure 15: Data Input Field – Design Data . 24Figure 16: Analysis Report – Good bar size, excessive bar spacing . 24Figure 17: Analysis Report – Good bar size and spacing . 25Table of Photographs:Photograph 1: External pipe braces utilized on a masonry wall under construction. . 2Photograph 2: Masonry walls under construction utilizing Internal Bracing. . 3Copyright 2013 of International Masonry Institute1
Section 1: Concepts for Bracing Masonry Walls Under Construction1. GeneralBracing masonry walls under construction requires predictable capacity to resist defined loadsthat may occur due to wind during construction and before the wall’s final lateral support is inplace. Applying rational engineering methods using material properties provides the basis forbracing design whether the masonry walls are braced in the traditional manner using externalcomponents or by Internal Bracing, that is, the more recent method of using the constructedmasonry’s inherent strength to provide stability during wall construction. It is important torealize that Internal Bracing provides verifiable engineering capacity and performance similar tosystems that incorporate external bracing components and provides tangible benefits to theproject that will be discussed later in this Guide.2. External BracingWhile not the focus of this Guide, it isimportant to note that masonry walls can bebraced using external components. Externalbracing has been used effectively for yearsand can provide appropriate capacity formasonry walls under construction and it maybe necessary for certain masonry wallconfigurations that cannot be adequatelybraced using the wall’s internal capacity.Advantages of this system includefamiliarity, visible components and theavailability of numerous proprietary systemswhich are readily available. Disadvantagesof this system may include lack of sufficientcapacity due to improper construction orinstallation, inappropriate considerationgiven to wall connections and base Photograph 1: External pipe braces utilized on a masonrywall under construction with anchorage to block pallet 'skids'anchorage, interference with and exposure to and column foundations. (Credit: Davenport Masonry, Holt,damage from site traffic and activities (for MI)example: construction equipment running into braces or their anchorage, trades removing bracessuch as steel erectors needing to set roof structure or electricians or plumbers needing to installtrenches for underground utilities and more), mobilization and de-mobilization time and expense,material acquisition/rental and storage expense as well as the need for anchorage connection tosomething with sufficient capacity to resist the loads imparted from the brace. External bracingis, however, an engineered system with a long track record of successful implementation thatprovides good value to the project team and the building owner.3. Internal BracingThis Guide presents a newer method for bracing masonry walls under construction: InternalBracing. This method provides a highly effective and efficient method to provide stability toCopyright 2013 of International Masonry Institute2
masonry walls prior to the installation of, andconnection to, the permanent lateral supportsystem. This new method is based on usingconventional masonry analysis methods,either Allowable Stress Design or StrengthDesign, derived from the ‘Building CodeRequirements for Masonry Structures.’ (TMS402/ACI 530/ASCE 5), referred to as the“Code” hereafter. The analysis is conductedwith modified criteria, specifically themasonry properties, based on green masonrysystem performance. The design method andcriteria are found in the ‘Standard PracticeforBracing Masonry Walls UnderPhotograph 2: Masonry walls under construction utilizingConstruction’– herein referred to as theInternal Bracing. (Credit: Koch Masonry, Dexter, MI)“Standard”The Standard was firstpublished in 1999. It was revised in 2001 and again in 2012. The methods for Internal Bracingpresented in this Guide are based on the 2012 Standard. The basic premises for analysis iscantilevered behavior, reduced masonry strengths, and full steel tensile strength after the grouthas cured for either 12 or 24 hours, depending on the length of lap used. Advantages of thissystem include greater safety due to the lack of elements that could be impacted by site traffic oractivities since there are no external braces, no additional mobilization or de-mobilization time, amore open, less complicated site without interferences to site traffic or construction activities, noexternal components including connectors, braces and foundations and none of the associatedcosts for those items. Other significant benefits found through using Internal Bracing are morepredictable capacity (since there are no concentrated loads at brace top support points and a moredirect load resistance path), and capacity that increases with time providing additional safetyuntil the final lateral support system is installed. Disadvantages associated with the method mayinclude unfamiliarity, the lack of external components that can be observed and inspected, lackof capacity due to improper construction and an occasional lack of design capacity based onconfiguration constraints which could lead to required modifications to the proposedconstruction and/or the application of external braces. However, Internal Bracing is anengineered method and it is believed that it provides better value to the project team and the enduser.4. Communication Between the Engineer and the Mason ContractorIt is imperative that the bracing design engineer understand several key aspects of the specificmasonry construction. The masonry capacity and the demand placed on the wall and bracingdepend on the manner and sequencing of the wall’s construction and of surroundingconstruction. To facilitate this understanding one or more meetings are often held between thebracing design engineer and mason contractor. Points that can influence Internal Bracingcapacity analysis include:MasonryLayoutMasonry layout including wall locations, heights, reinforcement size andspacing, joint location and opening information all can influence the demandplaced on the masonry during construction. The ‘For Construction’documents, including all addendums and bulletins, must be reviewed toCopyright 2013 of International Masonry Institute3
perform proper bracing analysis. The mason contractor should provide these documents,including drawings and specifications, to the bracing design engineer so that individual wallsegments can be properly evaluated.ReinforcedMasonry construction sequencing is amasonry can takeMasonryconstruction means that is often first consideredadvantage ofConstructionduring bid preparation and is then refined priorSequencingreinforcementto and during construction. The contractor needsto present the intended construction sequencingonce the groutto the bracing design engineer regarding which walls or wallhas cured eithersegments will be constructed first and how those walls may be12 hours withsupported or buttressed by other walls or constructed features. Theextended lapcontractor also needs to inform the bracing design engineer of thelengths, or 24individual wall segment construction phasing in terms of how muchhours withheight will be built each day, when reinforcement and grout will beplaced, what type of lintels and other horizontal elements will bestandard lapinstalled and when the final lateral support will be installed.lengths.Unreinforced masonry or reinforced masonry, prior to groutplacement and/or sufficient curing, rely on masonry weight and onmodest flexural tensile capacity to resist applied lateral wind loads. Reinforced masonry cantake advantage of reinforcement once the grout has cured either 12 hours with extended laplengths, or 24 hours with standard lap lengths. The sequencing of masonry lay-up andreinforcement and grout placement determines when the strength of the reinforcement can beincluded as the means to internally brace the wall under construction. Low lift groutingprocedures should be considered because this procedure allows the wall to gain strength as theconstruction progresses, as discussed later in this Guide.Masonry unit strength is the most common basis for determining the net areacompressive strength of the masonry, commonly referred to as f’m. Duringconstruction, masonry compressive strength is limited by the Standard to 50percent of the net area compressive strength of masonry. The bracing designengineer, therefore, needs to know the compressive strength of the masonry units to be used sothat the proper f’m can be determined and then reduced by 50 percent for use in calculating thecapacity of the masonry while it’s under construction. A current unit compliance report orcompressive strength test report should be used to verify unit strength. Preconstruction testing ofunits or assembled prisms should be conducted if an appropriate report is not provided or toprovide verification of the compressive strength for the units and/or masonry being used.Masonry UnitStrengthOtherMasonryPropertiesMasonry thickness and density or weight per square foot influence theresisting moment for global stability and axial compressive load thatcombines with flexural compression or tension. Masonry unit compliancesubmittals will provide dimensional and density/weight criteria forevaluation and should be provided by the mason contractor.Foundation size including depth and geotechnical information for the projectsite must be shared so the influence of foundation capacity can be evaluatedwith regard to global stability of the wall under consideration. The bracingdesign engineer needs to evaluate the foundation for bearing pressure,sliding and overturning using information such as foundation geometry, the wall placement onFoundationand SoilsCopyright 2013 of International Masonry Institute4
the foundation and the soil bearing capacity and other criteria such as active and passivepressures, friction and density.It is also imperative to include the controlling contractor or constructionmanager in the communication loop. While the mason contractor and thebracing engineer are developing the final masonry installation and bracingplan, the controlling contractor or construction manager should be includedto offer input where they may find s
and other qualified persons designing masonry bracing systems. It provides an outline of the process and illustrates the application of engineering principles for bracing masonry walls using the wall’s inherent strength rather than external bracing elements. This concept is known as
Bracing for steps in floors and ceilings 21 8. Wall bracing 26 9. Walls at angles to bracing lines 27 10. Roof bracing 30 11. Bracing ratings . magazine looks at the bracing requirements for . floors or ceilings
32 — Build 133 — December 2012/ January 2013 Wall bracing THIS THIRD ARTICLE IN A BUILD SERIES ON CALCULATING BRACING REQUIREMENTS FOR A BUILDING LOOKS AT WALL BRACING. TOM EDHOUSE, BRANZ TECHNICAL ADVISOR DESIGN RIGHT The same building is being used as in the previous article on subfloor bracing (see Build 132, pages 38–41) with additional information in
the G 15 stories steel building models is used with same configuration and different bracing systems such as Single-Diagonal, X bracing, Double X bracing, K bracing, V bracing is used. A commercial software package STAAD.Pro V8i is used for the analysis of steel buildings and different parameters are compared.
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The guide is divided into six sections intended to supplement and enhance the 2009 IRC wall bracing provisions: Section 1: Basic Concepts for Code-Compliant Wall Bracing Section 2: Wall Bracing Methods Section 3: Applying the Code Section 4: „Beyond Code‟ Bracing Solutions Section 5: Wall Bracing Options for Foam-Sheathed Wall Systems .
Note: SB083 may be used in lieu of SB103 for Type SW1 bracing units provided the capacities are reduced by 20%. Note: Refer to Pryda Wall Truss Brace design guide for an alternative solution to narrow wall bracing units 2. From the chosen wall height, width and brace type, obtain the bracing capacity from the tables below. Notes: I.
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