Presentation on theme: "TILT-UP CONSTRUCTION GUEST SPEAKER: KAREN S. HAND, P.E."— Presentation transcript:
1TILT-UP CONSTRUCTIONGUEST SPEAKER:KAREN S. HAND, P.E.
2Introduction Karen S. Hand, P.E. BSCE – University of Missouri-Rolla May 1993Needham & Associates, Inc.Consulting EngineersMay 1998-PresentTCA - Charter Member2004 Achievement Award Winner for Innovation
3Topics Panelizing the Building Connections Architectural Considerations
4Project ProcurementClients can be Architect, Engineer of Record, Subcontractor, General ContractorDesign Build Specialty EngineerEngineer of Record with Additional ScopeHow do we as a specialty Engineer get the job? Clients are from different AvenuesTypically we are the Specialty Engineer: Coordination can be tricky since the rest of the structural design and architectural design may already be done. Inevitably there are changes.Best case scenerio is to design the entire structure. Gear toward educating marketplace about the importance of coordination up front. Too often the tilt-up is thought of as a facade and not a structural system.
5Tackling the Project PLANNING!!!!!! With the Architect With the Engineer of RecordWith the ContractorOnce we are awarded a project, how do we tackle the job?Planning with the Architect, Planning with the Engineer, Planning with the Contractor
6Preliminary DesignKnow what your constraints are..Not the typical “design” issues…Think beyond the paper…know what assumptions have been made in the proposal by the contractor.Limited SiteCrane SizeWeatherPreliminary Design for Tilt Up is different from any other type of design. There are more issues or constraints to consider than the typical steel frame design. A limited site can restrict panel size. May need to do stack casting where the panel sizes should remain constant. May need casting areas somewhere away from the building slab, effecting the crane capacity for reach. Crane size can effect the entire design. An experienced tilt up engineer can tackle these issues.
7Planning Decide the approach Are there any unique issues to consider? New Millennium used tented stack cast panels to keep an efficient heated areaEPA had 16” and 32” thick panels…discussed 3 different options to determine feasibility before making a decision on how to proceed.
8Panelizing the Building One of the most important steps in DesignWhat is panelizing?Determining how the walls are divided into panels, what their shapes are and where the joints between them occur
9Panelizing the Building Coordinate with Architect and Steel Framing Engineer and ContractorGoal for Panel Sizes:Maximum Panel SizeMinimize Panel Joints
10Panelizing the Building Factors to ConsiderCrane Capacity and ReachSteel Framing Layout and Bearing Locations – Typical Embedment PatternOpening Locations – Adequate Jambs, Lintel Panels, Vertically Stack OpeningsLocate Girders at Center of Panel or at JointFooting Step Locations
11Panelizing the Building Takes the same time to lift and set a large panel as a small panel. Take Advantage.Efficient Panel Layout Effects the Cost of the entire project and should be considered one of the most important issues to coordinate.Cost in FormworkCost in Embeds/Connections
12Planning the Connections Base ConnectionsCorner ConnectionsRoof Framing ConnectionsMiscellaneous Connections
13Types of Connections Welded Embedded Metal Embedded Inserts Most CommonEmbedded InsertsAllows for Bolted ConnectionEliminates Field WeldingAccuracy in LocatingDrilled In AnchorsPost installedCast-In-Place ConcreteAt Slabs
14Base Connections What type of foundation system is being used? Continuous FootingReinforced Top and Bottom layerCentered Under PanelSpread FootingPanel Spans Corner to CornerAllow for Expansion and ContractionPad Footings used to be the standard.Continuous Footings are now the starndard.Shrinkage of the panels between the bearing pads after the panels are set can cause diagonal shrinkage cracks in the lower corners of the panels. Set shim packs or grout pads
15Base ConnectionsDiagonal Shrinkage cracks in the corners due to restraint of bearing padsGrout under the panels as soon as possibleShim Packs or Grout Pads should be located ¼ from the end of the panel
16Base Connections Friction – Old Days Pourback Strips and Slab Dowels Embedded Plates or AnglesTo Slab OptionTo Footing OptionFree Standing WallsSpandrel/Grade Beam TypeBy eliminating the panel to slab dowels, the floor slab can be cast all the way to the inside face of where the tilt up panel will be located. This also eliminates the backfilling and slab infill operations required around the panel braces to fill the closure strip.
17Pourback Strips and Slab Dowels Slab is poured short of the panel location with a “closure strip” of about 3’-0”.Dowels are “wet set” into the panel at the correct elevation to meet the center of the floor slab.Backfill and insert rebar between slab dowel and panel dowel.Closure strip is poured to finish off the slab.
19Pourback Strips and Slab Dowels Problems with the procedure“Wet setting” the dowels is cumbersomeAccurate placementFinishingVariations of DetailBackfilling becomes a safety concernBraces are still attachedAccess is a problemPanel layout on the slab could present access challenges to get these wet set.Epoxy the rebar to the panel and/or slabUse threaded inserts (not always accurately placed)
20Backfilling ACI 551 Section 4.10.2 Prior to backfilling, place a strip of felt over the joint between adjacent panels below grade and pack with plastic roof cement. This prevents dirt, mud or water from leaking through the joint in the panels
21Embedded Base Connections Allows for the slab to be poured to inside face of where tilt-up panel will goEliminates Backfilling on Inside of BldgConnections can me made immediately
22Embedded Base Connections To SlabAngle Embedded in the Slab, Plate Embedded in the Panel - WeldedConsider Expansion/Contraction in Slab and PanelTo FootingAngle Embedded at Base of PanelSecond Angle is welded to Embed and Bolted to FtgConsider Additional Unbraced Length for Panel DesignConsider CorrosionConsider Expansion/ContractionAdding concrete over the embeds do not protect them against corrosion!!!
23Dock High Walls Connection at Slab and at Footing Slab Connection Resists Lateral LoadReduces Unbraced Length for CompressionFooting ConnectionResists Lateral Soil Pressure behind PanelAdvantage - Base Fixity for Panel DesignBase Fixity can become very important with the small column strips at dock doors.
24Panel to Panel Connections Are they needed?Not typical for tilt upCommon in PrecastLarger Panels and Wider Panels
25Panel to Panel Connections Tie panels together for Overturning ForcesRe-entrant Corners with Drag Strut ForcesLaterally stabilize two adjacent panelsUse a Butterfly ConnectionExpansion and ContractionDo not restrain any more movement with the connection than structurally required.
26Corner Connections Thermal Bowing Caulked Joints can fail prematurely – Not a structural performance issueExpansion and ContractionDo not restrain any more movement with the connection than structurally required.Why do we make corner connections?What happens if we don’t make a corner connection?
27Roof Framing Connections Diaphragm – Chord Connections – Continuous Angle also acts as Deck Bearing AngleDrag Strut ConnectionsJoist Bearing ConnectionsEmbedded Plate and Bearing AngleJoist PocketGirder Bearing ConnectionsEmbedded Plate and Angle/PlateBeam PocketForming Issues with Pockets, Erection Issue with Pockets
28Ledger Connection Diaphragm Chord – Shear Forces Deck Bearing – Gravity ForcesLateral Restraint – Tension ForcesContinuous AngleDifferent Thermal Coefficient of ExpansionRigid Connection for Shear at Center of PanelSliding Connection for Gravity and Tension Forces
32Other Connections Mezzanine Connections Spandrels Smaller Joist SpacingResist Temptation to use a Continuous Angle Welded at each JoistSpandrels
33Expansion/Contraction Did I mention Expansion/Contraction is the most important thing to remember when designing connections?Expansion/Contraction is the most important thing to remember when designing connections.Let the panels “breathe”
34Design PanelsOnce connections have been planned you can design the panels for the constraints you have provided.Eccentric Loads due to Bearing ConnectionsUnbraced Length for Panel BucklingBase Fixity
35Reinforcing Schedules Once Panels have been designed, you will indicate the required reinforcing on the structural drawings.
36Reinforcing Design Note regarding Reinforcing: ACI 318 Section allows bar spacing up to 18 inches.Best practice is to use smaller bars not to exceed 15 inches o.c.When using a double mat of steel, you could stagger the mats to reduce the effective spacing if stretching to 18” but this requires additional chairs to support the upper and lower mat independently. Check with Contractor for cost impact.
37Engineering Documents Need to Transmit, with completeness and clarity, the general and specific requirements for tilt up panels.Key PlanLocate panels and indicate designationElevationsEach panel uniquely numberedDrawn from inside of building looking outPanel Dimensions and connection detail referencesJoint sizes
38Engineering Documents Connection DetailsAnchor sizes requiredEmbed Plate sizes and stud spacingReinforcement DetailsTypical rebar placementClear coveragesSpecial Tie ConfigurationsPilaster reinforcement if requiredSpecificationsShop Drawings – Panel Layout
39Detailing the PanelsBiggest Source of Field Problems are results of inadequate checking and correlating between Architectural and Structural drawings.Design Engineer typically isn’t too concerned about getting all the architectural features coordinated.Elevations on the Structural Drawings and on the Panel Layout Drawings are drawn from the inside of the building looking outward.
40Panel Layout Panel Identification Locate and Identify Embedded Items Locate OpeningsLocation of any recesses or reveals with detailsLocate Architectural FinishesPull all dimensions from upper left corner
42CommunicationCommunication with the Architect is vital to the success of the projectCommunication with the Engineer is vital to the success of the projectCommunication with the Contractor is vital to the success of the project