Presentation on theme: "BCSI 06 For information on: Jobsite storage Truss handling"— Presentation transcript:
1BCSI 06 For information on: Jobsite storage Truss handling Temporary bracingFall protectionConstruction loading
2Contents B1 – Handling, Installation and Bracing B2 – Installation and BracingB3 – Web Bracing/ReinforcementB4 – Construction LoadingB5 – Damage, Modifications and ErrorsB6 – Gable End Frame BracingB7 – Parallel Chord TrussesB8 – Toe-nailing for UpliftB9 – Multi-Ply TrussesB10 – Post Frame TrussesB11 – Fall ProtectionThe presentation will discuss the contents of the BCSI Booklet.
3Development of BCSI Engineers Manufacturers Suppliers Contractors To that end, the Wood Truss Council of America and the Truss Plate Institute developed and produced the BCSI 1-03 Guide to Good Practicewith input from dozens of industry engineers,component manufacturers,suppliers, and contractors. The booklet was released in October 2003.SuppliersContractors
4BCSI Booklet Replaces… The BCSI booklet is a direct replacement for the HIB-91 Booklet from TPI.Many component manufacturers use the BCSI booklet as a desk reference or provide copies to regular customers. It is not necessary to include them in jobsite packages.HIB-91 Booklet
5BCSI B-SeriesThe 93-page BCSI booklet contains ten sections developed to assist truss installers in the variety of details involved in the proper handling, installing, restraining and bracing of trusses.The ten sections are broken into individual “B-Series” summary documents. Each summary sheet version is a concise, economical version of the booklet information but in a format more suitable for inclusion in jobsite packages.
6BCSI B-Series Replaces... HIB-98 PosterHIB-91 SheetThe B-Series Summary Sheets were developed to contain both English and Spanish text. The B-series replaces the former jobsite bracing guides such asTPI’s HIB-91 Summary Sheet,the HIB-98 Post Frame Truss Posterthe WTCA-B1 Warning Poster andthe TTB WTCA-B2 on Temporary Bracing. In addition, several of WTCA’s Truss Technology in Building brochures have been modified and re-introduced as part of the B-series documents.Now let’s go through the eleven B-series documents, starting with B1…WTCA-B1 Warning PosterTTB WTCA-B2
7B1 Guide for Handling, Installing & Bracing Consequences of improper installation may be collapse of the structureSection B1 The Guide for Handling, Installing and Bracing of Metal Plate Connected Wood TrussesThe purpose of this section is to give a “big picture” view of how to properly store, handle, install and brace wood trusses, thereby improving jobsite safety and truss performance.It provides general information on the most important topics but relies on the succeeding B-series to get into the specifics.
8B1 Summary Sheet WTCA-B1 Warning Poster HIB-91 Sheet The B1 Summary Sheet replaces the HIB-91 Summary Sheet and the WTCA B1 Warning Poster.The B1 Summary Sheet presents the BCSI-B1 section in a one-page, 11x17 poster format (other poster sizes will be available). It is a full color, English/Spanish document that summarizes the main points of B1. It is blank on one side for printing Truss Placement Diagrams.WTCA-B1 Warning PosterHIB-91 Sheet
31B2 Truss Installation & Temporary Bracing The second section, B2, focuses on Truss Installation & Temporary Bracing. It replaces the Truss Technology in Bracing Document WTCA-B2 on temporary bracing.
64B3 Gable End Frame Bracing The Summary Sheet for B6 on Gable End Frame Bracing contains new information that was not previously published as a TTB.
65B3 Gable End Frames Designed to transfer vertical loads But may also experience lateral loadsSheathing, bracing and connections must be designed for this transferGable end frames contain vertical members arranged like flat studs. They are designed to transfer vertical loads from the roof to the gable end wall. Any lateral loads must be transferred by permanent bracing.
66B3 Load Transfer PathThere are number of factors that go into a properly designed system, but the goal is to get the lateral loads transferred safely into the upper and lower diaphragms. Some of items necessary to achieve this are specified by the Truss Designer and some are specified by the Building Designer.
67B3 Poorly Designed System Weaknesses in an un-designed, or under-designed, system probably won’t be evident until a temporary high load event.Here the high wind forces hit the unreinforced gable end frame and cause it to bow.The high lateral loads overcome the connection between the gable end frame and the wall, creating a hinge jointand the unblocked, undersized ceiling diaphragm buckles.
68B3 Design Considerations Gable End FrameReinforcement prevents failure of individual vertical websFrame to End WallCorrect connection prevents hinge jointBracing, blocking and diaphragm design creates safe load pathSome items that must be addressed in order to prevent these types of failures are the Gable End Frame itselfit must be reinforced so that the individual vertical members do not fail when they receive these lateral loads. The Truss Designer may specify this reinforcement. More on this in a minute…Then the Frame–to–End Wall connection must be designed to resist loads between each otherand the upper and lower diaphragms. This is the Building Designer’s responsibility and requires design of the lateral bracing system, thickness and type of sheathing, fastener schedules and all lateral load transfers.
69B3 Bracing and BlockingThis example shows a horizontal reinforcement (in red) and a diagonal brace (in purple) extending to roof diaphragm blocking. This requires proper design and specification of the diaphragm materials and fasteners, so it clearly is a Building Designer, not a Truss Designer, responsibility.
70B3 Bracing and BlockingThis option shows bottom chord bracing and blocking when there is no directly applied gypsum board ceiling. It also shows an alternative to the diagonal brace in the previous example. This diagonal brace in red extends from the gable end wall up to the roof diaphragm.
71B3 Gable End Reinforcement Horizontal reinforcement:In order to address the instability of the vertical members in the gable end frame, the Truss Designer may specify a horizontal reinforcement member.
72B3 Gable End Reinforcement Individual L- or T-reinforcementsOr the Truss Designer may specify individual reinforcement of vertical members using L- reinforcements or T-reinforcements.
73B3 Gable End Reinforcement Scab reinforcementsOr the Truss Designer may specify individual reinforcement using scabs, as in this case of structural gable end. In all cases, the Building Designer must still address how the lateral load will be transferred to the rest of the structure.
74B3 Building Designer Detail Here is an example of a well designed gable end bracing detail from a set of structural plans.
75B3 Building Designer Detail Among other things, notice the gable end frame is well connected to the end wall.
76B3 Avoid Hinge Joint Balloon Framed End Wall Here is one design strategy for avoiding the hinge joint between a gable end frame and the end wall. The wall studs are balloon framed, meaning they are continuous through the top plate and extend to the roof line.
77B3 Scissor Truss End Wall Scissor trusses must have a rake wall framed to the ceiling line in order to properly transfer loads into the ceiling diaphragm. A standard flat bottom gable end frame in this situation may lead to serviceability problems.
78B3 Avoid hinge points in walls! Additional Note: This wall will not meet the prescriptive method criteria under IRC for a braced wall.
79B4 Construction Loading B4 Construction Loading replaces the Truss Technology in Building Brochure by the same name.
95B6 SectionB6 used to be on Gable end bracing that information has now moved to section B3.B6 is intended to be used for additional topics in future additions of BCSI
96B7 Parallel Chord Trusses The Summary Sheet for B7 Temporary and Permanent Bracing for Parallel Chord Trusses contains new information that was not previously published as a TTB.
97Guidelines for 3x2 or 4x2 only B7 Lumber OrientationGuidelines for 3x2 or 4x2 onlyFor 2x_ orientationsee BCSI-B2Parallel Chord or Flat Trusses are any trusses that have tops and bottom chords at the same pitch. They are most often installed in flat roof or floor applications. These bracing and handling recommendations are for trusses with lumber oriented in the flat-wise direction, such as 3x2 and 4x2 trusses. Most often, floor trusses are built in this fashion.Flat trusses built with lumber oriented in the 2x_ direction are not covered in the B7 section, see the BCSI-B2 summary sheet for handling, bracing and installing guidelines for these types of trusses.
98B7 PCT BearingTop Chord Bearing trusses can be more stable during installation due to their center of gravity below the bearing surface,but all trusses should be braced before installation crews walk on them.
99B7 Temporary BracingTrusses in the 3x2 and 4x2 orientation are more stable than their 2x_ counterparts but still require bracing as outlined here.
100B7 Stabilize Truss Ends Temporary Bracing or Permanent Blocking Stabilize truss ends by installing the temporary bracing or permanent truss end blocking at the outset.
101B7 Correct PlacementParallel Chord Trusses can easily be placed upside down or wrong end-to-end. It is important to make sure they are installed correctly especially when the trusses may have interior bearings.
102B7 Truss TagsSome truss manufacturers mark trusses with these tags to avoid mis-installations on the jobsite.
103B7 Strongback Bridging Helps limit deflection and/or vibration Truss manufacturers recommend the installation of strongback bridging. Most fire rated assemblies require strongback bridging. At a minimum, it should be a 2x6 installed vertically at the bottom chord, every 10 feet on center. If there is no vertical web on which to attach the strongback, install a vertical block for this purpose, as shown in Fig. B7-11.
104B7 Construction Loads on PCT Follow the same precautions as outlined in section B4. Parallel Chord Trusses often see more construction loads because they provide a flat working surface.Be careful not to overload truss.Brace the trusses before applying any loads.Don’t overload single trusses, spread over as many trusses as possible.
105B8 Toe-Nailing for Uplift The Summary Sheet for B8 Toe-Nailing for Uplift Reactions replaces the TTB of the same name.
106B8 Uplift ForcesThe first example shows a truss subjected to wind uplift forces, in this case, both truss bearings will have to be designed for the uplift forces.The second example shows a off-center intermediate bearing truss under normal gravity loads. The exterior end of the shorter span will be subjected to uplift forces which create a “reverse deflection”. In this load case, the left side truss to bearing will have to be designed to account for uplift.
107B8 Toe-Nailed Connections Are three toe-nails enough?Many wood trusses are connected to the top plate using three toe-nails as shown here. Is this enough resistance for the design uplift forces? It depends on a three things…..
108B8 1- Proper Toenail Installation This diagram shows proper toe-nail installation. Toenail resistance is reduced by 33% as compared to straight nailing. If the toe-nail is not installed properly the actual reduction could be even larger.
109B8 2- Top Plate Lumber Grade and species Denser grades and species of top plates provide greater uplift resistance for toe-nails.
110B8 3- Type of NailsNail capacities are related to their shape and diameter. Listing just the pennyweight of a nail such as 10d, 16d, etc. is not descriptive enough to determine the capacity of the nail.That is why many Building Designers avoid confusion by calling out the diameter and length of the nail.0.162″ x 3.5″
111B8 Is Toe-Nailing Enough? Toe-nail values must exceed expected upliftFor example:A 16d common ina Southern Pinetop plate offers72 pounds ofuplift resistance.72If there are threetoe-nails, the totaluplift resistanceIs 3x72=216 poundsThis chart lists several types of nails frequently used on construction sites. Choose a nail type for the proposed connection. Look in the column for the top plate species to see the nail uplift value. Multiply this value by the number of nails in the connection. Then…..
112B8 Load Duration Factors The values for the uplift capacities can be adjusted using these load duration factors. Just be sure you understand how to apply these factors and under what circumstances to use them.For wind uplift condition, most geographical areas (except high wind areas like Florida) will use the factor of 1.6. The factored uplift resistance of the toe-nails is then 216x1.6=346 poundsFor wind uplift resistance use the factor of 1.6.Therefore, 216x1.6 = 346 pounds
113B8 Alternatives to Toe-Nailing Check published uplift capacities of mechanical connectorsIf the toe-nail resistance is not sufficient or the building codes requires a minimum mechanical connector, check the connector manufacturer’s specs to make sure the product meets or exceeds the expected design uplift force.
114R802.10.5 Truss to wall connection Trusses shall be connected to wall plates by the use of approved connectors having a resistance to uplift of not less than 175 pounds (79.45 kg.) and shall be installed in accordance with the manufacturer's specifications. For roof assemblies subject to wind uplift pressures of 20 pounds per square foot (0.958 kN/m2) or greater, as established in Table R301.2(2), adjusted for height and exposure per Table R301.2(3), see section R
115IRC RThe code requirement was added in the IRC 2003 in a perhaps well-intentioned effort to address a perceived issue from the proponent's point of view.Now that it is in the code, it is proving difficult to remove. A number of code jurisdictions have amended the language or struck the language out of their code adoption.The 175 lb value is unrelated to any real design parameters or linked to any truss length. It arbitrarily discriminates against one well respected construction method. No specific evidence was or can be provided to justify this requirement.
116IRC RTPI 1 requires that a Truss Design Drawing include reaction forces and directions, which would include a value for uplift based upon the structure's design parameters for wind.There is no valid reason for not using this calculated value in the consideration of the uplift connection requirements.
117IRC R802.10.5 Much of the US is in the 90 mph basic wind speed zone. The resistance for uplift, beyond the prescriptive fastening requirements of Table R602.3(1) is really seldom an issue, especially for structures categorized as Exposure B and with a Mean Roof Height of less than 30 feet.IRC Table R301.2(2) is used to trigger the need for special connection requirements per Table R Only high wind speed areas, highly exposed structures or extremely tall structures ever qualify for the special requirements. When the calculated uplift requires a connection of a specific value, WTCA supports providing resistance in a manner acceptable to the EOR or building code official, not based upon an arbitrary requirement.
118B9 Multi-ply GirdersThe Summary Sheet for B9 Multi-Ply Girders replaces the TTB of the same name.
119B9 Girders 4-ply 5-ply Designed to carry extra loads Max. 6 plies, fastened together to act as one4-ply5-plyMulti-ply trusses are comprised of identical trusses fastened together to act as one. Girders can be up to a maximum of six plies depending on the truss layout and loading configuration.
120B9 Fastener Schedule SAMPLE Specified on Truss Design Drawing The fastening method is indicated on the girder truss design drawing.
121B9 Nail FastenersFasteners using nails only are specified on girders with three plies or lessNails can be used on girders with up to three plies. The edge distances shown are a general recommendation based on information published the National Design Specification for Wood Construction from the American Forest & Paper Association.
122B9 Screw Fasteners Special screws on up to four plies Specially designed high strength screws may be specified for girders with up to four plies.
123B9 Screw Fasteners Screws on 2-ply 3x or 4x2 floor-type trusses These high strength screws can also be used on 4x2 or 3x2 floor girder trusses.
124B9 Bolt Fasteners Bolts on 4 to 6 plies In addition, nails may also be requiredBolts are required on four to six plies. The fastener schedule may indicate that additional nails are alo required.
125B9 Good Installation Practices Fasten plies together before lifting, if possibleA good practice is to fasten all the plies together before lifting into place and installing.
126B10 Post Frame Trusses HIB-98 Poster The Summary Sheet for B10 Post Frame Truss Installation and Bracing replaces the TPI poster called HIB-98 Post Frame Summary Sheet.HIB-98 Poster
127B10 Post Frame Trusses Part of an engineered building system Spaced at 4′ to 12′ o.c.Heels attached to posts fixed in ground or slabPurlins attached directly to truss top chords