Designing with Vulcraft 2017 by Vulcraft

More catalogs by Vulcraft | Designing with Vulcraft 2017 | 176 pages | 2017-09-01


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contents chapter 1 introduction 1.1 purpose 1.2 historical development 1.3 custom designs 1.4 current usage 1.5 codes and specifications 1.6 other specifications 1.7 reference standards 1.8 synopsis of chapters 1.9 conclusion 1 1 1 2 2 2 4 4 5 5 chapter 2 roofs 6 2.1 introduction 6 2.2 roofing types 6 2.3 deck types 7 steel decks 7 concrete deck 10 wood deck 10 2.4 roof loading 11 dead loads 11 collateral loads 11 roof live loads 12 snow loads 12 rain loads 12 live load reductions 12 wind uplift 12 load combinations 13

roofs when the structure has a high ratio of perimeter length to enclosed area e.g a long narrow building then a 30′x40′ or a 30′x50′ bay where the 30′ dimension is parallel to the long building dimension often proves to be the most economical this is due to the fact that with long narrow buildings the economy is heavily influenced by the wall system for example if a metal wall system is to be used then the most economical girt system is one in which light gage cold formed steel girts are used these are typically c or z girts the maximum span of such girts is approximately 30 feet if a bay spacing larger than 30 feet is required then wind columns are required to laterally support the c or z girts in mid bay the wind columns and their attachments to the structural steel at the roof have a significant impact on the cost of the framing system for metal wall structures with bays larger than 30 feet the designer is encouraged to investigate the use of steel

lateral load systems rimeter member is a joist or joist girder the forces resulting from diaphragm action must be provided to the manufacturer unless it can be determined that the perimeter member will not be overstressed by the diaphragm chord force chord forces from all load cases in combination with the diaphragm chord force must be specified it is not enough to simply provide the manufacturer with the diaphragm chord force because of the need to check specific code load combinations which include the diaphragm force suitable connections are also required for the diaphragm chords specifically force continuity must be provided between adjacent chord members just as would be provided in plate girder flange splices this is illustrated in the detail shown in figure 4.2.2 mfef fig 4.2.3 joist chord bending perimeter joists a better force path would be created if a top plate or tie angles were added to connect the adjacent joists for roofs either the detail shown in figure 4.2.4 or 4.2.5

lateral load systems steel joist fig 4.5.9 detail g the basic connection these columns depend on the exterior rigidly connected columns to provide the necessary resistance to prevent lateral sway buckling another way of describing the problem is to consider the fact that if interior columns are designed with a k factor of 1.0 it is required that the top of the column be laterally braced to laterally brace the top of a column requires a brace force and a brace stiffness the rigid frame must provide the necessary strength and stiffness for a proper design using “leaner” columns story stability must be checked the check is that the summation of the applied axial loads must be less than the summation of the allowable axial loads i.e Σp ≤ Σpallowable for the frame shown in fig.4.5.13 pa+3pb+pc must be less than the summation of the allowable buckling loads for columns a and c the allowable buckling loads for columns a and c are determined in the direction of sway

lateral load systems aisc sect e → fa 18.74 ksi o.k fa fa ry bottom chord cb 1.75 1.55 in kl/ry 1 16.1 12 1.55 125 → fa 9.56 ksi d/af 4.04 → fb 26.9 controls ksi l/rt 16.1 12 1.77 109 → fb 22.4 ksi determine the top plate weld required 3/16″ fillet weld vallow 2.78 kips/inch required weld length 32 2.78 11.51 inches use a total of 12 inches of 3/16 weld at each end of the plate pdl+ll 10+12 35/2 42 16.2 kips 1.45 ksi fa p/a pdl+ll+w 10+12 18 35/2 42 2.94 kips 0.26 ksi fa p/a 210 in kips mll fb m/sx 3.85 ksi 1033 in kips mw fb m/sx 18.92 ksi mdl+ll+w 210+1033 1243 in kips m/sx 1243/54.6 22.8 ksi fb determine the bottom chord connection to stabilizer plate try 6″x3/4″ plate min size for detailing a 4.5 in.2 fa 35/4.5 7.78 ksi fa 0.6 fy 22 ksi fa fa o.k size the weld from the girder chord to the stabilizer plate per aisc sect j 1/4 inch minimum weld is required vallow 3.71 kips/inch weld length 35

special topics construction the reinforcement in the shape of bars rods or angles must fit and the field welder must have room to weld the pieces in position the project site visit also allows the evaluation of the present actual loading condition on the joists if the engineer does not have access to the design drawings then the site visit is of course even more essential it may be possible to determine the joist designation from the joist tag each joist is supplied with a tag at one end this tag is intended to mark that specific joist for erection purposes the manufacturer will provide an erection plan that indicates where each joist is to be located the joists are identified on the plan by the mark on the tag besides the mark number the tag may also indicate the joist manufacturer the manufacturer could be contacted to determine if he has any records of the structure even if the manufacturer does not have records of the project the manufacturer may have helpful data about his

special topics the live load is applied over the plan length of the member and the dead load is applied over the slope length scissor ll arched chords dl θ to orient both loadings to the same axis multiply the live load by the cos θ bow string gable dl contact vulcraft for minimum depth at ends ll θ fig 5.10.2 non standard joist types to determine the normal component of each multiply again by the cos θ θ using the normal and parallel components of the loading the proper joist can be specified ∆h fig 5.10.3 loaded scissor joist this method produces several benefits in that it 1 eliminates the need for additional load tables 2 ensures the joist will be designed for the moment capacity for which it was specified 3 considers the actual joist length during selection preventing overspan conditions 4 102 provides a standard procedure compatible with current sji load

specification of components f 2.03 mechanical fasteners shall be teks as manufactured by buildex st charles road elgin illinois 60120 selection of teks fasteners not specified herein shall be in accordance with the manufacturer’s recommendations with a 3/8″ diameter hole side lap connections shall be screwed c arc spot welds puddle welds to support shall have a diameter weld nugget of 3/8″ minimum weld metal shall penetrate all layers of deck material at end laps and have adequate fusion to the supporting members welding shall be done in accordance with the american welding society standard “specification for welding sheet steel in structures” aws d1.3 d fastening of deck to supports and side laps fabrication a steel form deck metal centering shall have formed ribs of the type finish dimension and gage shown on drawings b deck shall be capable of supporting loads indicated on the drawings structural capacity of deck sections shall be established from

connection design e member extensions can be used on joists to increase the eccentric force capacity up to 56.6 kips 7.3 bottom chord extensions as mentioned in section 7.1 when the joist or joist girder bottom chords are extended and welded to the column continuity moments will be developed several situations must be examined when the bottom chords are extended these include 1 determining the magnitude of the continuity wind and seismic forces 2 design of the bottom chord for the continuity wind and seismic forces 3 design of the bottom chord connection to the column the engineer must perform a structural analysis in order to determine the forces in the bottom chord comments regarding rigid frame analysis are made in chapter 4 the specification of these forces to the manufacturer is discussed in chapter 6 it is the responsibility of the manufacturer to design the bottom chords of the joists and girders for the specified forces however it is the responsibility of the engineer to

responsibilities and erection of steel joists and joist girders” which is incorporated by reference in the sji code of standard practice this digest gives a thorough presentation of the issues involved in handling and erecting steel joists since the requirements for the erection of structural steel and the erection of steel deck steel joists and joist girders do not overlap and are not mutually cross referenced the common way to have these components erected into one uniform structural framework is to have one party erect all these components under one contract one aspect of steel erection is the employment of temporary bracing some steel frames do not rely on any element other than the structural steel for strength or stability thus when the work required to erect and finish the steel frame work is complete the temporary bracing can be removed at the erector’s discretion other steel frames rely on elements of the building to stabilize the structural steel framework these