hoist loads

8/10/2019 Hoist Loads

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Live loads specified in codes do account for ordinaryimpact loads When structural members are subject to unusual

vibration or impact we have to account for themoutside the code specs


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Type ofmember

Source of Impact Percentincrease

Supporting Elevators and elevator machinery 100Supporting Light machines, shaft, or motor driven 20Supporting Reciprocating machines or power-driven

units50

Hangers Floors or balconies 33


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Structures supporting cranes:Maximum wheel loads Allowance for impactMultiple cranesTraction and braking forcesUse of crane stopsCyclic loading / Fatigue

Crane live load is its fully rated capactity


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Max vertical wheel loadMonorail, cab operated, remote operated

increased by 25% for impactPendant operated overhead

Increased by 10% for impact

Impact increases do not have to be applied tosupporting columns, only runway


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Electic powered trolleys 20% (crane rated load + trolley weight + hoist weight) Assume applied by wheels at top of rails Acts normal to the railsDistributed, as appropriate to stiffness of rail support

Bridge or monorail with hand-gearingNo need for lateral load increase


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Runway must be designed for stop forces Velocity of crane at impact taken into accountFatigue and serviceability concerns

AISC Design Guide 7 AISE Standard No. 13


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Caused by changes in dimensions/geometry ofstructures due to

Behavior of materialType of framingDetails of construction

e.g.Foundation settlement

Temperature changesShrinkage restrained by adjoining structures


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Loads may act simultaneouslyBuilding codes specify various combinations that mustbe considered

Depends on whether allowable stress design (ASD) orLoad and Resistance Factor Design (LRFD) is usedSEI/ASCE 7-02 provides guidance.


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D = dead loadL = live floor load, including impactLr = roof live load

S = roof snow loadR = rain load (initial rainwater or ice, exclusive of ponding) W = wind loadE = earthquake loadT = restraint load


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DD + L + TD + (Lr or S or R)

0.75 [ L + (Lr or S or R) + T ] + D0.75 (W or 0.7E) + D0.75 [ L + (W or 0.7E) + (Lr or S or R) ] + D0.6D + W0.6D + 0.7E

Because E was calculated for LRFD it is reduced by 0.7for ASD design.


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1.4 D1.2(D+T) + 1.6L + 0.5(Lr or S or R)1.2D + 1.6(Lr or S or R) + (L or 0.8W)

1.2D + 1.6W + L + 0.5(Lr or S or R)1.2D + E + (L or 0.2S)0.9D + 1.6W0.9D + E


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International Building CodeInternational Code Council, Falls Church, VA

NFPA 5000, Building Construction and Safety Code

National Fire Protection Association, Quincy, MANational Building Code of CanadaNational Research Council of Canada, Ottawa, ON

Or local code


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Most fires are accidental or carelessnessStart small and require fuel and ventilation to growNoncombustibles (concrete, steel, brick) are not fuel

Combustibles (paper, wood, plastics) are fuel


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Fire loading is the amount of fuel, measured inequivalent pounds of wood per square foot of floorareaFire severity is the duration of the fire, in hours ofequivalent fire exposureMore modern approaches of fire load are expressed interms of potential heat energy

Fire loading correlates well with fire severity


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0

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0 10 20 30 40 50 60 70

F i r e

S e v e r i

t y ( h

r s )

Fire Load (lbs/ft2)


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Type of Occupancy Fire Load (lb/ft 2) Fire Severity (hrs) Assembly 5-10 0.5 1Business 5-10 0.5-1Educational 5-10 0.5-1

Hazardous Variable VariableIndustrial

Low hazard 0-10 0-1Moderate hazard 10-25 1-2.5

Institutional 5-10 0.5-1Mercantile 10-20 1-2Residential 5-10 0.5-1Storage

Low hazard 0-10 0-1

Moderate hazard 10-30 1-3


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Fire Resistance : Relative ability of constructionassemblies to prevent spread of fire to adjacent spaces,and to avoid structural collapseFire resistance requirements are a function ofoccupancy and size (height and area)Fire resistance is determined experimentally

ASTM E 119

Uses standard fire exposure Specified in terms of time of exposure


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Time during which an assemblycontinues to prevent spread of fire,does not exceed certain temperature limits, andSustains its structural loads without failure

Typically expressed in hours

Fire Resistance Directory, Underwriters Lab

Fire Resistant Ratings, American Insurance Services Gp.Fire Resistant Design Manual, Gypsum Association


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No building is fireproof. Avoid this term


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In general, steel can hold 60% of yield strength at1,000 FFailures rarely occur because during a fire building israrely loaded at design load.This is not recognized in the code structures areassumed to be fully loaded during testing.Thus, when building codes specify fire resistant

construction, fire protection materials are required toinsulate the structural steel.


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0

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0.8

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0 500 1000 1500 2000 2500

% Y

i e l d S t r e n g

t h

Temperature (F)


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Gypsum As a plaster, applied over metal lathe or gypsum lathe As wallboard, installed over cold-formed steel framingor furring

Effectiveness can be increased significantly withlightweight mineral aggregates (vermiculite, pearlite)

Mix must be properly proportioned and applied in required

thickness and the lathe correctly installed


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3 kinds:Regular, Type X, and proprietary

Type X:Specially formulated cores for fire resistance.

ProprietarySuch as Typc C, even greater fire resistance

Type of wall board must be specified clearly.

Type and spacing of fasteners (and furring channels ifapplicable) should be in accordance with specs


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Most widely usedLightweight mineral fiber and cementitious materialSprayed onto beams, girders, columns, floor decks,

roof decksSFRM: Spray-applied Fire Resistive MaterialsGenerally proprietary formulationsFollow manufacturers recommendations!

Underwriters Laboratories specifies these


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Cohesion/Adhesion are criticalMust be free of dirt, oil, loose scale

Generally light rust is OK

Paint can cause problems


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Concrete used to be common, but not highly efficient(weight and thermal conductivity)Concrete floor slabs are common for tops of f lexuralmembers.Concrete sometimes used to encase columns

for architectural or structural purposes,or for protection from abrasion or other physical damage


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AESS: easthetic choiceSteel Insulation Steel skin

Gives appearance of steel surface but has protection

Water filled tubular columnsPatented in 1884, but not used until 1960 in the 64 storyUS Steel Building in Pittsburgh

Flame shielded spandrel girders

Standard fire test is not representative of the exposurefor exterior structural elements.Can only be used if code allows engineered solutions


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Columns are interconnected with a water storage tank.In fire, water circulates by convection, keeping thesteel temperature below the critical value of 450C.

This system has economical advantage when applied to

buildings with more than 8 storeys.If the water flow is adequate, the resulting fire resistancetime is virtually unlimited.

In order to prevent freezing, potassium carbonate

(K2CO3) is added to the water.Potassium nitrate is used as an inhibitor againstcorrosion.


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Interior

ExteriorPainted girder


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ASTM E119 includes 2 test conditions: Restrained andUnrestrainedRestraint is against thermal expansionThis allows for thermal stresses from surrounding structureMost steel framing is tested as RestrainedUnrestrained:

Single span and simply supported end spans of multiple baysOpen web steel joists or beams, supporting precise units ormetal decking Wood construction


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4


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0

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F i r e

R e s i s t a n c e

( h r s

)

W/D (lb/ft/in)

1/2"5/8"

1"

1 1/4"

1 1/2"

1 7/8"

2"

2 1/2"

hoist loads

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