1. Impact Load
Live loads specified in codes do account for ordinary impact loads
When structural members are subject to unusual vibration or impact we have to account for them outside the code specs

2. Minimum % increase in live load on structural members due to impact
Type of member
Source of Impact
Percent increase
Supporting
Elevators and elevator machinery
100
Light machines, shaft, or motor driven 20
Reciprocating machines or power-driven units 50
Hangers
Floors or balconies 33

3. Crane Runway Loads Structures supporting cranes:
Maximum wheel loads
Allowance for impact
Multiple cranes
Traction and braking forces
Use of crane stops
Cyclic loading / Fatigue
Crane live load is its fully rated capactity

4. Cranes

5. Crane Runway

6. Crane load Max vertical wheel load
Monorail, cab operated, remote operated
increased by 25% for impact
Pendant operated overhead
Increased by 10% for impact
Impact increases do not have to be applied to supporting columns, only runway

7. Crane Lateral Loads Electic powered trolleys
≥ 20% (crane rated load + trolley weight + hoist weight)
Assume applied by wheels at top of rails
Acts normal to the rails
Distributed, as appropriate to stiffness of rail support
Bridge or monorail with hand-gearing
No need for lateral load increase

8. Crane Stop Forces Runway must be designed for stop forces
Velocity of crane at impact taken into account
Fatigue and serviceability concerns
AISC Design Guide 7
AISE Standard No. 13

9. Restraint Loads
Caused by changes in dimensions/geometry of structures due to
Behavior of material
Type of framing
Details of construction
e.g.
Foundation settlement
Temperature changes
Shrinkage restrained by adjoining structures

10. Combined Loads Loads may act simultaneously
Building codes specify various combinations that must be considered
Depends on whether allowable stress design (ASD) or Load and Resistance Factor Design (LRFD) is used
SEI/ASCE 7-02 provides guidance.

11. Load Sources D = dead load L = live floor load, including impact
Lr = roof live load
S = roof snow load
R = rain load (initial rainwater or ice, exclusive of ponding)
W = wind load
E = earthquake load
T = restraint load

12. ASD Loads (SEI/ASCE 7-02) D D + L + T D + (Lr or S or R)
0.75 [ L + (Lr or S or R) + T ] + D
0.75 (W or 0.7E) + D
0.75 [ L + (W or 0.7E) + (Lr or S or R) ] + D
0.6D + W
0.6D + 0.7E
Because E was calculated for LRFD it is reduced by 0.7 for ASD design.

13. LFRD Design Loads (SEI/ASCE 7-02)
1.2(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 + 1.6W
0.9D + E

14. Fire Protection International Building Code
International Code Council, Falls Church, VA
NFPA 5000, Building Construction and Safety Code
National Fire Protection Association, Quincy, MA
National Building Code of Canada
National Research Council of Canada, Ottawa, ON
Or local code

15. Combustible/Non-combustible
Most fires are accidental or carelessness
Start small and require fuel and ventilation to grow
Noncombustibles (concrete, steel, brick) are not fuel
Combustibles (paper, wood, plastics) are fuel

16. Fire Loading and Fire Severity
Fire loading is the amount of fuel, measured in equivalent pounds of wood per square foot of floor area
Fire severity is the duration of the fire, in hours of equivalent fire exposure
More modern approaches of fire load are expressed in terms of potential heat energy
Fire loading correlates well with fire severity

17. Fire Loading
Reasonable estimate for conventional wood frame construction:
7.5 – 10 lb/ft2
Reasonable heavy timber estimate
12.5 – 17.5 lb/ft2
Consequently building codes limit permitted size (height and area) of combustible buildings more than non-combustible buildings.
BUT ventilation is an important factor as well.

19. Occupancy Fire Loads and Severity
Type of Occupancy
Fire Load (lb/ft2)
Fire Severity (hrs)
Assembly
5-10
0.5 – 1
Business
0.5-1
Educational
Hazardous
Variable
Industrial
Low hazard
0-10
0-1
Moderate hazard
10-25
1-2.5
Institutional
Mercantile
10-20
1-2
Residential
Storage
10-30
1-3

20. Fire Resistance
Fire Resistance: Relative ability of construction assemblies to prevent spread of fire to adjacent spaces, and to avoid structural collapse
Fire resistance requirements are a function of occupancy and size (height and area)
Fire resistance is determined experimentally
ASTM E 119
Uses “standard” fire exposure
Specified in terms of time of exposure

21. Fire Resistance Time during which an assembly
continues to prevent spread of fire,
does not exceed certain temperature limits, and
Sustains 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

23. Fireproof
No building is fireproof.
Avoid this term

24. Effect of Temperature on Steel
In general, steel can hold 60% of yield strength at 1,000 F
Failures rarely occur because during a fire building is rarely loaded at design load.
This is not recognized in the code – structures are assumed to be fully loaded during testing.
Thus, when building codes specify fire resistant construction, fire protection materials are required to insulate the structural steel.

25. Steel Strength vs Temperature

26. Fire Protection Materials
Gypsum
As a plaster, applied over metal lathe or gypsum lathe
As wallboard, installed over cold-formed steel framing or furring
Effectiveness can be increased significantly with lightweight mineral aggregates (vermiculite, pearlite)
Mix must be properly proportioned and applied in required thickness and the lathe correctly installed

27. Gypsum 3 kinds: Type X: Proprietary
Regular, Type X, and proprietary
Type X:
Specially formulated cores for fire resistance.
Proprietary
Such as Typc C, even greater fire resistance
Type of wall board must be specified clearly.
Type and spacing of fasteners (and furring channels if applicable) should be in accordance with specs

30. Spray Applied Materials
Most widely used
Lightweight mineral fiber and cementitious material
Sprayed onto beams, girders, columns, floor decks, roof decks
SFRM: Spray-applied Fire Resistive Materials
Generally proprietary formulations
Follow manufacturers recommendations!
Underwriter’s Laboratories specifies these

31. SFRM Cohesion/Adhesion are critical
Must be free of dirt, oil, loose scale
Generally light rust is OK
Paint can cause problems

33. Suspended Ceiling Systems
Wide range of systems available to protect floors, beams and girders
Fire resistance ratings published by UL
Require careful integration of ceiling tile, grid and suspension system
Openings for light fixtures, air diffusers, etc. must be adequately limited and protected.
Sometimes code requires individual structural element protection, thus suspended ceilings are not permitted.

34. Concrete and Masonry
Concrete used to be common, but not highly efficient (weight and thermal conductivity)
Concrete floor slabs are common for tops of flexural members.
Concrete sometimes used to encase columns
for architectural or structural purposes,
or for protection from abrasion or other physical damage

36. Architecturally Exposed Structural Steel
AESS: easthetic choice
Steel – Insulation– Steel skin
Gives appearance of steel surface but has protection
Water filled tubular columns
Patented in 1884, but not used until 1960 in the 64 story US Steel Building in Pittsburgh
Flame shielded spandrel girders
Standard fire test is not representative of the exposure for exterior structural elements.
Can only be used if code allows engineered solutions

38. Water Filled Columns
Columns are interconnected with a water storage tank.
In fire, water circulates by convection, keeping the steel temperature below the critical value of 450°C.
This system has economical advantage when applied to buildings with more than 8 storeys.
If the water flow is adequate, the resulting fire resistance time is virtually unlimited.
In order to prevent freezing, potassium carbonate (K2CO3) is added to the water.
Potassium nitrate is used as an inhibitor against corrosion.

40. Flame Shields
Interior
Exterior
Painted girder

41. Restrained and Unconstrained
Major confusion from concept of Restrained and Unconstrained ratings
Only in ASTM E119 and US codes
No other country uses this
Part of problem is max test size is 15’ x 18’ – not full scale
When testing problems arise:
Floor slabs and roof decks are physically continuous over beams and girders, but this is too big
Beams join columns and girders in a number of different ways – can’t test them all

42. Restrained and Unconstrained
ASTM E119 includes 2 test conditions: Restrained and Unrestrained
Restraint is against thermal expansion
This allows for thermal stresses from surrounding structure
Most steel framing is tested as Restrained
Unrestrained:
Single span and simply supported end spans of multiple bays
Open web steel joists or beams, supporting precise units or metal decking
Wood construction

43. Temperature of exposed steel elements
Rate of temperature change depends on mass and surface area.
The weight to heated perimeter ratio is significant
W/D
W = weight per unit length
D = inside perimeter of fire protection material
W/D = Thermal Size (lbs/ft/in)