NYC Hurricane Irene Special! - Intro to Wind Forces

Bad weekend to start your construction project in the Tri-State area.  Or end your project.  Or be a contractor on a project:  just look at all of their responsibilities to comply with the NYC's Deparment of Buildings:  


To secure construction sites, builders, contractors and developers should take all precautionary measures including but not limited to the following: 

• Tie down and secure material and loose debris at construction sites.
• Cover electrical equipment from exposure to the weather.
• Store loose tools, oil cans and extra fuses in a tool box.
• Secure netting, scaffolding and sidewalk sheds.
• Suspend crane operations and secure crane equipment when wind speeds reach 30 mph or greater.
• Suspend hoist operations and secure exterior hoists when wind speeds reach 35 mph or greater, unless manufacturer specifications state otherwise.
• Brace and secure construction fences.
• Secure all windows.

Owners don't have it any easier:

• Bring inside loose, lightweight objects such as lawn furniture, potted plants, garbage cans, garden tools and toys.
• Anchor objects that would be unsafe outside, such as gas grills or propane tanks.
• Close up and secure patio umbrellas.
• Secure retractable awnings.
• Clear rooftop drains, gutters and leaders.
• Secure all windows.
• Remove aerial antennas and satellite television dishes.

Architects' responsibilities include:

• Do not go in to work.  Drink if necessary to prevent this.
• Continue to peruse job postings on Craig's List.

Now, on to wind:

EFFECTS OF WIND ON BUILDINGS

• direct pressure
• drag
• suction
• rocking, buffeting
• vibration
• clean-off effect:  wind gusts have more effect of building parts than the whole building

CRITICAL WIND EFFECTS

Codes provide critical wind velocity and design wind pressures.  Wind speeds are taken from the code, and are based on historical data measured at a standard height of 33' above the ground.  Factors considered by code are building size, building shape, openness and sheltering effect of surrounding landscape, and various special conditions.

Wind forces determined are:  

-  inward pressure and outward pressure (suction) on exterior walls

-  pressure on roof

-  overall force on the building

-  sliding and overturning forces - resisted by dead weight of building)

-  harmonic effects - resisted by stiffening/bracing/tightening of elements)

-  effects of openings - forces are increased at openings, these can be calculated via a wind tunnel test
torsional effects - twisting of elements about the centroid, or center of stiffness