What wind speed is used for pedestrian bridge design in Palm Beach County?
Palm Beach County uses design wind speeds ranging from 150 to 170 MPH depending on exact location per ASCE 7-22 wind speed maps. Coastal areas near the Atlantic require 170 MPH, while inland areas may use 150-160 MPH. Pedestrian bridges are classified as Risk Category III structures due to occupancy loads, requiring a 1.15 importance factor multiplier on wind pressures. This classification recognizes that failure during a hurricane could endanger many people using the walkway for evacuation or shelter access.
Does a glass pedestrian bridge need impact-rated glazing in Palm Beach County?
Yes. All glazing in the Wind-Borne Debris Region (WBDR) of Palm Beach County must be impact-rated or protected by approved storm shutters. For pedestrian bridges, laminated glass assemblies with minimum 0.060 inch PVB interlayer are typically required, meeting ASTM E1996 large missile impact testing for structures within 1 mile of coast or above 60 feet elevation. The entire county falls within the WBDR, so there are no exemptions for inland locations. Impact testing must be performed on the actual glass assembly, not just the laminate.
How do you calculate wind loads on a glass-enclosed bridge?
Glass-enclosed pedestrian bridges require component and cladding (C&C) pressure calculations per ASCE 7-22 Chapter 30. The elevated position increases velocity pressure (qz) based on height above ground. External pressure coefficients (GCp) range from +0.9 to -1.8 depending on location on the building envelope. Internal pressure coefficients (+/-0.18 for enclosed or +/-0.55 for partially enclosed) apply based on enclosure classification. Net design pressures typically range from +40 to -85 psf for typical bridge heights of 20-50 feet. Corner zones and edges require higher negative pressures than field areas.
What glass thickness is required for pedestrian bridge panels?
Glass thickness depends on panel size, design pressure, support conditions, and edge treatment per ASTM E1300. For typical 4'x6' panels at 50 psf design pressure, minimum laminated glass assembly is 1/4" + 0.060" PVB + 1/4" (approximately 9/16" total). Larger panels or higher pressures may require 3/8" + 0.090" PVB + 3/8" assemblies (approximately 13/16" total). All glass must meet deflection limits of L/60 for laminated glass under full design load. Heat-strengthened glass is often specified for better post-breakage behavior and higher allowable stress.
What structural connections are required for bridge glass panels?
Glass panels in pedestrian bridges require continuous structural support systems engineered to transfer full design wind loads to the bridge superstructure. Common methods include captured glazing in aluminum frames (most common, provides continuous edge support with minimum 1/2" edge bite), point-supported systems with spider fittings (requires tempered/laminated glass with polished holes at 2.5x glass thickness from edge), and structural silicone glazed curtain wall systems (adhesive bond calculated for wind load transfer). All connections must be designed by a structural engineer and account for thermal movement, live load deflections, and seismic forces.
Are there special requirements for bridge spans over 50 feet?
Bridges spanning over 50 feet experience increased dynamic effects from wind buffeting and vortex shedding. ASCE 7-22 requires dynamic analysis for flexible structures with natural frequencies below 1 Hz. Glass panel supports must account for bridge deflection and movement under wind, live load, and thermal effects. Expansion joints are typically required every 40-60 feet to accommodate thermal movement (approximately 1/8" per 10 feet temperature change) and structural deflection without stressing the glass. Wind tunnel testing may be required by the building official for unique configurations or spans exceeding 80 feet.