Verification of ASCE 7-16 Pressure Coefficients and Database-Assisted Design of Purlins and Girts Accounting for Wind Directionality.

Abstract

For the database-assisted design (DAD) of low-rise building purlins and girts, a method is proposed that explicitly accounts for wind directionality by using directional wind tunnel measurements, directional wind speed data, and publicly available software. The method consists of four steps: (1) assignment of wind loads induced by a unit directional wind speed on purlins and girts from pressure taps and their tributary areas; (2) development of bending moment and shear force influence coefficients for line loads on purlins and girts; (3) multiplication of loads from step 1 by influence coefficients from step 2 and estimation of the peak bending moments and shear forces thus obtained; and (4) use of nonparametric statistics to calculate peak moments and shear forces with a specified mean recurrence interval for various building orientations and accounting for wind directionality. For one example of wind effects on purlins, (1) comparison of the Envelope Method in ASCE 7-16 (taken as 100%) with the most demanding aerodynamic case from wind tunnel tests shows differences ranging between +10% and -25%; and (2) comparison of the ASCE 7-16 method accounting for the wind directionality factor Kd with directional wind loads using nonparametric statistical methods shows differences ranging between +21% and -25%. The unconservatism (+) of ASCE 7-16 is thus worse after Kd is applied. The proposed method is based on the rigorous DAD approach, accounts explicitly for the actual directional wind loading, entails no onerous computational requirements, and typically results in more economical designs while assuring risk-consistent safety.