Database-Assisted Design of Purlins and Girts for Wind Accounting for Directionality
Dat Duthinh, Emil Simiu
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; 4) from the results of step 3, use of non-parametric statistics to calculate peak moments and shear forces with specified mean recurrence interval by accounting for building orientation and directionality of the wind speeds. Comparison shows that, before the application of the wind directionality factor Kd, there is general good agreement between the peak wind effects predicted by ASCE 7-16 pressure coefficients and those obtained by the direct use of wind tunnel pressure measurements. However, the ASCE 7-16 Standard, which entails the application of the directionality factor Kd = 0.85, yields internal forces that, for the example considered, can differ by up to 33 %, depending on the building orientation, from those based on the rigorous DAD approach presented in this paper. This approach, that 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.