Studies were initiated for a simplified procedure for ultimate limit state design of the shell of hyperbolic cooling tower（HCT）which involves many different wind directions.It is primary to comprehensively understand the characteristics of internal forces under every single load.The internal forces of a representative HCT under different loads

including gravity（G）

wind（W）

thermal actions in winter and summer（TW

TS）

horizontal and vertical earthquakes（EH

EV）with reasonable load values

were illustrated individually and compared systematically.The predominant internal forces and their circumferential distributions are the main concerns.According to the results

load effects of G

TW and EV are uniformly distributed along the circumference

so they have no influence on the direction combination of load effects.The maximal internal forces under TSand EHare located on a stationary meridian line

and they are mainly bending moments and axial forces

respectively.So the most unfavorable combination of load effects emerges when the two load directions coincide.For wind load

its arbitrary wind direction

complex distribution of internal forces

and the coexistence of bending moment and axial force make it inevitable that many wind directions are involved in considering combination of load effects.However

the distribution characteristics of internal forces make it possible to simplify the combination of load effects of HCT shell.