Abstract: The steel structure of portal frame light-weight building has been widely used in petrochemical plants for its advantages of flexibly arranged column grid unrestricted by building modulus, easy prefabrication, short installation period, convenient disassembly, large venting area, easy to meet the explosion relief requirements of petrochemical plant, environmental protection and recyclable resources. However, irrational design and waste of resources occur from time to time. The rational design and optimization of portal frame light-weight building is systematic and complex. This paper analyzes the design rationality and the possibility of optimization from the aspects of the determination of structure type, importance level, load value, span and column spacing, purlin calculation, vertical support arrangement and connection nodes, so as to achieve rational structural design and lower investment

Key words: portal frame, steel structure, purlin, rational design