In the basic form, the serial verb construction (SVC) resembles unmarked coordination: two VPs are juxtaposed without overt marking of the relation between them: Depending on the ways in which the two described events can be related by virtue of our world knowledge, different semantic relations can be established between the two VPs.
in (8), the relation would most probably be interpreted as one of purpose: Zhangsan goes to the city in order to buy clothes.