Fill in the Blanks $(2$ point each, $20$ points totally $)$

$(1)$ Steel grade Q$235-$BF represents

$(2)$ Bolt property grade $8\mathrm{.}8$ represents

$(3)$ Through a standard tensile test of steel specimen, three strength indices, such as proportional limit$,$ and can be determined, which are three important mechanical behavior indices.

$(4)$ The overall stability factor $$ of axial compression members depends on the slenderness ratio, and

$(5)$ When calculating the overall stability of steel beams, if the value of ${}_b$ is greater than, it shall be replaced by ${}_b^{\text{'}}.$ It indicates the steel beam have worked in the plastic stage.

$(6)$ The types of welds include and

$(7)$ When calculating the overall stability of latticed columns, the equivalent slenderness ratio about virtual axis shall be used in order to consider