What is the meaning of roof frame upstringing and downstringing?

The top chord and bottom chord of a roof frame are the two main parts of the roof frame structure.

1. Top Chord Member: Located in the upper part of the roof frame, it is two inclined rods, usually constituting the waist of the roof frame, also known as herringbone or figure-of-eight timbers. Upper chord transverse horizontal bracing refers to the horizontal trusses set up between two neighboring roof frames or between a roof frame and a mountain wall, whose chord rods are the upper chord rods of the roof frame, and the web rods are composed of crossed diagonal rods and vertical rods.12

2. Bottom Cord Member: Located in the lower part of the roof frame, it is the rod in the horizontal position below the roof frame, also known as the scale’s big material or bottoming. Lower chord transverse horizontal bracing refers to the horizontal trusses set up in the plane of the lower chord between the end sections of the roof frame or in the middle of the roof frame, whose chord rods are the lower chord rods of the roof frame, and the web rods are also composed of crossed diagonal rods and vertical rods.

The top chord and bottom chord of the roof frame together support the whole structure of the roof frame to ensure its stability and load-bearing capacity.