2.1　Terms

2.1.1　Concrete-filled steel tube（CFST）arch bridge

A bridge whose main load-carrying component（s）is（are）concrete-filled steel tube（s）with a circular cross-section，which serve（s）as rib（s）for an arch.

2.1.2　CFST arch rib

An arch rib，whose main load-carrying element（s）is（are）concrete-filled steel tube（s）.

2.1.3　Steel tube arch rib

An arch rib of a hollow steel tube without filling of concrete inside.

2.1.4　Concrete in tube（core concrete）

Concrete that is filled in a steel tube.

2.1.5　CFST member

A member that is made of CFST，in which the steel tube and the concrete core act compositely to resist loads.

2.1.6　Single tube arch rib

An arch rib that is formed by a single CFST member with a circular section.

2.1.7　Dumbbell-shaped arch rib

An arch rib that is formed by two top and bottom CFST members with circular section connected by two steel web plates.

2.1.8　Truss arch rib

An arch rib that is formed by top and bottom CFST chords 　connected by web members to form trusses.

2.1.9　Laced CFST column

A laced column that is formed by multiple CFST members connected transversely by hollow steel tubes.

2.1.10　Rigid-frame tied arch

An arch structure whose rib is rigidly connected to piers and the horizontal thrust is partially balanced by pre-stressed ties.

2.1.11　Rigid-frame tied through arch

A bridge structure whose deck system is suspended below the rigid-frame tied arch.

2.1.12　Rigid-frame tied half-through arch

A multi-span bridge structure whose deck system at the main span is partially suspended below the rigid-frame tied arch，while its deck systems at two side spans are supported above two cantilever half arches.The ties are anchored on each end of the side spans.It is also known as a flying-bird arch.

2.1.13　Confinement（hooping）coefficient

A coefficient accounts for the confinement effect of the steel tube on the concrete core.

2.1.14　Initial stress or Preloading of steel tube

The initial axial stress in a steel tube caused by loads due to sequential construction procedures before composite action is fully formed in the CFST members，it is also called initial stress or preloading of CFST.

2.1.15　Initial stressing ratio or preloading ratio

The ratio of preloading stress to the yield stress of the steel tube.

2.1.16　Computational closure temperature The average temperature in the cross section at the moment of zero thermal stress which is converted from the stresses in the CFST arch rib when the concrete core reaches its design strength.

2.1.17　Intersection joint

Intersection line welding joint connecting the main CFST tube（chord）with the branch tube（web truss）.

2.1.18　Debonding

The phenomenon of separation of the steel tube from the concrete core that are attributed to factors other than quality issues including thermal gradient and shrinkage of the concrete core.

2.1.19　Debonding（angle）rate

The central angle（ratio）corresponding to the debonding region in the cross section of CFST members.