Design of Truss Members for Tensile Forces

Symbols

A_g: Gross area

A_e: Effective net area

A_n: Net area

A_gv: Gross shear area

A_nv : Net shear area

A_nt: Net tensile area

F_y: Specified yield stress of the type of steel being used, ksi (MPa)

F_u: Specified ultimate stress of the type of steel being used, ksi (MPa)

K: Twisting length coefficient

L: Element length between supported points

i: Radius of gyration

U: Non-uniform stress distribution coefficient

U_bs: A coefficient considering the distribution of tensile stresses

T_n: Design tensile strength

Strength of Truss Members Under Tensile Forces

• If axial tensile elements are used together with bolted joints, yield stress will be reached earlier in the areas where bolt holes are located. This situation will affect the strength computations made by using the load-displacement curve and assuming linear elastic.

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• In bolted and welded joints of tensile members, because of the uneven distribution of load, the cross-sectional area operating in load transfer is not equal to the entire cross-section.

• Since the L and U sections are used especially in the braces and are not connected with bolts or welding, a certain region that is called as the effective area works in load transfer. Due to this phenomenon called as 'Shear Lag' effect, the effective net area is used in the design of tensile members.

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• 3 different areas are used in the strength calculation in tensile members:

  • Gross Area (A_g)

  • Net Area (A_net)

  • Effective Net Area (A_e)

Design with ÇYTHYE 2018

• There are 3 different failure conditions in the members affected by the tensile force: Yielding Limit State, Rupture Limit State and Block Shear Limit State

• The design tensile strength is taken as the minimum strength to be calculated according to the yield limit state, rupture limit state and block shear limit state of the member under axial tensile force. Block shear limit situation used in connections of tensile members is given in ÇYTHYE 2018 Section 13.4.3. Block break limit state is an additional check for connections.

• Tensile member slenderness should be controlled. In accordance with article 7.1.1 of the regulation, the slenderness ratio should be less than 300.

Yielding Limit State

• The characteristic tensile strength T_n for the yielding limit state in tensile members is calculated by equation 7.2 using the gross cross-section area.

Rupture Limit State

• The characteristic tensile strength T_n for the yielding limit state in tensile members is calculated by equation 7.3 using the net cross-section area.

Block Shear Limit State

• The characteristic block shear strength is calculated by equation 13.19, based on the yield and rupture limit states along the R_n shear surface or surfaces and tensile rupture limit state along the vertical tensile surface.