PSI - Issue 64

Atsushi Sato et al. / Procedia Structural Integrity 64 (2024) 991–998 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

992

2

the limited seismic effective mass. However, the recent increase in wind intensity resulting from significant climate change has led to collapses, creating a high demand to reinforce existing conventional towers. The construction field typically uses lap joints to connect steel angle members (see Fig. 1b). This is done to ensure workability and for safety reasons. It is recommended to minimize the components. The lap joint uses high strength bolts that are tightened snugly. This accommodates slippage and introduces an eccentricity that generates a secondary bending moment. The design guideline explains how to evaluate the amount of eccentricity at the joints. However, in the past, the evaluation method for reinforcing the main post members was not shown as it was perceived to be unnecessary. Jaspart et al. (2020, 2021) have summarized the design rules for angle members subjected to compression and bending. Ono et al. (2007), Tamai et al. (2011), and Zhuge et al. (2012) have proposed a reinforcement method to increase the buckling strength of the angle members. This paper presents a method for evaluating the flexural buckling strength of reinforced steel angle members under eccentric load. The evaluation formula is derived using a theoretical approach that considers the effect of eccentric load and the amount of reinforcement. Small-scale experiments are conducted to validate the proposed design formula. The test results confirm that the proposed formula can effectively evaluate the strength of reinforced steel angle members.

a)

b)

Fig. 1. Electric transmission tower: (a) Structural member components; (b) Lap joint (with the same size of angles).

2. Flexural buckling strength of the eccentrically loaded member 2.1. Flexural buckling strength based on full-plastic strength

When a member is subjected to an axial force that is off-centre from its centre of gravity (C.G.), it results in an additional bending moment at the loading point (as shown in Fig. 2a). This combination of axial force and bending moment is known as a beam-column (Fig. 2b). Lap joints are commonly used in electric transmission towers, as seen in Fig. 1b. Assuming the eccentricity at the loading point is equal at both ends (as shown in Fig. 2a), the deflection at midpoint of the member can be calculated using an equilibrium equation. It is possible to determine the bending moment at the point of maximum stress on a member using this equation. This will be calculated using Eq. (2).

   

   

N



sec

1

(1)

u e =

−

2

c

N

0