Woo-Bum Kim

Method for estimating the clamping force of high strength bolts subjected to temperature variation

The torque control method is mainly used as a clamping method for high-strength bolts in Korea and Japan. However, the torque coefficient affects the tension that is required during the process of tightening by torque. This makes it difficult to assume the direct tension induced into the bolt. The determinant factor that affects the clamping force is the ambient temperature, as indicated by the Korean standard B 2819. This study was planned to assess the expected clamping force of two types of high-strength bolts considering a temperature range of-10 to 50°C. Based on laboratory data subjected to temperature parameters, equations to estimate the clamping force were extracted by regression analysis.

Ultimate strength of tube–gusset plate connections considering eccentricity

Abstract A numerical analysis and experimental study were performed to investigate the behavior and strength of tube–gusset connections subjected to axial and axial brace force. To investigate the behavior of the connections, experiments were conducted by applying three directional loads. Local buckling and local plastic bending deformation of the connection were observed from the test. Analytical results were compared with test results for the limited cases. Of primary interests here is the eccentricity which may increase the strength of the connection. To suggest a formula for the strength of tube–gusset connections, axial brace forces are replaced by equivalent wall moment and eccentric vertical component force of axial brace force. Ultimate strength formula for each of the forces were proposed. Finally, nondimensionalized ultimate strength interaction relationships between the wall moment of tube ( M w ), vertical axial force ( P v ), and eccentric vertical component force of axial brace force ( P e ) were formulated through parametric study.

Evaluating relaxation of high-strength bolts by parameters on slip faying surfaces of bolted connections

The clamping force of a high-strength bolt reduces within a certain time period after the initial clamping force. When special treatments are used on a faying surface, the clamping force is relaxed severely. Tests were conducted for slip critical joints subjected to various faying surface parameters. Relaxation occurred for slip resistant joints with an uncoated surface that had been shot-blasted, cleaned, milled or rusted. It was observed that the initial clamping force dropped from 6.2% to 8.0% after 744 hours. For joints with a 5 mil thick zinc coating, the clamping force of the bolts decreased by 8.37%, and in the case of 4.9 mil thick red lead painted treatment, the relaxation ratio was 24.6%. The standard deviation of the slip coefficients between the time immediately after tightening and 1,000 hours after tightening was 0.223. It is particularly noteworthy that, for red lead painted treatment, the slip coefficient dropped from 2.5 times to 2.8 times when compared with the slip coefficient before relaxation. Joints with inorganic zinc should not have thickness exceeding 5 mils, and joints with a red lead painted surface should not be allowed regardless of the thickness of coating.

A simplified method to determine the moment-curvature relationships of a damaged tubular segment

Abstract A method for analysing the behaviour and strength of a damaged tubular segment was developed. In developing a reliable and efficient analytical method, a finite element analysis was carried out on a dented segment, and the m - p - φ relationship for each specific dent geometry was obtained. Then, a database of the relationship between various dent geometries was created. Regression analysis was performed to generalize the relationship between M , P , φ , D / t , d / D and σ y . Then, the functional relationship between M (moment) and the parameters was determined. Using the reduction process, the end moment of the dented segment was expressed in terms of axial force and rotation only. This predetermined M - P - θ relationship was used in the numerical integration of the member. Separate comparisons between analytical and experimental results were made for the M - P - θ curves of the dented segment.