The Influence of the Inclination of Lattice Columns on the Safety of Combined Tower Crane

The combined tower crane foundation is widely used in construction sites due to its advanced utilization rate. However, the immature construction method, unavoidable construction deviation during the installation process, and influence of the surrounding construction generally cause the lattice columns to tilt. As the main force transmission components of the tower crane foundation, once its stress and deformation exceed the limit, the entire tower crane will collapse, which requires engineers to accurately control its safety. Therefore, the objective of the work reported here was to study the safety of the lattice columns during operation. A geometrically nonlinear finite element model was utilized to simulate the strain and deformation capacity of tower cranes under various working conditions, including vertical and inclined working conditions, operation and shutdown conditions, and conditions with the tower boom in different orientations. In addition, this study combines the simulation with the on-site measurement. The results of on-site measurement were also recorded to verify the correctness of the proposed calculation model. It was concluded that the inclination of lattice columns has a significant effect on the deformation and stress of the lattice columns of the tower crane foundation, and the measured data and the calculated data trend are consistent. Engineers can accurately judge the safety of the lattice columns of the tower crane foundation through geometric nonlinear finite element model analysis and on-site monitoring to avoid the failure of the lattice columns and the occurrence of safety accidents.

Study on the characteristics of pipe buckling strength under pure bending and external stress using nonlinear finite element analysis

Buckling and collapse are important failure modes for laying and operating conditions in a subsea position. The pipe will be subjected to various kinds of loads, i.e., bending moment, external pressure, and tension. Nonlinear finite element analysis was used to analyze the buckling strength of the pipe under pure bending and external pressure. The buckling of elastic and elasto-plastic materials was also studied in this work. The buckling strength due to external pressure had decreased and become constant on the long pipe when the length-to-diameter ratio (L/D) was increased. The non-dimensional parameter (β), which is proportionate to (D/t) (σy/E), is used to study the yielding influence on the buckling strength of pipe under combined bending and external pressure loading. The interaction curves of the buckling strength of pipe were obtained, with various the diameter-to-thickness ratio (D/t) under combination loads of external pressure and bending moment. For straight pipes L/D = 2.5 to 40, D = 1000 to 4000 mm, and D/t = 50 to 200 were set. The curved pipes D/t = 200, L/D =2.5 to 30 have been investigated by changing the radius of curvature-to-diameter ratio (R/D) from 50 to ∞, for each one. With decreasing R/D, the buckling strength under external pressure decreases slightly. This is in contrast to the bending of a curved pipe. When the value of R/D was decreased, the flexibility of the pipe was increased. However, the buckling strength of the pipe during bending was decreased due to the oval deformation at the cross-section.

PRESSURE-IMPULSE DIAGRAM OF THE FLNG TANKS UNDER SLOSHING LOADS

Sloshing impact loads can cause severe structural damage to cargo tanks in liquefied natural gas floating production storage offloading units (LNG-FPSOs or FLNGs). Studies of sloshing can be classified into two types, namely, hydrodynamics-related and structural mechanics-related studies. This study is a sequel to the authors’ previous studies (Paik et al. 2015; Lee et al. 2015), but is more related to issues of structural mechanics. In this study, a new method for probabilistic sloshing assessment, which has been previously developed by the authors, is briefly explained. The nonlinear impact structural response characteristics under sloshing impact loads are examined by a nonlinear finite element ANSYS/LS-DYNA method. An iso-damage curve, representing a pressure-impulse diagram, is derived for the self-supporting prismatic-shape IMO B type LNG cargo containment system of a hypothetical FLNG. The insights developed from this work can be useful for the damage-tolerant design of cargo tanks in FLNGs.