Buckling Of Compression Members Research Articles

Experimental and numerical study on the axial compression performance of the prestressed sleeved members

The progressive collapse of large-span spatial structures can be triggered by the buckling of compression members. To further improve the stable load capacity of compression members, this study proposes a prestressed sleeved member by combining a prestressed stayed column system with a sleeved member. The experimental results show that the prestressed sleeved members possess a high load capacity, large secondary stiffness and moderate recovery performance, with the buckling modes of the members including first-order and second-order buckling. A nonlinear finite element (FE) model for the prestressed sleeved members is developed based on the experimental model. In addition, a series of parametric analyses are conducted to investigate the effects of the initial imperfection amplitude ratio, inner tube length to slenderness ratio, strand cross-sectional area ratio, inner and outer tube cross-sectional stiffness ratio and central support plate equivalent height ratio on the axial compression performance of the specimens. Furthermore, a simplified calculation model of the prestressed sleeved members is proposed for the case of second-order buckling, and theoretical calculation formulas are presented for three key points of the axial force–displacement curves of specimens. In contrast to the theoretical and FE results, the maximum errors of axial displacement and axial force do not exceed 15%. In addition, the steel strand tension, the contact force, and the lateral deflection of the middle section of the inner half-tube are highly consistent, which verifies the proposed relevant assumptions and theoretical calculation formulae.

Experimental study and performance evaluation of compression members in space structures strengthened with assembled outer sleeves

The buckling of compression members in space structures leads to the local collapse or even progressive collapse of structures. This paper proposed an assembled outer sleeve to reinforce the compression member of space structures by restraining its buckling. The assembled outer sleeve was composed of two identical semicircular anchor plates using high-strength bolts. The compression member to be strengthened does not need to be reformed directly. The mechanical properties of a compression member strengthened by an assembled outer sleeve were studied through axial compression tests involving eight specimens. The ultimate bearing capacity of a compression member strengthened by an assembled outer sleeve increased by more than 68.6%. When the wall thickness of the assembled outer sleeve was larger and the length of the unrestrained segment for the compression member was shorter, the ultimate bearing capacity of the specimens was higher. The installation direction of the assembled outer sleeve had no noticeable effect on the mechanical properties of the specimen. Furthermore, failure modes of the compression member strengthened by the assembled outer sleeve were proposed. The failure modes included the global buckling of the specimen, local buckling of the unrestrained segment for the compression member, and the coupled buckling (including global buckling and local buckling). When the wall thickness of the assembled outer sleeve was thin, global buckling was more likely to occur. Moreover, when the unrestrained segment for the compression member was long, local buckling was more likely to occur. Compared with the unreinforced compression member, the ductility coefficient of the compression member strengthened by the assembled outer sleeve enhanced by more than 49.7%. Compression members strengthened with assembled outer sleeves have an excellent post-yield axial deformation capability.

Static Behaviors and Applications of Buckling Monitoring Members with Rigid Ends

The buckling of compression members may lead to the progressive collapse of spatial structures. Based on the sleeved compression member, the buckling monitoring member is introduced to control the buckling of compression member and raise buckling alert by sensing contact between the core tube and the restraining tube. Considering the rigid connection among the members in spatial structures, the buckling monitoring member with rigid ends needs to be further analyzed. An experimental test was conducted and finite element analyses were performed with calibrated finite element models. The results indicated that the ultimate bearing capacity and post-ultimate bearing capacity of the core tube were enhanced due to the restraint from the restraining tube. The contact was successfully sensed by pressure sensor, revealing that it sensed the buckling of the core tube. Parametric studies were conducted, indicating that the core protrusion, core slenderness ratio, the gap between the core tube and restraining tube, and the flexural rigidity ratio are the key parameters affecting the bearing capacity and the failure modes of the buckling monitoring member, and some key values of parameters were proposed to obtain good bearing capacity. Based on the parametric studies, the failure modes of buckling-monitoring members are summarized as global buckling and local buckling. The stress distribution and deformation mode of buckling monitoring members are presented in the non-contact, point-contact, line-contact, reverse-contact and ultimate bearing state. The buckling monitoring member is applied in a reticulated shell by substituting the buckling members. It can effectively improve the ultimate bearing capacity of reticulated shell.

Improving the performance of concentrically braced frame utilizing an innovative shear damper

Concentrically braced structures are one of the most common resistant systems in steel structures due to their high stiffness and lateral strength. However, when these structures are subjected to moderate and severe earthquakes, their compression member begins to buckle. Also, buckling of compression members in Concentrically Braced Frames (CBFs) decreases ductility and degradation of the hysteresis curve. Numerous studies have been performed to improve the behavior of CBFs. Using steel dampers is considered one of the appropriate ways to improve the behavior of CBFs. Although steel dampers improve the hysteretic behavior of the CBFs, they impose additional costs on structures. Therefore, in this paper, a steel damper with a shear yield mechanism is introduced, which in addition to being economical, has the ease of construction and replacement after an earthquake. The numerical results indicate an enhancement of the hysteretic behavior of the CBFs utilizing the proposed damper. The main goal of equipping CBFs with the proposed damper is to control the possible damage in the damper and to ensure the elastic behavior of other structural components. The results indicate that the proposed damper can act as a structural fuse by dissipating more than 99% of the system energy and concentrating most of the plasticity and damage, which effectively protect the main structural components from damage while being subjected to seismic excitations. Necessary relations are presented for designing this damper. Besides, a simple method is presented for estimating the nonlinear behavior of the braces equipped with the proposed damper without any need for finite element modeling.

Ring-Shaped Lateral Bracing System for Steel Structures

Buckling of compression members has a great impact on the reduction of energy dissipation capacity and ductility of the structural system such as concentrically braced frame systems (CBFs). As well, direct connection of tensile and compression members to beams and designation of the link beam as a fuse, and the formation of plastic hinges in the link beam in eccentrically braced systems (EBFs) endanger the safety of this type structural systems. This paper introduces a new ring-shaped lateral bracing system so-called the Shami lateral bracing system (SLBs) which removes the common tensile and compressive members along with their connections to the structure. As a substitute, SLBs introduces a new element with proper ductility and energy dissipation capacity and could be an appropriate alternative to the existing systems. Because of the high degree of statically indeterminacy of the proposed system, the structural stiffness does not lead to a steep reduction after the formation of the first plastic hinge. The performance of this lateral system is evaluated by numerical modeling, and the results show that the structures resist against the lateral loads with acceptable seismic performance. It seems that this system in comparison with CBF and EBF systems may not be cost-effective for bending of the ring, welding, etc., but from the seismic performance points of view, it has good performance.

Rehabilitation of jacket offshore platforms using friction damper device and buckling restrained braces under extreme loads

Some existing platforms may have some problems with probable extreme future loads such as earthquake. From economic point of view, it is preferable to retrofit and continue using of existing jackets in many cases, in comparison to a new installation. Two efficient rehabilitation methods of friction damper device and buckling restrained braces are presented and investigated numerically for seismic loads from far-fault and near-fault earthquakes. As an example, an existing four-leg service platform placed in the Persian Gulf (Ressalat) is considered and the results are presented. Because of low redundancy in jacket platforms (after buckling of compression members), it is important to investigate the effect of friction damper device on the structural behavior. Buckling restrained braces solves the law redundancy because of no buckling and no decrease in strength. The results show the high efficiency of both methods in reducing structural responses and increasing seismic performance level. Such studies are very useful for many existing jacket platforms that their lifetime is to be extended.

Finite Element-Based Investigation on Performance of Intermediate Length Thin-Walled Columns with Lateral Stiffeners

Distortional buckling of compression members usually comprises rotation and translation of each flange and lip about the flange-web juncture in opposite directions. The present study makes an attempt to possibly delay or prevent the distortional buckling mode by the introduction of lateral stiffeners. The stiffened channel section has been selected based on the elastic buckling analysis using CUFSM software to ensure the occurrence of distortional buckling. The test programme consisted of two pure axial compression tests under hinged–hinged end condition. A finite element model of the tested compression members was then developed and validated with the help of experimental results and also by the column test results conducted by Young and Yan (J Struct Eng 732:728–736, 2002). Geometric, material nonlinearities and initial geometric imperfection were included in the finite element model. An extensive series of parametric analyses was undertaken using the validated finite element model to investigate the effect of varying depth and many lateral stiffeners on the ultimate capacity of the columns. The details of the parametric study results are presented as charts. The lateral stiffeners effect on behaviour and strength is discussed.