Hieng Ho Lau

Wire rope isolators for vibration isolation of equipment and structures - A review

Vibrations and shocks are studied using various techniques and analyzed to predict their detrimental effect on the equipment and structures. In cases, where the effects of vibration become unacceptable, it may cause structural damage and affect the operation of the equipment. Hence, adding a discrete system to isolate the vibration from source becomes necessary. The Wire Rope Isolator (WRI) can be used to effectively isolate the system from disturbing vibrations. The WRI is a type of passive isolator that exhibits nonlinear behavior. It consists of stranded wire rope held between two metal retainer bars and the metal wire rope is made up of individual wire strands that are in frictional contact with each other, hence, it is a kind of friction-type isolator. This paper compiles the research work on wire rope isolators. This paper presents the research work under two categories, namely monotonic and cyclic loading behaviors of WRI. The review also discusses the different terminologies associated with vibration isolation system and highlights the comparison between various isolation systems.

Compression Test on Cold-Formed Steel Built-up Back-to-Back Channels Stub Columns

Built-up sections are used to resist load induced in a structure when a single section is not sufficient to carry the design load for example roof trusses. In current North American Specification, the provision has been substantially taken from research in hot-rolled built-up members connected with bolts or welds [1]. The aim of this paper is to investigate on built-up back-to-back channels stub columns experimentally and theoretically using Effective Width Method and Direct Strength Method. Compression test was performed on 5 lipped channel and 5 back-to-back channels stub columns fabricated from cold-formed steel sheets of 1.2mm thicknesses. The test results indicated that local buckling is the dominant failure modes of stub columns. Therefore, Effective Width Method predicts the capacity of stub columns compared to Direct Strength Method. When compared to the average test results, results based on EWM are 5% higher while results based on DSM are 12% higher for stub column.

Effect of screw spacing on behavior of axially loaded back-to-back cold-formed steel built-up channel sections

In cold-formed steel structures, such as trusses, wall frames, and portal frames, the use of back-to-back built-up cold-formed steel channel sections for the column members is becoming increasingly popular. In such an arrangement, intermediate fasteners at discrete points along the length prevent the individual channel sections from buckling independently. Current guidance by the American Iron and Steel Institute and the Australian and New Zealand Standards for built-up sections describes a modified slenderness approach, to take into account the spacing of the screws. Limited experimental tests or finite element analyses, however, have been reported in the literature for such sections to understand the effect of screw spacing. This issue is addressed herein. The results of 30 experimental tests are reported, conducted on back-to-back built-up cold-formed steel channel sections covering stub columns to slender columns. A finite element model is then described which shows good agreement with the experimental test results. The finite element model is then used for the purposes of a parametric study comprising 144 models. It is shown that while the modified slenderness approach is in general conservative, for stub columns it can be unconservative by around 10%.

Influence of Screw Spacing on the Strength of Self-Drilling Screw Connection for the High Strength Cold-Formed Steel

Self-drilling screws are the primary means of fastening for cold-formed steel members in cold-formed thin-gauge steel residential construction because it can drill their own holes and form their own threads. The fabrication of connections is the most labour intensive aspect of the cold-formed thin-gauge steel construction process, thus a better understanding of the behaviour of screw connections could lead to optimum connection design and reducing the cost of the fabrication. The study carried out to investigate the behaviour of single-shear connections using self-drilling screws in the cold-formed steel construction. The focus of this study is on the influence of the number of screws and screw spacing on the strength of self-drilling screw connection. These parameters are varied to determine their influences on the connection strength. The failure load and failure modes were obtained and observed from the tests carried out in the laboratory. Bearing and tilting failures occurred during the testing of these specimens. The predicted connection strengths were calculated using American Iron and Steel Institute (AISI) design equations. A total of 24 specimens of single shear test showed that connection strength is linearly proportional to the number of screw in the connection. Results of the specimen with spacing more than 3d show better correlation with the calculated results as compared to specimens with screw spacing less than 3d.

The influence of base connectivity on the ultimate load of columns

Abstract The carrying capacity of a column with one end pinned and the other end flat subjected to a combined axial load and a side load applied at the middle of the column has been investigated both theoretically and experimentally. The flat end is treated as fixed when in contact with the ground or as an eccentrically loaded, pinned connection rotating about one edge. The results show that columns with slenderness ratios in excess of 100 which have flat ends can carry loads in excess of the Euler pinned buckling loads if the side loads are kept below transition values.

Effects of the Plate Slenderness Ratio on Built-up Back-to-Back Channels Stub Columns

The purpose of this paper is to investigate the influence of plate slenderness ratio on the compression capacity and the performance of cold-formed steel built-up back-to-back C-channels sections. For stub columns, the overall slenderness ratio (KL/r) of the column has little effect on the load carrying capacity of the section. However, the plate element slenderness plays a major role in determining the performance of stub columns. The plate element slenderness for web or flanges needs to be less than the yield slenderness limit to be fully effective. Otherwise, only proportion of the web or flanges can be considered as effective. The study of the effects of plate element slenderness was carried out on the cold formed steel built-up columns fabricated by connecting two lipped C-channel columns back-to-back using self-drilling screws. Experimental results are compared with the calculated design results from the NAS specifications. Finite element model was created using commercial software LUSAS v14.4 to simulate the deformation curves and also to predict the load carrying capacities. Finite element results are validated by the test results. This study on the stub column shows that the plate element slenderness plays an important role in determining the compressive capacity and behavior of the stub column.

The influence of column base connections on the stability of slender multi-bay frame structures

Publisher Summary The chapter studies the behavior of column base connections and their influence on the overall stability of multi-bay slender frame structures. It discusses the testing and numerical modeling of two-bay portal frames. It identifies conditions for the transition of a floor connection from the frilly fixed to the all-pinned connection for multi-bay frames structures. These depend upon the nature of loading as well as on the geometry of the structure. The transition conditions at the column bases of two-bay frame are explored using the finite element method to predict the carrying capacity. An experimental program to validate these results is described in the chapter. The results showed good correlation between the finite element and the experimental results.