STRUCTURE AND STEEL
Year:2015 | Volume:10 | Issue:16|Papers Count:7

Lack of instruction and standards for seismic design of steel structures in 1370 (solar calendar) in IRAN, resulted to extensive use of castellated beams in eccentrically braced frames as a link. According to aforementioned issue the study of seismic behavior of such frames have been necessitated. Link beam, as the place for plastic hinge creation in EBFs, has the main role to damp the seismic energy and quality of seismic behavior of these frames. Due to web openings in castellated link beams, and to lack of extending plastic hinge in web and possibility of brittle fracture modes creation, the capacity of energy damping of EBFs decreases. In this experimental study, 4 link beam are built as samples, which one of them has no stiffener, another one has the recommended stiffener by AISC2010, and the last two samples have recommended details with longitudinal and diagonal stiffeners. Semi-statics cyclic loading apply to all the samples results have shown two ordinary link beams have non-ductile behavior, strength and rigidity reduction, and the two recommended details by authors have shown promoted seismic parameters.

Arc stud welds act as shear connectors in composite steel-concrete beam which are now widely used in the construction of roof of buildings. In this study shear studs 19 mm in diameter made of AISI 1010 steel are welded to steel beams and the effects of weld current, plung and lift heights, and arc time are investigated. Weld samples were characterized in terms of appearance, profile, weld penetration, strength and fracture location in bend test. The results showed the significance of the process parameters on the soundness and strength of the welded connection. It is also shown that weld appearance and just visual inspection cannot be regarded as a sufficient test for the day to day inspection of the stud welding work at site. It is also necessary and important to perform the site bend test at the beginning of each shift or round of site work as required by AWS D 1.1 standard.

This paper investigates the impressions of gypsum panel and fiber cement board sheathing on seismic performance of CFS stud walls. For this purpose, five 3600 in 3000 millimeter (length in height) specimens which three of them were strapped diagonally have been tested under cyclic loading. The hysteresis diagram, failure modes and ductility coefficient, were extracted for each specimen and compared. The experiments showed the nonstructural sheathing boards such as gypsum panel and fiber cement cladding would improve the lateral performance of the CFS walls-with or without the strap brace-by 40 percent in average.

As observed in Northridge (1994) and Kobe (1995) earthquakes, brittle failure of rigid connection caused premature collapse of steel moment frames and new rigid connections have been introduced in design guidelines of steel frames. Although the usage of new connections can lead to the appropriate function of steel moment frames, plastic hinges forms in beams which leaves the inelastic and permanent residual deformations after strong ground motions. Since this irremediable deformation increases repair cost, constructing rigid connections from reversible material such as Shape Memory Alloy (SMA) significantly reduce the residual strain and could be a solution to the problem. This paper focuses on the function of end plate connection using Iron-based SMA (possessing 5% of super elastic strain) by numerical study using ANSYS software. Following verification of cyclic behavior of an end plate connection tested by Sumner (designed on the basis of Thick Plate Theory), SMA is used as either connecting bolts for end plate-to-column connection or as plates located at plastic hinges. The result shows that using SMA plates is more efficient than SMA bolt in end plate connection which designed based on thick plate theory. Regarding appropriate weld ability and lower cost of iron-based SMA, hybrid connection equipped with mentioned plates is able to absorb lesser energy compared to steel connection. Moreover, it decrease repair cost whereas lower residual strain is seen.

There are various factors in the analysis and design of the steel frames that uncertainties in any one of them can have a significant effect on the structural safety. The rotational stiffness of the bases and beam-to-column connections and also, the transitional stiffness of the bracing system can be considered as examples of these variables. In this paper, firstly, based on the exact solution of the governing differential equation for an Euler-Bernoulli beam, the stability matrix of portal and gabled steel frames with flexible connections and supports and non-prismatic members are derived. It should be added, the flexibility of connections and supports are molded by the linear rotational or transitional springs. The accuracy of the proposed approach in the deterministic stability analysis with numerical examples verified. Then, by using of the Monte-Carlo simulation method, the probability of failure of mentioned frames for the stability is estimated. The rotational stiffness of the beam-to-column connections and bases and also, the transitional stiffness of lateral support are considered as the random variables in the stochastic stability analysis. Accordingly, by using of the presented formulation the buckling loads of the simulated frames for the hundred thousand times obtained and the effects of various coefficients of variations and different probabilistic distribution functions for random variables in the buckling resistance of the foregoing frames estimated. Moreover, the sensitivity of the probability of failure for the stability of frames with respect to uncertainty of the stiffness of the connections and supports investigated.

Recently self-centric moment resisting connections have been introduced as alternative welded moment resisting connections. These connections are comparing of post tensioned strands and energy dissipater parts. In construction of connection the high strength strands have been post tensioned and because of the post tensioned forces during earthquake period, the structure returns to the pre earthquake condition with less damage in comparison with usual moment resisting structures. One of the energy dissipater devices of these systems is bottom flange friction device (BFFD). In this paper, firstly the behavior of connection in 6 story 4 bay building have been verified with literature which OPENSEES software is used for this purpose. Then nonlinear dynamic and static analyses have been performed. In this study the number of post-tensioned strands, optimum force of strands, arrangement of strands in stories and shape memory alloy materials effect on strand’s behavior have been evaluated. The results shows increment of strands to 40 improves the behavior of connection and the increasing of post-tensioned forces up to determined value causes the improvement of connection behavior.

Unexpected brittle failures in steel rigid frame connections by concentrated tensions on the welded area and connection vulnerability in high ductility demands as occurred during the Northridge (1994) and Kobe (1995), have challenged ductility properties and ability to absorb seismic energy in this type of structural system. So in designing this type of structural system, creating ductility and ability to withstand cyclic large deformations is important. On this basis, in the present study a new beam-to-column moment connection with reduced beam section using Tubular Accordion Web called TAW-RBS is analytically studied. The results show that TAW-RBS creates a ductile fuse away from beam-to-column connection components, through removing web from beam flexural capacity. Reduction of beam flexural strength in the plastic hinge is calculated based on the dimensions of beam and tube. So bending strength of the remaining tubular web would be proportional to squared amount of the thickness of tube and inversely related to the thickness of flat web and the diameter of tube. The optimal location of the tubular web is determined due to the length of beam and the plastic modulus ratio at the plastic hinge to the total cross section. Also shear control at tubular web according to local and global shear buckling are other points discussed in this study. The results show that TAW-RBS reduces flexural stiffness about 14 to 19% in the plastic hinge locations that is equal with the RBS20%. Also the proposed connection, depending on the size of the beam, reduces bending strength between 22 to 28% in the plastic hinge location that is intermediate between RBS20% and RBS50%.