جستجوی مقالات مرتبط با کلیدواژه "bolted connections" در نشریات گروه "عمران"

During the construction of steel structures, the executive groups often fabricate some stories and tighten the connection bolts, defined as the snug-tightened bolt in this research. The lower stories, in which the connection bolts are snug-tightened, will be pre-tensioned at least to the level of preloading based on design codes, called pre-tensioned bolts, in this paper. The connections will be complete, while some upper stories will have snug-tightened bolts. As a result, the stiffness of the bolted connections varies throughout construction, and the structural characteristics change with time. So it is necessary to investigate the seismic behavior of bolted extended end-plate moment connections in both snug-tightened and pre-tensioned bolts while constructing high-rise structures. Bolted unstiffened end plate moment connections are one of the most usable connections used as prequalified connections in special steel moment frames. According to the AISC design code, this connection can be considered one of the most important parts of moment-resisting frames with enough bolt pre-tension levels. In this paper, using three full-scale bolted unstiffened end plate moment connections designed according to AISC, the effects of bolt pre-tension levels have been examined experimentally under SAC cyclic loading protocol. Bolt pre-tension level has been defined as α coefficient to show the pre-tensioning level in three specimens. The bolts of the first specimen are not pre-tensioned, called snug-tightened bolts, and is reference connection. The bolt pre-tension levels of the second and third specimens were created in accordance with AISC and Iranian National design code and more to Fu of bolts, called pre-tensioned and fully pre-tensioned, respectively. The bolts' moment capacity, total energy absorption, initial rotational stiffness, ductility of connection, and stress and strain variation are investigated. According to the results, an increase in bolt pre-tension level would significantly improve the cyclic behavior of connections. Further, an increase in bolt pre-tension led to the initiation of the inelastic deformation from a minor rotation, and the ductility of the connection improved. The results show that the increase in moment capacity and energy dissipation in the pre-tensioned compared to snug-tightened is 27 and 23%, respectively. However, In comparison with the pre-tensioned, the fully pre-tensioned specimen has increased by 11 and 9%, respectively. As a result, the connection with bolt pre-tension level, under design regulations in comparison with the reference connection, can be considered a connection of a special moment resisting frames. So bolt pre-tension level higher than the value mentioned in the design code is better but not needed.

Prying action in bolted beam-to-column connections may cause brittle failure due to increasing the bolt force to a value greater than its design strength. In the most common design methods, the prying force is generally determined using analytical models. Existing analytical models are based on the research for the bolted connections with rolled T-stubs. In the end plate connections, the T-stub is fabricated by the complete joint penetration welding of steel plates. In this research, an analytical model is proposed for determining the prying force in built-up T-stubs. For this purpose, three specimens were tested under monotonic loading to determine the load-displacement relationship and the load-carrying capacity of T-stubs. An advanced non-linear finite element model was established to evaluate the load-carrying capacity of the bolted T-stubs, and it was validated using the experimental data. A parametric study was performed to evaluate the effects of geometric and mechanical properties of the connections on the magnitude and location of the prying force resultant, the eccentricity of the bolt force, and the location of plastic hinges. Consequently, a formula was proposed to determine the location of the prying force resultant. It was shown that a plastic hinge is formed at a distance of about 10 mm from the T-stub web. Also, it was shown that the eccentricity of the bolt force reduces the nominal capacity of the bolt by about 35%. With these data, a simplified analytical model was developed to predict the T-stub load-carrying capacity assuming the location determined for the bolt force, prying force, and plastic hinge. The magnitude of prying force and T-stub load-carrying capacity were determined using the proposed model. The results showed that by using the proposed model, an average of 10.6% improvement in the accuracy of the bolted T-stub load-carrying capacity determination is achieved.

With their wide range of applications in the design and construction of steel structures, rigid connections are among the most prevalent types of connections. In many cases, hollow circular columns are used as a component in moment resisting frames. Circular columns have a wide range of applications, primarily due to their high flexural strength around the principal perpendicular axes, their ductility, energy dissipation, and low susceptibility to local buckling. These hollow sections are available and used in two forms: rolled sections and sections manually manufactured using plates. The most important weak point of these sections is when they are used in moment resisting frames and structures located in areas with a high level of seismicity. In these cases, design standards necessitate the use of continuity plates along the beam’s flanges. However, due to the inaccessibility of the inner spaces of these types of columns, using continuity plates is either impossible or very difficult. This study introduces an external diaphragm connection between the I -shaped beam and hollow circular column which uses continuity plates outside the section (column). Through an experimental investigation, the behavior and strength of welded and bolted connections are evaluated under cyclic loading. The results show that the proposed detail possesses suitable strength and ductility, and provides the connection with a suitable level of rigidity. The connection satisfies the specifications of existing seismic codes.

Precise investigation of the connections in a steel structure is important, and inaccuracy in the design and implementation of connections not only does cause failure in the connection, but also has a devastating effect on other members of the structure. Bolted end plate connections are commonly used in steel structures. There are two types of beam-to-column flange connections, four-bolt and eight-bolt. The four- bolt connection is used for low anchor values and the eight-bolt connection is used for large bending anchor values. In this study, the cyclic behavior of the restrained beam-to-column connections with end plate under cyclic loading has been evaluated. In the calculations, all of the parameters affecting the behavior of this connection have been investigated and solutions are proposed to reach the maximum connection capacity. Since the behavior of this connection depends on several factors, two general models of beam connection to different columns with beams of 30 and 40 cm depth are considered for research purposes. The thickness of end plate, shape of end plate, thickness of the column flange, strength or material of the bolts, the necessity of using continuity plate, stiffener and doubler plate are among the parameters considered in the analyzes. According to the results of this study, the use of a thin-walled end plate leads to local buckling of plate. The use of continuity plate is very important and prevents local buckling in the panel zone. Also, in cases where the thickness of the column web is low, the use of a doubler plate will also be necessary. In addition, the use of a stiffener improves the flexural strength of the section.

One of the types of ruptures in the tensile members of steel structures is the block shear failure in which by creating
tensile and shear stresses in the connection area, a part of section is torn away and it causes the strength loss of the
section. The main aim of this paper is to experimentally study and finite element analysis of block shear failure having
staggered pattern in connections of hot rolled steel tensile members. For this purpose, eight laboratory samples from
the gusset plate with staggered pattern and connections have eccentricity with constructional mild steel were applied
by a tensile axial loading. The main variables for the test specimens include the number of connection bolts, the bolt
spacing along parallel and perpendicular to the loading length. The results of laboratory studies were compared with
those obtained from the prediction of existing relationships (based on the rule (s2/4g )) as well as the plane
decomposition method of Samimi et al. (2016) and the strengths and weaknesses of each were identified. Furthermore,
the results of numerical analyses made by finite element method, which also have a good consistency with the test
results, confirm the basis of the plane decomposition method. Considering the results of the real tensile stress
distribution at the staggered planes of the block shear failure area of the connections have eccentricity, the effects of
loading eccentricity have been appeared which justifies the need for considering the factor of non-uniform tensile
stress distribution.