Performance of Fully Restrained Welded Beam-Column Connections Subjected to Column Loss

Alireza Salmasi,Mohammad Reza Sheidaii,Saeed Tariverdilo 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.4

The beam-column connections are known as a fundamental component in steel moment-resisting frames. The present investigation studies the progressive collapse behavior of four various welded types of beam-column connections including, welded unreinforced flange-welded web moment (WUF-W), reduced beam section (RBS), welded flange plate (WFP), and welded flange-weld web connection with internal diaphragms (I-W). The nonlinear analysis with suitable finite element modeling has been generated to assess the connection's performance under a column removal scenario. The load–displacement curves, fracture modes, Von-Mises stresses, and other comparable theoretical results were described. The results are verified with existing experimental data. The results of the analyses showed that the studied models' overall failure occurs in the beam-column connection regions in the large rotation under the catenary action mode. The plastic strain accumulation occurred around the access hole, and the failure was initiated from these areas. Each of the investigated connections showed sufficient strength under column removal scenario. WFP connections demonstrated the best performance due to the top and bottom plates' presence and the keep away of critical stresses from the connection area. The RBS connections exhibited the weakest behavior due to absorbing excessive stresses and fast fracture and tolerating minimum vertical loads. Also, it is observed that in the designing of buildings exposed to the phenomenon of progressive collapse, the considerable axial load generated in the connections area should be considered in the design phase.

Experimental and Numerical Study of a Tube in Tube Force Limiting Device

Jafar Ghalejoughi,Mohammad Reza Sheidaii,Saeed Tariverdilo 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4

The buckling and sudden capacity loss of the compression member can be prevented using a proposed tube in tube force limiting device (TTFLD). In this way, the brittle post-buckling behavior of the compression member can be converted into an elasto-plastic behavior. The TTFLD consists of two tubes with unequal diameter, one of which is placed into the other tube. The outer tube operates as a casing for the inner compression tube and the fl exural stiff ness of the outer tube restrains the buckling of the inner tube. The present study has experimentally investigated and evaluated a number of experimental specimens. Next, numerical analysis of these specimens has been done using fi nite element software. Further, the behavior of the tube in tube force limiting device have been investigated under important parameters such as the gap between the inner and outer tubes (gap), the inner tube or main member slenderness ratio (λ), and the ratio of outer tube length to inner tube length ( L 2∕L 1) , by extending the numerical studies to further examples. Using this TTFLD is an eff ective, simple and economical method to prevent the buckling of compression member and can lead to a favorable increase in the bearing and deformability capacity of the compression members with diff erent values of slenderness ratio. The compressive strength of the member will increase signifi cantly, if the gap size is less than about 43% of the inner tube’s gyration radius, and the length ratio is greater than about 55%.

Progressive Collapse Performance Evaluation of Shear Tab Connection Subjected to Column Loss

Masoud Ghalejoughi,Mohammad Reza Sheidaii 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.5

A shear tab connection is one of the most common simple beam-to-column connections that is widely used in steel structures. In ASCE41-17 (Seismic evaluation and retrofit of existing buildings, American Society of Civil Engineers, 2017) and DoD (UFC 4-023-03, Design of buildings to resist progressive collapse, Department of Defense, Washington, DC, 2009), the plastic rotation capacity of a shear tab connection is purely a function of the connection depth, which is over- and under-estimated, respectively. To address this shortcoming, the present paper tries to provide a better estimation of plastic rotation capacity under the column removal scenario by employing a validated finite element model and conducting a comprehensive parametric study under various effective parameters such as connection depth, adjacent span length, and connection plate thickness. In addition to improving the plastic rotation capacity relationship, since the connection depth and adjacent span length have a significant effect on the plastic rotation capacity of the connection, a new equation has been proposed in terms of these parameters. Also, the axial-shear force–bending moment interaction of the connection is investigated.

Improving Progressive Collapse Performance of Steel Moment-Resisting Frames Through X-Bracing Slack Cables

Maryam Musavi-Z,Mohammad Reza Sheidaii 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.5

The intended purpose of this study is the steel moment-resisting frames strengthening through cable elements to improve the progressive collapse and seismic performance of the structure simultaneously. To achieve this goal, X-bracing slack cables were applied to all surrounding bays of the top story of the model with variable parameters, including diff erent cable sizes and distinct amounts of slackness, to reach the most appropriate cable characteristics for one column removal or even two columns loss scenario. Increasing the number of paths to redistribute the loads developed due to initial local damage leads to improvement of the progressive collapse response in the existing or new structures. The progressive collapse and seismic performance of the non-strengthened and strengthened model structures were assessed using the nonlinear dynamic alternate path method recommended in the Unifi ed Facilities Criteria guidelines and the pushover analysis of ASCE 41, respectively. Finally, two diagrams were extracted to fi nd a relation between the size and slackness of the cables with the performance level of the structure. Obtained diagrams show that the proposed strengthening scheme can improve the progressive collapse resistance of the steel moment-resisting frames to the desired performance level corresponding to the selected slackness and minimum breaking load of cable. Pushover analysis results showed that the introduced strengthening scheme led to a more appropriate or at least unchanged seismic response. It should be considered in the design phase of columns and cables that adding cables leads to compression enhancement of columns after activation of cable elements.

Reliability analysis of double-layer domes with stochastic geometric imperfections

Gordini, Mehrdad,Habibi, Mohammad Reza,Sheidaii, Mohammad Reza,Tahamouliroudsari, Mehrzad Techno-Press 2017 Advances in computational design Vol.2 No.2

This study aimed to investigate the effect of initial member length an imperfection in the load carrying capacity of double-layer domes space structures. First, for the member length imperfection of each member, a random number is generated from a normal distribution. Thereupon, the amount of the imperfection randomly varies from one member to another. Afterwards, based on the Push Down analysis, the collapse behavior and the ultimate capacity of the considered structure is determined using nonlinear analysis performed by the OpenSees software and this procedure is repeated numerous times by Monte Carlo simulation method. Finally, the reliability of structures is determined. The results show that the collapse behavior of double-layer domes space structures is highly sensitive to the random distribution of initial imperfections.

Comparative Analysis of Code-Based Dynamic Column Removal and Impact-Induced Progressive Collapse in Steel Moment-Resisting Frames

Iman S. Janfada,Mohammad Reza Sheidaii,Foad Kiakojouri 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.6

Civil structures are subjected to accidental or intentional impacts, which can lead to an initial failure, and subsequently to a tragic progressive collapse. While progressive collapse studies have seen significant growth, most of the current research focuses on threat-independent approaches, neglecting the explicit consideration of impact effects on the building’s behavior. In this study, we investigate impact-induced progressive collapse, exploring various scenarios with different mass and velocity parameters. By doing so, this study aims to highlight the importance of explicitly accounting for impacts in progressive collapse analyses and provide possible solutions for safer structural design. For comparison, code-based dynamic column removal analyses are also performed and the results are compared and contrasted. Based on the obtained results, location of the damage and height of the building have important influence on the progressive collapse response in both threat-independent and threat-dependent approaches. Velocity plays a significant and critical role compared to mass in increasing the kinetic energy applied to the building, and the vertical vibration in the node on top of the impacted column. With the lower impactor velocities, the threat-independent method can be used safely, however, for the higher velocities the progressive collapse potential is much higher in threat-dependent approach compared with code-based dynamic column removal.