The Effect of Plan Geometry on Progressive Collapse of Tall Buildings with Diagrid Structure Based on Nonlinear Static and Dynamic Analyses

Maryam Shokoohimatin,Mahmood Hosseini,Maryam Firoozi Nezamabadi 한국강구조학회 2024 International Journal of Steel Structures Vol.24 No.2

So far, several studies have been conducted on progressive collapse of tall buildings, of which a few have been on the buildings with diagrid structures, however, in none of them the eff ect of the building’s plan geometry has been a concern. In this study the progressive collapse of a set of 50-story steel buildings with diagrid structures in three diff erent plan geometries of square, rectangular, and octagonal was investigated by nonlinear static and dynamic analyses. First, the considered buildings were designed according to ASCE 7 and AISC design provisions, trying to be close as much as possible to the optimal design, based on the demand to capacity ratios. Then, fi ve damage scenarios were considered including removal of columns and/or diagonal elements of the diagrid structure in the lowest, the 25th, and the top story of the building according to UFC provisions. Nonlinear static and dynamic analyses were conducted by Perform-3D software. Results show that robustness index, calculated by using the stiff ness method would be smaller for the cases of member removal in upper stories, and that the lowest robustness index corresponds to removal of two corner columns, and bracing element connected to them, in the fi rst and second stories. Results also show that removal of interior column in the fi rst story leads to progressive collapse in all three plan shapes. However, yielding and ultimate load factors in building with octagonal plan are more than other two buildings, implying that this type of buildings have more resistance against progressive collapse.

A fracture mechanics simulation of the pre-holed concrete Brazilian discs

Sarfarazi, Vahab,Haeri, Hadi,Shemirani, Alireza Bagher,Nezamabadi, Maryam Firoozi Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.3

Brazilian disc test is one of the most widely used experiments in the literature of geo-mechanics. In this work, the pre-holed concrete Brazilian disc specimens are numerically modelled by a two-dimensional discrete element approach. The cracks initiations, propagations and coalescences in the numerically simulated Brazilian discs (each containing a single cylindrical hole and or multiple holes) are studied. The pre-holed Brazilian discs are numerically tested under Brazilian test conditions. The single-holed Brazilian discs with different ratios of the diameter of the holes to that of the disc radius are modelled first. The breakage load in the ring type disc specimens containing an internal hole with varying diameters is measured and the crack propagation mechanism around the wall of the ring is investigated. The crack propagation and coalescence mechanisms are also studied for the case of multi-holes' concrete Brazilian discs. The numerical and experimental results show that the breaking mechanism of the pre-holed disc specimens is mainly due to the initiation of the radially induced tensile cracks which are growth from the surface of the central hole. Radially cracks propagated toward the direction of diametrical loading. It has been observed that for the case of disc specimens with multiple holes under diametrical compressive loading, the breaking process of the modelled specimens may occur due to the simultaneous cracks propagation and cracks coalescence phenomena. These results also show that as the hole diameter and the number of the holes increases both the failure stress and the crack initiation stress decreases. The experimental results already exist in the literature are quit agree with the proposed numerical simulation results which validates this simulation procedure.

A fracture mechanics simulation of the pre-holed concrete Brazilian discs

Vahab Sarfarazi,Hadi Haeri,Alireza Bagher Shemirani,Maryam Firoozi Nezamabadi 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.3

Brazilian disc test is one of the most widely used experiments in the literature of geo-mechanics. In this work, the pre-holed concrete Brazilian disc specimens are numerically modelled by a two-dimensional discrete element approach. The cracks initiations, propagations and coalescences in the numerically simulated Brazilian discs (each containing a single cylindrical hole and or multiple holes) are studied. The pre-holed Brazilian discs are numerically tested under Brazilian test conditions. The single-holed Brazilian discs with different ratios of the diameter of the holes to that of the disc radius are modelled first. The breakage load in the ring type disc specimens containing an internal hole with varying diameters is measured and the crack propagation mechanism around the wall of the ring is investigated. The crack propagation and coalescence mechanisms are also studied for the case of multi-holes' concrete Brazilian discs. The numerical and experimental results show that the breaking mechanism of the pre-holed disc specimens is mainly due to the initiation of the radially induced tensile cracks which are growth from the surface of the central hole. Radially cracks propagated toward the direction of diametrical loading. It has been observed that for the case of disc specimens with multiple holes under diametrical compressive loading, the breaking process of the modelled specimens may occur due to the simultaneous cracks propagation and cracks coalescence phenomena. These results also show that as the hole diameter and the number of the holes increases both the failure stress and the crack initiation stress decreases. The experimental results already exist in the literature are quit agree with the proposed numerical simulation results which validates this simulation procedure.

Simulation of crack initiation and propagation in three point bending test using PFC2D

Hadi Haeri,Vahab Sarfarazi,Zheming Zhu,Ahmadreza Hedayat,Maryam Firoozi Nezamabadi,Mohammadamin Karbala 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.4

Three points bending flexural test was modelled numerically to study the crack propagation in the pre-cracked beams. The pre-existing double internal cracks inside the beam models were considered to investigate the crack propagation and coalescence paths within the modelled samples. Notch configuration effects on the failure stress were considered too. This numerical analysis shown that the propagation of wing cracks emanating from the tips of the pre-existing internal cracks caused the final breaking of beams specimens. It was also shown that when two notches were overlapped, they both mobilized in the failure process and the failure stress was decreased when the notches were located in centre line. However, the failure stress was increased by increasing the bridge area angle. Finally, it was shown that in all cases, there were good agreements between the discrete element method results and, the other numerical and experimental results. In this research, it is tried to improve the understanding of the crack propagation and crack coalescence phenomena in brittle materials which is of paramount importance in the stability analyses of rock and concrete structures, such as the underground openings, rock slopes and tunnel construction.

Simulation of crack initiation and propagation in three point bending test using PFC2D

Haeri, Hadi,Sarfarazi, Vahab,Zhu, Zheming,Hedayat, Ahmadreza,Nezamabadi, Maryam Firoozi,Karbala, Mohammadamin Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.4

Three points bending flexural test was modelled numerically to study the crack propagation in the pre-cracked beams. The pre-existing double internal cracks inside the beam models were considered to investigate the crack propagation and coalescence paths within the modelled samples. Notch configuration effects on the failure stress were considered too. This numerical analysis shown that the propagation of wing cracks emanating from the tips of the pre-existing internal cracks caused the final breaking of beams specimens. It was also shown that when two notches were overlapped, they both mobilized in the failure process and the failure stress was decreased when the notches were located in centre line. However, the failure stress was increased by increasing the bridge area angle. Finally, it was shown that in all cases, there were good agreements between the discrete element method results and, the other numerical and experimental results. In this research, it is tried to improve the understanding of the crack propagation and crack coalescence phenomena in brittle materials which is of paramount importance in the stability analyses of rock and concrete structures, such as the underground openings, rock slopes and tunnel construction.