ارزیابی خرابی پیش‌رونده در سازه‌های بتن مسلح با سیستم دال حبابی

Usually, progressive collapse is defined as the progress of a primary local damage within the structures that, like a chain chemical reaction, causes to partial or total collapse of the structures. Although, many researches on progressive collapse under blast load have been made, it can be seen that rupture aroused in structures during strong earthquake events will not happen suddenly, but because of failure in structural design or performance, the weak elements will destroy easier. Subsequently, energy redistribution will occur that may disconnect the adjacent members. Further, the progressive collapse phenomenon will take place and subsequently cause to collapse all the structures. In the recent years, the incidence of catastrophic events such as September 11 has attracted a lot of attention to the issue of the progressive collapse and lead to be considered in the design of new structures. In order to prevent damages by reducing the progressive collapse, different strategies for designing against the progressive collapse have been presented in the government documents of USA, such as UFC and GSA. Although, many researches have been made on the progressive collapse in recent years, but the structures deck effect on the progressive collapse has not been considered sufficiently.

Nowadays, due to the increase of the speed of construction and lightweight construction, the usage of new systems has been increased. Among these systems, Bubble Deck system is notable. This structural system functions as a two-way slab and a lightweight structural member. In Bubble Deck system, the plastic spherical hollow core (PSHC) is used instead of the concrete situated in the central zone of the cross sections around the slab’s mid-span, where the shear stress is relatively small, compared to the supports. PSHC creates a hollow space in the slab. The Bubble Deck technology uses spheres, made of recycled industrial plastic, to create air voids, while providing the strength through the arch action.

The objective of this study is to evaluate the progressive collapse of reinforced concrete structures with Bubble Deck floor system. The behavior of structures, the amount, and the mode of the collapse distribution can be studied by various methods. SAP2000 software is used to model, design and analyze the structures. DoD2013 statement has been selected as the reference criteria, and based on that, all the uploading and collapse measurements has been determined. The equivalent nonlinear shell layered element is used to define the slab sections in numerical modeling. 48 structures with the same plans (3 spans on each direction) were modeled. Moment resisting system is chosen as lateral resisting systems. The models were in 4, 6 and 8 stories. Story height of all structures is 3.5 m, and also three types of span length to story height ratios including 1.5, 2.5 and 3.5 are investigated.

The results show by increasing the number of floors, the structure’s performance against progressive collapse will decrease and the middle-rise structures (6 stories) have shown the best performance rather than others. Also, by increasing the ratio of span length to floor height, progressive collapse resistance is reduced. The most observed damage in the Bubble Deck floors is less than 25 percent of floor area which affected by progressive collapse in the middle-column removal scenario. This value of damage satisfy DoD2013 targets.