Structural robustness of concrete flat slab structures

Abstract

Current building regulations for design against progressive collapse normally use prescriptive rules and riskbased qualitative scales which are insufficient to cover current needs in design. Structural robustness of concrete flat slab structures is examined using different theoretical models to capture the dynamic behavior under accidental events. In such extreme events, the large dynamic reactions at the connections could potentially lead to punching and progressive collapse. Punching formulae based on load-deformation response relationships such as the Critical Shear Crack Theory (CSCT) are particularly useful in dynamic situations. The Ductility-Centred Robustness Assessment developed at Imperial College London is also used in this paper to derive simple design formulae to assess punching of adjacent columns in the sudden column removal scenario which is commonly adopted in practice. The approach can be extended to assess flat slab systems upon considering membrane action in the slab and post-punching behavior in the connections. Analytical models for tensile membrane are used in combination with the CSCT to demonstrate that the tying forces required in codes of practice cannot be achieved without prior punching of the connections. It is also shown that numerical modelling of post-punching is a promising tool to review detailing provisions for integrity reinforcement.

Dynamic performance of a real-scale reinforced concrete building test under a corner-column failure scenario

“…The values of the dynamic amplification of the load obtained in this work (DAFLF = 1.24) are also consistent with test results of sudden corner column removal by Qian and Li [40] in which they report dynamic load increase factors between 1.13 and 1.23. These results are also comparable with dynamic amplification factors for internal column removal obtained experimentally [47], numerically [9] or theoretically [12] which can vary between 1.6 and 1.2.…”

“…threat-dependent approaches) [9,10]; and b) those that only attempted to minimise the consequences of a local failure, whatever its cause (i.e. threat-independent approaches) and avoid the failure spreading to other elements in the building [5,11,12]. Within this latter group, diverse numerical and experimental studies have analysed the structural response of buildings subjected to column removal as recommended in most current codes [13][14][15].…”

Research and practice on progressive collapse and robustness of building structures in the 21st century

“…Tying is generally provided through horizontal and vertical ties achieved by prescribing a minimum tying force requirement, which are generally consistent within the different codes shown in Table 5, except for IBC 2009 [46] that provides lower tying forces [55]. Research on the efficiency of tying to different types of construction including steel and concrete structures showed that the rotations required in the connections to form a pure tensile membrane that arrests progressive collapse are unachievable in some cases [63,[73][74][75][76]. In order to address this issue, some codes such as UFC 4-023-03 [45] have included rotation limits on their tying force requirements for different forms of construction.…”

Effects of sudden failure of shoring elements in concrete building structures under construction

“…The probability of occurrence of each cause was quantified in direct proportion to the number of times the cause was cited or appeared in the different accident reports studied in the previous work [10]. The local failure scenarios considered followed the conventional notional member removal approach used traditionally for permanent structures to assess whether the structure can develop alternative load paths after local damage [16,20,26,27,39,40]. The aim of this study was to determine the effects of sudden failure of one or more ground-floor shores, which carry the highest loads when the third floor is poured, with two cleared floors and one fully shored.…”