Keywords: progressive collapse, reinforced concrete framed structure, acceptance criteria, GSA 2003 Guidelines, linear static analysis, missing column scenarios, design shear force.

This study investigates the vulnerability to progressive collapse of an old and representative twelve-storey reinforced concrete framed building designed forty years ago for Braila, a zone with high seismic risk in Romania. A linear static analysis was conducted for the three-dimensional model created using the finite element computer program SAP 2000. The structure was analysed for four distinct cases of "missing column" scenarios provided by the GSA 2003 Guidelines [1].

The results show that the building, seismically designed and detailed according to much more permissive requirements of the older codes, is not expected to fail in bending and consequently the progressive collapse is not expected to occur for any of the analysed cases. All demand-capacity ratio (DCR) values for flexure determined for the beams are below the allowable value (2.0). At the same time, the distribution and magnitude of the DCR values indicate that the building is more vulnerable to progressive collapse when the interior column is removed from the structure, a case rarely investigated by structural designers.

The new provisions of the current code for concrete structures [2] have a significant impact on the results obtained. By applying the relationships from the old code [3], a maximum DCR value of 0.76 was obtained in the case C4 of "missing column" scenarios, which is well bellow the allowable value (1.0) and thus the acceptance criteria is fulfilled. On the contrary, by applying the provisions of the current code [2], all beams have sections with DCR values for shear above 1.0, even higher than 3.0 in some cases and thus, they are considered failed members.

Based on an experimental test results, the authors have proved that the design shear force evaluated using the old code [3] is much closer to the real behaviour of the beam elements than the design shear force predicted by the current code [2] which is extremely underestimated.

Therefore, the old and representative twelve-storey RC framed building is not expected to fail in bending or shear, a conclusion sustained by the real behaviour of the building which experienced four major earthquakes with no significant structural damage.

1

U.S. General Services Administration, "Progressive collapse analysis and design guidelines for new federal office buildings and major modernization projects", Washington, DC, 2003.

2

SR EN 1992-1-1:2004, "Eurocode 2: Design of concrete structures - Part 1-1: General rules and rules for buildings", ASRO, Bucharest, 2004. (in Romanian)

3

STAS 8000-67, "Designing element of concrete, reinforced concrete and prestressed concrete", Romanian Standard Institute, Bucharest, 1969. (in Romanian)

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