Earthquake and progressive collapse resistance based on the evolution of romanian seismic design codes

SUMMARY:

GSA (2003) Guidelines provides a detailed methodology to assess the potential to progressive collapse of

existing buildings, based on a linear static analysis and "missing column" scenarios. In this paper, the

progressive collapse potential of three distinct models representing a 13-storey RC framed structure located in an

area with high seismic risk is assessed. The models are designed according to Romanian seismic codes in use in

1992, 2006 and 2008, and detailed considering the provisions of concrete structures design codes STAS

10107/0-90 (1990) and Eurocode 2 (2004). The comparative results show that a mid-rise structure designed for a

zone with ag = 0.24g does not experience progressive collapse when subjected to abnormal loads. It might also

be concluded that the last 20 years of changes in the Romanian design codes, implicitly lead to improvements in

the resistance to progressive collapse of reinforced concrete framed buildings.

Keywords: progressive collapse, Romanian seismic codes, RC framed structures, GSA (2003) Guidelines, DCR

1. INTRODUCTION

Progressive collapse is defined as the spread of an initial local failure from element to element,

through a chain reaction, which leads to partial or even full collapse of an entire structure. The

abnormal loads, like explosions, vehicle collisions, human errors, represent the main causes that lead

to progressive collapse of buildings.

The seismic design and detailing of a structure provides it with certain levels of continuity, ductility

and redundancy, depending on the provisions for the seismic zone and for the ductility class. The

mentioned characteristics are extremely important and have a significant influence on the progressive

collapse behavior. A higher ductility improves the capacity of a structure to respond to a sudden

removal of a vertical element with an inelastic behavior and without the failure of other structural

elements.

The American Federal Guidelines GSA (2003), DOD (2005) and DOD (2009) propose different

procedures to assess the potential of progressive collapse of a structure. The GSA (2003) Guidelines is

based on the Alternative Path Method and consider the instantaneous loss of structural elements using

different "missing column" or "missing beams" scenarios.

Using the GSA (2003) Guidelines, Baldridge and Humay (2003), Bilow and Kamara (2004), Botez,

Bredean and Ioani (2012) assessed the progressive collapse potential of RC framed structures taking

into account the influence of the following parameters: number of stories and seismicity of the area. In

their works, Ioani and Cucu (2010) presented the effects on the progressive collapse resistance when

seismic design is made according to two former Romanian codes P100-92 and P100-1/2006; only one

damage case (corner column) was investigated. None of the previous investigations focuses on the

effect of the active seismic design code SR EN 1998-1-1:2004/NA: 2008 (Eurocode 8), when all four

damage cases are considered. How safe could be a reinforced concrete building, when the seismic

design provisions have changed three times (1992, 2006, 2008), and the code for concrete structures

has been changed two times (1990, 2004)? A complete answer to this question is offered by this paper.

The objective of this study is to assess the vulnerability to progressive collapse of three distinct models

representing a 13-storey RC framed building, designed and detailed according to Romanian seismic

codes in use, in 1992, 2006 and nowadays, when all four damage cases are considered. The paper, by

comparative studies, estimates the influence of the evolution of Romanian seismic design codes on the

progressive collapse resistance of a typical RC framed structures located in a region of high seismic

risk (Bucharest, Romania).