Seismic Vulnerability in Case of Fire of Existing R.C. Framed Buildings: Modelling and Nonlinear Dynamic Analysis

Mazza, Fabio; Luca, Antonio De

doi:10.7712/120115.3664.491

Cited by 6 publications

(4 citation statements)

References 14 publications

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“…related to the value qf,d corresponding to the surface area of the floor (Af). Further details on fire modelling can be found in [19]. Finally, the standard ISO-834 curve is defined as [18]  …”

Section: Fire Loading Before An Earthquake and Numerical Resultsmentioning

confidence: 99%

Incremental Dynamic Analysis of Fire-Exposed Base-Isolated R.C. Framed Buildings Subjected to Near-Fault Ground Motions

Mazza¹,

Alesina²

2015

Proceedings of the 5th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COM

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It is well known that near-fault ground motions are characterized by long-duration horizontal pulses, which can become critical for base-isolated reinforced concrete (r.c.) structures when the pulse intensity is so strong that the superstructure undergoes plastic deformations. There is, however, a lack of knowledge on the seismic response in case of fire; moreover, an amplification of the structural damage is expected in case of fire-exposed baseisolated structures which are not designed to withstand fire. To investigate the nonlinear seismic response following a fire, an incremental dynamic analysis is carried out with reference to five-storey base-isolated r.c. buildings with fire-protected High-Damping-Laminated-Rubber Bearings (HDLRBs), designed according to the Italian seismic code. Horizontal components of seven near-fault ground motions have been selected according to the design subsoil class C adopted for the test structures. More specifically, the nonlinear seismic response of base-isolated structures in a no fire situation is compared with that in which fire occurs, at 45 (i.e. R45) and 60 (i.e. R60) minutes of fire resistance, assuming both damaged (i.e. DS) and repaired (i.e. RS) stiffness conditions. Five fire scenarios are considered assuming the fire compartment confined to the area of the first level (i.e. F1), the first two (i.e. F1/2) and the upper (i.e. Fi, i=3-5) levels, with the parametric temperature-time fire curve evaluated according to Eurocode 1. The nonlinear seismic analysis is performed by using a step-by-step procedure based on a two-parameter implicit integration scheme and an initial-stress-like iterative procedure. At each step of the analysis, plastic conditions are checked at the critical (end) sections of the girders and columns, where thermal mapping with reduced mechanical properties is evaluated with the 500°C isotherm method proposed by Eurocode 2. A viscoelastic model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, simulates the response of an HDLRB.

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Section: Fire Loading Before An Earthquake and Numerical Resultsmentioning

confidence: 99%

Incremental Dynamic Analysis of Fire-Exposed Base-Isolated R.C. Framed Buildings Subjected to Near-Fault Ground Motions

Mazza¹,

Alesina²

2015

Proceedings of the 5th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COM

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“…related to the value qf,d corresponding to the surface area of the floor (Af). Further details on fire modelling can be found in [17,18]. Finally, the standard ISO-834 curve is defined as [16]  …”

Section: Steel Test Structure: Design and Fire Modellingmentioning

confidence: 99%

Comparative Study of the Wind and Earthquake Dynamic Responses of Fire Exposed Steel Framed Buildings

Mazza¹,

Fiore²

2015

Proceedings of the 5th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COM

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Wind design of steel-framed buildings aims to provide appropriate stiffness and strength properties of the structural elements, so as to obtain an elastic behaviour, at the same time as controlling floor displacements and accelerations. On the other hand, in a seismic design it is commonly accepted that the structural members can undergo inelastic deformations under strong ground motions, provided that these deformations be kept within an acceptable threshold; moreover, deformability thresholds are also imposed at the serviceability limit state. Nevertheless, knowledge on the wind and seismic responses in the case of fire is lacking and an amplification of the structural response is expected in the case of existing structures exposed to fire. To evaluate the wind and seismic responses following a fire, a numerical investigation is carried out with reference to the steel framed structure of a ten-storey office building, which was designed for a low-risk zone under the former Italian seismic code and in line with Eurocodes 1 and 3. More specifically, the dynamic response of the test structure in a no fire situation, along the in-plan principal directions, is compared with what would happen in the event of fire, at 500°C, 550°C and 600°C fire temperatures, hypothesizing a reduction of stiffness and strength due to fire. Four fire scenarios have been considered on the assumption that the fire compartment is confined to the area of the first level (i.e. F1), the first two (i.e. F1/2) and the upper (i.e. Fi, i=5, 10) levels, with the parametric temperature-time fire curve evaluated in accordance with Eurocode 1. Dynamic analyses are carried out in the time domain using a step-by-step initial stress-like iterative procedure. Along-wind loads are considered assuming, at each level, time histories of the wind velocity for two return periods (i.e. Tr=10 or 50 years), based on an equivalent spectrum technique. Real accelerograms, whose response spectra match those adopted by Italian seismic code for a mediumrisk seismic zone and a medium subsoil class, are considered to simulate the seismic loads.

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“…Further studies have been carried out on the residual seismic load capacity of fixed-base structures in case of earthquake following fire (e.g. Mostafaei et al 2009;Mostafaei 2013a, b;Mazza and De Luca 2015). A significant decrease in stiffness affects the structural members exposed to fire, in comparison with the no-fire condition.…”

Section: Introductionmentioning

confidence: 98%

“…Further details on fire modelling can be found in other works by the author(Mazza and De Luca 2015;Mazza and Fiore 2015). Finally, the standard ISO-834 curve is defined as(ISO834 1999) …”

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confidence: 99%

Effects of near-fault vertical earthquakes on the nonlinear incremental response of r.c. base-isolated structures exposed to fire

Mazza

2015

Bull Earthquake Eng

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High values of the ratio between the peak of the vertical and horizontal ground accelerations of near-fault ground motions can become critical once the strength level of a fire-weakened base-isolated structure is reduced especially as the ductility demand can increase much more rapidly for an ever-lower strength level. In the present work, the incremental dynamic analysis (IDA) of base-isolated structures exposed to fire is carried out considering the horizontal and vertical components of seven near-fault ground motions with different values of the peak acceleration ratio. To this end, six five-storey reinforced concrete office buildings, base-isolated with high-damping-laminated-rubber bearings (HDLRBs), are designed assuming different values of the ratio between the vertical and horizontal stiffnesses of the HDLRBs. The design of the test structures is carried out in a high-risk region considering (besides the gravity loads) the horizontal seismic loads acting in combination with the vertical ones. Five fire scenarios are considered at 45 (i.e. R45) and 60 (i.e. R60) min of resistance, with the parametric temperature-time fire curve evaluated in accordance with Eurocode 1: i.e. fire compartment at the fifth level (F5), the upper two (F4/5) and the other (Fi, i = 1-3) levels. The nonlinear IDA analysis is carried out in a step-by-step procedure, which is based on a two-parameter implicit integration scheme and an initial-stress-like iterative procedure. At each step of the analysis, plastic conditions are checked at the potential critical sections of the beams (i.e. end sections of the sub-elements in which a beam is discretized) and columns (i.e. end sections), where a bilinear moment-curvature law is adopted; the effect of the axial load on the ultimate bending moment (M-N interaction) of the columns is also taken into account. Finally, reduced strength and ultimate ductility of the cross-sections are evaluated in line with the 500°C isotherm method proposed by Eurocode 2.

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Seismic Vulnerability in Case of Fire of Existing R.C. Framed Buildings: Modelling and Nonlinear Dynamic Analysis

Abstract: Abstract. The seismic vulnerability of reinforced concrete (r.c.)

Cited by 6 publications

References 14 publications

Incremental Dynamic Analysis of Fire-Exposed Base-Isolated R.C. Framed Buildings Subjected to Near-Fault Ground Motions

Incremental Dynamic Analysis of Fire-Exposed Base-Isolated R.C. Framed Buildings Subjected to Near-Fault Ground Motions

Comparative Study of the Wind and Earthquake Dynamic Responses of Fire Exposed Steel Framed Buildings

Effects of near-fault vertical earthquakes on the nonlinear incremental response of r.c. base-isolated structures exposed to fire

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