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

Abstract

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.

Nonlinear Dynamic Behaviour of Base-Isolated Buildings With the Friction Pendulum System Subjected to Near-Fault Earthquakes

“…=rs) are considered for earthquakes with significant vertical component. A computer code is adopted for the nonlinear dynamic analysis of the test structures [22][23][24][25], considering an elastic-linear behaviour of the superstructure and a nonlinear force-displacement law of the FP bearings in the horizontal direction depending on sliding velocity and axial load. A gap model is also assumed to capture the uplift of the FP bearings in the vertical direction.…”

Multicomponent nonlinear incremental dynamic analysis of r.c. spatial framed structures subjected to near-fault earthquakes

“…Structural damage due to resonance, when the predominant vibration periods of both site and structure are close, is expected in the case of r.c. framed structures subjected to near-fault earthquakes [20][21][22][23]. In order to study their critical incidence angle in the nonlinear analysis of medium-to-high rise r.c.…”

Nonlinear dynamic analysis of high-strength concrete Bridge under post-fire earthquakes considering hydrodynamic effects

“…High temperature tests have been carried out on high-performance concrete and the investigation demonstrates that high temperature reduces the seismic performance of high-performance concrete shear walls [18] . The seismic analysis of the base-isolated structure affected by the fire shows that the occurrence of fire will obviously increase the ductility requirements of the structure, which means that the seismic performance of the structure will be reduced [19] . Comparing the dynamic analysis of an office building frame structure in the absence of fire and after fire, the results show that when the structure is exposed to wind and earthquake after a fire, the dynamic response of the structure is increased [20] .…”