Introducing new design spectra derived from Italian recorded ground motions 1972 to 2017

Summary A risk‐targeted design spectral acceleration and the corresponding seismic design action for the force‐based design of structures is introduced by means of two formulations. The first one called direct formulation utilizes the seismic hazard function at the site of the structure. Because the seismic action defined in the codes is often associated with a designated return period, an indirect formulation is also introduced. It incorporates a risk‐targeted safety factor that can be used to define a risk‐targeted reduction factor. It is shown that the proposed formulations give analogical results and provide an insight into the concept of the reduction of seismic forces for the force‐based seismic design of structures if the objective is defined by a target collapse risk. The introduced closed‐form solution for the risk‐targeted reduction factor can be used to investigate how the target collapse risk, the seismic hazard parameters, the randomness of the seismic action, and the conventional parameters (ie, the overstrength factor and the deformation and energy dissipation capacity) affect the seismic design forces in the case of force‐based design. However, collaborative research is needed in order to develop appropriate models of these parameters. In the second part of the paper, the proposed formulations are demonstrated by estimating the risk‐targeted seismic design action for a six‐storey reinforced concrete building. By verifying the collapse risk of the designed structure, it is demonstrated that the risk‐targeted seismic action, in conjunction with a conventional force‐based design, provided structure with acceptable performance when measured in terms of collapse risk.

Section: Determination Of Risk‐targeted Design Seismic Actionmentioning

confidence: 99%

Formulation of risk‐targeted seismic action for the force‐based seismic design of structures

Žižmond

Dolšek

2019

“…The application of the appropriate conceptual correction, as discussed in this paper, may result in even more relevant effects if spectra shapes with no constant velocity regions are considered, or when the spectra are used as a basis to derive floor spectra …”

Section: Discussionmentioning

confidence: 99%

“…The second one is applied in a revised version of the capacity spectrum method , originally proposed by Freeman . In this formulation, the capacity of the structure is described by the nonlinear envelope curve resulting from some push‐over analysis; the demand is represented by a combined spectral acceleration ( S a ) spectral displacement ( S d ) shape, as shown in Figure 2 …”

Section: Inelastic Displacement Spectra In Displacement‐based Design mentioning

confidence: 99%

On the correction of spectra by a displacement reduction factor in direct displacement‐based seismic design and assessment

Calvi

2019

Self Cite

The application of some design and assessment approaches, such as the direct displacement-based design (DDBD) and the capacity spectrum methods, requires the modification of elastic design spectra by some displacement reduction factor, to account for the appropriate energy dissipation capacity of different structures.While several equations to correlate dissipation and hysteresis cycles are available, once the displacement reduction factor has been obtained, the correction of the spectra is operated reducing the displacement demand accordingly and conserving the period of vibration at each point.This procedure is here discussed and proved to be conceptually inappropriate, because the spectral acceleration rather than the period should be kept at each point. The application of this alternative procedure may result in increased shear strength demand in design and in larger required displacement capacity for the same level of strength in assessment, if all other factors are not modified. However, the calibration of the reduction factors applied in DDBD has been extensive, and the method has proved to be effective in predicting displacement demands consistent with those resulting from refined nonlinear time history analysis; therefore, a possible introduction of the proposed correction will require equally extensive studies and possibly compensating corrections in the calculation of the equivalent damping.On the contrary, an appropriate calibration of the factors to be used in the application of the "capacity spectrum" method is still being developed, and the consideration of a constant acceleration may facilitate the derivation of effective equations.

“…The spectral shape proposed by Calvi 1 and Calvi et al 2 is defined as a function of two points (C and D in Figure 1), identified as the longest period (T C ) at which the spectral acceleration will be at 90% of the peak spectral acceleration (S aC ) and the shortest period (T D ) at which the spectral displacement will reach 90% of the maximum spectral displacement (S dD ). The formulation is completed by the coefficient α that defines the spectral ordinates in the intermediate region (Figure 1).…”

Section: Description Of Investigated Datamentioning

confidence: 99%

“…The formulation proposed in this study defines soil amplification factors from the ratio of spectral quantities of soil deposits (soil class B or C) to quantities defined for rock-like soil (soil class A), computed using Equations ( 1)- (2). The following equations of soil amplification factors (S SaC = SaC soil /SaC rock , S SdD = SdD soil /SdD rock , S T = T soil /T rock ) have been derived from the ratios of the fitting equations (the derivation of the equations is reported in Appendix A and the parameters in Table 2 and 3):…”

Section: Definitions Of the Analytical Formulation Of Soil Amplification Factorsmentioning

confidence: 99%

Nonlinear soil effects on observed and simulated response spectra

Andreotti

Calvi

2021

Soil effects are collectively referred to the influences that local geology and morphology of soil deposits have on ground motions coming from bedrock. The quantification of soil effects in building codes has a great impact in the design of structures because soil factors amplify the reference seismic input, which is typically defined for rock‐type soil class from probabilistic seismic hazards analysis. This topic, within earthquake engineering, represents one of the typical interfaces between structural engineering, geotechnical engineering and engineering seismology. In fact, this issue is generally addressed with different approaches depending on the background of the researchers. This article investigates soil effects combining the viewpoints of structural and geotechnical engineers and seismologists. It is shown that the averaging technique adopted for the definition of ground motion predictive models for spectral ordinates does not play a significant role in defining the results of rock‐like soil classes. However, for other soil classes characterized by soil effects, different methods of averaging the spectral ordinates produce significant differences. The main result of this study is the proposal of a new analytical formulation for the quantification of soil amplification factors for both acceleration and displacement response spectra. The proposed formulation is based on a database of real ground motions and simulated accelerograms. The latter have been obtained through stochastic ground response analyses, with the propagation of natural ground motions on rock‐like soil class through randomly generated soil deposits representative of different soil classes of Eurocode 8 and the Italian Building Code. The comparison between real and simulated data revealed the crucial role of soil nonlinearity in the definition of soil effects, which is also in relation with the variation of magnitude, fault distance and the intensity measures expected on outcropping rock.