Code inadequacies discouraging the earthquake-based seismic analysis of buildings

Abstract

Despite being the more accurate method to design earthquake-resistant buildings, the non-linear dynamic analysis still remains the least used in practice. The paper shows that some code inadequacies may even contribute to ward off the designer from this kind of seismic analysis. To this purpose, non-linear analyses under different sets of spectrum-compatible earthquakes and by considering two distinct plastic-hinge models were carried out for a multistory reinforced concrete (r/c) frame designed according to the Eurocode 8 provisions. It has been shown that owing to the inadequate limits imposed to the spectrum-compatible earthquakes, the European codes of practice may lead to significant inconsistencies in the seismic design of structures through the time-history non-linear analysis. Keywords: earthquake-resistant buildings, EC8 inadequacies, spectrum-compatible earthquakes, time-history non-linear seismic analysis. INTRODUCTIONThe seismic design philosophy typically requires that buildings may withstand events of moderate severity deforming in the elastic range, without suffering any irreversible structural damage. Conversely, during strong earthquakes structures are required to behave in a dissipative ductile way, even getting damaged severely but without collapsing. These achievements have to be reached regardless to which type of code-based analysis (linear or non-linear) is chosen. If a linear analysis is performed, in fact, a reduced response spectrum can be adopted to design the structure so as it can withstand moderate earthquakes in the elastic range, while compliance with the detailed code provisions (local ductility and strength hierarchy rules) ensure that the plastic deformation capacity of the system can satisfy the demand under stronger earthquakes. If a non-linear analysis is carried out instead, the elastic and postelastic behaviour of the structure can be straight monitored. Both a non-linear static analysis (often referred to as 'pushover') and a non-linear time-history analysis (NLTHA) are allowed by codes. The latter is expected to be the more powerful since it obtains the deformation time-history of the system through a numerical integration of the differential equations of motion under the considered earthquake.Despite its indubitable potentials, the NLTHA is still the least applied method of seismic analysis. This may be due to the difficulties that even an experienced designer has to overcome when (i) modelling the non-linear behaviour of the system, (ii) defining the suite of spectrum-compatible earthquakes, (iii) carrying out the numerical calculations and even (iv) interpreting the results and choosing the requirements to be met. To help the designer, some codes of practice, i.e. FEMA-356 [1] and ATC-40 [2], give default properties for r/c plastic hinges, which are implemented by finite element structural programs such as SAP2000 [3]. User-friendly software tools, as for instance REXEL [4], are also available to obtain code-based selections of accelerograms.Nevertheless, the ...

Optimal Design of Earthquake-Resistant Buildings Based on Neural Network Inversion

“…2021, 11, x FOR PEER REVIEW 2 of 14 seven spectrum-consistent earthquakes were carried out. Among the methods covered by the design regulations, the non-linear dynamic analysis is the most accurate to assess the seismic performance of ductile dissipative structures, although it requires higher computational burden and designer skill [3,4]. It can be successfully applied to both the design of new buildings [5] and the seismic retrofit of existing structures [6,7].…”

Seismic retrofit of existing buildings led by non-linear dynamic analyses

“…upper and lower tolerated deviation of the average spectrum from the target spectrum were both set to 10%. It can be noted, incidentally, that only the lower deviation is specified by Ec8 (it should not exceed 10%) while no indication about the upper deviation is provided, although the choice of the upper bound for the average spectrum might strongly affect the results of the analysis as discussed in [3].…”

“…This can be done through a non-linear time-history (NlTH) analysis. Despite being the most powerful kind of seismic analysis, the NlTH analysis is still scarcely adopted in practice, not only for the assessment of existing buildings but even for the design of new structures [1][2][3].…”

“…A concentrated-plasticity model is adopted in SAP2000 while fibre-based finite elements are introduced in SeismoStruct to simulate the plastic behaviour of the critical sections of the structure. both the concentrated plasticity and the fibre-based approaches are in fact adopted in the literature to perform pseudo-static and dynamic time-history seismic analyses [2][3][14][15][16][17].…”

A Contribution to Facilitate the Seismic Design in Lebanon Using Short-Length Spectrum-Consistent Earthquakes

“…On the other hand, a database of recorded ground motions should be at researcher's disposal to obtain suitable suites of synthetic SCEs. Inconsistencies in codes in the definition of DRS [8,9], as well as unavailability of suitable seismic records for the dynamic analyses are some of the obstacles that may compromise the seismic design/assessment of buildings.…”