Development of nonlinear methods of analysis and powerful software for simula-tion of seismic response of structures offered a possibility to overcome shortcomings of the standards for earthquake-resistant design of structures. Firstly, these shortcomings are brief-ly addressed, followed by anoverview of the nonlinear methods for seismic performance as-sessment of buildings. An emphasis is given on the envelope-based pushover analysis procedure, which was recently developed, and assumes that the seismic demand for each re-sponse parameter is controlled by a predominant system failure mode that may vary accord-ing to the ground motion and intensity level. The second part of the paper deals with the concept of risk-based design procedure, which is an iterative process based on different methods for seismic performance assessment of buildings. The proposed design procedure involves definition of the initial structure, which is then assessed in order to check whether the seismic risk is below the acceptable/tolerable level. However, since several or many itera-tions will be needed in order to fulfill the criteria of acceptable/tolerable risk it is foreseen that this step of therisk-based design procedure will be based on approximate procedures for seismic performance assessment. The next step of the proposed design procedurewill utilize the nonlinear response history analysis, which would be performed for few ground motions from a set of hazard-consistent ground motions. The risk-based design will be possible only by further development ofcomprehensive software for computational simulation. The paper is concluded with presenting pros and cons of the proposed design procedure. It is foreseenthat, the risk-based seismic design of structures will represent a major step towards scientifically oriented design procedures employing high level of technology.
B.01 Organiser of a scientific meeting
COBISS.SI-ID: 6302817Within the project a procedure for determination of the risk-based design and performance spectrum was developed. The procedure was applied to an eight storey reinforced concrete frame structure. The structure was designed to four different levels of target reliability associated with the structural collapse, which can be caused by earthquakes that may occur over the lifetime of the structure. The study was performed as a part of the Master Thesis of Damian Podgorelec under supervision of Matjaz Dolšek and co-supervision of Jure Žižmond, young researcher at IKPIR Institute. It was found that the escalation of acceptable risk by a factor of 50 resulted in an increase of the total design seismic forces by about a factor of 10. This was reflected in the quantity of materials used. The amount of reinforcement was increased by about 4,6 times, while the volume of the concrete was greater by a factor of 1,9. It appeared that the structural system is not suitable if the criterion of acceptable risk is very strict. Based on the results of the study it can be concluded that the proposed risk-targeting force-based design procedure is quite similar to that prescribed by Eurocode 8, as it essentially differs only in the definition of the seismic action, which, according to the new procedure, depends on the target reliability rather than the earthquake recurrence interval. For the study Damjan Podgorelec received Prešern’s Award of the Faculty of Civil and Geodetic Engineering.
D.10 Educational activities
COBISS.SI-ID: 6412129Design of earthquake-resistant structures according to Eurocod 8 is not based on the concept of acceptable/tolerable probability of exceedance of the near collapse limit state. Rather than that standard introduces fundamental non-collapse and damage limitation requirements, which are associated with the design seismic action. It is foreseen that the non-collapse requirement is satisfied when the regular structure does not collapse in the case of an earthquake with a return period of 475 years. Probability of such an event in 50 years is 10%. Therefore it is obvious that probability of failure of structures, which would be designed strictly according to the fundamental non-collapse requirement, would be unacceptable for society. Due to factors of safety involved in design the structures withstand much stronger earthquakes in comparison to an earthquake with a period of 475 years. In order to assess which factor of safety has the greatest impact on the overall safety of code-conforming buildings, two multi-storey reinforced concrete buildings were investigated. The strength and the system ductility of the six variants of the structures were evaluated on the basis of the pushover analysis gradually taking into account the requirements of the Eurocode 2 and 8, as well as gradually excluding the design assumptions. Safety in design of the buildings was evaluated by the difference between the calculated and prescribed behaviour factor, by the ratio between the design ground acceleration and that associated with the near collapse limit state, which was assessed using the N2 method, and by the escalation of safety in terms of probability of exceedance of the near collapse limit state. For the investigated buildings it is shown that the design seismic action has the greatest impact on the yield strength of the structure and the peak ground acceleration, which cause the near-collapse limit state. On the other hand, the partial factors of material strength contribute around 50% to the return period of the near-collapse limit state, whereas the contribution of the capacity design principles to overall safety is minor.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 6303073