Reliability of short seismic links in shear

This paper presents the results of research in reliability of short seismic links in shear based on tests. Four types of short links were analysed, each having the same cross section and the same length, but with different number of web stiffeners. The main purpose of the stiffeners is to preserve buckling of the seismic link web, i.e. to achieve plastification of the cross section by shear. The design model of shear resistance according to Eurocode 8 is applicable only to short links without web stiffeners. By adding the web stiffeners nonlinear inelastic behaviour of short seismic links differs depending on the number of stiffeners, so that the calculation model of shear resistance according to Eurocode 8 for short seismic link with stiffeners should be improved. This fact is considered by introducing the improve factors that were determined from the laboratory tests conducted on 16 specimens. On the base of tests in the second part of this paper the reliability of short seismic link is performed by forming limit state equations. These equations are formed by using the stochastic model, i.e. by describing the statistical nature of basic variables calculating the reliability index as an operational value of failure probability. The reliability level was determined by using the probabilistic analysis based on the first order reliability method which resulted with the conclusion that the short seismic links with two and three couples of web stiffeners designed according to requirements of Eurocode 8 have enough reliability for the reliability class RC2 and the mean recurrence interval of 50 years.     

Comparison between non-linear dynamic and static seismic analysis of structures according to European and US provisions

Several procedures for non-linear static and dynamic analysis of structures have been developed in recent years. This paper discusses those procedures that have been implemented into the latest European and US seismic provisions: non-linear dynamic time-history analysis; N2 non-linear static method (Eurocode 8); non-linear static procedure NSP (FEMA 356) and improved capacity spectrum method CSM (FEMA 440). The presented methods differ in respect to accuracy, simplicity, transparency and clarity of theoretical background. Non-linear static procedures were developed with the aim of overcoming the insufficiency and limitations of linear methods, whilst at the same time maintaining a relatively simple application. All procedures incorporate performance-based concepts paying more attention to damage control. Application of the presented procedures is illustrated by means of an example of an eight-storey reinforced concrete frame building. The results obtained by non-linear dynamic time-history analysis and non-linear static procedures are compared. It is concluded that these non-linear static procedures are sustainable for application. Additionally, this paper discusses a recommendation in the Eurocode 8/1 that the capacity curve should be determined by pushover analysis for values of the control displacement ranging between zero and 150% of the target displacement. Maximum top displacement of the analyzed structure obtained by using dynamic method with real time-history records corresponds to 145% of the target displacement obtained using the non-linear static N2 procedure.