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.
COBISS.SI-ID: 9012577
A comprehensive assessment of a new version of the macroscopic force-displacement based multiple-vertical-line element (SFI-MVLEM-FD), which can be used to simulate non-linear axial-shear-flexure interaction in RC walls, is presented. The element models the shear response taking into account all the basic physical mechanisms that transfer shear forces over cracks: (a) the dowel efect of vertical bars, (b) the axial resistance of horizontal/shear bars, and (c) the interlocking of aggregate particles in cracks. In order to provide a wide range of its use, and to enable the analysis of various types of buildings, the SFIMVLEM-FD element was included in the local version of the OpenSees program system. The element was assessed with respect to already performed quasi-static cyclic experiments of various RC shear walls. In this paper, the results of numerical analyses of two representative rectangular walls, where the infuence of shear on the overall response was of particularly signifcance, are presented and compared with those obtained in the experiments. In order to estimate the efciency of the new element in more general cases, it was also assessed by means of a large-scale shake-table test of a typical non-planar lightly reinforced RC coupled wall. The test examples showed that the SFI-MVLEM-FD model can capture all the important mechanisms of the response, as well as being able to efciently describe the axial-shear-flexure interaction in various types of RC walls: (a)...
COBISS.SI-ID: 8861281
The paper presents experimental and analytical studies of the dynamic in-plane response of typical fastening systems for horizontal cladding panels in RC precast industrial buildings in Central Europe. The system consists of two main parts: a pair of top bolted connections, which provide the horizontal stability of the panel, and a pair of bottom cantilever connections, which support the weight of the panel. A typical response mechanism of the fastening system consists of three distinct stages: sliding with limited friction, contact with the panel causing an increase in the connection stiffness, and failure. It has been found that the capacity of the complete system is limited by the displacement capacity of the top connections, which are the most critical components. Therefore, it is better to express the capacity of the entire system in terms of displacements. Appropriate numerical models for the complete fastening system have been proposed and validated by the results of the presented experiments. The top and bottom connections were analysed separately and showed physically different response behaviours. The typical Coulomb friction model was used to describe the friction in the top connection, whereas the viscous friction model better simulated variable friction in the bottom connection. The contacts that occur when the gap for sliding of panels closes were simulated by an abrupt increase of the stiffness of the connection.
COBISS.SI-ID: 25888003
This paper investigates the origin of increased strength and water resistance of air lime mortar prepared by Triassic dolomite aggregate when exposed to humid or wet environments. The mortar specimens were exposed to various ageing conditions and analysed using petrographic and scanning electron microscopy equipped with X-ray microanalysis. Parallel to these analyses, X-ray powder diffraction and strength tests were performed on the specimens. It was revealed that reactions associated with the dedolomitisation process of the dolomite grains in the lime binder (hereafter alkali-carbonate reactions or ACRs) are the source of the improved strength and water resistance. An increasingly alkaline environment accelerated the ACRs substantially. Two parallel processes during the ACRs (dedolomitisation and CaCO3 dissolution/reprecipitation) were described in detail. Ageing temperature decisively influenced the kinetics of the dedolomitisation and dictated the path of the CaCO3 dissolution/reprecipitation process. After two years of ageing in a water-saturated environment at 60°C, air lime mortar retained a great deal of its initial mechanical strength, and at 20°C its strength was considerably increased. This somewhat unexpected observation was explained as being a result of microstructural changes and/or phase transitions.
COBISS.SI-ID: 9109089
A five-grade grading system is introduced by combining together the concepts of long-term and short-term risk tolerance. Grades AA or A are related to a long-term tolerable risk, whereas grades B and C are considered acceptable only for a shorter period, depending on the facility performance, and grade D corresponds to a short- term intolerable risk. In the first step of the grading process, the initial grade is determined by comparing the estimated risk to a set of risk boundaries, which define the ranges between grades AA-A, A-B and B-C. If the estimated risk is found to be long-term intolerable (grade B or C), the second step follows. This approach utilizes the criterion of cumulative risk, which makes it possible to introduce a reduction in grades B or/and C over time, and in the additional grade D, which is associated with intolerable cumulative risk. The use of the proposed grading system is demonstrated by means of an example of two precast reinforced concrete buildings exposed to seismic risk, where grade B is initially assigned to the facility with better performance, whereas the other facility is evaluated by grade C. It is shown that the reduction of the grades to the lowest grade D is scheduled for 11.9 years and 3.8 years, respectively, in the case of the building with the lower and the higher risk. Such information can be used for communicating risk to stakeholders, and as a basis for the enhancing of the disaster risk management of communities. The inovative grading system was extended and used in the seismic stess test of building stock in Republic of Slovenia.
COBISS.SI-ID: 8665953