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  • SEISMIC DAMAGE PREDICTION FOR WATER SUPPLY TANKS

    A seismic damage prediction method of reinforced concrete water tanks in a water supply system based on wallboard crack width was modified. When the tensile stress of bars on wallboard exceeded its yield stress, the crack-width-based seismic damage rating system was no longer applicable. By adjusting the unreasonable influencing factors in the model, an empirical statistical regression model is proposed. Based on the analysis of the Tangshan earthquake, Haicheng earthquake and Wenchuan earthquake damage example, the results of the evaluation of the seismic damage grade of the clean water tanks based on the empirical statistical regression model showed that the empirical statistical regression model solves the defect that the system based on the crack width would no longer be applicable when the tensile stress of the wallboard reinforcement exceeds its yield stress.

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  • SEISMIC VULNERABILITY ASSESSMENT OF STEEL STORAGE PALLET RACKS

    Steel storage pallet racks are structures composed of cold-formed members designed to store goods. Despite worldwide usage, their dynamic behaviour is still not well known. The goal of this research is to propose a methodology for the seismic vulnerability assessment of steel racks, in terms of fragility curves. The latter are retrieved by means of Multiple-Stripe Analysis, in which the Generalized Conditional Intensity Measure approach is employed for record selection. Two typical rack configurations, unbraced and braced, are analysed, and epistemic uncertainty related to construction details is accounted for by considering different hysteretic connection behaviours and upright moment resistances. Nonlinear dynamic analyses are performed in the down-aisle direction, considering both geometric and material nonlinearities. The obtained results are related to different engineering demand parameters and limit states. The derived fragility functions, if combined with relevant hazard curves, would allow carrying out a seismic risk assessment and mitigation of steel storage racks.

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  • FOUNDATION-STRUCTURE INTERACTION AND BEAM-COLUMN CONNECTIONS ON THE SEISMIC RESPONSES OF STEEL MOMENT-RESISTING FRAMES

    The seismic behavior of special steel moment-resisting frames (SMRF) is a function of several parameters such as beams and columns cross-sectional shapes and its width to thickness ratios, column-to-beam strength ratio, beam-column connections, soil conditions, foundation types. The simultaneous modeling effects of some of these parameters are investigated in this paper. The soil-foundation-structure interaction (SFSI), shallow foundation types, and safety factor variation are the studied parameters. For this purpose, five and ten-story buildings with SMRFs resting on two soil types (SC and SE) are considered. The footing and strip foundations were designed for 5-story buildings, and strip foundation was only designed for 10-story buildings. The effect of simultaneously considering connections and SFSI impacts show that models rested on the SE have higher maximum lateral displacement. However, the maximum base-shear is reduced at these models. In models rested on the SC, by considering the impact of SFSI and connections, both structure responses are diminished, and the foundation types do not have any effect on the responses of these models. However, in models resting on the SE, the dependency of responses to the footing foundation is more than strip foundations.

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  • EFFECT OF STRUCTURAL STIFFNESS ON THE EFFICIENCY OF SEISMIC BASE ISOLATION USING LAYERS OF STONE PEBBLES

    The effect of structural stiffness on the efficiency of seismic base isolation using layers of stone pebbles is experimentally investigated by shake-table. The efficiency of the adopted layers is tested on four models with different stiffness, under four different earthquake accelerograms. A part of the study was carried out for one-time accelerations of the shake-table with strains in elastic range, and another part, for the most unfavourable accelerogram, was carried out by successive increase in the acceleration to the collapse of the model. It is concluded that efficiency of the considered seismic isolations systems decreased with decrease of model stiffness and that this concept shows great potential in increase of structural seismic resistance

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  • EXPERIMENTAL INVESTIGATION OF THE INELASTIC TENSILE BEHAVIOUR OF NON-PRELOADABLE GRADE 8.8 BOLTS

    Non-preloadable grade 8.8 bolts are widely adopted in European market of steel constructions. EN 1993:1-8 provides design rules for bolted connections based on simplified elastic perfectly plastic response of bolts, disregarding their ultimate deformation capacity. In case of seismic design of bolted connections, the bolt response is assumed to be unaffected by cyclic loading, even though the quantification of both ductility and low-cycle fatigue is essential to avoid brittle failure of bolted joints. In order to investigate these features, experimental monotonic and both variable and constant amplitude cyclic tests are carried out on non-preloadable grade 8.8 SB (Structural Bolting) assemblies considering three different diameters (i.e. 16, 20 and 24 mm). The results from monotonic tests enable to characterize the force-displacement monotonic response and ductility. The results from variable amplitude cyclic tests allow quantifying the strength degradation induced by cyclic actions, while the constant amplitude low-cycle fatigue tests enabled to investigate the fatigue capacity at different plastic strain and to determine both ε-N (i.e. strain amplitude-number of cycles to failure) and ε/εy -N (i.e. imposed ductility-number of cycles to failure) curves.

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  • THE OUTCOMES OF THE LAST ITALIAN CONFERENCE OF STEEL STRUCTURES HELD IN BOLOGNA: DESING AND ASSESSMENT OF STEEL AND COMPOSITES STRUCTURES

     Editorial

    The use of steel and composites structures for seismic resistant building has always been a fundamental topic of seismic engineering. During the last Italian Conference of Steel Structures – CTA 2019, held in Bologna, a great part of the conference proceedings was focused on seismic issues regarding the design and evaluation of seismic performances in new buildings and the use of steel for the retrofitting of existing buildings. Steel construction in seismic areas provides many advantages as the weight reduction with a consequent reduction in seismic actions demand. In addition, metalic members are usually able to develop wide and stable hysteresis loops under seismic loadings, thus affecting the global ductility of buildings [Chao et al., 2019; Mitsui et al., 2018; Montuori et al., 2020; Piluso et al., 2019a; Castaldo et al.; 2017a; 2017b] whose is of paramount importance for the correct evaluation of the building capacity [Giordano et al., 2017; Chisari et al., 2017; Montuori et al. 2019a]. Moment resisting frames behavior under seismic loadings can be strongly affected by the degradation phenomena occurring in dissipative zones [Bernuzzi et al., 2018; Bernuzzi et al., 2019; Dell’Aglio et al., 2017; Ferraioli et al. 2018a; 2018b; Sandoli et al., 2019; Pengfei et al., 2019; Wang et al., 2019]. Moment Resisting Frames are usually cheaper than other steel typologies and assures an adequate seismic dissipation, provided that, connections are appropriately detailed and able to support the required strength and behaving as rigid connections [Tartaglia et al., 2018b; 2019; D’Aniello et al., 2017; Tenchini et al., 2018, Xu et al., 2018]. However, Moment Resisting Frames could not be used for high-rise buildings because of their high deformability that makes this structural typology very sensitive against serviceability and second order effects [Tartaglia et al., 2018a; 2018c; Montuori et al., 2019b], therefore, braced frames or dual systems are preferred [Costanzo et al. 2017; Costanzo et al., 2018; Jia et al., 2019]. In the last years, also cold formed profiles are getting head in the seismic field, used not only as a system for the strengthening and retrofitting of existing buildings [Totter et al., 2018; Formisano et al., 2016; Barbagallo et al., 2020; Ferraioli et al., 2020; Di Lorenzo et al., 2020] or for pallet racks [Gabbianelli et al., 2017; Montuori et al., 2019b] but also as the main structural system of new buildings, [Poursadrollah et al., 2020; Monsef Ahmadi and De Matteis, 2020; Campiche et al. 2018; Fiorino et al., 2018; 2019; 2012; 2017a; 2017b; Landolfo et al., 2010] or as an innovative bracing system [De Matteis et al., 2018]. Other research fields regard the use of dissipative devices in place of traditional dissipative zones for both steel structures and composites structures [Lemos et al. 2018; Latour et al. 2018; Titirla et al., 2017; Di Lauro et al., 2019; Piluso et al., 2019b; Nastri et al., 2019; Farzampour et al., 2019; Colajanni et al., 2020]. The use of these devices, properly located in points where the high displacement demand is expected allow the structure to remain in service also after the seismic event and an adequate reparability, benefit the maintenance costs. From the other side, the use of base seismic isolation remains a useful strategy to limit the plastic excursion and the structural damage [Avossa et al., 2017; Fraternali et al., 2018; Palazzo and Ferrentino, 2019]. However, the attentions of the research and many efforts are focused on designing and retrofitting buildings showing, after a seismicevent, the chance to exhibit a residual drift compatible with a convenient reparability cost.

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  • DESIGN FOR SEISMIC UPGRADING OF EXISTING RC FRAMES BY FRICTION DAMPERS

    Nowadays, many buildings with RC framed structure need to be seismically upgraded. The insertion of steel braces equipped with friction dampers within the framed structure is a promising seismic upgrading technique. In fact, steel braces and friction dampers reduce the storey drift demand providing additional lateral stiffness and energy dissipation. Furthermore, friction dampers cap the forces transmitted by braces avoiding that the upgrading system overload the existing structure. In this paper a design procedure of the bracing-friction damper system is formulated. The design procedure is applied to a case study frame considering different combinations of the design parameters. The analysis of the seismic response of the bare and rehabilitated frames provides information on the effectiveness of the upgrading technique and proper setting of the design parameters.

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  • SEISMIC RETROFIT DESIGN METHOD OF RC BUILDINGS USING METALLIC YIELDING DAMPERS

    A study on the seismic retrofit of RC buildings using hysteretic dissipative braces is presented in the paper. By following a displacement-based design procedure, a fully multimodal approach based on an adaptive version of the capacity spectrum method is followed. Then, a dual RC-damped brace system idealized as bilinear is considered thus accounting for the effects of frame-damped braces interaction. Finally, the optimal distribution of dampers is determined using an iterative procedure. The proposed method is validated using nonlinear static and dynamic analyses. The results have shown the effectiveness of the proposed procedure to address the main issues of seismic design of damped braces: effect of force demands to the frame due to the dampers, higher modes contribution and effect of soft story irregularities.

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