• Current Issue
  • A NOVEL RESIDUAL DISPLACEMENT BASED DAMAGE INDEX FOR STRUCTURAL SYSTEMS

    The main motivation of current study is to present the results of an investigation conducted to obtain a relationship between damage index/damage level and residual displacement. SDOF systems with known lateral strength for periods ranging from 0.1 to 3.0 seconds are investigated for this purpose. Two hysteretic behaviours consisting of elastoplastic (non-degrading) and Modified Clough (degrading) models are assumed during analyses. A total of 140 ground motions including both far-field and near-field ground motions are considered in nonlinear dynamic time history analyses. A new damage index is proposed in terms of residual displacement, spectral displacement, maximum inelastic displacement and lateral strength. The comparison of proposed damage index with the analysis results is also presented.

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  • Current Issue
  • SEISMIC RELIABILITY ASSESSMENT OF ISOLATED MULTI-SPAN CONTINUOUS DECK BRIDGES

    The study evaluates the seismic reliability of isolated multi-span continuous deck bridges considering the influence of the friction pendulum isolators and provides seismic reliability-based design abacuses as a function of both the structural properties and reliability level expected. The behavior of these systems is analyzed by employing five degrees of freedom accounting for five vibrational modes of the elastic reinforced concrete pier and a single degree of freedom to model the response of the infinitely rigid deck equipped with the isolators. The reinforced concrete abutment is modelled as a fixed support. The non-linear FPS response is described also considering the velocity-dependent behavior. The uncertainty in the seismic input is taken into account through a set of natural records with different characteristics scaled to increasing intensity levels. The uncertainty on the friction coefficient is modelled through an appropriate probability density function. Within an extensive parametric study developed for different isolator and system properties, fragility curves of both the pier and isolation system supporting the deck are evaluated. In line with the hazard curve of the reference site, the corresponding seismic reliability curves are computed by means of the convolution integral. Finally, seismic reliability-based design abacuses for different structural properties are proposed.

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  • Current Issue
  • EFFECT OF LONGITUDINAL STIFFENING STEEL ON THE SEISMIC PERFORMANCE OF SPECIALLY SHAPED CFT COLUMNS

    In this research, cold formed steel sections have been used to reinforce and rectify the axial and shear performance of unstiffened, stiffened, L-shaped and T-shaped CFT columns. At first stage, Five L-shaped and Five T-shaped CFT columns, stiffened by various longitudinal internal steel plates and steel pipes subjected to axial and lateral loading, were numerically investigated. The variable study included the shape of CFT columns, various stiffening steel section, and the interaction between stiffening steel and concrete. Primarily FEM procedure had been verified with some available experimental results. The results indicate that the stiffening steel section have a great influence in the performance of L- and T- shaped CFT columns. Also, T-shaped CFT column shows the higher performance in terms of strength, stiffness and ductility than L-shaped section.
    At second stage, the base model was CFT column as a benchmark specimen and three new and innovative type of CFT columns with difference in their longitudinal stiffening steel were investigated under axial and cyclic loading. The results show that reinforcement of CFT columns by this method, lead to enhancement in load carrying capacity, enhancement in lateral drift ratio, ductility, preventing of local buckling in steel wall, and enhancement in energy dissipation.

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  • Current Issue
  • MULTI-HAZARD ROBUSTNESS OF SPECIAL AND INTERMEDIATE MOMENT FRAMES DUE TO EARTHQUAKE AND FIRE

    Special and intermediate moment resisting frames are two main types of lateral load resisting systems used in high-seismic regions, depending on the height of the building. Current design codes consider only earthquake risks in the design of these structures and neglect subsequent hazards. The current study compares the multi-hazard robustness of these alternative designs for earthquake and subsequent fire. For this purpose, two special and intermediate four-bay four-story steel moment frames were designed and subjected to different earthquake intensities and fire scenarios. Three types of failures, including local failure (failure of beams), partial failure (failure in some elements but not the entire structure), and global failure (overall instability of the structure), were encountered in the analyzed models. It was observed that the intermediate frame had higher fire resistance against one-bay fire scenarios than the special frame. On the contrary, when the fire was considered in an entire story, the fire resistance of both models decreased considerably with increasing earthquake intensity.

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