•Reductions in the ductility demand of RC piers by using inclined pile foundations.•Reductions in the input seismic energy to the system due to FIM peculiarities.•Displacement-based design ...methodologies requires a strategy to account for the SSI.•Takeda’s model is used to represent the non-linear response of the plastic hinges.•Good estimations of yielding energies and ductilities are obtained with simple rules.
This paper studies the effects of the use of inclined pile foundations on the seismic response of bridges, and shows that this type of foundation is able to promote significant reductions in the ductility demand of reinforced concrete piers. To this end, a set of nine multi-span roadway viaducts with different pier heights and span lengths is defined. Each configuration is designed and dimensioned in detail following a displacement-based approach, considering both linear and non-linear expected behaviours and assuming different target ductilities for piers. The systems are assumed to be founded on a specific soil profile, and suitable pile foundation layouts and dimensions are determined for each case, with four different pile rake angles (including the vertical case) in each configuration. Soil-structure interaction phenomena are incorporated through the corresponding frequency-dependent impedance functions and kinematic interaction factors. The transverse response of the viaducts, subject to a set of seven suitable scaled real accelerograms, is computed and analysed making use of a substructuring approach and non-linear time-domain analysis in which a lumped parameter model is adopted to represent the foundation response. Results, presented not only in terms of ductility demand but also of energy dissipated in the structural system by damping or by yielding, suggest that inclined piles are clearly beneficial to the seismic response of bridges, contributing to significant reductions in ductility demand due to the particular kinematic seismic response of this type of foundations and associated reductions in the input seismic energy to the system.
AbstractA large number of experimental curvatures in plastic hinges of concrete members are used alongside analytical moment-curvature relations to backestimate strains in the bars, the extreme ...concrete fibers of a section, or its confined core at the ultimate conditions of concrete sections in flexure with axial loads. Strain limits derived from these ultimate strains can support fiber models for prismatic members or models with finite-length plastic hinges at the ends. The measurements come from circular or rectangular columns (some tested diagonally), walls, or beams. The ultimate strains derived for steel bars and concrete are not local material properties (especially for cyclic loading): they depend on the geometric features of the section as a whole and of the immediate vicinity of the most critical point in the section. The size effects are clear: (1) concrete ultimate strains increase in a small compression zone, (2) the monotonic ultimate strain of tension bars increases with decreasing number of bars in the tension zone, (3) the ultimate strain of steel in cyclic tests increases with the increasing number of bars in the compression zone, and (4) the ultimate strain of confined concrete is larger at a section corner in biaxial bending than along the full side of a rectangular compression zone in uniaxial flexure, while at the perimeter of a circular section, it is in between these two extremes. The cyclic ultimate strain of steel in tension increases as the bar diameter–to–stirrup spacing ratio increases, thanks to the delay of bar buckling in previous compression half-cycles. The ultimate strains derived apply both as mean values in a plastic hinge and at the end section of prismatic members. Compared to experimental ultimate curvatures, those computed from the proposed ultimate strains do not have bias and exhibit much less scatter than those obtained from arbitrary ultimate strains specified in some codes. These code predictions are, in general, unsafe.
Previously, the authors proposed a novel Sliding Keys on Inclined Deflecting-cantilevers (SKID) device for application with the Post-Tensioned (PT) frames (the PT-SKID frame). The PT frame has a ...nonlinear elastic feature, providing a high initial lateral stiffness and softening at large displacement. The PT frame is self-centring; the SKID device provides additional damping as it is characterised by a triangular-shaped hysteretic curve with a zero-activation threshold. Thus, the PT-SKID frame has a full self-centring capability by featuring a dual-triangular-flag-shaped hysteretic curve. This paper proposes a novel Post-Tensioned Precast Warehouse structure with the Sliding Keys on Inclined Deflecting-cantilevers Device (the PTPW-SKID structure) following the concept of the PT-SKID frame for industrial buildings. The structural arrangement and the load path are discussed first. The structure comprises the PT outer frame and the SKID inner frame. The PT outer frame supports the roof and cladding systems and carries the loads applied to them. The SKID inner frame supports the SKID devices and carries a crane system. Differing from the PT-SKID frame, the SKID inner frame of the PTPW-SKID structure involves high support columns. The impact of their elastic deformation on the hysteretic curve of the SKID inner frame is discussed first. Then, the seismic design of the PTPW-SKID structure is presented by a case frame located in L′Aquila, Italy. The Direct Displacement-Based Design (DDBD) method is utilised for the seismic design. Finally, a 3D numerical model was built in OpenSees. Both quasi-static and seismic dynamic analyses were carried out. The hysteretic behaviour and the seismic response of the case structure were investigated and discussed.
To obtain elastic horizontal displacement spectra for different damping ratios for use in displacement-based seismic design, the influences of the moment magnitude, fault distance, and site class on ...the 5%-damped elastic horizontal displacement spectrum are first investigated using the ASK14 ground motion prediction equation (GMPE). Then, bilinear displacement spectrum models for different damping ratios are proposed based on the statistical characteristics of the displacement spectra of strong motion records with the principle of retaining the major influencing factors and neglecting the minor ones, and the models are used to describe uniform hazard displacement spectra for a point source site with a return period of 475 years. Finally, the method for implementing the proposed models in practical applications is discussed. The results of the study show the following. The moment magnitude is the main factor affecting the shape of the displacement spectrum. The proposed bilinear displacement spectrum models can reflect the influence of the moment magnitude, reflect the statistical characteristics of the displacement spectra of the actual strong motion records, and well describe the uniform hazard displacement spectra of the point source site with a return period of 475 years. The zoning map of the two spectral displacements and the corresponding site amplification factors and damping scaling factors of the bedrock site at each seismic hazard level are provided to enable the implementation of the proposed bilinear displacement spectrum models in practical applications.
Displacement-based methods, such as a non-linear static pushover analysis (e.g. the capacity spectrum method), have many advantages compared to traditional force-based design methods. However, ...implementing a non-linear analysis and design method in accordance with the Australian Standard for concrete structures (AS 3600) introduces many difficult technical issues into the design, of which the standard provides little guidance. The aim of this study is to provide a framework and general guidance for designers who wish to perform non-linear displacement-based analysis methods for RC wall buildings. The paper will present how these methods can be used in accordance with the Australian Standard for earthquake actions (AS 1170.4) to assess seismic compliance and then provide recommendations for the requirements stipulated by AS 3600, which includes an experimentally validated tension stiffening model, nonlinear stress-strain material curves, mean material properties and material strain limits. The paper is concluded with a case study example of how a displacement-based seismic assessment can be performed using a typical case study building.
The importance of non-structural elements on the seismic performance of buildings is now widely recognized. A building cannot achieve a life-safety or continuous functionality performance after an ...earthquake if all its non-structural elements are damaged and/or out of function. Suspended non-structural elements, such as piping and mechanical services, play a crucial role in maintaining life-safety and functionality of a building after an earthquake. The importance of non-structural elements for the seismic performance of buildings have prompted the development of both force-based and displacement-based seismic design methodologies that can be applied to suspended non-structural elements. This paper focuses on appraising force-based and displacement-based seismic design methodologies available in Europe for suspended non-structural elements by comparing fragility functions for a case-study suspended piping trapeze restraint installation layout located in a mid-to-high seismic zone in Italy. The aim of this study is to determine if the seismic design methodologies available for suspended non-structural elements are capable of producing archetypes that achieve a life-safety performance objective for a design level earthquake (return period of 475 years) and maintain a reasonable performance, in terms of life-safety, for other earthquake intensity levels. Advantages and disadvantages of these methodologies are also highlighted.
Displacement-based seismic design methods have been used in port industry for decades. For determining demand displacements of pile-supported wharves, the substitute structure method, a nonlinear ...static demand analysis methodology, is used in current practice. In the method, the estimation of equivalent damping does not account for damping from soil–pile interaction. In view of this, a new damping equation for pile-supported wharf system as a whole based on the total energy dissipation of soil and structure is proposed. The energy dissipated by soil is quantified by the p–y curves of soil springs and Masing hysteretic rule, and energy dissipated by structure is the sum of energy dissipated by all plastic hinges appeared in piles. Then, the equivalent damping of wharf as a whole is derived by Jacobsen's approach for steady-state harmonic response. To figure out the contribution of soil–pile interaction on system damping as well as the accuracy and rationality of the equation, a case study is presented. It is found that the soil–pile interaction contributes significantly to the dissipated energy of wharf system, and the displacement demands of wharf based on the proposed equation are closer to those based on time-history analyses than other equations in current practice.
•The equivalent damping equations utilized in practice of wharves are approximate.•A rational damping equation is proposed to consider soil–pile interaction.•Soil–pile interaction contributes significantly to the dissipated energy of wharf.•The proposed equation performs relatively well in determining displacement demands.
This study proposes a generally applicable equation for dynamic magnification factor (DMF) based on the conditions for static equilibrium of an equivalent mechanical model for actual wharf under ...horizontally bi-directional ground motion. The new equation can be expressed as a function of eccentricity ratio and aspect ratio for wharf segment. The applicability and accuracy of proposed equation are validated by conducting two case studies that compare DMF determined by equation with that determined by nonlinear time history analyses using bi-directional earthquake ground motion records. The validation shows that the new DMF equation has favorable applicability and accuracy.
► This manuscript studies the constant damage inelastic displacement ratios. ► It is found that the effect of site conditions is not very significant. ► Coefficients of variation are approximately ...period-independent and site-independent. ► A simplified expression is suggested based on the statistical results.
This paper summarizes the comprehensive statistical results of constant damage inelastic displacement ratios which allow the evaluation of maximum inelastic displacement demand for structures with constant damage performance. The inelastic displacement ratios are calculated with modified Park-Ang damage index and inelastic single-degree-of-freedom systems subjected to 573 ground motions. The influences of period of vibration, levels of damage, site conditions, earthquake magnitude, rupture distance, post-yield stiffness, stiffness degradation, strength deterioration, parameter β and ultimate ductility factor μu in damage index model are evaluated and discussed statistically. It is found that the effect of site conditions is not very significant. Specifically, coefficients of variation are approximately period-independent and site-independent. The degrading systems with short period of vibration would experience larger inelastic displacement than non-degrading systems. The effects of parameter β and ultimate ductility factor μu are moderate in short period region. A simplified expression is proposed for the application of constant damage inelastic displacement ratios.
A direct displacement-based design approach for damage-controlled structures using the best combination of stiffness and strength ratios between the main structure and added hysteretic energy ...dissipation systems is proposed. Choosing optimal values of the design parameters is an important step toward an efficient structural design; therefore, a parametric study using different combinations of design parameters is performed, from which a simple methodology to calculate a cost-efficiency index based on a cost-benefit analysis is developed. The DDBD methodology is verified and recommendations about adequate combinations of design parameters are given for an 8-story steel building with buckling restrained braces.
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