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Pseudostatic analysis can be an efficient approach to evaluating the dynamic response of structures for a preliminary design. In this paper, we present a pseudostatic method based on a pushover analysis to assess the seismic performance of bridge piers supported by rocking‐governed shallow foundations. The method has two stages. In the first stage, the capacity spectrum method (CSM) is applied to evaluate the maximum acceleration and displacement response of the bridge system. To have an appropriate system damping ratio in the CSM, we propose a method to consider various earthquake energy dissipation mechanisms for the pier and foundation. In the second stage, the footing settlement is evaluated based on the maximum footing rotation; an incrementally cyclic pushover analysis with a fixed footing rotation increment is performed to estimate the footing settlement. Examples are presented to demonstrate the applicability of the proposed method and the results of the proposed method are compared with the dynamic analysis results. Compared with the conventional CSM, the proposed method improves the estimation of system damping and can estimate the settlement after earthquakes. [ABSTRACT FROM AUTHOR]

Caissons are rigid foundation systems with huge mass that support a large variety of load combinations. Most studies ignore the resistance provided by the periphery of a caisson in providing resistance to applied external loading. In this study, the variation of resistive stresses generated on the base and sides of a caisson under various loading, interface, and seismic conditions, obtained from numerical analysis, is explored using finite-element method–based computer program ABAQUS. The shear forces and resistive moments thus generated have been studied to identify the resistive forces required for stability for different input parameters. The percentage of resisting moment shared by the caisson sides (lateral soil pressure, horizontal and vertical skin friction) has then been compared with that due to the caisson base (base reaction and base friction). Empirical correlation has been obtained using multiple linear regression analysis for the load shared by the caisson sides. It is observed that, with an increase in the horizontal and vertical seismic acceleration coefficients, the percentage of resisting moment contributed by the caisson sides increases. [ABSTRACT FROM AUTHOR]

The seismic stability analysis of slopes is frequently analyzed using the method of slices based on the pseudostatic approach. However, the time response analysis is considered to be one of the most competent tools to analyze the performance of slopes under seismic motion since this method provides details about deformation and stress distribution within the slope. In this paper, a finite-element-based time response analysis was performed to examine the seismic response of an existing hill slope located in the Kavalappara (11.414° N, 76.237° E) region of Kerala, India, where the shear strength of many slopes reduces considerably due to heavy rainfall. In this regard, a synthetic acceleration time history was developed from site-specific seismic hazard analysis. Also, a pseudostatic analysis based on the finite-element method was performed to estimate the factor of safety and corresponding stability measure. The finite-element model was developed based on Mohr-Coulomb and hardening soil with small stiffness (HSsmall) constitutive models to capture the soil behavior during an earthquake. Further, Newmark's sliding block analysis was conducted analytically to study the probable displacement after the seismic event and to validate the present finite-element analysis results. The pseudostatic analysis revealed that the slope is not safe against a pseudostatic loading of 0.12g. The seismic response of the slope under earthquake motion was described via displacement developed due to ground shaking. The results of time response indicated a continuous forward and downward earthquake-induced movement of the slope crest. The maximum displacement observed during the seismic event was 18.84 mm. Further, a sensitivity analysis was performed by considering Newmark's method and a few well-known empirical methods to check the variation of FS values with yield acceleration. Displacement and factor of safety values calculated using analytical methods were in good agreement with that obtained from finite-element-based time response analysis. Moreover, it has been concluded that there is potentially unstable slope condition exists due to combined groundwater variations and earthquake impact. [ABSTRACT FROM AUTHOR]

In this paper, upper bound limit analysis that includes a horizontal pseudostatic seismic force is used for the first time to obtain the limit load on strip footings seated on cohesive-frictional soils reinforced with a single geosynthetic layer. Reinforcement tensile rupture and sliding failure modes for the geosynthetic layer are included in the analyses. Results of analyses are presented as optimum reinforcement depths and a bearing capacity equation with a single term and different bearing capacity factors for tensile rupture and sliding failure modes. The bearing capacity factors are presented in tables and capture the combined influence of the reinforcement strength, soil frictional strength and cohesion, soil unit weight, footing geometry, uniform surcharge, and magnitude of horizontal ground acceleration. [ABSTRACT FROM AUTHOR]

Piles may be subjected to significant kinematic loading from ground movement under earthquakes. Pseudostatic analysis, which is based on the Winker beam model, traditionally adopts a single ground displacement profile, known as the characteristic ground displacement profile, for assessments of pile response under this loading condition. This study conducts dynamic analyses with different soil, pile-head-fixity, and seismic conditions and generates displacement, moment, and shear force response envelopes to evaluate the appropriateness of the characteristic displacement profiles of four common methods. These methods give inconsistent predictions because the maximum responses at different depths in the pile response envelopes occur at different points in time. To address this issue, we propose using multiple characteristic ground displacement profiles, which are determined by the maximum ground relative deformation or rotation. These multiple profiles, when used in pseudostatic analyses, give consistent predictions with dynamic pile response envelopes in most scenarios, thus overcoming the limitations of conventional single-profile methods. • The capability of common pseudostatic methods is assessed using dynamic analyses. • Traditional single ground displacement profiles are not suitable to all conditions. • The refined method adopts multiple characteristic ground displacement profiles. • Characteristic profiles are based on max. ground relative deformation or rotation. [ABSTRACT FROM AUTHOR]

Caissons are rigid foundations most commonly used to support bridge piers. In this study, numerical analysis using the finite-element method based computer program ABAQUS was carried out to study the response of caissons under static and pseudostatic conditions. The caisson was embedded in layered soil comprising a saturated clay layer sandwiched between two sand layers. Sand was modeled using an elastic, Mohr-Coulomb plastic model and clay was modeled using a porous elastic and clay plasticity model to account for soil consolidation. The wall friction angle (δ) and seismic acceleration coefficients (kh and kv) were varied in this study. Calculations were made by executing a mathematical code in MATLAB to obtain the lateral soil pressure, maximum and minimum base pressures, tilt, shift, and point of rotation of the caisson. The analysis was further extended to develop three-dimensional (3D) interaction diagrams relating the combination of applied vertical load (V), lateral load (Q), and moment (M) in nondimensional form required to cause caisson failure for different wall friction angles and seismic acceleration coefficients. These diagrams can be used for the safe design of caissons under different seismic conditions and ground conditions for a variety of design loads. [ABSTRACT FROM AUTHOR]

In this research study, the stability of a hydraulic fill dam located in a newly declared seismically hazardous zone in north Texas was evaluated, incorporating the effect of geomaterial variability existing in the dam. Hydraulic fill dams exhibit highly variable geomaterial conditions due to the method of construction and are prone to stability issues during earthquakes. Hence, a comprehensive study was needed to account for such variations in geomaterial properties and assess the stability of the dam rather than performing routine analysis using representative geomaterial properties for the shell, core, and foundation of the dam. Cone penetration tests were performed on the dam to study geomaterial properties and their variabilities. These results were used to develop three-dimensional (3D) visualization models using kriging analysis. The geomaterial properties obtained from the visualization models were subsequently used in the slope stability analyses. The developed visualization models depicted the variation of geomaterial properties within the dam. The use of the visualization models has led to the development of an innovative approach for performing stability analyses of earthen dams with high geomaterial variability. [ABSTRACT FROM AUTHOR]

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A novel unconventional pseudostatic analysis is proposed here to infer on the sensitivity of a landslide to earthquakes characterized by different physical properties. Several sine waves with different amplitudes, frequencies and phases were applied to the landslide mass assuming limit equilibrium conditions. The unconventional approach was used for the Diezma landslide case study. The landslide is located 25 km from the city of Granada (Spain). Although the slope had repeatedly suffered small-scale stability problems since the construction of the A-92 highway, a larger failure occurred on 18 March 2001 and damaged the highway between kilometers 272.6 and 272.8. The landslide had an estimated volume of 1.2 Mm 3 and involved a disordered deposit of silt and clay with heterometric blocks within the Numidoide Formation, which outcrops along the contact between the Maláguide and Dorsal domains of the Betic Cordillera mountain range. Despite the 18 million Euros spent since 1999 on geotechnical investigations and stabilization solutions, the numerous reactivations that occurred through 2010 and 2013 demonstrate the persistent activity of the landslide. The geometry of the large slope failure corresponding to the first activation of the Diezma landslide was used to back-analyze the stability of the slope based on a high-resolution engineering-geological model. The model was developed from the analysis of numerous borehole logs as well as from geophysical investigations consisting of seismic noise measurements. The results demonstrate that the safety factor (SF) of the Diezma landslide varies significantly for frequencies less than 1 Hz; moreover, unstable conditions are reached at frequency values between 0.5 and 1 Hz for water pressure distributions corresponding to Bishop factors (r u ) between 0 and 0.36. To estimate the co-seismic displacements, the geometrical and mechanical properties of the landslide mass were used to derive its characteristic periods for thickness (T s ) and length (T l ), which were compared with the characteristic period of the earthquake (T m ). The results indicate that the maximum expected co-seismic displacements are up to 2 m for an earthquake with a T m value close to 1 s and an Arias Intensity on the order of 1 m/s. [ABSTRACT FROM AUTHOR]

The 2008 Wenchuan earthquake with Ms8.0 triggered extensive throwing-pattern landslides in the area within or near the seismic faults. The resultant landslides from this earthquake brought to the fore the effect of vertical earthquake acceleration on landslide occurrence. The pseudostatic analysis and the dynamic response on landslide stability due to the Wenchuan earthquake are studied with the Chengxi (West Town) catastrophic landslide used as a case study. The results show that the epicenter distance is an important factor which affects the vertical acceleration and thus the stability of landslide. Also, the vertical acceleration was found to have a significant impact on the FOS of landslide if the earthquake magnitude is quite large. Within the seismic fault, the amplitude effect of vertical acceleration is very dominant with the FOS of landslide, for vertical acceleration ranging from positive to negative, having a variation of 25 %. The variation of FOS of landslide for vertical acceleration ranging from positive to negative are 15 and 5 % for landslides near seismic fault and outside seismic fault, respectively. For landslide with a slope angle <45°, the FOS of landslide with both horizontal and vertical accelerations is significantly greater than the one without vertical acceleration. Further, the results computed from both the pseudostatic method and dynamic analysis reveal that the FOS during the earthquake varied significantly whether vertical acceleration is considered or not. The results from this study explain why lots of throwing-pattern catastrophic landslides occurred within 10 km of the seismic fault in the Wenchuan earthquake. [ABSTRACT FROM AUTHOR]

Abstract: The resultant force of lateral earth pressure is commonly used in the design of nearly vertical walls while flatter slopes are designed to be internally stable using a factor of safety approach. An unstable slope is considered to have an unsatisfactory factor of safety unless supported by internal and/or external measures. However, from an analytical viewpoint, the distinction between walls and unstable slopes is unnecessary. Using a limit equilibrium analysis combined with a log spiral surface, a previous formulation is extended to deal with the pseudostatic instability of simple, homogeneous, cohesionless slopes. Hence, the original approach by Mononobe–Okabe (M–O) is extended to yield the resultant lateral force needed to stabilize an unstable slope. Given the slope angle, the design internal angle of friction, the backslope, the surcharge, the vertical and horizontal seismic coefficients, and the inclination of the resultant force, one can calculate the magnitude of this resultant force. The approach allows for the selection of a rational inclination of the resultant for cases where soil-face interaction is likely to develop along vertical segments only. The approach generalizes Coulomb’s (static) and M–O (pseudostatic) methods as all are in the same framework of limit equilibrium. While all methods yield identical results for vertical slopes, where the critical slip surface defining the active wedge degenerates to the same planar surface, the presented approach becomes more critical for flatter unstable slopes where the active wedge is augmented by a curved surface. Hence, the seamless extension of the M–O approach is produced. [Copyright &y& Elsevier]

Abstract: This paper evaluates a simple approximate pseudostatic method for estimating the maximum internal forces and horizontal displacements of pile group subjected to lateral seismic excitation. The method involves two main steps: (1) computation of the free-field soil movements caused by the earthquake, and (2) the analysis of the response of the pile group based on the maximum free-field soil movements (considered as static movements) as well as a static loading at the pile head, which depends on the computed spectral acceleration of the structure being supported. The methodology takes into account the effects of group interaction and soil yielding at pile–soil interface. The applicability of this approach has been validated by a similar approach for single piles and then verified by both experimental centrifuge models of pile-supported structures and field measurements of Ohba-Ohashi Bridge in Japan. It is demonstrated that the proposed method yields reasonable estimates of the pile maximum moment, shear, and horizontal displacement for many practical cases despite of its simplicity. Limitations and reliability of the methodology are discussed and some practical conclusions on the performance of the proposed approach are presented. [Copyright &y& Elsevier]

During the 1999 Chi-Chi earthquake, extensive slope failures were triggered by the earthquake in central Taiwan. Among those, a large-scale dip-slope slide in Tsao-Ling occurred, which involved the mass movement of 120 million cubic meters. Four catastrophic dip-slope rockslide events in history in Tsao-Ling are reported; furthermore, the stability analysis of the Tsao-Ling landslide caused by the Chi-Chi earthquake was conducted for the original and remaining slope. Results of pseudostatic analysis indicated that a reduction factor of 2/3 for both vertical and horizontal peak ground acceleration with 30% of material strength degradation were likely the case for inducing the Tsao-Ling landslide, and the effects of vertical acceleration were significant. Accordingly, it was concluded that ground motion and degradation of material strength were the major factors for the inducement of the Tsao-Ling landslide by the Chi-Chi earthquake. [Copyright &y& Elsevier]

In this study, the suitability of the pseudostatic approach for the seismic analysis of pile foundations in layered soils is explored by means of experimental data from centrifuge tests performed at 60 g. A free-head single pile and a capped (1 × 3) pile group, embedded in a two-layered soil comprising a soft clay layer underlain by dense sand, are tested in the centrifuge under sinusoidal and earthquake excitations. For the pseudostatic analysis, a one-dimensional Winkler model is developed using hyperbolic p-y curves from design codes. The kinematic and inertial loads on the pile foundations are derived using the experimentally measured free-field soil displacements and accelerations, respectively. Different approaches of modifying the p-y relationship to account for soil layering are compared. The importance of considering peak spectral acceleration in lieu of peak ground acceleration at the soil surface to compute the inertial force for the pseudostatic analysis is highlighted. Pile group effects are investigated by considering p -multipliers from literature to account for pile-soil-pile interaction. Results reveal that: (i) for low-intensity seismic motions, the pseudostatic approach with inertial pile-head loading stemming from peak ground acceleration (PGA) at soil surface led to a reasonable agreement of the maximum bending moment with experimental data for both single pile and pile group, (ii) for high-intensity base excitations, the use of the peak spectral acceleration, instead of PGA, at soil surface with suitable damping considerations to derive the inertial load in the pseudostatic model provided a maximum bending moment prediction that was acceptable for the single pile but conservative for the piles in the group compared to the centrifuge records. • Pseudostatic analysis of a single pile and pile group embedded in layered soil was performed by considering one-dimensional Winkler model. • Different approaches of modifying the p-y relationship to account for soil layering are compared. • The pseudostatic results are compared with the dynamic centrifuge data to evaluate the efficacy of pseudostatic methods and p-y relationships recommended by the design codes. • The importance of group effects and using peak spectral acceleration to compute the inertial force for pseudostatic analysis is highlighted. [ABSTRACT FROM AUTHOR]

• The pseudostatic approach considers piles under inertial and kinematic loadings. • A weighted motion is used to combine ground motions at different depths. • The system damping ratio combines viscous, radiation and hysteretic damping ratios. • Inertial/kinematic participation factors depend on normalized excitation frequency. • Near-fault motions impose pronounced kinematic loading on piles at deep depths. This study proposes a pseudostatic approach for analyzing the seismic response of an extended pile under inertial and kinematic loadings. A structure–pile–soil pushover model is established. In the model, the inertial loading is simulated as a static force that is applied at the pile head, and the kinematic loading is simulated by imposing a ground displacement profile on the pile–soil interaction springs. This approach, based on a dynamic structure–pile–soil interaction model, comprises three aspects: inertial loading, kinematic loading, and combination of inertial and kinematic loadings. For the inertial loading, the capacity spectrum method is applied to obtain the maximum acceleration of the superstructure mass, using a weighted motion that combines contributions of excitations at various soil depths and an equivalent system damping ratio in terms of linear viscous damping, radiation damping, and hysteretic damping. For the kinematic loading, the ground displacement profile corresponding to the maximum ground surface displacement is analyzed through ground response analysis. For the combined action of inertial and kinematic loadings, because their maximum effects may not occur simultaneously, we construct the relationships of participation factors with the ratio of the excitation frequency to the system frequency. Examples are used to demonstrate the applicability of the proposed method. [ABSTRACT FROM AUTHOR]