Effect of Footing Shape and Embedment on the Settlement, Recentering, and Energy Dissipation of Shallow Footings Subjected to Rocking

This paper presents a framework for the inclusion of transient and residual foundation deformations within performance‐based seismic design of buildings. A refinement of existing displacement‐based design procedures is proposed that reduces iteration when obtaining the expected peak foundation rotation. Empirical equations are developed based on numerical time‐history analyses that provide an estimation of foundation residual deformations based on the foundation peak rotation. Additional complexities due to deformation within the foundation are discussed regarding how they influence the design and building performance. The design framework is complemented by a simplified analytical design procedure (i.e., hand calculations) to design building‐foundation systems. A design example is given for a six‐storey concrete wall building, which is analyzed by time‐history analysis to demonstrate the application and accuracy of the design procedure.

Section: Performance‐based Design Processmentioning

confidence: 99%

An integrated performance‐based design framework for building‐foundation systems

Millen

Pampanin

Cubrinovski

2020

“…The influence of foundation shape and embedment on the rocking motion of a structure, including settlement and uplift, has been studied also by centrifuge experiments. 20 This paper differs from the literature [17][18][19] in that it involves a fully 3D rather than an axisymmetric model. Also, the results are presented in a form convenient for practical applications.…”

mentioning

confidence: 93%

“…More recently, Fu compared the dynamic response of a structure supported by a hemispherical foundation with that of a 2D slice of it supported by a semi‐cylindrical foundation with the same radius and concluded that the 2D model generally produced a smaller amplitude response. The influence of foundation shape and embedment on the rocking motion of a structure, including settlement and uplift, has been studied also by centrifuge experiments …”

Section: Introductionmentioning

confidence: 99%

Correction factors for SSI effects predicted by simplified models: 2D versus 3D rectangular embedded foundations

Todorovska

Liang

2018

Summary The effects of soil‐structure interaction (SSI) are often studied using two‐dimensional (2D) or axisymmetric three‐dimensional (3D) models to avoid the high cost of the more realistic, fully 3D models, which require 2 to 3 orders of magnitude more computer time and storage. This paper analyzes the error and presents correction factors for system frequency, system damping, and peak amplitude of structural response computed using impedances for linear in‐plane 2D models with rectangular foundations, embedded in uniform or layered half‐space. They are computed by comparison with results for 3D rectangular foundations with the same vertical cross‐section and different aspect ratios. The structure is represented by a single degree‐of‐freedom oscillator. Correction factors are presented for a range of the model parameters. The results show that in‐plane 2D approximations overestimate the SSI effects, exaggerating the frequency shift, the radiation damping, and the reduction of the peak amplitude. The errors are larger for stiffer, taller, and heavier structures, deeper foundations, and deeper soil layer. For example, for a stiff structure like Millikan library (NS response; length‐to‐width ratio ≈ 1), the error is 6.5% in system frequency, 44% in system damping, and 140% in peak amplitude. The antiplane 2D approximation has an opposite effect on system frequency and the same effect on system damping and peak relative response. Linear response analysis of a case study shows that the NEHRP‐2015 provisions for reduction of base shear force due to SSI may be unsafe for some structures. The presented correction factor diagrams can be used in practical design and other applications.

“…During the past several decades, column damages under seismic shaking have occurred in numerous case histories that require expensive and time‐consuming retrofit efforts . To improve the seismic performance of columns, recent studies have investigated the effectiveness of designs using rocking foundations . These studies demonstrated that the ductility demand of columns can be reduced and seismic energy can be absorbed by the soils.…”

Section: Introductionmentioning

confidence: 99%

“…1,2 To improve the seismic performance of columns, recent studies have investigated the effectiveness of designs using rocking foundations. [3][4][5][6][7][8][9][10][11] These studies demonstrated that the ductility demand of columns can be reduced and seismic energy can be absorbed by the soils. Because of the geometric and material nonlinearity (eg, foundation uplift and soil failure), excessive permanent deformations may occur at the pivot locations of the supporting soils, which will significantly increase the vertical and lateral displacements of the structure.…”

Section: Introductionmentioning

confidence: 99%

Seismic responses of bridges with rocking column‐foundation: A dimensionless regression analysis

Zhang

Xie

2018

Summary Rocking column‐foundation system is a new design concept for bridges that can reduce overall seismic damage, minimize construction and repair time, and achieve lower cost in general. However, such system involves complex dynamic responses due to impacts and highly nonlinear rocking behavior. This study presents a dimensionless regression analysis to estimate the rocking and shaking responses of the flexible column‐foundation system under near‐fault ground motions. First, the transient drift and rocking responses of the system are solved numerically using previously established analytical models. Subsequently, the peak column drifts and uplift angles are derived as functions of ground motion characteristics and the geometric and dynamic parameters of column‐foundation system in regressed dimensionless forms. The proposed response models are further examined by validating against the numerical simulations for several as‐built bridge cases. It is shown that the proposed model not only physically quantifies the influences of prominent parameters, but also consistently reflects the complex dynamics of the system. The seismic demands of rocking column‐foundation system can be realistically predicted directly from structural and ground motion characteristics. This can significantly benefit the design of bridges incorporating this new design concept.