Outline

  • Abstract
  • Keywords
  • Nomenclature
  • 1. Introduction
  • 2. Problem Definition
  • 3. Finite Difference Model (static Analysis)
  • 3.1. Flac3d Model
  • 3.2. Load-Displacement Response
  • 3.3. V:h:m Failure Envelope
  • 4. Simplified Nsr Model
  • 4.1. Model Description
  • 4.2. Model Calibration
  • 4.2.1. Initial Stiffness
  • 4.2.2. Coupled Bearing Capacity
  • 4.2.3. Hard-Coded Shape Parameters
  • 5. Nsr Model Validation
  • 5.1. Soil-Structure Model in Dynamic Analysis
  • 5.2. Methods and Results
  • 6. Limitations of Nsr Model
  • 7. Conclusions
  • References

رئوس مطالب

  • چکیده
  • کلیدواژه ها
  • 1.مقدمه
  • 2.تعریف مسئله
  • 3.مدل تفاضل محدود (تحلیل استاتیک)
  • 1.3 مدل
  • 2.3 پاسخ بار-جابه جایی
  • 3.3 پوش گسیختگی V:H:M
  • 4.مدل NSR ساده شده
  • 1.4 توصیف (شرح) مدل
  • 2.4 کالیبراسیون مدل
  • 1.2.4 سختی اولیه
  • 2.2.4 ظرفیت باربری زوج
  • 3.2.4 پارامترهای شکل سخت-کد گذاری شده (رمزی)
  • 5.اعتبارسنجی مدل NSR
  • 1.5 مدل خاک-ساختار در تحلیل های دینامیک
  • 2.5 روش ها و نتایج
  • 6.محدودیت های مدل NSR
  • 7. نتیجه گیری

Abstract

This paper presents a simplified Nonlinear Sway-Rocking model as a preliminary design tool for seismic soil-structure interaction analysis. The proposed model is intended to capture the nonlinear load-displacement response of shallow foundations during strong earthquake events where foundation bearing capacity is fully mobilised. Emphasis is given to heavily-loaded structures resting on a saturated clay half-space. The variation of soil stiffness and strength with depth, referred to as soil non-homogeneity, is considered in the model. Although independent springs are utilised for each of the swaying and rocking motions, coupling between these motions is taken into account by expressing the load-displacement relations as functions of the factor of safety against vertical bearing capacity failure (FSv) and the moment-to-shear ratio (M/H). The simplified model has been calibrated and validated against results from a series of static push-over and dynamic analyses performed using a more rigorous finite-difference numerical model. Despite some limitations of the current implementation, the concept of this model gives engineers more degrees of freedom in defining their own model components, providing a good balance between simplicity, flexibility and accuracy.

Keywords: - - - -

Conclusions

A simplified Nonlinear Sway-Rocking model has been developed in this paper for nonlinear dynamic soil-structure interaction analysis. The proposed model is intended to simulate the nonlinear load-displacement response for the coupled sway-rocking behaviour of shallow mat foundations supporting heavily-loaded buildings under earthquake ground motions.

To simplify the model, the building is represented as an equivalent SDOF structure, whereas the soil-foundation system is replaced by an assemblage of springs and dashpots. While utilising independent springs to simulate each of the sway and rocking responses of the foundation, the coupling between the two motions is also accounted for by expressing the spring properties as a function of the load paths experienced by the foundation in the V:H:M space. Spring properties are controlled by the factor of safety against vertical bearing capacity failure FSv, the moment-toshear ratio M/H, and the failure envelope defining the bearing capacities of the foundation in the V:H:M space. The effect of soil non-homogeneity on the stiffness and capacity of the soil foundation system is also considered.

In order to identify the load-displacement responses and the coupled bearing capacities of the foundation, a series of static load-control and displacement-control finite-difference analyses were carried out by using the FLAC3D program. The simplified model, developed in the OpenSees platform, was then calibrated against results from the static finite-difference analyses. The effectiveness and efficiency of the proposed model was validated against results from dynamic analyses performed using a FLAC3D model by utilising two artificial input motions and one real earthquake acceleration record. The comparison of results predicted by both models demonstrates that the simplified model is capable of efficiently capturing the foundation load-displacement behaviour, including the maximum and residual displacements, with sufficient accuracy.

Although the proposed simplified model has some limitations, it is able to provide parameters necessary for preliminary design of buildings on weak soil while achieving a good balance between simplicity and accuracy. In addition, the concept of the model allows engineers to select appropriate model properties in accordance with specific site conditions.

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