Расчет здания с учетом взаимодействия сооружения с основанием (2017 г.)

Calculation of Buildings Considering Soil Interaction

Introduction to the Webinar

• The webinar will focus on building calculations with an emphasis on soil interaction, primarily using flat soil models and a brief look at three-dimensional models.

• The session is divided into two parts: a theoretical section led by Marina Sergeevna Busalova from the Moscow State University of Civil Engineering, followed by a practical part conducted by the speaker.

Structure of the Webinar

• Marina's presentation will last approximately 40 minutes, after which there will be a five-minute break before continuing with questions and answers. Participants are encouraged to ask questions throughout the session.

Overview of Soil Models

• The discussion will cover various mathematical descriptions of soil models, highlighting their advantages and disadvantages. Key models include:

• Winkler model and its modifications.

• Elastic linear deformable half-space model.

• Non-linear elastic-plastic models.

Detailed Examination of the Winkler Model

• The Winkler model is based on the hypothesis that reactive pressure from soil is proportional to deflection in corresponding points of the structure. This model is widely used due to its simplicity and clarity in engineering practice.

• In this model, vertical displacements at points where structures rest are equal to foundation settlements, leading to specific assumptions about movement along the Y-axis being negligible.

Assumptions in Winkler Model Analysis

• Three main assumptions guide this analysis:

1. Vertical displacements (deflections) correspond directly with foundation settlements at those points.

2. Height of sections considered small compared to their length allows for planar section hypotheses.

3. Settlement occurs only at force application points; adjacent areas experience no settlement despite applied loads, which raises concerns about accuracy in real-world applications.

Limitations and Critiques of the Winkler Model

• A significant critique arises from assumption three: it suggests uniform settlement under distributed loads across all affected areas, which does not reflect reality as settlements occur beyond load application zones as well. This limitation highlights that effective use requires conditions similar to water properties—low resistance against shear forces in soils enhances accuracy in modeling behavior under load conditions.

Modifications to Address Limitations

Understanding Modified Models in Soil Mechanics

Overview of the Modified Winkler Model

• The modified model addresses a significant limitation of the Winkler model by incorporating soil's distribution capacity without complicating the mathematical formulation.

• This two-parameter model generates effective transverse forces at foundation edges, which are free from constraints. Currently, software uses one variable coefficient for bed stiffness (C1), while C2 is set to zero.

Limitations and Applications of Simplified Models

• The modified Winkler models are flat models used when detailed soil reactions under structural loads are unnecessary.

• For scenarios requiring insight into ground behavior, more complex volumetric finite element models must be employed.

Elasticity Theory and Its Challenges

• Questions arise regarding the applicability of elasticity theory to soils since they do not behave as elastic bodies; stress-deformation relationships in soils are non-linear.

• Soil heterogeneity and anisotropy further challenge the assumptions made in elasticity theory, which typically considers materials as homogeneous and isotropic.

Conceptual Shift in Soil Modeling

• A shift in terminology has been proposed: instead of "medium" from elasticity theory, "formable medium" or "soil form" is suggested to better describe soil behavior under load.

• The deformation modulus varies based on determination methods and is not a constant elastic characteristic; it changes with increasing load.

Nonlinear Models for Complex Structures

• In designing critical structures, it's essential to account for soil properties over a wide range of stress and deformation where relationships become significantly nonlinear.

• Significant plastic deformations occur under large loads (e.g., multi-story buildings), necessitating modeling soil as a nonlinear deformable half-space.

Key Nonlinear Soil Models

• Nonlinear models like Mohr-Coulomb and Drucker-Prager are crucial for accurately representing soil behavior under moderate static loads.

• The Mohr-Coulomb model utilizes parameters such as cohesion (c) and internal friction angle (φ), determined through geotechnical investigations.

Three-Dimensional Stress States

• Transitioning to three-dimensional stress states involves using three equations that define yield conditions forming a hexagonal pyramid known as the Mohr pyramid.

Ground Models and Their Advantages

Advantages of the Model

• The model accommodates various types of soils, which is its primary advantage.

• For practical calculations, only normative characteristics of the physical-mechanical properties of soils are required, typically provided in engineering-geological reports.

Disadvantages and Challenges

• The model has significant drawbacks; particularly, numerical modeling reveals substantial issues with the piecewise linear surface representation of yield surfaces.

• To achieve more accurate results, this surface must be approximated by a smoother surface to avoid large calculation errors.

Research Developments in Soil Mechanics

Current Research Findings

• Active theoretical research is ongoing, leading to proposed approximations for the piecewise linear yield surface based on Coulomb's theory into a smooth yield surface.

• This new function incorporates invariants from the stress tensor: first invariant I_1, second invariant G_2, and third invariant G_3.

Understanding Failure Mechanisms

• The model does not specify when soil failure occurs; it can be illustrated using stress diagrams where stresses increase until they plateau indefinitely.

• At some point, soil loses its capacity to deform as indicated by principal stress conditions around pyramidal representations in stress space.

Transitioning to Drucker-Prager Model

Overview of Drucker-Prager Model

• Transitioning from Coulomb's model to Drucker-Prager involves analyzing complex nonlinear stressed-deformed states in soils through equations proposed by Kher and Gera.

• This equation includes both first and second invariants of the stress tensor along with positive constants for each point in principal stress space forming a conical yield surface.

Surface Comparisons

• The conical yield surface aligns with hydrostatic axes similar to Coulomb’s model, suggesting that one can approximate Coulomb's surfaces using Drucker-Prager criteria if their vertices coincide within principal stress spaces.

Parameter Relationships in Soil Models

Finding Dependencies

• To effectively describe the Drucker-Prager model while adhering to standard parameters derived from engineering geological surveys, relationships between constants and internal friction angles need identification.

Cases Analyzed

• Two cases were analyzed: one where a cone inscribed within a pyramid corresponds with specific relationships for angle alpha and another where a cone circumscribes around it yielding different dependencies on cohesion parameters.

Extended Criteria Development

Extended Drucker-Prager Criterion

• Kher and Gera developed an extended criterion incorporating additional parameters such as hydrostatic pressure expressed through deformation variables related to intensity tensors' second invariant.

Parameter Definitions

• Parameters include:

• R: Related to the third invariant of the stress tensor.

• T: A parameter dependent on intensity tensors.

• Beta (beta): Friction angle defined via internal friction data.

• D: Cohesion parameter influenced by internal friction angles derived from geological studies.(t = 1548 s)

This structured approach provides clarity on key concepts discussed throughout the transcript while ensuring easy navigation through timestamps for further exploration or review.

Understanding the Extended Coulomb Criterion

Overview of the Extended Coulomb Criterion

• The discussion begins with an introduction to the extended Coulomb criterion, highlighting its geometric representation involving a pyramid and a cone that describes the flow surface around it.

• A significant limitation of this criterion is noted: all flow surfaces are smooth except for one point at the apex of the cone. This necessitates modifications to address this shortcoming.

Modifications to Address Limitations

• The conversation shifts to a new model gaining traction in Russia, referred to as the "tent model" of soil. It treats soil behavior as an elastoplastic strengthening material with a flow function similar to previous models.

• Two main features introduced in this modified approach include closing the flow surface and utilizing porosity as a strengthening parameter for determining subsequent positions of the flow surface in stress space.

Development of New Models

• Under Roska's guidance, a new model called "Come Clay" was developed in 1971, which later evolved into what is now known as the tent model.

• These models can be applied across various materials, including rocks and soils. However, they face challenges related to defining initial parameters and describing pore pressure during undrained conditions.

Transitioning to Practical Applications

Introduction by Alexey Kolesnikov

• Alexey Kolesnikov takes over, indicating that questions will be addressed later according to webinar regulations. He prepares to delve into practical case studies using software tools.

Software Demonstration: Lira

• Kolesnikov opens Lira software, preparing to create a new task focused on simple cases involving elastic foundations through single wells before progressing to well fields.

• He announces updates regarding version 102 R2 of Lira software available for download from their website, emphasizing improvements in graphical interface and functionality.

Creating Structural Models

• A basic structural design is created within Lira using simple soil models for verification calculations; he emphasizes familiarity with all tools available within Lira.

• Kolesnikov sets up boundary conditions for loading scenarios while noting that multiple loadings will be considered in more complex structures later on.

Load Analysis Procedures

• He discusses measuring dimensions necessary for calculating foundation coefficients and highlights functions within Lira for measuring linear sizes and contours effectively.

• Various methods for accounting elastic foundations are presented; manual input or data from subcontractors can be utilized depending on circumstances surrounding coefficient acquisition.

Finalizing Load Calculations

Analysis of Load Parameters in Foundation Design

Overview of Load Analysis

• The discussion begins with the removal of certain rods from the analysis, indicating a focus on load parameters.

• A total load of 300 tons is mentioned, emphasizing the importance of accurately summing loads in foundation design.

Parameter Settings for Foundations

• Various formulas and regulatory documents are referenced, highlighting the need to select appropriate parameters based on geological conditions.

• The ability to edit layer thicknesses and switch between layers is discussed, showcasing flexibility in modeling different soil strata.

Soil Properties and Deformation Modules

• The distinction between elastic modulus and deformation modulus for soils is clarified, stressing that these should be defined according to specific geological data.

• Recommendations suggest multiplying deformation modules by specific coefficients based on regulatory guidelines for dynamic tasks.

Documentation and Exporting Results

• Emphasis is placed on documenting results effectively; outputs can be saved in Word or Excel formats for further analysis.

• The speaker notes that various methods exist within regulatory documents for calculating coefficients related to soil interaction.

Application of Coefficients in Calculations

• Results from selected methods are applied to foundation plates, demonstrating how coefficients influence calculations.

• Discussion includes resetting certain parameters as advised by laboratory recommendations before running calculations.

Observations on Settlement and Interaction

• The concept of settlement due to varying loads across a foundation plate is introduced, indicating real-world complexities in structural interactions.

• A simple method for accounting interactions between structures and foundations using single boreholes is presented.

Advanced Modeling Techniques

• Adding multiple boreholes allows for more accurate modeling when dealing with columnar foundations or piles.

• It’s noted that bed coefficients must vary across different sections of a foundation plate due to uneven loading conditions.

Realistic Load Distribution Considerations

• An example illustrates how uniform load assumptions can lead to inaccuracies; actual loads differ significantly at points like columns or walls.

Practical Application in Software Modeling

• Transitioning into software use, the speaker prepares an existing model rather than creating one from scratch to save time during demonstrations.

Managing Vertical Movements in Structural Modeling

Importance of Limiting Movements

• The necessity to restrict vertical movements is emphasized, as it relates to the foundational stability and integrity of structures.

• A connection between vertical movements and geometric changes in the system is established, highlighting the need for controlled modeling.

Initial Steps in Foundation Plate Design

• The process begins with assigning parameters to the foundation plate, indicating that various fragmentation methods can be applied based on cross-sections.

• Introduction of a context menu feature in the software allows users to customize their workspace with frequently used tools for efficiency.

Context Menu Features

• Users are encouraged to personalize their context menus further, enhancing usability by adding relevant functions tailored to individual needs.

• The software retains previous settings upon reopening, which aids in maintaining continuity during modeling sessions.

Transitioning Between Modules

• Transitioning from data modeling to calculation results preserves fragmentation settings, allowing users to work seamlessly without needing to redraw models.

Calculating Load Coefficients

• To refine soil model coefficients for plates, calculations require knowledge of load and area specifics related to the foundation.

• Area measurements are crucial; users must accurately assess contours for effective load distribution analysis.

Load Analysis Techniques

• Manual summation of loads is necessary unless automated options are utilized within the software for efficiency.

• An example calculation illustrates how total loads (e.g., 261 tons from wind pressure on a small structure) can be divided by area for preliminary assessments.

Assigning Soil Parameters

• After calculating initial load values (e.g., pz = 1.9), these figures are assigned back into the model for further refinement.

Utilizing Geological Data

• The program's load analysis focuses only on visible elements within the calculation model; hidden elements must be revealed for comprehensive analysis.

Finalizing Load Values

• A calculated value of pz = 7.8 emerges after dividing total loads by foundation area, serving as an initial approximation before adjustments.

Setting Up Boreholes

• Users create boreholes within their models using intuitive navigation tools that allow zooming and moving through different layers effectively.

Customizing Geological Elements

Configuring Soil Layers in Ground Modeling

Initial Setup of Soil Properties

• The process begins with filling out parameters such as moisture content, fluidity, and porosity coefficients for the soil layers.

• Users can expand settings for better visibility and adjust the depth of various soil types, starting with fill sand at a depth of 1 meter.

Adding Different Soil Types

• The next layer is dusty sand; if not available, users can select loamy sand with a specified thickness of 2 meters.

• Users are encouraged to utilize the cross-section feature to verify the accuracy of their well assignments while creating the soil model.

Visualizing Soil Layers

• Cross-sections can be generated through wells to visualize different soil characteristics, which are color-coded based on user selections.

• Multiple wells can be created to ensure a heterogeneous model both horizontally and vertically.

Adjusting Well Parameters

• A second well is configured with varying depths: loam at 4 meters followed by clay up to 10 meters, ensuring diverse layer representation.

• Cross-sections allow users to observe the arrangement of layers; adjustments can be made for clarity in visual representation.

Finalizing Model Configuration

• Additional wells are copied and modified for varied depths and layer thicknesses, resulting in four distinct wells for foundation modeling.

• Absolute elevation marks can be set within well configurations according to project specifications.

Calculation Methods and Efficiency Improvements

• The software offers multiple calculation methods compliant with local standards (e.g., SP or Ukrainian norms), enhancing computational speed significantly compared to previous versions.

• Users can view calculated coefficients quickly after selecting their foundation slab within the program interface.

Addressing User Queries

• Questions regarding program capabilities are addressed; it includes settings for stiffness parameters relevant to specific tasks.

• Previous task setups retain all necessary stiffness data, allowing users to revisit earlier configurations without loss of information.

Water Saturation Indicators

Water Saturation and Soil Parameters

Understanding Water Saturation in Soil

• The water saturation of the soil is considered in the parameters, indicated by a column labeled "water" in the table. Checking this box adjusts calculations accordingly.

Coefficients Calculation

• The coefficients for beddings have been calculated and visualized on an elastic foundation, showing distribution across the area. The coefficient c_12 remains consistent throughout.

Adjusting Coefficients

• There is a feature to modify values without recalculating bedding coefficients from scratch. By multiplying them with a corresponding factor, adjustments can be made efficiently.

Model Calculation and Results

Initial Model Assessment

• To determine p_z , initially set at 7.8, it must be recalculated as it varies at different points within the model.

Static Analysis of Structures

• A static analysis of the structure has been performed, with results automatically transferred back into the foundational plate data for further evaluation.

Visualizing Results and Transformations

Load Combinations

• The load combinations are switched to analyze variations in r_z . This value fluctuates across different points but needs to be consistently applied as p_z .

Transformation Process

• To apply r_z as p_z , results are visualized first before transforming them into original data formats using specified coefficients for various elements.

Iterative Calculations and Adjustments

Evaluating Changes in Load

• After applying transformations, changes in load percentages and shifts in center of gravity are assessed to determine when to cease recalculating bedding coefficients.

Returning to Original Data

• Once adjustments are made, returning to original data allows for verification without needing to reselect previously highlighted components.

Finalizing Bedding Coefficient Calculations

Recalculating with New Parameters

• With updated parameters reflecting varying p_z , new bedding coefficients need recalculation which may require multiple iterations depending on structural complexity.

Speed of Computation

• Despite increased complexity due to varied p_z , computations remain efficient even with four boreholes involved.

Convergence on Final Values

Assessing Stability of Results

• After several iterations, stability is observed in results; minor changes indicate that further refinement may not yield significant improvements.

Confidence in Structural Interaction Analysis

• Multiple recalibrations allow confidence that interactions between structures and foundations have been adequately accounted for during analysis processes.

Comparative Analysis Using Different Methods

Visual Representation of Bedding Centers

• A visual representation will be created showcasing bedding centers based on previous calculations using screen capture methods for clarity.

Method Comparison Outcomes

Analysis of Vertical Displacement and Soil Characteristics

Overview of Vertical Movement Measurement

• Discussion on vertical displacement measurement methods, specifically focusing on a particular attachment used for assessing vertical movement.

• Emphasis on the importance of foundational geometry, load characteristics, and soil properties in calculating bed coefficients.

Calculation Process and Results

• Explanation of the calculation process involving load combinations and resulting displacements; significant differences in results are noted.

• Visual representation of results is discussed, with plans to include images in reports for better understanding.

Report Generation Features

• Introduction to report generation features within the software, including options for inserting tables and images into reports.

• Clarification sought regarding soil characteristics—whether to use specific or average values based on geological data provided by geologists.

Soil Properties and Recommendations

• Insight into laboratory characteristics versus recommended parameters from geologists; importance of using reliable data sources emphasized.

• Guidance provided on selecting Poisson's ratio from standards if not supplied by geologists; different ratios apply depending on soil type.

Advanced Calculations and Modeling Techniques

• Discussion about lateral pressure calculations without automated tools; manual application of known formulas suggested for estimating loads.

• Mention of upcoming webinar recordings available online for further learning opportunities related to these topics.

Three-Dimensional Soil Modeling Insights

• Exploration of three-dimensional modeling capabilities within the software, highlighting nonlinear material models as discussed previously.

• Comparison between initial calculations and updated models showing significant differences in settlement outcomes due to varying bed coefficients.

Conclusion on Settlement Differences

• Summary of findings indicating that settlement can differ significantly based on input parameters; examples given show nearly double the displacement under certain conditions.

Nonlinear Analysis of Structural Elements

Overview of Nonlinear Problems

• The discussion begins with the complexity of nonlinear problems in structural analysis, emphasizing that traditional linear assumptions do not apply. Instead, it involves modules of elasticity for three-dimensional finite elements.

Calculation Duration and Results

• The speaker notes that nonlinear calculations take a significant amount of time, citing a specific example where the calculation lasted 13 minutes. They suggest reviewing the results instead of performing live calculations to save time.

Stress Distribution Analysis

• A focus is placed on analyzing stress distribution within foundational soil during nonlinear loading scenarios. The speaker demonstrates how to assess real stress distributions effectively.

Use of Modern Methods in Calculations

• It is highlighted that modern methods allow for comprehensive assessments beyond traditional coefficients, enabling detailed evaluations of soil behavior and structural responses.

Evaluation Techniques for Foundation Slabs

• The speaker discusses evaluating foundation slabs using filters to isolate specific components, allowing for an in-depth analysis of internal forces and moments within the structure.

Future Webinars and Topics

Upcoming Webinar Details

• Information about an upcoming webinar scheduled for April 23rd is shared, focusing on large-span structures. Key topics will include checks on limit states and local stability assessments.

Literature Recommendations

• Questions regarding recommended literature are addressed; participants can request a list via email. Suggested authors include Voznesensky and Tyapin Tsitovich.

Software Version Updates

Enhancements in Software Versions

• Discussion includes improvements made in version 102 compared to version 96, particularly regarding new analytical strength theory methods which were not available previously.

Transitioning Between Software Versions

• Participants are encouraged to evaluate performance differences between software versions when transitioning from older versions while considering updated methodologies as per current standards (SNiP).