What all our users have been waiting for for a long time has finally come true: in PC LIRA 10.6 a new finite element 57 has appeared - “Pile”, implementing the provisions of SP 24.13330.2011 “Pile foundations”. The appearance of this final element significantly expands the capabilities of the software package when calculating buildings on pile foundations, allowing such calculations to be made faster and more accurately. If previously PC LIRA users had to model 56 FE piles, and their stiffness was calculated either in third-party programs or manually, now the program will do everything; you just need to enter the initial data.
Implementation
The following design situations are implemented in PC LIRA 10.6:
Single pile (clauses 7.4.2 – 7.4.3, SP 24.13330.2011);
Pile bush (clauses 7.4.4 – 7.4.5, SP 24.13330.2011);
Conditional foundation (clauses 7.4.6 – 7.4.9, SP 24.13330.2011);
The following assumptions are made:
It is conventionally accepted that the load-bearing capacity of the pile is ensured; - The soil on which the pile rests is considered as a linearly deformable half-space; - The following relation is fulfilled: (l – length, d – reduced diameter of the pile shaft).
The following types of piles have been implemented (Fig. 1):
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Shell;
Rectangular;
Square.
In this case, the end of the pile can be either pointed or club-shaped.
Rice. 1. Types of piles. PC LIRA 10.6
Calculation of a single pile
For each pile, be it single or as part of a bush/conditional foundation, the following parameters are set (Fig. 2):
- Pile length
- Number of split sections - the larger this number, the more accurate the calculation is.
- The modulus of elasticity of the trunk is a characteristic of the material from which the pile is made;
- Poisson's ratio of the material;
- Depth from the surface of the earth, at which the resistance of the soil along the lateral surface is not taken into account (under seismic influences).
- Volumetric weight of the pile material.
Rice. 2. Setting the parameters of the pile. PC LIRA 10.6
Calculation parameters for a single pile are set by clicking on the “Calculate the stiffness of a single pile” button (Fig. 3).
Rice. 3. Parameters for calculating the rigidity of the pile. PC LIRA 10.6
In this case, the lateral coefficient of the bed on the surface of the pile is calculated by the formula:
Where K is the proportionality coefficient adopted depending on the type of soil surrounding the pile (Appendix B, table B.1); γс - coefficient of soil operating conditions. For a single pile γс =3.
Calculation of the settlement of a single pile is carried out in accordance with SP 24.13330.2011: for a pile without widening according to clause 7.4.2 a, for a pile with widening according to clause 7.4.2 b.
Calculation of pile bush
To create a pile bush, you need to call the “Pile groups” command, which is located on the toolbar or in the “Assignments” menu item. To define a pile bush, you need to select a group of piles that will be included in the bush and click on the “Add pile bush” button (Fig. 4).
Rice. 4. Setting up a pile bush. PC LIRA 10.6
The method for calculating the pile bush corresponds to clauses 7.4.4 – 7.4.5 SP 24.13330.2011. In this case, the rigidity characteristics of the pile are calculated automatically in the Soil Editor, for which the latter added four columns to the table for specifying the physical and mechanical characteristics (Fig. 5):
- Type of soil for a pile foundation (Table B.1 SP 24.13330.2011). Used to interpolate “K” values from a given soil fluidity index “IL” or porosity coefficient “e”.
Flow index “IL” for silt-clay soils;
Porosity coefficient “e” for sandy soils;
Proportionality coefficient “K”, which can be set numerically or interpolated by selecting soil from the “Soil type for pile foundation” column;
Rice. 5. Table of physical and mechanical characteristics of IGE. PC LIRA 10.6
In the calculation parameters (Fig. 6), a new tab has appeared - “Piles”, in which the parameters necessary for the calculation are indicated:
k - coefficient of depth under the heel (clause 7.4.3 SP 24.13330.2011);
γ c - coefficient of operating conditions for calculating piles for the combined action of vertical and horizontal forces and moment (clause B.2, Appendix 2, SP 24.13330.2011);
γ с а - coefficient of soil compaction when immersing a pile, is taken into account to reduce the proportionality coefficient K when working piles as part of a bush (clause B.2, Appendix 2, SP 24.13330.2011).
Rice. 6. Pile calculation tab. PC LIRA 10.6
Calculation of the settlement of the Pile Bush is carried out in accordance with clauses 7.4.4 - 7.4.5 SP 24.13330.2011. When calculating the settlement of a group of piles, their mutual influence is taken into account. The calculation of the soil bed coefficient Cz on the side surface of the pile, taking into account the influence of piles in the bush, is carried out as for a single pile, but the proportionality coefficient K is multiplied by the reduction factor αi.
The mutual influence of settlement of pile clusters is taken into account in the same way as when calculating conditional foundations. Calculation of the stiffness of piles in pile bushes is carried out using the same method as for single piles, but taking into account their mutual influence both in the bush and between the bushes.
Calculation of conditional foundation
Setting a conditional foundation from a pile bush differs only in that the “Conditional foundation” item is selected in the “Pile Group”. It is also necessary to additionally specify Acf - the area of the conditional foundation and the method of arrangement of piles - ordinary or chessboard.
Geological conditions, as well as physical and mechanical characteristics of foundation soils, are specified in the Soil Editor.
The total settlement of the foundation pile field is determined by the formula:
Where: - settlement of the conditional foundation,
Additional settlement due to pushing piles at the level of the base of the conditional foundation,
Additional settlement due to compression of the pile shaft.
Additional settlement due to compression of the pile shaft is calculated using the formula:
Finding the settlement of a conditional foundation, as well as calculating the mutual influence of groups of piles (including pile bushes) can be done by analogy with slab foundations using 3 different methods:
- Method 3 - modified Pasternak model.
Method 1 - Pasternak's foundation model,
Method 2 - Winkler-Fuss foundation model,
If the calculation is carried out in the Soil module, it is necessary, as for the calculation of plate elements, to assign an initial load to the piles, which can then be refined using the function of converting the results into initial data (Fig. 7). This is done in the “Elastic Foundation” command.
Rice. 7. Assigning an initial load to the piles. PC LIRA 10.6
After the calculation in the Soil module, by calling the “Model Analysis” function, you can track settlements, stiffness, and other parameters of piles and soil (Fig. 8).
Fig.8. Visualization of calculations. PC LIRA 10.6
Thus, we examined a new function that appeared in PC LIRA 10.6, which allows you to calculate buildings on pile foundations.
State educational institution of higher education
vocational education
St. Petersburg State Polytechnic University
Faculty of Civil Engineering
Department of Technology, Organization and Economics of Construction
Design of a residential building made of monolithic reinforced concrete in collaboration mode Allplan - SCAD
Guidelines for course design
Working version from 03/10/2006 02:57
all comments and suggestions are accepted at [email protected]
Saint Petersburg
Introduction........................................................ .............................................. 5
1. Initial formation of an object model in Allplan.... 6
1.1. Features of monolithic buildings................................................................... ................... 6
1.2. 3D model of an object in Allplan.................................................... ........................... 6
1.2.1. Building a parametric model in Allplan.................................................... 6
1.2.2. Possibility of exporting from AutoCAD.................................................... ................ 6
1.2.3. Features of building a model in Allplan for subsequent calculations 7
2. Exporting a model from Allplan to FORUM.................................................... 8
2.1. Exporting a model from Allplan.................................................... .................................. 8
2.2. Model control in the FORUM.................................................... ............................. 9
2.3. Model control in SCAD................................................................... ............................... 10
2.4. Preparing the model for calculation.................................................... .......................... 10
2.4.1. Aligning Axes for Voltage Output.............................................................. 10
2.4.2. Assignment of connections in nodes................................................................. .......................... 10
2.4.3. Trial calculation................................................... .......................................... 10
3. Specifying impacts and loads.................................................... 11
3.1. Types of impacts and loads................................................................. ......................... eleven
3.2. Constant loads........................................................ ....................................... eleven
3.2.1. Self-weight of load-bearing structural elements.................................... 12
3.2.2. Load from enclosing walls.................................................... ................... 12
3.2.3. Load from interior partitions and from surface (area) materials and elements of building structures................................................... ................. 12
3.2.4. Backfill soil pressure.................................................................... .......... 12
3.3. Long-term loads........................................................ ...................................... 12
3.3.1. Loads from people, animals, equipment on floors.................................. 12
3.3.2. Snow loads........................................................ ...................................... 12
3.4. Short-term loads........................................................ ............................ 13
3.5. Special loads........................................................ ............................................... 13
3.6. Load combinations................................................... .......................................... 13
4. Loads, load cases, their combinations (combinations) in SCAD 14
4.1.1. Loads and load cases, their combinations and combinations in SCAD.................................... 14
4.1.2. Entering loads and load cases.................................................... ........................ 14
4.1.3. Design combinations of forces, design combinations of loads.................................. 14
5. Design and calculation of foundations........................ 15
5.1.1. Construction of the foundation................................................... .................. 15
5.1.2. Load-bearing capacity of hanging piles.................................................... .......... 16
5.1.3. Longitudinal stiffness of piles................................................... ....................... 16
6. Calculation of the load-bearing frame of the building and its elements in SCAD for strength and stability.................................... ................................. 18
6.1. Movements........................................................ ........................................................ .. 18
6.1.1. Rules for signs for movement.................................................................... ............. 18
6.1.2. Motion analysis................................................................ .................................. 18
6.2. Checking the overall stability of the building................................................................... ......... 18
6.3. Efforts and tensions......................................................... ........................................ 18
6.3.1. Rule of signs for efforts (stresses)................................................... .... 18
6.3.2. Analysis of forces and stresses................................................... ....................... 19
7. Exporting the results of selecting reinforcement in a slab to Allplan and subsequent reinforcement.................................................... ............................ 20
8. List of sources used.................................... 21
8.1. Regulatory materials........................................................ ........................... 21
8.2. Literature................................................. ........................................................ ....... 21
The guidelines are intended for students of construction specialties at universities, as well as for students of advanced training courses in the field of “Construction”.
In the methodological instructions, the design of a multi-storey monolithic building is explained using the example of a civil building being erected in St. Petersburg, with a foundation on a pile foundation made of driven or bored hanging piles and a slab grillage.
The project is carried out in accordance with the architectural design assignment, technical specifications for structural design and current SNiP.
During the design process, a space-planning and structural solution for a multi-storey building is developed, a design scheme and calculation method are selected and calculations of the reinforcement of elements of a monolithic structure are performed, working documentation is generated (for some of the building elements), estimate calculations are performed, a calendar plan is developed, and an explanatory note is drawn up.
The drawings include plans of the main non-repeating floors, a sectional diagram, facade diagrams, and reinforcement drawings.
Currently, various building designs are used in construction. Of these, monolithic buildings are increasingly used.
The spatial stability of the building is ensured by the rigidity of the building frame, which consists of a system of load-bearing building elements: longitudinal and transverse walls, monolithic reinforced concrete floors that work like hard drives.
For multi-storey residential buildings, floors and load-bearing walls have small thicknesses (from 130 mm). The floors have a complex configuration in plan, due to the presence of a large number of irregularly located balconies, bay windows, loggias, and openings; Within the premises, the floors are usually beamless and capitalless.
Enclosing non-load-bearing walls are usually supported floor by floor on the edge of the floor.
To ensure an open layout, vertical load-bearing walls inside apartments or civil premises are replaced with columns, pylons, or made with wide openings. Over wide openings in the load-bearing wall, hidden beams and lintels are made in the form of reinforcement reinforcement.
The foundation in most cases is piled with a slab grillage, or slab-pile.
The calculation of a monolithic building comes down to analyzing the joint work of all load-bearing elements: and the foundation with a soil foundation.
1.2.1. Building a parametric model in Allplan
Design begins with building a 3D model in the Allplan construction design program (http://www.nemetschek.ru/products/allplan.html).
The model in Allplan must contain data on the material of each structural element of the building (which determines their rigidity, thermal engineering, cost and other characteristics that are used later in the design). This data is entered initially at the stage of creating the model, or after importing plans from AutoCAD.
In the course project, as a first approximation, it is recommended to set:
As a material for floors and load-bearing walls, concrete with strength class B25;
Class AIII fittings,
The thickness of load-bearing walls and ceilings is 160 mm.
The final choice of thicknesses, classes of concrete and reinforcement is determined based on the calculation results.
All graphic materials of the project (plans of the main non-repeating floors, drawings or section diagrams, drawings or facade diagrams) are built only based on a 3D model of the object in Allplan. This ensures internal consistency of materials.
1.2.2. Ability to export from AutoCAD
If architectural solutions are specified in the form of 2D floor plans in AutoCAD, then it is advisable to import them and build (“raise”) a 3D model based on them. At the same time, in AutoCAD it is necessary to simplify the site plan as much as possible, leaving only those elements (walls, partitions) that need to be transferred to Allplan to create the model (as a rule, it is enough to turn off unnecessary layers), and resave the AutoCAD file in .dxf format. Data import from AutoCAD to Allplan is carried out in the menu File/Import/Import/Import data from AutoCAD .
1.2.3. Features of building a model in Allplan for subsequent calculations
The Allplan model of the design object, which is exported for calculations in SCAD, must be constructed with special care. Particular attention should be paid to the joints of walls and ceilings.
To make the task easier in educational projects, it is highly recommended to use the following techniques:
Work with the grid turned on, snapping to the grid turned on (it is recommended to set the grid step along the x and y coordinates to 300 mm);
Create coordination axes and load-bearing elements only with reference to grid nodes;
Create all load-bearing walls in the “thickening at the center” mode;
Create floors snapped to a grid node at the intersection of walls,
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and not tied to the corner of the walls;
Using the dynamic panel,
select a mode to limit the possibility of drawing only horizontal and vertical lines;
Replace circular arcs and indirect lines in plan with straight line segments.
These techniques ensure that the model is transferred from Allplan to SCAD with minimal distortion.
To transfer a model from Allplan Junior to SCAD, you need to download (if this file is not on the installation disk) and install the transfer file test.exe. From Allplan to SCAD (www.scadgroup.com) you should transfer the architectural (not formwork) model, and only the load-bearing elements. The model is transferred to the FORUM preprocessor. The model is formed by pressing the button with the image of the SCAD symbol (stylized red letter S) on the toolbar.
To use the SCAD export function, this button must first be placed on some Allplan toolbar. For this:
Launch Allplan
Go to menu "View" -> "Toolbars" -> "Customize"
Drag the "SCAD" symbol to the desired toolbar
Click on the "Close" button.
After starting to export the model, a dialog box appears Save as…, which specifies the name of the project file with the extension opr. Then the “Manage Data Export to SCAD” window appears. In it you need to set the parameter for snapping walls along their axes and set the automatic convergence of walls and floors. Based on the data in the “Export Results” window, it is recommended to check the completeness of the data transfer to SCAD. It is advisable to check the number of transferred walls, floors, columns, and beams with those available in the Allplan model.
In the FORUM, it is necessary to check the correctness of the model formation and, if necessary, adjust it. Control is performed by the function Model control on the tab Control, as well as visually.
During visual inspection, you should check the verticality and horizontality of the elements and from the faces, the coincidence of the nodes of the FORUM model at the points where the elements meet. If there is a discrepancy or deviation of the nodes of the FORUM model, “move the nodes in a given direction” on the tab Operations with nodes .
The following is an example of transferring to FORUM a joint at right angles between two monolithic walls covered with a monolithic ceiling. In the first case (on the left), the floor was created, as we recommend, with reference to the nodes of the Allplan grid, in the second (on the right) - with reference to the outer corner of the walls.
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The right figure shows the consequences of not matching the floor to the Allplan grid nodes. In FORUM, two nodes of the FORUM model are created (instead of one node): a wall junction node and a floor corner node.
Then on the tab Scheme The SCAD project is generated (model export). At this stage, the steps of dividing the model into finite elements are specified. For an educational project, we recommend an initial subdivision step of 2 m, thickening of the meshes under the columns and a minimum area of the processed element of 0.2 m.
When generating a SCAD project, as can be seen in the figures below, in the second case, a “cornice” of small finite elements is created from the FORUM model. These elements distort the model and can be a source of errors in SCAD calculations.
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A detailed description of the operation of the FORUM preprocessor is available in the book: SCAD Office. Computer complex SCAD: Textbook / V.S. Karpilovsky, E.Z. Kriksunov, A.A. Malyarenko, M.A. Mikitarenko, A.V. Perelmuter, M.A. Perelmuter. - 592 pages
In SCAD, visual control of the model is performed, express control of the model on the tab Control, removing duplicate stiffness types (tab Purpose), merge matching nodes, and merge matching items (tab Nodes and Elements).
If necessary, the nodes are aligned vertically and horizontally.
2.4.1. Aligning Axes for Voltage Output
During the initial construction of the design scheme, each finite element has its own coordinate system.
It is necessary to specify axes for calculating element stresses that are different from the local coordinate system of the element (on the tab Appointments). This is especially important when it is intended to select reinforcement.
2.4.2. Assignment of connections in nodes
Boundary conditions for the model are specified in the form assignment of connections in nodes. For example, in the preliminary calculation of a typical floor with a floor, it is assumed that it will be rigidly supported on the underlying structures. This support is modeled by prohibiting all six degrees of freedom of the lower nodes of the floor walls. In other words, connections along x, y, z, Ux, Uy, and Uz are superimposed on the nodes.
2.4.3. Trial calculation
In order to detect errors in the model, it is recommended to make a trial calculation. To do this, you need to set some kind of load. The easiest way is to set the load from the self-weight of the structures, which is generated automatically. After this, a trial linear calculation is carried out and the calculation protocol is analyzed. If errors are found, they should be corrected by correcting the model in Allplan.
If there are no errors, you should proceed to specifying impacts and loads.
2.4.4. Checking the model as it is built
The construction of a model usually begins with the monolithic walls of a typical floor. The walls of a typical floor are transferred to the Forum, where the absence of errors (mismatched nodes, etc.) is checked.
After the construction of the floor covering the walls of a typical floor, the floor and monolithic walls are transferred to the Forum and further to.
Based on the results of the calculation in SCAD (assuming its rigid support on the underlying structures), the configuration of the walls is specified, ensuring reasonable deflections of the floor slab.
Then openings are made in the slab for the stairs and elevators. The quality of the openings is controlled by transmitting only the ceiling without walls to the Forum.
SNiP 2.01.07-85* “Loads and impacts” describes in detail the process of specifying loads. Let us illustrate it using the example of a monolithic residential building being erected in St. Petersburg.
The calculation begins with specifying loads in accordance with SNiP 2.01.07-85* “Loads and impacts” and GOST 27751-88 “Reliability of building structures and foundations. Basic provisions for calculation."
Building structures and foundations should be calculated using the limit state method. Limit states are divided into two groups.
The first group includes limit states that lead to complete unsuitability for use of structures, foundations (buildings or structures as a whole) or to a complete (partial) loss of the load-bearing capacity of buildings and structures as a whole;
The second group includes limit states that impede the normal operation of structures (foundations) or reduce the durability of buildings (structures) compared to the intended service life.
When designing, one should take into account the loads arising during the construction and operation of structures, as well as during the manufacture, storage and transportation of building structures.
The main characteristics of loads are their standard values. A load of a certain type is characterized, as a rule, by one standard value.
For loads from people, animals, equipment on the floors of residential, public and agricultural buildings, from bridge and overhead cranes, snow, temperature and climatic influences, two standard values are established: complete And reduced(introduced into calculations if it is necessary to take into account the influence of load duration, endurance testing and in other cases specified in the design standards for structures and foundations).
Standard load values are determined:
for loads from its own weight - according to the design values of geometric and design parameters and density;
for atmospheric loads and impacts - according to the highest annual values corresponding to a certain average period of their excess;
for technological static loads (for example, from equipment, devices, materials, furnishings, people) - according to the greatest expected ones.
Possible deviation of loads in an unfavorable (more or less) direction from their standard values is taken into account load reliability factors. The values of the coefficients may be different for different limit states and different situations. Design load value should be defined as the product of its standard value and the load safety factor corresponding to the limit state under consideration.
Depending on the duration of the load, one should distinguish between permanent and temporary (long-term, short-term, special) loads.
a) the weight of parts of structures, including the weight of load-bearing and enclosing building structures;
b) weight and pressure of soils (embankments, backfills), rock pressure.
The forces from prestressing remaining in the structure or foundation should be taken into account in calculations as forces from permanent loads.
3.2.1. Self-weight of load-bearing structural elements
The self-weight of load-bearing structural elements was formed in automatic SCAD mode based on the volumetric weight and rigidity characteristics of the elements’ sections. For all reinforced concrete elements, take the load safety factor = 1.1.
3.2.2. Load from boundary walls
The load from the enclosing walls, as a linear load (t/m) along the perimeter of one floor, was determined from the volumetric weight of the enclosing wall and the weight per unit area of the cladding. Load safety factors for the weight of building structures are assumed to be equal to 1.3.
3.2.3. Load from interior partitions and from surface (area) materials and elements of building structures
Loads of horizontally distributed surface (area) materials and elements (screeds, backfill, waterproofing, inverse roof “pie”, etc.) of building structures are conveniently determined in the VeST program (http://www.scadgroup.com/prod_vest. shtml).
The total weight of interior partitions per floor is determined in Allplan. Usually this weight is taken into account as a load evenly distributed on the floor.
Load reliability factors for the weight of building structures should be taken according to table 1, clause 2.2 of SNiP 2.01.07-85*. The load should be applied to the horizontal disc of the floor.
3.2.4. Backfill soil pressure
We will take into account the pressure of backfill soils along the outer contour of the building on the walls of buried rooms as a linear distribution in height. Load safety factors t for the weight of the backfilled soils, take equal to 1.15.
3.3.1. Loads from people, animals, equipment on floors
The payload from people and equipment is assumed to be uniformly distributed over the area of the premises and applied to the floor slabs. The value of the standard load is taken according to SNiP 2.01.07-85*.
Reducing coefficients of combinations y A and y n are accepted in accordance with paragraphs. 3.8 and 3.9 SNiP 2.01.07-85*.
3.3.2. Snow loads
All structures are developed under the influence of snow zoning loads for St. Petersburg (snow region III).
The total calculated value of the snow load on the horizontal projection of the coating should be determined using the formula
where S g is the calculated value of the weight of snow cover per 1 m 2 of the horizontal surface of the earth, taken in accordance with clause 5.2 of SNiP 2.01.07-85* equal to 180 kg/m 2 ;
m is the coefficient of transition from the weight of the snow cover of the ground to the snow load on the cover, taken in accordance with paragraphs. 5.3 - 5.6 SNiP 2.01.07-85*.
In many cases, the VeST program (http://www.scadgroup.com/prod_vest.shtml) included in SCAD Office can be used to determine the estimated snow load value.
The transition to a load with a reduced standard value is determined by multiplying the full standard value by a factor of 0.5.
From the complete list of short-term loads (see clause 1.8 of SNiP 2.01.07-85*) we take into account:
Loads from people and equipment on floors with full standard values;
Snow loads with full standard value;
Wind loads.
Wind loads for wind zoning of St. Petersburg will be taken into account for wind region II, terrain type B or C, standard wind pressure 30 kg/m 2.
Wind load is calculated using the VeST program (http://www.scadgroup.com/prod_vest.shtml), which is part of SCAD Office.
Special loads, namely:
a) seismic impacts;
b) explosive effects;
c) loads caused by sudden disruptions in the technological process, temporary malfunction or breakdown of equipment;
d) impacts caused by deformations of the base, accompanied by a radical change in the structure of the soil (when soaking subsidence soils) or its subsidence in mining areas and in karst areas
for the designed building are missing.
A load combination is a linear combination of loads taken with certain numerical coefficients.
Permissible combinations are those that can be implemented based on the logic of the joint action of loads or certain restrictions on their number, but not in accordance with the load-bearing capacity of the structure.
Unfavorable combinations are those combinations of loads under which the structure is in the limit state or is closer to the limit state than under other permissible load combinations.
According to SNiP 2.01.07-85*, calculations of structures and foundations for limit states of the first and second groups should be performed taking into account unfavorable combinations of loads or corresponding forces. These combinations are established from the analysis of real options for the simultaneous action of various loads for the considered stage of operation of the structure or foundation.
Because in this case special loads are absent, the calculation should be made for the main load combinations.
The main combinations of loads consist of the constant, long-term and short-term loads we defined above. Their combinations are compiled according to SNiP 2.01.07-85* “Loads and impacts”.
4.1.1. Loads and load cases, their combinations and combinations in SCAD
The SCAD interface and documentation uses the terms “load”, “load group”, “loads”, “load combination”, “design combination of forces”.
The meaning of the term “load” in SCAD coincides with its meaning in SNiP 2.01.07-85*. Loads are something that has a specific physical meaning and quantitative definition: own weight, snow, etc.
It is sometimes convenient to combine individual loads acting on one group of nodes and elements into “load groups”.
Loads (and groups of loads) are used to create “loads”. Loads are what the structure is calculated for with the solution of a simultaneous system of linear equations. In a particular case, a load case may consist of one load (a load of one type, for example, its own weight). The concept of “loading” is close in meaning to the term “load combinations” in SNiP 2.01.07-85*.
Loads taken with certain coefficients and logical connections constitute a “combination of loads” and are used in the “design combination of forces” mode.
4.1.2. Entering Loads and Load Cases
Before creating a new load case (or group of loads), you must save the current load case (or group of loads), and then clear the buffer memory of loads.
Creating a load case requires some thought, since the possibilities for further analysis depend on how it is done, especially when focusing on finding design force combinations (DCF). To do this, in particular, when forming load cases, it should be remembered that the loads of one load case must:
Always act simultaneously;
Have the same type in terms of duration of action;
Have the same load safety factors;
Have equal ratios between full and reduced load values.
4.1.3. Design combinations of forces, design combinations of loads
In calculation practice, two similar but fundamentally different concepts are used: design force combinations (DCF) and load combinations (design load combinations).
Their use was discussed in detail in 2004 and 2005. at the seminars “Calculation and design of structures in the SCAD Office environment”, organized by SCAD developers. Seminar materials can be found at the following links:
Http://www.scadgroup.com/download/Load_2004.ppt,
http://www.scadgroup.com/download/RSU.ppt.
To perform a calculation for a combination of load cases is to obtain indicators of the stress-strain state of a system that is simultaneously subject to several load cases.
The building is subject to many of the loads and impacts listed above. The calculation is performed for individual (elementary) loading cases under the assumption that any real system loading option can be represented as a linear combination of elementary ones. This approach is justified with a linear approach to calculation, since the superposition principle is valid only for linear systems.
Determining the design combinations of forces means finding those combinations of individual loads that can be decisive (the most dangerous) for each element being tested or each section of the element (this applies to the rod).
Finding an unfavorable combination of load cases (for example, for stress in a certain section or element) is precisely the task solved in the “Calculation combinations of forces” mode of the SCAD complex.
An example of the selection of coefficient values for design combinations of forces is presented in the table.
The calculation of design combinations of forces is carried out on the basis of criteria characteristic of the corresponding types of finite elements - rods, plates, shells, massive bodies. Extreme values of stresses at characteristic points of the cross section of the element are taken as such criteria. The calculations take into account the requirements of regulatory documents and logical connections between load cases.
The design and calculation of foundations is carried out in accordance with
SNiP 2.02.02-83* “Foundations of buildings and structures”,
SNiP 2.02.03-85 “Pile foundations”,
TSN 50-302-2004 “Design of foundations of buildings and structures in St. Petersburg.”
Pile foundations, depending on the placement of piles in the plan, should be designed in the form:
Single piles - for free-standing supports;
Pile belts - under the walls of buildings and structures when transferring loads distributed along the length to the foundation with piles arranged in one, two rows or more;
Pile bushes - under columns with piles arranged in plan on an area of square, rectangular, trapezoidal and other shapes;
Continuous pile field - for heavy structures with piles evenly spaced under the entire structure and united by a continuous grillage, the base of which rests on the ground.
The location of the piles in the plan and their number are determined based on the following criteria:
The load on the pile must be less than its calculated load-bearing capacity;
Movements of the grillage plate should not exceed permissible values;
Piles should be placed under the walls of the next floor;
The presence of piles is mandatory in the corners of the building, under columns and at the intersection of load-bearing walls;
The projection of the center of gravity of the building and the center of the pile field should approximately coincide in plan.
5.1.1. Determination of the number of piles
Calculation of piles, pile foundations and their foundations in terms of bearing capacity is carried out for basic and special combinations of loads with safety factors greater than one, and in terms of deformations - for main combinations of design loads with a safety factor equal to one. Calculations of piles of all types are carried out on the effects of loads transmitted to them from a building or structure, and driven piles, in addition, on the forces arising in them from their own weight during the manufacture, storage, transportation of piles, as well as when lifting them onto a pile driver in one a point distant from the head of the piles by 0.3l, where l is the length of the pile.
In the case under consideration, the foundation is designed for vertical loads (including useful ones):
Constant loads (own weight);
Long-term loads (payload, snow load);
Short-term loads (wind).
For residential buildings, the vertical load transmitted to the foundation can be estimated as 0.5 tons per m 3 of building volume. A ten-story section of a residential building transfers a load of approximately 10,000 tf to the foundation.
To approximately determine the number of piles in a plan, it is necessary to set a preliminary value for the load-bearing capacity of the pile based on soil conditions and design experience. It can range from approximately 60 to 120 tf for a multi-storey building.
The number of piles is determined by dividing the amount of vertical load transmitted to the foundation by the bearing capacity of a single pile. The bearing capacity of a single pile is defined as the design bearing capacity of the pile divided by the load safety factor (usually ). The piles are placed in rows or in a checkerboard pattern. The pitch of the piles in the bush is selected as a multiple of 5 cm.
5.1.2. Load bearing capacity of friction piles
The load-bearing capacity of the pile is taken to be the lower of two values - the load-bearing capacity of the soil or the load-bearing capacity of the pile material. For selected piles, the load-bearing capacity of the pile material is its passport characteristic.
The load-bearing capacity of a pile on the ground can be determined from table L.1 (Calculated resistance under the lower end of driven piles) and L.2 (Calculated resistance along the side surface of driven piles) from TSN 50-302-2004 “Design of foundations of buildings and structures in St. -Petersburg."
5.1.3. Pile modeling in SCAD
5.1.4. Longitudinal stiffness of piles
The complex nonlinear behavior of a pile in its interaction with the soil in SCAD is modeled with special linear finite elements (type 51) - finite stiffness links. For calculations, it is necessary to specify the longitudinal rigidity of the piles in its interaction with the soil. The amount of rigidity is numerically equal to the ratio of the force on the pile to its settlement. The stiffness of a pile is determined by the load on the pile, the characteristics of the pile itself, and the soil conditions.
5.1.4.1. Determination of settlement of a single pile
The settlement of a single pile is determined according to SNiP 2.02.03-85 “Pile foundations”. It is also recommended to use the Foundation program.
5.1.4.2. Pile stiffness modeling
The calculation is performed in several iterations.
The load on each pile is calculated and its settlement is determined.
The initial stiffness is assigned to the springs (pile models) as the ratio of the design force on the pile to its settlement.
Then the building is calculated. After recalculation, the forces in the piles will change (as a rule).
Based on the new forces, the settlement is again determined, the rigidities are calculated and inserted into the design diagram, etc. The calculation is repeated until the magnitude of the forces in the pile between the last approaches differs by 10-15%.
The elasticity coefficient (stiffness) of the pile model directly depends on the settlement, the settlement on the load, and the load, in turn, on the stiffness of the springs (pile models).
5.1.4.3. Simplified modeling of pile stiffness
For buildings with a relatively uniform distribution of load on the piles and uniform ground conditions in plan, a simplified approach is applicable. The stiffness of piles can be specified as the ratio of the load-bearing capacity of the pile to half of its permissible pile settlement during static tests.
During static tests, the limit is taken to be a load that causes 20% of the settlement of the maximum permissible for the building or structure being designed.
The permissible settlement of a building or structure is determined according to table 4.1 (Average S and maximum S¢ maximum settlements and relative uneven settlements) from TSN 50-302-2004 “Design of foundations of buildings and structures in St. Petersburg”.
Taking into account the previously obtained load-bearing capacity of the piles, we obtain rigidity as the ratio of the load-bearing capacity to half of the pile settlement in the form . Typically, the rigidity of the pile is from 3000 to 10000 tf/m.
In calculations for deformations, the safety factor for load is assumed to be equal to one (unless other values are established in the design standards for structures and foundations). In other words, the calculation is made based on standard load values.
6.1.1. Rule of signs for movements
The sign rule for movements is adopted such that linear movements are positive if they are directed in the direction of increasing the corresponding coordinate, and rotation angles are positive if they correspond to the rule of the right screw (when looking from the end of the corresponding axis to its beginning, the movement occurs counterclockwise).
6.1.2. Motion Analysis
The calculated values of linear displacements and rotations of nodes from load combinations are analyzed using the table of calculation results “Movements of nodes from combinations” for the first group of limit states. A comparison of the maximum displacements with the permissible ones is carried out.
In calculations for deformations, the safety factor for load is assumed to be equal to one (unless other values are established in the design standards for structures and foundations). In other words, the calculation is made based on standard (and not calculated) load values. Floor deflections obtained when calculating for standard load values should be compared with the maximum permissible according to SNiP 2.01.07-85*.
SCAD allows you to perform such a check for a building (structure) of arbitrary shape. Robustness testing can answer three questions:
What is the safety factor, i.e. how many times does the load need to be increased for stability to occur?
What is the form of buckling;
What are the calculated lengths of the rod elements according to Yasinsky, i.e. what is the length of a simply supported rod that loses stability at the value of the longitudinal force at which the system under consideration loses stability.
Calculation parameters are specified on the page Sustainability. Calculations should be made using combinations of load cases. It is necessary to set the search range for the value of the safety factor. If the safety factor exceeds this value, then its search stops. It is also necessary to set the calculation accuracy (or accept the default values).
Based on the calculation results, the safety factor for the overall stability of the system is obtained, as well as the smallest safety factor for local loss and the number of the element on which it is detected.
6.3.1. Rule of signs for efforts (stresses)
The rules of signs for efforts (stresses) are adopted as follows:
The following forces are calculated in the finite elements of the shell:
Normal voltages NX, NY;
Shear stress TXY;
Moments MX, MY and MXY;
Shear forces QX and QY;
Reactive resistance of the elastic base RZ.
6.3.2. Force and stress analysis
The SCAD post-processor determines the design reinforcement of the main load-bearing structures. The analysis of forces and stresses for the first group of limit states comes down to an analysis of the feasibility of reinforcement corresponding to stresses in horizontal slabs.
1. TSN 50-302-2004 St. Petersburg. “Design of foundations of buildings and structures in St. Petersburg.”
2. SP 50-102-2003 “Design and installation of pile foundations (set of rules).”
3. SNiP 2.01.07-85* “Loads and impacts”.
4. SNiP 2.02.03-85 “Pile foundations”.
5. Razorenov V.F. Mechanical properties of soils and load-bearing capacity of piles. - Voronezh, 1987.
6. SCAD Office. Computer complex SCAD: Textbook / V.S. Karpilovsky, E.Z. Kriksunov, A.A. Malyarenko, M.A. Mikitarenko, A.V. Perelmuter, M.A. Perelmuter. - 592 pages
7. SCAD Office. Implementation of SNiP in design programs: Textbook / Second edition, supplemented and corrected / V.S. Karpilovsky, E.Z. Kriksunov, A.A. Malyarenko, M.A. Mikitarenko, A.V. Perelmuter, M.A. Perelmuter, V.G. Fedorovsky. - 288 p.
8. Nekrasov A.V., Nekrasova M.A. Allplan FT-17.0. The first project from sketch to presentation.
9. Calculation and design of structures of high-rise buildings made of monolithic reinforced concrete / A.S. Gorodetsky, L.G. Batrak, D.A. Gorodetsky, M.V. Laznyuk., S.V. Yusipenko. – K.: ed. “Fakt”, 2004 – 106 p.
10. A.V.Perelmuter, V.I.Slivker. Calculation models of structures and the possibility of their analysis. – Kyiv, WPP “Compass”, 2001. – 448 p.
The SCAD software package, in addition to the finite element modeling calculation module, includes a set of programs capable of solving more specific problems. Due to its autonomy, the set of satellite programs can be used separately from the main SCAD calculation module, and it is not prohibited to perform joint calculations with alternative software packages (Robot Structural Analysis, STARK ES). In this article we will look at several examples of calculations in SCAD Office.
An example of selecting reinforcement in the edge of a pre-fabricated slab in the SCAD program
The slab will be mounted on a construction site, for example, on brick walls hingedly. For such a task, I consider it inappropriate to model the entire slab, part of the building, or the entire building, since the labor costs are extremely disproportionate. The ARBAT program can come to the rescue. It is recommended that the rib be calculated as a reinforced concrete T-section. The menu of the SCAD software package is intuitive: for a given section, reinforcement and force, the engineer receives a result on the load-bearing capacity of the element with reference to the clauses of the regulatory documents. The calculation result can be automatically generated in a text editor. It takes approximately 5-10 minutes to enter data, which is significantly less than the formation of a finite element model of a ribbed floor (let’s not forget that in certain situations the finite element method provides more calculation capabilities).
An example of calculating embedded products in SCAD
Now let’s remember the calculation of mortgage products for fastening structures to reinforced concrete sections.
I often meet designers who set parameters for design reasons, although checking the load-bearing capacity of the embedded parts is quite simple. First, you need to calculate the shear force at the attachment point of the embedded part. This can be done manually by collecting loads over the load area, or using the Q diagram of the finite element model. Then use the special calculation side of the ARBAT program, enter data on the design of the embedded part and the forces, and ultimately get the percentage of load-bearing capacity used.
With another interesting example of calculation in SCAD An engineer may encounter: determining the load-bearing capacity of a wooden frame. As we know, for a number of reasons, FEM (finite element method) calculation programs do not have in their arsenal modules for calculating wooden structures according to Russian regulatory documents. In this regard, the calculation can be done manually or in another program. The SCAD software package offers the engineer the DECOR program.
In addition to the data on the section, the DECOR program will require the engineer to enter calculated forces, which can be obtained using PC LIRA 10. Having assembled the calculation model, you can assign a parametric section of the tree to the rods, set the modulus of elasticity of the tree and obtain the forces according to the deformation scheme:
In this example of calculation in SCAD, the critical value turned out to be the flexibility of the element, the margin for the limiting moment of the sections is “solid”. The information block of the DECOR program will help you remember the maximum flexibility value of wooden elements:
An example of calculating the bearing capacity of a foundation in SCAD
An integral part of modeling a pile-slab foundation is the calculation of the bearing capacity and settlement of the pile. The REQUEST program will help the engineer cope with this kind of task. In it, the developers implemented the calculation of foundations in accordance with the standards of “foundations and foundations” and “pile foundations” (you will not find such capabilities in FEM calculation programs). So, to model a pile, it is necessary to calculate the stiffness of a single-node finite element. Stiffness is measured in tf/m and is equal to the ratio of the load-bearing capacity of the pile to its settlement. It is recommended to perform modeling iteratively: at the beginning, set the approximate stiffness, then refine the stiffness value using the calculated parameters of the pile. The constructed finite element calculation model will allow us not only to accurately find the load on the pile, but also to calculate the grillage reinforcement:
After calculating the structure, the user of PC LIRA 10 will be able to calculate the required load on the pile by drawing a mosaic of forces in a single-node finite element. The resulting maximum force will be the required design load on the pile; the load-bearing capacity of the selected pile must exceed the required value.
As initial data, the type of pile (drilled, driven), parameters of the pile section and soil conditions according to geological survey data are entered into the REQUEST program.
Example of calculation of nodal connections in SCAD
Calculation of nodal connections is an important part of the analysis of the load-bearing capacity of buildings. However, designers often neglect this calculation; the results can be extremely disastrous.
The figure shows an example of the lack of provision of the load-bearing capacity of the wall of the upper chord of the rafter truss at the point of attachment of the rafter truss. According to the joint venture “Steel Structures”, such calculations are made without fail. You won’t find such a calculation in a finite element calculation program either. The COMET-2 program may be a way out of the situation. Here the user will find calculations of node connections in accordance with current regulations.
Our node is a truss node and to calculate it you need to select an advising item in the program. Next, the user shaves the outline of the belt (our case is V-shaped), the geometric parameters of the panel, and the forces of each rod. Forces are usually calculated in FEM calculation programs. Based on the entered data, the program generates a drawing to visually represent the design of the unit and calculates the load-bearing capacity for all types of testing in accordance with regulatory documents.
An example of constructing an MCI calculation in SCAD
The construction of finite element calculation models is not complete without the application of loads, manually calculated values are assigned to the element in FEM calculation programs. The engineer will be assisted in collecting wind and snow loads by the WEST program. The program includes several calculation modules that allow you to calculate wind and snow loads based on the entered construction area and the outline of the building outline (the most common calculation modules of the WEST program). So, when calculating a canopy, the designer must indicate the height of the ridge, the angle of inclination and the width of the slope. Based on the obtained diagrams, the load is entered into a calculation program, for example, PC LIRA 10.4.
As a conclusion, I can say that the SCAD software package and its satellites allow the user to significantly reduce labor costs when calculating local problems, as well as create accurate calculation models, and also contain reference data necessary in the work of civil engineers. The autonomy of the programs allows designers to use them in combination with any calculation systems based on calculations by the finite element method.
An engineer faced with the calculation of the frame of a building, one of the load-bearing elements of which is a column, will come to the need to calculate a free-standing foundation. For calculations in the SCAD computer complex, the developers have provided almost complete functionality for determining the bearing capacity according to all foundation verification criteria.
So, having completed the construction of a frame, for example, a metal one, you will need to calculate separate foundations. To do this, in the SCAD computer complex it is necessary to specify nodes that are secured against displacement in specified directions and angles of rotation (it is in these nodes that the reaction of the supports can be calculated). Most often, the vertical reaction, the horizontal reaction, and the moment in the plane of operation of the structure are analyzed. The SCAD computer complex displays reactions for all nodes marked by the user; as a rule, three combinations of loads are considered for:
Rz max, Rx resp, Ruy resp
Rz resp., Rx max, Ruy resp.
Rz resp., Rx resp., Ruy max.
Fig.1 Considered building frame (vertical reaction) in a computer complexSCAD
It is not easy to visually determine the maximum values when the circuit is heavily loaded; you can use the “documentation” tool, where the necessary cells of numbers are filtered by displaying a table of all values from the SCAD computer complex in MS Excel.
The resulting value combinations must then be used when calculating a free-standing foundation. The calculation of free-standing foundations can also be performed manually; for this purpose, the pressure under the base of the foundation is calculated.
Due to the torque that arises, the pressure is uneven. The boundary values are calculated using the formula
The next step in calculating a free-standing foundation is to determine the calculated soil resistance. Calculations are made according to SP 22.13330.2011 “Foundations of buildings and structures”, formula 5.7. For the calculation, engineering-geological surveys of the soil layers of the construction site in question (or directly under a separate foundation) are required.
Calculations of the design soil resistance for a free-standing foundation can also be made using the REQUEST program (satellite of the SCAD computer complex). The program implements calculations according to SP 22.13330.2011 “Foundations of buildings and structures”.
The resulting value R must necessarily be greater than the pressure value P. Otherwise, a decrease in pressure on the ground is required, for example, by increasing the area of a free-standing foundation. The area of the foundation and the moment of resistance of the foundation section are in the denominator of the formula for finding pressure P, which forces the pressure indicator to be reduced.
When calculating a free-standing foundation, one should also not forget about the calculation of the foundation slab for punching and the calculation of bearing capacity. The bearing capacity of the foundation slab is calculated as a double cantilever beam, the load on which is equal to the pressure on the ground (Newton’s III law). The result of the calculation is the installation of the working “lower” reinforcement of the slab section.
The force on the slab from the column is quite significant, so when calculating the punching force, it may be necessary to install additional stages of a separate foundation.
Punching, as well as the calculation of two cantilever beams, can be performed by the ARBAT program (satellite of the SCAD computer complex).
When the entire algorithm described above is completed, the calculation of a free-standing foundation can be considered completed.
Now let's return to the building frame diagram. Any foundation on a soil foundation (except rock) sags under the influence of one load or another. The resulting additional deformation of the circuit contributes to a change in the redistribution of forces already in the elements of the circuit. Hence the need arises in some cases (the most critical ones) to install not a rigid pinching, but an elastic connection, at the junction of the column with a free-standing foundation. The SCAD computer complex does not automatically calculate the stiffness of the elastic connection, but this operation can be performed manually. The rigidity of the elastic connection during vertical displacement is equal to the ratio of the bearing capacity of a free-standing foundation to its settlement, the resulting value is measured in t/m. The settlement can be calculated using the REQUEST program (a satellite of the SCAD computer complex).
By calculating free-standing foundations, we obtain a more accurate picture of the deformation of the building, and therefore more accurate forces in the finished elements.
Fig.2 Deformed diagram of the building frame.Computing complexSCAD
So, with the help of the SCAD computer complex, the user will be able to perform the required calculation of free-standing foundations, select the required base area, perform punching calculations, determine the tilt of the building, and also take into account the redistribution of forces depending on the resulting settlement of the structure.
As a basis for calculating the settlement of pile foundations, the technology proposed by SergeyKonstr in this topic was adopted: “OFZ according to SP 24.13330.2011”, on dwg.ru, revised to the best of our understanding, to suit our own tools and capabilities.
SP 24.13330.2011: S=Sef+Sp+Sc
where, S - settlement of the pile, Sef - settlement of the conditional foundation, Sp - settlement due to punching, Sc - settlement due to compression of the pile shaft.
The technology is as follows:
1. I calculate the scheme as if on a natural basis in (SCAD+Cross) I get the average draft (Sef)
2. I arrange the piles on the plan. I am creating an additional design scheme that includes only the foundation slab and piles. In order to load the slab with a unit load (1T/m2), and find out the load area of the placed piles, or the “pile cell area” which is needed to calculate the punching settlement. There is a catch - what area should be taken for the extreme and corner piles? Just for intuitive reasons, I added a coefficient to the cell area equal to 2 and 4
4. Calculating Sc is not a problem, knowing the load on the pile and its parameters.
5. Knowing Sef, Sp, Sc, I obtain the stiffness of the piles and perform several iterations of the calculation.
To model the piles, I decided to use universal rods. It is much more convenient to work with them in SCADA than, for example, with connections of finite stiffness.
Using SPDS Graphics, a parametric object "Pile" and a "table for calculations" were developed. All calculations are performed inside this object, we just need to give it initial parameters:
1. Set the piles parameters (section, length) and soil parameters (E1, Mu1, E2, Mu2,)
2. Set the load on the pile (to a first approximation, the total vertical load on the building / number of piles).
3. Set the piles to the settlement of the conditional foundation, calculated using SCAD+Cross, and the depth of the subsidence layer. Here is the isofield of the settlement of my slab, respectively, the piles were given Sef depending on which field they fell into.
4. Set the load areas (reaction in the pile from a unit load).
5. The parametric object, receiving all these parameters, calculates the total settlement, and accordingly the rigidity (E=N/S), and builds a vertical rod with a length equal to 1000/E.
6. Actually, we dismember these objects, leaving only the vertical bars, and import them into CAD, where we assign stiffness EF = 1000 to all bars.
7. It is unrealistic to set settlement, load, etc. for each pile in a large pile field. Assignment of data to piles occurs using Excel - SPDS table. But this is only possible if the pile numbers in SCADA correspond to the pile numbers on the plan in AutoCAD. Therefore, piles in AutoCAD are sorted by X, Y and numbered using a table. Before importing the rods into SCAD, they must be rebuilt in the same order as the piles. Users Nanocad can use macro , who designed swell(d) . You can also use PC Lyra for this purpose, which can renumber the rods depending on their X, Y coordinates.
