Calculation of foundations on scad screw piles. Foundations on a pile foundation. Design and calculation. Calculation of a single pile

Geometric characteristics of the building

The building has a rectangular plan, dimensions 75.0 x 24.0 m, height 15.9 m at the top point. The building includes 3 floors. The first floor is 4.2 m high; second floor – 3.6 m; third floor – 3.5 m.

Supporting system of the building

The level of the finished floor of the first floor is taken as the relative level of 0.000, which corresponds to the absolute elevation of +12.250m. Grillage base elevation +10.700. The building has a rectangular shape in plan dimensions: 75.0x24.0 m. The transverse frames of the building are installed in increments of 6 m and 3 m. The span of the building is 24.0 m. The building has 2 internal levels of floors, the finished floor level of the first floor is 0.000, the second floor +4,200 and third floor +7,800. The elevation of the bottom of the supporting structure of the covering (truss) is +12,000.

The structural design of the building is a frame-braced frame.

The building frame is designed metal with a covering of trusses made of bent-welded steel pipes of square section. The trusses span 24 m with a slope of the upper chords of 3% from the ridge in both directions. The lower belts are horizontal. The main load-bearing structures of the frame are steel columns, united by a system of vertical and horizontal connections.

Strength and spatial stability are ensured by rigid embedding of columns in the foundations in the plane of the frames and vertical connections along the columns from the plane of the frames. The trusses are hinged to the columns.

The stability of the coating is created by the hard disk of the coating - a system of horizontal rod connections and a profiled sheet along the upper chords of the trusses. The horizontal ties of the covering are located along the upper chords of the trusses. To ensure the stability of the trusses during installation, removable inventory spacers are used, developed in the work project.

Building frame

According to the coating loading schemes, two types of roof trusses are accepted:

1.Ф1, in axes 2-4;

2.Ф2 in axes 1, 5-13.

Rafter trusses are made of two mounting grades. The upper chords are connected on flanges, the lower ones - using linings on high-strength bolts (friction joints). The sections used are steel bent closed welded square profiles in accordance with GOST 30245-2003.

Rafter truss brand F1:

1. The upper belt is a bent square profile 180x10;

2. Bottom belt - bent square profile 140x8;

3. Support braces - bent square profile 120x8;

4. Stretched/compressed braces - bent square profile 120x6;

Rafter truss brand F2:

1. The upper belt is a bent rectangular profile 180x140x8;

2. Bottom belt - bent square profile 140x7;

3. Support braces - bent square profile 120x5;

4. Stretched/compressed braces - bent square profile 100x4;

5. Racks - bent square profile 80x3.

The frame columns have a section that is constant along the height of the building and are designed from a rolled I-section type “K”, 35K2 (STO ASChM 20-93);

The interfloor floor beams are designed from a rolled I-section type “B” (STO ASChM 20-93):

The main beams are of I-section 70B1;

Secondary beams - I-section 40B2;

The covering beams in axes 14/A-D are designed from a rolled I-section type “B” (STO ASChM 20-93), 60B2.

Monorail for hoist – 45M (STO ASChM 20-93);

The connections (horizontal and vertical) are designed from bent-welded steel pipes of square section. The sections taken are steel bent closed welded square profiles in accordance with GOST 30245-2003:

1. Vertical connections - bent square profile 180x5;

2. Horizontal connections - bent square profile 150x4.

The floors are made of monolithic reinforced concrete slabs, made of profiled steel sheet SKN50-600-0.7, used as permanent formwork. Floor thickness 110 mm. Concrete classes B25, W4, F100 are accepted. The ceilings are made along the upper chords of metal beams.

The spacers are designed from bent steel closed welded square profile in accordance with GOST 30245-2003.

1. Spacers along the upper chords of the trusses (P1) - bent square profile 120x5;

2. Spacers along the lower chords of the trusses (P2) - bent square profile 120x5;

3. Spacer in axes 1-2/B (P3) - bent square profile 120x5;

4. Spacers in the plane of the second floor (P4) - bent square profile 120x5.

Base and foundation

The foundations of the workshop building are piles, adopted on the basis of geotechnical survey data. The grillages for the columns of the supporting frame of these buildings are columnar monolithic reinforced concrete made of B20, W6 concrete. The height of the grillages is 1.6 m. The foundation beams are monolithic reinforced concrete made of B20, W6 concrete. The piles are prefabricated reinforced concrete piles with a length of 6.0 m, a section of 30 x 30 cm, made of concrete class B20, W6, F150. The embedding of piles into grillages is rigid, to a depth of 350 mm.

The piles are driven hanging piles, with a cross-section of 30x30 cm, a length of 18.0 m, supported in the soils IGE 9, IGE 10 and IGE 11, depending on the location on the site.

The site of pile foundations for the workshop building is divided into the following sections depending on the number of piles in the bush:

1. Grillages P1 for columns in axes 2-5/B-G - 6 piles in a bush;

2. Grillages P2 for columns in axes 2-5/A, D - 5 piles in a bush;

3.P3 grillages for columns in axes 1/A-D, 6-12/A-D - 4 piles in a bush;

4. P4 grillages for columns in axes 13-14/A-D - 4 piles in a bush.

The bearing capacity of the piles is determined by calculation and based on static sounding data. Before starting mass pile driving, static tests of the piles noted in the project should be performed in accordance with the requirements of GOST 5686-94 “Soils. Methods for field testing of piles.” If the test results show a different load-bearing capacity of the piles, the foundations must be adjusted.

The settlement of the building foundations was calculated using the Foundation 12.4 program and the layer-by-layer summation method. The calculated settlement values of pile grillages do not exceed 6 mm.

External walls, partitions, covering

The covering is prefabricated using profiled sheet H114-750-1. with effective basalt fiber insulation and Technoelast finishing coating, a profiled sheet of covering is attached to the upper chords of the trusses, it is attached according to a two-span continuous design, with a sheet length of 12 meters.

The flights of stairs are designed as prefabricated ones. The basis is stringers supported on steel beams of an I-profile frame. The interfloor landings of the stairs are made in the form of monolithic reinforced concrete slabs on permanent formwork made of profiled sheets.

The external enclosing walls are designed from three-layer suspended thermal panels. The walls are attached to the supporting structures of the building's steel frame.

General requirements for reinforced concrete structures

Reinforcing steel was adopted by the project in accordance with Chapter 5.2 SP 52-101-2003 "Concrete and reinforced concrete structures without prestressing reinforcement" for classes A400 (A-III) (steel grade 25G2S, GOST 5781-82 * "Hot-rolled steel for reinforcing reinforced concrete structures. Technical conditions"), A240 (A-I) (steel grade St3sp3; St3ps3).

The thickness of the protective layer of concrete for working reinforcement is at least 25 mm. To ensure the thickness of the protective layer, it is necessary to install appropriate clamps to ensure the design position of the reinforcement.

Engineering and geological conditions of the construction site

The geological structure of the territory within the drilling depth of 25.0 m involves:

1. Modern - technogenic (t IV), biogenic (b IV), marine and lacustrine (m, l IV) sediments;

2. Upper Quaternary of the Ostashkovo horizon – lacustrine-glacial deposits of the Baltic glacial lake (lg III b), lacustrine-glacial (lg III lz) and glacial deposits of the Luga stadial (g III lz).

Calculation of models in PC SCAD

The calculations use SCAD version 11.5.

The calculation was performed for two types of problem solution:

1. Linear setting.

Circuit type

The design scheme is defined as a system with feature 5. This means that a general system is considered, the deformations of which and its main unknowns are represented by linear displacements of nodal points along the X, Y, Z axes and rotations around these axes.

Quantitative characteristics of the design scheme

The design scheme is characterized by the following parameters:

Number of nodes - 831

Number of finite elements - 1596

Total number of unknown movements and turns - 4636

Number of loads - 15

Number of load combinations - 5

Selected static calculation mode

The static calculation of the system was performed in a linear formulation.

For a general view of the calculation models, see Fig. 1

Fig.1 General view of the calculation model

Border conditions

The boundary conditions are specified as follows. The columns in the plane of the frames are rigidly fixed at all degrees of freedom, and from the plane - hinged.

Loads and impacts

Loads and impacts on the building are determined in accordance with SP 20.13330.2011 “SNiP 2.01.07 - 85 “Loads and impacts. General provisions." In the calculation complex SCAD Full design loads are applied. Using a combination of load cases and the DCS module, a system of coefficients is taken into account for calculation according to I and II PS groups. The names of the accepted loads are presented in table. 1

Table 1 . Loads and impacts

Load type

γf

K lasts

K 1

Permanent:

· s.v. load-bearing structures

SCAD*

1,05

SCAD*

· s.v. enclosing structures:

192 kgf/pm

231 kgf/pm

· s.v. monolithic reinforced concrete slabs on corrugated sheets

with cargo area, 1.5 m

with cargo area, 0.75 m

527 kgf/rm

263 kgf/pm

579 kgf/rm

290 kgf/rm

· s.v. prefabricated staircases

1150 kgf

1265 kgf

· s.v. roofs:

with cargo area, 6.0 m

with cargo area, 4.5 m

with cargo area, 3.0 m

with cargo area, 1.5 m

282 kgf/pm

212 kgf/pm

141 kgf/pm

71 kgf/rm

338.4 kgf/pm 254 kgf/rm

169 kgf/pm

85 kgf/rm

· s.v. floors

with cargo area, 1.5 m

with cargo area, 0.75 m

375 kgf/rm

188 kgf/pm

413 kgf/pm

206 kgf/pm

Temporary:

- long acting:

· s.v. temporary partitions

with cargo area, 1.5 m

with cargo area, 0.75 m

81 kgf/rm

40 kgf/rm

105 kgf/pm

53 kgf/rm

0,95

· s.v. stationary equipment:

· at elevation 0.000

· at elevation +4,200:

with cargo area, 1.5 m

· from cargo area, 0.75 m at elevation. +7,800:

with cargo area, 1.5 m

with cargo area, 0.75 m

1000

1500 kgf/rm

750 kgf/rm

4500 kgf/rm

2250 kgf/rm

1,05

1050

1575 kgf/pm

788 kgf/pm

5400 kgf/rm

2700 kgf/rm

0,95

Temporary:

- short-term:

· crane

vertical

horizontal

7500 kgf

750 kgf

9000

0,95

· useful (1st-3rd floors)

· first floor

· from 2nd to 3rd floor:

with cargo area, 1.5 m

· from cargo area, 0.75 m per cover:

with cargo area, 6.0 m

with cargo area, 4.5 m

with cargo area, 3.0 m

with cargo area, 1.5 m

600 kgf/rm

300 kgf/rm

323 kgf/pm

242 kgf/pm

162 kgf/pm

81 kgf/rm

720 kgf/pm

360 kgf/rm

420 kgf/rm

315 kgf/rm

210 kgf/rm

105 kgf/pm

0,35

· snow

in r/o 4-13/width 18 m

with cargo area, 6.0 m

with cargo area, 4.5 m

756 kgf/rm

687 kgf/pm

1,429

1080

· snow bag

along the parapet, 2.8 m

with cargo area, 6.0 m

with cargo area, 4.5 m

with cargo area, 1.5 m

· in district 1-4/A-D

with cargo area, 6.0 m

with cargo area, 3.0 m

205,5

1236 kgf/pm

927 kgf/pm

309 kgf/pm

252 kgf/rm

1512 kgf/pm

756 kgf/rm

1,429

1766 kgf/pm

1325 kgf/pm

442 kgf/pm

360 kgf/rm

2161 kgf/pm

1080 kgf/pm

· wind

Fig.2-3

table 2

±0.9

note: SCAD* - load is determined automatically by the software;

where: P n – standard load value, kgf/m 2 (except as specified);

γ f – load reliability factor;

P – calculated load value, kgf/m2 (except as specified);

Kdt – coefficient of transition from full values of short-term load to reduced values of long-term temporary load (duration fraction);

К 1 – coefficients for combination #1, determining the calculated values of loads taking into account the reduction coefficients of combinations, including permanent and at least two temporary loads (for calculations according to

Wind loads were determined using the West program. Wind region – II. Terrain type - B (urban areas, forested areas and other areas evenly covered with obstacles more than 10 m high). The values are presented in the form of graphs (Fig. 2 and Fig. 3). The values are presented in the form of graphs (Fig. 4.4 and Fig. 4.5). Forces are applied to the columns in height. The values of the applied forces are presented in table. 2.

Table 2. Wind loads

Height, m	*Windward surface, kgf/pm**	*Leeward surface, kgf/pm**
From 0.0 to 5.0 m
From 5.0 to 14.0 m
14.0 m

note: * - wind pressure values are calculated, applied to columns taking into account the width of the loading area b = 6.0; 1.4 m (parapet).

Load combinations and design combinations

The calculation of structures and foundations based on the limit states of the first and second groups was carried out taking into account unfavorable combinations of loads or the forces corresponding to them.

These combinations were established from an analysis of real options for the simultaneous action of various loads for the considered stage of operation of the structure or foundation.

Depending on the load composition taken into account according to SP 20.13330.2011, paragraph 6, the following are assigned (Table 4.8):

a) the main combinations of loads, consisting of constant, long-term and short-term;

Name of loads, combinations of loads, summary list of loads, see table 3-4. When specifying design combinations, the mutual exclusion of loads (wind) and alternation of signs (wind) were taken into account.

Table 3. Load Case Names

Load Case Names

Name

Own weight

S.v. enclosing structures

S.v. monolithic slab on corrugated sheets

S.v. floors

S.v. roofs

Weight of stationary equipment

S.v. stairs

Weight of temporary partitions

Useful for floors

Useful for coating

Table 4. Load Combinations

Load Combinations

(L1)*1+(L2)*1+(L3)*1+(L4)*1+(L5)*1+(L7)*1

(L6)*1+(L8)*0.95+(L9)*1+(L10)*0.7+(L11)*0.7+(L12)*0.9+(L14)*0.7+(C1)*1

(L6)*1+(L8)*0.95+(L9)*0.7+(L10)*0.9+(L11)*0.7+(L12)*1+(L14)*0.7+(C1)*1

(L6)*1+(L8)*0.95+(L9)*0.7+(L10)*0.7+(L11)*1+(L13)*0.9+(L14)*0.7+(C1)*1

(L6)*1+(L8)*0.95+(L9)*0.7+(L10)*0.7+(L12)*0.9+(L14)*0.7+(L15)*1+(C1)*1

Conclusions. Main calculation results

Calculation according to I

All building structures to prevent destruction under the influence of force during the construction process and the estimated service life.

Calculation according to II group of limit states tested:

Suitability of all building structures for normal use during construction and design service life.

Movements

Maximum deflection at the center of the truss:

1.For combination No.2 is 57.36mm;

2.For combination No.3 is 63.45mm;

3.For combination No.4 is 38.1mm;

4. For combination No. 5 it is 57.19 mm.

The permissible deflection value according to SP 20.13330.2011 is 24000/250=96 mm.

The maximum deflection of the building is 63.45 mm with load combination No. 3, which does not exceed the permissible value.

The movement of the top of the building along the Y axis under the combined influence of vertical and horizontal loads does not exceed f = 52.0 mm (f< l /200 = 14670/200= 73,35 мм).

The movement of the top of the building along the X axis under the combined influence of vertical and horizontal loads does not exceed f = 4.6 mm (f< l /200 = 14670/200= 73,35 мм).

Main beam deflection:

The permissible deflection value according to SP 20.13330.2011 is 6000/200=30 mm.

The maximum deflection of the main beam is 10.94 mm for load combination No. 2, which does not exceed the permissible value.

Deflection of the beam under the monorail hoist:

The permissible deflection value according to SP 20.13330.2011 is 6000/500=12 mm.

The maximum deflection of the main beam is 4.7 mm for load combination No. 3, which does not exceed the permissible value.

Efforts

Maximum value of longitudinal force N in the base:

1. Columns in axes 2-4/B-G is 152.35 tf;

2. Columns in axes 5/B-G is 110.92 tf;

3. Columns in axes 6-12/A-D is 77.97 tf;

4. Columns in axes 1/A-D is 78.45 tf;

5. Columns in axes 2-5/A, D is 114.37 tf;

6. Columns in axes 13-14/A-D is 77.97 tf.

System stability margin factors

Stability safety factors for load combinations are presented in Tables 5 below.

Table 5 Safety margin factors

Stability safety factors for load combinations

Number

Name of load case/combination

Meaning

Safety factor > 3.0000

Conclusions: The minimum safety factor for the stability of the building structure for load combinations No. 1-5 is not lower than the minimum value of 1.5.

Calculation and testing of steel structure elements was carried out using the SCAD Office 11.5 computer software package in accordance with the requirements of SNiP II-23-81*. The results of testing the elements of steel structures are presented in the calculation file.

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 a prefabricated slab edge in the SCAD program

The slab will be mounted on a construction site, for example, on brick walls hingedly. I consider it inappropriate to model the entire slab, part of the building, or the entire building for such a task, 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.

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.

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):

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):

Flow index “IL” for silty 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;

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”.

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 1 - Pasternak's foundation model,

Method 2 - Winkler-Fuss foundation model,

Method 3 - modified Pasternak 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.

Keywords

PILE-PLATE FOUNDATION / LINEAR-DEFORMABLE BASE / WINKLER AND PASTERNAK MODEL/ SCAD OFFICE / SMATH STUDIO / PILE-AND-SLAB FOUNDATION / LINEARLY ELASTIC FOUNDATION / WINKLER AND PASTERNAK GROUND BASE MODELS

annotation scientific article on construction and architecture, author of the scientific work - Nuzhdin L.V., Mikhailov V.S.

A detailed overview of the main methods for constructing analytical and numerical models is provided. pile-slab foundations in accordance with the requirements of current standards in the SCAD Office calculation complex. The correlation between the results of analytical methods and numerical ones is demonstrated for two cases of foundation: with a flexible grillage and a rigid grillage reinforced by the walls of the basement floor. The analysis is performed on a homogeneous soil base, without taking into account soil watering. Using the example of seven solved problems, the authors consider three analytical methods for modeling a pile foundation in accordance with the provisions of SNiP 2.02.03-85 and SP 24.13330.2011, as well as two numerical methods for modeling an elastic half-space, based solely on the use of the finite element method in a linear formulation. The implementation of analytical calculation models regulated by regulatory documents is carried out in the mathematical package SMath Studio in addition to the standard functionality of the SCAD Office calculation complex. The complete calculation technology involves the use of standard functionality of a mathematical package for importing and exporting data into common data exchange formats in a structured form, available for import and export into the SCAD calculation and analytical complex. The article describes in detail the technologies for performing calculations, indicating the limits of applicability of the models under consideration and recommendations for their use in a static formulation. All considered examples demonstrate sufficient convergence of calculation results for practical purposes, with the exception of Pasternak’s foundation model. The scientific and applied nature of the research and its results may be of interest to design engineers, graduate students and undergraduates.

Text of scientific work on the topic “Numerical modeling of pile foundations in the SCAD Office calculation and analytical complex”

Nuzhdin L.V., Mikhailov V.S. Numerical modeling of pile foundations in the calculation and analytical complex SCAD Office // Bulletin of PNIPU. Construction and architecture. - 2018. - No. 1. - P. 5-18. DOI: 10.15593/2224-9826/2018.1.01

Nuzhdin L.V., Mikhaylov V.S. Numerical modeling of pile foundations in the structural analysis software SCAD Office. Bulletin of PNRPU. Construction and Architecture. 2018. No. 1.Pp. 5-18. DOI: 10.15593/2224-9826/2018.1.01

PNIPU NEWSLETTER. CONSTRUCTION AND ARCHITECTURE No. 1,2018 PNRPU BULLETIN. CONSTRUCTION AND ARCHITECTURE http://vestnik.pstu. ru/arhit/about/inf/

DOI: 10.15593/2224-9826/2018.1.01 UDC 624.154.1

NUMERICAL SIMULATION OF PILE FOUNDATIONS IN THE SCAD OFFICE CALCULATION AND ANALYTICAL COMPLEX

L.V. Nuzhdin1, 2, V.S. Mikhailov1

1Novosibirsk State University of Architecture and Civil Engineering, Novosibirsk, Russia 2Perm National Research Polytechnic University, Perm, Russia

ANNOTATION

Keywords:

pile-slab foundation, linearly deformable foundation, Winkler and Pasternak model, SCAD Office, SMath Studio

A detailed overview of the main methods for constructing analytical and numerical models of pile-slab foundations in accordance with the requirements of current standards in the SCAD Office calculation complex is provided. The correlation between the results of analytical methods and numerical ones is demonstrated for two cases of foundation: with a flexible grillage and a rigid grillage reinforced by the walls of the basement floor. The analysis is performed on a homogeneous soil base, without taking into account soil watering. Using the example of seven solved problems, the authors consider three analytical methods for modeling a pile foundation in accordance with the provisions of SNiP 2.02.03-85 and SP 24.13330.2011, as well as two numerical methods for modeling an elastic half-space, based solely on the use of the finite element method in a linear formulation.

The implementation of analytical calculation models regulated by regulatory documents is carried out in the mathematical package SMath Studio in addition to the standard functionality of the SCAD Office calculation complex. The complete calculation technology involves the use of standard functionality of a mathematical package for importing and exporting data into common data exchange formats in a structured form, available for import and export into the SCAD calculation and analytical complex. The article describes in detail the technologies for performing calculations, indicating the limits of applicability of the models under consideration and recommendations for their use in a static formulation. All considered examples demonstrate sufficient convergence of calculation results for practical purposes, with the exception of Pasternak’s foundation model.

The scientific and applied nature of the research and its results may be of interest to design engineers, graduate students and undergraduates.

Leonid V. Nuzhdin - Ph.D. in Technical Sciences, Professor, e-mail: [email protected]. Victor S. Mikhaylov - Postgraduate Student, e-mail: [email protected].

NUMERICAL MODELING OF PILE FOUNDATIONS USING SCAD OFFICE STRUCTURAL ANALYSIS SOFTWARE

L.V. Nuzhdin1, 2, V.S. Mikhaylov1

Novosibirsk State University of Architecture and Civil Engineering, Novosibirsk, Russian Federation Perm National Research Polytechnic University, Perm, Russian Federation

ARTICLE INFO ABSTRACT

The analytical modeling, which is regulated by standards, is carried out using the mathematical package SMath Studio. It is supposed that the complete analysis technology will use a standard mathematical package for import and export to and from the common data interchange format (DIF) in a structured view, which is acceptable for import and export in the SCAD system. A detailed description of the calculation technology is presented by the authors, thus indicating the applicability limits of these methods and recommendations for their use in static conditions. The demonstrated example tests a fine precision of the considered methods.

The research could be of great interest for design engineers, university postgraduates and undergraduates.

An urgent problem in design is the choice of a method for solving the problem that most closely reflects the behavior of the analyzed foundation structure. Modern calculation systems include many numerical tools for creating foundation models in both linear (elastic) and nonlinear-elastic or elastoplastic formulations. If taking into account the physical nonlinear properties of the soil is a more complex task that requires extensive engineering-geological surveys, then solving the problem of calculation in an elastic formulation in accordance with the requirements of the standards is generally accepted in engineering practice on the basis of standard surveys. This is due to the fact that most modern regulatory documents are based on two foundation models: the Winkler contact model with one constant bed coefficient and a linearly deformable half-space in an analytical representation, either in the form of a contact two-parameter Pasternak model, or in a numerical form with volumetric finite elements .

For columnar and strip foundations in standard calculation methods, the rigidity of the pile foundation is described by the Winkler contact one-parameter key model, which does not take into account the distribution effect of the foundation. In SNiP 2.02.03-85, the Winkler model with one bed coefficient is also the main one when calculating hanging piles in a bush as a conditional foundation. This approach to calculating the settlement of pile func-

pile-and-slab foundation, linearly elastic foundation, Winkler and Pasternak ground base models, SCAD Office, SMath Studio

daments excludes taking into account the mutual influence of piles. Deformations of a pile cluster according to the Winkler model are ensured by assigning each individual pile the same constant stiffness C1, kN/m3, in the form of a distributed coefficient over the area of the slab grillage, or by introducing into the finite element model in each lower node of the pile identical single-node connections of final stiffness Cz1, kN/ m, which is equal to the ratio of the load on one pile to the total settlement of the foundation:

where - is the total average long-term standard pressure at the base of the slab grillage, kPa; ^ - average settlement of a pile-slab foundation, as a conditional one; N is the standard long-term load transferred to one pile, kN.

Indeed, when the rigidity of the grillage connecting the piles increases to infinitely large values, for example, as part of a monolithic columnar foundation on a pile foundation under a single column, the grillage tends to a rigid stamp with synchronous deformations of the piles. However, the load-bearing capacity of each pile does not remain the same and decreases towards the center of the grillage due to the inclusion of common soil near the pile as stresses in the soil increase in the place of greater concentration of piles. When calculating pile foundations, the current regulatory document SP 24.13330.2011 “Pile foundations”, compared to the original edition of SNiP.02.03-85, offers two more accurate methods for taking into account the mutual influence of piles in a group. The first analytical method takes into account the noted effect of reducing the bearing capacity of piles in a bush in accordance with the model of a linearly deformable foundation and regulates the calculation in paragraphs. 7.4.4-7.4.5 using a method that was first presented in the works of V.G. Fedorovsky, S.N. Levacheva, S.V. Kurillo and Yu.M. Kolesnikova. The implementation of this method when calculating the supports of a bridge crossing together with the SCAD calculation complex is considered in detail by G.E. Edigarov. The principles of constructing a discrete model of a pile bush, taking into account the rigidity of the grillage, are discussed in the monograph by D.M. Shapiro.

The second analytical technique, implemented in SP 24.13330.2011 in paragraphs. 7.4.6-7.4.9, is intended for calculating a large pile field using the cell method, taking into account the compliance of the grillage as a conditional foundation on a natural foundation, but unlike the previous edition of SNiP, it takes into account additional settlement from pushing piles in the soil mass, taking into account the density of the pile field, and also settlement due to deformation of the pile shaft. The solution to this problem was proposed in the monograph by R.A. Mangusheva, A.L. Gotman, V.V. Znamensky, A.B. Ponomareva, N.Z. Gottman. It is recommended to carry out the calculation using load-settlement graphs or simplified formulas at the center of gravity of symmetrical trapezoidal sections of the slab.

The authors chose mathematical modeling based on analytical and numerical solutions to the problem as research methods. The table presents seven considered numerical and numerical-analytical models, on the basis of which the analysis of settlement and stress-strain state of the pile foundation was carried out. For all implemented models, a comparison is made of the settlement of the flexible slab -

grillage (Index “1” in the first column of the table) and a grillage reinforced with basement walls (Index “2”). The introduction of ribs in the form of monolithic walls increases the overall rigidity of the grillage and reduces the difference in settlement,

The first five models under consideration are numerical-analytical due to the introduction into the finite element model of the base stiffness determined by analytical calculation in accordance with current standards. Models No. 1 and No. 2 differ only in the method of specifying stiffness and are based on the first analytical method according to SNiP 2.02 ,03-85, in which the pile-slab foundation is considered as conditional on a natural foundation, Model No. 3 of the pile cluster is based on the analytical methodology SP 24,13330,2011, in which the foundation is considered as a rigid stamp with variable bearing capacity of a group of piles in the cluster, Model No. 4 describes the analytical method SP 24.13330.2011 for calculating large pile fields. Model No. 5 is an extended pile field method with the introduction of variable rigidity of the pile foundation. The last two models - No. 6 and No. 7 - use exclusively numerical tools implemented in SCAD Office for a linearly deformable base in the form of a contact two-parameter model and in the form of an elastic half-space model of volumetric finite elements,

Comparative analysis of calculation results for models of pile-and-slab foundation

Model number Base type and model name Max, settlement s, cm Min, settlement s, cm Average settlement s, cm As, % Mmax, kNm Longitudinal reinforcement, t

1.1 Winkler model. Conditional foundation according to SNiP 2.02.03-85 with bonds of finite stiffness 14.96 14.39 14.68 0.6 146 13.8

1,2 14,77 14,64 14,71 0,1 61 13,8

2.1 Winkler model. Conditional foundation according to SNiP 2.02.03-85 with a bed coefficient on the slab of 14.7 14.7 14.7 0 0 13.8

2,2 14,7 14,7 14,7 0 0 13,8

3.1 LDO. Pile bush according to SP 24.13330.2011 pp. 7.4.4-7.4.5 17.90 7.02 12.46 11 3,557 148.7

3,2 16,65 10,19 13,42 6,5 2 463 192,8

4.1 LDO. Pile field SP 24.13330.2011 p. 7.4.6-7.4.9 Ksh* 11.93 11.93 11.93 0 0 13.8

4,2 11,93 11,93 11,93 0 0 13,8

5.1 Winkler model. Pile-slab foundation SP 24.13330 pp. 7.4.6-7.4.9 s Kuag 11.06 9.81 10.43 1.2 457 19.1

5,2 10,73 10,35 10,538 0,4 153 14,2

6.1 Pasternak's model. Conditional foundation on an imaginary slab of low rigidity 6.53 4.51 5.52 1.1 538 36.1

6,2 6,06 5,66 5,26 0,8 287 17,7

7.1 LDO. Pile-slab foundation with a base in the form of OKE 14.98 12.07 9.16 5.8 1,525 67.0

7,2 13,27 12,13 10,99 19 782 91,4

First of all, when calculating pile foundations, one should consider a relatively simple analytical method for determining the rigidity of piles as part of the foundation by assessing their settlement as a conditional foundation in accordance with the requirements of the previously valid SNiP 2.02.03-85. This calculation is performed for models No. 1 and No. 2 by determining the settlement of a conditional foundation as an absolutely rigid columnar foundation on a natural foundation in the “REQUEST” satellite program, followed by

analysis of deformations in the SCAD calculation complex. Such a simple calculation should always be performed as an estimate at a preliminary stage before moving on to more complex analytical and numerical models.

As part of models No. 3 and No. 4, the technology used by the authors for calculating piles in a group in accordance with standard analytical methods is based on the integrated use of the SCAD Office calculation and analytical system and the freely distributed mathematical package SMath Studio. The main calculation is performed based on the finite element method in the SCAD calculation package. In the mathematical package SMath Studio, an additional clarifying calculation of the mutual influence of piles in a group is carried out in accordance with two methods regulated by SP 24.13330.2011 based on data on the geometry and stress-strain state of structures in SCAD Office. In model No. 3, the results of the clarifying calculation in a mathematical package are exported in the form of a simple calculation subcircuit for the SCAD calculation complex with nodes at the lower ends of the piles and additional forces calculated at each node, allowing in a linearly deformable model to obtain deformations in the form of a general sedimentary funnel of the pile field with taking into account the mutual influence of neighboring piles.

In the mathematical package in problem No. 4, the analytical method SP 24.13330.2011 is implemented based on the cell method for a pile field with a pliable slab grillage. In SCAD, core finite elements of piles with finite stiffness connections at the lower ends are replaced by a distributed bed coefficient applied directly to the slab grillage. Model No. 5 introduces an additional difference from model No. 4, in which the first constant bed coefficient K0 is applied in the center of the slab, and variable coefficients Kx and Ky are applied along strip areas of constant pitch along the perimeter of the slab grillage.

Verification of settlements obtained by analytical calculations according to SP 24.13330.2011 with a sufficient degree of correlation is carried out using numerical methods based on the strength characteristics of the soil under the assumption of its linear deformation. The first numerical method for model No. 6 involves the creation of a conditional foundation on the Pasternak elastic half-space in the form of an imaginary plate with two assigned constant proportionality coefficients for compression C1 and shear C2. The use of the CROSS program with the bilinear Fedorovsky model with variable bed coefficients was not considered, since it is intended for wide slabs. The second numerical method in SCAD in problem No. 7 is a model of a linearly deformable foundation (LDF) using volumetric finite elements.

Let us give examples of solving problems using previously described analytical and numerical methods. The object of study is a pile-slab foundation, with a grillage size of 26.6^17.3 m and a laying depth of 2 m from the planning surface. Two groups of models are considered. In the first group, only the rigidity of a flexible slab grillage 1000 mm thick made of B20 grade concrete, modeled by plate four- and three-node finite elements of types 44 and 42, is taken into account. In the second group, the rigidity of the foundation is increased by introducing monolithic walls 400 mm thick made of B20 grade concrete. The pile field is represented by square-section piles with a side of 300 mm and a length of 10 m made of concrete grade B20, modeled by universal rod finite elements of the 5th type or in model No. 7 by isoparametric volumetric finite elements of the 34th type. The pitch of the piles in both directions is 1.075 m with a symmetrical arrangement

NI. The conditionally homogeneous soil base is composed of soft plastic loams with the following characteristics: y = 19.1 kN/m3, f = 14°, c = 0.012 MPa, E = 10.0 MPa. There is no underground water. The average standard pressure on the foundation and the weight of the piles ozp is 294 kPa, domestic pressure from the weight of the soil ozg = 229.2 kPa.

Let's consider solving the first problem using the SNiP 2.02.03-85 method. In the “REQUEST” program as part of the SCAD Office calculation complex, the “Foundation Settlement” section is intended for this task, under the conditional assumption that the pile field operates as a foundation on a natural foundation. When entering the above parameters, the foundation settlement s is 147 mm, the depth of the compressible strata is 11.6 m. A similar calculation of the depth of the compressible strata using the layer-by-layer summation method according to SP 24.13330.2011 gives a close result of -11.38 m. “QUERY” allows you to calculate the Winkler bed coefficient C1, equal to 2001 kN/m3 when applied to a slab grillage, or Oz1, equal to 2300.9 kN/m when applied to the lower nodes of meter-long fragments of pile caps. Transferring the rigidity parameters of the pile foundation calculated using the first method into the SCAD design scheme makes it possible to take into account the work of above-foundation structures with the foundation in strict accordance with SNiP 2.02.03-85. In the case of applying a bed coefficient C1 = 2001 kN/m3 uniformly distributed over the area to the slab grillage, the settlement of all points of the grillage is almost uniform and corresponds to the value s = 147 mm calculated in “REQUEST” (Fig. 1, 1).

When the Winkler bed coefficient is applied to the lower ends of meter-long fragments of piles, the settlement becomes inhomogeneous due to the slight difference in the load areas of the outermost piles and the deformability of the heads of the core elements of the piles themselves under the influence of bending moments, increasing from the center of the grillage to its edges. Nevertheless, the differences in settlement of different points of the slab do not exceed ±3 mm from the average value, and they can be neglected (Fig. 1, 2).

The settlements of the reinforced grillage, braced by the vertical monolithic walls of the basement, in the case of a constant bed coefficient over the area also remain homogeneous (Fig. 1, 3). When applying bed coefficients to the lower nodes of the piles, the grillage settlements turn out to be non-uniform, however, due to an increase in rigidity, their variability is reduced by six times - to ±0.5 mm (Fig. 1, 4). A model with increased grillage rigidity, by introducing vertical walls as reinforcing ribs, clearly demonstrates that the compliance becomes negligible within 0.002% in the direction of the greatest extent of the foundation and its lower rigidity. From this follows the validity of performing the calculation of a pile foundation according to the SP 24.13330.2011 method (clauses 7.4.4-7.4.5) for a pile cluster, assuming that the grillage operates as an absolutely rigid stamp.

Mathematical model No. 4 within the framework of the analytical methodology SP 24.13330.2011 for a pile field was developed in strict accordance with paragraphs. 7.4.6-7.4.9. This technique, like the first two models - No. 1 and No. 2, is based on the assumption of the behavior of the pile foundation as conditional with the base at the level of the lower ends of the piles and uses the Winkler foundation model with a single proportionality coefficient C0 (Fig. 1, 5, 7). The difference between this method and a conditional foundation is that it takes into account additional average settlements of piles due to soil punching and compression of the pile shaft. Of great interest is model No. 5, which also considers only one bed coefficient Oi, but with a variable value depending on the distance of the piles from the center of the slab. The proportionality coefficient in the center of the slab C0 is taken to be the same as in the previous model No. 4. The distribution of the calculated values of the proportionality coefficient and de-

formations for model No. 5 with a flexible and wall-reinforced grillage is shown in Fig. 1, 6 and fig. 1, 8 respectively. In the case of a single bed coefficient, the model receives only the average draft. In the case of a variable bed coefficient, a slight deflection of the slab appears.

Rice. 1. Settlement of the slab grillage (mm) with the reduced rigidity of the pile foundation to the lower surface of the slab according to the Winkler model: 1 - model 1.1; 2 - model 2.1; 3 - model 1.2;

4 - model 2.2; 5 - model 4.1; 6 - model 5.1; 7 - model 4.2; 8 - model 5.2 Fig. 1. Pile-slab settlement (mm) of Winkler subgrade model: 1 is model 1.1; 2 is model 2.1; 3 is model 1.2; 4 is model 2.2; 5 is model 4.1.; 6 is model 5.1.; 7 is model 4.2.; 8 is model 5.2

Let's move on to considering discrete models of pile foundations (Fig. 2). When constructing such finite element models, the first step is to assign bed coefficients along the lateral surface of the piles in order to describe the horizontal stiffness of the foundation, which increases in depth as the degree of compression of the piles by soil increases. Accounting for the horizontal influence of piles in a group is based on the works of K.S. Zavrieva. Calculation of horizontal soil resistance along the lateral surface of piles within the framework of the study

tion is produced in SMath Studio. First, the reduction factor a is calculated using formula B.5 SP 24.13330.2011. Then the values of bed coefficients Cz on the side faces are calculated according to Appendix B.2.

Rice. 2. Settlements of the slab grillage (mm) with a discrete foundation model: 1 - bed coefficient along the lateral surface of the piles (kN/m3); 2 - initial vertical connections of final stiffness along the lower nodes of the piles (kN); 3 - calculated non-uniform reduction in rigidity along the tips of the piles with mutual influence vertically with the application of additional nodal forces (kN); 4 - model 3.1; 5 - model 3.2; 6 - model 6.1; 7 - model 6.2; 8 - model 6.1; 9 - model 6.2 Fig. 2. Pile-slab settlement (mm) with a discrete subgrade model: 1 is the lateral surface coefficient of subgrade reaction on piles (kN/m3); 2 are the vertical elastic constraints in lower pile nodes (kN); 3 is the estimated non-uniform reduction of stiffness along the edges of the piles under the mutual effect of vertically applied additional nodal efforts (kN); 4 is model 3.1.; 5 is model 3.2.; 6 is model 6.1.;

7 is model 6.2.; 8 is model 6.1.; 9 is model 6.2

The reduction coefficient a is calculated using the empirical formula with adjusted coefficients given in Appendix B.5 SP 24.13330.2011. For the case under consideration, with a symmetrical distance of adjacent piles by 1.075 m, the required reduction factor in the load-bearing capacity a when accepting horizontal loads due to work in a group is 0.1. The bed coefficients were calculated for the core finite elements of the piles in the directions of the local axes Y1 and Z1, indicating the value of the width of the pile in the “Width of the support area” field (Fig. 2, 1).

The initial vertical boundary conditions are assigned at the second step of the calculation and first without taking into account the mutual influence of the piles in the group. Calculation of the preliminary vertical stiffness of piles is carried out in accordance with clause 7.4.2. SP 24.13330.2011. Since the example uses homogeneous soil, calculations of averaged characteristics are simplified. The shear modulus G1 of the soil layers cut through by the pile is calculated based on the averaged deformation modulus E1 and Poisson's ratio v1 of the layers cut through by the pile. The shear modulus G2 is calculated in a similar way for the soil layers located under the lower ends of the piles. The deformation modulus E2 of the soil layers located under the pile is taken to be averaged within a depth equal to half the length of the pile 0.5L, or equal to 10d of the reduced diameters of the pile from the lower ends of the piles. Poisson's ratio v2 is specified directly for the layer below the base of the conditional foundation. In the case of homogeneous soil under consideration, we have the same values of deformation moduli - E1 = E2 = 10 MPa, shear moduli - G1 = G2 = 3620 kN/m2 and Poisson's ratios - v = v1 = v2 = 0.38.

The initial constraint of the final stiffness kz, kN/m, introduced into the lower end of single piles to take into account the interaction with the surrounding soil in the finite element method without taking into account the mutual influence of neighboring piles in a group vertically, is determined by the formula

k7 = = 52,800 kN/m, (3)

where ß" is the coefficient of the rigid pile, ß" = 0.17ln[(kv G L)/G2 d] = 0.686; kv - intermediate coefficient for calculating ß", kv = 2.82 - 3.78v + 2.18v2.

The multiple excess of the initial value of vertical stiffness compared to the SNiP method according to the Winkler model is explained by the fact that the final stiffness will decrease as a result of iterative refinement during the next stage of calculating the mutual influence of piles in a group under joint vertical deformations with the formation of a common sedimentary crater. For this calculation, data on the coordinates of the lower nodes of the piles in the pile field and the values of the effective loads are required. This information can be displayed in the “Reactions in special elements” post-processor, for which, at the time of launching the linear calculation in the SCAD calculation complex, the “Calculate reactions in connections” option should be checked in the parameters. In the “Reactions in Special Elements” post-processor, the scheme is fragmented along the lower nodes of the piles and the vertical reactions Rz from standard combinations of constant and long-term loads are analyzed for the color scale of the visible fragment (Fig. 2, 2).

When analyzing small design schemes, data on the coordinates of the lower nodes of piles in the horizontal plane and the values of the calculated reactions from standard long-term impacts can be entered directly into the mathematical package SMath Studio in the form of a matrix or numerical series. In case of large pile fields, direct import is necessary

into a mathematical data package from the SCAD calculation complex. The easiest way to transfer data is in Excel format. If a fragment of the diagram is visible, containing only the nodes of the lower ends of the piles, in the table panel on the “Nodes” tab, click the button to export all currently visible nodes to a separate Excel file. The file must be saved to a specially created directory on your hard drive at the address that will later be specified when executing the command to import data in Excel format into the SMath Studio mathematical package. Similarly, in the SCAD interface, in the table panel, go to the “Efforts in special” tab. elements" and click the button to export to a separate Excel file the forces in the currently visible finite stiffness connections under the ends of the piles. In a mathematical package using linear programming tools, an array with imported coordinates of pile nodes is converted into two numerical series with coordinates X and Y. Based on the coordinates of the lower pile nodes, the next step is to form a general matrix “a” of the relative position of piles in the bush in the form of calculated distances between piles . The size of the square matrix corresponds to the number of piles in the foundation. Based on the relative position of the piles, the matrix “5” of the vertical mutual influence of the piles in the bush is calculated according to the theory of elastic half-space. This is ensured by performing multiple calculations of each member of the matrix in accordance with the formulas of SP 24.13330.20111 (clause 7.4.4), which provide for the zeroing of the coefficient of mutual influence of one pile on another when a certain distance between them is exceeded. In our case, this distance is 8.5 m. The last step is to calculate the additional forces ANh, which are the sum of the vertical reactions Nh in closely spaced piles, taking into account the mutual influence coefficient 5. The resulting forces ANh should be entered manually into each corresponding lower node of the pile or into automatically generate a corresponding subdiagram with nodes and forces, which can be inserted into the general design diagram in SCAD. The specified forces are necessary for the occurrence of additional deformations in the lower node of each pile in the design scheme and the formation of a common sedimentary funnel (Fig. 2, 3). Therefore, in the area where the largest number of piles are located within the 8.5 m circle, the additional settlements will be greater. In the edge areas of the grillage (and especially at its corners), the concentration of piles within this circle will decrease, which will provide a smaller depth of the sedimentary funnel. In Fig. 2, 4 and fig. 2, 5 show the settlements of compliant and rib-reinforced grillages, taking into account the mutual influence of piles in a group with redistribution of loads and the formation of a funnel.

In problem No. 6, due to the fact that bed coefficients in the Pasternak model are assigned only to plate elements, it is necessary to construct an imaginary slab of low rigidity under the lower ends of the piles. In addition, it is recommended to provide at least one additional row of nodes around the outer perimeter of the pile field. Using this outer row of nodes, two- and one-node contour elements will be constructed. An imaginary slab of low rigidity should not have intermediate nodes that do not belong to the ends of the piles in the interpile space, otherwise these nodes will receive excessively high deformations. Along the perimeter of a conditional pile foundation in the form of an imaginary slab based on Pasternak, for the correct use of contour elements there should be no internal corners. Such corners should be described by diagonal sections, adding additional nodes between adjacent external nodes. After specifying the necessary nodes for the external office, a finite element mesh is generated on the plane and a mesh of shells is created with the rigidity of the underlying soil only at the specified nodes with a thickness of 1 mm.

On the resulting mesh of triangular and quadrangular plate finite elements, bed coefficients C1 and C2 are assigned, equal in the example under consideration to 1560 kN/m3 and 14500 kN/m3, respectively. To complete the Pasternak model, two-node and one-node contour elements with the same bed coefficients are specified along the contour of the imaginary slab. The horizontal stiffness along the lateral surface of the piles is assumed to be identical to model No. 3. For single-node contour elements, it is necessary to set the corresponding sector angle. Finally, the vertical stiffness of the finite-stiffness bonds should be removed or reduced by six orders of magnitude so that they are switched off from work and vertical deformations are perceived over the entire area of the imaginary slab on the elastic half-space (Fig. 2, 6 and Fig. 2, 7).

The last method under consideration for calculating a pile-slab foundation in the form of a spatial model of the foundation is useful in connection with the possibility of a clear visual analysis of the joint deformation of the soil mass and reinforced concrete pile structures united by a monolithic slab grillage. In this numerical method, it is recommended to model piles in the form of six- or eight-node isoparametric volumetric elements of type 32 or 36 in order to reduce stress concentrations. The size of the soil base is taken in height in accordance with the previously determined depth of the compressible thickness. The width of the modeled area from the boundaries of the slab grillage should exceed the depth of the compressed thickness at least twice. Absolutely rigid connections along all six degrees of freedom at the base of the soil mass and limitation of only horizontal translational deformations along the lateral faces (X, Y) were taken as boundary conditions. The calculation results for model No. 7 are shown in Fig. 2, 8 and Fig. 2, 9.

From the results of the comparative analysis presented in the table above, it is clear that foundation models made using the one-parameter Winkler model make it possible to transfer averaged settlements determined by analytical methods into a numerical model of the finite element method with sufficiently high accuracy. In this case, there is no redistribution of forces at the base of the Winkler, as a result of which the characteristic sedimentary funnel does not form and bending moments do not arise in the slab grillage. The longitudinal reinforcement of the grillage will be minimal under distributed loads. Under concentrated loads from the columns, the slab in the span will receive a reverse bend, oriented convexly upward, which will lead to unreasonably increased upper reinforcement. Winkler models are only applicable to control average settlements and can also be useful when taking into account dynamic soil stiffness for the analysis of above-foundation structures.

The results of calculating the deformations of the grillage using the mathematical model No. 3 of a pile cluster on a linearly deformable foundation implemented by the authors in SMath Studio in accordance with the analytical method SP 24.13330.2011 according to paragraphs. 7.4.4-7.4.5 turned out to be close to the calculation of the model from volumetric finite elements. At the same time, the nature of deformations in the form of a sedimentary funnel on the surface of the base is also very similar due to the use of a unified theory of elastic half-space in the two models. In both cases, extreme stress values are observed in the outermost piles, in which it is necessary to take into account the “edge pile effect” and the transition of the base to an elastic-plastic state by reducing the soil deformation modulus.

Model of pile-slab foundation No. 4, also implemented in a mathematical package in accordance with SP 24.13330.2011 pp. 7.4.6-7.4.9, has a constant stiffness according to

slab area and is based on the Winkler model. This model can be used to estimate the average settlement of a structure. The next model - No. 5 - with variable bed coefficients makes it possible to obtain minor bending moments, but relatively small compared to models No. 3 and No. 7 on the elastic half-space. The authors consider the possibility of further refinement of this model by taking into account not the averaged pressures in each pile of a pile-slab foundation, but their actual values calculated in each pile in the finite element model.

Model No. 6 with an imaginary plate in Pasternak’s two-parameter contact model showed unreasonably low precipitation, which indicates the need to analyze other available methods with two bed coefficients. In contrast to the contact models of Winkler or Pasternak, model No. 7 of a linearly deformable half-space of volumetric finite elements, when jointly calculating the structure with the foundation, allows for a more detailed analysis of the stress-strain state of the soil in the thickness of the foundation. However, it should be noted that the lack of consideration of the plastic properties of foundation soils allows only a qualitative assessment to be made in order to identify the need to make changes to design solutions to eliminate zones of high stress concentrations. On the other hand, the LDO model of volumetric finite elements has an overestimated distribution capacity, as a result of which it may be necessary to refine the depth of the compressible strata using the method of successive iterations based on the results of other previously described calculations to achieve compliance with the average settlement. Thus, this method can only be considered as an additional one, useful for improving the quality of the analysis of the stress-strain state. It should also be noted that the deformations of the pile nodes of the LDO model occur parallel to the surface of the sedimentary funnel, which does not correspond to reality and the deformations in model No. 3, in which the rigidity should increase as the depth increases due to compression of the pile by the soil (see Fig. 2, 1) . This problem can be eliminated by taking into account the quasi-anisotropic properties in the volumetric finite elements of the foundation.

Bibliography

1. Perelmuter A.V., Slivker V.I. Calculation models of structures and the possibility of their analysis. - 4th ed. - M.: SKAD SOFT Publishing House, 2011. - 736 p.

2. Garagash B.A. Reliability of spatially adjustable systems “base-structure” with uneven deformations of the base: in 2 volumes. T. 1. - M.: Publishing house ASV, 2012. - 416 p.

3. Tsudik E. Analysis of structures on elastic foundations. - FL: J. Ross Publ., 2013. - 585 p.

4. Tsytovich N.A. Soil mechanics: Short course: textbook. - 6th ed. - M.: Book house "LIBROKOM", 2011. - 272 p.

5. Piles in hydraulic engineering construction / V.G. Fedorovsky, S.N. Levachev, S.V. Qurillo, Yu.M. Kolesnikov. - M.: Publishing House ASV, 2003. - 240 p.

6. Edigarov G.E. Experience of using SCAD OFFICE in calculating the intermediate support of a bridge taking into account the mutual influence of piles in a bush // CADMASTER. - 2015. - No. 3. - P. 88-97.

7. Shapiro D.M. Theory and calculation models of foundations and geotechnical objects. - M.: Publishing house ASV, 2016. - 180 p.

8. Piles and pile foundations / R.A. Mangushev, A.L. Gotman, V.V. Znamensky, A.B. Ponomarev; edited by R.A. Mangusheva. - M.: Publishing house ASV, 2015. - 320 p.

9. Geotechnician's Handbook. Foundations, foundations and underground structures / under general. ed. V.A. Ilyicheva, R.A. Mangusheva. - M.: Publishing House ASV, 2016. - 1040 p.

10. Tomlinson M., Woodward J. Pile design and construction practice. - New York: Taylor&Francis, 2008. - 566 p.

11. Day R.W. Foundation engineering handbook: Design and construction with the 2009 International Building Code. - San Diego, California: McGrawHill, 2010. - 1006 p.

13. The effect of an edge pile and its consideration when calculating a slab grillage / V.P. Petrukhin, S.G. Bezvolev, O. A. Shulyaev, A.I. Kharichkin // Development of cities and geotechnical construction. - 2007. - No. 11. - P. 90-97.

14. Mikhailov V.S., Busygina G.M. Determination of roll and joint settlement of slab foundations // Polzunovsky almanac. - 2016. - No. 3. - P. 141-145.

15. Mikhailov V.S., Teplykh A.V. Taking into account the characteristic features of various foundation models when calculating the mutual influence of buildings on large foundation slabs using the SCAD Office calculation and analytical system // Current problems of computer modeling of structures and structures: VI Int. symposium - Vladivostok, 2016. - pp. 133-134.

1. Perel "muter A.V., Slivker V.I. Raschetnye modeli sooruzheniy i vozmozhnost" ikh analiza. 4th ed. Moscow, SCADSOFT, 2011, 600 p.

2. Garagash B.A. Nadezhnost" prostranstvennykh reguliruemykh sistem "osnovanie -sooruzhenie" pri neravnomernykh deformatsiiakh osnovaniia. Vol. 1. Moscow, ASV, 2012, 416 p.

3. Tsudik E. Analysis of structures on elastic foundations. FL, J. Ross Publ., 2013, 585 p.

4. Tsytovich N.A. Mekhanika gruntov: Kratnyi kurs. 6th ed. Moscow, LIBROKOM, 2011, 272 p.

5. Fedorovskiy V.G., Levachev S.N., Kurillo S.V., Kolesnikov. Svai v gidrotekhnicheskom stroitel "stve. Moscow, ASV, 2003, 240 p.

6. Edigarov G.E. Opyt primeneniya SCAD OFFICE v raschete promezhutochnoy svaynoy dvukhryadnoy opory mosta s uchetom vzaimnogo vliyaniya svay v kuste. CADMASTER, 2015, no. 3, pp. 88-97.

7. Shapiro D.M. Teoriya i raschetnye modeli osnovaniy i ob»ektov geotekhniki. Moscow, ASV, 2016, 180 p.

8. Mangushev R.A. Gotman A.L., Znamenkskiy V.V., Ponomarev A.B. Svai i svaynye fundamenty. Konstruirovanie, proektirovanie, tekhnologii. Eds. R.A. Mangushev. Moscow, ASV, 2015, 320 p.

9. Reference book geotekhnika. Osnovaniia, fundamenty i podzemnye sooruzheniia. . Eds. V.A. Il"ichev, R.A. Mangushev. 2nd ed. Moscow, ASV, 2016, 1040 p.

10. Tomlinson M., Woodward J. Pile Design and Construction Practice. New York, Taylor&Francis, 2008, 566 p.

11. Day R. W. Foundation Engineering Handbook: Design and Construction with the 2009 International Building Code. San Diego, California, McGrawHill, 2010, 1006 p.

12. Zavriev K.S., Shpiro G.S. et al. Rekomendatsii po raschetu fundamentov glubokogo zalozheniya opor mostov. Moscow, Rotaprint TsNIIS, 1970, 95 p.

13. Petrukhin V.P., Bezvolev S.G., Shulyat "ev O.A., Kharichkin A.I. Effekt kraevoy svai i ego uchet pri raschete plitnogo rostverka. Razvitie gorodov i geotekhnicheskoe stroitel"stvo, 2007, no. 11, pp. 90-97.

14. Mikhaylov V.S., Busygina G.M. Opredelenie krena i sovmestnykh osadok dvukh plitnykh fundamentov. Polzunovskii almanac, 2016, no. 3, Barnaul, Altaiiskii gosudarstvennyi technicheskii universitet, pp. 141-145.

15. Mikhailov V.S., Teplykh A.V. Uchet kharakternykh osobennostei razlichnykh modelei osnovaniia pri raschete vzaimnogo vliianiia zdanii na bol"shikh fundamentnykh plitakh s ispol"zovaniem raschetno-analiticheskoi systemy SCAD Office. VI Mezhdunarodnyi simpozium. Aktual"nye problemy komp"iuternogo modelirovaniia konstruktsii i sooruzhenii. Vladivostok, 2016, pp. 133-134.

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