Angle edge and feather definition. Calculation of welds. Construction of farm nodes. Centering the rods. Outline and attachment of gussets

The design force in the section of paired equal angles is distributed as follows: 70% falls on the butt (i.e. N about = 0,7N) and 30% per pen (i.e. N P = 0,3N).

When calculating welds, the values \u200b\u200bof the legs of the seams along the backing ( ) and by pen ( ) and determine the required length of the seams along the backing (
) and by pen (
).

When appointing a leg leg, the following recommendations should be taken into account:


(corner or gusset). The thickness of the gussets is assigned according to the table. 13 app. 2.

The required length of the butt weld is taken according to the largest value found by the formulas:

when calculating the weld metal

; (4.4)

, (4.5)

where γ wf = γ wz = 1 (p. 11.2 *) - coefficients of weld seam working conditions;

f = 0,7, z = 1 (table 34 *) - coefficients of penetration depth corresponding to semi-automatic welding in the lower position;

(Table 6 *) - coefficient of working conditions of the structure;

R wf and R w z (see item 2) - calculated shear resistance of the connection with fillet welds.

The required length of the weld along the pen is taken according to the largest value found by the formulas:

when calculating the weld metal

; (4.6)

when calculating for metal fusion boundaries

. (4.7)

When assigning the lengths of welds along the backing ( ) and by pen ( ) should be guided by the following:

1. - whole number of centimeters;

2. ≥ 4 cm;

3.
;

4.
;

5.values and take as little as possible.

Figure: 2. To the calculation of welds

The detail (working) drawing shows the facade of the truss, plans of the upper and lower chords, side view. The nodes are depicted on the facade, and for clarity of the drawing, the nodes and sections of the rods are drawn at a scale of 1:10 on the diagram of the axes of the truss, drawn

noah on a scale of 1:20.

Lattice rods are usually cut normally to the rod axis. For large rods, oblique cutting is allowed in order to reduce the size of the gussets. Lattice rods are not brought to the chords at a distance a = 6 t f – 20 mm(Where t f – gusset thickness in mm), but not more than 80 mm(fig. 2).

In a farm with rods from paired corners made up by a brand, the nodes are designed on gussets that lead between the corners. It is recommended to attach the minimum leg with continuous seams to the girder belt. The gussets are produced for the butts of the belt corners by 10 ... 15 mm (fig. 2).

The basis for designing truss nodes is the intersection of the axes of all members converging at a node in the center of the node. The main dimensions of the node are the distances from the center of the node to the ends of the lattice bars to be attached and to the edge of the gusset. These distances are used to determine the required length of the bars of the lattice, which is assigned a multiple of 10 mm, and the sizes of gussets. The dimensions of the gussets are determined by the required length of the seams for fastening the elements. It is necessary to strive for the simplest outlines of gussets in order to simplify their manufacture and reduce the number of scraps.

To ensure the joint work of the corners, they are connected with spacers. The clear distance between the spacers should be no more than 40 i x for compressed elements and 80 i x for stretched, where i x - radius of gyration of one corner about the axis x - x... The thickness of the spacers is assigned equal to the thickness of the knot gussets. Spacers are accepted in width 60 mm and are produced for the dimensions of corners by 10 ... 15 mm in each direction.

On the facade of the truss, the dimensions (legs and length) of the welds are indicated.

The base plate should be 20 mm and dimensions in plan 300 x300 mm.

The drawing contains the bill of materials (in the established form) for the truss and notes are given.

ATTACHMENT 1

Table 1

Initial data for students of the specialty 270301 "Architecture"

The last two digits of the cipher

Truss length L (m)

Step of roof trusses

Truss height h (m)

Steel grade

table 2

Initial data for students of the specialty 270302 "Design of architectural environment"

The last two digits of the cipher

Truss length L (m)

Step of roof trusses

Truss height h (m)

Steel grade

APPENDIX 2

Table 3

Standard and calculated tensile strength,

compression and bending of rolled products in accordance with GOST 27772-88 for steel

structures of buildings and structures (sample from table 51 * 2)

rolled, mm

Standard resistance of structural shapes, MPa

Design resistance of structural shapes, MPa

R уn

R un

R at

R u

St. 20 to 40

St. 20 to 30

St. 10 to 20

St. 20 to 40

St. 10 to 20

St. 10 to 20

St. 10 to 20

St. 20 to 40

St. 10 to 20

St. 20 to 40

Table 4

Welding materials and design resistances

(sample from tables 55 * and 56)

Table 5

Hot-rolled steel I-beams with a slope of the inner edges of the shelves (GOST 8239-89)

Dimensions, mm

section, cm 2

Axis x - x

Axis y - y

Weight 1 m, kg

I x , cm 4

W x , cm 3

i x , cm

S x , cm 3

I y , cm 4

W y , cm 3

i y , cm

Table 6

Hot-rolled steel channels with a slope of the inner edges of the shelves (GOST 8240-89)

Dimensions, mm

section, cm 2

Axis x - x

Axis y - y

z 0 ,

Weight 1 m, kg

I x , cm 4

W x , cm 3

i x , cm

S x , cm 3

I y , cm 4

W y , cm 3

i y , cm

T
table 7

Hot-rolled steel equal angles (GOST 8509-86)

About the meaning: b – shelf width; t – shelf thickness; R - radius of internal curvature; r – shelf curvature radius; I – moment of inertia; i – radius of gyration; z 0 – distance from the center of gravity to the outer edge of the shelf

Dimensions, mm

section, cm 2

Reference values \u200b\u200bfor axes

Weight 1 m, kg

x - x

x 0 - x 0

at 0 - at 0

x 1 - x 1

z 0

I x , cm 4

i x , cm

I x 0 , cm 4

i x 0 , cm

I y 0 , cm 4

i y 0 , cm

I x 1 , cm 4

Continuation of table 7

End of Table 7

Figure: 3. Determination of efforts in the elements of the truss graphically (Maxwell-Cremona diagram)

Table 8

Stability factor

Conditional flexibility

Stability factor

Conditional flexibility

Stability factor

Note.

For intermediate values  magnitude should be determined by linear interpolation.

Table 9

Vertical limiting deflections of structural elements

(sample from Table 19)

Note.

For intermediate values l in pos. 2, a magnitude n 0 should be determined by linear interpolation.

Table 10

Selection of cross-sections of truss rods

Rod No.

Calculated effort N, kN

Cross-sectional area A, cm 2

Estimated length l x , cm

Radius of gyration i x , cm

Flexibility λ

Ultimate flexibility [ λ ]

Conditional flexibility

Stability factor

Working conditions coefficient γ from

Section check,

stretching

strength

sustainability

Upper belt

) ┘└ 12512

21,51 < 23,75

Lower belt

23,66 < 23,75

constructively

15,68 < 23,75

23,748< 23,75

┘└ 10010

Table 11

Calculation of welds

Rod No.

An effort N, kN

Butt seam

Per seam

N about , kN

, cm

, cm

N p , kN

, cm

, cm

┘└ 10010

Table 12

Minimum legs of seams (table 38 *)

Connection type

Welding type

Yield strength, MPa

Minimum legs k f , mm, with a thickness of the thickest of the welded elements t, mm

T-shaped with double-sided fillet seams; lap and corner

St. 430 to 530

Automatic and

semi-automatic

St. 430 to 530

T-bar with one-sided fillet welds

Automatic and

semi-automatic

Table 14

Calculated bar lengths

(sample from Table 11)

Designation: l - distance between centers of nodes

Table 15

Limit slenderness of rods

(sample from tables 19 * and 20 *)

Table 16

Working condition factor

(sample from table 6 *)

L I T E R A T U R A

1.SP 53-102-2004. General rules design of steel structures. Gosstroy of Russia. - M .: TsNIISK im. Kucherenko, 2005.

2. SNiP II-23-81 *. Steel structures. Design standards / Ministry of Construction of Russia. - M .: GP TsPP, 2000 .-- 96 p.

3. SNiP 2.01.07-85 *. Loads and Impacts / Gosstroy of Russia. - M .: FGUP TsPP, 2004.-44 s

4. Faibishenko V.K. Metal structures: Textbook. manual for universities. - M .: Stroyizdat, 1984 .-- 336 p.

General information ……………………………………… .. ……………………

1. Initial data ………………………………………………………

2. Selection of the main design characteristics ……………………………

3. Calculation of the coverage run ………………………………………………

4. Design of a truss truss …………………………………….

4.1. Determination of loads on a truss ……………………………………… ..

4.2. Determination of the design forces in the truss rods ………………… ...

4.3. Selection of cross-sections of truss rods ………………………………………

4.4. Calculation of welds for attaching a brace and struts to gussets ……

Appendices ………………………………………………………………… ...

Literature…………………………………………………………………….

Farm design. Details of knots

Centering the rods. Outline and attachment of gussets

The design of the truss begins with drawing the center lines that form the geometric design of the structure. In this case, one should strictly ensure that the axial lines of the elements converging at the nodes intersect at the center of the node; only in this case the forces converging at the node can be balanced.

Further, the contour lines of the rods are applied to the drawing so that the axial lines, if possible, coincide with the center of gravity of the section or be as close to it as possible. In this case, in welded trusses, the distance from the center of gravity to the butt z is rounded up to the nearest integer multiple of 5 mm; in riveted trusses, the corners are centered on riveted risks.

As a rule, cutting the corners of the lattice should be done perpendicular to the axis, without bringing the ends of the rods to the belt by 10 - 20 mm. The shape of the gussets in the nodes is determined by the conditions for placing welds or rivets that attach the lattice elements and should be as simple as possible.

Since the gusset transmits force from one rod to another, each of its sections must be strong and capable of absorbing the corresponding force flow.

Figure a shows the incorrect design of the gusset, which in section I - I has a smaller area than the sectional area of \u200b\u200bthe attached brace from two corners, and therefore can break. In addition, the seam k, located at the butt, the corners of the rack and taking up most of the force of the rack, cannot transfer it to the gusset due to the lack of space for the normal power flow.

In this section, the gusset will experience a great overvoltage. Figure b shows a correctly designed gusset having an angle α between the edge of the gusset and the shank of about 20 ° (from 15 to 25 °).

It is better to attach gussets to the waist corners on both sides. - from the side of the butt and feather, since otherwise the belt corners can easily bend as a result of accidental reasons (for example, during transportation).

However, it is not always constructively convenient to release the gusset over the edge of the belt, for example, when installing the girders along the upper belt, attached to the corner stubs. In this case, the gusset is not brought to the edge of the corners by 5 mm and is attached only with seams at the feather.

At the same time, it is advisable to weld the gap formed between the edges of the corners and the gusset, however, this seam cannot be considered as calculated, since it is difficult to ensure its good penetration (the seam is fused, not boiled). Thus, the main working design seams in this case are the seams imposed at the feather.

The force for which the fastening of the gusset is calculated and which seeks to shift it relative to the belt is the resultant of the forces in the lattice elements converging at this node.

In a particular case, in the absence of an external load in the node, this force is equal to the difference in efforts in adjacent panels of the belt:

where N f is the force shifting the gusset along the belt;

N 2 and N 1 - efforts in adjacent panels of the belt.

Force N f is applied in the center of the node in the direction of the belt axis. If the gusset is not released beyond the edge of the belt, this force will cause in the seams located at the feather of the belt corners not only a cut along their length, but also a bend caused by the moment M \u003d N f e.

Usually, the normal stresses from bending are low, and therefore the seam is checked only for a cut with a reduced design seam resistance (by about 15 - 20%).

The principles of designing riveted assemblies remain essentially the same, only rivets are inserted instead of welds.

The dimensions that determine the gusset are dictated, as in welded trusses, by the conditions for attaching the braces; in this case, especially powerful braces can be attached using an additional short stack (figure Attaching corners and channels to gussets). In this case, the number of rivets on one of the shelves of the short stack increases by 50% against the calculated one.

Table - Number of corner types

Calculation of truss nodes

The truss rods in the nodes are connected by sheet gussets, to which they are attached using electric welding.

Determined by the formula

the length of the seam along the feather is determined by the formula

where α is a coefficient that takes into account the share of the effort applied to the butt

N- force in the rod, kN

βf-penetration coefficient (at manual welding βf \u003d 0.7)

Kf1, Kf2 - thickness of seams, respectively, along the butt and feather, cm

Rwf- design resistance of cut fillet welds for weld metal,

equal when using electrodes of type E50: Rwf \u003d 21 kN / cm2

γwf- coefficient of seam working conditions; γwf \u003d 1

The coefficient α is taken equal: for equal angles α \u003d 0.7.

The thickness of the seam along the angle bar is taken 2 mm less than the thickness of the angle shelf, but not less than 4 mm. The maximum seam thickness along the edge of the corner should not exceed 1.2t min, where tmin is the thickness of the thinner element (gusset or corner shelf).

The minimum joint length should be 4 Kf or 40 mm. The maximum design seam length should not exceed 85βf Kf.

Determine the length of the seams of the belts "6" and "7" (δ \u003d 6mm):

Structural length of the backing seam

We accept lw1 \u003d 22 cm.

Seam length along the feather

Kf1 \u003d 8mm \u003d 0.8cm. Kf2 \u003d 6 mm \u003d 0.6 cm.

Determine the length of the seams of the belt "30" and "26" (δ \u003d 6mm):

Structural length of the backing seam

We take lw1 \u003d 4 cm.

Seam length along the feather

Kf1 \u003d 8 mm \u003d 0.8 cm. Kf2 \u003d 6 mm \u003d 0.6 cm.

Determine the length of the seams of the belt "22" (δ \u003d 6mm):

Structural length of the backing seam

We take lw1 \u003d 4 cm.

seam length along the feather

Kf1 \u003d 8 mm \u003d 0.8 cm. Kf2 \u003d 8 mm \u003d 0.8 cm.

The calculated seam lengths are applied to the knot diagram, after which the dimensions of the gusset and its outline are revealed. The accepted outline of the gusset should be simple, preferably rectangular.

Node E must have a support rib of 16 ... 25mm. Minimum rib width 180 mm.

Truss Node Weld Table

The total estimated length of welds (cm) attaching the horizontal plate to the corner flanges on one side of the joint:

where N is the force in the rod of the lower chord, adjacent to the mounting unit, kN.

For more details on the structures of truss truss assemblies and the features of their calculation, refer to the recommended literature (1); (5); (7).

The result of the design of the truss truss is the compilation of a metal specification for the sending element, the form of which should be taken according to the textbook (1).

5.Calculation of the transverse frame of the frame

Determination of frame loads.

Frame loads

a) constant - from the dead weight of structures

b) short-term: snow; crane - vertical from the pressure of the overhead crane wheels and horizontal from the braking of the trolley; wind.

Figure: Frame

A) Constant load on the frame. The support reaction of the girder (kN) Vg \u003d g1L / 2, where L is the span of the girder (truss), will act on the frame post; g1 - linear design load, kN / m2

Vg \u003d 23.88 24/2 \u003d 286.56 kN

b) Snow load on the frame. The corresponding support reaction of the girder (kN) Vр \u003d S1L / 2 will act on the frame post, where S1 is the linear design snow load, kN / m2

Vр \u003d 4.2 24/2 \u003d 50.4 kN

Vertical crane loads. The crane load on the transverse frame is determined from two adjacent cranes, positioned so that the load is greatest.

Calculated vertical force (kN) acting on the rack (column), to which the crane trolleys are approached

Dmax \u003d γf nc Fn max Σyi + G,

where Fn max is the maximum wheel pressure

γf - load safety factor, γf \u003d 1.1

Σyi- the sum of the influence ordinates for the support pressure on the column

nc - combination factor: nc \u003d 0.85

G- weight of crane girder, kN

Influence line ordinates y1 \u003d 0.267, y2 \u003d 1; y3 \u003d 0.8; y3 \u003d 0.066.

Dmax \u003d 1.1 0.85 315 (0.267 + 1 + 0.8 + 0.066) +10.5 \u003d 717.36 kN

Calculated vertical force acting on another frame post

Dmin \u003d γf nc Fn min Σyi + G,

where Fn min is the smallest wheel pressure on the crane (kN)

Fn min \u003d (P + Gc) / n0- Fn max

P - lifting capacity of the crane

Gc- total weight of the crane with trolley

n0 is the number of wheels on one side of the crane n0 \u003d 2

Fn min \u003d (300 + 520) / 2- 315 \u003d 95 kN

Dmin \u003d 1.1 · 0.85 · 95 · 2.4 + 10.5 \u003d 223.68 kN

Horizontal crane loads.

Design horizontal force (kN)

Tc \u003d γf nc Tn Σyi,

where Tn is the normative horizontal force when braking the bogie,

per one crane wheel.

The horizontal force Tc can act on the left or right frame post, both in one direction and in the other direction.

where, - coefficients of penetration depth

Seam service factors

MPa- design resistance for the weld metal (point 4.4);

MPa - design resistance of the fusion boundary metal;

MPa- tensile strength of steel S245 for structural shapes in accordance with GOST 27772-88 with a thickness of 2 to 20 mm (point 2.3);

The calculation is carried out for the metal of the fusion boundary, since

MPa> MPa.

It is recommended to attach the lattice elements from the corners to the gussets with two flank seams.

Distribution of efforts between the seams along the butt and feather

Section type k 1 k 2
y x x y 0.7 0.3

The value of the coefficients taking into account the distribution of the force in the element between the seams along the butt and the feather of the corner, the butt of the corner K 1 \u003d 0.7; corner pen K 2 \u003d 0.3;

Required calculated seam lengths:

On the back; by pen;

The leg of the seam should be set based on design constraints:

On the back; -by pen,

Constructive seam length mm. The lengths of the seams obtained according to the calculation are rounded up to a size multiple of 5 mm. If, according to the calculation, the seam length is less than 50 mm, then we take 50 mm. It is convenient to calculate the seams in tabular form (table 6.)

Table 6 - Calculation of the lengths of welds

,
,
,
, mm mm mm mm mm mm top belt 125x10 0.1 0.03 0.02 lower belt 90x8 358.5 119.6 61.52 braces 125x10 409.4 136.6 70.25 50x5 186.9 74.8 4/5 41.90 63x5 55.1 22.1 4/5 11.82 63x5 39.6 15.9 4/5 8.49 racks 50x5 28.6 11.5 4/5 6.13 50x5 54.8 21.9 4/5 11.75 50x5 50.2 20.1 4/5 10.77

3.5 Calculation and design of truss nodes



According to the obtained lengths of the seams for fastening the braces and racks, we determine the dimensions of the gusset. We do not bring the bars of the lattice to the chords at a distance of mm, but not more than 80 mm, - the thickness of the gusset in mm. For the calculated truss mm<80мм, принимаем а=55мм.

Node 1.

The length of the welded seams of the post to the gusset plate. We accept. The estimated length of the seams, we include in the calculation

We rely on the joint action of efforts and

Stresses in the most loaded seams along the feather of the corners:

Node 2.

Length of welded seams for fastening the belt to the gusset plate. We accept. The estimated length of the seams, we include in the calculation

The welded seams of the belt fastening are counting on the joint action of efforts and.

Stresses in the most loaded joints along the edges of the corners:

Node 4.

We design the assembly on high-strength M20 bolts made of 40X “select” steel; for fastening the belts we accept 4 sheet plates with a section of 125x10.

We check the strength of the joint by force

The cross-sectional area of \u200b\u200bthe joint is determined taking into account the weakening of the cross-section of each lining by one hole in diameter, then the net area of \u200b\u200bthe horizontal and vertical lining is:

Force perceived by one pad:

where is the coefficient of working conditions;
R y \u003d 240 MPa - design resistance of steel S245 for sheet metal according to GOST 27772-88 with a thickness of 2 to 20 mm (point 2.3);

Medium stresses in pads:

Determine the bearing capacity of one plane of friction of one high-strength bolt:



where A bh\u003d 2.45 cm 2 - net area of \u200b\u200bone bolt (point 5.5);

Design tensile strength of bolts;

The smallest temporary resistance (point 5.7);

Coefficient of working conditions when the number of bolts in the joint on one side is less than n< 5 (т.5.3);

Coefficient of friction for gas-flame treatment of contact surfaces without preservation and control of the bolt tension by the torque (point 5.9);

To attach one horizontal plate with one plane of friction, the number of bolts on one side of the joint axis:

We accept 4 bolts M20.

Since the area of \u200b\u200bthe weakened section of the lining, it is necessary to check its strength according to the following formula:

where is the calculated cross-sectional area;

The number of bolts in the section under consideration;

The total number of bolts on the pad on one side of the joint axis.

The welded seams of fastening the gusset to the belt are taken constructively of the minimum thickness

Node 3.

We accept the sections of the overlays.

We check the strength of the joint by force:

since the condition is not met, then the cross-sections of the overlays are accepted.

Sectional area of \u200b\u200bone pad, taking into account weakening by one hole:

Average stress in pads:

We accept the same bolts as in node 4. The force perceived by one pad,

Required number of high-strength bolts for attaching one horizontal strip to one side of the joint axis:

We accept 3 bolts.

The same number of bolts is required to attach the vertical braces to the assembly. Place the bolts in 1 row.

Since, it is necessary to check the strength of the weakened section.

We accept the seams of fastening the gusset to the belt constructively.

Node 5.

The length of the seams for attaching the belt to the gusset is: 18 cm along the edge, 12.6 cm along the feather. We accept. We do not perform strength calculations.

Node 6.

The seams of fastening the belt to the gusset are counting on the combined action of longitudinal forces in the adjacent panels of the belt and and the nodal load F.

Design combination of frame loadings - 11.4:

According to the dimensions of the gusset obtained during the design of the knot, the length of the belt fastening seams is l \u003d 62.7 cm.

Estimated seam length 1:, therefore we include in the calculation.

Estimated seam length 2:, therefore we include in the calculation.

Stresses in the most loaded seam along the backing:

Additional voltages from nodal load F:

where: is the total length of the sections of the seams that transmit the force F.

Node 8.

The length of the seams for attaching the belt to the gusset is: along the edge 18 cm, along the feather - 12.6 cm. We accept them. We do not check their strength, since these seams transmit the same force as the seams for attaching the post 3 to the gusset, the length of which is less.

Connecting gaskets.

To ensure the joint work of the corners, they must be connected with spacers. The distance between spacers should be no more than 40i for compressed members and 80i for stretched members, where i is the radius of gyration of one corner about an axis parallel to the plane of the spacer. In this case, at least two spacers are placed in the compressed elements. The width of the gaskets is taken equal to 60mm, the length -, thickness - 12mm, equal to the thickness of the gussets.


If the ratio of the standard weight of the cover to the standard weight of the snow cover, then

Page 6

Table - Number of corner types

Calculation of truss nodes

The truss rods in the nodes are connected by sheet gussets, to which they are attached using electric welding.

Determined by the formula

the length of the seam along the feather is determined by the formula

where α is a coefficient that takes into account the share of the effort applied to the butt

N- force in the rod, kN

βf-penetration factor (for manual welding βf \u003d 0.7)

Kf1, Kf2 - thickness of seams, respectively, along the butt and feather, cm

Rwf- design resistance of cut fillet welds for weld metal,

equal when using electrodes of type E50: Rwf \u003d 21 kN / cm2

γwf- coefficient of seam working conditions; γwf \u003d 1

The coefficient α is taken equal: for equal angles α \u003d 0.7.

The thickness of the seam along the angle bar is taken 2 mm less than the thickness of the angle shelf, but not less than 4 mm. The maximum seam thickness along the edge of the corner should not exceed 1.2t min, where tmin is the thickness of the thinner element (gusset or corner shelf).

The minimum joint length should be 4 Kf or 40 mm. The maximum design seam length should not exceed 85βf Kf.

Determine the length of the seams of the belts "6" and "7" (δ \u003d 6mm):

Structural length of the backing seam

We accept lw1 \u003d 22 cm.

Seam length along the feather

Kf1 \u003d 8mm \u003d 0.8cm. Kf2 \u003d 6 mm \u003d 0.6 cm.

Determine the length of the seams of the belt "30" and "26" (δ \u003d 6mm):

Structural length of the backing seam

We take lw1 \u003d 4 cm.

Seam length along the feather

Kf1 \u003d 8 mm \u003d 0.8 cm. Kf2 \u003d 6 mm \u003d 0.6 cm.

Determine the length of the seams of the belt "22" (δ \u003d 6mm):

Structural length of the backing seam

We take lw1 \u003d 4 cm.

seam length along the feather

Kf1 \u003d 8 mm \u003d 0.8 cm. Kf2 \u003d 8 mm \u003d 0.8 cm.

The calculated seam lengths are applied to the knot diagram, after which the dimensions of the gusset and its outline are revealed. The accepted outline of the gusset should be simple, preferably rectangular.

Node E must have a support rib of 16 ... 25mm. Minimum rib width 180 mm.

Truss Node Weld Table

 

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