Edge and feather corner definition. Calculation of welds. Design of truss units. Centering the rods. Outlining and attaching gussets

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

When calculating welds, the values ​​of the seam legs along the butt are specified ( ) and by pen ( ) and determine the required lengths of seams along the back (
) and by pen (
).

When assigning a suture leg, the following recommendations must be taken into account:


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

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

when calculating weld metal

; (4.4)

, (4.5)

Where γ wf = γ wz = 1 (clause 11.2*) – coefficients of operating conditions of the weld;

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

(Table 6*) – coefficient of operating conditions of the structure;

R wf And R w z(see paragraph 2) – calculated shear resistance of the connection with fillet welds.

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

when calculating weld metal

; (4.6)

when calculating metal fusion boundaries

. (4.7)

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

1. - integer number of centimeters;

2. ≥ 4 cm;

3.
;

4.
;

5. values And take as little as possible.

Rice. 2. To the calculation of welds

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

noah on a scale of 1:20.

Grating rods are usually cut normal to the axis of the rod. For large rods, oblique cutting is allowed to reduce the size of the gussets. The grille rods are not brought to the distance from the belts a = 6 t f – 20mm(Where t f – gusset thickness in mm), but not more than 80 mm(Fig. 2).

In a truss with rods made of paired angles formed by a brand, the nodes are designed on gussets that are inserted between the angles. It is recommended to attach the gussets to the truss belt with continuous seams of minimum leg length. The gussets are released behind the edges of the waist corners at 10...15 mm(Fig. 2).

The basis for designing truss nodes is the intersection of the axes of all the rods converging in the node in the center of the node. The main dimensions of the assembly are the distances from the center of the assembly to the ends of the attached lattice rods and to the edge of the gusset. Based on these distances, the required length of the lattice rods is determined, which is assigned as a multiple of 10 mm, and 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 the gussets in order to simplify their production and reduce the number of trimmings.

To ensure that the corners work together, they are connected with gaskets. The clear distance between the gaskets should be no more than 40 i x for compressed elements and 80 i x for stretched ones, where i x – radius of inertia of one corner relative to the axis x - x. The thickness of the gaskets is assigned equal to the thickness of the nodal gussets. Spacers are accepted with a width of 60 mm and are produced for corner dimensions of 10...15 mm in each direction.

On the façade of the truss the dimensions (legs and lengths) of the welds are indicated.

Take the base plate with a thickness of 20 mm and dimensions in plan 300 x 300 mm.

The drawing contains a specification of parts (according to the established form) for the truss and provides notes.

ANNEX 1

Table 1

Initial data for students of specialty 270301 "Architecture"

The last two digits of the cipher

Truss length L(m)

Truss spacing

Truss height h(m)

Steel grade

table 2

Initial data for students of specialty 270302 "Architectural Environment Design"

The last two digits of the cipher

Truss length L(m)

Truss spacing

Truss height h(m)

Steel grade

APPENDIX 2

Table 3

Standard and calculated tensile strengths,

compression and bending of rolled products according to GOST 27772-88 for steel

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

rolled, mm

Standard resistance of shaped rolled products, MPa

Design resistance of shaped steel, MPa

R ун

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 sloped internal flange faces (GOST 8239-89)

Dimensions, mm

cross-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 sloped internal flange faces (GOST 8240-89)

Dimensions, mm

cross-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 equal flange steel angles (GOST 8509-86)

Designations: b – shelf width; t – shelf thickness; R – radius of internal curvature; r – radius of curvature of the shelf; 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

cross-section, cm 2

Reference values ​​for axes

Weight 1 m, kg

x – x

X 0 - X 0

at 0 – y 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

Rice. 3. Determination of forces in truss elements graphically (Maxwell-Cremona diagram)

Table 8

Stability factor

Conditional flexibility

Stability factor

Conditional flexibility

Stability factor

Note.

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

Table 9

Vertical maximum deflections of structural elements

(sample from table 19)

Note.

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

Table 10

Selection of cross sections for truss rods

Rod no.

Design force N, kN

Cross-sectional area A, cm 2

Effective length l x, cm

Radius of inertia i x, cm

Flexibility λ

Ultimate flexibility [ λ ]

Conditional flexibility

Stability factor

Working conditions coefficient γ With

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

Seam along the hem

Feather seam

N about , kN

, cm

, cm

N P , kN

, cm

, cm

┘└ 10010

Table 12

Minimum seam lengths (Table 38*)

Type of connection

Type of welding

Yield strength, MPa

Minimum legs k f, mm, with the thickness of the thicker element being welded t, mm

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

St. 430 to 530

Automatic and

semi-automatic

St. 430 to 530

T-shaped with one-sided fillet welds

Automatic and

semi-automatic

Table 14

Design lengths of bars

(sample from table 11)

Designation: l – distance between node centers

Table 15

Ultimate flexibility of rods

(sample from tables 19* and 20*)

Table 16

Working conditions 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.: FSUE TsPP, 2004.-44 p.

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

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

1. Initial data…………………………………………………………

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

3. Calculation of the coating run……………………………………………………………………

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

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

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

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

4.4. Calculation of welds for attaching braces and struts to gussets......

Applications…………………………………………………………………………………...

Literature…………………………………………………………………….

Construction of trusses. Unit details

Centering the rods. Outlining and attaching gussets

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

Next, contour lines of the rods are drawn on the drawing so that the center lines, if possible, coincide with the center of gravity of the section or are 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 whole number, a multiple of 5 mm; in riveted trusses, the corners are centered along the rivet marks.

Trimming the corners of the grille, as a rule, should be done perpendicular to the axis, without bringing the ends of the rods to the waist by 10 - 20 mm. The outline of the gussets in the nodes is determined by the placement conditions of the welds or rivets attaching the lattice elements, and should be as simple as possible.

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

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

In this area, the gusset will experience a large overstress. Figure b shows a correctly designed gusset having an angle α between the edge of the gusset and the rod 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 back and feather, since otherwise the waist corners can easily bend as a result of accidental reasons (for example, during transportation).

However, it is not always structurally convenient to extend the gusset beyond the edge of the belt, for example, when installing purlins attached to the corner shorts along the upper belt. 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.

In this case, it is advisable to weld the gap formed between the edges of the corners and the gusset, however, this seam cannot be considered as a design seam, since it is difficult to ensure good penetration (the seam is welded, not welded). Thus, the main working design seams in this case are the seams placed at the feather.

The force for which the attachment of the gusset is calculated and which tends to move it relative to the belt is the resultant of the forces in the lattice elements converging at a given node.

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

where N f is the force that moves the gusset along the belt;

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

The force Nf is applied at 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 waist corners not only a cut along their length, but also a bend caused by the moment M = N f e.

Typically, normal bending stresses are small, and therefore the seam is checked only for shear with a reduced design resistance of the seam (by about 15 - 20%).

The design principles of riveted assemblies remain essentially the same, only rivets are used 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 piece (figure Attaching corners and channels to gussets). In this case, the number of rivets on one of the shelves of the shorty increases by 50% compared to the calculated one.

Table - Number of types of corners

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 force on the butt

N - force in the rod, kN

βf-penetration coefficient (at manual weldingβf=0.7)

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

Rwf is the calculated resistance of fillet welds to shear metal,

equal when using E50 type electrodes: Rwf= 21 kN/cm2

γwf - coefficient of weld operating conditions; γwf=1

The coefficient α is taken equal to: for equal angles α=0.7.

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

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

Let us determine the lengths of the seams of the belts “6” and “7” (δ=6mm):

Structural seam length along the back

We take lw1 = 22 cm.

Feather seam length

Kf1 = 8mm = 0.8cm. Kf2 = 6 mm = 0.6 cm.

Let us determine the lengths of the belt seams “30” and “26” (δ=6mm):

Structural seam length along the back

We take lw1 =4 cm.

Feather seam length

Kf1 = 8 mm = 0.8 cm. Kf2 = 6 mm = 0.6 cm.

Let's determine the length of the seams of the belt “22” (δ=6mm):

Structural seam length along the back

We take lw1 =4 cm.

seam length along feather

Kf1 = 8 mm = 0.8 cm. Kf2 = 8 mm = 0.8 cm.

The calculated lengths of the seams are plotted on the knot diagram, after which the dimensions of the gusset and its outline are revealed. The adopted outline of the gusset should be simple, preferably rectangular.

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

Table of welds in truss nodes

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

where N is the force in the lower chord rod pushing towards the mounting unit, kN.

More detailed information on the designs of truss truss units and the features of their calculation should be found in the recommended literature (1); (5); (7).

The result of designing a truss is the preparation of a metal specification for the starting element, the shape of which should be taken according to the textbook (1).

5.Calculation of the transverse frame of the frame

Determination of loads on the frame.

Loads act on the frame

a) constant – from the structure’s own weight

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

Rice. Frame

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

Vg=23.88·24/2=286.56 kN

b) Snow load on the frame. The frame support will be subject to the corresponding support reaction of the crossbar (kN) Vр=S1L/2, where S1 is the linear design snow load, kN/m2

Vр=4.2·24/2=50.4 kN

Vertical crane loads. The crane load on the transverse frame is determined from two close cranes located in such a way that the load is greatest.

Estimated vertical force (kN) acting on the rack (column) to which the crane trolleys are close

Dmax=γf nc Fn max Σyi+G,

where Fn max is the highest wheel pressure

γf - load reliability factor, γf=1.1

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

nc – combination coefficient: nc=0.85

G - weight of the crane beam, kN

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

Dmax=1.1·0.85·315·(0.267+1+0.8+0.066)+10.5 =717.36 kN

Design vertical force acting on another frame leg

Dmin=γf nc Fn min Σyi+G,

where Fn min is the lowest wheel pressure on the valve (kN)

Fn min=(P+Gc)/n0- Fn max

P - crane lifting capacity

Gc - total weight of the crane with trolley

n0- number of wheels on one side of the crane n0=2

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

Dmin=1.1·0.85·95·2.4+10.5=223.68 kN

Horizontal crane loads.

Design horizontal force (kN)

Tc= γf·nc·Tn·Σyi,

where Tn is the standard horizontal force when braking the trolley,

per one crane wheel.

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

where , are penetration depth coefficients

Coefficients of seam operating conditions

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

MPa- calculated resistance of the metal of the fusion boundary;

MPa– tensile strength of steel C245 for shaped rolled products according to GOST 27772-88 with a thickness from 2 to 20 mm (t. 2.3);

We carry out calculations based on the metal of the fusion boundary, since

MPa> MPa.

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

Distribution of forces between 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 force in the element between the seams along the butt and the feather of the corner is taken corner butt K 1 = 0.7; corner feather K 2 =0.3;

Required design seam lengths:

By the heel; according to the pen;

The weld leg should be specified based on design limitations:

By the heel; - from the pen,

Constructional seam length mm. We round up the seam lengths obtained from the calculation to a multiple of 5 mm. If according to calculation the length of the seam is less than 50 mm, then we accept 50 mm. It is convenient to calculate seams in tabular form (Table 6.)

Table 6 - Calculation of weld lengths

,
,
,
, mm mm mm mm mm mm upper belt 125x10 0.1 0.03 0.02 bottom 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 units



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

Node 1.

Length of welds attaching the rack to the gusset. We accept. The estimated length of the seams is included in the calculation

We rely on the joint action of forces and

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

Node 2.

Length of weld seams attaching the belt to the gusset. We accept. The estimated length of the seams is included in the calculation

We rely on the joint action of forces and for the welded seams of the belt fastening.

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

Node 4.

We design the unit using high-strength M20 bolts made of 40X “select” steel; to fasten the belts, we use 4 sheet plates with a section of 125x10.

We check the strength of the joint by force

The cross-sectional area of ​​the joint is determined taking into account the weakening of the cross-section of each overlay by one hole with a diameter of , then the net area of ​​the horizontal and vertical overlays is:

Force perceived by one pad:

where is the coefficient of working conditions;
Ry= 240 MPa – design resistance of steel C245 for rolled sheets according to GOST 27772-88 with a thickness of 2 to 20 mm (t. 2.3);

Average stresses in linings:

We determine the load-bearing capacity of one friction plane of one high-strength bolt:



Where A bh= 2.45 cm 2 – net area of ​​one bolt (t.5.5);

Design tensile strength of bolts;

Lowest temporary resistance (t.5.7);

The operating conditions coefficient when the number of bolts in a joint on one side is less than n< 5 (т.5.3);

Friction coefficient for gas-flame treatment of contact surfaces without conservation and control of bolt tension by tightening torque (t.5.9);

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

We take 4 M20 bolts.

Since the area of ​​the weakened section of the lining is , it is necessary to check its strength using the following formula:

where is the calculated cross-sectional area;

Number of bolts in the section under consideration;

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

Weld seams attaching the gusset to the belt are assumed to have a structurally minimum thickness

Node 3.

We accept the cross-sections of the linings.

We check the strength of the joint by force:

because the condition is not met, then we accept the cross-sections of the linings.

Cross-sectional area of ​​one lining, taking into account weakening by one hole:

Average tension in pads:

We use the same bolts as in node 4. The force perceived by one lining is

Required number of high-strength bolts to attach one horizontal pad on one side of the joint axis:

We accept 3 bolts.

The same number of bolts are required to attach the vertical pads to the assembly. We place the bolts in 1 row.

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

We accept the seams for attaching the gusset to the belt constructively.

Node 5.

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

Node 6.

We rely on the joint action of longitudinal forces in adjacent panels of the belt and the nodal load F for the seams attaching the belt to the gusset.

Design combination of frame loads - 11.4:

According to the gusset dimensions obtained during the design of the unit, the length of the belt fastening seams is l = 62.7 cm. We accept

The estimated length of the seam is 1:, therefore we include in the calculation.

The estimated length of the seam is 2:, therefore we include in the calculation.

Stresses in the most loaded seam along the butt:

Additional stresses from nodal load F:

where: - the total length of the seam sections transmitting force F.

Node 8.

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

Connecting gaskets.

To ensure that the corners work together, they must be connected with gaskets. The distance between the gaskets should be no more than 40i for compressed elements and 80i for tensile elements, where i is the radius of inertia of one corner relative to the axis parallel to the plane of the gasket. In this case, at least two gaskets are placed in the compressed elements. We take the width of the gaskets to be 60mm, length - , thickness - 12mm, equal to the thickness of the gussets.


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

Page 6

Table - Number of types of corners

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 force on the butt

N - force in the rod, kN

βf-penetration coefficient (for manual welding βf=0.7)

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

Rwf is the calculated resistance of fillet welds to shear metal,

equal when using E50 type electrodes: Rwf= 21 kN/cm2

γwf - coefficient of weld operating conditions; γwf=1

The coefficient α is taken equal to: for equal angles α=0.7.

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

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

Let us determine the lengths of the seams of the belts “6” and “7” (δ=6mm):

Structural seam length along the back

We take lw1 = 22 cm.

Feather seam length

Kf1 = 8mm = 0.8cm. Kf2 = 6 mm = 0.6 cm.

Let us determine the lengths of the belt seams “30” and “26” (δ=6mm):

Structural seam length along the back

We take lw1 =4 cm.

Feather seam length

Kf1 = 8 mm = 0.8 cm. Kf2 = 6 mm = 0.6 cm.

Let's determine the length of the seams of the belt “22” (δ=6mm):

Structural seam length along the back

We take lw1 =4 cm.

seam length along feather

Kf1 = 8 mm = 0.8 cm. Kf2 = 8 mm = 0.8 cm.

The calculated lengths of the seams are plotted on the knot diagram, after which the dimensions of the gusset and its outline are revealed. The adopted outline of the gusset should be simple, preferably rectangular.

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

Table of welds in truss nodes

 

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