What is reinforcement overlap

Correct overlap of reinforcement when knitting

When carrying out activities related to the reinforcement of concrete structures, it becomes necessary to connect reinforcing bars to each other. When performing work, it is necessary to know what overlap of reinforcement is, how many diameters according to SNiP the amount of overlap of rods is.

The strength of the foundation, or reinforced belt, depends on the correctly selected overlap length, which takes into account the cross-sectional area of ​​the reinforcement. Correctly performed calculation of reinforced concrete elements, taking into account the type of connection, ensures the durability and strength of construction projects.

Wanting to understand the possible options for joining reinforcing bars, many craftsmen turn to the requirements of current regulatory documents. After all, a successfully executed connection provides the required margin of compressive and tensile strength.

Some developers are trying to find an answer in accordance with SNiP 2 01. Others are studying building codes and regulations numbered 52-101-2003, which contain recommendations for the design of structures made of reinforced concrete reinforced with non-stressed steel reinforcement.

In accordance with the requirements of current regulatory documents, steel reinforcement is used to strengthen non-stressed elements, in contrast to stressed structures, where reinforcing ropes of classes K7 and higher are used for reinforcement. Let us dwell on the methods used for fixing reinforcing bars.

The current building codes and regulations (SNiP) describe in detail the fastening of reinforcement using all currently existing methods.

The following options are possible:

• overlapping connection of knitted rods without welding. Fixation is carried out using additional curved steel rods that repeat the configuration of the reinforcement connection. According to SNiP, it is allowed to overlap straight rods with transverse fastening of elements using tying wire or special clamps.

The overlap of the reinforcement when knitting depends on the diameter of the rods. Concrete-filled structures made of knitted rods are widely used in private housing construction. The developer is attracted by the simplicity of the technology, ease of connection and reasonable cost of building materials;

• fixing reinforcing bars using household electric welding equipment and professional units. The technology for connecting reinforcement using welding installations has certain limitations. After all, significant internal stresses arise in the welding zone, which negatively affect the strength characteristics of the reinforcement cages.

It is possible to overlap reinforcing bars using electric welding using reinforcement of certain brands, for example, A400C. The technology of welding steel reinforcement is mainly used in the field of industrial construction.

Building codes and regulations contain instructions on the need to strengthen the concrete mass with at least two solid reinforcement contours. To implement this requirement, steel rods are connected to the ceiling.

SNiP allows the use of rods of various diameters. In this case, the maximum cross-sectional size of the rod should not exceed 4 cm.

SNiP prohibits overlapping rods using tying wire and welding in places where there is a significant load located along or across the axis.

These include mechanical and welded butt-type joints, as well as overlap joints made without welding

Fixation of reinforcing bars by electric welding

Joining of reinforcement using electric welding is used in the areas of industrial and special construction. When connecting using electric welding, it is important to achieve a minimum distance between the rods and fix the elements without a gap. Increased load capacity of the connection zone, stretched from action, is achieved when using reinforcing bars marked A400C or A500C.

Professional builders pay attention to the following points:

• It is inadmissible to use common reinforcement marked A400 for welded joints. As a result of heating, strength is significantly reduced and susceptibility to corrosion increases;
• increased likelihood of damage to the integrity of the rods under the influence of significant loads. Current rules allow the use of electric arc welding for fixing reinforcement with a diameter of up to 25 mm;
• the length of the weld and the class of rods used are interrelated. The table of the regulatory document contains all the necessary information about fixing rods using electric arc welding.

The regulatory document allows the use of electrodes with a diameter of 0.4-0.5 cm when performing welding activities and regulates the amount of overlap exceeding ten diameters of the rods used.

It is forbidden to connect reinforcement in places of maximum stress on the rods and in areas where (concentrated) load is applied to them

Overlapping reinforcement connection without welding when installing an armored belt

Using rods marked A400 AIII, which are popular in construction, it is easy to overlap the reinforcement using annealed knitting wire.

SNiP contain recommendations for tying reinforcement and provide various options for connecting rods:

• connection with overlap of straight ends of reinforcing bars;
• fixation of overlapping rods using additional reinforcement elements;
• tying rods with ends curved in the shape of peculiar loops or hooks.

Using knitting wire, it is possible to connect reinforcement with a profile section with a diameter of up to 4 cm. The amount of overlap increases in proportion to the change in the diameter of the rods. The amount of overlap of rods increases from 25 cm (for rods with a diameter of 0.6 cm) to 158 cm (for rods with a diameter of 4 cm). The amount of overlap, according to the standard, should exceed the diameter of the rods by 35-50 times. SNiP allows the use of screw couplings along with knitting wire.

The distance between the reinforcing bars that are overlapped in the horizontal and vertical direction must be 25 mm and above

Requirements of regulatory documents for reinforcement connections

When connecting rods using the knitting method, it is important to consider a number of factors:

• relative arrangement of reinforcement in the spatial frame;
• features of placement of areas with overlap relative to each other;
• the length of the overlap section, determined by the cross-section of the rod and the grade of concrete.

When locating a section with overlapping rods in the zone of maximum load, the amount of overlap should be increased to 90 times the diameter of the rods being connected. Building codes clearly indicate the dimensions of joint areas.

The length of the joint is affected not only by the cross-sectional diameter, but also by the following points:

• magnitude of the effective load;
• brand of concrete mixture used;
• class of steel reinforcement used;
• placement of butt joints in the spatial frame;
• purpose and scope of reinforced concrete products.

It should be noted that the amount of overlap decreases with increasing grade of concrete used.

In cases where tying wire is used, the distance between the rods is often taken equal to zero, since in this situation it depends solely on the height of the profile protrusions

Let's consider the change in the amount of overlap that takes up compressive loads for class A400 reinforcement with a diameter of 25 mm:

• for concrete grade M250, the rods are fixed with a maximum overlap of 890 mm;
• concreting the reinforcing grid with M350 mortar makes it possible to reduce the overlap to 765 mm;
• as the grade of concrete used increases to M400, the overlap of the rods decreases to 695 mm;
• Filling the reinforcement frame with concrete mortar M450 allows you to reduce the overlap to 615 mm.

To reinforce the tension zone of the reinforcement cage, the overlap for the specified reinforcement is increased and amounts to:

• 1185 mm for M200 concrete;
• 1015 mm for concrete M350;
• 930 mm for M400 concrete;
• 820 mm for M450 concrete.

When carrying out activities related to reinforcement, it is important to correctly position the overlap areas and take into account the requirements of building codes and regulations.

The following recommendations should be followed:

• distribute connections evenly throughout the reinforcement frame;
• maintain a minimum distance between joints of at least 610 mm;
• take into account the brand of concrete mortar and the cross-section of reinforcing bars.

Compliance with the requirements of building codes guarantees the strength and reliability of concrete structures reinforced with a reinforcing frame. Having studied the recommendations of SNiP in detail, it is easy to independently select the required amount of reinforcement overlap, taking into account the design features of the reinforced concrete product. Recommendations from professional builders will help you avoid mistakes.

Source: https://pobetony.expert/armirovanie/naxlest-armatury-pri-vyazke

How to correctly overlap reinforcement during tying and welding

When connecting steel rods, reinforcing a strip foundation, many people have a natural question: how to correctly overlap the reinforcement, and what its length should be. After all, the correct assembly of a metal load-bearing frame will prevent deformation and destruction of a monolithic concrete structure from the loads acting on it and increase its trouble-free service life. What are the technical features of making butt joints, we will consider in this article.

Types of lap reinforcement connections

According to the requirements of SNiP, the concrete foundation must have at least two continuous, unbroken reinforcement contours. This condition can be met in practice by joining the reinforcing rods with an overlap. In this case, connections at joints can be of several types:

• Lap without welding
• Welded and mechanical connections.

The first connection option is widely used in private housing construction due to its ease of execution, availability and low cost of materials. In this case, the common reinforcement class A400 AIII is used. The joining of overlapping reinforcing bars without the use of welding can be carried out both with and without the use of tying wire. The second option is most often used in industrial housing construction.

According to building codes and regulations, the connection of overlapping reinforcement during tying and welding requires the use of rods with a diameter of up to 40 mm. The American Cement Institute ACI allows the use of rods with a maximum cross-section of 36mm. For reinforcing rods whose diameter exceeds the specified values, the use of overlap joints is not recommended due to the lack of experimental data.

According to construction regulations, it is prohibited to overlap reinforcement when knitting and welding in areas of maximum load concentration and places of maximum stress on metal rods.

Joining overlapping reinforcing bars by welding

For country house construction, welding overlapping reinforcement is considered an expensive pleasure, due to the high cost of metal rods of the A400C or A500C brand. They belong to the weldable class. Which significantly increases the cost of materials. It is unacceptable to use rods without the “C” index, for example: the common class A400 AIII, since when heated the metal significantly loses its strength and corrosion resistance.

However, if you decide to use weldable class rods (A400C, A500C, B500C), their connections should be welded with 45 mm diameter electrodes. The length of the weld seam and the overlap itself depends on the class of reinforcement used.

Overlapping weld length

Reinforcing bar class	The length of the overlap weld in the diameters of the reinforcement being connected
А400С	8 ᴓ
А500С	10 ᴓ
В500С	10 ᴓ

Based on the data presented, it can be seen that when using steel rods of class B400C for knitting, the amount of overlap, and therefore the weld, will be 10 diameters of the reinforcement being welded. If ᴓ12 mm rods are taken for the load-bearing frame of the foundation, then the length of the seam will be 120 mm, which, in fact, will correspond to GOST 14098 and 10922.

According to American codes, reinforcing bar crosses cannot be welded. Effective loads on the base can cause possible ruptures of both the rods themselves and their connections.

Overlapping reinforcement connection when knitting

In cases of using common rods of the A400 AIII brand, in order to transfer the calculated forces from one rod to another, a connection method without welding is used. In this case, the places where the reinforcement overlaps are connected with a special wire. This method has its own characteristics and special requirements are placed on it.

Reinforcement overlap options

In accordance with the current SNiP, non-welding connection of rods during the installation of a reinforced concrete frame can be made using one of the following options:

• Overlay of profile rods with straight ends;
• Overlap of a reinforcing profile with a straight end with welding or installation throughout the entire bypass of transversely located rods;
• With curved ends in the form of hooks, loops and claws.

Such connections can be used to knit profiled reinforcement with a diameter of up to 40 millimeters, although the American standard ACI-318-05 allows the use of rods with a diameter of no more than 36 mm.

The use of bars with a smooth profile requires the use of lap joint options either by welding transverse reinforcement or using bars with hooks and tabs.

Basic requirements for making overlap joints

When performing overlapping reinforcement joints, there are rules defined by construction documentation. They define the following parameters:

• The size of the rod lining;
• Features of the location of the connections themselves in the body of the concreted structure;
• The location of adjacent bypasses relative to each other.

Taking these rules into account allows you to create reliable reinforced concrete structures and increase the period of their trouble-free operation. Now about everything in more detail.

Where to place reinforcement overlap joints when knitting

SNiP does not allow the location of overlapping reinforcement ties in areas of the greatest load on them. It is not recommended to place joints in places where steel rods experience maximum stress. It is best to place all connecting rod connections in unloaded areas of reinforced concrete, where the structure is not under stress. When pouring a strip foundation, the bypass ends of the reinforcement are placed in places with minimal torque and minimal bending moment.

If it is not technologically possible to fulfill these conditions, the length of the overlap of the reinforcing rods is taken at the rate of 90 diameters of the joined rods.

What is the amount of overlap of reinforcement when knitting?

Since the overlap of the reinforcement is determined by the technical documentation, the length of the joint connections is clearly indicated there. In this case, the values ​​can vary not only from the diameter of the rods used, but also from such indicators as:

• Nature of the load;
• Concrete grade;
• Reinforcing steel class;
• Connection points;
• Purpose of reinforced concrete products (horizontal slabs, beams or vertical columns, pylons and monolithic walls).

Splicing reinforcing bars when performing overlaps

In general, the length of the overlap of reinforcement bars during tying is determined by the influence of the forces arising in the rods, the perceived adhesion forces with concrete acting along the entire length of the joint, and the forces that provide resistance in the anchoring of the reinforcing bars.

The fundamental criterion when determining the length of the reinforcement overlap during tying is its diameter.

For the convenience of calculating the overlap of reinforcing bars when knitting the load-bearing frame of a monolithic foundation, we suggest using a table with the indicated diameter values ​​and their overlap. Almost all values ​​are reduced to 30 times the diameter of the rods used.

The amount of reinforcement inlet in diameters

Diameter of reinforcing steel A400, mm	Overlap amount
in diameters	in mm
10	30	300 mm
12	31,6	380 mm
16	30	480 mm
18	32,2	580 mm
22	30,9	680 mm
25	30,4	760 mm
28	30,7	860 mm
32	30	960 mm
36	30,3	1090 mm

Depending on the loads and purpose of the reinforced concrete products, the length of the lap joints of the steel rods changes upward:

Inlet of reinforcement depending on the purpose of reinforced concrete products

Type of load	Purpose of concrete products
Horizontal use, in diameters	Vertical use, in diameters
In compressed concrete	33.8 ᴓ	48.3 ᴓ
In stretched concrete	47.3 ᴓ	67.6 ᴓ

Depending on the grade of concrete and the nature of the load used for pouring the monolithic foundation strip and other reinforced concrete elements, the minimum recommended values ​​for the bypass of reinforcement during the binding process will be as follows:

For compressed concrete

Diameter of reinforcing steel A400 used in compressed concrete, mm	Length of overlap of reinforcing bars for concrete grades (concrete strength class), in mm
M250 (B20)	M350 (B25)	M400 (B30)	M450 (B35)
10	355	305	280	250
12	430	365	335	295
16	570	490	445	395
18	640	550	500	445
22	785	670	560	545
25	890	765	695	615
28	995	855	780	690
32	1140	975	890	790
36	1420	1220	1155	985

For stretched concrete

Diameter of reinforcing steel A400 used in tensile concrete, mm	Length of overlap of reinforcing bars for concrete grades (concrete strength class), in mm
M250 (B20)	M350 (B25)	M400 (B30)	M450 (B35)
10	475	410	370	330
12	570	490	445	395
16	760	650	595	525
18	855	730	745	590
22	1045	895	895	275
25	1185	1015	930	820
28	1325	1140	1040	920
32	1515	1300	1185	1050
36	1895	1625	1485	1315

How to position reinforcement bypasses relative to each other

To increase the strength of the foundation's load-bearing frame, it is very important to correctly position the reinforcement overlaps relative to each other in both planes of the concrete body. SNiP and ACI recommend spacing connections so that there are no more than 50% bypasses in one section. In this case, the spacing distance, as defined in regulatory documents, must be at least 130% of the length of the connecting connection of the rods.

Mutual arrangement of reinforcement bypasses in the concrete body

If the centers of overlap of the knitted reinforcement are within the specified value, then it is considered that the connection of the rods is located in the same section.

According to ACI 318-05 standards, the relative position of the connecting connections must be at a distance of at least 61 centimeters. If the distance is not maintained, then the likelihood of deformation of the concrete monolithic base from the loads exerted on it during the construction of the building and its subsequent operation increases.

Source: https://postroim-dachu.ru/stroitelstvo-fundamenta/kak-sdelat-nahlest-armatury-pri-vyazke-i-svarke.html

Reinforcement overlap during tying (SNiP)

• Connection types
• Connecting rods by welding
• Installation of armored belt without welding
• Essential connection requirements

When reinforcing a foundation or making any type of armored belt, almost every person has a question about what the length of the overlap should be and how to do it correctly. Indeed, it makes a big difference. Correctly executed joining of steel rods makes the connection of the reinforcement more durable. The building structure becomes protected from various types of deformation and destruction. The impact on the foundation is minimized. As a result, the trouble-free service life increases.

Overlapping reinforcement when knitting is the simplest and at the same time truly reliable option for connecting reinforcement

Connection types

The current building codes and regulations (SNiP) describe in detail the fastening of reinforcement using all currently existing methods. Today, such methods of joining reinforcing bars are known as:

• Overlapping joints made without welding:

• overlap when joining using curved parts (loops, tabs, hooks).
• overlap in connections of straight reinforcement bars with transverse fixation;
• overlap of straight ends of rods.

• Mechanical and welded types of butt joints:

• using welding machines;
• using professional mechanical units.

It is recommended to overlap reinforcement with a cross-section of no more than 40 millimeters

The SNiP requirements state that at least 2 continuous reinforcement cages must be installed in the concrete foundation.
They are performed by fixing the reinforcing rods with an overlap. The option of weaving overlapping rods is popular in private construction.

And there is an explanation for this - this method is accessible, and the necessary materials are low cost. You can join overlapping reinforcement bars without welding using tie wire.

Industrial construction often uses the second option for connecting reinforcing bars.

Building codes allow the use of rods of different sections (diameters) when connecting overlapping reinforcement. But they should not exceed 40 mm due to the lack of technical data supported by research. In those places where the loads are maximum, overlapping fixation is prohibited, both when knitting and when using welding.

Connecting rods by welding

Overlap of reinforcement using welding is allowed only with rods of grades A400C and A500C. Reinforcement of this class is considered weldable. But the cost of such rods is quite high. The most common class is A400.

But its use is unacceptable, since when it is heated, strength and corrosion resistance are noticeably reduced.
It is prohibited to weld places where there is overlap of reinforcement, regardless of the class of the latter. There is a possibility of rods breaking when exposed to heavy loads. This is what foreign sources say.

Russian regulations allow the use of electric arc welding in these places, but the diameters should not exceed 2.5 cm.

It is forbidden to connect reinforcement in places of maximum stress on the rods and in areas where (concentrated) load is applied to them

The length of welding seams and reinforcement classes are directly related. The work uses electrodes with a cross section of 4-5 mm. The overlap length during welding work is less than 10 diameters of the rods used, which meets the requirements of regulatory GOSTs 14098 and 10922.

Installation of armored belt without welding

When installing overlapping joints during knitting, rods of the most popular brand are used - A400 AIII.
The places where the overlap is made are tied with knitting wire. SNiP impose special requirements when choosing this method of bonding. How many options are there for fixing rods without welding?

Reinforcement connection:

• overlap of end rods;
• overlap of rods with straight ends with welding of transverse rods;
• with curved ends.

If the rods have a smooth profile, only the 2nd or 3rd option can be used.

The reinforcement connection should not be placed in places of concentrated load application and places of greatest stress

Essential connection requirements

When knitting joints using the overlap method without welding, the rules determine some parameters:

• Overlay length.
• Features of the location of nodes in the structure.
• The location of the overlaps in relation to each other.

As already mentioned, it is prohibited to place lap-tied reinforcement in places of the highest load and maximum stress. They should be located in those places of the reinforced concrete product where there is no load, or where it is minimal.

If there is no such technological possibility, the size of the connection is selected based on 90 sections (diameters) of the joining rods.
Technical standards clearly regulate what the dimensions of such connections should be. However, their value may depend not only on the cross section.

It is also influenced by the following criteria:

• degree of load;
• brand of concrete used;
• reinforcement class;
• location of connection nodes in the structure;
• place of application of the reinforced concrete product.

In cases where tying wire is used, the distance between the rods is often assumed to be zero

The fundamental condition when choosing the length of the overlap is the diameter of the reinforcement.
The following table can be used to conveniently calculate the dimensions of the joining of rods when knitting without using the welding method. As a rule, their size is adjusted to 30 times the cross-section of the reinforcement used.

Reinforcement cross-section, cm	Overlap size
In centimeters	In millimeters
1	30	300
1,2	31,6	380
1,6	30	480
1,8	32,2	580
2,2	30,9	680
2,5	30,4	760
2,8	30,7	860
3,2	30	960
3,6	30,3	1090

There are also minimized values ​​for overlapping rod bundles. They are assigned based on the strength of concrete and the degree of pressure.

The distance between the reinforcing bars that are overlapped in the horizontal and vertical direction must be 25 mm and above

In the compressed area of ​​concrete:

Reinforcement cross-section (class A400), cm	Concrete class (strength)
IN 20	V/25	V/30	V/35
Concrete grade
M/250	M/350	M/400	M/450
Overlap size (in centimeters)
1	35,5	30,5	28	25
1,2	43	36,5	33,5	29,5
1,6	57	49	44,5	39,5
1,8	64	55	50	44,5
2,2	78,5	67	56	54,5
2,5	89	76,5	69,5	61,5
2,8	99,5	85,5	78	69
3,2	114	97,5	89	79
3,6	142	122	115,5	98,5

List of measurements on the tensile concrete zone:

Reinforcement cross-section (class A400), cm	Concrete class (strength)
IN 20	V/25	V/30	V/35
Concrete grade
M/250	M/350	M/400	M/450
Overlap size (in centimeters)
1	47,5	41	37	33,0
1,2	57	49	44,5	39,5
1,6	76	65	59,5	52,5
1,8	85,5	73	74,5	59,0
2,2	104,5	89,5	89,5	27,5
2,5	118,5	101,5	93	82,0
2,8	132,5	114	104	92,0
3,2	151,5	130	118,5	105,0
3,6	189,5	162,5	148,5	131,5

The correct location of the overlap relative to each other and the entire structure is of enormous importance for increasing the strength of the foundation skeleton.

Connections must be made in such a way that they are evenly distributed, and no more than 50% of the ligaments are concentrated in each section of the structure. And the gap between them should be less than 130% of the size of the joints of the reinforced rods.

The requirements of the building codes and regulations (SNiP) already mentioned above state that the distance between the joint connections must be more than 61 cm. If such a distance is not observed, the concrete base may be subject to deformation due to all the loads placed on it at the stage of construction of the building, as well as during its operation.

Source: http://yastroyu.ru/obzori/24556-nakhlest-armatury-pri-vyazke-snip.html

Technical features of reinforcement overlap when knitting

The simplest and yet truly reliable way to connect metal products is to overlap the reinforcement during knitting (SNiP 52-101-2003). This is a 100% guarantee of long-term operation of the foundation or other concrete structure.

Reinforcement overlap when knitting according to SNiP

The sanitary standards and regulations of 2003 indicate all currently existing types of connecting reinforcing bars for construction. We are talking about mechanical and welded butt joints, as well as non-welded overlap joints. Mechanical ones are produced using threaded or pressed couplings using special units.

Welding is carried out by welding, and overlap joints are classified as follows:

1. Straight rods mounted or welded on the overlap of transverse rods;
2. Straight profile periodic rods;
3. Rods having legs, hooks, loops (bends).

Reinforcement with a diameter of no more than 40 mm is overlapped. According to a similar document of sanitary standards (ACI 318–05), the connection of rods with a cross-section of no more than 36 mm is allowed. This limitation is due to the fact that the reinforcement with a large cross-section has not been tested for reliability. This indicates a lack of supporting data in this regard.

The reinforcement is not connected in the tension zone of the rods and the place where the load on them is concentrated. These manipulations can be performed with or without a knitting wire. In the latter case, wire is used for tying reinforcement. Experts recommend the use of pressed connections or screw couplings when working with rods with a diameter greater than 25 mm for the following reasons:

• increasing the level of safety of the structure (the volume of concrete at the joints is limited);
• reducing financial costs for reinforcement (overlaps usually require a significant overuse of reinforcement - up to 20-25%).

The distance between overlapping reinforcing bars in the horizontal and vertical directions should be 25 mm or more. If this condition is met, it becomes possible to unhindered penetration of concrete into the “problem” areas of the frame. For reinforcing bars over 25 mm, it is better to select the recommended distance, which is similar to the cross-section of the bars. The largest distance between reinforcement bars along the width of the foundation strip is considered to be up to 8 reinforcement sections.

In cases where tying wire is used, the distance between the rods is often zero due to the height of the protrusions of the profiles. Moreover, the largest distance between the reinforcing elements will be that which is no more than 4 diameters of the reinforcing bars. The distance between butt pairs next to each other when overlapping will be at least 30 mm (less than 2 rod diameters).

Technical features of weldless joint

It is necessary to space adjacent connections apart. Moreover, in such a way as to achieve simultaneous connection in one section of up to 50% (no more) of the reinforcing elements. The design section, which we will determine in order to determine the value of the joining reinforcements, is understood as the area of ​​130% of the total overlap parameter (measured along the bars).

Here it is necessary to understand that when designing, the joints of the rods are considered as lying in the same section, provided that the centers are located exactly in the specified zone. The shortest distance between joints according to SNiP is 610 mm. According to ACI 318–05 and sanitary standards, it is recommended that untied (free) connections of rods be made in structures without prestressing.

This advice is quite logical, because the concrete mixture with such a connection will flood the rods from all sides. And this is a guarantee of ultra-reliable fixation of each rod, which cannot be achieved when pouring an incomplete circle of reinforcement and an adjacent rod tied with binding wire. In addition, the overlap in length cannot be less than 25 cm.

Another important provision of the Sannorm is that in the 1st design section the connection can have no more than 50% of steel rods in the foundation strip. In addition, it is possible to join welded mesh and individual reinforcing elements using the described option without the necessary separation. However, such an assumption will only be valid when using reinforcement for structural reinforcement.

An overlap of 30 cm or more is possible provided that the reinforcement is functioning in compression. In many foreign countries, in construction documentation, the overlap was set at a level of 40 diameters of the connecting reinforcing elements. In the CIS countries, this value is equal to 50 diameters (A400 fittings).

Also, the value of the recommended overlap depends on the grade of concrete for pouring the foundation. For example, for the M300 mixture it has 35 diameters, M250 - 40, M200 - 50. But for reinforcing bars A-II and A-I, the overlap is always selected based on 40 diameters. But it should be borne in mind that all this will be true for the indicators in the calculation. In practice, real (not minimum) overlap values ​​are usually several times larger.

Real values ​​of reinforcement overlap

The length of the overlap of the rods during anchoring is set based on the force acting in the reinforcement structure and the perception of the resistance forces of the steel elements, as well as the adhesion forces of concrete and reinforcing rods along the entire length of the connection. Sanitary standards for overlap of reinforcement when knitting recommend the following overlap lengths (all parameters in mm) overlap/section:

• 1090 / 36;
• 960 / 32;
• 860 / 28;
• 760 / 25;
• 680 / 22;
• 580 / 18;
• 480 / 16;
• 380 / 12;
• 300 / 10.

The SNiP tables also contain the anchorage overlap length for various grades of concrete mix for compression/tension reinforcing bars.

There are some other important points of SNiP that were discussed in this publication:

1. installation of transverse additional reinforcement is mandatory in the overlap anchoring area;
2. preventing the anchoring of adjacent rods from being separated by at least 61 cm;
3. cross-shaped overlaps must be connected using plastic clamps or clamps or annealed viscous wire.

According to these tables, the shortest overlap length for concrete mix M450 with a cross-section of A400 rod of 6 mm = 20 cm. But for concrete M250 and reinforcement with a cross-section of 40 mm, the length will be already 158 cm.

Source: https://Metagarant-Minsk.by/articles/nahlest-armatury-vyazke/

Reinforcement overlap when knitting

Correctly calculated overlap of reinforcement during tying affects the final quality of the structure. The reliability of this method is difficult to challenge, however, there are certain nuances in the work process, if not observed, the result of the connection may turn out to be fragile and short-lived. This can also affect the rate at which the concrete hardens, causing the base to become very soft.

Why is it necessary to comply with reinforcement overlap standards when knitting?

When pouring the foundation of a house or when erecting any other concrete structure (column or monolithic block), the issue of strength and durability of the structure remains pressing. Subject to compliance with all building codes, an additional metal frame will greatly strengthen the structure and make it durable, and the base unaffected by natural conditions and time.

If the rules are not followed, the foundation of the house may soon collapse, which will lead not only to the loss of a large amount of materials, but also to human casualties. This is due to the fact that incorrectly calculated overlap of reinforcement leads to non-hardening of concrete in some places, which leads to weakening of the entire structure as a whole. To build a strong and reliable frame, several methods are used, including knitting, for which it is necessary to use an overlap.

The amount of overlap when connecting reinforcement according to SNIP

The Sanitary Standards and Rules of 2003 (abbreviated SNiP) describe all types of fittings connections that currently exist. Overlapping joints are created without the use of welding machines, in this they differ from mechanical (for which couplings and special equipment are used) and welded (for which a welding machine is respectively required). There are three types of overlap joints:

1. Rods with hooks and claws (bends) at the ends.
2. Rods with a straight end (with welding or installation at the intersection of reinforcement).
3. Rods with straight ends (profile).

The Sanitary Standards and Rules of 2003 recommend overlapping reinforcement with a cross-section of up to 40 mm. In turn, the world analogue of building codes, namely ACI 318-05, states the maximum permissible value of the cross-section of the rods is 36 mm. This is due to the lack of evidence base for the reliability of connections of larger diameter, since no tests have been carried out. Also during knitting, it is worth leaving a certain free space around the overlap.

It must be taken into account that the minimum distance that must be left for reserve, both horizontally and vertically, is 25 mm. However, if the cross-section of the reinforcement itself is more than 25 mm, then the margin must be calculated according to the diameter step. The largest distance between elements is 8 sections of the rod. But when using wire in knitting, the distance is reduced to 4 sections.

It is not recommended to use tying in areas of greatest pressure, since the joint is not designed for such loads, but only for fastening the reinforcement and maintaining them as a single structure.

Reinforcement overlap table

Diameter of reinforcing steel A400	Overlap amount
10mm	300mm
12mm	380mm
16mm	480mm
18mm	580mm
22mm	680mm
25mm	760mm
28mm	860mm
32mm	960mm
36mm	1090mm

The joint locations of the reinforcement and the location of the lattice should be determined by the designer, not the builders. Since the overall picture of the project, as well as knowledge of the load in different places, is known only to him. Otherwise, the design may be damaged.

For example, when reinforcing a column, several fundamentally important steps should be followed:

1. The outlet must be bent to a slightly longer length than the cross-section of the reinforcement (for a diameter of 16mm it is 20mm).
2. It is necessary to bend the reinforcement without heating, but with the help of special means that can provide the required bending radius.
3. The bend radius must be indicated in the project and emphasis should be placed on it, since builders are unlikely to do this without instructions.

Consumption rates for reinforcement for overlap

The required length of reinforcement bars varies according to several criteria:

1. For compression reinforcement, the required length will be as follows. So, for fittings with a diameter of 6 mm - length 20-22cm; 8mm - length 20-29cm; 10mm - length 25-36cm; 12mm - length 30-43cm; 14mm - length 35-50cm.
2. For tensile reinforcement, the required overlap length of the bars must be greater. For example, for a diameter of 6 mm - length 20-29cm; 8mm - length 27-38cm; 10mm - length 33-48cm; 12mm - length 40-57cm; 14mm - length 46-67cm.

The higher the strength class of concrete, the shorter the length of the overlap rods should be. The only exceptions are 20, 28 and 32 mm fittings. With concrete strength class B35, the length of the rods should be 655, 920 and 1050 mm, respectively.

Important nuances and requirements for viscous connections

The process of connecting reinforcement using wire seems much easier than the welding option or the use of pressed couplings and special devices. However, it also has its own subtleties and nuances.

It must be taken into account that you should not connect reinforcement in places with increased load (for example, corners of buildings). Moreover, it is desirable that there is no load at all at the knitting site.

If it is technically impossible to meet this requirement, then you should use a simple formula: Connection size = 90 * Cross-section of the rods used.

You also need to pay attention to the main parameters:

• rod cover length;
• location of the connection and features of this place;
• the location of the overlaps in relation to each other.

There must be a distance between adjacent points of connection of the reinforcement bars, which can be calculated using the formula: Distance = 1.5 * Length of the overlap, however, the resulting value must be no less than 61 cm.

Also, do not forget that the dimensions of such connections are regulated by technical standards and the overlap depends not so much on the cross-section of the reinforcement, but on:

• brand of concrete used for pouring;
• purposes for using connections;
• class of operated fittings;
• load exerted on the base.

The facts, formulas and figures set out in SNiP give an idea of ​​how exactly to knit reinforcement to build a strong and reliable frame. This knowledge is necessary for owners of summer cottages who want to build something on their own.

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Source: https://dvabrevna.ru/stroitelstvo/nahlest-armaturyi-pri-vyazke.html

Reinforcement overlap – Reinforcement overlap during tying – SNiP, key nuances +

When reinforcing concrete, one of the most common methods of tying reinforcement is overlapping. The size of the allowances is determined by many factors (joint locations, the nature of the loads that the structure will absorb, the type of concrete used), but in most cases the type of wire is fundamental.

Overlap length

As a rule, corrugated reinforcement A3 or other grades with a cross-section of up to 36 mm (in rare cases, 40 mm rods are used) is selected as the material for creating reinforcing structures, which determines the length of the overlap when knitting it. According to SNiP, these values ​​should not be less than:

• for fittings ∅ 6 mm –250 mm;
• for ∅ 10 – 300;
• for ∅ 12 – 380;
• for ∅ 16 – 480;
• for ∅ 18 – 580;
• for ∅ 22 – 680;
• for ∅ 25 – 760;
• for ∅ 28 – 860;
• for ∅ 32 – 960;
• for ∅ 36 – 1090;
• for ∅ 40 – 1580.

The regulatory and technical documentation of our country regulates the average overlap value within 50 diameters of the reinforcement used. And depending on the brand of concrete used:

• M300 – 35 diameters;
• M250 – 40;
• M200 – at least 50 sections of connected elements.

To connect rods with a diameter of more than 25 mm, experts advise using screw couplings or knitting (annealed) wire.

Recommendations for overlapping reinforcement

It is not allowed to knit reinforcement in places of concentrated load on the rods and maximum stress on them. Loose connections of rods are allowed only in pre-stressed structures.

The joining of adjacent rods is carried out staggered - more than 50% of all rods should not be connected in one section. The distance between nearby joints should not be less than 610 mm.

Cross-shaped overlaps must be connected with clamps or binding wire. In anchorage areas, the structure must be reinforced with additional transverse reinforcement.

Overlapping elements must be located in places with minimal torque and bending moments. If this is technologically impossible, the overlap value is set at 90 times the diameter of the reinforcement being connected.

To more accurately study all the norms and rules for knitting reinforcing structures, you should seek help from the relevant design documentation. It is important to understand that strict compliance with the requirements is the key to long-lasting and trouble-free operation of reinforced concrete products.

Source: https://martand.ru/raznoe/naxlest-armatury-naxlest-armatury-pri-vyazke-snip-klyuchevye-nyuansy-video.html

Reinforcement overlap when tying table

A strong and durable foundation is a reinforced foundation. But reinforcement is an operation that requires precision, and knitting reinforcement bars overlapping or end-to-end requires knowledge of the length of the rods.

Extra centimeters of reinforcing bars can deform the foundation under applied lateral loads, compromising its integrity and overall reliability. And vice versa - correct installation of the reinforced concrete frame will avoid deformation and cracking of the concrete reinforced concrete slab, increase the service life and reliability of the foundation.

Knowledge of technical features, methods for calculating the length of rods, installation of joints and the requirements of snips will help in construction more than once. Competent overlap of reinforcement

Regulatory basis and types of connections

The requirements of SNIP 52-101-2003 require the fulfillment of rigidity conditions for mechanical and welded connections of reinforcing bars, as well as for overlapping connections of rods. Mechanical connections of reinforcing bars are threaded and pressed fasteners.

Not only Russian SNIP and GOST are applied to construction operations, materials and tools - the world standardization ACI 318-05 approves the standard cross-section of the rod for knitting ≤ 36 mm, while documentation for internal use on the Russian market allows the cross-section of the rod to be increased to 40 mm.

This disagreement arose due to the lack of appropriate documented testing of reinforcement with large diameters. Methods of knitting reinforcing bars

The connection of reinforcement bars is not allowed in local areas where the permissible loads and applied stresses are exceeded. Lap joint is traditionally knitted reinforcement bars with soft steel wire. If reinforcement Ø ≤ 25 mm is used to reinforce the foundation, then it will be more practical and efficient to use pressed fasteners or threaded couplings to increase the safety of the connection itself and the object as a whole.

In addition, screw and pressed connections save material - overlapping of rods when knitting causes excess material consumption of ≈ 25%. Building codes and regulations No. 52-101-2003 regulate the requirements for the strength of the foundation of a building - the foundation must have two or more continuous contours of reinforcing rods.

To implement this requirement in practice, overlapping rods are knitted according to the following types:

1. Lap joint without weld;
2. Connection by welding, threading or crimping.

Overlapping joint without welding

A joint without welding is most often used in individual construction due to the availability and low cost of the method. Affordable and inexpensive reinforcement for tying the frame - class A400 AIII. According to ACI and SNiP, it is not allowed to overlap reinforcement in places of extreme loads and in areas of high tension for reinforcement.

Connecting reinforcement bars by welding

For private construction, welding overlapping reinforcement bars is expensive, since it is recommended to use welded class A400C or A500C reinforcement.

Using rods without the “C” symbol in the marking will result in a loss of strength and corrosion resistance. Reinforcement grades A400C - A500C should be welded with electrodes Ø 4-5 mm.

Reinforcement class	Weld length in rod Ø
A 400 C	Ø 8
A 500 C	Ø 10
At 500 C	Ø 10

Thus, according to the table, the length of the weld when knitting rods of the B400C brand should be 10 Ø of the rod. When using 12mm rods the seam will be 120mm long.

 Overlapping weld joint

Lap joint by knitting

A cheap and common class of fittings for connections without welding is A400 AIII. The joints are fastened with knitting wire; special requirements are imposed on the knitting areas.

Anchoring or overlap of reinforcement during tying, the table of values ​​​​of which is given below for tying in BIO grade concrete with a strength of 560 kg/cm2, assumes the use of certain brands and classes of reinforcement bars with a certain type of metalworking for certain diameters:

 Work of reinforcement under compression and tension

Mechanical joining of rods in a frame for reinforced concrete products is carried out in one of the following ways:

1. By placing straight rods on top of each other;
2. Overlapping rod with a straight end with welding or mechanical fastening throughout the entire overlap of the cross bars;
3. Mechanical and welded fastening of rods with ends bent in the form of hooks, loops and claws.

The use of smooth reinforcement requires knitting it overlapping or welding it to the transverse rods of the frame.

Requirements for knitting overlapping rods:

1. It is necessary to knit the rods in compliance with the length of the rods;
2. Observe the location of bonding points in concrete and reinforcement bypasses in relation to each other;

Compliance with the requirements of SNiP will allow the use of durable reinforced concrete slabs in foundations with a long and guaranteed service life. Methods of hand-knitting reinforcement

Location of lap reinforcement joints

Regulatory documents do not allow the placement of tie-in reinforcement connection areas in areas of extreme loads and stresses. It is recommended to place all joints of rods in reinforced concrete structures with unloaded areas and without applying stress.

For strip monolithic foundations, areas for bypassing the ends of the rods should be placed in local areas with no application of torsional and bending forces, or with a minimum vector of them. If it is impossible to meet these requirements, the length of the bypass of the reinforcement bars is taken as 90 Ø of the reinforcement being connected.

Location of reinforcement when knitting

The total length of all knitted bypasses in the frame depends on the applied forces to the rods, the level of adhesion to concrete and the stresses arising along the length of the connection, as well as the resistance forces in the overlaps of the reinforced rods. The main parameter when calculating the length of the bypass of the reinforcement to be connected is the diameter of the rod.

Calculator

The table below allows you to determine the overlap of reinforcing rods when installing a reinforcing foundation frame without complex calculations. Almost all values ​​in the table are based on Ø 30 bonded reinforcement bars.

Bypass of rods in Ø
Ø steel class A 400, mm	Bypass
in Ø	in mm
10	30	300
12	31,6	380
16	30	480
18	32,2	580
22	30,9	680
25	30,4	760
28	30,7	860
32	30	960
36	30,3	1090

To increase the strength of the reinforced frame of the base of the house, the overlaps in the reinforcement must be correctly positioned in relation to each other. Moreover, control the placement in both the horizontal and vertical planes in concrete.

In this regard, Russian and international norms and rules recommend spacing the ligaments so that no more than 50% of the overlaps are in one section.

The spacing distance determined by SNiP and ACI should not be more than 130% of the total length of the joints of the reinforcing rods. How to place overlapping rods

International requirements ACI 318-05 define the spacing of joints at a distance of ≥ 61 cm. If this value is exceeded, the likelihood of deformation of the concrete foundation from stresses and loads increases significantly.

Source: http://jsnip.ru/normy/nahlest-armatury-pri-vjazke-tablica.html

Reinforcement overlap, how many diameters - ProBuildingmaterials

A strong and durable foundation is a reinforced foundation. But reinforcement is an operation that requires precision, and knitting reinforcement bars overlapping or end-to-end requires knowledge of the length of the rods.

Extra centimeters of reinforcing bars can deform the foundation under applied lateral loads, compromising its integrity and overall reliability. And vice versa - correct installation of the reinforced concrete frame will avoid deformation and cracking of the concrete reinforced concrete slab, increase the service life and reliability of the foundation.

Knowledge of technical features, methods for calculating the length of rods, installation of joints and the requirements of snips will help in construction more than once. Competent overlap of reinforcement

Reinforcement overlap when knitting: tables of dimensions for joining all diameters according to SNiP, rules for connecting overlap

Reinforcement is an important part of the design of all monolithic structures, on which the long-lasting and reliable future of the structure depends. The process involves creating a frame from metal rods. It is placed in formwork and filled with concrete.

To create this frame, they resort to knitting or welding. In this case, a correctly calculated overlap for the reinforcement plays an important role in knitting. If it is insufficient, the connection will not be strong enough, and this will affect performance.

Therefore, it is important to figure out what kind of overlap to make when knitting.

Types of connections

There are two main methods of fastening reinforcement, according to building codes and regulations (SNiP), namely clause 8.3.26 SP 52-101-2003. It states that the connection of rods can be performed using the following types of joining:

1. Joining of reinforcement bars without welding, overlapping.
   • overlapping using parts with bends at the ends (loops, legs, hooks); for smooth rods, only loops and hooks are used;
   • overlap with straight ends of reinforcing bars of periodic profile;
   • overlapped with straight ends of reinforcing bars with transverse type fixation.
2. Mechanical and welded connection.
   • when using a welding machine;
   • using a professional mechanical unit.

SNiP requirements indicate that a concrete foundation requires the installation of at least two continuous reinforcement frames. They are made by fixing the rods overlapping. For private housing construction, this method is used most often.

This is due to the fact that it is available and cheap. Even a beginner can start creating a frame, since you need the rods themselves and soft knitting wire. You don't need to be a welder or have expensive equipment.

And in industrial production, the welding method is most often used.

Note! Clause 8.3.27 states that overlapping reinforcement connections without welding are used for rods whose working cross-section does not exceed 40 mm. Places with maximum load should not be overlapped by bonding or welding.

Connecting rods by welding

Overlapping of rods by welding is used exclusively with reinforcement grades A400C and A500C. Only these grades are considered weldable. This also affects the cost of products, which is higher than usual. One of the common classes is class A400. But merging products with them is unacceptable. As the material heats up, it becomes less durable and loses its resistance to corrosion.

In places where there is overlap of reinforcement, welding is prohibited, regardless of the class of the rods. Why? If you believe foreign sources, there is a high probability of the connection breaking if it is subjected to heavy loads. As for Russian rules, the opinion is as follows: using electric arc welding for joining is allowed if the diameter size does not exceed 25 mm.

Important! The length of the weld directly depends on the class of the reinforcing rod and its diameter. For work, electrodes with a cross section of 4 to 5 mm are used. The requirements regulated in GOSTs 14098 and 10922 state that overlaps can be made by welding with a length less than 10 diameters of the reinforcing bars used for the work.

Docking reinforcement using the knitting method

This is the easiest way to ensure a reliable rebar structure. For this work, the most popular class of rods is used, namely A400 AIII. The overlapping reinforcement connection without welding is performed using a binding wire.

To do this, two rods are placed next to each other and tied in several places with wire. As mentioned above, according to SNiP, there are 3 options for fixing reinforcing bars with viscous.

Fixation with straight ends of a periodic profile, fixation with straight ends of the transverse type, and also using parts with bends at the ends.

It is absolutely impossible to connect reinforcement bars with an overlap. There are a number of requirements for these connections so that they do not become the weak point of the entire structure. And it’s not just about the length of the overlap, but also other points.

Overlapping under different conditions

So what is the overlap of the reinforcement when knitting? What is the exact data? Let's start by looking at examples. The first factor on which the overlap depends is the diameter of the rods.

The following pattern is observed: the larger the diameter of the reinforcement used, the greater the overlap becomes. For example, if reinforcement with a diameter of 6 mm is used, then the recommended overlap is 250 mm.

This does not mean that for rods with a cross section of 10 mm it will be the same. Typically, 30-40 times the reinforcement cross-section is used.

An example of joining 25-diameter reinforcement in a beam using tying. The amount of overlap is 40d=1000 mm.

So, to simplify the task, we use a special table that shows what overlap is used for rods of different diameters.

Diameter of used fittings A400 (mm)	Number of diameters	Estimated overlap (mm)
10	30	300
12	31,6	380
16	30	480
18	32,2	580
22	30,9	680
25	30,4	760
28	30,7	860
32	30	960
36	30,3	1090
40	38	1580

With this data, everyone can do the job correctly. But there is another table that indicates overlap when using compressed concrete. It depends on the class of concrete used. Moreover, the higher the class, the smaller the spacing of reinforcement joints.

Section of A400 reinforcement used for work (mm)	Length of overlap, depending on concrete grade (mm)
B20 (M250)	B25 (M350)	B30 (M400)	B35 (M450)
10	355	305	280	250
12	430	365	355	295
16	570	490	455	395
18	640	550	500	445
22	785	670	560	545
25	890	765	695	615
28	995	855	780	690
32	1140	975	890	790
36	1420	1220	1155	985

As for the stretched concrete zone, in contrast to the compressed zone, the overlap will be even greater. As in the previous case, as the brand of solution increases, the length decreases.

Section of A400 reinforcement used for work (mm)	Length of overlap, depending on concrete grade (mm)
B20 (M250)	B25 (M350)	B30 (M400)	B35 (M450)
10	475	410	370	330
12	570	490	445	395
16	760	650	595	525
18	855	730	745	590
22	1045	895	895	775
25	1185	1015	930	820
28	1325	1140	1140	920
32	1515	1300	1185	1050
36	1895	1625	1485	1315

If the overlap is correctly positioned relative to each other and made to the required length, then the base skeleton will receive a significant increase in strength. The connections are evenly distributed throughout the structure.

According to the norms and regulations (SNiP), the minimum distance between connections should be 61 cm. More is better. If you do not maintain this distance, the risk that the structure will deform under heavy loads and during operation increases. It remains to follow the recommendations to create high-quality reinforcement.

Source: https://VseoArmature.ru/armirovanie/nahlest-armatury