Calculation of armored belt. Under the interfloor ceiling (with the exception of a monolithic reinforced concrete floor) in a block/brick house, it is necessary to install a reinforced reinforced concrete belt - an armored belt. The main purpose of the reinforced belt under the interfloor ceiling is to evenly distribute the load on the walls. In some special cases, the armored belt can be located directly above the window openings and serve as jumpers. The cross-sectional dimensions of the armored belt and the diameter of the working reinforcement must be determined by calculating reinforced concrete structures. The diameter of the auxiliary fittings should not be less than 6 mm. As an example, let’s calculate a special case where the armored belt is located directly above the window opening and serves as a reinforced concrete lintel. An example of calculating an armored belt. It is required to calculate an armored belt 250×200mm (height×width) over a window opening 2.1m wide; for lightweight PNO floor slabs measuring 6280x990x160mm and weighing 1500 kg. Calculation. M = qL²/8, where q is the distributed load per meter of the reinforced belt q = dead weight of the reinforced belt + load from the PNO plates + operational load q = 2500 kg/m³×1m×0.2m×0.25m +1500kg/2 +400 kg /m²×6m/2 = 125 kg/m + 750kg/m + 1200 kg/m = 2075 kg/m h0 = 21cm - distance from the center of the reinforcement section to the edge of the compressed zone of the reinforced concrete floor Calculated compressive strength for concrete class B20 - Rpr (Rb) = 117 kgf/cm2 (11.5 MPa). b = 0.2 m, the same value as in my previous calculations in the group we will build our own house. The calculated tensile strength for class A-III reinforcement is Ra = 3600 kgf/cm2 (355 MPa). M = 2075×2.1²/8= 1143.84 kg m A0 = M/b×h0²×Rpr = 1143.84 /(0.2×0.21²×1150000) = 0.1127 According to the auxiliary table for calculating bending elements of rectangular cross-section reinforced with single reinforcement (according to the “Manual for the design of concrete and reinforced concrete structures made of heavy and light concrete without prestressing reinforcement (to SNiP 2.03.01-84)”) we find η = 0.94 and ξ = 0.12. Required cross-sectional area of the reinforcement: Fa = M/η×h0×Ra = 1143.84 /(0.94×0.21×36000000) = 0.000165 m2 = 1.61 cm2. The main working reinforcement of the reinforcement belt: 2 Alll rods d12mm, the center of the reinforcement section is located at a distance of 4 cm from the bottom of the reinforcement belt. Fa(actual)= 2.26 cm² Fa ≤ Fa(actual) 1.61 cm²< 2,26см² Условие выполняется. Коэффициент армирования - μ = Fa/b×h, Процент армирования - μ% = 100×μ μ% = 100×2,26/25×20 = 0,452 % Проверка соблюдения граничных условий: ξ ≤ ξR ξR = ξ0/{1+σа/400(1+ξ0/1,1)} ξ0 = a - 0.008Rпр, где Rпр принимается в МПа; коэффициент а = 0.85 для тяжелого бетона и а = 0.8 для бетона на пористых заполнителях. ξ0 = 0.85 - 0.008 11,5 = 0,758 ξR = ξ0/{1+σа/400(1+ξ0/1,1)} ξR = 0.758/(1 + 365/400(1 + 0.758/1.1)) = 0,2984 0,12 < 0,2984 Граничное условие выполнено. Проверка прочности по касательным напряжениям. Так как арматуру в верхнем слое и поперечное армирование в армопоясе (хомуты или вертикальные стержни) мы не предусматривали, то следует проверить прочность армопояса по касательным напряжениям: Qmax ≤ 2.5×Rbt×b×ho , где Qmax - максимальное значение поперечной силы (определяется по эпюре поперечных сил). При нашей расчетной схеме Qmax = ql/2 = 2075 2,1/2 = 2178,75 кг; Rbt - расчетное сопротивление бетона растяжению, для класса бетона B20 Rbt = 9,18 кгс/см2; 2178,75 кг < 2,5×9,18×20×21= 9639 кг Q ≤ 1.5Rbt×b×h0²/с или Qmax ≤ 0.5Rbt×b×ho + 3ho×q , где Q - поперечная сила в конце наклонного сечения, начинающегося от опоры; значение с принимается не более сmax = 3ho. При нашей расчетной схеме значение Q на расстоянии 3×21 = 63 см или 0,63м от опоры составит Q = ql/2 - 0,63q = 2178,75 - 2075 0,63= 871,5кг; 871,5 кг < 1.5 9,18 20 21²/63 = 1927 кг Условия прочности по касательным напряжениям выполняется и в этом случае расчёта поперечной арматуры по сечениям, наклонным к продольной оси, не требуется. Однако это вовсе не означает, что арматура в верхней части ж/б армопояса и поперечная арматура совсем не нужны. Арматура верхнего пояса и поперечная арматура перераспределяет внутренние напряжения, а потому использование арматуры в верхнем поясе и поперечной арматуры необходимо, так как все возможные нагрузки и их сочетания предусмотреть невозможно. Диаметр стержней арматуры верхнего пояса и поперечной арматуры можно выбрать меньше диаметра рабочей арматуры.
After erecting the walls of a house from piece materials (bricks or blocks), the next important operation is usually pouring the reinforced belt. This element of the overall design acquires particular importance when building houses from gas silicate blocks - such an upper frame is needed both to give rigidity to the entire “box” and to attach the Mauerlat, that is, as a kind of “strip foundation” for the subsequent installation of the roof.
It happens that land owners conducting independent construction, trying to save on everything, are looking for ways to do without an armored belt, what technologies are available for attaching the mauerlat directly to block or brickwork. And although, yes, such methods theoretically exist, it is very difficult to call them absolutely reliable. Therefore, good advice: never give up a reinforced belt, especially since in some cases it will not require too much financial and labor costs.
And to estimate the scale of the upcoming work, use the calculator for the amount of concrete for pouring the armored belt - it will not only show the amount of solution, but also give a “layout” of the initial ingredients for preparing it yourself.
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Some explanations on the calculations will be given below.
The need to create an armored belt under the Mauerlat when constructing a roof is not always obvious to novice builders. They often have the wrong idea about reinforced reinforcement of the base for the construction of a roof as something unnecessary and superfluous. However, the armored belt is an important intermediary that distributes the load of the roof onto the walls of the building. Let's consider why an armored belt under the roof is needed, what functions it performs and how to install it yourself.
In this article
The need for an armored belt
Let's start looking at the reinforced roof base with its main functions.
Load conversion
The rafter legs transfer the load to the mauerlat, the main concentration of which is in the places where the rafters support the walls of the house. The task of the Mauerlat and armored belt is to transform this load, making it uniform. The Mauerlat is subject to two types of loads. This is the weight of the roof itself, the snow accumulated on it, the effect of gusts of wind on the roof and other natural phenomena.
Another load is associated with the bursting of the building walls by the rafters. As the weight of the roof increases, it increases significantly. Modern materials for building construction, such as expanded clay concrete and aerated concrete, with a number of positive characteristics, are not able to withstand such a bursting load. Before installing the Mauerlat on them, it is imperative to create a reinforced belt.
Brick walls are more resistant to point loads, so to install the Mauerlat on them, it is enough to use anchors or embedded parts. However, experts recommend the use of armored belts for brick walls if the building is being built in an earthquake-prone region.
Attaching the roof to the house
The most important and main task of the Mauerlat is to firmly attach the roof to the house. Thus, the Mauerlat itself must be securely mounted to the building. 
The main tasks of a reinforced roof base can be reduced to the following points:
- Maintaining the strict geometry of the building in any situation: seasonal soil fluctuations, earthquakes, shrinkage of the house, etc.;
- Alignment of walls in horizontal projection, correction of inaccuracies and flaws made during the construction of walls;
- Ensuring rigidity and stability of the entire structure of the building;
- Uniform and distributed distribution of the roof load on the walls of the building;
- The ability to firmly attach important roof elements, primarily the Mauerlat, to the reinforced base.
Calculation of a reinforced base for a roof
The process of reinforcing the base under the Mauerlat begins with planning and calculations. It is necessary to calculate the dimensions of the armored belt. According to building standards, it should be equal to the width of the wall, and not less than 25 cm. The recommended height of the reinforced base is around 30 cm. The armored belt and the mauerlat laid on it should encircle the entire house.
If the walls are built from aerated concrete, then the top row is made of stone in the shape of the letter U, which creates the formwork. It is necessary to lay reinforcing elements in it and fill the entire structure with cement mortar. 
Before starting the actual construction work, it is also necessary to prepare the necessary tools and building materials. To create a reinforced base for the roof you will need:
- Concrete mixer for high-quality mixing of cement mortar;
- A specialized vibrator that accelerates the cement mortar in the formwork, preventing the creation of air voids in the structure;
- Materials for the construction of formwork;
- Fittings.
Installation technology
Installation of the armored belt begins after masonry work. It is necessary to wait until the masonry is completely dry.
Creating formwork and laying reinforcement
The first stage is the construction of formwork. In buildings made of aerated concrete blocks, the outermost row of masonry is made of blocks in the shape of the letter U. If these are not available, then the outer part of the formwork is created from sawn 100 mm blocks, and the inner part from boards. Installation is carried out in strict compliance with the horizontal level.
A frame made of reinforcement is laid in the formwork. Its longitudinal part is formed from 4 reinforcement rods with a diameter of 12 mm. Transverse fastenings are made from rods of 8 mm diameter, maintaining a pitch of no more than 25 cm. In projection, the frame looks like a square or rectangle. The frame parts are mounted with an overlap of up to 20 cm. The joints are connected with knitting wire. In solution, such a reinforced frame exists as a monolithic one.
Laying the frame requires compliance with certain rules:
- The thickness of the concrete from the frame to the formwork is at least 5 cm;
- To comply with this rule, place stands made of bars of the required height under the frame.
An important part of the work is strengthening the formwork frame. If this is not done, then it will collapse from the weight of the concrete. This can be done in various ways:
Installation of fasteners for the Mauerlat
After working with the formwork and laying the reinforcement, you can begin installing fasteners for the Mauerlat. We recommend using threaded rods. It is convenient to purchase studs with a diameter of 12 mm. The length of the studs is calculated taking into account the fact that their bottom is attached to the frame, and the top protrudes above the Mauerlat by 2-2.5 cm.
Installation of studs is carried out taking into account:
- There is at least one stud between two rafters;
- The maximum installation step is no more than 1 meter.
Pouring with cement mortar
The main feature of the reinforced base for the Mauerlat is its strength. This can only be achieved by pouring the concrete solution at a time.
To create a concrete mixture, concrete of at least M200 is used. The best mixture for filling the belt is prepared according to the following proportions:
- 1 part cement M400;
- 3 parts of washed sand and the same amount of crushed stone.
The use of plasticizers will help increase the strength and speed of hardening of the mixture.
Since creating an armored belt requires a lot of mixture at once, it is advisable to use a concrete mixer and a special pump to supply the solution. In the absence of equipment, the help of several people will be required to prepare and continuously supply the finished mixture.
After pouring concrete into the formwork, it is important to expel all air from any possible air pockets. For this, a special device, a vibrator, and simple fittings can be used, with which the mixture is pierced along the entire perimeter.
Mauerlat installation
Removing the formwork from the armored belt is possible as soon as the concrete has hardened sufficiently, and installation on the Mauerlat structure can begin no earlier than 7-10 days after pouring the armored belt.
Before laying, the Mauerlat parts must be specially prepared:
- The Mauerlat timber is treated with antiseptics;
- Connections of its individual elements are made using the direct lock method or oblique cutting;
- The Mauerlat is applied to the armored belt and the places for the pins are marked. Holes for fastenings are drilled.
Laying the Mauerlat is preceded by covering the reinforced base with a layer of rolled waterproofing; as a rule, roofing felt is used for these purposes.
The Mauerlat is secured with a large washer and nut; locknuts are used for security. After tightening all the fasteners, the remaining tops of the studs are cut off with a grinder.
Let's sum it up
A reinforced base for the Mauerlat is more of a necessity than a luxury. The roofing structure has a fairly large impact on the walls of the house, which, although distributed evenly thanks to the Mauerlat, can negatively affect the strength of the entire building.
The creation of an armored belt is necessary in buildings made of gas and expanded clay concrete due to the fragility of these materials, in areas with high seismic activity. It is also advisable to strengthen the walls under the Mauerlat when creating heavy roofing structures.
Reinforcing the upper part of the walls is not a difficult job requiring the involvement of specialists. If you follow a number of rules and involve assistants, it can be done on your own.
span length (m) - 2.3
floor slab weight (kg/m2) - 330
screed (kg/m2) + furniture, etc. - 270
Wall (according to the formula - 1900*0.38*(span length/2)*1.2(finishing)(kg/m.p.) - 996
Roofing (+snow, etc.) (kg/m.p.) - 1000
Jumper width (m) - 0.38
h (according to the formula (h01+h02)/2) (m) - 0.17
Own weight of the jumper (kg/m) - 279.68
Slab length ((5+4.8)/2)(m) - 4.9
The estimated load per linear meter will be (kg/m.p.) - 7176.04
The maximum bending moment for such a beam will be (M max./1.5) (kgm) - 3163.437633
(Here divided by 1.5, because “If the beam is part of an armored belt, then it should be considered as a rigidly clamped beam. That is, the maximum moment will be on the supports and will be 1.5 times less than for a simply supported beam . And it is the upper reinforcement that will work on the supports.")
A0 - 0.198659727
According to the table? - 0.89
According to the table ξ - 0.22
Coef. quality of concrete compression of reinforcement (vibration quality), Ko - 0.8
Required cross-sectional area of reinforcement (cm2) (Here multiplied by Ko) - 7.259853568
At the moment, the reinforced belt contains a section (3 at the top + 3 at the bottom)* 1.5386 (reinforcement area Ø14 mm) = 9.2316
Are my calculations correct? Is there enough safety margin for me to sleep peacefully :)?
20-07-2015: Doctor Lom
Your diligence is worthy of all praise, but you have also made enough mistakes. I think the safety margin is enough, although it’s worth recalculating taking into account (or not taking into account) the following errors:
1. The load on the slab is taken with a good margin, but I only welcome it.
2. With such dimensions of your opening and provided that the partitions on each side of the opening are at least 0.8-0.9 m, the design load from the overlying wall takes on a smaller value; for details, see the article “Calculation of a metal lintel for load-bearing walls.” And in this case the load from the roof will go to the walls.
3. For simplified calculation, only ho1 should be used. If you want to take into account the presence of reinforcement in a compressed zone, then the methodology for such a calculation is described in the article “Calculation of reinforced concrete beams with reinforcement in a compressed zone.”
4. Formula for determining the moment on supports M = ql^2/12.
20-07-2015: Vladimir
Thanks for the quick response.
I calculated it again using the method for calculating the cross-sectional area of reinforcement laid in one row for the lower part of the beam and got a value of 3.05 cm2. I have 3 threads of 14th reinforcement, which is 4.62 cm2. It turns out that there is a reserve.
But I have two rows, which means that in the bottom row the cross-sectional area of the reinforcement should be less than the resulting 3.05 cm2. We calculate according to the method given in the article “Calculation of reinforced concrete beams with reinforcement in a compressed zone.” The article considers the situation when the condition am< aR не выполняется.
Given my data, the condition am< aR выполняется, т.е. нет необходимости использовать арматуру в сжатой части. Если продолжить вычисления то имеем отрицательное значение A"s=-9,2 см2. Если и дальше продолжить вычисления, то As=ξRRbbho/Rs + A"s и равняется 7,79 см2. Получается что при условии am < aR по приведенным формулам рассчитывать площадь сечения нельзя. Как же мне зная площадь сечения в сжатой зоне найти необходимую площадь сечения в растянутой зоне?
21-07-2015: Doctor Lom
If, according to your calculations, even in the tension zone, the reinforcement is laid with a good margin, then it makes no sense to complicate the calculations by taking into account the reinforcement in the compressed zone, since the reinforcement in the compressed zone will further increase the safety margin, in other words, your structure will withstand an even greater load.