Crack Width Calculation As Per Eurocode
Prisc Chandola
2. According to help "To limit the bars used in calculation of the width, use the mouse to box around the required bars. Click once to start the box, then move the mouse and click a second time to finish the box, and the enclosed bars will be selected, and will change colour"
How and when should I use this option? I have quite heavily reinforced beam with bars in 3 layers. They are absolutely necessary for bending capacity and also for limiting cracks. Now, if I select only bottom layer of reinforcement my crack width become 0,134, looks very optimistic.
3. Last question. If I move all bars from side edges by 30mm "inside", then cracks remain widths remain almost the same 0,248 mm and 0,322mm versus 0,245mm and 0,319mm. Beam outer face is less reinforced right now and I assume that governing crack should move there but this doesn't happened, max crack location still remain to be on bottom edge... Any comments?
I went ahead and moved side bars again for next 30mm, so now they are moved totally by 60mm in comparison with initial model. The results are very strange. Crack width remain always 0,245mm!!! for "crack width calcs" only and with "extreme face only" option selected. Is it possible? Max. crack location moved to corner, which looks logical.
The strain is relatively easily obtained from the strain compatibility analysis, but the spacing to an adjacent bar and the cover to these bars is open to interpretation, especially when several layers of tensile reinforcement are present together with bars along the side faces. In this respect the program provides a method of restricting the number of bars to used in the calculations and also to restrict the faces of the beam that are used to determine the cover. By default there are no restrictions so the calculations are carried out for all bars in the tension area and uses all faces to determine the appropriate cover. The bar that produces the largest crack width together with the adjacent bar for the spacing and the location of the max crack are marked on the diagram.
By checking the "Use Extreme faces Only" will limit the concrete faces at which crack calculations are performed to those faces intersected by a line through the reinforcing bar or tendon and perpendicular to the neutral axis. So the side faces will not be used in the calculation of cracks.
I hope this has helped. It is also useful to look at the calculation "Results..." for each of your different cases to establish what parameters have changed and whether he programs interpretation is what you expected.
The SkyCiv Crack Width Calculator is a free tool to help engineers calculate the crack width of a wall based on its width, thickness, and reinforcement. When designing concrete cracks can occur due to a range of reasons. These cracks can affect the durability of concrete increase the chances of deterioration. The calculations include service stress due to moment and tension, and strain. This tool uses the British Standard 8007 standard for its calculations. Enter the dimensions of the wall and reinforcement details below to begin.
Cracks can form in concrete due to various reasons. These reasons can include temperature variations, insufficient tension reinforcement, excessive bending moments, and shear forces. Concrete crack width is the width of the crack that forms in concrete.
The crack width of concrete and its durability are inversely proportional to each other. The larger the crack the more ingress is allowed for the passage of water and the higher the chances of deterioration of the reinforcement present in the concrete. As time progresses, the cracks will get widened and the strength of the concrete starts to decrease ultimately reducing the life of the concrete.
Crack width classification is usually based on the environmental exposure condition. Every country code has its own set of limitations. However, the commonly observed values of limiting crack widths are 0.1mm, 0.2mm, and 0.3 mm which generally pertain to mild, moderate, and severe conditions respectively.
The calculations in this calculator are based on British Standard 8007. This includes the strain theory calculations used in this calculator which are based on those given in BS 8007. The unit system of this calculator is limited to metric units only.
Yes, you can enter the member's desired width and thickness and the top and bottom face rebar configuration. Based on these details, the program can calculate the crack width and compare it with the allowable one. You can estimate and compare crack widths for walls, slabs, and beams using this calculator.
A flange section is that which has a rectangular extension from the main rectangular body. The extension is called a flange while the rectangular body is called web. This type of section mostly occurs when a beam is cast monolithically with a slab.
The design of a flange beam is similar to that of a rectangular beam only that the flange gives additional area of concrete which adds to the overall compressive strength of the section. So instead of using the breadth of the rectangular section only in estimating the compressive strength of the section, the breath of the rectangular section plus that of the flange is used thereby augmenting the compressive strength of the beam. This increase in compressive strength means flange beams, when the flanges are in compression throughout the member as in the case of a simply supported beam, rarely require to be designed as doubly reinforced.
However, it is very pertinent to note that this increase in compressive strength due to the flange area will be valid only when the flange is in compression. Whenever the flange is in tension as in the case above columns in a continuous beam, the section should be designed as a rectangular beam as more concrete area in tension will actually serve little or no purpose.
The L sections are mostly found in perimeter beams of building as the slab is only spanning from the beam on one side while the T section on the other hand is mostly found in buildings intermediate beams as slab spans from both sides of the beam.
When the flange of a beam is exploited in designing a beam, the total span of the adjoining slab when large does not often act with the supporting beam to resist the loads on the beam, only some portion of the slab does. To calculate the portion of the slab that act together with the beam to resist loads results to the concept of effective width of flange.
lo is defined as the distance between point where moment is zero. The value of for different support configurations is defined in fig (5) as shown below. Other parameters in the formular are defined in fig (4)
In designing a flange section, when the area of concrete within the flange section is enough to develop the strength required to resist the compressive force, then the beam is designed as a rectangular section with breath beff (effective flange width). Therefore, the moment of resistance of the section can be calculated using:
To calculate the actual depth of the web that partakes in resisting compression can be very tedious, as a work around, the author prefers conservatively taking the depth of the web that resist compression to be 0.45d.
After analyzing a T-beam section In Reinforced Concrete Design to Eurocode 2 by Mosley, Bungey, and Hulse; the formula for calculating the area of tensile reinforcement for singly reinforced section when the depth of the neutral axis is assumed as 0.45d is rendered as:
Shear force is an internal force that tends to make the part of a structural member slide against another. It is often significant close to supports and under point loads. BS EN 1992-1-1: 2004 adopts the approach of variable strut inclination method for shear design; this method allows for flexibility in the angle of inclination of the compressive strut between 22 and 45.
Before shear reinforcement are designed, it is important that the concrete section is checked whether it has sufficient shear capacity (VRd.c) to resist the maximum design shear force (VEd) that will act on it without shear reinforcement. The shear capacity of the concrete section without shear reinforcement is often sufficient for lightly loaded beams of minor importance, however minimum area of shear reinforcement is always provided.
As for section which has the member shear capacity (VRdc) less than the design shear force (VRdc) the shear reinforcement is required and designed using the variable strut inclination method. This method is based on an imaginary truss model where concrete acts as the top chord and also acts as the diagonal strut members inclined at an angle ϴ, the bottom chords are the main tensile reinforcement while the designed links serve as the transverse tension members. The angle ϴ changes in value proportionately to the shear force acting on the member. The angle ranges between the lower and upper limit of 22 and 45 degrees respectively. It should be noted that in this imaginary truss, the contribution of the concrete to shear resistance is ignored.
Before the vertical stirrup is designed, it is important to check whether the design shear force is not too large enough to cause the crushing of the inclined compressive strut. To ensure this does not happen, the maximum resistance of the section must be greater than the design shear force.
The value of ϴ to be used to check whether the section is adequate such that the compressive strut is not crushed is 45 degrees as this is the highest value of ϴ allowed by EC2 which gives the maximum resistance. When 45 is substituted for ϴ then the equation becomes:
Should VRdmax be less than VEd, the compressive strut will fail by crushing so the section is inadequate and have to be resized. However, if VRdmax is greater than VEd then we can proceed to designing the vertical links that will be required to resist the shear in the member. Different values of ϴ can be tried to achieve a shear resistance greater than the design shear force. The first value to be tried is 22 degrees as this angle gives the least resistance. If substituting 22 for ϴ does not give sufficient resistances, then a higher value of ϴ will be tried.
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