In
the previous section we formed table.8.8 which gives the number and dia. of bars that we intend to give at various supports and midspans. In this section we will see the arrangement of bars that will give these required steel at the various points. First we will take midspan AB. The following fig. gives the details:
Fig.8.21
Bottom bars at midspan AB
The above fig.8.21 shows the bars required to resist the sagging moment at midspan AB.
• Bar type: 'a' has a shorter length. It is provided in the middle of the cross section of the beam. This can be seen in section XX. There is only one bar of this type.
• Bar type : 'b' are longer. They extend from support to support. They are provided at the sides of the cross section of the beam. This can be seen in section YY. There are two bars of this type.
These three bars should be provided together. They work together to resist the sagging moment at midspan AB.
We can see that the two 'b' bars extend from support to support. In fact they extend from the first end support A to the last end support E. This is because, we compulsorily require two bars at the sides (for holding the stirrups), through out the length of ABCDE.
Thus we have successfully provided the required three bars at the midspan AB. Out of the three bars, 'a' have a shorter length. This is because all the three bars are not required at sections away from the midsection. We will learn more about this in the next section about curtailment of bars. Now we will see the top bars at supports A & B. The fig. below gives the details:
Fig.8.22
Top bars at supports A & B
The above fig.8.22 shows the top bars at supports A and B.
• Bar type: 'c' has a shorter length. It is provided in the middle of the cross section of the beam. This can be seen in section XX. There is only one bar of this type.
• Bar type : 'd' are longer. They extend from support to support. They are provided at the sides of the cross section of the beam. This can be seen in section YY. There are two bars of this type.
At support B, these three bars should be provided together. They work together to resist the hogging moment at support B
We can see that the two 'd' bars extend from support to support. In fact they extend from the first end support A to the last end support E. This is because, we compulsorily require two bars (to act as 'stirrup suspenders') at the sides, through out the length of ABCDE. These 'stirrup suspenders' serve another purpose also: They act as top bars at support A.
Thus we have successfully provided the required three top bars at the support B, and also the required two top bars at support A. Out of the three bars, 'c' have a shorter length. This is because all the three bars are not required at sections away from the support. We will learn more about this in the next section about curtailment of bars. Now we will see the bottom bars at midspan BC. The fig. below gives the details:
Fig.8.23
Bottom bars at midspan BC
The above fig.8.23 shows only one type of bar, which is 'b'. They are given at the sides as shown in section XX. There are two numbers of this type. Recall that, these are the same bars given at the bottom of span AB. There we said that these two bars will continue upto the other end-support E. This is for holding the stirrups properly. Thus we meet them again in our present span BC. Also note that we need only two no. bottom bars of 16 mm dia in BC. So these bars will serve two purposes: To hold the stirrups, and to resist the sagging moment.
At this point of our discussion, we have completed the following types of supports and spans:
• An end support (support A)
• An intermediate support (support B)
• An end span (span AB)
• An intermediate span (span BC)
Based on this we can now give a satisfactory arrangement at other spans and supports of our beam ABCDE. Because CD is an intermediate span, DE is an end span, C and D are intermediate supports and E is an end support. The fig. showing the complete details of the whole beam is given below:
Fig.8.24
Sectional elevation of the continuous beam ABCDE
So we have completed the design of the continuous beam. We will now see the various checks. The pdf file given below gives the detailed steps involved in the various checks:
Solved example 8.2 final checks
In the next section we will discuss about the curtailment of bars in a continuous beam.
Fig.8.21
Bottom bars at midspan AB
The above fig.8.21 shows the bars required to resist the sagging moment at midspan AB.
• Bar type: 'a' has a shorter length. It is provided in the middle of the cross section of the beam. This can be seen in section XX. There is only one bar of this type.
• Bar type : 'b' are longer. They extend from support to support. They are provided at the sides of the cross section of the beam. This can be seen in section YY. There are two bars of this type.
These three bars should be provided together. They work together to resist the sagging moment at midspan AB.
We can see that the two 'b' bars extend from support to support. In fact they extend from the first end support A to the last end support E. This is because, we compulsorily require two bars at the sides (for holding the stirrups), through out the length of ABCDE.
Thus we have successfully provided the required three bars at the midspan AB. Out of the three bars, 'a' have a shorter length. This is because all the three bars are not required at sections away from the midsection. We will learn more about this in the next section about curtailment of bars. Now we will see the top bars at supports A & B. The fig. below gives the details:
Fig.8.22
Top bars at supports A & B
The above fig.8.22 shows the top bars at supports A and B.
• Bar type: 'c' has a shorter length. It is provided in the middle of the cross section of the beam. This can be seen in section XX. There is only one bar of this type.
• Bar type : 'd' are longer. They extend from support to support. They are provided at the sides of the cross section of the beam. This can be seen in section YY. There are two bars of this type.
At support B, these three bars should be provided together. They work together to resist the hogging moment at support B
We can see that the two 'd' bars extend from support to support. In fact they extend from the first end support A to the last end support E. This is because, we compulsorily require two bars (to act as 'stirrup suspenders') at the sides, through out the length of ABCDE. These 'stirrup suspenders' serve another purpose also: They act as top bars at support A.
Thus we have successfully provided the required three top bars at the support B, and also the required two top bars at support A. Out of the three bars, 'c' have a shorter length. This is because all the three bars are not required at sections away from the support. We will learn more about this in the next section about curtailment of bars. Now we will see the bottom bars at midspan BC. The fig. below gives the details:
Fig.8.23
Bottom bars at midspan BC
The above fig.8.23 shows only one type of bar, which is 'b'. They are given at the sides as shown in section XX. There are two numbers of this type. Recall that, these are the same bars given at the bottom of span AB. There we said that these two bars will continue upto the other end-support E. This is for holding the stirrups properly. Thus we meet them again in our present span BC. Also note that we need only two no. bottom bars of 16 mm dia in BC. So these bars will serve two purposes: To hold the stirrups, and to resist the sagging moment.
At this point of our discussion, we have completed the following types of supports and spans:
• An end support (support A)
• An intermediate support (support B)
• An end span (span AB)
• An intermediate span (span BC)
Based on this we can now give a satisfactory arrangement at other spans and supports of our beam ABCDE. Because CD is an intermediate span, DE is an end span, C and D are intermediate supports and E is an end support. The fig. showing the complete details of the whole beam is given below:
Fig.8.24
Sectional elevation of the continuous beam ABCDE
So we have completed the design of the continuous beam. We will now see the various checks. The pdf file given below gives the detailed steps involved in the various checks:
Solved example 8.2 final checks
In the next section we will discuss about the curtailment of bars in a continuous beam.
Thanks very much honor to share you
ReplyDeleteI appreciated your effort thanks
ReplyDeleteBest wishes
Engineer Mohamed tantway
Great to know that a lot of professionals find this blog useful. A video showing a small scale experiment on continuous systems can be seen here: https://youtu.be/PYRjOqyM4YY
Deletecan you show me how the bars arrange in support and mid span?
ReplyDeleteWe can right click with the mouse on any image. Then select 'open in new tab'. Thus the fig.8.24 can be viewed in full size.
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