Thursday, December 22, 2016

Force method for Indeterminate continuous Beam - Matrix Approach

Hi,
In force method of structural analysis,

  • the first step is to find the Redundancy/indeterminacy of the structure. For example for the given beam in the following example there are total five number of support reactions, therefore the redundancy is 2.
  • Second step is to convert the indeterminate structure into a basic determinate by replacing the the two of the unknown support reactions with redundants.  
  • Third step is to find out the displacements of the basic determinate structure along the redundants due to the given loading conditions. 
  • fourth step is to find out the flexibility matrix by applying the unit loads along the redundants and finding out the corresponding displacements at these two places.
  • Next, form the equations as per the compatibility conditions and form the matrices. 
  • Solve the matrix problem to find out the unknown reaction forces.
Example: Let us consider a continuous beam with a total span of 10m, EI constant, udl acting on the first half and a couple acting at 7.5m from the left. There are hinge and roller support at B and C, while beam is fixed at the left end A. Find out the support reactions at B and C using the force method (matrix approach.)

Solution: 




Thanks You!

Tuesday, November 29, 2016

Tension member connected to Gusset plate(fail in Rupture/Fracture or yield?)

Hi,
A tension member - a rectangular plate of dimension 1/2"*8" connected with two rows of bolts, determine the bolt size so that the tension member fails in rupture but not yield. Steel of grade A36 grade is used.
It must be kept in mind that the capacity factors are different for the rupture and yield, its lower for finding the rupture capacity, the section where bolts are inserted into the member are considered critical. Solution is written in the image shown below.

Moment of Inertia of spoked Wheel with inner and outer Ring.

Hi,
I was stuck at this problem of finding the mass moment of inertia of a spoked wheel/ring, which is necessary to find out the angular acceleration or the kinetic energy of the wheel.

It's easy to determine the moment of inertia of a spoked wheel with the given weights of the outer rim/ring, inner rim/ring and weight of spokes. The moment of inertia about the centroid and an axis parallel to the centroidal axis can also be easily found. Please refer the image below for knowing the process.



Thanks! please share your views.

Sunday, July 6, 2014

Flexure Stress and Normal Stress

Hello there,

Its a long time since I have posted in my Structural Engineering blog, so today I thought to discuss something in here. If I ask you the type of stresses, you may come up with the following types:

  1. Normal Stress
  2. Shear Stress
  3. Flexure Stress
    Flexure Stress Vs Normal Stress
These are the three types of stresses which we deal all along our structural engineering, arising out of so many different types of loading on the structure. I asked this question to one of my student, if there is any similarity between the first one and the third one. 

Normal stress is calculated simply as Force divided by the cross section area under action. Flexure stress is calculated with the help of the flexure formula. Now, to find out the similarility between the two, you have to consider the nature of them.
We know normal stress are either tensile or compressive, similarly, you know that the flexure stresses are also either tensile or compressive.

The main difference between the two, is that the normal stress remains constant throughout the section, but the flexure stress varies along the cross section. This shows that the similarity between the two is that the flexure stresses are also the normal stresses but with a constant variation along the cross section on which applied. 

Thanks for your kind visit!

Sunday, June 15, 2014

List of Civil Engineering Softwares used these days

Hi, I was going through the online website of the Autodesk and found a list of the softwares, which caught my interest because many of them are new to me. I have worked with the AutoCad and am little aware of Revit, but there is this huge list of the softwares, titled as given below:
  1. Building Design suite
  2. AutoCAD
  3. Revit
  4. Simulation Mechanical
  5. AutoCAD 360
  6. Buzzsaw
  7. Robot Structural Analysis Professional
  8. Vault
  9. Advance Steel
  10. Point Layout
  11. Simulation 360
  12. AutoCAD LT
  13. Advance Concrete
    License page for downloading the trial versions of Autodesk 
Now, if I was in the software industry related with the Civil Engineering projects, hopefully I would have been associated with the other 11 softwares too, but I have ignored them till now. Now that I am thinking of pursuing my M.Tech. in Structural Engineering, I think I should have the knowledge of these softwares. 

I think to learn about all these softwares, you need a lot of free time. At the same time, interest matters a lot. If you are interested, you can go the website and try them for free, and if they fulfill your thirst, you can buy them and yes they are very costly.
What do you think, is it important to have the knowledge of every new software product in the market?

Saturday, March 1, 2014

Welding (Design of Steel Structure)

Hi,
Welding is a method in which metals are joined together by melting them. In this post going to cover Fillet welds and Slot weld, just in brief with you.

Fillet Welds

  • Size of fillet weld. It should not be less than the minimum allowable value given in the table  in the image above. Size of the fillet weld used along tee of an angle or rounded edge of a flange should not exceed three-forth the nominal thickness of an angle of flange leg.
  • Throat of fillet weld. It is length of perpendicular from right angle corner to the hypotenuse.
Effective throat thickness = k*fillet size
Value of k depends upon angle between fusion faces. Value of k decreases with increase in angle between fusion face.
In most cases, a right angled fillet weld is used, for which k = 0.7.
  • Effective length of fillet weld. It is equal to its overall length minus twice the weld size. Effective length of a fillet weld designed to transmit the loading should not be less than four times weld size. Equal return should be made equal to twice the size of the weld.
  • Overlap. Overlap in lap joint should not be less than five times the thickness of the thinner plate as shown in the figure to right.
  • Side Fillet. In a lap joint made by a side or longitudinal fillet weld, length of each fillet weld should not be less than perpendicular distance between them; the perpendicular distance between side fillets should not exceed sixteen times thickness of the thinner part connected. 
  • Intermittent fillet weld. Any section of an intermittent fillet weld should have an effective length of not less than four time the weld size or 40 mm, whichever is greater. Clear spacing between ends or effective lengths of intermittent weld carrying stresses should not exceed 12.t for compression and 16.t for tension and in no case should be more than 20cm, 't; is the thickness of thinner part joined.
  • Permissible stress and strength of fillet weld. Permissible stress in fillet weld is 108 MPa or 1100 kgf/cm2.
Permissible stresses in shear and tension are reduced to 80% for the fillet welds made during erection. Permissible stresses are increased by 25% if wind or earthquake load are taken into account. However, size of the weld should not be less than the size required when the wind or earthquake load is considered or neglected.

Slot or Plug Weld

Following specifications are used for the design of slot or Plug welds:
  1. Width or diameter of slot should not be less than three times the thickness of the part in which slot is formed or 25 mm, whichever is greater.
  2. Corners at the enclosed ends should be rounded to a radius not less than 1.5 times the thickness of upper plate or 12 mm, whichever is greater.
  3. Distance between edges of the plates and slot or between edges of adjacent slots should not be less than twice the thickness of the upper plate.
  4. Permissible stress is taken as 108 MPa or 1100 kgf/cm2.
Thanks!

Monday, January 20, 2014

Two Way Slabs - IS Codes Specification

Hi,

Indian Standard codes give following specification for two way slabs for their analysis.

  • Case 1: Simply supported slabs which do not have adequate provision to resist torsion at corners, and to prevent the corners from lifting. 

Bending moment for short span,  Mx= Ax.w.Lx^2
Bending moment for long span, My = Ay.w.Ly^2
Where, Ax and Ay are moment co-efficients depending on the ratio Lx/Ly.

  • Case 2. Simply supported on the four edges and corners of the slabs are held down.
If Mx and My are maximum bending moments per unit width in the middle strip of the slab in short and long spans respectively, then
                                                   Mx = Ax.w.Lx^2
                                                  My = Ay.w.Ly^2
Where Ax and Ay are co-efficients depending on the ratio Ly/Lx.
At the corners, top and bottom reinforcement should be provided for torsion.

Thanks for visit!