Answer the following (4 x 5)
Explain various components of the Plate girder through a neat sketch.
The vertical plate of the plate girder is termed a web plate. The angles connected at the top and bottom of the web plate are known as flange angles. The horizontal plates connected with the flange angles are known as flange plates or cover plates. The web plate, flange angles and flange plates are shown in the following figure.
The bearing stiffeners, intermediate stiffeners and horizontal stiffeners used with the plate girder are shown in the following figure.
Compare HSFG bolts and bearing bolts.
The high strength bolts are also called high strength friction grip bolts. Briefly, these are called HSFG bolts. The high strength friction grip bolts have many advantages over rivets.
- Whereas the rivets are subjected to shear and bearing stresses, the bolts are subjected to uniform tensile stresses only.
- The high strength friction grip bolts have higher fatigue strength because there is no concentration of the stress in the hole.
- The bolts do not bear against the plates. Therefore, the uneven distribution of stress does not occur.
- These bolts are advantageously used in bridges and machine foundations subjected to vibrations.
- These bolts also simplify the problem of alterations and additions to structures as they can be assembled more easily than rivets.
Discuss Wind load calculation for the design of roof truss.
In order to determine the wind load on roofs and other inclined surfaces, the direction of the wind is assumed as horizontal. The roof surfaces are also inclined to the horizontal. The normal component and tangential component of wind on inclined roof surfaces may be found. It is to note that the tangential component of wind pressure is small and it is neglected. The normal component of wind pressure can be found from the empirical formula.
In order to find the wind load on individual structural elements/members (e.g., roofs and walls, and individual cladding units and their fittings, it is essential to consider the pressure difference between the opposite faces of such elements or units. For cladding, it is, therefore, necessary to know the internal pressure as well as the external pressure. The wind load, WL acting in a direction normal to the individual structural element or cladding unit may be determined from the following expression
where,
Cpe = external pressure coefficient
Cpi = internal pressure coefficient
A = surface area of a structural element or cladding unit, and
pd = design wind pressure
Enlist advantages and disadvantages of Bolted and Welded connections.
The advantages of bolted connections are as follows:
- There is silence in preparing bolted connection. In riveting, hammering is done. The hammering causes noise in the riveting.
- There is no risk of fire in bolted connection. The rivets are made red hot in riveting and there is a risk of fire.
- The bolted connections may be done quickly in comparison to the riveting.
- Though the cost of bolts is more than the cost of rivets, the bolted connections are economical to use than rivets because fewer persons are required for installation, and the work proceeds quickly.
- The bolted connections facilitate the erection because of the ease with which these connections can be done.
The following are disadvantages of bolted connections:
- If bolted connections become loose, their strength reduces considerably.
- Tire unfinished bolts are not uniform in diameter and they have less strength.
- The bolted connections have less strength when they are subjected to axial tension because the area at the root of the thread is less.
- Generally, the diameter of the hole is kept 16 mm more than the nominal diameter of the black bolt. The bolt does not fill the hole and there remains a clearance in bolted connections.
Advantages of riveted joints
- A riveted joint is more reliable than welded joints in applications which are subjected to vibrations and impact forces.
- Riveted joints can be used for non-ferrous metals like aluminium alloy, copper, brass or even non-metal like plastic and asbestos.
- Riveted joints are free from thermal after-effects because no heat required in this joint.
- Quality inspection is easy in a riveted joint.
- When the riveted joint is dismantled, the connected components are less damaged as compared to a welded joint.
Disadvantages of riveted joints
- The material cost of a riveted joint is more.
- The labour cost of riveted joints is also more than that of the welded joint.
- Overall cost if the riveted joint is also high.
- The riveted assembly has more weight than the welded assembly.
- The riveting process creates more noise because of hammer blows.
- Holes required to insert rivets cause stress concentration.
- Production time is more for assembly.
- Riveted assemblies are not tight and leak proof.
- The projection of the riveted head adversely affects the appearance of the riveted structure.
Kinematic indeterminacy
It is defined as the number of non-zero joint displacements of the structure. It is also called the Degree of freedom.
- A fixed ended beam is kinematically determinate as at both of its ends all the displacement components are known to be zero on compatibility consideration.
- A cantilever beam has three degrees of kinematic indeterminacy corresponding to the free end as three unknown displacements are likely to occur there.
- In case any axial change in length is neglected its kinematic indeterminacy will be only two.
In short, the total kinematic indeterminacy of a structure represents the sum of all the possible displacements that various joints of a structure can undergo.
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