Week 1 Challenge

Q1. Truss type reasoning

Out of the two through type truss systems shown below, which is the most efficient in carrying gravity load? Reason it out.

Aim : To find out between Truss A and Truss B which is the most efficient in carrying gravity load

Observation :

We can clearly see that Truss A is Pratt truss and B is Howe truss

Pratt truss is one of the most common forms of truss and is made up of vertical and diagonal members that form an N shape or pattern.The diagonal members are arranged so that they only develop tensile forces.As such ,they can be designed to resist axial tension only,avoiding the need for a compression buckling analysis.The vertical members in a Pratt truss develop compression forces.This means they will typically be more robust and capable of resisiting buckling

• It is composed of alternative vertical and inclined members
• It has diagonal members that slant down towards the middle
• The tension and compression members are shown

Howe Trusses are essentially the opposite of pratt truss in terms ofgeometry.In fact,looking at pratt truss upside down will visualize a Howe truss of sorts.The entire structure in still relatively the same ,but the diagonal braces are now occupying the opposite or the unoccupied joints.This switch in position of the diagonal members has a very important effect structurally.

• It consists of alternative vertical and inclined members
• It has diagonal members that slant down away from the the middle
• The tension and compression members are shown

Conclusion:

• Pratt trusses have their vertical members in compression and diagonal members in tension upto the application of gravity loads at the joints of the top chord.For Howe trusses,the reverse becomes true as diagonal members are now in compression ,while the vertical loads are in tension.
• Pratt trusses can have more unloaded members than Howe trusses
• Hence PATT TRUSSES(Truss A) is most efficient in carrying gravity loads.

Q2. Deflection shape & Bending Moment Drawing (Qualitative approach)

For the beam & Frame below draw deflected shape and bending moment drawing. (Qualitative approach). E & I are constants.

3. Determine MOI, Weight, C/S area of sections below

4. Load calculation problem

For the floor framing below, Calculate the load on interior beam, Exterior beam, Interior Girder and exterior girder having Floor Load of 10kN/m²

Q5. Expansion joint size determination for temperature stated problem

Assuming a bridge, made of steel, with an initial total length of 2000 m at -20 ºC, calculate the length difference at 40 ºC and its total length.

Coefficient of Thermal expansion of steel = 12x10^-6/°C

Aim :

To calculate the load on the interior beam , Exterior beam, interior grider and exterior girder having floor load of 10Kn/m^2

Soln:

Change in length = Coefficient of thermal expansion X original length X change in temperature

= 12x10^-6/°C X 2000 X 20

= 0.48m