Week 1 Challenge

CHALLENGE WEEK 1

Question: -1

1. 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 & Truss B which is the most efficient in carrying gravity load.

OBSERVATION-

We can clearly see that the Truss A is "Pratt truss" & Truss 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 resisting buckling.

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

Howe trusses are essentially the opposite of Pratt trusses in terms of geometry. In fact, looking at a Pratt truss upside-down will visualize a Howe truss of sorts. The entire structure is 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 alternate vertical and inclined members.
• It has diagonal members that slant down away from the middle.
• The tension and compression members are as shown

FINAL OBSERVATION-

The main differences are that the Pratt truss has no force on the ends and the compression members are vertical.

The Howe truss has no force on the center and the tension members are vertical instead.

CONCLUSION-

Pratt trusses have their vertical members in compression and diagonal members in tension upon 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.

As they are similar in structure to Pratt trusses, their uses are generally the same. To maximize the efficiency of the truss, the truss can be loaded at the joints of the bottom chord.

• Pratt trusses can have more unloaded members than Howe trusses.

"HENCE "Pratt trusses(Truss A)" is most efficient in carrying gravity loads.’’

Question:- 2

2. 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.

Question:- 3

Aim:- To Determine MOI, Weight, C/S area of sections below

Ans:-

Question:- 4

4. Load calculation problem

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

Ans:-

Floor Load -10KN/m2

Tributary width of exterior girder – 0.5(8+8)=4m

Tributary width of interior girder – 0.5(8+8)= 8m

Tributary width of exterior beam – 0.5(0+2)=1m

Tributary width of interior beam – 0.5(2+2)=2m

Load on beam = Tributary width x floor load

Load on exterior girder = 4 x 10 = 40 kn/m

Load on beam interior girder = 8 x 10 = 80 kn/m.

Load on beam exterior beam = 1 x 10 = 10 kn/m.

Load on beam interior beam = 2 x 10 = 20 kn/m.

Question:- 5

Aim:- To 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

Ans:-

Change in length = coifficient of thermal expansion x original length x change in temperature

= 12x10^-6 /°C x 2000 x 20

=0.48m