Correct Answer - Option 2 : Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)
Statement I: True
Purlins are beams used on trusses to support the sloping roof system between the adjacent trusses. They are placed in an inclined position over the main rafters (top chord) of the trusses.
To avoid bending in the top chord, it is theoretically desirable to place purlins at panel points however; they are placed at very closed intervals for the economic point of view.
They may be designed as simply supported by considering maximum BM to be WL2/8 and may be designed as continuous by considering maximum moment be WL2/10.
Statement II: True
Typical components of a truss are shown in the following figure:
Components
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Functions
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Struts
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Stiffen the bridge laterally
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Portal Bracing
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Transfer the wind and seismic load from the top of end posts to bearing.
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Bottom Floor Beams
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Resist the Load coming from bridge deck up to some extent by bending action and remaining load gets transferred to bridge piers
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Top and Bottom Lateral Bracings
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Prevent the buckling of the top chord and bottom chord respectively. The top chord is continuous through the nodes of the truss.
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