Prestressed Concrete Structures Multiple Choice Questions on “Structural Form Bridges”.
1. One of the structural forms used for bridges are ____________
a) Solid slabs
b) Dense slabs
c) Rigid slabs
d) Open slabs
Clarification: For medium and long spans prestressed concrete is ideally suited for the super structure of bridges and the structural forms generally used for bridges are listed as follows solid slabs(10-15m), voided or hollow slabs(15-25m), rigid frame bridges(15-30m), Tee beams and slabs(20-40m), two cell box girders(30-70m), multi cell box girders(40-80), balanced cantilever type bridges(20-30m), continuous girders of variable depth(30-40), cable stayed bridges(100-500m).
2. Prestressed concrete has more or less replaced ____________
a) Reinforced concrete
b) Prestressed concrete
c) Aluminium concrete
d) Voids concrete
Clarification: Prestressed concrete has more or less replaced reinforced concrete as the most suitable material for bridge construction due to its inherent advantages of high strength coupled with durability, energy absorption under dynamic loads, ability to resist repetitive loads, freedom from cracks, easy mould ability to desired shape, economy and ease of maintenance.
3. The floors and girders of through type structures should be placed in ____________
a) Two continuous
b) One continuous
c) Span continuous
d) Limit continuous
Clarification: The floor and girders of through type structures should be placed in one continuous unless otherwise specified in which case a special sear anchorage should be provided to ensure monolithic action between the girders and floor and the case of tee beam slab floors, it is preferable to deposit concrete first up to the top of the girder ribs followed by concreting of the slab in one continuous operation and if the slab concrete is delayed, suitable shear keys should be formed by roughening the top of the girder before depositing the centre in the slab.
4. Prestressed concrete members should be compacted by which type of vibration?
a) Mechanical vibration
b) Structural vibration
c) Internal vibration
d) External vibration
Clarification: Prestressed concrete members should be compacted by mechanical vibrations expect when certain types of extrusion machines are used which consolidate the concrete by tamping and depending on the type of structural members, internal, external or surface type vibrators are used and normally vibrators having frequencies in the range of at least 3200-3600 cycles per minute are used.
5. The vibrations should be used only for ____________
Clarification: Vibration should be well distributed so that the concrete reaches a state of plastic mass with uniform density and vibrators should be used for compaction only and not for moving concrete horizontally along the forms.
6. When vibrators are used for horizontal and vertical operation, the spacing should ____________
d) Made wet
Clarification: When vibrators are used for horizontal and vertical operation, the spacing of points of vibration should be such that their zones of influence overlap and when concrete is deposited in layers such as that in column, the vibrator should be inserted vertically.
7. When concrete is deposited in layers it should be allowed to ____________
Clarification: When concrete is deposited in layer it is allowed to sink due to its own weight to the bottom of the layer and then slowly withdrawn and during vibration of succeeding layers, the vibrator should preferably penetrate the surface of the preceding layer by at least 150mm and good vibration should result in a surface without honey combing, aggregate or mortar pockets or excessive air bubbles.
8. The self compacting concrete (SCC) is generally referred as ____________
a) Spatial concrete
b) Pores concrete
c) Rheodynamic concrete
d) Flexible concrete
Clarification: Rheodynamic concrete generally referred to as self compacting concrete (SCC) is able to flow under its own weight and completely fill the formwork, even in the presence of dense reinforcements without the need for any vibration whilst maintaining homogeneity and resulting in concrete of high early strength and durability.
9. Degussa-MBT construction chemicals (INDIA) have developed revolutionary type of admixtures based on?
a) Micro science
b) Nano science
c) poly science
d) Animal science
Clarification: Degussa-MBT construction chemicals (INDIA) have developed revolutionary type of admixtures using nano polymers which can be used to bring together functional groups aimed at targeted performances in concrete and based on nano science.
10. A system of polymers with longer side and shorter side chains is called ____________
a) Zero energy system
b) Elastic energy system
c) Bonded energy system
d) Force energy system
Clarification: A system of polymers with longer side chains and shorter main chains to facilitate high early strengths in concrete without steam curing and with specific applications in precast reinforced and prestressed concrete units manufacturing industry.