iday, 10 December 2010 Interview Questions for Structural Engineers
1. Draw Deflected Shape, Shape, Shear Shear Fo Force rce and Bending Moment Moment Diagram Diagram f or all r all abov abovee structures tructures 2. What What is effect of C f Creep in R einf einf orced Concrete Concrete Beams? eams? 3. Com pute maxim aximum soil soil pre press ssure ure f or 3m r 3m x 3m size size isolated solated pad pad f ooting ooting with with Force Force = 1000kN and Moment Moment abo about one axis axis 600kNm 4. Define Ductility? Ductility? 5. Pleas lease des describe the metho ethod ds to find Flexural tens tensile strength trength of of cconcrete? ncrete? 6. What What is reaso reason n beh behind k eeping eeping lim limit on maxim aximum shear shear sstrength trength of of Co Concrete ncrete?? 7. How How to arriv arrive at structural wor k king i ng load capacity of axially f axially loaded pile aded pile?? 8. Com pute maxim aximum com pre om press ssiio n in Pile f or G r Gr oup of 9 f 9 Pile P iless ( 3 Row Ro w x 3 Colu Colum mns) s paced at 3m c/c, Force Force trans transferred on Pile Cap, F = 1000t 1000t (Down) wn) , Moment Momentss, Mx = 400t 400tm My My = 200t 200t m Posted Posted by Er . He Hemant Gor Gor at at 21:01 0 comm omment entss
Wednesday,
21 October 2009
Initial Sizing of Steel Beam Section
The
fir st step of preliminary / detailed design of structure is initial sizing of main structural mem ber s. This blog gives quick method of selecting steel section f or Beam/Girder . The design of beam requires to satisfy the strength and ser viceability pr ovisions of codes. The
Minimum Second Moment of Inertia of Beam Section I ( in cm^4) required is
I = 0.5 x R atio x K x L x M Here, M is Mid S pan Beam Bending Moment is kNm L is S pan of Beam in m K is constant based on loading and end supports, it is based on Bending moment diagram of s pan The value of K is tak en fr om Table 1. ( R eference Table 3.1 of BS 8110-2:1985) R atio is S pan / Allowable Deflection. It means Allowable Deflection = S pan/R atio The
value of "R atio" can be 250,360,400,500 or 600 based on what is going to be put on Beam/Girder Table
1 Values of K f or various Bending Moment Diagram
f or allowable deflection = S pan/400, The I required f or Beam=0.5x400xK L M
I= 200K L M I is in cm^4 unit. Posted by Er . Hemant Gor at 12:15 0 comments
Saturday, 29 August 2009 Bridge Superstructure Bridge Super structure The
loads coming over bridge super structure are tak en by f o llowing actions in individual mem ber s y y y
Bending ( Flexure and Shear in Mem ber ) Axial elongation or axial shortening ( Tension or Com pression in Mem ber ) Com bination of Bending and Axial Def or mation (Flexure, Shear and Tension/Com pression)
Girder Bridges In this structural f or m the loads are tak en fully by bending of super structure. In this type of super structure the loads are tak en by mem ber s as flexure and shear . The design of super structure is governed by flexure, shear and deflection criteria. Girder bridges can be anyone of f o llowing type y y y y
Solid Slab ( S pan 4m ± 12m) Voided Slab ( S pan 8m-16m) T Girder ( Girder and Slab) ( S pan 12m-25m) Box Girder ( Single or Multi Cell) (25m ± 60m)
The
girder can be sim ply supported between two adjacent pier s or continuous over more than one pier . The Continuous girder pr ovide f o llowing advantage over sim ply supported girder y
Shallower depth super structure com pared to sim ply supported girder s
y
R educe num ber of expansion joints
y
R educe num ber of Bearing required to support super structure
y
The
continuous girder s have redundancy
The
continuous girder s are not used under weak soil f oundation. The settlement of support (Uneven settlement) will generate additional moments and shear in super structure in case of continuous girder . In Girder only extreme fibres are only stressed to maximum limit. Truss
Bridges
In this structural f or m the loads are tak en by axial def or mation of individual mem ber s. In truss bridges the loads are tak en by mem ber s as axial tension or axial com pression. Under axial tension/com pression action all fibre of section are stressed to same limit. Hence truss bridges are best structural f or m f or long s pans. The truss bridge can be thr ough type or deck type based on traffic movement. The
truss bridges are of f o llowing type
y y y y
Pratt Truss Warren Truss Modified Warren Truss K Bracing Truss
Posted by Er . Hemant Gor at 07:40 0 comments
Saturday, 22 August 2009 Bridge Classification Bridges are br oadly classified based on f o llowing three criteria 1. Material of Construction 2. Structural For m 3. Construction Technology Bridge Classsifcation based on Material of Construction y y y y y
R einf orced Concrete Prestressed Concrete ( Post-Tenions / Pre - Tension) Com posite Steel Masonary
Bridge Classification based on Structural For m y y
Girder Bridges ( Slab / Girder and Slab ( T Beam) / Box Girder (Single Cell/Multi Cell)) Truss ( Thr ough Type / Deck T ype)
y y
Cable Supported Bridges ( Cable Stayed / Sus pension / Extradosed Bridges) Arch Bridges ( Arch Bridges / Bow String Arch Bridges)
Bridge Classification based on Construction Methodology y y
Balanced Cantilever Bridges Incremental Launched Bridges
Posted by Er . Hemant Gor at 07:41 0 comments
Wednesday,
12 August 2009
Bridge Bearing Layout
The bearing
y y
has f o llowing main two functions
Transfer super structure
load ( Vertical / Transver se ) to substructure Allow ther mal movement
For bridge s pan more than 40m POT bearings/ POT PTFE bearings are used. Figure 1 shows bridge bearing layout f or sim ply supported s pan
Figure 2 shows bridge bearing layout f or two s pan continuous bridge
Figure 3 shows bridge bearing layout f or f our s pan continuous bridge
Posted by Er . Hemant Gor at 21:20 0 comments
Saturday, 8 August 2009 Economical Span of Bridge Fixing length of typical s pan in design of bridges acr oss river/elevated r oad/metr o pr o ject is very im portant structural design decision. The cost of building one typical s pan can be br oadly divided into f ollowing two com ponents
1. Cost of Substructure 2. Cost of Super structure The
cost of substructure is cover s cost of bridge bearing, pier cap/pier head, pier and f oundation (O pen/Pile/Cassion). To tak e decision on most economical length of typical s pan, initial design and cost estimate is done f or f our to five different s pan lengths. A graph is plotted with s pan length as abscissa and cost as ordinate. The graph is com pleted using cost of super structure and substructure f or all different s pans. Figure 1 shows typical graph of S pan ver sus cost. Point A on this graph corres pondence to the economical s pan f or the bridge pr o ject.
Figure 1 S pan Ver sus Cost f or Super structure/Substructure Posted by Er . Hemant Gor at 09:36 0 comments
Wednesday,
5 August 2009
Continuous Beam / Bridge Span Arrangement
In case of continuous beam /girder bridges the end s pan is k ept 80% of internal s pan. This s pan arrangement leads to unif or m sagging momnet in mid s pan com pared to sagging momment o btained in all equal s pan arrangement. Figure 1 shows bending moment diagram f or two s pan
arrangement, a) Last s pan equal to 0.8 times internal s pan b) All s pans equal under unif or mly distributed load. One of bridge designed in Middle East had s pan arrangement of 40m - 50m - 50m -40m and this arrangement lead to unif or m depth of box girder with least consum ption of post-tenisoned tendon.
Figure 1 Bending Moment Diagram f or unif or mly distributed load on all f our s pans Posted by Er . Hemant Gor at 11:54 0 comments Labels: http://2. bp. blogs pot.com/_i10MiAfl4 pY/SnsJSd3v8EI/AAAAAAAACEA/ef mmWnGW3o8/s16 00-h/bending+moment. jpg Home Subscribe to: Posts (Atom)
