SESSIONALS- MID SUBMISSION
1. Explain Load Combinations for the design of steel structures
as per IS: 800- 2007 ?
• Load combinations for design purposes shall be those that produce
maximum forces and effects and consequently maximum stresses and
deformations. The following combination of loads with
a) Dead load + imposed load,
b) Dead load + imposed load+ wind or earthquake load,
c) Dead load + wind or earthquake load, and
d) Dead load+ erection load.
• The effect of wind load and earthquake loads shall not be considered to act
simultaneously. The load combinations are outlined in detail in Cl. 3.5 of IS
800:2007.
2. Classify the steel sections as per code with suitable sketches.
ie; plastic , compact ,unit compact, slender etc. ?
DIFFERENT TYPES OF STEEL CROSS SECTIONS
As per IS 800-2007, the classification of the steel cross sections depends on the
load that the section can carry before failing, local buckling, moment redistribution
capacity and the width to thickness ratio of the sections in consideration.
The steel cross sections are mainly classified into four types based on the above
criteria as per IS 800-2007.
1. Plastic section
2. Compact section
3. Semi-compact section
4. Slender section
So What Are These Sections?
This can be better understood by the graph shown here. The following can be
inferred from the graph about the sections.
1. Plastic Section
The plastic section is capable of developing plastic moment and plastic hinges with
sufficient rotation capacity without local buckling.
2. Compact Section
These sections can develop the plastic moment but the plastic hinge rotation
capacity is inadequate because of local buckling.
3. Semi-Compact Section
The extreme fibre stress attains yield stress but cannot develop plastic moment. The
maximum moment it can attain is Yield Moment. The member fails by local buckling
even before it forms a mechanism.
4. Slender Section
Even the extreme fibre does not reach yield stress in these sections. the elements
buckle locally even before reaching yield stress.
.3. Write down the maximum values of the effective slenderness
ratio for various members ?
4
Distinguish between non sway and sway frames. Also write
down the assumption in analysis of structures ?
#Any 3
# ANY 5 ASSUMPTION
1. Rigid Joints: It is often assumed that the connections or joints between members are perfectly
rigid
2. Linear Material Behavior: Materials used in the frame members are assumed to exhibit linear
elastic behavior. Nonlinear material behavior, such as plasticity, is typically ignored.
3. Small Displacements: The analysis often assumes that the frame undergoes small displacements
and deformations.
4. Plane Frame: The analysis is typically conducted in two dimensions, assuming that the frame lies
in a single plane.
5. No P-Delta Effect: In many simplified analyses, these effects are neglected.
6. Constant Axial Load: The axial loads on the frame members are assumed to remain constant
throughout the analysis
7. Linear Static Analysis: assume that the structure behaves linearly under applied loads. Nonlinear
effects, such as large deformations or material nonlinearity, are not considered.
8. No Wind or Seismic Effects: Initial analyses may neglect wind loads, seismic forces, or other
dynamic loads that can induce lateral sway in the structure.
9. Idealized Loadings: Simplified loadings, such as uniform or concentrated loads, are used
assumption in analysis of structures of non sway frames
1. Rigid Joints: Similar to sway frames, it is often assumed that the connections or joints between
members are perfectly rigid
2. Linear Material Behavior: As with sway frames, materials used in the frame members are assumed
to exhibit linear elastic behaviour.
3. Small Displacements: The analysis typically assumes that the structure undergoes small
displacements and deformations.
4. Plane Frame: The analysis is often conducted in two dimensions, assuming that the frame lies in a
single plane
5. No P-Delta Effect: In many cases, the P-Delta effect (second-order effects due to axial loads and
lateral displacements) is neglected in the initial analysis of non-sway frames.
6. Constant Axial Load: It is assumed that the axial loads on the frame members remain constant
throughout the analysis. In reality, these loads may vary, but this simplification is made for
simplicity.
7. Linear Static Analysis: assume that the structure behaves linearly under applied loads.
8. Idealized Loadings: Simplified loadings, such as uniform or concentrated loads, are used
9. No Sway Consideration:the analysis may not consider lateral displacement or sway as a critical
factor.
10. Idealized Boundary Conditions: Simplified boundary conditions may be assumed, such as pinned
or roller supports at specific locations.
5. Explain briefly : Elastic analysis, plastic analysis, frame
buckling analysis, limit state and serviceable ?
1. Elastic Analysis:
Description: Elastic analysis is a structural analysis method that assumes
linearelastic material behavior.
•
Application: Commonly used for analyzing structures under normal working
loads where deformations are expected to remain within the elastic range.
2. Plastic Analysis:
• Description: Plastic analysis is a structural analysis method that goes beyond
the elastic limit and considers the plastic (permanent) deformation of the
material.
•
Application: Useful for assessing the strength and stability of structures under
extreme loads, helping to identify failure modes and prevent sudden collapses.
3. Frame Buckling Analysis:
• Description: Frame buckling analysis involves studying the stability and
strength of structural frames against lateral-torsional buckling.
•
Application: Important in the design of tall and slender structures such as
buildings and towers to ensure they can withstand lateral forces without
collapsing.
4. Limit State:
• Description: Limit state refers to the condition at which a structure or structural
element reaches the limit of its performance or safety.
•
Application: Structural design codes set limit state criteria to ensure that
structures are safe and meet performance expectations under various
conditions.
5. Serviceable:
• Description: Serviceability in structural engineering refers to the ability of a
structure to meet functional and aesthetic requirements during its intended
service life.
•
Application: Designing for serviceability ensures that structures not only meet
strength and safety requirements but also provide a satisfactory level of
performance and user comfort throughout their lifespan.
6. Explain the basic of limit state design as per IS: 800-2007 ?
LIMIT STATE DESIGN: BASIS FOR DESIGN
In the limit state design method, the structure shall be designed to withstand
safely all loads likely to act on it throughout its life. It shall not suffer total
collapse under accidental loads such as from explosions or impact or due to
consequences of human error to an extent beyond the local damages. The
objective of the design is to achieve a structure that will remain fit for use during
its life with acceptable target reliability. In other words, the probability of a limit
state being reached during its lifetime should be very low. The acceptable limit
for the safety and serviceability requirements before failure occurs is called a limit
state. In general, the structure shall be designed on the basis of the most critical
limit state and shall be checked for other limit states.
Steel structures are to be designed and constructed to satisfy the design
requirements with regard to stability, strength, serviceability, brittle fracture,
fatigue, fire, and durability such that they meet the following: a) Remain fit with
adequate reliability and be able to sustain all actions (loads) and other influences
experienced during construction and use; b) Have adequate durability under
normal maintenance; c) Do not suffer overall damage or collapse
disproportionately under accidental events like explosions, vehicle impact or due
to consequences of human error to an extent beyond local damage. The potential
for catastrophic damage shall be limited or avoided by appropriate choice of one
or more of the following:
Avoiding, eliminating or reducing exposure to hazards, which the struc ture
is likely to sustain.
Choosing structural forms, layouts and details and designing such that: i) the
structure has low sensitivity to hazardous conditions; and ii) the structure survives
with only local damage even after serious damage to any one individual element
by the hazard.
Choosing suitable material, design and detailing procedure, construction
specifications, and control procedures for shop fabrication and field construction
as relevant to the particular structure.
7. Discuss about partial safety factors for load and partial safety
factor for materials ?
PARTIAL SAFETY OF FACTOR
Materials :
The value of partial safety factor for material strength should account for the following
parameters:
(a). Possibility of deviation of the strength of material.
(b). Deviation of the sectional dimensions.
(c). Accuracy of the calculation procedure, and
(d). Risk to life and economic consequence
Loads :
The value of partial safety factor for loads should account for the following
parameters:
(a). Unusual increase in loads beyond that used for deriving characteristics values.
(b). Unforeseen stress redistribution
(c). Inaccurate assessment of the effects of loading, and
(d). Importance of the limit state considered.
Design values are obtained when partial safety factor are applied to characteristics
load and materials.
1. Materials : The design of the materials fd is given by
Fd = fck /ϒms
Fck = characteristics strength of the material
ϒms = partial safety of factor for material
2. Loads : The design load Fd is given by
Fd = Fϒf
F = Characteristics load
ϒf = Partial safety of factor load
8. Compare steel structures with R.C.C structures.
(I) from material properties considerations
(ii) from load carrying mechanism considerations
I. Material Properties Considerations:
1. Strength:
Steel
Structures:
High tensile strength, allowing for long spans and flexibility in
design.
R.C.C. Structures: Good compressive strength, strengthened by reinforcing bars for
improved tensile strength.
2. Weight:
Steel Structures: High strength-to-weight ratio, leading to lighter structures.
R.C.C. Structures: Denser and heavier compared to steel.
3. Durability:
Steel Structures: Susceptible to corrosion; requires protective coatings.
R.C.C. Structures: More resistant to environmental conditions; less prone to corrosion.
4. Construction Speed:
Steel Structures: Can be prefabricated off-site, leading to faster on-site construction.
R.C.C. Structures: Construction may take more time due to curing and setting of
concrete.
5. Flexibility:
Steel Structures: Flexible, allowing for adaptable designs and modifications.
R.C.C. Structures: Less flexible after construction.
6. Fire Resistance:
Steel Structures: Weakens under high temperatures, but fire-resistant coatings can be
applied.
R.C.C. Structures: Better fire resistance; maintains strength at higher temperatures
compared to steel.
II. Load Carrying Mechanism Considerations:
1. Steel Structures:
Load-carrying through a combination of tension and compression in members.
High ductility, allowing for redistribution of loads in case of failure in one part.
2. R.C.C. Structures:
Concrete carries compressive loads, while steel reinforcement carries tensile loads.
Bending and shear are primary load-carrying mechanisms.
3. Deflection and Deformation:
Steel Structures: Tend to deform elastically, with significant ductility before failure.
R.C.C. Structures: Experience more inelastic deformation, with cracking in concrete
before ultimate
failure.
4. Behavior under Overload:
Steel Structures: Can undergo large deformations before failure, providing warning
signs.
R.C.C. Structures: May exhibit brittle failure without warning.
5. Connections:
Steel Structures: Use bolted or welded connections, facilitating easier disassembly
and
modification.
R.C.C. Structures: Connections are typically rigid, requiring more effort for
modification.
6. Load Redistribution:
Steel Structures: Better ability to redistribute loads in case of local failures.
R.C.C. Structures: Local failures can lead to more significant consequences if not
properly addressed.